Managing reconfiguration of serving configuration and LTM configuration

Abstract

A serving radio access network (RAN) node communicates with a user equipment (UE) according to a serving configuration. The RAN node configuring the UE with for a lower-layer triggered mobility (LTM) switch to a target cell associated with a target RAN node and determines, after the configuring but prior to initiating the LTM switch, that a change in the serving configuration is required. In response to the determining, the RAN node performing one of: (i) initiating a procedure to add or modify radio resources configured for the UE, or (ii) transmitting, to the UE, a command to initiate the LTM switch.

Description

PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 MANAGING RECONFIGURATION OF SERVING CONFIGURATION AND LOWER LAYER TRIGGERED MOBILITY CONFIGURATIONCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of the filing date of provisional U.S. Patent Application No. 63 / 746,905 entitled “Managing Reconfiguration of Serving Configuration and Lower Layer Triggered Mobility Configuration,” filed on January 17, 2025. The entire content of the provisional application is hereby expressly incorporated herein by reference.FIELD OF THE DISCLOSURE

[0002] This disclosure relates to wireless communications and, more particularly, to managing reconfigurations of a serving configuration and a lower layer triggered mobility configuration for a user equipment.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] In telecommunication systems, the Packet Data Convergence Protocol (PDCP) sublayer of the radio protocol stack provides services such as transfer of user-plane data, ciphering, integrity protection, etc. For example, the PDCP layer defined for the Evolved Universal Terrestrial Radio Access (EUTRA) radio interface (see 3GPP specification TS 36.323) and New Radio (NR) (see 3GPP specification TS 38.323) provides sequencing of protocol data units (PDUs) in the uplink direction (from a user device, also known as a user equipment (UE), to a base station) as well as in the downlink direction (from the base station to the UE). Further, the PDCP sublayer provides signaling radio bearers (SRBs) and data radio bearers (DRBs) to the Radio Resource Control (RRC) sublayer. Generally speaking, the UE and a base station can use SRBs to exchange RRC messages as well as non-access stratum (NAS) messages, and can use DRBs to transport data on a user plane.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0005] UEs can use several types of SRBs and DRBs. When operating in dual connectivity (DC), the cells associated with the base station operating the master node (MN) define a master cell group (MCG), and the cells associated with the base station operating as the secondary node (SN) define the secondary cell group (SCG). So-called SRB1 resources carry RRC messages, which in some cases include NAS messages over the dedicated control channel (DCCH), and SRB2 resources support RRC messages that include logged measurement information or NAS messages, also over the DCCH but with lower priority than SRB1 resources. More generally, 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, and also can be referred to as MCG SRBs. SRB3 resources allow the UE and the SN to exchange RRC messages related to the SN, and can be referred to as SCG SRBs. Split SRBs allow the UE to exchange RRC messages directly with the MN via lower layer resources of the MN and the SN. Further, DRBs using the lower-layer resources of only the MN can be referred as MCG DRBs, DRBs using the lower-layer resources of only the SN can be referred as SCG DRBs, and DRBs using the lower-layer resources of both the MCG and the SCG can be referred to as split DRBs.

[0006] A UE in some scenarios can concurrently utilize resources of multiple radio access network (RAN) nodes (e.g., base stations or components of a distributed base station), interconnected by a backhaul. When these network nodes support different radio access technologies (RATs), this type of connectivity is referred to as Multi-Radio Dual Connectivity (MR-DC). When a UE operates in MR-DC, one base station operates as a master node (MN) that covers a primary cell (PCell), and the other base station operates as a secondary node (SN) that covers a primary secondary cell (PSCell). The UE communicates with the MN (via the PCell) and the SN (via the PSCell). In other scenarios, the UE utilizes resources of one base station at a time. One base station and / or the UE determines that the UE should establish a radio connection with another base station. For example, one base station can determine to hand the UE over to the second base station, and initiate a handover procedure.

[0007] When a UE moves from the coverage area of one cell to the area of coverage of another cell in a RAN, the UE must at some point perform a serving cell change. To perform this operation, the RAN configures the UE to transmit Layer 3 (L3) measurement results. Based on L3 measurement results received from the UE, the RAN transmits an RRC reconfiguration message instructing reconfiguration with synchronization (e.g., the RRCPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 reconfiguration message includes a ReconfigurationWithSync information element (IE)) for the change of the serving cell (e.g., PCell or PSCell). When the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN has to release at least one SCell due to the change of the PCell or PSCell. The serving cell change involves complete L2 (and LI) resets, