Configuring channel state information reporting for mobility in dual connectivity

Abstract

This disclosure provides systems, methods and apparatuses for configuring lower layer-triggered mobility (LTM) channel state information (CSI) resources and LTM CSI reports for an inter-central unit (inter-CU) LTM cell switch for network entities (104, 106) in dual connectivity with a user equipment (UE) (102). A network entity and UE communicate via a serving cell (124A). The UE is configured with an LTM candidate configuration for a first cell (124B). The first network entity transmits a request to a second network entity to prepare a second cell as an LTM candidate cell for the UE. The first network entity transmits, to the second network entity, an LTM CSI resource configuration for the first cell specifying LTM CSI resources the UE is to use for measuring CSI. The second network entity transmits, to the first network entity, an LTM CSI report configuration that configures one or more reports associated with the LTM CSI resources.

Description

CONFIGURING CHANNEL STATE INFORMATION REPORTING FOR MOBILITY IN DUAL CONNECTIVITYRELATED APPLICATIONS

[0001] This application claims the priority benefit of U.S. Provisional Patent Application Serial No. 63 / 574,890, filed April 4, 2024, and entitled "CONFIGURING CHANNEL STATE INFORMATION REPORTING FOR MOBILITY IN DUAL CONNECTIVITY / ’ and U.S. Provisional Patent Application Serial No. 63 / 673,251, filed July 19, 2024, and entitled “CONFIGURING CHANNEL STATE INFORMATION REPORTING FOR MOBILITY IN DUAL CONNECTIVITY,” the entire contents of each of which is hereby incorporated by reference herein.FIELD OF THE DISCLOSURE

[0002] This disclosure relates generally to wireless communication and some aspects relate to configuring channel state reporting for mobility in dual connectivity.BACKGROUND

[0003] This background description is provided for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0004] A user equipment (UE) can operate in a dual connectivity (DC) mode. In DC mode, the UE can concurrently utilize resources of multiple radio access network (RAN) nodes. The RAN nodes may be network entities such as monolithic base stations or distributed base stations (also referred to as disaggregated base stations). In a distributed base station, the functionality of the base station may be distributed across a central unit (CU) and one or more distributed units (DUs) interconnected by a backhaul. When the RAN nodes support different radio access technologies (RATs), this type of connectivity is referred to as Multi-Radio Dual Connectivity (MR-DC). In DC. one RAN node operates as a master node (MN) that covers a primary cell (PCell), and another RAN node operates as a secondary node (SN) that covers a primary' secondary' cell (PSCell). The UE communicates with the MN (via the PCell) and theSN (via the PSCell). The cells of the MN are referred to as a master cell group (MCG), and the cells of the SN are referred to as a secondary' cell group (SCG).

[0005] When the UE moves from coverage area of one cell to another cell, at some point a serving cell change has to be performed for the UE. To perform the serving cell change, the RAN may configure the UE to transmit layer 3 (L3) measurement results. Based on L3 measurement results received from the UE, the RAN transmits a radio resource control (RRC) reconfiguration message configuring Reconfiguration with Synchronization (e.g., the RRC reconfiguration message includes a ReconfigurationWithSync IE) for change of the serving cell (e.g., PCell or PSCell). In cases where the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN releases the at least one SCell due to the change of the PCell or PSCell. The serving cell change involves complete layer 2 (L2) and layer 1 (LI) resets, leading to longer latency, larger overhead, and longer interruption time.

[0006] While a base station of the RAN communicates with the UE via a serving cell, the base station receives one or more L3 (e.g., RRC) measurement results from the UE. One of the DU(s) operating the serving cell is a serving DU. Based on the L3 measurement result(s). the base station may configure a lower layer-triggered mobility (LTM, also referred to as “L1 / L2- triggered mobility”) candidate cell for LTM cell switch. To configure the LTM candidate cell for the UE, the base station transmits an LTM candidate configuration configuring the LTM candidate cell to the UE via RRC signaling. Later, the base station receives one or more LI measurement results from the UE. Based on the one or more LI measurement result(s), the base station determines that the LTM candidate cell qualifies to be a serving cell for the UE. Therefore, the base station transmits an LTM cell switch command to the UE to command the UE to perform the LTM cell switch to the LTM candidate cell.BRIEF SUMMARY

[0007] The systems, methods, and apparatuses of this disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

[0008] One innovative aspect of the subject matter described in this disclosure can be implemented as a method for wireless communication by a first network entity. The method also includes transmitting, to a user equipment (UE) operating in dual connectivity with thefirst network entity and a second network entity, a first lower layer-triggered mobility (LTM) channel state information (CSI) resource configuration for a first cell that configures one or more first LTM CSI resources associated with the first cell. The method also includes transmitting, to a third network entity, a second LTM CSI resource configuration for the first cell that configures one or more second LTM CSI resources associated with the first cell.

[0009] Another innovative aspect of the subject matter described in this disclosure can be implemented as a method for wireless communication by a first network entity. The method also includes receiving, from a second network entity7, a request to prepare a second cell as an LTM candidate cell for a UE in a dual connectivity mode in a first cell. The method also includes receiving, from the second network entity, an LTM CSI resource configuration that configures one or more LTM CSI resources associated with the first cell.

[0010] Another innovative aspect of the subject matter described in this disclosure can be implemented as a method for wireless communication by a first network entity. The method also includes receiving, from a second network entity7, a request to prepare a handover from a first cell to a second cell for the UE, the request including an LTM CSI resource configuration that configures one or more LTM CSI resources associated with the first cell. The method also includes transmitting, to the second network entity, an acknowledgement of the request to prepare the handover.

[0011] Another innovative aspect of the subject matter described in this disclosure can be implemented as an apparatus that includes a communication unit and a processing system configured to control the communication unit to implement any one of the above-referenced methods.

[0012] Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 A is a block diagram of an example wireless communication system in which a network entity configures lower layer-triggered mobility (LTM) channel state information (CSI) resources and LTM CSI reporting for inter-central unit (CU) cell switches.

[0014] FIG. IB is another block diagram of an example wireless communication system in which a network entity configures LTM CSI resources and LTM CSI reporting for inter-central unit (CU) cell switches.

[0015] FIG. 1C is a block diagram of an example base station including a central unit (CU) and a distributed unit (DU) that can operate in the system of FIG. 1A or FIG. IB.

[0016] FIG. 2A is a block diagram of an example protocol stack according to which the UE of FIG. 1A communicates with base stations.

[0017] FIG. 2B is a block diagram of an example protocol stack according to which the UE of FIG. 1 A communicates with a CU and a DU.

[0018] FIG. 3 is a sequence diagram illustrating example operations of a communications process for an intra-CU intra-DU cell switch.

[0019] FIG. 4 is a sequence diagram illustrating example operations of a communications process for an intra-CU inter-DU cell switch.

[0020] FIG. 5 is a sequence diagram illustrating example operations of a communications process for an example inter-CU cell switch where a first base station operates as a serving or source base station (S-BS) and a second base station operates as a candidate base station (C- BS).

[0021] FIG. 6A is a sequence diagram illustrating example operations of a communications process for a first example inter-CU cell switch where a first base station operates as a master node (MN), a second base station operates as a candidate SN (C-SN), and a third base station operates as a serving or source SN (S-SN).

[0022] FIG. 6B is a sequence diagram illustrating example operations of a communications process for a second example inter-CU cell switch where a first base station operates as an MN, a second base station operates as a C-SN, and a third base station operates as an S-SN.

[0023] FIG. 6C is a sequence diagram illustrating example operations of a communications process for a third example inter-CU cell switch where a first base station operates as an MN, a second base station operates as a C-SN, and a third base station operates as an S-SN.

[0024] FIG. 6D is a sequence diagram illustrating example operations of a communications process for a fourth example inter-CU cell switch where a first base station operates as an MN. a second base station operates as a C-SN, and a third base station operates as an S-SN.

[0025] FIG. 7A is a flow chart diagram illustrating first example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by an MN.

[0026] FIG. 7B is a flow chart diagram illustrating second example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by an MN.

[0027] FIG. 8 is a flow chart diagram illustrating third example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by an MN.

[0028] FIG. 9A is a flow chart diagram illustrating first example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a candidate secondary node (C-SN).

[0029] FIG. 9B is a flow chart diagram illustrating second example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a C-SN.

[0030] FIG. 10A is a flow chart diagram illustrating first example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a central unit (CU) of a C-SN.

[0031] FIG. 10B is a flow chart diagram illustrating second example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a central unit (CU) of a C-SN.

[0032] FIG. 11 is a flow chart diagram illustrating example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a target SN (T-SN).

[0033] FIG. 12 is a flow chart diagram illustrating example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a CU of a T-SN.

[0034] FIG. 13 is a flow' chart diagram illustrating first example operations of a method for wireless communication by a first network entity.

[0035] FIG. 14 is a flow chart diagram illustrating second example operations of a method for wireless communication by a first network entity.

[0036] FIG. 15 is a flow chart diagram illustrating third example operations of a method for wireless communication by a first network entity.

[0037] FIG. 16 is a block diagram illustrating example configurations of a network entity and a user equipment.DETAILED DESCRIPTION

[0038] The following description is directed to certain implementations for the purpose of describing innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. Some of the examples in this disclosure are based on wireless communication according to the 3rd Generation Partnership Project (3GPP) wireless standards, such as ambient intemet- of-things (A-IoT), the 4th generation (4G) Long Term Evolution (LTE) and 5th generation (5G) New Radio (NR) standards. However, the described techniques can be implemented in any device, system, or netw ork that is capable of transmitting and receiving radio frequency signals according to any of the wireless communication standards, including any of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 or 802.16 wireless standards, or other known signals that are used to communicate within a wireless, cellular, or loT network, such as a system utilizing 4G, 5G, 6thgeneration (6G), ZigBee, Bluetooth, WiFi, or future radio technology7.

[0039] As noted above, a base station of a RAN communicates with a UE via a serving cell. The base station may be a distributed base station in which the functionality of the base station is distributed across a central unit (CU) and one or more distributed units (DUs). The base station may configure a lower layer-triggered mobility (LTM, also referred to as “L1 / L2- triggered mobility”) candidate cell for LTM cell switch. During operations the base station receives one or more LI measurement results from the UE. Based on the one or more LI measurement result(s), the base station determines that the LTM candidate cell qualifies to be a serving cell for the UE. Therefore, the base station transmits an LTM cell switch command to the UE to command the UE to perform the LTM cell switch to the LTM candidate cell. If the LTM candidate cell is operated by the serving DU, the LTM cell switch is referred to as an intra-CU intra-DU LTM cell switch. If the LTM candidate cell is operated by a candidate DUin the DU(s), the LTM cell switch is referred to as an intra-CU inter-DU LTM cell switch. The two aforementioned switches take place in the context of the same base station or same CU of a distributed base station and are thus referred to as “intra-CU” cell switches. While existing systems may provide support for intra-CU LTM cell switches (e.g., intra-CU intra-DU and intra-CU inter-DU cell switches), existing systems may not support inter-CU LTM cell switches between a first cell associated with a first network entity such as a first base station or CU of the first network entity and a second cell associated with a second netw ork entity such as a second base station or CU of the second base station.

[0040] Various aspects of this disclosure relate to techniques for configuring lower layer- triggered mobility (LTM) (also referred to as “Ll / L2-triggered mobility) channel state information (CSI) resources and LTM CSI reports for an inter-central unit (CU) LTM cell switch for netw ork entities operating in a dual connectivity environment with a user equipment (UE). A network entity and a UE communicate via a serving cell. The network entity may configure the UE with a first LTM candidate configuration for a first cell. The first network entity can transmit a request to a second network entity requesting that the second network entity7prepare a second cell as an LTM candidate cell for the UE. The first network entity can configure LTM CSI resources for a second LTM candidate configuration specifying the first cell as a candidate cell. For example, the first network entity may transmit, to the second network entity, a second LTM CSI resource configuration for the first cell specifying LTM CSI resources for the first cell. The second network entity can use the LTM CSI resource configuration to configure a UE for measuring CSI of the first cell. The second network entity may transmit, to the first network entity, an LTM CSI report configuration that configures one or more reports associated with the LTM CSI resources. After an LTM switch to a candidate cell (e.g., the second cell), LTM CSI resources are already configured and available for use with respect to the first cell, which, after the cell switch, is now a candidate LTM cell with respect to the second cell.

[0041] One potential technical advantage of this disclosure is a first network entity such as a base station (or distributed base station) can configure a second network entity with LTM CSI resources, and the second network entity can configure CSI reports associated with the LTM CSI resources prior to an LTM cell switch from a first cell to a second cell. After the LTM cell switch, the LTM CSI resources are immediately available for use by the UE for measuring and reporting CSI that the second network entity can use for determining whetherto perform an LTM cell switch back to the first cell. This can result in reduced latency associated with such an LTM cell switch.

[0042] FIG. 1 A is a block diagram of an example wireless communication system 100A in which a network entity configures LTM CSI resources and LTM CSI reporting for inter-CU cell switches. The wireless communication system 100A includes a UE 102, a first network entity (e.g.. base station (BS) 104), a second network entity (e.g.. base station 106) and a core network (CN) 110. The UE 102 may initially connect to the base station 104. In some scenarios, the base station 104 may configure another base station (e.g., base station 106) as a secondary' node (SN) and may configure the UE 102 to operate in dual connectivity (DC) with the base station 104 and the base station 106. The base stations 104 and 106 may operate as an MN and an SN for the UE 102, respectively.

[0043] In addition to base stations 104 and 106. a network entity may be an Evolved Universal Terrestrial Radio Access Network Node B (E-UTRAN Node B), evolved Node B (eNodeB or eNB), Next Generation Node B (gNodeB or gNB), Next Generation E-UTRAN Node B (ng-eNB), access point, radio head or the like. The network entity may be implemented in a macrocell, microcell, small cell, picocell, or the like, or any combination thereof. In some aspects, a base stations such as base station 104 and / or base station 106 may be a monolithic base station in which the functionality' of the base station is implemented as a single unit. In some other aspects, a base station may be a distributed base station in which the functionality of the base station may be distributed among two or more units such as a central unit (CU) and one or more distributed units (DUs).

[0044] In various configurations of the wireless communication system 100A, the base station 104 may be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station 106 may be implemented as a secondary gNB (SgNB). In some aspects, the UE 102 may communicate with the base station 104 and the base station 106 via the same radio access technology (RAT) such as evolved universal terrestrial radio access (EUTRA) or new radio (NR). In some other aspects, the UE 102 may communicate with the base station 104 and the base station 106 via different RATs. When the base station 104 is an MeNB and the base station 106 is a SgNB, the UE 102 may be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0045] In some aspects, an MeNB or an SeNB may be implemented as an ng-eNB. When the base station 104 is a master ng-eNB (Mng-eNB) and the base station 106 is a SgNB, theUE 102 may be in next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. When the base station 104 is an MgNB and the base station 106 is an SgNB, the UE 102 may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the base station 104 is an MgNB and the base station 106 is a Secondary ng-eNB (Sng-eNB). the UE 102 may be in NR-EUTRA DC (NE-DC) with the MgNB and the Sng-eNB.

[0046] In the scenarios where the UE 102 hands over from the base station 104 to the base station 106, the base stations 104 and 106 operate as a source base station (S-BS) and a target base station (T-BS), respectively. The UE 102 may operate in DC with the base station 104 and an additional base station (not shown in FIG. 1 A) for example prior to the handover. The UE 102 may continue to operate in DC with the base station 106 and the additional base station or operate in single connectivity (SC) with the base station 106 after completing the handover. The base stations 104 and 106 in this case operate as a source MN (S-MN) and a target MN (T-MN), respectively.

[0047] A core network (CN) 110 may be an evolved packet core (EPC) 111 or a fifthgeneration core (5GC) 160, both of which are depicted in the example of FIG. 1A. The base station 104 may be an eNB supporting an SI interface for communicating with the EPC 111, an ng-eNB supporting an NG interface for communicating with the 5GC 160, or a gNB that supports an NR radio interface as well as an NG interface for communicating with the 5GC 160. To directly exchange messages with each other during the scenarios discussed below, the base stations 104 and 106 may support an X2 or Xn interface. Among other components, the EPC 111 may include a serving gateway (SGW) 112, a mobility management entity (MME) 1 14, and a packet data network gateway (PGW) 116. The SGW 112 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, and the like. The MME 114 is configured to manage authentication, registration, paging, and other related functions. The PGW 116 provides connectivity from the UE to one or more external packet data networks, e.g., an Internet network and / or an Internet Protocol (IP) multimedia subsystem (IMS) network. The 5GC 160 includes a user plane function (UPF) 162 and an access and mobility management function (AMF) 163, and / or session management function (SMF) 166. The UPF 162 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, and the like. The AMF 163 is configured to manage authentication, registration, paging, and other related functions. The SMF 166 is configured to manage PDU sessions.

[0048] Tn the example shown in FTG. 1 A, the base station 104 supports cell 124A, and the base station 106 supports a cell 126A. The cells 124A and 126A can partially overlap, so that the UE 102 can communicate in DC with the base station 104 and the base station 106, where one of the base stations 104 and 106 is an MN and the other is an SN. The base station 104 can support additional cell(s) such as cells 124B and 124C, and the base station 106 can support additional cell(s) (not shown in FIG. 1A). The cells 124A, 124B and 124C can partially overlap, so that the UE 102 can communicate in carrier aggregation (CA) with the base station 104. The base station 104 can operate the cells 124A, 124B and 124C via one or more transmit and receive points (TRPs, not shown in FIG. 1A). More particularly, when the UE 102 is in DC with the base station 104 and the base station 106, one of the base stations 104 and 106 operates as an MeNB, an Mng-eNB or an MgNB, and the other operates as an SgNB or an Sng- eNB.

[0049] In general, the wireless communication system 100A may include any suitable number of base stations supporting NR cells and / or EUTRA cells. More particularly, the EPC 111 or the 5GC 160 may be connected to any suitable number of base stations supporting NR cells and / or EUTRA cells. An example configuration in which the CN 110 is connected to additional base stations is discussed below' with reference to FIG. IB. Although the examples below' refer specifically to specific CN types (EPC, 5GC) and RAT types (5G NR and EUTRA), in general the techniques of this disclosure also may apply to other suitable radio access and / or core network technologies such as sixth generation (6G) radio access and / or 6G core netw ork or 5G NR-6G DC.

[0050] The base station 104 is equipped with processing hardware 130 that can include one or more general-purpose processors (e.g., CPUs) and a non-transitory computer-readable memory storing instructions that the one or more general-purpose processors execute. Additionally or alternatively, the processing hardware 130 can include special-purpose processing units. The processing hardware 130 can include a PHY controller 132 configured to transmit data and control signal on physical downlink (DL) channels and DL reference signals with one or more user devices (e g. UE 102) via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The PHY controller 132 is also configured to receive data and control signal on physical uplink (UL) channels and / or UL reference signals with the one or more user devices via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The processing hardware 130, in an example implementation, includes a medium access control (MAC) controller 134 configured to perform MAC functionswith one or more user devices. The MAC functions include a random access (RA) procedure, managing UL timing advance (TA) for the one or more user devices, and / or communicating UL / DL MAC PDUs with the one or more user devices. In some aspects, the MAC functions may include lower triggered mobility (LTM) related functions described herein. In some other aspects, an LTM controller 137 may perform the LTM functions described herein. The processing hardware 130 can further include a radio resource control (RRC) controller 136 to implement procedures and messaging at the RRC sublayer of the protocol communication stack. For example, the RRC controller 136 may be configured to support RRC messaging associated with handover procedures, and / or to support the necessary operations when the base station 104 operates as an MN relative to an SN or as an SN relative to an MN. The base station 106 can include processing hardware 140 that is similar to processing hardware 130. In particular, components 142. 144, 146, and 147 of base station 106 may be similar to the components 132. 134, 136, and 137. respectively, of base station 104.

[0051] The UE 102 is equipped with processing hardware 150 that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors and / or special -purpose processing units. The PHY controller 152 is configured to receive data and control signals on physical DL channels and / or DL reference signals with the base station 104 or 106 via one or more cells (e.g., the cells 124A, 124B, 124C and / or 126A) and / or one or more TRPs. The PHY controller 152 is also configured to transmit data and control signals on physical UL channels and / or UL reference signals with the base station 104 or 106 via one or more cells (e.g.. the cell(s) 124A, 124B, 124C and / or 126A) and / or one or more TRPs. The processing hardware 150 in an example implementation includes a MAC controller 154 configured to perform MAC functions with base station 104 or 106. For example, the MAC functions may include a random access procedure, managing UL timing advance for the one or more user devices, and communicating UL / DL MAC PDUs with the base station 104 or 106. In some aspects, the MAC functions may include LTM related functions as described below. The processing hardware 150 may further include an RRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack. Although described as being included with processing hardware 150, some of the functionality described above may be implemented as firmware or in software modules (e.g., software modules stored in the computer-readable memory.

[0052] Tn operation, the UE 102 in DC can use a radio bearer to communicate with a base station such as base station 104 or base station 106. Generally speaking, the UE and a base station can use signaling radio bearers (SRBs) to exchange RRC messages as well as non- access stratum (NAS) messages. The UE 102 and the base station 104 or 106 can use data radio bearers (DRBs) to transport data on a user plane.

[0053] UEs may use several t pes of SRBs and DRBs. When operating in dual connectivity (DC), the cells associated with a base station operating as an MN define a master cell group (MCG), and the cells associated with a base station operating as a secondary node (SN) define a secondary cell group (SCG). SRB1 resources may carry RRC messages, which in some cases may include NAS messages exchanged (e.g., transmitted and / or received) over the dedicated control channel (DCCH). SRB2 resources support RRC messages that may include logged measurement information or NAS messages. SRB2 resources may also be exchanged over the DCCH but with lower priority than SRB1 resources. SRB1 and SRB2 resources allow the UE and the MN to exchange RRC messages related to the MN and embed RRC messages related to the SN. These SRB1 and SRB2 messages may be referred to as MCG SRBs. SRB3 resources may be used by the UE and the SN to exchange RRC messages related to the SN. These SRB3 resources may be referred to as SCG SRBs. SRBs used by the UE to exchange RRC messages directly with the MN via lower layer resources of both the MN and the SN may be referred to as split SRBs. Similarly, DRBs using the lower-layer resources of only the MN can be referred to as MCG DRBs. DRBs using the lower-layer resources of only the SN can be referred to as SCG DRBs. DRBs using the lower-layer resources of both the MCG and the SCG can be referred to as split DRBs.

[0054] In the example shown in FIG. 1 A, the UE 102 operating in DC can use a radio bearer (e.g., a DRB or an SRB) that at different times terminates at the base station 104 operating as an MN or the base station 106 operating as an SN. The UE 102 can apply one or more security keys when communicating on the radio bearer, in the uplink (UL) direction (e g., from the UE 102 to a base station) and / or downlink direction (e.g., from a base station to the UE 102).

[0055] FIG. IB is another block diagram of an example wireless communication system 100B in which a network entity' configures LTM CSI resources and LTM CSI reporting for inter-central unit (CU) cell switches. In the example shown in FIG. IB, the base station 104A may be an implementation of the base station 104 of FIG. 1 and the base station 106A may be an implementation of the base station 106 of FIG. 1A. The example shown in FIG. IB alsodepicts additional base stations 104B and 106B, which may be included in the wireless communication system 100B. The UE 102 initially connects to the base station 104A. The base stations 104B and 106B may have similar processing hardware as the base station 106A.

[0056] In some scenarios, the base station 104A can perform an SN addition procedure (e.g., an "‘immediate SN addition”) to configure the UE 102 to operate in dual connectivity (DC) with the base station 104A (via a PCell) and the base station 106 A (via a PSCell other than cell 126 A). In such scenarios, the base stations 104 A and 106A operate as an MN and an SN for the UE 102, respectively. The UE 102 in some cases can operate using the MR-DC connectivity mode, e g., communicate with the base station 104 A using 5G NR and communicate with the base station 106A using EUTRA, or communicate with the base station 104A using EUTRA and communicate with the base station 106A using 5G NR. Multiconnectivity coordination can help the two base stations coordinate shared UE capabilities including operational frequencies (e.g., band combinations, frequency ranges), UE measurements and reporting (e.g.. intra-frequency measurements, inter-frequency measurements, inter-RAT measurements, measurement gaps), reception timing (e.g., DRX configurations, offset timing), and uplink power control (e.g., power headroom, maximum transmit power).

[0057] The base station 104 A acting as an MN may perform an SN change procedure (e.g., an “immediate SN change”) to change the SN of the UE 102 from the base station 106A (referred to as a source or serving SN, “S-SN”) to the base station 104B (referred to as a target SN, or “T-SN”) while the UE 102 is communicating in DC with the base station 104A and the S-SN 106 A. In another scenario, the S-SN 106A can perform a PSCell change procedure (e.g., an “immediate PSCell change”) to change the PSCell of the UE 102 to the cell 126A. In one implementation, the S-SN 106A can transmit, to the UE 102. a configuration changing the PSCell to cell 126A via a signaling radio bearer (SRB) (e.g., SRB3) for the PSCell change. In another implementation, the S-SN 106A can transmit, to the UE 102, a configuration changing the PSCell to the cell 126A via the base station 104A for the PSCell change. The base station 104A may transmit the configuration changing the PSCell to the cell 126A to the UE 102 via SRB1. Extending multi-connectivity coordination can help the newly added base station coordinate shared UE capabilities.

[0058] FIG. 1C depicts an example distributed implementation of a base station 164. In some aspects, the base station 164 may be an implementation of the base station 104 or 106 ofFIG. 1 A or the base stations 104 A, 104B, 106 A or 106B of FIG. I B. The base station 1 4 in this implementation can include a central unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 is equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In one example, the CU 172 is equipped with the processing hardware 130. In another example, the CU 172 is equipped with the processing hardware 140 of FIG. 1A. The processing hardware 140, in an example implementation, includes an SN RRC controller (e.g.. RRC controller 146 of FIG. 1A) configured to manage or control one or more RRC configurations and / or RRC procedures when the base station 164 operates as an SN. The DU 174 is also equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In some examples, the processing hardware in an example implementation includes a MAC controller configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure) and a radio link control (RLC) controller configured to manage or control one or more RLC operations or procedures when the base station 164 operates as an MN or an SN. The process hardware may include further a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0059] FIG. 2A is a block diagram illustrating an example protocol stack 200 according to which a UE communicates with base stations. For instance, the UE 102 may communicate with an eNB, ng-eNB 230 or a gNB 232 (e g., one or more of the base stations 104A. 106A) via the example protocol stack 200.

[0060] In the example protocol stack 200. a physical layer (PHY) 202A of EUTRA provides transport channels to the EUTRA MAC sublayer 204 A, which in turn provides logical channels to the EUTRA RLC sublayer 206A. The EUTRA RLC sublayer 206A in turn provides RLC channels to an EUTRA packet data convergence protocol (PDCP) sublayer 208 and, in some cases, to an NR PDCP sublayer 210.

[0061] Similarly, the NR PHY 202B provides transport channels to the NR MAC sublayer 204B, which in turn provides logical channels to the NR RLC sublayer 206B. The NR RLC sublayer 206B in turn provides data transfer services to the NR PDCP sublayer 210. The NRPDCP sublayer 210 in turn can provide data transfer services to service data adaptation protocol (SDAP) sublayer 212 or an RRC sublayer (not shown in FIG. 2A). The UE 102, in some implementations, supports both the EUTRA and the NR stack as shown in FIG. 2A, to support handover between EUTRA and NR base stations and / or to support DC over EUTRA and NR interfaces. Further, as illustrated in FIG. 2A, the UE 102 can support layering of NR PDCP sublayer 210 over EUTRA RLC sublayer 206A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

[0062] The PDCP sublayers of the example protocol stack 200 provide services such as transfer of user-plane data, ciphering, integrity protection, etc. For example, the EUTRA PDCP sublayer 208 defined for the EUTRA radio interface (e.g., as defined in 3GPP Technical Specification (TS) 36.323) and the NR PDCP sublayer 210 defined for the NR interface (e.g., as defined in 3GPP TS 38.323) provide sequencing of user data and control signaling in the uplink direction as well as in the downlink direction. For instance, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 receive packets that can be referred to as service data units (SDUs), and output packets that can be referred to as protocol data units (PDUs). PDCP sublayers 208 and 210 may receive packets, e.g., from an Internet Protocol (IP) layer, layered directly or indirectly over the EUTRA PDCP sublayer 208 or NR PDCP sublayer 210. PDCP sublayers 208 and 210 may output packets, e.g., to the RLC sublayer 206A or 206B. Except where the difference between SDUs and PDUs is relevant, this disclosure for simplicity refers to both SDUs and PDUs as “packets.”

[0063] On a control plane, in some aspects the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide SRBs. In some other aspects, an RRC sublayer (not shown in FIG. 2 A) of a UE 102 and a base station can exchange RRC messages or non-access-stratum (NAS) messages. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide DRBs to support data exchange. Data exchanged on the NR PDCP sublayer 210 can be SDAP PDUs, IP packets, or Ethernet packets.

[0064] FIG. 2B is a block diagram of an example protocol stack 250 according to which the UE 102 of FIG. 1A communicates with a CU and a DU. For instance, the UE 102, may communicate w ith a DU (e.g., DU 174) and a CU (e.g., CU 172) via the example protocol stack 250. The example protocol stack 250 is functionally split as shown by the example protocol stack 250 in FIG. 2B. The CU at any of the base stations 104, 104A, 104B. 106, 106A, or 1 6B can hold all the control and upper layer functionalities (e.g., RRC 214, SDAP 212, NRPDCP sublayer 210), while the lower layer operations (e.g., NR RLC sublayer 206B, NR MAC sublayer 204B, and NR PHY 202B) are delegated to the DU. To support connection to a 5GC, NR PDCP sublayer 210 provides SRBs to RRC 214, and NR PDCP sublayer 210 provides DRBs to SDAP 212 and SRBs to RRC 214.

[0065] FIGs. 3-5 and 6A-6D are sequence diagrams illustrating several example communications processes in which a base station transmits a configuration to a UE and later activates a configuration for communication between the UE and base station. Generally speaking, events and procedures in FIGs. 3-5 and 6A-6D that are similar are labeled with similar reference numbers (e.g., event 302 is similar to event 402 of FIG. 4 and event 502 of FIG. 5. procedure 390 is similar to procedure 490 of FIG. 4 and procedure 590 of FIG. 5), with differences discussed below where appropriate. With the exception of the differences show n in the figures and discussed below, any of the alternative implementations discussed with respect to a particular event (e.g., for messaging and processing) may apply to events labeled with similar reference numbers in other figures.

[0066] The discussion of FIGs. 3-5 and 6A-6D refers to tuples. A tuple may be represented in the discussion as a comma separated list of elements enclosed in curly brackets (e.g., {element 1, element 2, ... element N}).

[0067] FIG. 3 is a sequence diagram illustrating example operations of a communications process 300 for an intra-CU intra-DU cell switch. The base station 301 of FIG. 3 may be an implementation of the base station 104 of FIG. 1 A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, or the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A.

[0068] In the example shown in FIG. 3, the base station 301 includes a CU 172 and DU 174 and the DU 174 operates the cell 124A. At event 302, the UE 102 initially communicates with the DU 174 on a serving cell (e.g.. the cell 124A), using a serving DU configuration, and communicates with the CU 172 via the DU 174, using a serving CU configuration. The DU 174 is a serving or a source DU (S-DU) for the UE 102. In other words, the DU 174 is a serving DU (S-DU) that communicates with the UE 102. In some implementations, the UE 102 may be configured for carrier aggregation (CA) and communicates with the DU 174 on the cell 124A and one or more other cells (e g., any of cells 124B or 124C of FIG. 1A) usingthe serving DU configuration. The DU 174 operates the one or more other cell(s). The cell 124 A and / or the one or more other cells are serving cells for the UE 102. In other implementations, the UE 102 communicates with the DU 174 on the cell 124A only. In some implementations, the UE102 communicates with the DU 174 on the cell 124A and / or one or more other cells (i.e., serving cells) via one or more TRPs. In the following description, procedure 394 and events 324, 350, 352, 354, and 326 occur or are performed on the serving cell(s). In some implementations, the cell 124A can be a PCell. In such cases, the other cell(s) include SCell(s) and / or one or more additional cells associated with the PCell or an SCell. In other implementations, the cell 124A can be an SCell, and one of the other cells is a PCell. In such cases, remaining other cells may be other SCells and / or additional cells associated with the PCell or a SCell. In the following description, the base station 301 can be the DU 174, the CU 172 alone or both the DU 174 and CU 172.

[0069] In the event 302, the UE 102 may transmit UL PDUs and / or UL control signals to the base station 301 on the cell 124A and / or other cell(s) via one or multiple TRPs. In some implementations, the UE 102 communicates UL PDUs and / or DL PDUs with the base station 301 via radio bearers which can include SRBs and / or DRBs. The base station 301 can configure the radio bearers to the UE 102. In some aspects, the UE 102 may apply one or more security functions (e.g., integrity protection and / or encryption) to UL data packet to generate a security-protected UL data packet, using at least one security key (e.g., integrity protection key and / or encryption key) and at least one security algorithm (e.g., integrity' protection algorithm and / or encryption algorithm), and includes the security-protected data packet in the UL PDU. In such aspects, when the CU 172 receives a UL PDU from the UE 102 via the DU 174, the CU 172 retrieves a security -protected UL data packet from the UL PDU and may apply one or more security functions (e.g., decryption and / or integrity check) to the security -protected UL data packet to obtain a UL data packet, using at least one security key (e.g., integrity protection key and / or encryption key) and at least one security algorithm (e.g.. integrity protection algorithm and / or encryption algorithm). In some implementations, the UL control signals may include one or more of UL control information (UCI), CSI, hybrid automatic repeat request (HARQ) acknowledgements (ACKs), HARQ negative ACKs, scheduling requests and / or sounding reference signals (SRSs).

[0070] Similarly, the UE 102 can receive DL PDUs and / or DL control signals from the base station 301 on the cell 124A and / or one or more other cells via one or more TRPs. In some implementations, the DL control signals include downlink control information (DCI) and reference signals (e.g., synchronization signal block (SSB), CSI reference signals (CSI-RSs), and / or tracking reference signals). The base station 301 can transmit the DCIs on a physical downlink control channel (PDCCH) monitored by the UE 102. on the cell 124A and / or othercell(s) via one or more TRPs. Tn some aspects, to transmit the DL PDUs, the CU 172 may apply one or more security functions (e.g., integrity protection and / or encryption) to a DL data packet to generate a security-protected DL data packet, using at least one security key (e.g.. integrity protection key and / or encryption key), and includes the DL security-protected packet in the DL PDU. In such aspects, when the UE 102 receives a DL PDU from the CU 172 via the DU 174, the UE 102 may obtain the DL data packet by retrieving a security -protected DL data packet from the DL PDU and applying one or more security functions (e.g., decryption and / or integrity check) to the security-protected DL data packet using at least one security key and at least one security algorithm (e.g., integrity protection algorithm and / or encryption algorithm). In some implementations, the security keys used by the CU 172 are the same as the security keys used by the UE 102. In other implementations, the security keys used by the CU 172 are different from the security keys used by the UE 102.

[0071] A security function can include an integrity protection and / or encry ption function, and a security key can include an integrity key and an encryption key for integrity protection / integrity checking and encryption / decry ption respectively. When integrity protection is enabled, a transmitter (e.g., one of the UE 102 and the CU 172) can generate a message authentication code for integrity (MAC-I) to protect the integrity' of the UL or DL data packet. The transmitter can use an integrity key and an integrity algorithm to encrypt the UL or DL data packet to obtain an encrypted packet, using an encryption algorithm. Thus, the transmitter in this case generates a security-protected UL or DL packet including the data packet and the MAC-I.

[0072] When encryption is enabled, the transmitter may use an encryption key and an encry ption algorithm to encry pt a data packet and may include the encry pted data packet in the security-protected packet. When both integrity protection and encryption are enabled, the transmitter can generate a MAC-I for protecting integrity of the data, using an integrity key and an integrity algorithm and encrypt the data along with the MAC-I to generate an encrypted packet and an encrypted MAC-I, using an encryption key and an encryption algorithm. The transmitter then can transmit the security-protected packet to a receiver (i.e., the other of the UE 102 and the CU 172).

[0073] When encryption is enabled, the receiver decrypts the security-protected packet to obtain a data packet using an encryption key and an encryption algorithm. The encryption key may be the same as, or different from, the encryption key used by the transmitter. Similarly,the encryption algorithm may be the same as, or different form, the encryption algorithm used by the transmitter.

[0074] When integrity protection is enabled, the receiver may perform an integrity check on the security-protected packet using an integrity key and an integrity algorithm. In some aspects, the integrity key may be the same integrity key used by the transmitter. In some aspects, the integrity algorithm may be the same as the integrity algorithm used by the transmitter.

[0075] When both encryption and integrity protection are enabled, the receiver decrypts the security-protected packet to obtain an integrity -protected data packet, using an encryption key and an encryption algorithm. As noted above, the encryption key may be the same as, or different from, the encryption key used by the transmitter. Similarly, the encryption algorithm may be the same as, or different form, the encryption algorithm used by the transmitter. The receiver then may perform an integrity check on the integrity-protected data packet using an integrity key and an integrity' algorithm. The integrity' key may be the same integrity key used by the transmitter. The integrity algorithm may be the same as the integrity' algorithm used by the transmitter.

[0076] The security' protection described above may be applied to measurement reports (e.g., at event 304), RRC reconfiguration message (e.g., at event 318), RRC reconfiguration complete message (e.g., at events 320 and 336), and data communication (e.g., at event 340). In some implementations, a security key may include an integrity’ key for integrity protection of controlplane data packets such as RRC messages (e.g., at events 304, 318, 320 and 336). In other implementations, a security key may include an encryption key for encryption / decry ption of control-plane data packets such as RRC messages (e.g., at events 304. 318, 320 and 336). In yet other implementations, a security key may include an integrity key for integrity' protection of user-plane data packets (e.g., communicated via one or more DRBs). In yet other implementations, a security key may include an encryption key for encryption / decryption of user-plane data packets (e.g., communicated via one or more DRBs).

[0077] In some implementations, the serving DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some implementations, the serving DU configuration includes at least one first non-LTM transmission configuration indicator (TCI) state configuration for the serving cells. In some implementations, the DU 174 can transmit these configuration parameters and / or the one or more first non-LTM TCI state configurations to the CU 172. The CU 172 may generateone or more messages (e.g., RRC reconfiguration messages) including the configuration parameters and / or the one or more first non-LTM TCI state configurations and may transmit the one or more messages to the UE 102 via the DU 174. In other implementations, the DU 174 may transmit the configuration parameters and / or the one or more first non-LTM TCI state configurations to the UE 102 directly. In some implementations, the serving DU configuration is CellGroupConfig information element (IE) (e.g., as defined in 3GPP TS 38.331). In other implementations, the serving DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the serving CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the serving CU configuration includes a MeasConfig IE and / or a RadioBear er Config IE (e.g., as defined in 3GPP TS 38.331) or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. The radio configuration parameters or the RadioBearerConfig IE may configure one or more DRBs. In some implementations, the serving DU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and reporting. In other implementations, the serving CU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and reporting. In some implementations, the UE 102 may receive the serving CU configuration or the configuration parameters in the serving CU configuration from the CU 172 via the DU 174. In other implementations, the UE 102 may receive a portion of the serving CU configuration and / or a portion of the serving DU configuration from a base station other than the base station 301 and the remaining portion of these configuration parameters from the base station 301.

[0078] In some implementations, the DU 174 and the UE 102 may communicate with each other using one or more first non-LTM TCI state configurations, e.g., in the events 302, 318, 320, 324, 350, 354, and / or 326. In some implementations, the DU 174 may transmit at least one first non-LTM TCI state Activation / Deactivation command (e.g., via a MAC control element (CE)) to the UE 102 to activate the one or more first non-LTM TCI state configurations. The UE 102 activates the one or more first non-LTM TCI state configurations in response to the one or more first non-LTM TCI state Activation / Deactivation commands. In some implementations, the DU 174 includes a serv ing cell identity (ID) (e.g., a serving cell index) in each of the one or more first non-LTM TCI states Activation / Deactivation commands to identity’ the first non-LTM TCI state configurations. Each serving cell ID may indicate a respective serving cell of the serving cells. In some implementations, the serving DUconfiguration includes the serving cell IDs and may configure associations between the serving cell IDs and the one or more first non-LTM TCI state configurations.

[0079] While communicating with the base station 301, at event 304, the UE 102 may transmit at least one measurement report to the DU 174. In some implementations, the measurement report includes measurement results for a serving cell (e.g., FIG. 1A, cell 124A or FIG. 2, cell 124A) of the UE 102 and / or at least one non-serving cell. In some aspects, for each of the measurement reports, at event 306, the DU 174 may transmit a DU-to-CU message including the measurement report to the CU 172. In some implementations, the DU-to-CU message of the event 306 is an Fl application protocol (F1AP) message (e.g., a UL RRC Message Transfer message). The serving cell includes the cell 124A and / or other cell(s), and the at least one non-serving cell includes the cell 124B and / or additional cell(s). In some implementations, the serving CU configuration includes at least one measurement configuration. In accordance with the at least one measurement configuration, at event 304, the UE 102 may perform measurements and may transmit the measurement reports to the DU 174. In some implementations, the at least one measurement configuration may include one or more Layer 3 (L3) measurement configurations (e.g., MeasConfig IES) and the measurement report may include one or more L3 measurement reports.

[0080] After (e.g., in response to) receiving one or more measurement reports from the UE 102, the CU 172 determines to prepare a first cell (also referred to as ‘‘cell U') as an LTM candidate cell for the UE 102. For example, cell 1 may be FIG. 1A, cell 124B. In some implementations, the base station 301 determines to prepare the first cell for the UE 102 in response to the one or more measurement reports indicating that the first cell might be used by the base station 301 to communicate with the UE 102. In some implementations, the base station 301 determines to prepare the first cell for the UE 102 in response to the one or more measurement reports indicating that the first cell qualifies to be an LTM candidate cell that might be used for communication with the UE 102. In some aspects, the CU 172 determines to prepare the first cell as an LTM candidate cell for the UE 102 if the one or more measurement reports indicate that signal strength and / or quality of the first cell is above a first predetermined threshold, the signal strength of the first cell is better than the strength and / or quality of the serving cell (e.g., cell 124A), and / or the signal strength of the first cell is better than strength and / or quality of the serving cell by a first predetermined threshold. In some other aspects, the CU 172 determines to prepare the first cell as an LTM candidate cell for the UE 102 regardless of whether a measure report is received from the UE 102 or not.

[0081] Tn response to determining to prepare the first cell as a candidate cell for LTM, at event 308 the CU 172 may transmit a first CU-to-DU message to the DU 174 to prepare the first cell as an LTM candidate cell for the UE 102. In some implementations, the CU 172 includes a cell identity (ID) 1 of the first cell in the first CU-to-DU message to request the DU 174 to prepare the first cell as an LTM candidate cell for the UE 102. As one example, the cell ID 1 may be a cell global identity (CGI). As another example, the cell ID 1 may be a portion of the CGI. As a further example, the cell ID 1 may be a physical cell ID (PCI). In some implementations, the CU 172 includes an LTM indicator in the first CU-to-DU message to indicate that the DU 174 is to prepare the first cell for LTM. In some implementations, the CU 172 includes the LTM indicator in an LTM Information Setup IE and includes the LTM Information Setup IE in the first CU-to-DU message. In other implementations, the CU 172 includes the LTM indicator in an LTM Information Modify IE and includes the LTM Information Modify IE in the first CU-to-DU message.

[0082] In response to the first CU-to-DU message, the DU 174 may generate a first LTM DU configuration (referred to as LTM DU configuration 1) for the UE 102, which configures the first cell for LTM. In some implementations, the CU 172 includes a first LTM configuration ID (referred to as LTM ID 1) in the first CU-to-DU message and the DU 174 may associate the LTM ID 1 and / or the cell ID 1 with the LTM DU configuration 1. At event 310, the DU 174 transmits a first DU-to-CU message including the LTM DU configuration 1 to the CU 172 in response to the first CU-to-DU message.

[0083] The events 308 and 310 are collectively referred to in FIG. 3 as an LTM preparation procedure 390.

[0084] In some implementations, the DU 174 includes, in the first DU-to-CU message, the cell ID 1 of the first cell associated with the LTM DU configuration 1 to indicate that the LTM DU configuration 1 is configured for or associated with the first cell. In cases where the CU 172 performs multiple LTM preparation procedures (e.g.. the procedure 390 and the LTM preparation procedures 2-N described below) with the DU 174 to prepare multiple LTM candidate cells, the CU 172 may determine that the LTM DU configuration 1 is configured for or associated with the first cell, based on the cell ID 1 in the first DU-to-CU message.

[0085] In some implementations, the CU 172 does not include an LTM reference DU configuration in the first CU-to-DU message. In such cases, the DU 174 may generate an LTM reference DU configuration and includes the LTM reference DU configuration in the first DU-to-CU message. In some implementations, the DU 174 may generate the LTM DU configuration 1 as a delta configuration to augment the LTM reference DU configuration. For example, the LTM DU configuration 1 may include changes, deletions, and / or additions to the LTM reference DU configuration. In other implementations, the DU 174 may generate the LTM DU configuration 1 as a complete configuration, e.g., a standalone configuration and not with respect to the LTM reference DU configuration.

[0086] In some implementations, the CU 172 includes an LTM reference DU configuration request in the first CU-to-DU message. In such implementations, the DU 174 may generate the LTM reference DU configuration and includes the LTM reference DU configuration in the first DU-to-CU message in response to the request. In some implementations, the CU 172 determines whether the UE 102 supports an LTM reference configuration. If the CU 172 determines that the UE 102 supports an LTM reference configuration, the CU 172 includes the LTM reference DU configuration request in the first CU-to-DU message. The DU 174 includes the LTM reference DU configuration in the first DU-to-CU message in response to the LTM reference DU configuration request. If the CU 172 determines that the UE 102 does not support an LTM reference configuration, the CU 172 may not include the LTM reference DU configuration request in the first CU-to-DU message. In this case, the DU 174 may generate the LTM DU configuration 1 as a complete configuration and may not include a LTM reference DU configuration in the first DU-to-CU message. In other implementations, the CU 172 transmits an additional CU-to-DU message including the LTM reference DU configuration request to the DU 174 instead of the first CU-to-DU message. In response, the DU 174 includes an additional DU-to-CU message including the LTM reference DU configuration to the CU 172. In yet other implementations, the DU 174 determines whether the UE 102 supports an LTM reference configuration. If the DU 174 determines that the UE 102 supports an LTM reference configuration, the DU 174 includes the LTM reference DU configuration in the first DU-to-CU message. If the DU 174 determines that the UE 102 does not support an LTM reference configuration, the DU 174 may not include a / the LTM reference DU configuration in the first DU-to-CU message.

[0087] In some implementations, the CU 172 includes an LTM reference DU configuration in the first CU-to-DU message. In some implementations, the CU 172 may receive the LTM reference DU configuration from an additional DU during an LTM preparation procedure as described above and also described below' with respect to FIG. 4. In other implementations, the CU 172 is preconfigured with the LTM reference DU configuration. In someimplementations, the DU 174 may generate the LTM DU configuration 1 as a delta configuration with changes, deletions, and / or deletions to augment the LTM reference DU configuration. In other implementations, the DU 174 ignores the LTM reference DU configuration and generates the LTM DU configuration 1 as a complete (e.g., standalone) configuration, i.e., not on top of the LTM reference DU configuration.

[0088] If the DU 174 generates the LTM DU configuration 1 as a complete configuration, the DU 174 may include a complete configuration indication in the first DU-to-CU message to indicate that the LTM DU configuration 1 is a complete configuration. In some implementations, if the first CU-to-DU message does not include an LTM reference DU configuration, the CU 172 may determine that the LTM DU configuration 1 is a complete configuration. If the first CU-to-DU message includes an LTM reference DU configuration, the CU 172 may determine that the LTM DU configuration 1 is a delta configuration.

[0089] In some implementations, the LTM reference DU configuration is different from the serving DU configuration. In some implementations, a portion of the LTM reference DU configuration is the same as a portion of the serving DU configuration and the rest of the LTM reference DU configuration is different from the rest of the serving DU configuration. In yet other implementations, the LTM reference DU configuration is the same as the serving DU configuration. In some implementations, the LTM reference DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some implementations, the LTM reference DU configuration is the CellGroupConfig IE (e.g., as defined in 3GPP TS 38.331). In other implementations, the LTM reference DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the LTM reference DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and / or reporting.

[0090] To prepare the first cell as an LTM candidate cell for the UE 102, at event 312, the CU 172 may transmit a second CU-to-DU message to the DU 174. The second CU-to-DU message may include a CSI resource configuration (referred to as CSI resource configuration 1) and / or an LTM SSB configuration (referred to as LTM SSB configuration 1) to request the DU 174 to generate one or more CSI report configurations (e.g., LTM CSI report configuration 1, potentially among other CSI report configurations). The CSI resource configuration (e.g., LTM CSI resource configuration 1) may include configuration parameters configuring at leastone reference signal (RS) transmited on the first cell. The at least one RS may include one or more SSBs and / or one or more CSI-RSs. The LTM SSB configuration may include SSB configuration parameters configuring a SSB frequency, a subcarrier spacing, a SSB periodicity', SSB positions and / or SSB power for SSB(s) transmited on the first cell.

[0091] After (e.g., in response to) receiving the CSI resource configuration, the DU 174 may generate one or more CSI report configurations based on the CSI resource configuration and includes the one or more CSI report configurations in a serving DU configuration (referred to as a second serving DU configuration to distinguish from the serving DU configuration in event 302). In some implementations, the one or more CSI report configurations configure the UE 102 to transmit CSI reports based on measurements of the RS(s).

[0092] At event 314, the DU 174 transmits a second DU-to-CU message including the second serving DU configuration to the CU 172. In some implementations, the CSI resource configuration includes one or more LTM-CSI-ResourceConfig-rl8 lEs. In other implementations, the CSI resource configuration includes an Itm-CSI- ResourceConfigToAddModList field or IE. In some implementations, the second serving DU configuration is a CellGroupConflg IE.

[0093] In some implementations, the CU 172 includes the cell ID 1 and / or the LTM ID 1 in the second CU-to-DU message. In one implementation, the CU 172 does so to indicate that the CSI resource configuration is associated with the first cell. In another implementation, the CU 172 does so for the DU 174 to associate the LTM ID 1 with the first cell, the cell ID 1, the LTM DU configuration 1, and / or the one or more CSI report configurations. Based on the above implementations, the DU 174 can associate the LTM ID 1 and / or the cell ID 1 with configurations (e.g., LTM DU configuration 1, the CSI resource configuration, and / or the one or more CSI report configurations) related to the first cell. In such implementations, the CU 172 may or may not include the LTM ID 1 in the first CU-to-DU message.

[0094] In some other implementations, the CU 172 includes the CSI resource configuration in the first CU-to-DU message and the DU 174 includes the one or more CSI report configurations in the first DU-to-CU message.

[0095] In some implementations, the DU 174 may transmit the LTM SSB configuration or the SSB configuration parameters to the CU 172. e.g., in the first DU-to-CU message, the second DU-to-CU message or an additional DU-to-CU message. In some implementations, the DU 174 may transmit the additional DU-to-CU message in response to receiving an additionalCU-to-DU message from the CU 172. In other implementations, the DU 174 may transmit the fourth DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message or the second CU-to-DU message.

[0096] The events 312 and 314 are collectively referred to in FIG. 3 as an LTM CSI report configuration and / or LTM ID configuration procedure 392.

[0097] After receiving the first DU-to-CU message, the CU 172 may generate a first LTM candidate configuration (referred to as LTM candidate configuration 1) including the LTM DU configuration 1 and may generate a first RRC reconfiguration message including the LTM candidate configuration 1 and the LTM ID 1. In some implementations, the CU 172 includes LTM CU configuration 1 in the LTM candidate configuration 1. In other implementations, the CU 172 does not include an LTM CU configuration in the LTM candidate configuration 1.

[0098] At event 316, the CU 172 may transmit a third CU-to-DU message including the first RRC reconfiguration message to the DU 174.

[0099] At event 318, the DU 174 may transmit the first RRC reconfiguration message to the UE 102.

[0100] At event 320, in response to receiving the first RRC configuration message, the UE 102 may transmit a first RRC reconfiguration complete message to the DU 174.

[0101] At event 322, the DU 174 then may transmit a third DU-to-CU message including the first RRC reconfiguration complete message to the CU 172.

[0102] If the first DU-to-CU message includes the LTM reference DU configuration, the CU 172 may generate an LTM reference configuration including the LTM reference DU configuration. In such cases, the CU 172 may include the LTM reference configuration in the first RRC reconfiguration message. In some implementations, the CU 172 includes an LTM reference CU configuration in the LTM reference configuration. In such cases, the CU 172 may generate the LTM CU configuration 1 as a delta configuration based on the LTM reference CU configuration. For example, the delta configuration may include changes, additions, or deletions with respect to the LTM reference CU configuration. In other implementations, the CU 172 does not include an LTM reference CU configuration in the LTM reference configuration. In such cases, the CU 172 may generate the LTM CU configuration 1 as a complete (e.g., standalone) configuration. Additionally or alternatively, the CU 172 may transmit a second RRC reconfiguration message including the LTM reference configuration tothe UE 102 via the DU 174, similar to the events 316 and 318 described above. In response, the UE 102 may transmit a second RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322 described above. In some implementations, if the CU 172 does not receive an LTM reference DU configuration, the CU 172 may generate an LTM reference configuration including only the LTM reference CU configuration. In other implementations, if the CU 172 does not receive an LTM reference DU configuration, the CU 172 may not generate an LTM reference configuration.

[0103] In some implementations, if the first DU-to-CU message includes the complete configuration indication, the CU 172 may determine that the LTM DU configuration 1 is a complete configuration. If the first DU-to-CU message does not include the complete configuration indication, the CU 172 may determine that the LTM DU configuration 1 is a delta configuration. In some implementations, if the LTM DU configuration 1 is a complete configuration, the CU 172 may generate the LTM candidate configuration 1 as a complete configuration. If the LTM DU configuration 1 is a delta configuration, the CU 172 may generate the LTM candidate configuration 1 as a delta configuration. If the LTM candidate configuration 1 is a complete configuration, the CU 172 includes, in the first RRC reconfiguration message, a complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration. If the LTM candidate configuration 1 is a delta configuration, the CU 172 excludes the complete configuration indication from the first RRC reconfiguration message to indicate that the LTM candidate configuration 1 is a delta configuration.

[0104] In the case that the CU 172 performs the procedure 392, the CU 172 may include the second serving DU configuration in the first RRC reconfiguration message. In the case that the CU 172 does not perform the procedure 392, the CU 172 may transmit a third RRC reconfiguration message including the second serving DU configuration to the UE 102 via the DU 174, similar to the events 31 and 318 described above. In response, the UE 102 may transmit a third RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322 described above.

[0105] In some implementations, the CU 172 includes the CSI resource configuration in the first RRC reconfiguration message, the second RRC reconfiguration message, or the third RRC reconfiguration message. In other implementations, the CU 172 may transmit a fourth RRC reconfiguration message including the CSI resource configuration to the UE 102 via the DU174, similar to the events 316 and 318 described above. In response, the UE 102 may transmit a fourth RRC reconfiguration complete message to the UE 102 via the DU 174, similar to the events 320 and 322 described above.

[0106] In some implementations, the DU 174 may transmit a DU-to-CU message to the CU 172 that includes early synchronization information for the UE 102. The DU-to-CU message may be the first DU-to-CU message, the second DU-to-CU message or a fourth DU-to-CU message. In some implementations, the DU 174 may transmit the fourth DU-to-CU message in response to receiving a fourth CU-to-DU message from the CU 172. In other implementations, the DU 174 may transmit the fourth DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message or the second CU-to-DU message. In such implementations, the DU 174 may transmit the fourth DU- to-CU message if the DU 174 determines that the UE 102 supports (i.e., is capable of) early UL synchronization with an LTM candidate cell (e.g., the UE 102 supports early TA acquisition with an LTM candidate cell, early RA on an LTM candidate cell, or UE measured TA). If the DU 174 determines that the UE 102 does not support the early UL synchronization with an LTM candidate cell, the DU 174 does not transmit the early synchronization information to the CU 172. In other implementations, the CU 172 may transmit a CU-to-DU message including an early synchronization information request (e.g., an IE) to the DU 174, and the DU 174 includes the early synchronization information in the DU-to-CU message in response to the early synchronization information request. The CU-to-DU message may be the first CU-to-DU message, the second CU-to-DU message or the fourth CU-to-DU message. In such implementations, the CU 172 does so if the CU 172 determines that the UE 102 supports the early UL synchronization with an LTM candidate cell. If the CU 172 determines that the UE 102 does not support the early UL synchronization with an LTM candidate cell, the CU 172 does not request the DU 174 to provide the early synchronization information for the UE 102. If the CU 172 receives the early synchronization information, the CU 172 includes the early synchronization information in the first, second, third or fourth RRC reconfiguration message. If the CU 172 receives the early synchronization information, the CU 172 may transmit a fifth RRC reconfiguration message including the early synchronization information to the UE 102 via the DU 174, similar to the events 316 and 318 described above. In response, the UE 102 may transmit a fifth RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322 described above.

[0107] Tn some implementations, the early synchronization information may include a random access channel (RACH) configuration (referred to as RACH configuration 1) and / or one or more TCI state configurations (referred to as TCI state configuration 1). In some implementations, the early synchronization information request may include a request for a RACH configuration. If the early synchronization information request includes the request for a RACH configuration, the DU 174 includes the RACH configuration in the early synchronization information or in a DU-to-CU message (e.g., the first, second or fourth DU- to-CU message). If the early synchronization information request does not include the request for a RACH configuration, in some aspects, the DU 174 neither includes the RACH configuration in the early synchronization information nor in the DU-to-CU message.

[0108] In some implementations, the CU 172 may include, in the first, second, third, fourth and / or fifth RRC reconfiguration messages, one or more other LTM related configurations for the first cell. For example, the other LTM related configuration(s) include a PCI of the first cell and / or the LTM SSB configuration.

[0109] The events 316, 318, 320, 322 are collectively referred to in FIG. 3 as an LTM configuration delivery procedure 394. In the following description, LTM configuration delivery procedure 1 may be used to represent the procedure 394. The second, third, fourth and / or fifth RRC reconfiguration messages and the second, third, fourth and / or fifth RRC reconfiguration complete messages, the related CU-to-DU message(s) and / or the related DU- to-CU message(s) may also be considered to be part of the LTM configuration delivery procedure 394. In some implementations, the RRC reconfiguration message and the RRC reconfiguration complete message described above may be an RRC Reconfiguration message and an RRCReconfigurationComplete message, respectively.

[0110] In some implementations, the first CU-to-DU message may be a UE Context Modification Request message, and the first DU-to-CU message may be a UE Context Modification Response message. In some implementations, the second CU-to-DU message may be a UE Context Modification Request message, and the second DU-to-CU message may be a UE Context Modification Response message or a UE Context Modification Required message. In the case of the UE Context Modification Required message, the CU 172 may transmit a UE Context Modification Confirm message to the DU 174 in response to the UE Context Modification Required message. In some implementations, the third CU-to-DU message may be a DL RRC Message Transfer message. In other implementations, the thirdCU-to-DU message may be a UE Context Modification Request message. In some implementations, the third DU-to-CU message may be a UL RRC Message Transfer message. In other implementations, the third DU-to-CU message may be a UE Context ModificationResponse message.[OHl] In some implementations, the LTM reference CU configuration may be different from the serving CU configuration. In some implementations, a portion of the LTM reference CU configuration may be the same as a portion of the serving CU configuration and the rest of the LTM reference CU configuration may be different from the rest of the serving CU configuration. In yet other implementations, the LTM reference CU configuration may be the same as the serving CU configuration.

[0112] In some implementations, the LTM reference CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 includes a MeasConfig IE and / or a RadioBear er Config IE (e.g., as defined in 3GPP TS 38.331) or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE.

[0113] In some implementations, the LTM CU configuration 1 and / or the LTM reference CU configuration may include PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 or the LTM reference CU configuration may include a MeasConfig IE and / or a RadioBearerConfig IE (e.g., as defined in 3GPP TS 38.331) or may include configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE.

[0114] In some implementations, the LTM DU configuration 1 may include a plurality of configuration parameters for the UE 102 to communicate with the DU 174 on the first cell. In some implementations, the plurality of configuration parameters may include physical layer configuration parameters (e.g., PhysicalC ellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE) and / or RLC configuration parameters (e.g., RLC- BearerConfig IE(s)). In some further implementations, the plurality of configuration parameters may include a special cell configuration (e.g., SpCellConfig IE) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some implementations, the LTM DU configuration 1 may be a CellGroupConfig IE (e.g., as defined in 3GPP TS 38.331). In other implementations, the LTM DU configuration 1 may include configuration parameters in the CellGroupConfig IE.

[0115] Tn some implementations, the LTM DU configuration 1 may include a first LI measurement configuration (e.g., a CSI-MeasConfig IE) and / or at least one first TCI state configuration. In other implementations, the LTM CU configuration 1 includes the first TCI state configuration(s). In some implementations, the first LI measurement configuration includes at least one first RS resource configuration and / or at least one first report configuration. In some implementations, the first RS resource configuration(s) may configure one or more RSs or one or more RS resources associated with the cell 1. The RS(s) may include SSB(s) and / or CSI-RS(s). The RS resource(s) may include SSB resource(s) and / or CSI-RS resource(s). In some implementations, each of the first RS resource configuration(s) may include a RS resource configuration ID. In some implementations, the first RS resource configuration(s) is / are (similar to) CSI-ResourceConfig IE(s). In some implementations, the first report configuration(s) configures one or more UL resources (e.g., physical uplink control channel (PUCCH) resources or physical uplink shared channel (PUSCH) resources) on the first cell for the UE 102 to transmit measurement results (e.g., CSI reports or LTM CSI reports). In some implementations, each of the first report configuration(s) may include one or more RS resource configuration IDs identifying one or more RS resource configurations included in the first RS resource configuration(s). In some implementations, each of the first TCI state configuration(s) configures a TCI state that associates one or two DL RSs with a corresponding quasi-colocation (QCL) type. The DL RS(s) may be associated with the cell 1.

[0116] After receiving the LTM-related configurations and the second serving DU configuration or after receiving the RRC reconfiguration message(s) described above, the UE 102 may perform measurements on at least one first RS, may generate at least one first LI measurement result based on the measurements, and. at event 324, may transmit at least one first LI measurement report including the first LI measurement result(s) to the DU 174. The first RS(s) may comprise SSB(s) and / or CSI-RS(s). In some implementations, the first RS(s) and / or transmission pattem(s) of the first RS(s) are configured in the CSI report configuration(s), the LTM SSB configuration, and / or the CSI resource configuration. The UE 102 may perform the measurements on the first RS(s) in accordance with the CSI report configuration(s), the LTM SSB configuration, and / or the CSI resource configuration.

[0117] After receiving the LTM-related configurations and the second serving DU configuration or after receiving the RRC reconfiguration message(s) described above, the UE 102 may perform measurements on at least one second RS, may generate at least one second LI measurement result based on the measurements, and may transmit at least one second LImeasurement report including the first LI measurement result(s) to the DU 174. The second RS(s) may comprise SSB(s) and / or CSI-RS(s). In some implementations, the second RS(s) and / or transmission pattem(s) of the second RS(s) are configured in one or more second CSI report configurations and / or one or more second CSI resource configuration that are included in the serving DU configuration (used in communication between the UE 102 and S-DU at event 302) and / or the second serving DU configuration. The UE 102 may perform the measurements on the second RS(s) in accordance with the second CSI report configuration(s) and / or the second CSI resource configuration(s). The second CSI report configuration(s) may include non-LTM CSI report configuration(s) and / or LTM CSI report configuration(s). The second CSI resource configuration(s) may include non-LTM CSI resource configuration(s) and / or LTM CSI resource configuration(s).

[0118] At event 350, after transmitting the RACH configuration to the UE 102 via the CU 172, the DU 174 may transmit a PDCCH order to the UE 102 to command the UE 102 to transmit a RA preamble on the first cell. In response to the PDCCH order, the UE 102 may transmit a RA preamble on the first cell. The DU 174 may include the PDCCH order information in the PDCCH order. The PDCCH order information may include an RA preamble index, a UL or a supplemental UL indicator, an SSB index, and / or a physical RACH mask index. In some implementations, the DU 174 includes the LTM ID 1 in the PDCCH order to indicate the first cell.

[0119] At event 352, the UE 102 identifies the first cell based on the LTM ID 1 in the PDCCH order and may transmit the RA preamble on the first cell to the DU 174, using the PDCCH order information. Correspondingly, the DU 174 may receive the RA preamble in accordance with the PDCCH order information. In some implementations, the DU 174 may determine the SSB index based on LI measurement report(s) received at event 324, the CSI resource configuration, the CSI report configuration, and / or the LTM SSB configuration. In some implementations, the LI measurement report(s) may include the SSB index. In other implementations, the LI measurement report(s) may include a synchronization signal / physical broadcast channel (SS / PBCH) block resource indicator (SSBRI) corresponding to the SSB index. In such implementations, the DU 174 determines the SSB index based on the SSBRI.

[0120] At event 324, in some implementations, the DU 174 determines whether to transmit the PDCCH order based on the LI measurement result(s). In some implementations, if the LI measurement result(s) indicate that the first cell qualifies for the UE 102 to perform RA forearly UL synchronization, the DU 174 may transmit the PDCCH order. If the L 1 measurement result(s) indicate that the first cell does not qualify for the UE 102 to perform RA for early UL synchronization, the DU 174 refrains from transmitting the PDCCH order. In other implementations, if the LI measurement result(s) indicate that the first cell qualifies for the UE 102 to access, the DU 174 may transmit the PDCCH order. If the LI measurement result(s) indicate that the first cell does not qualify for the UE 102 to access, the DU 174 refrains from transmitting the PDCCH order. In yet other implementations, the DU 174 may transmit the PDCCH order after receiving the RRC reconfiguration complete message (event 320), regardless of the LI measurement result(s).

[0121] At event 354, after transmitting the LI measurement report(s) (event 324) or the RA preamble (event 352), the UE 102 may transmit additional LI measurement report(s) to the DU 174, similar to the event 324. The DU 174 determines to command the UE 102 to perform an LTM cell switch to the first cell based on the additional LI measurement report(s) and / or the LI measurement report(s) obtained at event 324.

[0122] At event 326, in response to the determination, the DU 174 may generate an LTM Cell Switch Command (e.g.. a MAC CE) including the LTM ID 1 and may transmit the LTM Cell Switch Command to the UE 102.

[0123] At event 328, in response to the determination, the DU 174 may transmit a DU-CU Cell Switch Notification message to the CU 172.

[0124] At event 332, in response to the LTM Cell Switch Command, the UE 102 may perform an LTM cell switch to the first cell. For example, when the UE 102 receives the LTM Cell Switch Command, the UE 102 may identify7the LTM candidate configuration 1 from the LTM ID 1 and may access the first cell using the LTM candidate configuration 1. Depending on the implementation, the UE 102 may stop communicating on the serving cell(s) in response to the LTM Cell Switch Command.

[0125] At event 334, the DU 174 detects the UE 102 has accessed the first cell in the event 332. In response to the detection, the DU 174 may transmit an Access Success message to the CU 172 to indicate that the UE 102 has accessed the first cell.

[0126] At event 336, as part of the LTM cell switch, the UE 102 may access the first cell and may transmit an RRC reconfiguration complete message to the DU 174 via the first cell.

[0127] At event 338, the DU 174 may transmit a DU-to-CU message (e.g., UL RRC Message Transfer message) including the RRC reconfiguration complete message to the CU 172. In turn, the DU 174 may transmit a fifth DU-to-CU message including the RRC reconfiguration complete message to the CU 172.

[0128] In some implementations, the DU 174 includes, in the LTM Cell Switch Command, a TA value for UL synchronization with the first cell. In one implementation, the DU 174 may derive the TA value based on the RA preamble (e.g., reception timing of the RA preamble). In another implementation, the DU 174 may derive the TA value from an UL transmission on the serving cell (e.g., the cell 124A of FIGs. 1A and / or IB) from the UE 102. The UE 102 may apply the TA value to synchronize with the first cell in UL transmission. After applying the TA value, the UE 102 may transmit the first UL transmission on the first cell based on the LTM candidate configuration 1 without performing a RA procedure on the first cell. In some implementations, the UE 102 may transmit the first UL transmission on the first cell using a UL grant. In such cases, the first UL transmission is a PUSCH transmission. In some implementations, the PUSCH transmission includes the RRC reconfiguration complete message of event 336. In some implementations, the UL grant is a configured grant and the LTM candidate configuration 1 or the LTM DU configuration 1 includes the configured grant configuration configuring the configured grant. In other implementations, the UL grant is a dynamic grant that the UE 102 may receive on a PDCCH on the first cell. After transmitting the first UL transmission, the UE 102 may receive a PDCCH transmission addressing to a cell radio network temporary' identifier (C-RNTI) of the UE 102 and determines that the LTM cell switch is completed successfully in response to receiving the PDCCH transmission.

[0129] The PDCCH transmission may include an UL grant or a DL assignment. In the case of the UL grant, the UE 102 may transmit a PUSCH transmission to the DU 174 on the first cell using the UL grant. In the case of the DL assignment, the DU 174 may transmit a physical downlink shared channel (PDSCH) transmission to the UE 102 on the first cell in accordance with the DL assignment. The DU 174 may transmit, at event 334, the Access Success message to the CU 172 after receiving (e.g., in response to) the first UL transmission, transmitting the PDCCH transmission, receiving the PUSCH transmission, or transmitting the PDSCH transmission.

[0130] In other implementations, the DU 174 does not include a TA value in the LTM CellSwitch Command of event 326. If the LTM Cell Switch Command does not include a TAvalue, at event 332, the UE 102 may perform an RA procedure on the first cell in accordance with the RA configuration parameters. In some implementations, the RA configuration parameters are included in the LTM candidate configuration 1. the LTM DU configuration 1 and / or the LTM Cell Switch Command. In some implementations, the RA configuration parameters configure physical random access channel (PRACH) resources, an association between SSB and PRACH resources, and / or one or more PRACH occasions. If the UE 102 successfully completes the RA procedure of event 332, the UE 102 determines the LTM cell switch to the first cell is completed successfully. Depending on implementations and / or the RA configuration parameters, the RA procedure can be a four-step RA procedure or a two-step RA procedure. Depending on implementations and / or the RA configuration parameters, the RA procedure can be a contention-free RA (CFRA) procedure or a contention-based RA (CBRA) procedure. During the four-step RA procedure, the UE 102 may transmit an RA preamble (i.e., Message 1) on the first cell and may receive a RA response (i.e., Message 2) on the first cell from the DU 174 in response to the RA preamble. The UE then may transmit Message 3 on the first cell using a UL grant in the RA response, and the DU 174 may transmit a Message 4 on the first cell to the UE 102 in response. In some implementations, the Message 4 is a DCI. In the case where the RA procedure is a CBRA procedure, the UE 102 determines contention resolution is successful in response to receiving the Message 4. In the case where the RA procedure is a CBRA procedure, the RA preamble is a dedicated preamble and the UE 102 determines contention resolution is successful in response to receiving the RA response. During the two-step RA procedure, the UE 102 may transmit a Message A on the first cell and the DU 174 may transmit a Message B to the UE 102 on the first cell in response. In the case where the RA procedure is a CFRA or CBRA procedure, the UE 102 determines contention resolution is successful in response to receiving the Message B. The UE 102 may include the RRC reconfiguration complete message of event 336 in the Message 3 or Message A. Alternatively or additionally, the UE 102 may transmit the RRC reconfiguration complete message of event 336 after completing the RA procedure. The DU 174 may transmit the Access Success message of event 334 to the CU 172, after receiving the Message 3 or Message A, the RRC reconfiguration complete message of event 336, or transmitting the Message 4 or Message B.

[0131] In some implementations, the DU 174 may include a first set of LTM CFRA configuration parameters in the LTM Cell Switch Command to configure the UE 102 to perform a CFRA procedure to access the first cell. In some implementations, the first set of LTM CFRA configuration parameters may include one or more of a first RA preamble index,a first SSB index, a first PRACH Mask index, and / or a first UL / suppl emental UL(SUL) indicator. In some implementations, the first UL / NUL indicator configures the UE 102 to perform the CFRA procedure on a normal UL (NUL) or a SUL. For example, if the first UL or SUL indicator indicates UL (e.g., the first UL or SUL indicator is set to a first value), the UE 102 may perform the CFRA procedure on UL. If the first UL or SUL indicator indicates SUL (e.g., the first UL or SUL indicator is set to a second value), the UE 102 may perform the CFRA procedure on the SUL. The UE 102 may perform the CFRA procedure to access the first cell using the LTM CFRA configuration parameters and at least one RACH configuration at event 332. The LTM candidate configuration 1 may include the RACH configuration(s). In some aspects, the RACH configuration(s) may not be configured for early UL synchronization. In some implementations, the RACH configuration(s) may be configured for an LTM cell switch. In some implementations, the at least one RACH configuration may include a common RACH configuration (e.g., RACH-ConflgCommon IE) and / or a generic RACH configuration (e.g., RACH-ConfigGeneric IE). In some implementations, the RACH configuration(s) does not include a dedicated RACH configuration (e.g., RACH-ConfigDedicated IE). In other implementations, the RACH configuration(s) includes a dedicated RACH configuration (e.g., RACH-ConflgDedicated IE). The DU 174 may perform the CFRA procedure with the UE 102 in accordance with the first set of LTM CFRA configuration parameters and the RACH configuration(s).

[0132] In some implementations, the DU 174 may determine whether to include the first set of LTM CFRA configuration parameters in the LTM Cell Switch Command, based on the measurement report(s) received at event 354. In some implementations, the DU 174 may obtain (e.g., retrieve, derive, calculate, and / or determine) one or more measurement results from the measurement report(s). In some implementations, the one or more measurement results may include a measurement result for a first SSB identified by the first SSB index. The DU 174 may transmit the first SSB on the first cell. In such cases, if the measurement result for the first SSB is above (or equal to) a second predetermined threshold, the DU 174 includes the first set of LTM CFRA configuration parameters in the LTM Cell Switch Command. If the measurement result for the first SSB is below (or equal to) the second predetermined threshold, the DU 174 refrains from including the first set of LTM CFRA configuration parameters in the LTM Cell Switch Command.

[0133] In some implementations, the DU 174 may configure the first set of LTM CFRA configuration parameters. The DU 174 may configure one or more additional sets of LTMCFRA configuration parameters and each of the one or more additional sets may include one or more of an RA preamble index, an SSB index, a PRACH mask index, and / or a UL or SUL indicator for the first cell. In some implementations, the first set and / or the one or more additional sets may be configured specifically for the first cell. In other implementations, the DU 174 may configure the first set and / or the one or more additional sets for any cell operated by the DU 174. In some implementations, the DU 174 may configure the first set and / or the one or more additional sets for one of UL (i.e., NUL) and SUL. In other implementations, the DU 174 may configure the first set for one of UL and SUL and configures the additional set for the other of UL and SUL.

[0134] In some implementations, the DU 174 identifies the first SSB index based on the measurement report(s) as described above, and the DU 174 identifies the first set of LTM CFRA configuration parameters based on the first SSB index. In some implementations, the DU 174 may determine a value of the first UL or SUL indicator based on the measurement result for the first SSB. For example, if the measurement result is below (or equal to) a third predetermined threshold, the DU 174 sets the first UL or SUL indicator to a first value indicating UL (i.e., NUL). If the measurement result for the first SSB is above (or equal to) the third predetermined threshold, the DU 174 sets the first UL or SUL indicator to a second value indicating SUL. In another example, if the measurement result is above (or equal to) a third predetermined threshold, the DU 174 sets the first UL or SUL indicator to a first value indicating UL (i.e., NUL). If the measurement result for the first SSB is below (or equal to) the third predetermined threshold, the DU 174 sets the first UL or SUL indicator to a second value indicating SUL. In other implementations, the DU 174 may determine a value of the first UL or SUL indicator based the LTM DU configuration 1. For example, if the LTM DU configuration 1 includes a RACH configuration for UL and does not include a RACH configuration for SUL, the DU 174 sets the first UL or SUL indicator to the first value. If the LTM DU configuration 1 includes a RACH configuration for SUL and might or might not include a RACH configuration for UL, in some aspects, the DU 174 may set the first UL or SUL indicator to the second value. In some other aspects, the DU 174 may determine a value of the first UL or SUL indicator based on the measurement result for the first SSB as described above. In yet other implementations, the DU 174 sets the first UL or SUL indicator to a preconfigured value (e.g., the first value), e.g., because the DU 174 does not support SUL. In yet other implementations, the DU 174 sets the first UL or SUL indicator to a preconfigured value (e.g., the second value), e.g., because the DU 174 is preconfigured to do so.

[0135] Tn some implementations, the first, second and third predetermined thresholds may be the same threshold (e.g., have the same threshold value). In other implementations, at least two of the first, second and third predetermined thresholds are different or set to different values.

[0136] At event 340, after completing the LTM cell switch to the first cell as described above, the UE 102 communicates with the DU 174 and the CU 172 via the first cell using the LTM candidate configuration 1. In the case of the LTM reference configuration, in some aspects, the UE 102 may apply the LTM reference configuration first and then apply the LTM candidate configuration 1 to augment the LTM reference configuration.

[0137] In some implementations, each of the TCI state configuration(s) may include a TCI state ID. In some implementations, the DU 174 includes a first TCI state ID indicating a first one of the TCI state configuration(s) in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command. The UE 102 may identify the first one of the TCI state configuration(s) based on the first TCI state ID and may apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions with the DU 174 in the events 332, 336 and / or 340. The DU 174 may apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions with the UE 102 in the events 332, 336 and / or 340. In other implementations, in the case where the DU 174 uses separate TCI states, the DL TCI state and the UL TCI state may have different TCI state IDs. In such cases, the DU 174 may include, in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command, a first TCI state ID for DL and / or a second TCI state ID for UL that identify a first one and a second one of the TCI state configuration(s). The UE 102 may identify the first TCI state configuration and the second TCI state configuration based on the first TCI state ID and the second TCI state ID respectively. The UE 102 may apply the first TCI state configuration and the second TCI state configuration to communicate DL transmissions and UL transmissions, respectively, with the DU 174 in the events 332, 336 and / or 340. The DU 174 may identify the first TCI state configuration and the second TCI state configuration based on the first TCI state ID and the second TCI state ID respectively. The DU 174 may apply the first TCI state configuration and the second TCI state configuration to communicate DL transmissions and UL transmissions, respectively, with the UE 102 in the events 332, 336 and / or 340.

[0138] In some implementations, the CU 172 may prepare additional cell(s) (i.e., cell(s) 2-N) as LTM candidate cell(s) for the UE 102 with the DU 174, before or after transmitting theLTM Cell Switch Command or during, before or after the procedure 390 or 392, as described above. N is an integer greater than 1. For example, the CU 172 may perform additional LTM preparation procedure(s) 2-N with the DU 174 to prepare the cell(s) 2-N respectively. Each of the LTM preparation procedure(s) 2-N is similar to the procedure 390. In the LTM preparation procedure(s) 2-N, the CU 172 may receive LTM DU configuration(s) 2-N configuring the cell(s) 2-N for LTM, respectively. The CU 172 may generate LTM candidate configuration(s) 2-N including the LTM DU configuration(s) 2-N, respectively. The CU 172 assigns LTM ID(s) 2-N to identify the LTM DU configuration(s) 2-N and the LTM candidate configuration(s) 2-N, respectively. The CU 172 may obtain CS1 resource configuration 2-N and perform CSI report configuration and / or LTM ID configuration procedure(s) 2-N with the DU 174 to obtain the CSI report configuration(s) 2-N, respectively, as described for the CSI resource configuration 1 and the CSI report configuration(s) 1. The CU 172 may obtain RACH configuration 2-N for the cell(s) 2-N respectively, as described for the RACH configuration 1. The CU 172 may obtain TCI state configuration(s) 2-N for the cell(s) 2-N respectively, as described for the TCI state configuration(s) 1. Each of the CSI report configuration and / or LTM ID configuration procedure(s) 2-N is similar to the procedure 392. The CU 172 may obtain LTM SSB configuration 2-N for the cell(s) 2-N, respectively, as described for the LTM SSB configuration 1. In some implementations, the CU 172 may perform LTM configuration delivery procedure 2-N with the UE 102 to transmit a list of tuples: {the LTM ID 2, the LTM candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained)}. .... {the LTM ID N, the LTM candidate configuration N. the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained)} to the UE 102, respectively. Each of the LTM configuration delivery' procedure(s) 2-N is similar to the procedure 394. In other implementations, the CU 172 includes the list of tuples in the first RRC reconfiguration message.

[0139] To simplify the following description, tuples 1-N are used to represent {the LTM ID 1, the LTM candidate configuration 1, the CSI resource configuration 1 (if obtained), the TCI state configuration 1 (if obtained), the RACH configuration 1 (if obtained), the LTM SSB configuration 1 (if obtained)}. .... {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained)}, respectively. Insome implementations, the CU 172 includes the tuples 1-N in RRC reconfiguration messages 1, ... N in the LTM configuration delivery procedure 1-N, respectively. The RRC reconfiguration message 1 is the first RRC reconfiguration message of events 316 and / or 318. In some implementations, the CU 172 includes the tuples 1-N in container IE (e.g., an LTM- ConfiglE) 1-N and includes the container IE 1-N in the RRC reconfiguration messages 1-N, respectively. In other implementations, the CU 172 includes the tuples 1-N in container IE 1 (e.g., an UVM-Config IE) and includes the container IE 1 in the first RRC reconfiguration message.

[0140] In some implementations, the CU 172 may include the CSI resource configuration(s) 1-N in the container IE instead of the tuple, where N is an integer greater than zero.

[0141] At event 342, after receiving the Access Success message at event 334 or the DU-to- CU message at event 338, in some implementations the CU 172 may transmit a CU-to-DU message to the DU 174. In one implementation the CU 172 may transmit the CU-to-DU message to release radio resources and / or configurations of the serving cell(s) configured for the UE 102. In another implementation, the CU 172 may transmit the CU-to-DU message to release some of the LTM candidate cell(s) 2-N.

[0142] At event 344, in response to the CU-to-DU message, the DU 174 may transmit a DU- to-CU message to the CU 172. In some implementations, the CU-to-DU message of event 342 and the DU-to-CU message of event 344 are a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0143] In some implementations, an LTM ID in a PDCCH order, an LTM Cell Switch Command, and an RRC reconfiguration message may be represented in different formats. For example, the PDCCH order or the LTM Cell Switch Command may include a first field to include the LTM ID 1 and the first RRC reconfiguration message may include a second field to include the LTM ID 1. In some implementations, the first field and the second field have different formats or coding schemes. For example, the first field may use a binary' format (i.e., a field 3 bits wide) with bits representing a value range of 0, . .. , 7 and the second field may use an integer format with a value range of 1 , .... 8. In this example, the first field with binary value 000b is equivalent to the second field with integer value 1, the first field with binary value 001b is equivalent to the second field with integer value 2, . . . , the first field with binary value 111b is equivalent to the second field with integer value 8. In this example, the first field is a bitmap of binary values and there is a mapping from the binary value of the first field to the integer value of the second field.

[0144] The events 304, 306, and 324 along with procedures 390, 392, 394 are collectively referred to in FIG. 3 and elsewhere in the disclosure as an intra-CU intra-DU LTM configuration procedure 396. The events 304, 306. 350, 352. 354, 326, 328, 332, 334, 336, 338, and 340 along with procedures 390. 392. 394 are collectively referred to in FIG. 3 and elsewhere in the disclosure as an intra-CU intra-DU LTM procedure 380.

[0145] FIG. 4 is a sequence diagram illustrating example operations of a communications process 400 for an intra-CU inter-DU cell switch. The base station 401 of FIG. 4 may be an implementation of the base station 104 of FIG. 1A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, or the eNB. ng-eNB 230 or the gNB 232 of FIG. 2A.

[0146] In the example shown in FIG. 4, the base station 401 includes a CU 172, a S-DU 174A and a candidate DU (e.g., a C-DU) 174B. As an example, the S-DU 174A may operate the cell 124A and optionally one or more additional cells, while the C-DU 174B may operate a different first cell (e.g., cell 124C). The communications process 400 is an intra-CU inter- DU communications process, similar to the communications process 300. Thus, the descriptions for the communications process 300 can generally apply to the communications process 400. Some descriptions for the DU 174 in FIG. 3 may apply to the S-DU 174A in FIG. 4, and some descriptions for the DU 174 in FIG. 3 may apply to the C-DU 174B. The differences between the communications processes 300 and 400 are described below.

[0147] At event 402, the UE 102 communicates with the S-DU 174A on one or more serving cells (e.g., the cell 124 A and / or other cell(s)) using a serving DU configuration and communicates with the CU 172 via the S-DU 174A using a serving CU configuration. The UE 102 and CU 172 may perform security protection to data communicated between the UE 102 and CU 172 via the S-DU 174A and C-DU 174B, as described above with respect to Fig 3. For example, the data for which security protection may be performed may include data packets (e.g., data packets starting at event 402), the measurement report (event 404), the RRC reconfiguration message and the RRC reconfiguration complete message (procedure 494). the RRC reconfiguration complete message (event 436), and data packets (data packets of event 440).

[0148] In some implementations, the CU 172 and S-DU 174A may perform the LTM configuration procedure 396 or the LTM procedure 380 with the UE 102, as described abovewith respect to FIG. 3. In the case of the procedure 380, the UE 102 may perform an LTM cell switch to the first cell (e.g. cell 124B) as described above with respect to FIG. 3. Upon successfully completing the LTM cell switch, the first cell becomes a serving cell and cell 124A and / or the other cell(s) is / are no longer serving cell(s) for the UE 102. In the case of the procedure 396, the UE 102 does not perform an LTM cell switch.

[0149] During the communication starting at event 402, the UE 102 may transmit, at event 404 and / or event 406 at least one measurement report (e.g., L3 measurement report(s)) to the CU 172 via the S-DU 174A. Based on the measurement report(s), the CU 172 determines to prepare cell 1 (e.g., cell 124C operated by the C-DU 174B) for LTM for the UE 102. The cell 1 is identified by a cell ID (i.e., cell ID 1). In response to the determination, the CU 172 may perform an LTM preparation procedure 490 with the C-DU 174B to (request the C-DU 174B to) prepare the cell 1 as an LTM candidate cell for the UE 102. In the LTM preparation procedure 490, the CU 172 may transmit a first CU-to-DU message including a cell ID 1 of the cell 1 to the C-DU 174B to request the C-DU 174B to prepare the cell 1 as an LTM candidate cell for the UE 102, similar to the event 308. In response, the C-DU 174B may transmit a first DU-to-CU message including an LTM DU configuration (e.g., LTM DU configuration 1) to the CU 172, similar to the event 310. The CU 172 may or may not request an LTM reference DU configuration in the first CU-to-DU message, as described above with respect to FIG. 3. The C-DU 174B may or may not include an LTM reference DU configuration in the first DU- to-CU message, as described above with respect to FIG. 3.

[0150] In some implementations, if the CU 172 receives an LTM reference DU configuration from the S-DU 174A as described above with respect to FIG. 3, the CU 172 may include the LTM reference DU configuration in the first CU-to-DU message and the C-DU 174B may generate the LTM DU configuration as a delta configuration based on the LTM reference DU configuration. In such cases, the C-DU 174B does not transmit an LTM reference DU configuration for the UE 102 to the CU 172. In other implementations, the CU 172 may receive an LTM reference DU configuration from the C-DU 174B, e.g., in the first DU-to-CU message or an additional DU-to-CU message as described above with respect to FIG. 3. In such cases, the CU 172 may generate an LTM reference configuration including the LTM reference DU configuration. The CU 172 may or may not include an LTM reference CU configuration in the LTM reference configuration.

[0151] To prepare the cell 1 for LTM, the CU 172 may perform an LTM CSI report configuration and / or LTM ID configuration procedure 492 with the S-DU 174A. In the procedure 492, the CU 172 may transmit a second CU-to-DU message including a CSI resource configuration (e.g., CSI resource configuration 1) and / or an LTM SSB configuration (e.g., LTM SSB configuration 1) to the S-DU 174A, similar to the event 312. In response, the S-DU 174A may transmit a second DU-to-CU message including one or more CSI report configurations (e.g., CSI report configuration(s) 1) to the CU 172. In some implementations, the CU 172 may generate an LTM candidate configuration (e.g., LTM candidate configuration 1) including the LTM DU configuration and assigns an LTM ID (e.g., LTM ID 1) for identifying the LTM DU configuration and / or the LTM candidate configuration as described above with respect to FIG. 3. In some implementations, the CU 172 includes a tuple {the LTM ID 1, the cell ID 1} in the second CU-to-DU message.

[0152] To prepare the cell 1 as an LTM candidate cell for the UE 102, the CU 172 mayreceive early synchronization information for the cell 1 in a DU-to-CU message (e g., the first DU-to-CU message or an additional DU-to-CU message) from the C-DU 174B. In some implementations, the C-DU 174B may transmit the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other implementations, the C-DU 174B may transmit the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message. The early synchronization information may include a RACH configuration (e.g., RACH configuration 1) and / or at least one TCI state configuration (e.g., TCI state configuration(s) 1), as described above with respect to FIG. 3. In some implementations, the C-DU 174B includes, in the early synchronization information or in the DU-to-CU message, the PDCCH order information (identified herein as PDCCH order information 1) for early UL synchronization with the cell 1.

[0153] In some implementations, the CU 172 may receive the LTM SSB configuration or SSB configuration parameters in the LTM SSB configuration from the C-DU 174B, e.g., in the first DU-to-CU message or an additional DU-to-CU message. In some implementations, the CU 172 may receive a PCI of the cell 1 from the C-DU 174B in the first DU-to-CU message or the additional DU-to-CU message. In some implementations, the C-DU 174B may transmit the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other implementations, the C-DU 174B may transmit the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message.

[0154] In some implementations, the C-DU 174B includes a first set of LTM CFRA configuration parameters in the first DU-to-CU message of the LTM preparation procedure 490. In some implementations, the first set of LTM CFRA configuration parameters include a first RA preamble index, a first SSB index, a first PRACH Mask index, and / or a first UL or SUL indicator. In such cases, the CU 172 may include the first set of LTM CFRA configuration parameters in the second CU-to-DU message of the LTM ID configuration procedure 492. The C-DU 174B may include at least one additional set of LTM CFRA configuration parameters in the first DU-to-CU message of the LTM preparation procedure 490. Each of the additional set(s) of LTM CFRA configuration parameters may include a RA preamble index, a SSB index, a PRACH Mask index, and / or a UL or SUL indicator. In such cases, the CU 172 includes the additional set(s) of LTM CFRA configuration parameters in the second CU-to-DU message of the LTM ID configuration procedure 492. In some implementations, the C-DU 174B configures the first set and / or the additional set(s) for the UE 102. In some implementations, the first set and / or the additional set(s) are configured specifically for the cell 1. In other implementations, the C-DU 174B may configure the first set and / or the additional set(s) for any LTM candidate cell for the UE 102.

[0155] In some implementations, the first set and the additional set(s) do not include separate UL or SUL indicators. In some implementations, the C-DU 174B may configure the first set and / or the additional set(s) for one of the ULs (e.g., the NUL) or the SUL and may include, in the first DU-to-CU message, a single UL or SUL indicator indicating the first set and / or the additional set(s) are configured for the indicated one of UL and SUL. In such cases, the CU 172 may include, in the second CU-to-DU message, a single UL or SUL indicator indicating the first set and / or the additional set(s) are configured for the one of UL or SUL. In other implementations, if the C-DU 174B configures the first set and / or the additional set(s) for UL, the C-DU 174B may include, in the first DU-to-CU message, the first set and / or the additional set(s) in a first field or IE in the first DU-to-CU message. If the C-DU 174B configures the first set and / or the additional set(s) for SUL, the C-DU 174B may include, in the first DU-to-CU message, the first set and / or the additional set(s) in a second field or IE in the first DU-to-CU message. In such cases, the first field or IE and the second field or IE are defined for UL and SUL respectively. In some implementations, if the first DU-to-CU message includes the first set and / or the additional set(s) in the first field or IE, the CU 172 may include the first set and / orthe additional set(s) in a first field or IE in the second CU-to-DU message. If the first DU-to- CU message includes the first set and / or the additional set in the second field or IE, the CU 172 may include the first set and / or the additional set(s) in a second field or IE in the second CU- to-DU message. In such cases, the first field or IE and the second field or IE are defined for UL and SUL respectively.

[0156] In some implementations, the C-DU 174B configures the first set for one of UL and SUL and configures the additional set for the other of UL and SUL. In some implementations, the C-DU 174B sets the first UL or SUL indicator to a value indicating the one ofUL and SUL and sets the UL or SUL indicator in the additional set to a value indicating the other of the UL and SUL. In other implementations, if the C-DU 174B configures the first set for one of UL and SUL and configures the additional set for the other of UL and SUL, the C-DU 174B may include the first set and the additional set in one and the other of the first field or IE and the second field IE respectively in the first DU-to-CU message. In such cases, the CU 172 may include the first set and the additional set in one and the other of the first field or IE and the second field IE respectively in the second CU-to-DU message.

[0157] As described above with respect to FIG. 3, the CU 172 may perform an LTM configuration delivery procedure 494 with the UE 102 to transmit the LTM ID and the LTM candidate configuration to the UE 102. In some implementations, the CU 172 may transmit {LTM ID, the LTM candidate configuration} as a tuple in a first RRC reconfiguration message in the LTM configuration delivery procedure 494. Depending on the implementations, the CU 172 may include the LTM reference configuration, the CSI report configuration(s), the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration, and / or the PCI of the cell 1 to the UE 102 in the first RRC reconfiguration message and / or other RRC reconfiguration message(s) transmitted to the UE 102, as described above with respect to FIG. 3. The CU 172 may include the LTM ID in the first RRC reconfiguration or the other RRC reconfiguration message(s) to indicate the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration, and / or the PCI of the cell 1 are associated with the cell 1. For example, the CU 172 may include the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration, and / or the PCI of the cell 1 in the tuple. In another example, the CU 172 may include {LTM ID, the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration, and / or the PCI of the cell 1 } as a tuple (e.g., tuple 1) in the other RRC reconfiguration message(s). Inresponse to each of the other RRC reconfiguration message(s), the UE 102 may transmit an RRC reconfiguration complete message to the CU 172 via the S-DU 174A.

[0158] In some implementations, the PDCCH order information includes a frequency domain resource assignment, a RA preamble index, an UL or a supplemental UL indicator, a SSB index, and / or a physical RACH mask index. The CU 172 may transmit a CU-to-DU message (e.g., the second CU-to-DU message or an additional CU-to-DU message) including the PDCCH order information to the S-DU 174A. In some implementations, the CU 172 may include the LTM ID 1 or the cell ID 1 in the CU-to-DU message to indicate that the PDCCH order information is associated with the LTM ID 1 or the cell ID 1. For example, the CU 172 may include {the cell ID 1, the PDCCH order information} as a tuple in the CU-to-DU message. In the case of the additional CU-to-DU message, the S-DU 174A may transmit an additional DU-to-CU message to the CU 172 in response.

[0159] At event 424, the UE 102 may transmit at least one first measurement report including the first measurement result(s) to the S-DU 174. The at least one first measurement report and the first measurement result(s) may be at least one first LI measurement report and first LI measurement result(s), respectively.

[0160] At event 450, the S-DU 174A may transmit a PDCCH order to the UE 102, based on the PDCCH order information. For example, the S-DU 174A may transmit a PDCCH order to the UE 102, including the PDCCH order information. In some implementations, the S-DU 174A may determine an SSB index included in the PDCCH order, based on LI measurement report(s) of event 424, and / or the CSI resource configuration, the CSI report configuration, and / or the LTM SSB configuration. In some implementations, the S-DU 174A may include the LTM ID 1 in the PDCCH order to indicate the cell 1. In the case of the additional CU-to-DU message, the S-DU 174A may transmit an additional DU-to-CU message to the CU 172 in response.

[0161] At event 452, the UE 102 may transmit a RA preamble to the C-DU 174B on the cell 1, using the RACH configuration and / or the PDCCH order information. The C-DU 174B may derive a TA value based on the RA preamble.

[0162] At event 456, the C-DU 174B may transmit a DU-CU TA Information Transfer message including the TA value to the CU 172.

[0163] At event 458, the CU 172 in turn may transmit a CU-DU TA Information Transfer message including the TA value to the S-DU 174A. In some implementations, the C-DU 174Bmay include the cell ID 1, the RA preamble index, a RA radio network temporary identifier (RA-RNTI), and / or a DU ID of the S-DU 174A in the CU-DU TA Information Transfer message. In such cases, the CU 172 may include the cell ID 1, the RA preamble index, the RA- RNTI, and / or the DU ID of the S-DU 174A in the message.

[0164] At event 454, the UE 102 may transmit additional measurement report(s) to the DU 174, similar to the event 424. In some aspects, the additional measurement reports may be LI measurement reports. The DU 174 determines to command the UE 102 to perform an LTM cell switch to the first cell based on the additional measurement report(s) and / or the measurement report(s) obtained at event 424.

[0165] At event 426, in response to determining to command the UE 102 to perform an LTM cell switch to the cell 1, the S-DU 174A may transmit the LTM Cell Switch Command including the LTM ID 1 to the UE 102. If the S-DU 174A receives a TA value as described above, the S-DU 174A may include the TA value in the LTM Cell Switch Command. The S- DU 174A may include a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID may indicate a first one of the TCI state configuration(s).

[0166] In some implementations, the C-DU 174B determines the RA-RNTI based on a PRACH occasion in which the C-DU 174B receives the RA preamble at event 452 discussed above. In some implementations, the C-DU 174B calculates the RA-RNTI as:RA-RNTI = 1 + s_id + 14 x t_id + 14 * 80 x f_id + 14 x 80 x 8 x ul_carrier_id where s_id is the index of the first orthogonal frequency-division multiplexing (OFDM) symbol of the PRACH occasion (0 < s_id < 14), t_id is the index of the first slot of the PRACH occasion in a system frame (0 < t_id < 80), where the subcarrier spacing to determine t_id is based on the value of p (e.g., as specified in clause 5.3.2 in 3GPP TS 38.211) for p = {0, 1, 2, 3} and for p = {5, 6}, t_id is the index of the 120 kHz slot in a system frame that contains the PRACH occasion (0 < t_id < 80). f id is the index of the PRACH occasion in the frequency domain (0 < f id < 8), and ul_carrier_id is the UL carrier used for the RA Preamble transmission (0 forNUL carrier, and 1 for SUL carrier).

[0167] At event 428, in response to determining to command the UE 102 to perform an LTM cell switch or transmitting the LTM Cell Switch Command, the S-DU 174A may transmit a DU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 may perform an LTM cell switch to the cell 1.

[0168] At event 430, in response, the CU 172 may transmit a CU-DU Cell Switch Notification message to the C-DU 174B to indicate that the UE 102 is to perform an LTM cell switch to the cell 1.

[0169] At event 432, the UE 102 may access the cell 1 in response to the LTM Cell Switch Command. In some implementations, the S-DU 174A determines to include and / or includes the first set of LTM CFRA configuration parameters in the LTM Cell Switch Command to configure the UE 102 to perform a CFRA procedure to access the cell 1 as described above with respect to FIG. 3. The UE 102 may perform the CFRA procedure to access the cell 1, using the LTM CFRA configuration parameters and at least one RACH configuration as described above with respect to FIG. 3. The C-DU 174B may perform the CFRA procedure with the UE 102 in accordance with the LTM CFRA configuration parameters and the RACH configuration(s) as described above with respect to FIG. 3.

[0170] In some implementations, the S-DU 174A determines (whether) to include the first set of LTM CFRA configuration parameters in the LTM Cell Switch Command, based on the measurement report(s) received at event 454. In some implementations, the S-DU 174A may obtain (e.g., retrieve, derive, calculate, or determine) one or more measurement results from the measurement report(s). In some implementations, the measurement result(s) include a measurement result for a first SSB identified by the first SSB index. The C-DU 174B may transmit the first SSB on the cell 1. In such cases, if the measurement result for the first SSB is above (or equal to) a second predetermined threshold, the S-DU 174A may include the first set of LTM CFRA configuration parameters in the LTM Cell Switch Command. If the measurement result for the first SSB is below (or equal to) the second predetermined threshold, the S-DU 174A refrains from including the first set of LTM CFRA configuration parameters in the LTM Cell Switch Command.

[0171] In some implementations, in the case where the first set includes the first UL or SUL indicator, the S-DU 174A may include the first UL or SUL indicator in the LTM Cell Switch Command as described above with respect to FIG. 3. In other implementations, in the case where the first set does not include a UL or SUL indicator, the S-DU 174A may determine a value of a UL or SUL indicator and may include the UL or SUL indicator in the LTM Cell Switch Command as described below and / or above with respect to FIG. 3. In some implementations, if the second CU-to-DU message includes the first set of LTM CFRA configuration parameters in the first field or IE for UL, the S-DU 174A sets the UL or SULindicator to the first value for UL. If the second CU-to-DU message includes the first set of LTM CFRA configuration parameters in the second field or IE for UL, the S-DU 174A sets the UL or SUL indicator to the second value for SUL. In other implementations, the S-DU 174A determines a value of the UL or SUL indicator in the LTM Cell Switch Command based on a measurement result for the first SSB that the S-DU 174A obtains from the measurement report(s) at event 454. In one implementation, if the measurement result is above (or equal to) a predetermined threshold, the S-DU 174A sets the UL or SUL indicator to the first value and may include the first set in the LTM cell switch command. If the measurement result is below (or equal to) the predetermined threshold, the S-DU 174A sets the UL or SUL indicator to the second value and may include the additional set in the LTM cell switch command instead of the first set. In other implementations, the S-DU 174A sets the UL or SUL indicator to a preconfigured value (e g., the first value), e.g.. because the C-DU 174B does not support SUL. In yet other implementations, the S-DU 174A sets the UL or SUL indicator to a preconfigured value (e g., the second value), e g., because the S-DU 174A is preconfigured to do so.

[0172] In some implementations, the S-DU 174A may include the first TCI state ID in the DU-CU Cell Switch Notification message and the CU 172 in turn may include the first TCI state ID in the CU-DU Cell Switch Notification message. The UE 102 and the C-DU 174B identify the first one of the TCI state configuration(s) based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in the events 432, 436, and / or 440.

[0173] In other implementations, in the case where the S-DU 174A uses separate TCI states, the DL TCI state and the UL TCI state may have different TCI state IDs. In such cases, the S- DU 174A may include, in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command, a first TCI state ID for DL and a second TCI state ID for UL that identify a first one and a second one of the TCI state configuration(s). The CU 172. in response to the DU-CU Cell Switch Notification message, in turn may include the first TCI state ID and the second TCI state ID in the CU-DU Cell Switch Notification message sent to the C-DU 174B. The UE 102 identifies the first TCI state configuration and the second TCI state configuration based on the first TCI state ID and second TCI state ID. The UE 102 may apply the first TCI state configuration and the second TCI state configuration to communicate DL transmissions and UL transmissions, respectively, with the C-DU 174B in the events 432, 436 and / or 440. The C-DU 174B identifies the first TCI state configuration and the second the TCI state configuration based on the first TCI state ID and second TCI state ID respectively. The C-DU174B may apply the first TCI state configuration and the second TCI state configuration to communicate DL transmissions and UL transmissions, respectively, with the UE 102 in the events 432. 436, and / or 440.

[0174] In some implementations, each of the TCI state configuration(s) may include or may be associated with a TCI state ID. In some implementations, the CU 172 may transmit a CU- to-DU message (e.g., the second CU-to-DU message or an additional CU-to-DU message) including the TCI state configuration(s) and / or the associated TCI state ID(s) to the S-DU 174A. In some implementations, the CU 172 may include the LTM ID 1 or the cell ID 1 in the CU-to-DU message to indicate that the TCI state configuration(s) is associated with the LTM ID 1 or the cell ID 1. For example, the CU 172 may include {the cell ID 1, the TCI state configuration(s)} as a tuple in the CU-to-DU message. In the case of the additional CU-to-DU message, the S-DU 174A may transmit an additional DU-to-CU message to the CU 172 in response. In some implementations, the S-DU 174A may include, in the LTM Cell Switch Command of event 426. a first TCI state ID indicating a first one of the TCI state configuration(s). In some implementations, the S-DU 174A determines the first TCI state configuration or the first TCI state ID. The UE 102 identifies the one of the TCI state configuration(s) based on the first TCI state ID and may apply the first TCI state configuration in UL transmissions and / or DL receptions in the events 432, 436, and / or 440.

[0175] In some implementations, the CU 172 may prepare additional cell(s) (i.e., cell(s) 2- N) as LTM candidate cell(s) for the UE 102 with the C-DU 174B, before or after transmitting the LTM Cell Switch Command or during, before or after the LTM preparation procedure 490 or LTM ID configuration procedure 492.

[0176] In some implementations, the first CU-to-DU message and the first DU-to-CU message may be a UE Context Setup Request message and a UE Context Setup Response message, respectively. In some implementations, the first CU-to-DU message and the first DU- to-CU message may be a UE Context Modification Request message and a UE Context Modification Response message, respectively. In some implementations, the LTM preparation procedure 490 may be a UE Context Setup procedure and the additional LTM preparation procedure may be a UE Context Modification procedure. In other implementations, the LTM preparation procedure 490 and the additional LTM preparation procedures may be UE Context Setup procedures. In yet other implementations, the LTM preparation procedure 490 and the addition LTM preparation procedures are UE Context Modification procedures.

[0177] At event 442, after receiving the Access Success message at event 434 or the DU-to- CU message at event 438, in some implementations the CU 172 may transmit a CU-to-DU message to the DU 174A. In one implementation the CU 172 may transmit the CU-to-DU message to release radio resources and / or configurations of the serving cell(s) configured for the UE 102. In another implementation, the CU 172 may transmit the CU-to-DU message to release some of the LTM candidate cell(s) 2-N or some of the LTM candidate cell(s) prepared by the DU 174A for the UE 102.

[0178] At event 444, in response to the CU-to-DU message, the DU 174A may transmit a DU-to-CU message to the CU 172. In some implementations, the CU-to-DU message of event 442 and the DU-to-CU message of event 444 are a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0179] The events 404, 406, and 424 along with procedures 490, 492, and 494 are collectively referred to in FIG. 4 as an intra-CU inter-DU LTM configuration procedure 496. The events 404, 406, 424, 450, 452, 454456, 458, 426, 428, 430, 432, 434, 436, 438, 440, 442, and 444 along with procedures 490, 492, and 494 are collectively referred to in FIG. 4 as an intra-CU inter-DU LTM procedure 480.

[0180] FIG. 5 is a sequence diagram illustrating example operations of a communications process 500 for an example inter-CU cell switch where a first base station operates as a serving or source base station (S-BS) and a second base station operates as a candidate base station (C- BS). In the example show n in FIG. 5, S-BS 501 may be an implementation of the base station 104 of FIG. 1A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, or the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A. C-BS 506 of FIG. 5 may be an implementation of the base station 106 of FIG. 1 A, the base stations 106A or 106B of FIG. IB, the base station 164 of FIG. 1C, or the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A.

[0181] In some implementations, the C-BS 506 may include a CU 172 and a DU 174. The communications process 500 is similar to the communications processes 300 and 400, except that the communications process 500 is an inter-CU communications process (i.e., inter-base station communications process) while the communications processes 300 and 400 are intra- CU (i.e., intra-base station) communications processes. The S-BS 501 may include a CU and a DU (not shown in FIG. 5), similar to the base station 301 of FIG. 3 and base station 401 of FIG. 4.

[0182] At event 502, the UE 102 communicates with the S-BS 501 via serving cell(s) using a serving configuration. In some implementations, the S-BS 501 may include an S-DU and a CU, and the serving configuration may include a serving CU configuration and a serving DU configuration, as described above with respect to FIGs. 3 and 4. The UE 102 may perform security protection to data communicated with the S-BS 501 using at least one first security key and at least one first security algorithm, as described above with respect to FIGs. 3 and 4. Similarly, the S-BS 501 may perform security protection to data communicated with the UE 102 using at least one first security key and at least one first security algorithm, as described above with respect to FIGs. 3 and 4. Depending on the implementation, the first security key(s) and the first security7algorithm(s) used by the UE 102 and the S-BS 501 can be the same or different.

[0183] In some aspects, while communicating with the UE 102 at event 502, the S-BS 501 may perform intra-CU LTM procedure 580 with the UE 102, similar to the procedures 380 and / or 480 of FIGs 3 and 4 respectively. In some other aspects, while communicating with the UE 102 at event 502, the S-BS 501 may perform intra-CU LTM configuration procedure(s) 596 with the UE 102, similar to the procedures 396 and / or 496 of FIGs 3 and 4 respectively.

[0184] At event 504, while communicating with the S-BS 501, the UE 102 may transmit at least one measurement report to the S-BS 501. The measurement report(s) may include measurement results for a serving cell of the UE 102 and / or at least one non-serving cell (e.g., cell 126 of FIG. 1 and cell 126A of FIG. IB). The S-BS 501 determines to prepare a first cell (e.g., the cell 126A) as an LTM candidate cell for the UE 102, based on the measurement report(s). For example, the measurement report(s) may include a PCI of the first cell and measurement result(s) of the cell 126A. The S-BS 501 identifies that the first cell is operated by the C-BS 506 based on the PCI and may determine that the first cell qualifies for LTM preparation based on the measurement result(s).

[0185] After (e.g.. in response to) determining to prepare the first cell as an LTM candidate cell for the UE 102, the S-BS 501 (e.g., the CU of the S-BS 501) may generate a Handover Request message including a first cell ID (i.e., cell ID 1) of the first cell (i.e., cell 1).

[0186] At event 505, the S-BS 501 may transmit the Handover Request message to the CU 172. In some implementations, the Handover Request message may include an LTM indicator indicating the Handover Request message concerns LTM for the first cell ID. After (e.g., in response to) receiving the Handover Request message, the CU 172 may perform an LTMpreparation procedure 590 with the DU 174 to prepare the first cell as an LTM candidate cell for the UE 102, similar to the LTM preparation procedure 390 or 490 of FIGs 3 and 4, respectively, discussed above. In the procedure 590, the CU 172 may transmit a first CU-to- DU message including the first cell ID to the DU 174 to request that the DU prepare the first cell, similar to the event 308 of FIG. 3 discussed above. In response, the CU 172 may receive a first DU-to-CU message including an LTM DU configuration 1 from the DU 174, similar to the event 310 of FIG. 3. The CU 172 may generate a first LTM candidate configuration (LTM candidate configuration 1).

[0187] At event 507, in response to the Handover Request message, the CU 172 may transmit a Handover Request Acknowledge message including the first LTM candidate configuration to the S-BS 501. In some implementations, the CU 172 may include the first cell ID in the Handover Request Acknowledge message to indicate that the first LTM candidate configuration is provided for or associated with the first cell (ID).

[0188] The events 505 and 507 along with the LTM preparation procedure 590 are collectively referred to in FIG. 5 as an inter-CU LTM preparation procedure 598 (also referred to as an inter-MN LTM preparation procedure).

[0189] In some implementations, the Handover Request message may include a DU ID of the S-DU of the S-BS 501. In such cases, the CU 172 may include the DU ID in the first CU- to-DU message. In some implementations, the Handover Request message may include a BS ID of the S-BS 501. When receiving the BS ID, the CU 172 may include the BS ID in the first CU-to-DU message. For example, the BS ID may be a gNB ID.

[0190] The CU 172 may or may not request an LTM reference DU configuration in the LTM preparation procedure 590. as described above with respect to procedures 390 and 490 of FIGs. 3 and 4, respectively. The DU 174 may or may not transmit an LTM reference DU configuration to the CU 172 in the LTM preparation procedure 590, as described above with respect to procedures 390 and 490 of FIGs. 3 and 4, respectively. In some implementations, the S-BS 501 (e g., the CU of the S-BS 501) may obtain an LTM reference configuration, as described above with respect to FIGs. 3 and 4. In other implementations, the S-BS 501 may receive an LTM reference configuration from another BS (not shown in FIG. 5) in another inter-CU LTM preparation procedure as described above and below. If the S-BS 501 obtains an LTM reference configuration, the S-BS 501 may include the LTM reference configuration (e.g., an S-BS generated LTM reference configuration) in the Handover Request, message. Insome implementations, the S-BS 501 may include the LTM reference configuration in the internode RRC message HandoverPreparationlnformation or as an Xn Application Protocol (XnAP) IE or field and may include the inter-node RRC message or the XnAP IE in the Handover Request message. Alternatively or additionally, the S-BS 501 determines to request or cause the C-BS 506 to provide a complete LTM candidate configuration so that the S-BS 501 does not include the LTM reference configuration in the Handover Request message. If the S-BS 501 does not obtain an LTM reference configuration, the S-BS 501 does not include an LTM reference configuration in the Handover Request message. If the Handover Request message includes an LTM reference configuration, the CU 172 may include the LTM reference configuration in the first CU-to-DU message. The DU 174 may extract an LTM reference DU configuration from the LTM reference configuration. Alternatively or additionally, the CU 172 extracts an LTM reference DU configuration from the LTM reference configuration and may include the LTM reference DU configuration in the first CU-to-DU message. The DU 174 may generate an LTM DU configuration as a delta configuration based on the LTM reference DU configuration, as described above with respect to FIG. 3. Alternatively or additionally, the DU 174 may ignore the LTM reference (DU) configuration and generate an LTM DU configuration as a complete configuration, as described above with respect to FIG. 3.

[0191] If the Handover Request message does not include an LTM reference configuration, the CU 172 may or may not receive an LTM reference DU configuration from the DU 174 as described above with respect to FIG. 3. If the CU 172 receives an LTM reference DU configuration (e.g., in the first DU-to-CU message), the CU 172 may generate an LTM reference configuration (C-BS generated LTM reference configuration) including the LTM reference DU configuration. The CU 172 may include an LTM reference CU configuration (candidate CU (C-CU) generated LTM reference CU configuration). If the CU 172 does not receive an LTM reference DU configuration from the DU 174 as described above with respect to FIG. 3, the CU 172 does not generate an LTM reference configuration. Alternatively or additionally, the CU 172 may generate an LTM reference configuration (e g., a C-BS generated LTM reference configuration) only including a C-CU generated LTM reference CU configuration. In cases where the CU 172 generates an LTM reference configuration (e.g., a C- BS generated LTM reference configuration), the CU 172 may include the C-BS generated LTM reference configuration in the Handover Request Acknowledge message.

[0192] In some implementations, if the LTM DU configuration 1 is a complete configuration, the CU 172 may generate the LTM candidate configuration 1 as a completeconfiguration. The CU 172 may include a complete configuration indication (e.g., a BS-to-BS interface protocol field or IE) in the Handover Request Acknowledge message to indicate that the LTM candidate configuration 1 is a complete configuration. In some implementations, the BS-to-BS interface protocol is an Xn application protocol (e.g., as defined in 3GPP TS 38.423). In some implementations, the complete configuration indication is anew field or IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the complete configuration indication is an existing field or IE (e.g., as defined in 3GPP TS 38.423). If the LTM DU configuration 1 is a delta configuration, the CU 172 may generate the LTM candidate configuration 1 as a delta configuration. The CU 172 may exclude the complete configuration indication from the Handover Request Acknowledge message to indicate that the LTM candidate configuration 1 is a delta configuration. Alternatively or additionally, the CU 172 may include a delta configuration indication (e.g., a BS-to-BS interface protocol field or IE) in the Handover Request Acknowledge message to indicate that the LTM candidate configuration 1 is a delta configuration. In some implementations, the BS-to-BS interface protocol is an Xn application protocol (e.g., as defined in 3GPP TS 38.423). In some implementations, the delta configuration indication is a new field or IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the delta configuration indication is an existing field or IE defined in 3GPP specification 38.423. In some implementations, the BS-to-BS interface protocol field or IE may have two values (i.e., a first value and a second value). The BS-to-BS interface protocol field or IE set to the first value may be the complete configuration indication and the BS-to-BS interface protocol field or IE set to the second value may be the delta configuration indication.

[0193] In some implementations, the S-BS 501 may be preconfigured with a CSI resource configuration (e.g., (LTM) CSI resource configuration 1) and / or an LTM SSB configuration (LTM SSB configuration 1) for the first cell. In other implementations, the S-BS 501 may receive the CSI resource configuration and / or the LTM SSB configuration from an operations, administration and maintenance (0AM) node. In yet other implementations, the S-BS 501 may receive the CSI resource configuration and / or the LTM SSB configuration from the CU 172. For example, the CU 172 may include the CSI resource configuration and / or the LTM SSB configuration in the Handover Request Acknowledge message. In some implementations, the CU 172 may include a PCI (identified herein as PCI 1) of the first cell in the Handover Request Acknowledge message. To prepare the first cell as a candidate LTM cell for the UE 102, the CU of the S-BS 501 may perform an LTM CSI report configuration and / or LTM IDconfiguration procedure (not shown in FIG. 5) with an S-DU of the S-BS 501, similar to the procedure 392 of FIG. 3. In the LTM CSI report configuration and / or LTM ID configuration procedure, the CU of the S-BS 501 may transmit the CSI resource configuration and / or the LTM SSB configuration to the S-DU of the S-BS 501. In response, the CU of the S-BS 501 may receive one or more CSI report configurations for the UE 102 from the S-DU of the S-BS 501. In some implementations, the CU of the S-BS 501 may receive the CSI report configuration(s) in a second serving DU configuration from the S-DU.

[0194] To prepare the first cell as an LTM candidate cell for the UE 102, the CU 172 may receive early synchronization information (identified herein as early synchronization information 1) for the first cell from the DU 174 in a DU-to-CU message (e.g., the first DU-to- CU message or an additional DU-to-CU message). In some implementations, the DU 174 may transmit the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other implementations, the DU 174 may transmit the additional DU-to-CU message (e.g.. a UE Context Modification Required message) in response to receiving the first CU-to-DU message. The CU 172 may include the early synchronization information in the Handover Request Acknowledge message. The early synchronization information may include a RACH configuration (identified herein as RACH configuration 1) and / or at least one TCI state configuration (identified herein as TCI state configuration(s) 1). In some implementations, the DU 174 may include, in the early synchronization information or in the DU-to-CU message, PDCCH order information for early UL synchronization with the first cell. The CU 172 may include the PDCCH order information in the Handover Request Acknowledge message.

[0195] In some implementations, the CU 172 may assign an LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration and may include the LTM ID in the Handover Request Acknowledge message. In other implementations, the S-BS 501 assigns an LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration.

[0196] At event 518, after (e.g., in response to) receiving the Handover Request Acknowledge message, the S-BS 501 (e.g., the CU of the S-BS 501) may transmit a first RRC reconfiguration message to the UE 102, including {the LTM ID 1, the LTM candidate configuration 1 } as a tuple (e.g.. tuple 1), similar to the event 318 of FIG. 3. If the Handover Request Acknowledge message includes the LTM reference configuration, the S-BS 501 may include the LTM reference configuration in the first RRC reconfiguration message. The S-BS501 may include the CSI resource configuration 1 , the TCI state configuration(s) 1 , the RACH configuration 1, the LTM SSB configuration 1, and / or the PCI of the first cell in the tuple, e.g., if received in the Handover Request Acknowledge message. Alternatively or additionally, the S-BS 501 may transmit one or more additional RRC reconfiguration messages to the UE 102, including the CSI resource configuration 1, the TCI state configuration(s) 1, the RACH configuration 1, the LTM SSB configuration 1, and / or the PCI of the first cell. In each of the additional RRC reconfiguration message(s), the S-BS 501 may include the LTM ID 1 to indicate that the CSI resource configuration 1. the TCI state configuration(s) 1, the RACH configuration 1, the LTM SSB configuration 1. and / or the PCI of the first cell are associated with the first cell or configured for the first cell.

[0197] At event 520, the UE 102 may transmit a first RRC reconfiguration complete message to the S-BS 501 in response to the first RRC reconfiguration message. The UE 102 may transmit an additional RRC reconfiguration complete message to the S-BS 501 in response to each of the additional RRC reconfiguration complete message(s). The RRC reconfiguration message(s) (i.e., the first RRC reconfiguration message and / or the additional RRC reconfiguration message(s)) and the RRC reconfiguration complete message(s) (i.e., the first RRC reconfiguration complete message and / or the additional RRC reconfiguration complete message(s)) form an LTM configuration delivery procedure. The S-BS 501 may include the second serving DU configuration in the first RRC reconfiguration message or one or the additional RRC reconfiguration message(s).

[0198] In some implementations, the S-BS 501 (e.g., the CU of the S-BS 501) may include first security information in t e Handover Request message. In some implementations, the first security information may include a RAN level security key (e.g., key-NG-RAN-Star) and / or a next hop chaining count. In some implementations, the S-BS 501 may include security capabilities of the UE 102 in the Handover Request message.

[0199] In some implementations, the CU 172 may generate a first security configuration for the UE 102 based on the first security' information. In one implementation, the CU 172 may include the first security configuration in the Handover Request Acknowledge message. In another implementation, the CU 172 may include the first security configuration in the first LTM candidate configuration or the LTM reference configuration.

[0200] In other implementations, the S-BS 501 (e.g., the CU of the S-BS 501) may generate the first security configuration based on the first security information instead of the CU 172. Insuch cases, the CU 172 does not include a security configuration (e.g., the first security configuration) for the UE 102 in the Handover Request Acknowledge message, the first LTM candidate configuration, and / or the LTM reference configuration.

[0201] In some implementations, the S-BS 501 may include the first security configuration in a container IE (e g., LTM-Config IE) that may include the tuple 1 and may include the container IE in the first RRC reconfiguration message. In other implementations, the S-BS 501 may include the first security configuration in the tuple 1.

[0202] In some implementations, the first security configuration may include at least a portion of the first security' information. For example, the first security configuration includes the next hop chaining count and does not include a RAN level security key. In some implementations, the first LTM candidate configuration, the LTM reference configuration, or the first security configuration configures at least one second security algorithm. In some implementations, the S-BS 501 (e g., the CU of the S-BS 501) or the CU 172 may determine the second security- algorithm(s) based on the security capabilities. In some implementations, the second security algorithm(s) may include an encryption algorithm and / or an integrity algorithm that may be the same as or different from the first security algorithm(s).

[0203] In some implementations, the first security configuration may include a key set change indicator (e.g.. keySetChangelndicator) indicating whether a new BS key (e.g., a new KgNB) needs to be derived from anew CN key (e.g., anew KAMF) or anexthop (NH) parameter. In some implementations, the S-BS 501 (e.g., the CU of the S-BS 501) or the CU 172 sets the key set change indicator to a first value indicating the first new key is derived from the NH parameter. In other implementations, the S-BS 501 or the CU 172 may be pre-configured to set the key set change indicator to a first value indicating the first new key is derived from the NH parameter. This is because the inter-CU LTM may not support derivation of a new BS key based on a new CN key.

[0204] In some implementations, if the Handover Request Acknowledge message includes the complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration, the S-BS 501 may include, in the first RRC reconfiguration message, a complete configuration indication (e.g., an RRC field or IE) to indicate that the LTM candidate configuration l is a complete configuration. If the Handover Request Acknowledge message does not include the complete configuration indication or includes the delta configuration indication to indicate that the LTM candidate configuration 1 is a deltaconfiguration, the S-BS 501 excludes or does not include, in the first RRC reconfiguration message, the complete configuration indication (e.g., an RRC field or IE) to indicate that the LTM candidate configuration 1 is a delta configuration.

[0205] At event 524, the UE 102 may transmit at least one first measurement report including the first measurement result(s) to the S-BS 501. The at least one first measurement report and the first measurement result(s) may be at least one first LI measurement report and first LI measurement result(s), respectively.

[0206] At event 550, if the Handover Request Acknowledge message includes the PDCCH order information (e.g., PDCCH order information 1), the S-BS 501 may transmit a PDCCH order, based on the PDCCH order information. If the S-BS 501 is a distributed base station, the CU of the S-BS 501 may transmit the PDCCH order information to the S-DU of the S-BS 501. For example, the S-BS 501 or the S-DU of the S-BS 5 1 may transmit a PDCCH order to the UE 102, including the PDCCH order information. In some implementations, the S-BS 501 or the S-DU of the S-BS 501 may determine an SSB index included in the PDCCH order, based on the LI measurement report(s) of event 524, the CSI resource configuration, the CSI report configuration, and / or the LTM SSB configuration. In some implementations, the S-DU or the S-BS 501 may include the LTM ID 1 in the PDCCH order to indicate the first cell.

[0207] At event 552, the UE 102 may transmit an RA preamble to the DU 174 on the first cell, using the RACH configuration and / or the PDCCH order information. The DU 174 may derive a TA value based on the RA preamble.

[0208] At event 556, the DU 174 may transmit a DU-CU TA Information Transfer message including the TA value to the CU 172.

[0209] At event 558, the CU 172 may transmit a CU-CU TA Information Transfer message including the TA value to the S-BS 501 (e.g., the CU of the S-BS 501). In some implementations, the DU 174 may include the cell ID 1. the RA preamble index, an RA-RNTI, the DU ID of the S-DU of the S-BS 501, and / or the BS ID of the S-BS 501 in the message. In some implementations, the DU 174 does not include the BS ID in the DU-CU TA Information Transfer message of event 556. In some implementations, the CU 172 may include the cell ID 1, the RA preamble index, the RA-RNTI, the DU ID of the S-DU, and / or the BS ID of the S- BS 501 in the message of event 558. In some implementations, the CU 172 does not include the BS ID in the message of event 558. The CU of the S-BS 501 may transmit a CU-DU TA Information Transfer message including the TA value, the cell ID 1, the RA preamble index,the RA-RNTI, and / or the DU ID of the S-DU, and / or the BS ID of the S-BS 501 to the S-DU of the S-BS 501. In some implementations, the CU of the S-BS 501 does not include the BS ID in the CU-DU TA Information Transfer message.

[0210] In some implementations, the CU 172 determines an address (e.g., an IP address) of the S-BS 501 or the CU of the S-BS 501. based on the BS ID of the S-BS 501. In other implementations, the CU 172 determines an address (e.g., an IP address) of the S-BS 501 or the CU of the S-BS 501, based on the DU ID of the S-DU of the S-BS 501. In such implementations, the CU 172 sends the CU-CU TA Information Transfer message to the S-BS 501 or the CU of the S-BS 501 in accordance with the address.

[0211] At event 554, the UE 102 may transmit additional measurement report(s) to the S- BS 501 (or the CU of the S-BS 501), similar to the event 524. In some aspects, the additional measurement reports may be LI measurement reports. The S-BS 501 determines to command the UE 102 to perform an LTM cell switch to the first cell based on the additional measurement report(s) and / or the measurement report(s) of event 524.

[0212] At event 526, in response to determining to command the UE 102 to perform an LTM cell switch to the first cell, e g., based on the measurement report(s) at events 524 and / or 554, the S-DU of the S-BS 501 may transmit the LTM Cell Switch Command including the LTM ID 1 to the UE 102. In response to the LTM Cell Switch Command, the UE 102 may stop communication on the serving cell(s).

[0213] At event 527, in response to determining to command the UE 102 to perform an LTM cell switch or transmitting the LTM Cell Switch Command, the S-BS 501 may transmit a CU- CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 is perform an LTM cell switch to the cell 1.

[0214] At event 530. in response, the CU 172 may transmit a CU-DU Cell Switch Notification message to the C-DU 174B to indicate that the UE 102 is to perform an LTM cell switch to the cell 1.

[0215] At event 532, in response to the LTM Cell Switch Command, the UE 102 may access the first cell.

[0216] At event 536, the UE 102 may transmit an RRC reconfiguration complete message to DU 174 while or after accessing the first cell.

[0217] At event 538, the DU 174 in turn may transmit a DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some implementations, the UE 102 may derive at least one second security key based on the first security configuration. In some implementations, the UE 102 may derive a new BS key (e.g., a new K§NB) based on the first security configuration and may derive the second security key(s) from the new BS key. In some implementations, if the UE 102 receives the second security algorithm(s) for the first cell (i.e., the LTM candidate cell) as described above, the UE 102 may derive the second security key(s), based on the new BS key and the second security algorithm(s). If the UE 102 does not receive the second security algorithm(s) for the first cell, the UE 102 may derive the second security key(s), based on the new BS key and the first security algorithm(s).

[0218] In some implementations, the UE 102 may derive the second security key(s) in response to receiving the LTM Cell Switch Command at event 526. In other implementations, the UE 102 may derive the second security key(s) after receiving the first security' configuration and before receiving the LTM Cell Switch Command. The UE 102 may apply the second security key(s) to communicate with the CU 172 in the events 536 and 540. If the UE 102 receives the second security algorithm(s) as described above, the UE 102 may apply the second security key(s) and the second security algorithm(s) to communicate with the CU 172 in the events 536 and 540. If the UE 102 does not receive the second security algorithm(s), the UE 102 may apply the second security key(s) and the first security algorithm(s) to communicate with the CU 172 in the events 536 and 540. In some implementations, the second security key(s) include an integrity key for integrity protection of control-plane data packets (e.g., data packets of event 536 and / or RRC messages in event 540). In other implementations, the second security key(s) include an encryption key for encryption / decryption of control-plane data packets (e.g., event 536 and / or RRC messages in event 540). In yet other implementations, the security key(s) include an integrity' key for integrity protection of user-plane data packets (e.g., data packets communicated via DRB(s)) in event 540. In yet other implementations, the security key(s) include an encryption key for encryption / decryption of user-plane data packets (e.g.. data packets communicated via DRB(s)) in event 540. In some aspects, the UE 102 stops using the first security key(s) to communicate with the CU 172 when the UE 102 begins using the second security key(s) to communicate with the CU 172.

[0219] In some implementations, the CU 172 may derive at least one second security key based on the first security information. In some implementations, the CU 172 may derive a new BS key (e.g., a new KSB) based on the first security information and may derive the atleast one second security key from the new BS key. In some implementations, if CU 172 transmits the second security algorithm(s) to the UE 102 as described above, the CU 172 may derive the second security key(s) based on the new BS key and the second security algorithm(s). If the CU 172 does not transmit the second security algorithm(s) to the UE 102, the CU 172 may derive the second security key(s) based on the new BS key and the first security algorithm(s). The CU 172 may apply the second security key(s) to communicate with the UE 102 in the events 536 and 540. If the CU 172 transmits the second security algorithm(s) to the UE 102 as described above, the CU 172 may apply the second security key(s) and the second security algorithm(s) to communicate with the UE 102 in the events 536 and 540. If the CU 172 does not transmit the second security algorithm(s) to the UE 102, the CU 172 may apply the second security key(s) and the first security7algorithm(s) to communicate with the UE 102 in the events 536 and 540.

[0220] In some implementations, the CU 172 may derive the second security key(s) in response to receiving the CU-to-CU Cell Switch Notification message at event 527. the Access Success message at event 534, or the DU-to-CU message of event 538. In other implementations, the CU 172 may derive the second security7key(s) after generating or transmitting the first security configuration and before receiving the CU-to-CU Cell Switch Notification message of event 527, the Access Success message of event 534, or the DU-to- CU message of event 538. The CU 172 may apply the second security key(s) to communicate with the UE 102 in the events 536 and 540. In some implementations, the second security key(s) include an integrity key for integrity7protection of control-plane data packets (e.g., event 536 and / or RRC messages in event 540). In other implementations, the second security key(s) include an encryption key for encryption or decryption of control-plane data packets (e.g., data packets of event 536 and / or RRC messages of event 540). In yet other implementations, the second security key(s) include an integrity key for integrity protection of user-plane data packets (e.g., communicated via DRB(s)) in event 540. In yet other implementations, the second security key(s) include an encryption key for encryption or decryption of user-plane data packets (e.g., data packets communicated via DRB(s)) in event 540. In some implementations, the second security key(s) applied by the CU 172 are the same as the second security key(s) applied by the UE 102.

[0221] At event 540, after receiving the DU-to-CU message or the RRC reconfiguration complete message at event 538, the C-BS 506 may communicate with the UE 102 in accordance with the first LTM candidate configuration and / or the LTM referenceconfiguration. In some implementations, the UE 102 may include the LTM ID 1 in the RRC reconfiguration complete message of event 536 to indicate that the UE 102 applies the first LTM candidate configuration. In accordance with the LTM ID 1, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration. In other implementations, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration based on the first cell ID included in the Access Success message of event 534. In such implementations, the CU 172 maintains or stores association information between the first cell ID, and the first LTM candidate configuration, and / or the LTM reference configuration. When the CU 172 receives the first cell ID in the Access Success message, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration in accordance with the first cell ID and the association information.

[0222] In some implementations, the UE 102 may perform a RA procedure to access the first cell in the event 532. The RA procedure can be a four-step RA procedure or a two-step RA procedure. The RA procedure can be a CBRA procedure or a CFRA procedure. In some implementations, the S-BS 501 may include a first set of LTM CFRA configuration parameters in the LTM Cell Switch Command to configure the UE 102 to perform a CFRA procedure to access the first cell. The UE 102 may perform the CFRA procedure using the first set of LTM CFRA configuration parameters. In some implementations, the DU 174 may include the first set of the LTM CFRA configuration parameters in the first DU-to-CU message of the LTM preparation procedure 590.

[0223] As described for the LTM preparation procedure 590, the CU 172 in turn may include the first set of the LTM CFRA configuration parameters in the Handover Request Acknowledge message. In some implementations, the DU 174 may include at least one additional set of LTM CFRA configuration parameters in the first DU-to-CU message as described above for the LTM preparation procedure 590. The CU 172 in turn may include the additional set(s) of the LTM CFRA configuration parameters in the Handover Request Acknowledge message.

[0224] In some implementations, the DU 174 configures the first set and / or the additional set(s) for UL (e.g., NUL) or SUL and may indicate such configurations in the first DU-to-CU message, as described for the C-DU 174B in FIG. 4. In cases where the DU 174 configures the first set and / or the additional set(s) for one of UL and SUL, the CU 172 may include, in the Handover Request Acknowledge message, a single UL or SUL indicator indicating the first set and / or the additional set(s) are configured for the one of UL and SUL. In cases where the DU174 configures the first set and / or the additional set(s) for UL, the CU 172 may include the first set and / or the additional set(s) in a first field or IE in the Handover Request Acknowledge message. In cases where the DU 174 configures the first set and / or the additional set(s) for SUL. the CU 172 may include the first set and / or the additional set(s) in a second field or IE in the Handover Request Acknowledge message. In such cases, the first field or IE and the second field or IE are defined for UL and SUL respectively.

[0225] In some implementations, the DU 174 configures the first set for one of UL and SUL and configures the additional set for the other of UL and SUL and may indicate such configurations in the first DU-to-CU message, as described for the C-DU 174B in FIG. 4. In such cases, the CU 172 sets a UL or SUL indicator in the first set to a value indicating the one of UL and SUL and sets a UL or SUL indicator in the additional set to a value indicating the other of the UL and SUL. Alternatively or additionally, the CU 172 may include the first set and the additional set in one and the other of the first field or IE and the second field IE respectively in the Handover Request Acknowledge message.

[0226] In some implementations, if the S-DU of the S-BS 501 receives a TA value as described above, the S-DU of the S-BS 501 may include the TA value in the LTM Cell Switch Command. In some implementations, the S-DU of the S-BS 501 may include a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID may indicate a first one of the TCI state configuration(s). If the LTM Cell Switch Command includes the TA value, the UE 102 may skip performing an RA procedure to access the first cell in the event 532. Otherwise, the UE 102 may perform the RA procedure to access the first cell in the event 532 as described above.

[0227] In response to determining to command the UE 102 to perform the LTM cell switch or transmitting (event 526) the LTM Cell Switch Command, the S-DU of the S-BS 501 may transmit nDU-CU Cell Switch Notification message (not shown in FIG. 5) to the CU of the S- BS 501 to indicate that the UE 102 is to perform or is performing an LTM cell switch to the first cell.

[0228] At event 527, in response to receiving the DU-CU Cell Switch Notification message, the CU of the S-BS 501 may transmit a CU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 is to perform an LTM cell switch to the first cell.

[0229] At event 530, in response, the CU 172 may transmit a CU-DU Cell Switch Notification message to the DU 174 to indicate that the UE 102 is to perform an LTM cellswitch to the first cell. In some implementations, the S-BS 501 may include the first TCI state ID in the CU-CU Cell Switch Notification message and the CU 172 then may include the first TCI state ID in the CU-DU Cell Switch Notification message. The UE 102 and the DU 174 may identity the first one of the TCI state configuration(s) based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in the events 532, 536 and / or 540. In other implementations, in the case that separate TCI states are used, the DL TCI state and the UL TCI state use different TCI state IDs. In such cases, the S-DU of the S-BS 501 may include, in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command, a first TCI state ID for DL and a second TCI state ID for UL that identify a first one and a second one of the TCI state configuration(s), respectively. The CU of the S-BS 501, in response to the DU-CU Cell Switch Notification message, in turn may include the first TCI state ID and the second TCI state ID in the CU-CU Cell Switch Notification message to the CU 172. The CU 172 then may include the first TCI state ID and the second TCI state ID in the CU-DU Cell Switch Notification message to the DU 174. The UE 102 may identify' the first TCI state configuration and the second TCI state configuration based on the first TCI state ID and the second TCI state ID, respectively . The UE 102 may apply the first TCI state configuration and the second TCI state configuration to communicate DL transmissions and UL transmissions, respectively, with the DU 174 in the events 532, 536, and / or 540. The DU 174 may identify' the first TCI state configuration and the second TCI state configuration based on the first TCI state ID and second TCI state ID, respectively. The DU 174 may apply the first and / or the second TCI state configuration to communicate DL transmissions and / or UL transmissions, respectively, with the UE 102 in the events 532, 536, and / or 540.

[0230] At event 531, in some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting the LTM Cell Switch Command at event 526, or receiving the DU-CU Cell Switch Notification message at event 527, the S-BS 501 (e.g., the CU of the S-BS 501) may transmit one or more Early Status Transfer messages to the CU 172, each including a DL COUNT value or a DISCARD DL COUNT value for a DRB over which the UE 102 and the S-BS 501 communicate data with each other (e.g., at the communication starting with event 502).

[0231] At event 539, in some implementations, after receiving the Access Success message at event 534, or receiving the DU-to-CU message or the RRC reconfiguration complete message at event 538, the CU 172 may transmit an LTM Success message to the S-BS 501(e.g., the CU of the S-BS 501) to indicate that the LTM cell switch is completed successfully. In some implementations, the LTM Success message may be a Handover Success message. In some implementations, the CU 172 may include the first cell ID in the LTM Success message. In other implementations, the CU 172 does not transmit a BS-to-BS message to the S-BS 501 (e.g., the CU of the S-BS 501) to indicate that the LTM cell switch is completed successfully.

[0232] At event 541, in some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting the LTM Cell Switch Command at event 527, receiving the DU-CU Cell Switch Notification message at event 527, or receiving the LTM Success message at event 539, the S-BS 501 (e.g., the CU of the S-BS 501) may transmit an SN Status Transfer message to the CU 172, including a DL COUNT value and / or a UL COUNT value for a DRB over which the UE 102 and the S-BS 501 communicate data with each other (e.g., communication starting at event 502).

[0233] At event 543, in some implementations, after (e.g., in response to) receiving the Access Success message at event 534, receiving the DU-to-CU message or the RRC reconfiguration complete message at event 538, or receiving the SN Status Transfer message at event 541. the CU 172 may transmit a UE Context Release message to the S-BS 501. In response to the UE Context Release message, the S-BS 501 may release a UE context of the UE 102.

[0234] In some implementations, the S-BS 501 (e.g., the CU of the S-BS 501) may prepare additional cell(s) (i.e., cell(s) 2-N) as LTM candidate cell(s) for the UE 102 with the CU 172, before or after transmitting the LTM Cell Switch Command or during, before or after the inter- CU LTM preparation procedure 598, as described above. The cell(s) 2-N are identified by cell ID(s) 2-N, respectively and operated by the DU 174 and / or other DU(s) of the C-BS 506. N is an integer greater than 1. For example, the S-BS 501 may perform additional inter-CU LTM preparation procedure(s) 2-N with the CU 172 to prepare the cell(s) 2-N respectively. Each of the inter-CU LTM preparation procedure(s) 2-N is similar to the inter-CU LTM preparation procedure 598. In the inter-CU LTM preparation procedure(s) 2-N, the S-BS 501 may receive LTM candidate configuration(s) 2-N configuring the cell(s) 2-N for LTM, respectively. As described above, the S-BS 501 or the C-BS 506 may assign LTM ID(s) 2-N to identify the LTM candidate configuration(s) 2-N. respectively. The S-BS 501 may obtain CSI resource configuration 2-N for the cell(s) 2-N respectively, as described for the CSI resource configuration 1. The S-BS 501 may obtain CSI report configuration(s) 2-N, for the cell(s) 2-N or the CST resource configuration 2-N, respectively, as described for the CSI report configuration(s) 1. The S-BS 501 may obtain RACH configuration 2-N for the cell(s) 2-N respectively, as described for the RACH configuration 1. The S-BS 501 may obtain TCI state configurations 2-N for the cell(s) 2-N respectively, as described for the TCI state configuration(s) 1. The S-BS 501 may obtain LTM SSB configurations 2-N for the cell(s) 2- N, respectively, as described for LTM SSB configuration 1. The S-BS 501 may obtain PCI(s) 2-N for the cell(s) 2-N respectively, as described for the PCI 1. In some implementations, the S-BS 501 may perform LTM configuration delivery procedures 2-N with the UE 102 to transmit a list of {the LTM ID 2. the LTM candidate configuration 2. the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained), the PCI 2 (if obtained)}, {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained), the PCI N (if obtained)} to the UE 102, respectively. Each of the LTM configuration delivery procedures 2-N is similar to the procedures 394, 494 and / or LTM configuration delivery procedure 1 (i.e., events 518 and 520). In other implementations, the S-BS 501 may include the list in the first RRC reconfiguration message.

[0235] To simplify the following description, tuples 1-N are used to represent {the LTM ID 1, the LTM candidate configuration 1, the CSI resource configuration 1 (if obtained), the TCI state configuration 1 (if obtained), the RACH configuration 1 (if obtained), the LTM SSB configuration 1 (if obtained)}, .... {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained)}, respectively. In some implementations, the S-BS 501 may include the tuples 1-N in RRC reconfiguration messages 1-N in the LTM configuration delivery' procedure 1-N, respectively. The RRC reconfiguration message 1 is the first RRC reconfiguration message of event 518. In some implementations, the S-BS 501 may include the tuples 1-N in container IE 1-N and may include the container lEs 1-N in the RRC reconfiguration messages 1-N, respectively. In other implementations, the CU 172 may include the tuples 1-N in the container IE 1 and may include the container IE 1 in the first RRC reconfiguration message. In some aspects, a container IE may be an LTM-Conflg IE.

[0236] Tn other implementations, the S-BS 501 may perform the inter-CU LTM preparation procedure 598 with the CU 172 to prepare one or more of the cells 1-N as LTM candidate cells for the UE 102. In such implementations, the S-BS 501 may include the cell IDs 1-N in the Handover Request message of event 505, as described for the cell ID 1. In some implementations, upon receiving the Handover Request message, the CU 172 determines or selects the cells 1-M from the cells 1-N as LTM candidate cells. M is a positive integer and M < N. In other implementations, CU 172 prepares the cells 1-N for LTM as requested in the Handover Request message. The CU 172 may perform LTM preparation procedures 2-M with the DU 174 to prepare the cells 2-M as LTM candidate cells for the UE 102, respectively. The LTM preparation procedures 2-M are similar to the LTM preparation procedure 590 that the CU 172 may perform with the DU 174 to prepare the cell 1. The CU 172 may obtain the LTM candidate configuration(s) 2-M for the cells 2-M as a result of the LTM preparation procedures 2-M respectively, similar to obtaining the LTM candidate configuration 1. The C-BS 506 may generate the LTM candidate configuration(s) 2-M as complete configuration(s) or generate delta configuration(s) based on the LTM reference configuration, as described for the LTM candidate configuration 1. The CU 172 may include the LTM candidate configuration(s) 2-M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 501 assigns LTM IDs 2-M to identify the LTM preparation procedures 2-M respectively, as described for the LTM ID 1. In the case the CU 172 assigns the LTM IDs 1-M, the CU 172 may include the LTM IDs 1-M with the LTM candidate configuration(s) 1-M, respectively in the Handover Request Acknowledge message, as described for the LTM ID 1 and the LTM candidate configuration 1.

[0237] In some implementations, the CU 172 may obtain early synchronization information 2-M for the cells 2-M, respectively, as described for the early synchronization information 1. The CU 172 may include the early synchronization information 2-M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 501 may obtain CSI resource configurations 2-M for the cells 2-M, respectively, as described for the CSI resource configuration 1. In the case that the CU 172 may obtain the CSI resource configurations 2-M. the CU 172 may include the CSI resource configurations 2-M in the Handover Request Acknowledge message.

[0238] In some implementations, the CU 172 or the S-BS 501 may obtain LTM SSB configurations 2-M for the cells 2-M, respectively, as described for the LTM SSB configuration 1. In the case that the CU 172 obtains the LTM SSB configurations 2-M, the CU172 may include the LTM SSB configurations 2-M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 501 may obtain PCI(s) 2-M for the cells 2-M, respectively, as described for the PCI 1. In the case that the CU 172 obtains the PCI(s) 2-M, the CU 172 may include the PCI(s) 2-M in the Handover Request Acknowledge message.

[0239] In some implementations, the CU 172 may include a list of tuples: {the cell ID 1. the UTM ID 1 (if obtained or optional), the UTM candidate configuration 1, the CSI resource configuration 1 (if obtained or optional), the TCI state configuration 1 (if obtained or optional), the early synchronization information 1 (if obtained or optional), the UTM SSB configuration 1 (if obtained or optional). PCI 1 (if obtained or optional)}, , {the cell ID M. the LTM ID M (if obtained or optional), the LTM candidate configuration M, the CSI resource configuration M (if obtained or optional), the TCI state configuration M (if obtained or optional), the early synchronization information M (if obtained or optional), the LTM SSB configuration M (if obtained or optional), the PCI M (if obtained or optional)} in the Handover Request Acknowledge message.

[0240] In some implementations, the CU 172 may obtain PDCCH order information 2-M for the cell(s) 2-M, respectively, as described for the PDCCH order information 1. In one implementation, the CU 172 may include the PDCCH order information 2-M in the Handover Request Acknowledge message. In another implementation, the CU 172 may include the PDCCH order information 2-M in the early synchronization information 2-M, respectively. The S-BS 501 may obtain RACH configuration 2, TCI state configuration(s) 2, and / or the PDCCH order information 2, . .. ., RACH configuration M, TCI state configuration(s) M, and / or the PDCCH order information M from the early synchronization information 2-M, respectively or from the Handover Request Acknowledge message.

[0241] In some implementations, the S-BS 501 may perform the LTM configuration delivery procedure 2-M with the UE 102 to transmit tuples 2-M to the UE 102, respectively. In some implementations, the S-BS 501 may include the tuples 1-M in container IES 1-M and may include the container IEs 1-M in the RRC reconfiguration messages 1-M, respectively. In other implementations, the S-BS 501 may include the tuples 1-M in the first RRC reconfiguration message. In some implementations, the S-BS 501 may include the tuples 1-M in container IE 1 (e.g., an LTM-Cow / zg IE) and may include the container IE 1 in the first RRC reconfiguration message. In some aspects, a container IE may be an LTM-Cow / zg IE.

[0242] Tn some implementations, the S-BS 501 may include measurement result(s) 1-N for the cell(s) 1-N respectively in the Handover Request message. The S-BS 501 may receive the measurement result(s) from the UE 102. The C-BS 506 may select or determine the cell(s) 1- M, based on the measurement result(s) 1-N. In other implementations, the C-BS 506 may select or determine the cell(s) 1-M based on one or more other factors (e.g., capacity or load of the cell(s) 1-N and / or a maximum number of LTM candidate cell(s)). In one implementation, the maximum number is included in the Handover Request message. In another implementation, the maximum number is a predetermined number.

[0243] In some implementations, the S-BS 501 (e g., the CU of the S-BS 501) or the CU 172 may generate the first security configuration (i.e., a single security configuration) for the LTM candidate cell(s) 1-M of the UE 102 or the LTM candidate configuration(s) 1-M for the UE 102. In some implementations, the S-BS 501 may indicate the LTM candidate configuration(s) 1-M associated with the first security configuration in the first RRC reconfiguration message of event 518 and / or RRC reconfiguration messages 1-M in the LTM configuration delivery procedures 2-M. To indicate the association, the S-BS 501 may include the first security configuration and a first security configuration ID identifying the first security configuration in the container IE 1 and include the first security configuration ID in the tuples (e.g., LTM- Candidate lEs) 1-M. Based on the first security configuration ID, the UE 102 identifies that the LTM candidate cell(s) 1-M of the UE 102 or the LTM candidate configuration(s) 1-M share the same security configuration (i.e., the first security configuration). In some implementations, the S-BS 501 may include, in the first RRC reconfiguration message or the container IE 1, a serving security configuration ID associated with the serving cell. In some implementations, the serving security configuration ID may indicate (e.g., identify) that the first security key(s), the first security algorithm(s) and / or security parameters used to derive the first security key(s) are associated with serving cell. The serving security configuration ID (i.e., value) is different from the first security configuration ID (i.e., value). Because the first security’ configuration ID is different from the serving security configuration ID, the UE 102 may determine a security configuration change for the LTM cell switch to the cell 1 from the serving cell and may apply the first security configuration to communicate with the C-BS 506 via the cell 1 as described above.

[0244] The UE 102, in the communication starting at event 540, may receive an LTM Cell Switch Command from the C-BS 506, commanding the UE 102 to perform an LTM cell switch to the cell 2. In such cases, the UE 102 may perform the LTM cell switch to the cell 2 inresponse to the LTM Cell Switch Command as described for the LTM cell switch to the cell 1 . Because the UE 102 identifies the same security configuration (i.e., the first security configuration) applies to the cell 1 and the cell 2 (or the LTM candidate configuration 1 and the LTM candidate configuration 2), the UE 102 uses or continues using the second security key(s) to communicate with the C-BS 506 on the cell 2. If the UE 102 uses the second security algorithm(s) to communicate with the C-BS 506 on the cell 1, the UE 102 uses or continues using the second security algorithm(s) to communicate with the C-BS 506 on the cell 2. If the UE 102 uses the first security algorithm(s) to communicate with the C-BS 506 on the cell 1, the UE 102 uses or continues using the first security algorithm(s) to communication with the C-BS 506 on the cell 2. Similarly, the C-BS 506 may perform similar actions to communicate with the UE 102 as described above. “M” may be changed to “N” in the above description.

[0245] In some implementations, the S-BS 501 may perform an inter-CU LTM preparation procedure for the UE 102 with another, second C-BS to obtain an LTM candidate configuration and a second security configuration for an LTM candidate cell (e.g., a cell operated by the second C-BS), similar to the inter-CU LTM preparation procedure 598. The S-BS 501 may transmit the LTM candidate configuration and the second security configuration to the UE 102, similar to the events 518 and 520. The S-BS 501 may transmit second security information to the second C-BS as described for the first security information. Examples and implementations described for the first security configuration and the first security information can apply to the second security configuration and the second security information, respectively. In some implementations, the second security information and / or the second security configuration are different from the first security information and / or the first security configuration.

[0246] In some implementations, the S-BS 501 may include the CSI resource configuration(s) 1-N in the container IE instead of the tuple, where N is an integer and greater than zero.

[0247] FIGs. 6A-6D are sequence diagrams illustrating example operations of communications processes 600A-600D respectively. The communications processes 600A- 600D are described with respect to an MN 601B, a C-SN 606, and an S-SN 601A. MN 601B and S-SN 601 A may be implementations of the base station 104 of FIG. 1, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C or the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A. C-SN 606 may be an implementation of the base station 106 of FIG. 1A. thebase stations 106 A or 106B of FIG. IB, the base station 164 of FIG. 1C or the eNB, ng-eNB 230 and the gNB 232 of FIG. 2A.

[0248] FIG. 6A is a sequence diagram illustrating example operations of a communications process for a first example inter-CU cell switch where a first base station operates as an MN 601B, a second base station operates as a candidate SN (C-SN) 606, and a third base station operates as a serving or source SN (S-SN) 601A.

[0249] In some aspects, the C-SN 606 includes a CU 172 and a DU 174. The MN 60 IB may include a CU and a DU (not shown in FIG. 6A), similar to the base station 301 in FIG. 3. The S-SN 601 A may include a CU and a DU (not shown in FIG. 6A), similar to the C-SN 606. The communications process 600A is similar to the communications process 500, except that the communications process 600A is an SN communications process and the communications process 500 is an MN communications process.

[0250] At event 602, the UE 102 in DC may communicate with the MN 601B and with S- SN 601 A. In some implementations, the UE 102 communicates with the DU of the S-SN 601 A on cell 124A (FIGs. 1A and IB) using a serving DU configuration and communicates with the CU of the S-SN 601 A via the DU of the S-SN 601 A using a serving CU configuration, similar to the event 302. In some implementations, the UE 102 in DC can communicate UL PDUs and / or DL PDUs with the MN 601B and / or S-SN 601A via radio bearers which can include SRBs and / or DRB(s). The MN 601B and / or the S-SN 601 A can configure the radio bearers to the UE 102. The UE 102 in DC may communicate UL PDUs and / or DL PDUs with the S-SN 601 A on an SCG (i.e., SCG radio resources) that the S-SN 601 A configures for communication with the UE 102. The UE 102 in DC may communicate UL PDUs and / or DL PDUs with the MN 601B on an MCG (i.e., MCG radio resources) in accordance with an MN configuration (i.e., MCG configuration). In some implementations, the serving DU configuration may be an SN configuration (e.g., an SCG configuration).

[0251] In the MN configuration, the MN 601B configures the MCG which includes at least one serving cell (e.g., the cell 124B and / or other cell(s)) operated by the MN 601B. In the serving DU configuration, the S-SN 601 A configures the SCG which includes at least one serving cell (e.g., the cell 124A and / or other cell(s)) operated by the S-SN 601A. In some implementations, the MN configuration may include multiple configuration parameters and the UE 102 may receive the configuration parameters in one or more RRC messages from the MN 60 IB. As described above with respect to FIG. 3, the serving DU configuration may includemultiple configuration parameters. In some implementations, the UE 102 may receive these configuration parameters in one or more RRC messages from the S-SN 601 A, e.g. , via the MN 601B and / or on an SRB (e.g., SRB3) that the MN 601B or S-SN 601A configures to exchange RRC messages between the UE 102 and the S-SN 601 A.

[0252] The UE 102 may perform security protection to data communicated with the MN 601 B using at least one first master security key and at least one first master security algorithm, as described above with respect to FIGs. 3-5. The MN 601 B may perform security protection to data communicated with the UE 102 using at least one first master security7key and at least one first master security algorithm, as described above with respect to FIGs. 3-5. Depending on the implementation, the first master security7key(s) and the first master security algorithm(s) used by the UE 102 and the MN 601 B may be the same or different.

[0253] The UE 102 may perform security7protection on data communicated with the S-SN 601 A using at least one first secondary security key and at least one first secondary security algorithm, as described above yvith respect to FIGs. 3 and 4. The S-SN 601A may perform security protection on data communicated with the UE 102 using at least one first secondary security key and at least one first secondary security algorithm, as described above yvith respect to FIGs. 3 and 4. Depending on the implementation, the first secondary security key(s) and the first secondary security algorithm(s) used by the UE 102 and the S-SN 601 A may be the same or different.

[0254] In some aspects, yvhile communicating with the UE 102 in DC yvith the MN 60 IB and S-SN 601A, the S-SN 601A may perform an intra-CU LTM configuration procedure 696 with the UE 102, similar to the procedures 396 and / or 496 described above with respect to FIGs. 3 and 4. In some other aspects, while communicating with the UE 102 in DC yvith the MN 601B and S-SN 601 A, the S-SN 601 A may perform an intra-CU LTM procedure 680 yvith the UE 102, similar to the procedures 380 and / or 480 described above with respect to FIGs. 3 and 4. In the procedure 696 or 680, the CU of the S-SN 601 A may transmit one or more RRC reconfiguration messages, each including one or more LTM candidate configurations, to the UE 102 via the SRB3, similar to the procedure 394 or 494 described above with respect to FIGs. 3 and 4. Alternatively or additionally, the CU of the S-SN 601A may transmit one or more RRC reconfiguration messages, each including one or more LTM candidate configurations, to the UE 102 via the MN 601B. In response to each ofthe RRC reconfigurationmessage(s), the UE 102 may transmit an RRC reconfiguration complete message to the S-SN 601A via the MN 601B.

[0255] At event 604A, while communicating in DC with the MN 601B and S-SN 601A, the UE 102 may transmit at least one measurement report to the S-SN 601 A directly, e.g. via the SRB3, similar to the events 304 or 306, the events 404 or 406, and the event 504 discussed above with respect to FIGs 3-5. Alternatively or additionally, the UE 102 may transmit the measurement report(s) to the MN 601B. The MN 601B may generate at least one SN message including the measurement report(s) and may transmit the SN message(s) to the CU 172. In one implementation, the SN message(s) include RRC Transfer message(s) and / or SN Modification Request message(s). The S-SN 601A (e.g., the CU of the S-SN 601A) may generate a measurement configuration to configure the UE 102 to transmit the measurement report(s) and may transmit the measurement report to the UE 102 directly (e.g., via the S-DU of the S-SN 601 A) or via the MN 601B.

[0256] After (e.g., in response to) receiving one or more of the measurement report(s) from the UE 102, the S-SN 601 A (e.g., the CU of the S-SN 601A) may determine to prepare a first cell (e.g.. the cell 126A of FIG. IB) as an LTM candidate cell for the UE 102. In response to the determination, the S-SN 601 A may generate an SN Required message (a first SN Required message) including a first cell ID (e.g., cell ID 1) of the first cell (e.g., cell 1) and / or a target SN ID indicating the C-SN 606. In some implementations, the SN Required message may include an LTM indicator indicating the SN Required message concerns LTM for the first cell ID

[0257] At event 603, the S-SN 601 A may transmit the SN Required message to the MN 601B.

[0258] At event 605, after (e.g.. in response to) receiving the SN Required message, the MN 601B may transmit an SN Request message (a first SN Request message) including the first cell ID to the CU 172 to request preparing the first cell as an LTM candidate cell for the UE 102.

[0259] In response to the SN Request message, the CU 172 may perform an LTM preparation procedure 690 with the DU 174 to prepare the first cell as an LTM candidate cell for the UE 102, similar to the LTM preparation procedure 390, 490 or 590. In the procedure 690, the CU 172 may transmit a first CU-to-DU message including the first cell ID to the DU 174 to request preparing the first cell, similar to the event 308. In response, the CU 172 mayreceive a first DU-to-CU message including an LTM DU configuration 1 from the DU 174, similar to the event 310. The CU 172 may generate a first UTM candidate configuration (UTM candidate configuration 1).

[0260] At event 607, in response to the SN Request message, the CU 172 may transmit an SN Request Acknowledge message (a first SN Request Acknowledge message) including the first LTM candidate configuration to the MN 601B. In some implementations, the CU 172 may include the first cell ID in the SN Request Acknowledge message to indicate that the first LTM candidate configuration is provided for or associated with the first cell (ID).

[0261] At event 609 A, the MN 601B may transmit an SN Confirm message (e.g., a first SN Confirm message) including the first LTM candidate configuration to the S-SN 601 A. In some implementations, the MN 601B may include the first cell ID in the SN Confirm message to indicate that the first LTM candidate configuration is provided for or associated with the first cell (ID).

[0262] The events 603, 605, 607 and 609A along with the LTM preparation procedure 690 are collectively referred to in FIG. 6A as an SN-initiated inter-SN LTM preparation procedure 698A.

[0263] In some implementations, the SN Required message and the SN Confirm message may be an SN Change Required message and an SN Change Confirm message, respectively. In other implementations, the SN Required message and the SN Confirm message may be an SN Modification Required message and an SN Modification Confirm message, respectively. In some implementations, the SN Request message and the SN Request Acknowledge message may be an SN Addition Request message and an SN Addition Request Acknowledge message, respectively. In other implementations, the SN Request message and the SN Request Acknowledge message may be an SN Modification Request message and an SN Modification Request Acknowledge message, respectively.

[0264] In some implementations, the SN Required message may include a DU ID of the S- DU of the S-SN 601 A. In such cases, the MN 60 IB may include the DU ID in the SN Request message and the CU 172 may include the DU ID in the first CU-to-DU message. In other implementations, the SN Required message may include a first BS ID of the S-SN 601A. In some implementations, the MN 601B may include the first BS ID in the SN Request message. When receiving the first BS ID, the CU 172 may include the first BS ID in the first CU-to-DU message. In some implementations, the MN 601B may include a second BS ID of the MN601 B in the SN Request message. When receiving the second BS ID, the CU 172 may include the second BS ID in the first CU-to-DU message. In some implementations, the first BS ID and the second BS ID may be gNB IDs.

[0265] The CU 172 may or may not request an LTM reference DU configuration in the procedure 690, as described above with respect to FIGs. 3, 4 and 5. The DU 174 may or may not transmit an LTM reference DU configuration to the CU 172 in the procedure 690, as described above with respect to FIGs. 3, 4 and 5. In some implementations, the S-SN 601 A (e.g., the CU of the S-SN 601A) may obtain an LTM reference configuration, as described above with respect to FIGs. 3 and 4. In other implementations, the S-SN 601 A may receive an LTM reference configuration from the MN 60 IB in another inter-SN LTM preparation procedure as described above and below. If the S-SN 601 A obtains an LTM reference configuration, the S-SN 601A may include the LTM reference configuration (e.g., an S-SN generated LTM reference configuration) in the SN Required message. In turn, the MN 60 IB may include the LTM reference configuration in the SN Request message. Alternatively or additionally, the S-SN 601 A determines to request or cause the C-SN 606 to provide a complete LTM candidate configuration so that the S-SN 601A does not transmit the LTM reference configuration to the C-SN 606. If the S-SN 601 A does not obtain an LTM reference configuration, the S-SN 601A does not include an LTM reference configuration in the SN Required message. If the SN Required message includes an LTM reference configuration, the MN 60 IB may include the LTM reference configuration in the SN Request message. If the SN Required message does not include an LTM reference configuration, the MN 601B may not include the LTM reference configuration in the SN Request message.

[0266] If the SN Request message includes an LTM reference configuration as described above, the CU 172 may include the LTM reference configuration in the first CU-to-DU message. Alternatively or additionally, the CU 172 may extract an LTM reference DU configuration from the LTM reference configuration and may include the LTM reference DU configuration in the first CU-to-DU message. If the SN Request message does not include an LTM reference configuration, the CU 172 may or may not receive an LTM reference DU configuration from the DU 174 as described above with respect to FIG. 3. If the CU 172 receives an LTM reference DU configuration (e.g., in the first DU-to-CU message), the CU 172 may generate an LTM reference configuration (e.g., a C-SN generated LTM reference configuration) including the LTM reference DU configuration. The CU 172 may include an LTM reference CU configuration (e.g., a C-CU generated LTM reference CU configuration)in the LTM reference configuration. If the CU 172 does not receive an LTM reference DU configuration from the DU 174 as described above with respect to FIG. 3, the CU 172 does not generate an LTM reference configuration. Alternatively or additionally, the CU 172 may generate an LTM reference configuration (e.g., a C-SN generated LTM reference configuration) including a C-CU generated LTM reference CU configuration. In some aspects, the LTM reference configuration only includes the C-CU generated LTM reference CU configuration. In cases where the CU 172 generates an LTM reference configuration (e.g., a C-SN generated LTM reference configuration), the CU 172 may include the C-SN generated LTM reference configuration in the SN Request Acknowledge message.

[0267] In some implementations, if the LTM DU configuration 1 is a complete configuration, the CU 172 may generate the LTM candidate configuration 1 as a complete configuration. The CU 172 may include a complete configuration indication (e.g., a BS-to-BS interface protocol field or IE) in the SN Request Acknowledge message to indicate that the LTM candidate configuration 1 is a complete configuration. In some implementations, the BS- to-BS interface protocol is an Xn application protocol (e.g., as defined in 3GPP TS 38.423). In some implementations, the complete configuration indication may be a new field or IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the complete configuration indication may be an existing field or IE (e.g., as defined in 3GPP TS 38.423).

[0268] If the LTM DU configuration 1 is a delta configuration, the CU 172 may generate the LTM candidate configuration 1 as a delta configuration. The CU 172 may exclude the complete configuration indication from the SN Request Acknowledge message to indicate that the LTM candidate configuration 1 is a delta configuration. Alternatively or additionally, the CU 172 may include a delta configuration indication (e.g., a BS-to-BS interface protocol field or IE) in the SN Request Acknowledge message to indicate that the LTM candidate configuration 1 is a delta configuration. In some implementations, the BS-to-BS interface protocol is an Xn application protocol (e.g., as defined in 3GPP TS 38.423). In some implementations, the delta configuration indication is a new field or IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the delta configuration indication is an existing field or IE (e.g., as defined in 3GPP TS 38.423). In some implementations, the BS-to-BS interface protocol field or IE may have two values (i.e., a first value and a second value). The BS-to-BS interface protocol field or IE set to the first value isthe complete configuration indication and the BS-to-BS interface protocol field or IE set to the second value is the delta configuration indication.

[0269] In some implementations, the S-SN 601A is preconfigured with a CSI resource configuration (e.g., (LTM) CSI resource configuration 1) and / or an LTM SSB configuration (e.g., LTM SSB configuration 1) for the first cell. In other implementations, the CU 172 may receive the CSI resource configuration and / or the LTM SSB configuration from an 0AM node. In yet other implementations, the S-SN 601A may receive the CSI resource configuration and / or the LTM SSB configuration from the CU 172. For example, the CU 172 may include the CSI resource configuration and / or the LTM SSB configuration in the SN Request Acknowledge message. In this case, the MN 60 IB may include the CSI resource configuration and / or the LTM SSB configuration in the SN Confirm message. In some implementations, the CU 172 may include a PCI of the first cell in the SN Request Acknowledge message. In this case, the MN 601B may include the PCI of the first cell in the SN Confirm message. To prepare the first cell as a candidate LTM cell for the UE 102, the CU of the S-SN 601 A may perform an LTM CSI report configuration and / or LTM ID configuration procedure (not show n in FIG. 6A) with an S-DU of the S-SN 601 A, similar to the procedure 392 or 492 of FIGs 3 and 4, respectively. In the LTM CSI report configuration and / or LTM ID configuration procedure, the CU of the S-SN 601A may transmit the CSI resource configuration and / or the LTM SSB configuration to the S-DU of the S-SN 601 A. In response, the CU of the S-SN 601 A may receive one or more CSI report configurations for the UE 102 from the S-DU of the S-SN 601 A. In some implementations, the S-SN 601A may receive a second serving DU configuration including the CSI report configuration(s).

[0270] In some implementations, the CU 172 may receive early synchronization information for the first cell and / or PDCCH order information from the DU 174, as described above with respect to FIG. 5. In some implementations, the early synchronization information may include aRACH configuration (e.g., RACH configuration 1) and / or at least one TCI state configuration (e.g., TCI state configuration(s) 1). The CU 172 may include the early synchronization information and / or the PDCCH order information in the SN Request Acknowledge message. The MN 601B may include the early synchronization information and / or the PDCCH order information in the SN Confirm message.

[0271] In some implementations, the CU 172 may assign an LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration and may include the LTM ID and / or anassociated (or mapped) cell ID for the LTM ID in the SN Request Acknowledge message. The MN 601B may include the LTM ID and / or an associated (or mapped) cell ID for the LTM ID in the SN Confirm message. In other implementations, the S-SN 601 A may assign an LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration. In yet other implementations, the MN 60 IB assigns an LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration. In such cases, the MN 60 IB may include the LTM ID in the SN Confirm message. After receiving or assigning the LTM ID, the CU of the S-SN 601 A maytransmit the LTM ID and the first cell ID to the S-DU in an LTM ID configuration procedure, similar to the procedure 390 or 392 of FIG. 3 or procedure 492 of FIG. 4.

[0272] After (e.g.. in response to) receiving the SN Confirm message, the S-SN 601 A (e.g., the CU of the S-SN 601 A) may perform LTM configuration delivery procedure 694A with the UE 102 to transmit the LTM ID and the LTM candidate configuration to the UE 102. In some implementations, the S-SN 601A may transmit {LTM ID, the LTM candidate configuration} as a tuple (e.g., tuple 1) in a first RRC reconfiguration message in the procedure 694A. Depending on the implementation, the S-SN 601 A may include the LTM reference configuration, the CSI report configuration(s), the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the first cell in the tuple in the first RRC reconfiguration message and / or other RRC reconfiguration message(s) transmitted to the UE 102, as described above with respect to FIGs. 3 and 4. The S-SN 601 A may include the LTM ID in the first RRC reconfiguration message or the other RRC reconfiguration message(s) to indicate that the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the first cell are associated with the first cell. For example, the S-SN 601A may include the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1 in the tuple. In another example, the S-SN 601 A may include the tuple in RRC reconfiguration message(s) other than the first RRC reconfiguration message. In response to each of the other RRC reconfiguration message(s), the UE 102 may transmit an RRC reconfiguration complete message to the CU 172 via the S-DU 174A.

[0273] In some implementations, the MN 601B (e.g.. the CU of the MN 601B) may include a first MN-to-SN LTM security configuration in the SN Request message. In some aspects, the first MN-to-SN LTM security configuration may be a list of LTM security configurations or configuration parameters. In some implementations, the first MN-to-SN LTM security configuration may include a list of tuple(s) 1-L, where L is an integer greater than zero. Thetuple(s) 1-L may include {RAN level security key (e.g., S-NG-RAN node Security Key) 1 and / or a security key (SK) counter L}, {RAN level security' key (e.g., S-NG-RAN node Security' Key) L and / or a SK counter L}. In some implementations, the MN 601B may include security’ capabilities of the UE 102 in the SN Request message.

[0274] In some implementations, the MN 601B (e.g., the CU of the MN 601B) may generate a first UE LTM security configuration based on the first MN-to-SN LTM security configuration and may include the first UE LTM security configuration in the SN Confirm message. In some aspects, the first UE LTM security' configuration may be a list of LTM security' configurations or configuration parameters. In some implementations, the S-SN 601A may include the first UE LTM security configuration in a container IE (e.g., LTM-Config IE) that includes the tuple 1 and may include the container IE in the first RRC reconfiguration message. In other implementations, the S-SN 601 A may include the first UE LTM security' configuration in the tuple 1.

[0275] In some implementations, the first UE LTM security configuration may include at least a portion of the first MN-to-SN LTM security' configuration. For example, the first UE LTM security configuration may include a list of the SK counters (e.g., SK counter(s) 1-L) included in the first MN-to-SN LTM security configuration and does not include any RAN level security key in the in the first MN-to-SN LTM security configuration. In some implementations, the first LTM candidate configuration, the LTM reference configuration, or first UE LTM security configuration configures at least one second security algorithm. In some implementations, the CU 172 determines the second security algorithm(s) based on the security capabilities of the MN and / or SN. In some implementations, the second security' algorithm(s) may include an encry ption algorithm and / or an integrity' algorithm that may be the same as or different from the first security algorithm(s).

[0276] In some implementations, if the SN Required message includes the complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration, the S-SN 601 A may include, in the first RRC reconfiguration message, a complete configuration indication (e.g., an RRC field or IE) to indicate that the LTM candidate configuration 1 is a complete configuration. If the SN Required message does not include the complete configuration indication or includes the delta configuration indication to indicate that the LTM candidate configuration 1 is a delta configuration, the S-SN 601A excludes or does not include, in the first RRC reconfiguration message, the complete configuration indication(e.g., an RRC field or IE) to indicate that the LTM candidate configuration 1 is a delta configuration.

[0277] At event 624A, the UE 102 may optionally transmit at least one measurement report including measurement result(s) to the S-SN 601A. In some aspects, the measurement report may be an LI measurement report including LI measurement results.

[0278] At event 650A, if the SN Confirm message of event 609A includes the PDCCH order information (PDCCH order information 1), the S-SN 601 A may optionally transmit a PDCCH order to the UE 102, based on the PDCCH order information. If the S-SN 601 A is a distributed base station, the CU of the S-SN 601A may transmit the PDCCH order information to the S- DU of the S-SN 601A and the S-DU may transmit the PDCCH order to the UE 102. For example, the S-SN 601 A or the S-DU of the S-SN 601 A may transmit a PDCCH order to the UE 102, including the PDCCH order information. In some implementations, the S-SN 601A or the S-DU may determine to transmit the PDCCH order, based on (e.g., in response to) the measurement report(s) of event 624 A. In some implementations, the S-SN 601 A or the S-DU may determine an SSB index included in the PDCCH order, based on the LI measurement report(s) of event 624 A. and / or the CSI resource configuration, the CSI report configuration, and / or the LTM SSB configuration. In some implementations, the S-DU or the S-SN 601A may include the LTM ID 1 in the PDCCH order to indicate the first cell.

[0279] At event 652, the UE 102 may transmit an RA preamble to the DU 174 on the first cell, using the RACH configuration and / or the PDCCH order information. The S-DU or the S- SN 601 A may derive a TA value based on the RA preamble.

[0280] At event 656, the DU 174 may transmit a DU-CU TA Information Transfer message including the TA value to the CU 172. In some implementations, the DU 174 may include the cell ID 1, the RA preamble index, a RA-RNTI, and / or the DU ID of the S-DU of the S-SN 601 A in the DU-CU TA Information Transfer message. The DU 174 may include the first BS ID and / or the second BS ID in the DU-CU TA Information Transfer message.

[0281] At event 657, the CU 172 may transmit a CU-CU TA Information Transjer message including the TA value to the MN 601B (e.g., the CU of the MN 601B). In some implementations, the CU 172 may include the cell ID 1, the RA preamble index, the RA-RNTI, and / or the DU ID of the S-DU in the CU-CU TA Information Transfer message. In some implementations, the CU 172 may additionally include the first BS ID and / or the second BS ID in the CU-CU TA Information Transfer message.

[0282] Tn some implementations, the CU 172 determines an address (e.g., an IP address) of the MN 601B or the CU of the MN 601B, based on the second BS ID. In such implementations, the CU 172 may transmit the CU-CU TA Information Transfer message of event 657 to the MN 60 IB in accordance with the address.

[0283] At event 658, the MN 60 IB may transmit a CU-CU TA Information Transfer message including the TA value to the S-SN 601 A. In some implementations and depending on the elements transmitted at events 656 and / or 657, the MN 601B may include the cell ID 1, the RA preamble index, the RA-RNTI, and / or the DU ID of the S-DU in the CU-CU TA Information Transfer message. In some implementations, if the first BS ID and / or the second BS ID are included in the DU-CU TA Information Transfer messages of event 656 and / or the CU-CU TA Information Transfer message of event 657, the MN 601B may additionally include the first BS ID and / or the second BS ID in the CU-CU TA Information Transfer message.

[0284] In some implementations, the MN 601B may determine an address (e.g., an IP address) of the S-SN 601A or the CU of S-SN 601A, based on the first BS ID. In other implementations, the MN 601B may determine an address (e.g.. an IP address) of the S-SN 601 A or the CU of the S-SN 601 A. based on the DU ID of the S-DU of the S-SN 601 A. In such implementations, the MN 601B sends the CU-CU TA Information Transfer message of event 658 to the S-SN 601A or the CU of the S-SN 601 A in accordance with the address.

[0285] At event 654A, the UE 102 may transmit at least one measurement report including measurement result(s) to the S-SN 601A. In some aspects, the measurement report may be an El measurement report including LI measurement results.

[0286] At event 626A, in response to determining to command the UE 102 to perform an LTM cell switch to the first cell, e.g., based on the LI measurement report(s) of event 624A and / or event 654A. the S-DU or the S-SN 601 A may transmit the LTM Cell Switch Command including the LTM ID 1 to the UE 102.

[0287] At event 632, in response to the LTM Cell Switch Command, the UE 102 the UE 102 may stop communication on the serving cell(s) and may access the first cell. When detecting the UE 102 access to the first cell, at event 634, the DU 174 may transmit an Access Success message to the CU 172. At event 636A, the UE 102 may transmit an RRC reconfiguration complete message to DU 174 during or after the access at event 632. At event 638, the DU 174 in turn may transmit a DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some other implementations, the UE 102 may transmit the RRCreconfiguration complete message to the C-SN 606 via the MN 601 B instead of via the DU 174.

[0288] In some implementations, the UE 102 may derive at least one second security key based on the first UE LTM security configuration (e.g., SK counter 1). In some implementations, the UE 102 may derive a new SN key (e.g., a new S-K§NB) based on the first UE LTM security configuration and may derive the second security key(s) from the new SN key. In some implementations, if the UE 102 receives the second security algorithm(s) for the first cell (i.e., the LTM candidate cell), the UE 102 may derive the second security' key(s) based on the new SN key and the second security algorithm(s). If the UE 102 does not receive the second security’ algorithm(s), the UE 102 may derive the second security key(s). based on the new SN key and the first security algorithm(s). In some implementations, the UE 102 may derive the second security key(s) in response to receiving, at event 626A, the LTM Cell Switch Command. In other implementations, the UE 102 may derive the second security' key(s) after receiving the first UE LTM security configuration and before receiving, at event 626A, the LTM Cell Switch Command.

[0289] The UE 102 may apply the second security key(s) to communicate with the CU 172 in the events 636A and 640. If the UE 102 receives the second security’ algorithm(s) as described above, the UE 102 may apply the second security- key(s) and the second security algorithm(s) to communicate with the CU 172 in the events 636A and 640. If the UE 102 does not receive the second security algorithm(s), the UE 102 may apply the second security- key(s) and the first security algorithm(s) to communicate with the CU 172 in the events 636A and 640. In some implementations, the second security key(s) include an integrity key for integrity protection of control-plane data packets (e.g., event 636A and / or RRC messages in event 640). In other implementations, the second security key(s) include an encryption key for encryption / decryption of control-plane data packets (e.g., the RRC reconfiguration complete message of event 636A and / or RRC messages in event 640). In yet other implementations, the security- key(s) include an integrity' key for integrity protection of user-plane data packets (e.g., communicated via DRB(s)) in event 640. In still other implementations, the security key(s) include an encryption key for encryption / decryption of user-plane data packets (e.g., communicated via DRB(s)) in event 640. The UE 102 may stop using the first security’ key(s) to communicate with the CU 172.

[0290] Tn some implementations, the CU 172 may derive at least one second security key based on the first MN-to-SN LTM security configuration (e.g., RAN level security key 1 and SK counter 1). In some implementations, the CU 172 may derive a new SN key (e.g., anew S- KgNB) based on the first MN-to-SN LTM security configuration and may derive the second security key(s) from the new SN key. In some implementations, if the CU 172 transmits the second security' algorithm(s) for the first cell (i.e., the LTM candidate cell) to the UE 102, the CU 172 may derive the second security' key(s), based on the new SN key and the second security algorithm(s). If the CU 172 does not transmit the second security algorithm(s) to the UE 102, the CU 172 may derive the second security key(s). based on the new SN key and the first security algorithm(s).

[0291] In some implementations, the CU 172 may derive the second security key(s) in response to receiving the CU-to-CU Cell Switch Notification message of event 628, the Access Success message of event 634, or the DU-to-CU message of event 638. In other implementations, the CU 172 may derive the second security key(s) after receiving the first MN-to-SN LTM security configuration and before receiving the CU-to-CU Cell Switch Notification message of event 628, the Access Success message of event 634, or the DU-to- CU message of event 638. The CU 172 may apply the second security key(s) to communicate with the UE 102 in the events 636A and 640. In some implementations, the second security key(s) include an integrity key for integrity’ protection of control-plane data packets (e.g., event 636A and / or RRC messages in event 640). In other implementations, the second security key(s) include an encryption key for encryption / decry ption of control-plane data packets (e.g., event 636A and / or RRC messages in event 640). In yet other implementations, the second security key(s) includes an integrity key for integrity protection of user-plane data packets (e.g., communicated via DRB(s)) in event 640. In yet other implementations, the second security key(s) include an encryption key for encryption / decryption of user-plane data packets (e.g., communicated via DRB(s)) in event 640. In some implementations, the second security key(s) applied by the CU 172 are the same as the second security key(s) applied by the UE 102.

[0292] In some implementations, the UE 102 may perform an RA procedure to access the first cell in the event 632. The RA procedure can be a four-step RA procedure or a two-step RA procedure. The RA procedure can be a CBRA procedure or a CFRA procedure. In some implementations, the S-SN 601 A may include a first set of LTM CFRA configuration parameters in the LTM Cell Switch Command of event 626A to configure the UE 102 to perform a CFRA procedure to access the first cell. The UE 102 may perform the CFRAprocedure using the first set of LTM CFRA configuration parameters. In some implementations, the DU 174 may include the first set of the LTM CFRA configuration parameters in the first DU-to-CU message of the LTM preparation procedure 690 as described for the LTM preparation procedure 490. The CU 172 in turn may include the first set of the LTM CFRA configuration parameters in the SN Request Acknowledge message. In some implementations, the DU 174 may include at least one additional set of LTM CFRA configuration parameters in the first DU-to-CU message as described for the LTM preparation procedure 490. The CU 172 in turn may include the additional set(s) of the LTM CFRA configuration parameters in the SN Request Acknowledge message of event 607.

[0293] In some implementations, the DU 174 configures the first set and / or the additional set(s) for UL (i.e., NUL) or SUL and may indicate such configurations in the first DU-to-CU message, as described for the C-DU 174B in FIG. 4. In cases where the first set and / or the additional set(s) are configured for one of UL and SUL, the CU 172 may include, in the SN Request Acknowledge message, a single UL or SUL indicator indicating the first set and / or the additional set(s) are configured for the one of UL and SUL. In cases where the DU 174 configures the first set and / or the additional set(s) for UL, the CU 172 may include the first set and / or the additional set(s) in a first field or IE in the SN Request Acknowledge message. In cases where the DU 174 configures the first set and / or the additional set(s) for SUL, the CU 172 may include the first set and / or the additional set(s) in a second field or IE in the SN Request Acknowledge message. In such cases, the first field or IE and the second field or IE are defined for UL and SUL respectively.

[0294] In some implementations, the DU 174 configures the first set for one of UL and SUL and configures the additional set for the other of UL and SUL and may indicate such configurations in the first DU-to-CU message, as described for the C-DU 174B in FIG. 4. In such cases, the CU 172 sets a UL or SUL indicator in the first set to a value indicating the one of UL and SUL and sets a UL or SUL indicator in the additional set to a value indicating the other of the UL and SUL. Alternatively or additionally, the CU 172 may include the first set and the additional set in one and the other of the first field or IE and the second field or IE respectively in the SN Request Acknowledge message.

[0295] After receiving the Access Success message of event 634 or the DU-to-CU message including the RRC reconfiguration complete message of event 638, at event 640, the C-SN 606 communicates with the UE 102 in DC with the MN 601 B and the C-SN 606 in accordance withthe first LTM candidate configuration and / or the LTM reference configuration. Tn some implementations, the UE 102 may include the LTM ID 1 in the RRC reconfiguration complete message of event 636A to indicate that the UE 102 applies the first LTM candidate configuration. In accordance with the LTM ID 1, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration. In other implementations, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration based on the first cell ID included in the Access Success message of event 634. In such implementations, the CU 172 may maintain or store association information between the first cell ID, and the first LTM candidate configuration and / or the LTM reference configuration. When the CU 172 receives the first cell ID in the Access Success message, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration in accordance w ith the first cell ID and the association information.

[0296] In some implementations, if the S-DU or the S-SN 601A receives a TA value as described above, the S-DU or the S-SN 601 A may include the TA value in the LTM Cell Switch Command of event 626A. In some implementations, the S-DU or the S-SN 601 A may include a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID may indicate a first one of the TCI state configuration(s).

[0297] In response to determining to command the UE 102 to perform the LTM cell switch or transmitting the LTM Cell Switch Command at event 626A, the S-DU of the S-SN 601A may transmit a DU-CU Cell Switch Notification message to the CU of the S-SN 601A to indicate that the UE 102 is to perform an LTM cell switch to the first cell.

[0298] At event 627A. in response to receiving the DU-CU Cell Switch Notification message, the CU of the S-SN 601A may transmit a CU-CU Cell Switch Notification message to the MN 60 IB to indicate that the UE 102 is to perform or is performing an LTM cell switch to the first cell.

[0299] At event 628, in response to receiving the CU-CU Cell Switch Notification message, the MN 601B may transmit a CU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 is to perform or is performing an LTM cell switch to the first cell.

[0300] At event 630, in response to receiving the CU-CU Cell Switch Noti fication message, the CU 172 may transmit a CU-DU Cell Switch Notification message to the DU 174 to indicate that the UE 102 is to perform or is performing an LTM cell switch to the first cell. In some implementations, the S-SN 601A may include the first TCI state ID in the CU-CU Cell SwitchNotification message of event 627 A. In such cases, the MN 60 IB may include the first TCI state ID in the CU-CU Cell Switch Notification message of event 628. The CU 172 may then include the first TCI state ID in the CU-DU Cell Switch Notification message. The UE 102 and the DU 174 identify the first one of the TCI state configuration(s) based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in the events 632, 636A, and / or 640. In other implementations, in the case that separate TCI states are used, the DL TCI state and the UL TCI state may use different TCI state IDs. In such cases, the S-DU of the S-SN 601 A may include, in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command, a first TCI state ID for DL and a second TCI state ID for UL that identify a first one and a second one of the TCI state configuration(s). The CU of the S-SN 601 A, in response to the DU-CU Cell Switch Notification message, in turn may include the first TCI state ID and the second TCI state ID in the CU-CU Cell Switch Notification message to the MN 601B. The MN 601B may include the first TCI state ID and the second TCI state ID in the CU-CU Cell Switch Notification message to the CU 172. The CU 172 then may include the first TCI state ID and the second TCI state ID in the CU-DU Cell Switch Notification message to the DU 174. The UE 102 identifies the first TCI state configuration and / or the second TCI state configuration based on the first TCI state ID and the second TCI state ID respectively. The UE 102 may apply the first TCI state configuration and the second TCI state configuration to communicate DL transmissions and UL transmissions, respectively, with the DU 174 in the events 632, 636A and / or 640. The DU 174 identifies the first TCI state configuration and the second the TCI state configuration based on the first TCI state ID and second TCI state ID respectively. The DU 174 may apply the first and / or the second TCI state configuration to communicate DL transmissions and / or UL transmissions, respectively, with the UE 102 in the events 632, 636A, and / or 640.

[0301] At event 631, in some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch or transmitting the LTM Cell Switch Command at event 626A, the S-SN 601A may transmit one or more Early Status Transfer messages to the MN 601 B, each including a DL COUNT value or a DISCARD DL COUNT value for a DRB over which the UE 102 and the S-SN 601 A may communicate (e.g., at event 602) data with each other.

[0302] At event 633, the MN 601B may transmit one or more Early Status Transfer messages to CU 172, each including the DL COUNT value or the DISCARD DL COUNTvalue for the DRB over which the UE 102 and the S-SN 601 A communicate (e.g., at event 602) data with each other.

[0303] At event 639, in some implementations, after receiving the Access Success message of event 634 or receiving the DU-to-CU message or the RRC reconfiguration complete message of event 638, the CU 172 may transmit an LTM Success message to the MN 601B (e.g.. the CU of the MN 601B) to indicate that the LTM cell switch is completed successfully. In some implementations, the LTM Success message is an SN Modification Required message or a BS-to-BS Access Success message. In some implementations, the CU 172 may include the first cell ID in the LTM Success message. In other implementations, the CU 172 does not transmit a BS-to-BS message to the MN 601B (e.g., the CU of the MN 601B) to indicate that the LTM cell switch is completed successfully. In some implementations, after (e.g., in response to) receiving the LTM Success message or receiving the RRC reconfiguration complete message from the UE 102, the MN 601B may transmit an SN message (as shown at event 645 in FIG. 6C) to the S-SN 601A. The SN message may indicate that the LTM cell switch is completed successfully, indicate the S-SN 601 A is to suspend communication with the UE 102, or indicate the S-SN 601 A is to release a UE context of the UE 102 and resources configured for the UE 102. The MN 601B may include the first cell ID and / or the RRC reconfiguration complete message of event 636C in the SN message. In some implementations, the SN message is an SN Modification Request message, an SN Release Request message, an SN Access Success message, or the like.

[0304] At event 641, in some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting the LTM Cell Switch Command at event 626A, receiving the DU-CU Cell Switch Notification message from the S- DU, or receiving the SN message, the S-SN 601A (e.g., the CU of the S-SN 601 A) may transmit an SN Status Transfer message to the MN 60 IB. including a DL COUNT value and / or a UL COUNT value for a / the DRB over which the UE 102 and the S-SN 601 A communicate data with each other.

[0305] At event 642, after (e.g., in response to) receiving the SN Status Transfer message at event 641, the MN 601B may transmit an SN Status Transfer message to the CU 172, including the DL COUNT value and / or the UL COUNT value.

[0306] In some implementations, the S-SN 601A (e.g., the CU of the S-SN 601A) may prepare additional cell(s) (i.e., cell(s) 2-N) as LTM candidate cell(s) for the UE 102 with theMN 60 IB and one or more C-SNs (including the C-SN 606), before or after transmitting the LTM Cell Switch Command or during, before or after the procedure 698A, as described above. N is an integer greater than 1. The C-SN(s) may operate cell(s) 2-N. For example, the S-SN 601 A may perform additional inter-SN LTM preparation procedure(s) 2-N with the MN 601B to prepare the cell(s) 2-N respectively. Each of the inter-SN LTM preparation procedure(s) 2- N is similar to the procedure 698A. In the inter-SN LTM preparation procedure(s) 2-N, the S- SN 601 A may receive LTM candidate configuration(s) 2-N configuring the cell(s) 2-N for LTM, respectively. As described above, the MN 601B, S-SN 601A or C-SN(s) assign LTM ID(s) 2-N to identify the LTM candidate configuration(s) 2-N. respectively. The S-SN 601A may obtain CSI resource configuration(s) 2-N for the cell(s) 2-N respectively, as described for the CSI resource configuration 1. The S-SN 601A may obtain CSI report configuration(s) 2-N for the cell(s) 2-N. respectively, as described for the CSI report configuration(s) 1. The S-SN 601 A may obtain RACH configuration 2-N for the cell(s) 2-N respectively, as described for the RACH configuration 1. The S-SN 601 A may obtain TCI state configuration(s) 2-N for the cell(s) 2-N respectively, as described for the TCI state configuration(s) 1. The S-SN 601 A may obtain LTM SSB configuration 2-N for the cell(s) 2-N, respectively, as described for LTM SSB configuration 1. In some implementations, the S-SN 601 A may perform LTM configuration delivery procedure 2-N with the UE 102 to transmit a list of tuples, for example, {the LTM ID 2, the LTM candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained), and / or a PCI 1 of the cell 1 } , . .. , {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained), and / or a PCI N of the cell N} to the UE 102, respectively. Each of the LTM configuration delivery procedure 2-N is similar to the procedures 394 of FIG. 3, 494 of FIG. 4, and / or events 518 and 520 of FIG. 5. In other implementations, the S-SN 601 A may include the list in the first RRC reconfiguration message.

[0307] To simplify the following description, tuples 1-N are used to represent {the LTM ID 1, the LTM candidate configuration 1, the CSI resource configuration 1 (if obtained), the TCI state configuration 1 (if obtained), the RACH configuration 1 (if obtained), the LTM SSB configuration 1 (if obtained), and / or the PCI 1 }, ... , {the LTM ID N, the LTM candidate configuration N. the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (ifobtained), and / or the PCT N}, respectively. In some implementations, the S-SN 601 A may include the tuples 1-N in RRC reconfiguration messages 1-N in the LTM configuration delivery' procedure 1-N, respectively. The RRC reconfiguration message 1 is the first RRC reconfiguration message of the procedure 694A. In some implementations, the S-SN 601 A may include the tuples 1-N in container IE (e.g., an LTM -Con fig IE) 1-N and may include the container IE 1-N in the RRC reconfiguration messages 1-N, respectively. In other implementations, the S-SN 601A may include the tuples 1-N in container IE 1 (e.g., an LTM- Conflg IE) and may include the container IE 1 in the first RRC reconfiguration message.

[0308] In some implementations, the S-SN 601A may include the CSI resource configuration(s) 1-N in the container IE instead of the tuple, where N is an integer greater than zero.

[0309] In some implementations, an SN Required message and an SN Confirm message in each of the inter-SN LTM preparation procedure(s) 2-N may be an SN Modification Required message and an SN Modification Confirm message, respectively. In other implementations, an SN Required message and an SN Confirm message in each of the inter-SN LTM preparation procedure(s) 2-N may be an SN Change Required message and an SN Change Confirm message, respectively. In some implementations, an SN Request message and an SN Request Acknowledge message in each of the inter-SN LTM preparation procedure(s) 2-N may be an SN Addition Request message and an SN Addition Request Acknowledge message, respectively. In other implementations, the SN Request message and the SN Request Acknowledge message in each of the inter-SN LTM preparation procedure(s) 2-N may be an SN Modification Request message and an SN Modification Request Acknowledge message, respectively. In some implementations, the information provided in the SN Confirm message (e.g., LTM candidate configuration. LTM reference configuration, first cell ID, or LTM ID) may be alternatively provided in an SN Modification Request message from the MN 60 IB to the S-SN 601 A (i.e., similar to the event 609B which will be described in the communications process 600B of FIG. 6B).

[0310] In other implementations, the S-SN 601A may perform the procedure 698A with the CU 172 to prepare one or more of the cell 1 and cell(s) 2-N as LTM candidate cell(s) for the UE 102. The cell(s) 2-N are identified by cell ID(s) 2-N respectively and operated by the DU 174 and / or other DU(s) of the C-SN 606. In such implementations, the S-SN 601 A may include the cell ID(s) 2-N in the SN Required message of event 603 for LTM and the MN 60 IB mayinclude the cell ID(s) 2-N in the SN Request message, as described for the cell ID 1 above. In some implementations, upon receiving the SN Request message, the CU 172 determines or selects the cell(s) 1-M from the cell(s) 1-N as LTM candidate cell(s). M is a positive integer and M < N. In other implementations. CU 172 prepares the cell(s) 1-N for LTM as requested in the SN Request message. The CU 172 may perform LTM preparation procedure(s) 2-M with the DU 172 to prepare the cell(s) 2-M as LTM candidate cell(s) for the UE 102, respectively. The LTM preparation procedure(s) 2-M are similar to the procedure 690 that the CU 172 may perform with the DU 174 to prepare the cell 1. The CU 172 may obtain the LTM candidate configuration(s) 2-M for the cell(s) 2-M as a result of the LTM preparation procedure(s) 2-M respectively, similar to obtaining the LTM candidate configuration 1. The C-SN 606 may generate the LTM candidate configuration(s) 2-M as complete configuration(s) or generate delta configuration(s) based on the LTM reference configuration, as described for the LTM candidate configuration 1. The CU 172 may include the LTM candidate configuration(s) 2-M in the SN Request Acknowledge message. In some implementations, the CU 172, the MN 601B or the S-SN 601A assigns LTM ID(s) 2-M to identify the LTM preparation procedure(s) 2-M respectively, as described for the LTM ID 1 and the LTM candidate configuration 1. In the case the CU 172 assigns the LTM ID(s) 1-M, the CU 172 may include the LTM ID(s) 1-M with the LTM candidate configuration(s) 1-M, respectively in the SN Request Acknowledge message, as described for the LTM ID 1 and the LTM candidate configuration 1.

[0311] In some implementations, the CU 172 may obtain early synchronization information 2-M for the cell(s) 2-M, respectively, as described for the early synchronization information 1. The CU 172 may include the early synchronization information 2-M in the SN Request Acknowledge message. In some implementations, the CU 172 or the S-SN 601A may obtain CSI resource configuration(s) 2-M for the cell(s) 2-M, respectively, as described for the CSI resource configuration 1. In the case that the CU 172 obtains the CSI resource configuration(s) 2-M, the CU 172 may include the CSI resource configuration(s) 2-M in the SN Request Acknowledge message.

[0312] In some implementations, the CU 172 or the S-SN 601A may obtain LTM SSB configuration(s) 2-M for the cell(s) 2-M, respectively, as described for the LTM SSB configuration 1. In the case that the CU 172 obtains the LTM SSB configuration(s) 2-M, the CU 172 may include the LTM SSB configuration(s) 2-M in the SN Request Acknowledge message. In some implementations, the CU 172 or the S-SN 601 A may obtain PCI(s) 2-M forthe cell(s) 2-M, respectively, as described for the PCI 1. Tn the case that the CU 172 obtains the PCI(s) 2-M, the CU 172 may include the PCI(s) 2-M in the SN Request Acknowledge message.

[0313] In some implementations, the CU 172 may include a list of tuples including {the cell ID 1. the LTM ID 1 (if obtained or optional), the LTM candidate configuration 1, the CSI resource configuration 1 (if obtained or optional), the TCI state configuration 1 (if obtained or optional), the early synchronization information 1 (if obtained or optional), the LTM SSB configuration 1 (if obtained or optional), PCI 1 (if obtained or optional)}, , {the cell ID M, the LTM ID M (if obtained or optional), the LTM candidate configuration M, the CSI resource configuration M (if obtained or optional), the TCI state configuration M (if obtained or optional), the early synchronization information M (if obtained or optional), the LTM SSB configuration M (if obtained or optional), the PCI M (if obtained or optional)} in the SN Request Acknowledge message. The MN 60 IB may include the list or a portion of the list in the SN Confirm message.

[0314] In some implementations, the CU 172 may obtain PDCCH order information 2-M for the cell(s) 2-M, respectively, as described for the PDCCH order information 1. In one implementation, the CU 172 may include the PDCCH order information 2-M in the SN Request Acknowledge message. In another implementation, the CU 172 may include the PDCCH order information 2-M in the early synchronization information 2-M, respectively. The MN 60 IB may include the PDCCH order information 2-M in the SN Confirm message as described for the PDCCH order information 1. The S-SN 601 A may obtain RACH configuration 2, TCI state configuration(s) 2 and / or the PDCCH order information 2, ...., RACH configuration M, TCI state configuration(s) M and / or the PDCCH order information M from the early synchronization information 2-M, respectively, or from the SN Confirm message.

[0315] In some implementations, the S-SN 601 A may perform the LTM configuration delivery procedure 2-M with the UE 102 to transmit the tuples 2-M to the UE 102, respectively. Each of the LTM configuration delivery procedures 2-M is similar to the procedures 394 of FIG. 3, 494 of FIG. 4, and / or events 518 and 520 of FIG. 5. In some implementations, the S-SN 601 A may include the tuples 1-M in a container IE (e.g., an LTM- Conflg IE) 1-M and may include the container IE 1-M in the RRC reconfiguration messages 1-M, respectively. In other implementations, the S-SN 601 A may include the tuples in the firstRRC reconfiguration message. In some implementations, the S-SN 601 A may include the tuples 1-M in a container IE 1 (e.g., an LTM-Config IE) and may include the container IE 1 in the first RRC reconfiguration message.

[0316] In some implementations, the MN 601B may include measurement result(s) 1-N for the cell(s) 1-N respectively in the SN Request message. In some implementations, the MN 601 B may receive the measurement result(s) from the UE 102 and / or in the SN Required message from the S-SN 601A. The C-SN 606 may select or determine the cell(s) 1-M based on the measurement result(s) 1-N. In other implementations, the C-SN 606 may select or determine the cell(s) 1-M based on other factors (e.g., capacity or load of the cell(s) 1-N and / or a maximum number of LTM candidate cell(s)). In one implementation, the maximum number of LTM candidate cell(s) may be included in the SN Request message. In another implementation, the maximum number may be a predetermined number.

[0317] The events 626A, 627 A, 628, 630, 631, 632, 633, and 634 are collectively referred to in FIG. 6A as an LTM execution procedure 699.

[0318] In some implementations, the MN 601B (e.g., the CU of the MN 601B) or S-SN 601 A (e.g., the CU of the S-SN 601A) may associate the first UE LTM security' configuration (i.e., a single security configuration) for the LTM candidate cell(s) 1-M of the UE 102 or the LTM candidate configuration(s) 1-M for the UE 102. In some implementations, the S-SN 601 A may indicate the LTM candidate configuration(s) 1-M associated with the first LTM security configuration (list) in the first RRC reconfiguration message and / or RRC reconfiguration messages 1-M in the LTM configuration delivery procedure 2-M. To indicate the association, the S-SN 601 A may include the first UE LTM security’ configuration and a first security configuration ID identifying the first UE LTM security’ configuration in the container IE 1 and include the first security configuration ID in the tuples (e.g., LTM-Candidate IES) 1- M. Based on the first security’ configuration ID, the UE 102 identifies that the LTM candidate cell(s) 1-M of the UE 102 or the LTM candidate configuration(s) 1-M share the same security configuration (i.e., the first UE LTM security configuration. In some implementations, the S- SN 601 A may include, in the first RRC reconfiguration message or the container IE 1, a serving security configuration ID for or associated with the serving cell of the S-SN 601A. In some implementations, the serving security configuration ID may indicate (e.g., identifies) that the first security key(s), the first security algorithm(s) and / or security parameters used to derive the first security key(s) are associated with the serving cell. The serving security configurationID (i.e., value) may be different from the first security configuration ID (i.e., have a different value). Because the first security configuration ID is different from the serving security configuration ID, the UE 102 determines a security configuration change for the LTM cell switch to the cell 1 from the serving cell and may apply the first UE LTM security configuration to communicate with the C-SN 606 via the cell 1 as described above.

[0319] The UE 102 in the communication at event 640 may receive a second LTM Cell Switch Command from the C-SN 606, commanding the UE 102 to perform an LTM cell switch to the cell 2. In such cases, the UE 102 may perform the LTM cell switch to the cell 2 in response to the second LTM Cell Switch Command as described above for the LTM cell switch to the cell 1. Because the UE 102 identifies the same security configuration (i.e.. the first security configuration) applies to the cell 1 and the cell 2 (or the LTM candidate configuration 1 and the LTM candidate configuration 2), the UE 102 may use or continue using the second security key(s) to communicate with the C-SN 606 on the cell 2. If the UE 102 uses the second security algorithm(s) to communicate with the C-SN 606 on the cell 1. the UE 102 uses or continues using the second security algorithm(s) to communicate with the C-SN 606 on the cell 2. If the UE 102 uses the first security algorithm(s) to communicate with the C-SN 606 on the cell 1, the UE 102 may use or continue using the first security algorithm(s) to communicate with the C-SN 606 on the cell 2. Similarly, the C-SN 606 may perform similar actions to communicate with the UE 102 as described above. “M” may be changed to “N” in the above description.

[0320] In some implementations, the S-SN 601 A may perform another inter-CU LTM preparation procedure for the UE 102 with another, second C-SN to obtain an LTM candidate configuration and a second UE LTM security configuration for an LTM candidate cell (e.g., a cell operated by the second C-SN) and transmit the LTM candidate configuration and the second UE LTM security configuration to the UE 102, similar to the procedures 698 A and 694A. The MN 601 B may transmit a second MN-to-SN LTM security configuration to the second C-SN 606 as described for the first MN-to-SN LTM security configuration. Examples and implementations described for the first UE LTM security configuration and the first MN- to-SN LTM security configuration may apply to the second UE LTM security configuration and the second MN-to-SN LTM security configuration, respectively. In some implementations, the second UE LTM security configuration and / or the second MN-to-SN LTM security configuration may be different from the first UE LTM security configuration and the first MN- to-SN LTM security configuration.

[0321] Tn some implementations, the S-SN 601 A may include the CSI resource configuration(s) 1-N in the container IE instead of the tuple, where N is an integer greater than zero.

[0322] FIG. 6B is a sequence diagram illustrating example operations of a communications process 600B for a second example inter-CU cell switch where a first base station operates as an MN. a second base station operates as a C-SN, and a third base station operates as an S-SN. Communications process 600B is generally similar to the communications process 600A, except that the communications process 600B includes events 604B, 609B and 611 instead of events 603 and 609A. In the communications process 600B, the MN 601B initiates the inter- SN LTM preparation procedure 698B, while in the communications process 600 A, the S-SN 601 A initiates an inter-SN LTM preparation procedure 698A.

[0323] At event 602, the UE 102 in DC may communicate with the MN 601B and with S- SN 601 A as described above with respect to FIG. 6A. In some aspects, while communicating with the UE 102 in DC with the MN 601B and S-SN 601A, the S-SN 601A may perform an intra-CU LTM configuration procedure 696 or intra-CU LTM procedure 680 with the UE 102, as described above with respect to FIG. 6A.

[0324] At event 604B, while communicating in DC with the MN 601B and S-SN 601A, the UE 102 may transmit at least one measurement report to the MN 601B, e.g. via the SRBL similar to the events 304 and / or 306 of FIG. 3, the events 404 and / or 406 of FIG. 4, and the event 504 of FIG. 5. If the MN 601B is a distributed base station, the MN 601B may include a CU and a DU. The CU of the MN 60 IB may receive the measurement report(s) from the UE 102 via the DU of the MN 601B. The MN 601B (e.g., the CU of the MN 601B) may generate a measurement configuration to configure the UE 102 to transmit the measurement report(s) and may transmit the measurement configuration to the UE 102 (e.g., via the DU of the MN 601B).

[0325] After (e.g., in response to) receiving one or more of the measurement report(s) from the UE 102, the MN 60 IB (e.g., the CU of the MN 60 IB) may determine to prepare a first cell (e.g., the cell 124B of FIG. 1A and FIG. IB) as an LTM candidate for the UE 102.

[0326] At event 605, in response to the determination, the MN 601B may generate an SN Request message (a first SN Request message) including a first cell ID (e.g.. cell ID 1) of the first cell (e.g., cell 1) and may transmit the SN Request message to the C-SN 606.

[0327] Tn response to the SN Request message, the CU 172 may perform the LTM preparation procedure 690 with the DU 174 and, at event 607, may transmit the SN Request Acknowledge message to the MN 60 IB, as described above with respect to FIG. 6A.

[0328] At event 609B, after (e.g., in response to) receiving the SN Request Acknowledge message, the MN 601B may transmit an SN Modification Request message to the S-SN 601A, including a first LTM candidate configuration (LTM candidate configuration 1). an LTM reference configuration, and / or the first cell ID, similar to the event 609A. If the SN Request Acknowledge message includes LTM related configurations such as the RACH configuration, the TCI state configuration(s), the CSI resource configuration, the LTM SSB configuration, and / or the PCI of the first cell for configuring the first cell as an LTM candidate cell, the MN 601 B may include the LTM related configurations in the SN Modification Request message.

[0329] At event 611, in response to the SN Modification Request message, the S-SN 601 A may transmit an SN Modification Request Acknowledge message to the MN 601 B and may perform the LTM configuration delivery procedure 694A with the UE 102 to transmit the first LTM candidate configuration and / or the LTM reference configuration to the UE 102.

[0330] The events 605, 607, 609B, and 611 along with LTM preparation procedure 690 are collectively referred to in FIG. 6B as an MN-initiated inter-SN LTM preparation procedure 698B.

[0331] As described above with respect to FIG. 6A, the SN Request Acknowledge message of event 607 may include the PDCCH order information. If the SN Request Acknowledge message includes the PDCCH order information, the MN 601B may include the PDCCH order information in the SN Modification Request message. If the SN Modification Request message includes the PDCCH order information, the S-SN 601 A may transmit 650A a PDCCH order to the UE 102, based on the PDCCH order information, as described above with respect to FIG. 6A. If the SN Modification Request message includes the TCI state configuration(s), the S-SN 601A may include a first TCI state ID in the LTM Cell Switch Command as described above with respect to FIG. 6A.

[0332] In some implementations, the MN 601B (e.g., the CU of the MN 601B) may perform one or more LTM preparation procedures to prepare additional cell(s) (i.e., cell(s) 2-N) as LTM candidate cell(s) for the UE 102 with the CU 172 or other C-SN(s), and each of the LTM preparation procedures is similar to the procedure 698B. The MN 601 B may perform the LTMpreparation procedure(s) before or after transmitting the LTM Cell Switch Command or during, before or after the procedure 698B.

[0333] In other implementations, the MN 60 IB may perform the procedure 698B with the CU 172 to prepare one or more of the cell 1 and cell(s) 2-N as LTM candidate cell(s) for the UE 102, where N is an integer greater than 1. The cell(s) 2-N are identified by cell ID(s) 2-N, respectively and operated by the DU 174 and / or other DU(s) of the C-SN 606. In such implementations, the MN 60 IB may include the cell ID(s) 2-N in the SN Request message 605, as described for the cell ID 1 above.

[0334] Events 624A, 650A, 652, 656, 657, 658, 654A, 636A, 638, 639, 641, 642, and 640 along with procedures 694A and 699 shown in FIG. 6B are as described above with respect to FIG. 6A.

[0335] FIG. 6C is a sequence diagram illustrating example operations of a communications process 600C for a third example inter-CU cell switch where a first base station operates as an MN, a second base station operates as a C-SN, and a third base station operates as an S-SN. The communications process 600C is generally similar to the communications processes 600A and 600B, except that the communications process 600C may include events and procedures 694C, 636C, and 645 instead of events and procedures 694A, 636A, and 638.

[0336] In the LTM configuration deliver}' procedure 694C of communications process 600C, the MN 601B may transmit, to the UE 102, the second serving DU configuration (including the CSI report configuration), the LTM ID, the first LTM candidate configuration, the LTM reference configuration, the CSI resource configuration, the LTM SSB configuration, the RACH configuration, the TCI state configuration(s), and / or the PCI of the first cell for configuring the first cell as an LTM candidate cell in one or more RRC reconfiguration messages, similar to the procedure 394 of FIG. 3, 494 of FIG. 4, or 594 of FIG. 5. In some implementations, the MN 60 IB may generate the RRC reconfiguration message(s) in the procedure 694C, while the S-SN 601A generates the RRC reconfiguration message(s) in the procedure 694A. In some implementations, the MN 601B may assign the LTM ID in the communications process 600C, while the S-SN 601 A may assign the LTM ID in the communications processes 600 A and 600B.

[0337] At event 636C, when the UE 102 performs the LTM execution procedure 699. the UE 102 may transmit an RRC reconfiguration message to the MN 601 B, similar to the event 636A described above with respect to FIG. 6A. In some implementations, the UE 102 mayinclude the LTM ID in the RRC reconfiguration complete message to indicate that the UE 102 applies the first LTM candidate configuration.

[0338] At event 645, after (e.g., in response to) receiving the RRC reconfiguration message, the MN 601B may transmit the SN message to the S-SN 601 A as described above with respect to FIG. 6A. In some implementations, the MN 60 IB may include a first cell ID of the first cell in the SN message. The MN 60 IB may determine the first cell ID based on the LTM ID received in the RRC reconfiguration complete message.

[0339] In some implementations, the MN 601B (e.g., the CU of the MN 601B) may generate a first UE LTM security configuration based on the first MN-to-SN LTM security configuration and may include the first UE LTM security configuration in the first RRC reconfiguration message of the procedure 694C. In some implementations, the MN 601B may include the first UE LTM security configuration in a container IE (e.g.. LTM-Config IE) that may include the tuple 1 and may include the container IE in the first RRC reconfiguration message. In other implementations, the MN 601B may include the first UE LTM security configuration in the tuple 1. The descriptions above for the S-SN 601 A of FIG. 6A can apply to the MN 601B.

[0340] FIG. 6D is a sequence diagram illustrating example operations of a communications process 600D for a fourth example inter-CU cell switch where a first base station operates as an MN. a second base station operates as a C-SN. and a third base station operates as an S-SN. The communications process 600D is generally similar to the communications processes 600A, 600B and 600C, except that the communications process 600D includes events 624D, 650D, 654D, 626D, 627D instead of events 624A, 650A, 654A, 626A, and 627 A. The events 624D, 650D, 654D. and 626D are similar to the events 624A, 650A, 654A, and 626A respectively, except that the MN 601B is involved in the events 624D, 650D, 654D, and 626D, while the S- SN 601 A is involved in the events 624 A, 650A, 654A, and 626A. The event 627D is different from the 627A in that in the event 627D, the MN 601B may transmit the CU-CU Cell Switch Notification message which may include the first TCI state ID and / or the second TCI state ID to the S-SN 601 A.

[0341] In some implementations, the MN 601B may generate the CSI report configuration(s) based on a CSI resource configuration, as described for S-SN 601A. The CSI resource configuration may configure RS(s) transmitted on the first cell. The MN 601B may transmit the CSI report configuration(s) to the UE 102 in the procedure 694C. In some implementations, the MN 601B is preconfigured with CSI resource configuration. In other implementations, theMN 601 B may receive the CSI resource configuration from an OAM node. Tn yet other implementations, the MN 60 IB may receive the CSI resource configuration from the CU 172 or the S-SN 601A.

[0342] Next, several example methods, which can be implemented in a RAN (e.g., the S-SN 601A, MN 601B, C-SN 606 or CU 172 in FIGs. 6A-6D), are discussed next with reference to FIGs. 7A, 7B, 8. 9A. 9B, 10A. 10B. 11. and 12. Descriptions provided for FIGs. 3-5 and 6A- 6D can apply to FIGs. 7A, 7B, 8, 9A, 9B, 10A, 10B, 11, and 12. Operations of blocks that are similarly labeled to events (e.g., 302, 402, 502, 602, etc.) are similar to one another and individual descriptions are therefore omitted for a block that has been previously described.

[0343] FIG. 7A is a flow chart diagram illustrating first example operations of a method 700A for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by an MN. As examples, the MN may be an implementation of the base station 104 of FIG. 1A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or the MN 601B of FIGs. 6A- 6D.

[0344] At block 702, and as described above with respect to FIGs. 6A-6D event 602, the MN communicates with a UE via a serving cell.

[0345] At block 780, and as described above with respect to FIGs. 6A-6D procedure 680, the MN may transmit a first LTM candidate configuration, a first LTM configuration ID identifying the first LTM candidate configuration, first (LTM) CSI resource configuration(s), and / or an LTM CSI report configuration to the UE. In some aspects, the first LTM candidate configuration may configure a first cell as an LTM candidate cell. In some aspects, the first LTM CSI resource configuration(s) may configure first LTM CSI resource(s). In some aspects, the first LTM report configuration may configure a CSI report of the first LTM CSI resource(s).

[0346] At block 705A, and as described above with respect to FIGs. 6A-6D event 605, the MN may transmit a first interface message to a first C-SN, requesting to prepare a second cell as an LTM candidate cell for the UE and including the first LTM configuration ID and / or second LTM CSI resource configuration(s). The second LTM CSI resource configuration(s) may configure second LTM CSI resource(s). The first C-SN may be an implementation of the base station 106 of FIG. 1A. the base stations 106A or 106B of FIG IB. the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or C-SN 606 of FIGs 6A-6D. To prepare a subsequent inter-SN LTM cell switch to the first cell, the MN may include thefirst configuration ID and / or the second LTM CSI resource configuration(s) in the first interface message.

[0347] At block 707A, and as described above with respect to FIGs. 6A-6D event 607, the MN may receive a second interface message from the first C-SN, including a second LTM candidate configuration for the UE. The second LTM candidate configuration may configure the second cell as an LTM candidate cell and may include a second LTM CSI report configuration configuring a CSI report of the second LTM CSI resource(s).

[0348] At block 718A, the MN may transmit a first RRC message to the UE. The first RRC message may include the second LTM candidate configuration. In some implementations, the MN may include, in the first RRC message, a second LTM configuration ID identifying the second LTM candidate configuration.

[0349] In some implementations, the MN may perform an inter-SN LTM configuration procedure with an additional C-SN to obtain the first LTM candidate configuration and / or the first LTM CSI report configuration (e.g., similar to procedures 698A or 698B described above). In some implementations, the first LTM CSI report configuration may be included in the first LTM candidate configuration. In other implementations, the MN may receive the first LTM candidate configuration and / or the first LTM CSI report configuration from an S-SN. The S- SN may configure the first LTM candidate configuration and / or the first LTM CSI report configuration (i.e., intra-SN LTM configuration). In some aspects, the S-SN may be an implementation of the base station 104 of FIG. 1 A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, the eNB. ng-eNB 230 or the gNB 232 of FIG. 2A, or the S- SN 601 A of FIGs. 6A-6D.

[0350] In some implementations, the first interface message and the second interface message may be an SN Request message or an SN Request Acknow ledge message, respectively. In other implementations, the first interface message and the second interface message are new next generation application protocol (NGAP) messages different from the SN Request message or the SN Request Acknowledge message. For example, the first interface message and the second interface message are LTM-specific NGAP messages. In some implementations, the first interface message may include a first cell ID of the first cell and may indicate the first configuration ID and / or the second CSI resource configuration(s) are associated with the first cell ID. In other implementations, the first interface message may include an ID of the secondC-SN. In some implementations, the first interface message may include a second cell ID of the second cell to indicate a request to prepare the second cell as an LTM candidate cell.

[0351] In some implementations, the second LTM CSI resource configuration(s) may be the same as the first LTM CSI resource configuration(s). In such cases, the “second LTM CSI resource configuration(s)’' can be replaced by the “first LTM CSI resource configuration(s)”. In other implementations, the second LTM CSI resource configuration(s) may be different from the first LTM CSI resource configuration(s). In yet other implementations, the first LTM CSI resource configuration(s) may include the second LTM CSI resource configuration(s). In still other implementations, the second LTM CSI resource configuration(s) may include the first LTM CSI resource configuration(s). In some implementations, the MN may include at least a portion of the second LTM CSI resource configuration(s) in the first RRC message. In some other implementations, the portion(s) are not included in the first LTM CSI resource configuration(s).

[0352] In some implementations, the S-SN may transmit an LTM cell switch command to the UE via the serving cell, commanding the UE to perform an LTM cell switch to second cell (e.g., as described above with respect to event 626A). In some implementations, the S-SN may indicate (e.g., includes) the second LTM configuration ID in the LTM cell switch command and the UE identifies the second LTM candidate configuration based on the second LTM configuration ID. In response, the UE may access the second cell and may communicate with the first C-SN in accordance with the second LTM candidate configuration (e.g.. as described above with respect to events 632, 636A, and / or 640). After the UE successfully completes the LTM cell switch to the second cell, the S-SN is no longer an S-SN for the UE and the first C- SN may become an S-SN for the UE. The UE may perform measurements on the second LTM CSI resource(s), may obtain LI measurement report(s) (e.g., CSI report(s)) based on the measurements, and may transmit the L 1 measurement report(s) to the first C-SN via the second cell in accordance with the second LTM CSI report configuration. Based on the LI measurement report(s), the first C-SN may determine to trigger an LTM cell switch to the first cell for the UE. In cases where the first C-SN determines to trigger an LTM cell switch to the first cell for the UE, the first C-SN may transmit an LTM cell switch command to the UE (e.g., via the second cell), commanding the UE to perform an LTM cell switch command to the first cell. In some implementations, the first C-SN may indicate (e.g., include) the first LTM configuration ID in the LTM cell switch command and the UE may identify the first LTM candidate configuration based on the first LTM configuration ID. In response to the LTM cellswitch command, the UE may access the first cell and may communicate on the first cell in accordance with the first LTM candidate configuration. After the UE successfully completes the LTM cell switch to the first cell, the additional C-SN becomes an S-SN for the UE and the first C-SN is no longer an S-SN for the UE.

[0353] In some implementations, the MN may transmit a first additional interface message to a second C-SN, requesting the second C-SN to prepare a third cell as an LTM candidate cell for the UE and including third LTM CSI resource configuration(s), similar to block 705 A described above. In response, the MN may receive, from the second C-SN, a second additional interface message including a third LTM candidate configuration configuring the third cell as an LTM candidate cell for the UE, similar to block 707A. The third LTM candidate configuration may include a third LTM CSI report configuration configuring CSI report of the third LTM CSI resource(s). In some implementations, the MN may include the third LTM candidate configuration in the first RRC message. In other implementations, the MN maytransmit an additional RRC message including the third LTM candidate configuration to the UE. The MN may include, in the first or additional RRC message, a third LTM configuration ID identifying the third LTM candidate configuration.

[0354] In some implementations, the third LTM CSI resource configuration(s) may be the same as the second LTM CSI resource configuration(s). In such cases, the “third LTM CSI resource configuration(s)” can be replaced by the “second LTM CSI resource configuration(s).'’ In other implementations, the third LTM CSI resource configuration(s) may be different from the second LTM CSI resource configuration(s). In yet other implementations, the third LTM CSI resource configuration(s) may include the second LTM CSI resource configuration(s). In still other implementations, the second LTM CSI resource configuration(s) may include the third LTM CSI resource configuration(s). In some implementations, the MN may include at least a portion of the third LTM CSI resource configuration(s) in the first RRC message and / or the additional RRC message. In some implementations, the portion(s) are not included in the first and / or second LTM CSI resource configuration(s). In some implementations, the first RRC message and the additional RRC message may be RRC reconfiguration messages.

[0355] In some implementations, the first, second and / or third LTM CSI resource configuration(s) may configure LTM CSI resource(s) (e.g.. SSB(s) and / or CSI-RS(s)) for the first cell. In some implementations, the LTM CSI resources are configured specifically for LTM. In other implementations, the LTM CSI resources may be configured for LTM and other3GPP functions / features. In some implementations, the MN may receive the first, second and / or third LTM CSI resource configuration(s) from the S-SN.

[0356] In some implementations, the MN may obtain fourth LTM CSI resource configuration(s) of the second C-SN. The MN may receive the fourth LTM CSI resource configuration(s) from the second C-SN, e.g., in the second additional interface message. In some implementations, the fourth LTM CSI resource configuration(s) may configure fourth LTM CSI resource(s) (e g., SSB(s)) for the third cell. In some implementations, the fourth LTM CSI resource(s) may be configured specifically for LTM. In other implementations, the fourth LTM CSI resource(s) may be configured for LTM and other 3GPP functions / features. In some implementations, the MN may include the third LTM configuration ID and / or the fourth LTM CSI resource configuration(s) in the first interface message. In such cases, the first C-SN may generate a fourth LTM CSI report configuration configuring CSI report of the fourth LTM CSI resource(s) and includes the fourth LTM CSI report configuration in the second LTM candidate configuration. After the UE successfully accesses the second cell, the first C-SN becomes an S-SN for the UE and the S-SN is no longer an S-SN for the UE. The UE may then perform measurements on the fourth LTM CSI resource(s), may obtain LI measurement report(s) (e.g., CSI report(s)) based on the measurements, and may transmit the LI measurement report(s) to the first C-SN in accordance with the fourth LTM CSI report configuration. Based on the LI measurement report(s), the first C-SN may determine to trigger an LTM cell switch to the third cell for the UE. In cases where the first C-SN determines to trigger an LTM cell switch to the third cell for the UE, the first C-SN may transmit an LTM cell switch command to the UE (e.g., via the second cell), commanding the UE to perform an LTM cell switch command to the third cell. In some implementations, the first C-SN may indicate (e.g., includes) the third LTM configuration ID in the LTM cell switch command and the UE identifies the third LTM candidate configuration based on the third LTM configuration ID. In response to the LTM cell switch command, the UE may access the third cell and may communicate with the second C- SN in accordance with the third LTM candidate configuration. After the UE successfully completes the LTM cell switch to the third cell, the second C-SN becomes an S-SN for the UE and the first C-SN is no longer an S-SN for the UE.

[0357] In other implementations, the MN determines not to include or does not include the third LTM configuration ID and / or the fourth LTM CSI resource configuration(s) in the first interface message.

[0358] FIG. 7B is a flow chart diagram illustrating second example operations of a method 700B for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by an MN. The example method 700B is similar to the method 700 A, except that the method 700B includes blocks 705B-1. 707B-1, 705B-2, 707B-2, and 718B instead of blocks 705A and 707A. As examples, the MN may be an implementation of the base station 104 of FIG. 1 A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or MN 601B of FIGs. 6A-6D.

[0359] At block 705B-1, and as described above with respect to FIGs. 6A-6D event 605, the MN may transmit a first interface message to a first C-SN, requesting to prepare a second cell as an LTM candidate cell for the UE.

[0360] At block 707B-1, and as described above with respect to FIGs. 6A-6D event 607, the MN receives a second interface message from the C-SN. including a second LTM candidate configuration for the UE, where the second LTM candidate configuration configures the second cell as an LTM candidate cell.

[0361] At block 705B-2, the MN may transmit a third interface message for LTM and the UE to the first C-SN, including the first LTM configuration ID and / or second LTM CSI resource configuration(s). The second LTM CSI resource configuration(s) may configure second LTM CSI resource(s).

[0362] At block 707B-2, and as described above with respect to FIGs. 6A-6D event 607. the MN may receive a fourth interface message from the first C-SN, including an additional LTM candidate configuration for the UE. The additional LTM candidate configuration may include a second LTM CSI report configuration configuring CSI report of the second LTM CSI resource(s) and may update the second LTM candidate configuration.

[0363] At block 718B, the MN may transmit a second RRC message to the UE, including the additional LTM candidate configuration.

[0364] In some implementations, the MN may include the second LTM configuration ID in the second RRC message to indicate that the additional LTM candidate configuration updates (e.g., modifies or replaces) the second LTM candidate configuration. When the UE receives the second LTM configuration ID and the additional LTM candidate configuration (e.g., as a tuple), the UE identifies the second LTM candidate configuration based on the second LTM configuration ID and updates the second LTM candidate configuration with the additional LTM candidate configuration.

[0365] In FIG. 7 A, the MN prepares the second cell for LTM and prepares a subsequent inter-CU LTM to the first cell of the MN from the first C-SN with blocks 705A and 707A. In FIG. 7B, the MN prepares the second cell for LTM with the first C-SN with blocks 705B-1 and 707B-1 and prepares a subsequent inter-CU LTM to the first cell of the MN from the first C- SN with blocks 705B-2 and 707B-2. In some implementations, the MN can perform actions similar to blocks 705B-1, 707B-1, 705B-2, and 707B-2 to prepare a third cell for LTM and may prepare a subsequent inter-CU LTM to the first cell of the MN from the second C-SN.

[0366] Examples and implementations described above with respect to FIG. 7 A may apply to FIG. 7B.

[0367] In some implementations, the third interface message and the fourth interface message may be an SN Request message or an SN Request Acknowledge message, respectively. In other implementations, the third interface message and the fourth interface message are new NGAP messages different from the SN Request message or the SN Request Acknowledge message. For example, the third interface message and the fourth interface message may be LTM-specific NGAP messages. In some implementations, the third interface message may include a first cell ID of the first cell and may indicate the first configuration ID and / or the second CSI resource configuration(s) are associated with the first cell ID. In some implementations, the third interface message does not include a second cell ID of the second cell to indicate a request to prepare the second cell as an LTM candidate cell.

[0368] In some implementations, the first RRC message and the second RRC message may be combined as a single RRC message (e.g., RRC reconfiguration message). In other implementations, the first RRC message and the second RRC message may be separate RRC messages (e g., RRC reconfiguration messages).

[0369] FIG. 8 is a flow chart diagram illustrating third example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by an MN. As examples, the MN may be an implementation of the base station 104 of FIG. 1A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or the MN 60 IB of FIGs. 6A-6D. In some aspects, the example method 800 is similar to the method 700A of FIG. 7A.

[0370] The method 800 begins at blocks 702 and 780, which have been described above with respect to FIG. 7 A.

[0371] At block 805, and as described above with respect to FIGs. 6A-6D event 605, the MN may transmit an SN Request message to a target SN (T-SN), requesting to prepare an SN change to a second cell for the UE and including the first LTM configuration ID and / or second LTM CSI resource configuration(s) for the first cell. The second LTM CSI resource configuration(s) may configure second LTM CSI resource(s) for the first cell. The T-SN may be an implementation of the base station 106 of FIG. 1A, the base stations 106A and 106B of FIG. IB, the base station 164 of FIG. 1C, or the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A.

[0372] At block 807, and as described above with respect to FIGs. 6A-6D event 607, the MN may receive an SN Request Acknowledge message from the T-SN. The SN Request Acknowledge message may include an RRC reconfiguration message for the SN change. The RRC reconfiguration message may configure the second cell for the SN change and may include a second LTM CSI report configuration configuring a CSI report of the second LTM CSI resource(s).

[0373] At block 818, the MN may transmit the RRC reconfiguration message to the UE.

[0374] In some implementations, the SN Request message may include a first cell ID of the first cell. In some implementations, the SN Request message may include a second cell ID of the second cell. In some implementations, the T-SN may be a C-SN (e.g.. the first C-SN or the second C-SN described above with respect to FIG. 6A). In other implementations, the T-SN is not a C-SN.

[0375] The UE may perform the SN change to the second cell upon receiving the RRC reconfiguration message. After the UE successfully performs the SN change to the second cell, the T-SN becomes an S-SN for the UE and the S-SN is no longer an S-SN for the UE. After successfully performing an SN change to the second cell, the UE may perform measurements on the second LTM CSI resource(s). may obtain LI measurement report(s) (e.g., CSI report(s)) based on the measurements, and may transmit the LI measurement report(s) to the T-SN via the second cell in accordance with the second LTM CSI report configuration. Based on the LI measurement report(s), the T-SN may determine to trigger an LTM cell switch to the first cell for the UE. In cases where the T-SN determines to trigger an LTM cell switch to the first cell for the UE, the T-SN may transmit an LTM cell switch command to the UE (e.g., via the second cell), commanding the UE to perform an LTM cell switch to the first cell. In some implementations, the T-SN may indicate (e.g., includes) the first LTM configuration ID in the LTM cell switch command and the UE identifies the first LTM candidate configuration basedon the first LTM configuration ID. In response to the LTM cell switch command, the UE may access the first cell and may communicate on the first cell with the first S-SN or the additional C-SN in accordance with the first LTM candidate configuration. After the UE successfully completes the LTM cell switch to the first cell, the S-SN or the additional C-SN becomes an S-SN for the UE and the T-SN is no longer an S-SN for the UE.

[0376] In cases where the MN obtains the fourth LTM CSI resource configuration(s) from the third BS as described above with respect to FIG. 7A, the MN may include the fourth LTM CSI resource configuration(s) in the SN Request message. Alternatively or additionally, the MN may not include the fourth LTM CSI resource configuration(s) in the SN Request message.

[0377] The examples and implementations described above with respect to FIG. 7A can apply to FIG. 8.

[0378] FIG. 9A is a flow chart diagram illustrating first example operations of a method 900A for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a candidate secondary node (C-SN). The C-SN may be an implementation of the base station 106 of FIG. 1 A, the base stations 106A or 106B of FIG. IB, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or the C- SN 606 of FIGs. 6A-6D.

[0379] At block 905A, and as described above with respect to FIGs. 6A-6D event 605, the first C-SN may receive a first interface message from a MN, requesting to prepare a second cell as an LTM candidate cell for a UE. The first interface message may include a first LTM configuration ID and / or second LTM CSI resource configuration(s) for the first cell, where the second LTM CSI resource configuration(s) configure second LTM CSI resource(s).

[0380] At block 907A, and as described above with respect to FIGs. 6A-6D event 607, the first C-SN may transmit a second interface message to the MN, including a second LTM candidate configuration for the UE. The second interface message may include a second LTM candidate configuration to configure the second cell as an LTM candidate cell and may include a second LTM CSI report configuration configuring a CSI report of the second LTM CSI resource(s). In some implementations, the second LTM candidate configuration does not include the second LTM CSI report configuration.

[0381] Examples and implementations described above with respect to FIG. 7A can apply to FIG. 9A.

[0382] FIG. 9B is a flow chart diagram illustrating second example operations of a method for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a C-SN. The C-SN may be an implementation of the base station 106 of FIG. 1A, the base stations 106A or 106B of FIG. IB, the base station 164 of FIG. 1C. the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or C-SN 606 of FIGs. 6A-6D.

[0383] At block 905B- 1 , and as described above with respect to FIGs. 6A-6D event 605. the first C-SN may receive a first interface message from an MN. The MN may be an implementation of the base station 104 of FIG. 1 A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or the MN 601B of FIGs. 6A-6D. The first interface message may be a request to prepare a second cell as an LTM candidate cell for a UE.

[0384] At block 907B-1, and as described above with respect to FIGs. 6A-6D event 607. the first C-SN may transmit a second interface message to the MN, including a second LTM candidate configuration for the UE. The second LTM candidate configuration may configure the second cell as an LTM candidate cell.

[0385] At block 905B-2, and as described above with respect to FIGs. 6A-6D event 605, the first C-SN may receive, from the MN, a third interface message for configuring LTM for the UE. The third interface message may include a first LTM configuration ID and / or one or more second LTM CSI resource configurations for the first cell. The one or more second LTM CSI resource configurations may configure one or more second LTM CSI resources.

[0386] At block 907B-2, and as described above with respect to FIGs. 6A-6D event 607, the first C-SN may transmit a fourth interface message to the MN, including an additional LTM candidate configuration for the UE. The additional LTM candidate configuration may include a second LTM CSI report configuration configuring a CSI report of the second LTM CSI resource(s) and updates the second LTM candidate configuration.

[0387] Examples and implementations described above with respect to FIGs. 7A and 7B may apply to FIG. 9B.

[0388] FIG. 10A is a flow chart diagram illustrating first example operations of a method 1000A for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a central unit (CU) of a C-SN. The C-SN may be an implementation of the base station 106 of FIG. 1 A, the base stations 106A or 106B of FIG. IB, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or the C-SN 606 of FIGs. 6A-6D. Example method 1000A is similar to the method 900A described above.

[0389] The method 1000 A begins at block 905 A (described above with respect to FIG. 9 A). The flow proceeds to block 1008A from block 905 A.

[0390] At block 1008 A, the CU may transmit a CU-to-DU message to a DU requesting the DU to prepare the second cell as an LTM candidate cell for the UE. The CU-to-DU message may include one or more second LTM CSI resource configurations.

[0391] At block 1010A, the CU may receive, from the DU, a DU-to-CU message including a first LTM DU configuration for the UE, where the first LTM DU configuration may include a second LTM CSI report configuration configuring a CSI report of the second LTM CSI resource(s).

[0392] At block 1007 A, and as described above with respect to FIGs. 6A-6D event 607, the CU may transmit a second interface message to the MN, including a second LTM candidate configuration for the UE. The second LTM candidate configuration may configure the second cell as an LTM candidate cell and may include the first LTM DU configuration. Block 1007A is similar to block 907A described above with respect to FIG. 9A.

[0393] Examples and implementations described above with respect to FIG. 7A can apply to FIG. 10A.

[0394] In some implementations, the CU-to-DU message and the DU-to-CU message may be a UE Context Setup Request message and a UE Context Setup Response message, respectively.

[0395] FIG. 10B is a flow chart diagram illustrating second example operations of a method 1000B for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a central unit (CU) of a C-SN. The C-SN may be an implementation of the base station 106 of FIG. 1 A, the base stations 106A or 106B of FIG. 1 B, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or C-SN 606 of FIGs. 6A-6D. Example method 1000B is similar to the methods 1000A and 900B described above, except that the method 1000B includes blocks 1008B-1, 1010B-1, 1008B-2, 1010B-2 and 1007B instead of blocks 1008 A and 1010A.

[0396] The method 1000B begins at block 905B-1 (described above with respect to FIG. 9B). The flow proceeds to block 1008B-1 from block 905B-1.

[0397] At block 1008B-1 , the CU may transmit a first CU-to-DU message to a DU, requesting the DU to prepare the second cell as an LTM candidate cell for the UE.

[0398] At block 1010B-1, the CU may receive, from the DU, a first DU-to-CU message including a first LTM DU configuration for the UE. In some implementations, the first LTM DU configuration does not include an LTM CSI report configuration configuring CSI report of the second LTM CSI resource(s).

[0399] At block 1008B-2, the CU may transmit a second CU-to-DU message for LTM to the DU, including the second LTM CSI resource configuration(s).

[0400] At block 1010B-2. the CU may receive, from the DU, a second DU-to-CU message including a second LTM DU configuration, where the second LTM DU configuration includes a second LTM CSI report configuration configuring a CSI report of the second LTM CSI resource(s) and updates the first LTM DU configuration.

[0401] At block 1007B, and as described above with respect to FIGs. 6A-6D event 607, the CU may transmit a fourth interface message to the MN, including an additional LTM candidate configuration for the UE. The additional LTM candidate configuration may update the second LTM candidate configuration.

[0402] Blocks 1007A and 1007B are similar to blocks 907A and 907B-2, respectively, which have been described above with respect to FIGs. 9A and 9B respectively. In some implementations, the first CU-to-DU message and the first DU-to-CU message may be a UE Context Setup Request message and a UE Context Setup Response message, respectively. In some implementations, the second CU-to-DU message and the second DU-to-CU message may be a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0403] Examples and implementations described above with respect to FIGs. 7A and 7B may apply to FIG. 10B.

[0404] FIG. 11 is a flow chart diagram illustrating example operations of a method 1100 for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a T-SN. The T-SN may be an implementation of the base station 106 of FIG. 1A, the base stations 106A or 106B of FIG. IB, the base station 164 of FIG. 1C, or the eNB, ng-eNB 230 or the gNB 232 of FIG. 2 A.

[0405] At block 1 105, and similar to the process described above with respect to FIGs. 6A- 6D event 605, where the T-SN may receive an SN Request message from an MN, requesting the T-SN to prepare an SN for a second cell for a UE. The MN may be an implementation of the base station 104 of FIG. 1A. the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or the MN 60 IB of FIGs. 6A-6D. The SN request may include a first LTM configuration ID and / or second LTM CSI resource configuration(s) for the first cell, where the second LTM CSI resource configuration(s) may configure second LTM CSI resource(s).

[0406] At block 1107, and similar to the process described above with respect to FIGs. 6A- 6D event 607. the T-SN may transmit an SN Request Acknowledge message to the MN, including an RRC reconfiguration message for the UE. The RRC reconfiguration message may configure an SN change to the second cell and may include a second LTM CSI report configuration configuring a CSI report of the second LTM CSI resource(s).

[0407] At block 1172, the T-SN may perform a random access procedure for the SN change with the UE via the second cell.

[0408] At block 1174, the T-SN may receive an RRC reconfiguration complete message from the UE via the second cell or the MN, in response to the RRC reconfiguration message.

[0409] Examples and implementations described above with respect to FIGs. 7A and 8 can apply to FIG. 11.

[0410] FIG. 12 is a flow chart diagram illustrating example operations of a method 1200 for configuring LTM CSI resources and LTM CSI reports for an inter-CU cell switch that may be implemented by a CU of a T-SN. The T-SN may be an implementation of the base station 106 of FIG. 1A, the base stations 106A or 106B of FIG. IB, the base station 164 of FIG. 1C, or the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A.

[0411] The method 1200 begins at block 1105, which has been described above with respect to FIG. 11.

[0412] At block 1208, the CU may transmit a CU-to-DU message including the second LTM CSI resource configuration(s) to a DU.

[0413] At block 1210. the CU may receive, from the DU, a DU-to-CU message including a DU configuration. The DU configuration may include a second LTM CSI report configuration configuring a CSI report of the second LTM CSI resource(s).I l l

[0414] At block 1207, and similar to the process described above with respect to FTGs. 6A- 6D event 607, the CU may transmit an SN Request Acknowledge message to the MN. The MN may be an implementation of the base station 104 of FIG. 1A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or the MN 601B of FIGs. 6A-6D. The SN Request Acknowledge message may include an RRC reconfiguration message for the UE, where the RRC reconfiguration message may configure an SN change to the second cell and may include the DU configuration.

[0415] At block 1274, the CU may receive an RRC reconfiguration complete message from the UE via the DU or the MN, in response to the RRC reconfiguration message.

[0416] Examples and implementations described above with respect to FIGs. 7A, 8, and 10A can apply to FIG. 12. Examples and implementations for the serving DU configuration described above with respect to FIG. 3 can apply to the DU configuration.

[0417] FIG. 13 is a flow chart diagram illustrating first example operations of a method 1300 for wireless communication by a first network entity. As examples, the first network entity may be an implementation of the base station 104 of FIG. 1A, the base stations 104A or 104B of FIG. IB, the base station 164 of FIG. 1C, the eNB, ng-eNB 230 or the gNB 232 of FIG. 2A, or the MN 60 IB of FIGs. 6A-6D

[0418] At block 1380, and as described above with resp...

Claims

CLAIMSWhat is claimed is:

1. A method for wireless communication by a first network entity (104, 104 A, 60 IB), the method comprising: transmitting (680, 696, 780, 1380), to a user equipment (UE) (102) operating in dual connectivity with the first network entity and a second network entity (106, 106A, 601 A), a first lower layer-triggered mobility (LTM) channel state information (CSI) resource configuration for a first cell (124A) that configures one or more first LTM CSI resources associated with the first cell; and transmitting (605, 705 A, 705B-2. 805, 1305), to a third network entity. (106. 106A, 106B, 606) a second LTM CSI resource configuration for the first cell that configures one or more second LTM CSI resources associated with the first cell.

2. The method of claim 1. wherein the transmitting the second LTM CSI resource configuration includes at least one of: transmitting the second LTM CSI resource configuration in at least one of a secondary node (SN) Addition Request message, an SN Modification Request message, or a next generation application protocol (NGAP) message; or transmitting the second LTM CSI resource configuration in a request to prepare a second cell as an LTM candidate cell.

3. The method of claim 1 or 2, wherein the transmitting the second LTM CSI resource configuration includes transmitting a first cell identity (ID) of the first cell, and wherein the second LTM CSI resource configuration is associated with the first cell ID.

4. The method of any one of claims 1 to 3, further comprising: transmitting (680, 696, 780), to the UE, a first LTM CSI report configuration configuring at least one first CSI report associated with the one or more first LTM CSI resources; and receiving (607, 707A, 707B-2, 807), from the third network entity, a second LTM CSI report configuration configuring at least one second CSI report associated with the one or more second LTM CSI resources.

5. The method of claim 4, wherein the receiving the second LTM CSI report configuration includes at least one of: receiving the second LTM report configuration in an updated LTM candidate configuration; or receiving the second LTM CSI report in at least one of an SN Addition Request Acknowledge or an SN Modification Request Acknowledge message.

6. The method of any one of claims 1 to 5, wherein: the first network entity comprises a master node (MN) (60 IB), the second network entity comprises a source secondary node (S-SN) (601A), and the third network entity comprises one of: a candidate secondary node (C-SN) (606); a base station (BS); or a target secondary node (T-SN).

7. A method for wireless communication by a first network entity (106, 106A. 106B, 606), the method comprising: receiving (605, 905 A, 905B-1, 1405-1), from a second network entity (104, 104A, 601B), a request to prepare a second cell as a lower layer-triggered mobility (LTM) candidate cell for a user equipment (UE) operating in a dual connectivity mode in a first cell; and receiving (605, 905 A, 905B-2, 1405-2), from the second network entity, an LTM channel state information (CSI) resource configuration that configures one or more LTM CSI resources associated with the first cell.

8. The method of claim 7, wherein the receiving the LTM CSI resource configuration includes at least one of: receiving the LTM CSI resource configuration in at least one of a secondary node (SN) Addition Request message, an SN Modification Request message, or a next generation application protocol (NGAP) message; receiving the LTM CSI resource configuration as part of the request to prepare the second cell as the LTM candidate cell; or receiving a first cell identity (ID) of the first cell.

9. The method of claim 7 or 8, wherein:the first network entity comprises a candidate secondary node (C-SN) (606), and the second network entity comprises a master node (MN) (601B).

10. The method of any one of claims 7 to 9. further comprising: transmitting (907B-2), to the second network entity, an updated LTM candidate configuration.

11. The method of any one of claims 7 to 10, wherein the receiving the LTM CSI resource configuration includes receiving the LTM CSI resource configuration by a central unit (CU) of the first network entity, the method further comprising: transmitting, by the CU to a distributed unit (DU), a first CU-to-DU message including one or more of: the request that the DU prepare the second cell as the LTM candidate cell for the UE; or the LTM CSI resource configuration.

12. The method of claim 11, wherein the first CU-to-DU message comprises a UE Context Setup Request message.

13. The method of claim 11, further comprising: transmitting, by the CU to the DU, a second CU-to-DU message including the LTM CSI resource configuration.

14. The method of any one of claims 11 to 13, further comprising: receiving, by the CU from the DU. a UE Context Modification Response message including an LTM DU configuration.

15. The method of any one of claims 11 to 14, further comprising: receiving (1010A, 1010B-2), by the CU from the DU, an LTM CSI report configuration associated with the one or more LTM CSI resources.

16. A method for wireless communication by a first network entity (106, 106 A, 106B, 606). the method comprising: receiving (1105, 1505), from a second network entity (104, 104A, 601B), a request to prepare a handover from a first cell to a second cell for a user equipment (UE) operating in a dual connectivity mode in the first cell, the request including a lower lay er- triggeredmobility (LTM) channel state information (CST) resource configuration that configures one or more LTM CSI resources associated with the first cell; and transmitting (1107, 1507), to the second network entity, an acknowledgement of the request to prepare the handover, the acknowledgement including an LTM CSI report configuration associated with the one or more LTM CSI resources.

17. The method of claim 16, wherein: the first network entity comprises asecondary node (SN) (104, 104A, 104B, 601A), and the second network entity comprises a master node (MN) (104, 104A, 104B, 601B).

18. The method of claim 16 or 17, wherein the receiving the request to prepare the handover includes receiving, by a central unit (CU) of the first network entity, the request to prepare the handover, the method further comprising at least one of: transmitting, to a distributed unit (DU), a CU-to-DU message including the LTM CSI resource configuration; or receiving, from the DU. an LTM CSI report configuration associated with the one or more LTM CSI resources.

19. An apparatus, comprising: a communication unit; and a processing system configured to control the communication unit to implement any one of the methods of any one of claims 1 to 18.

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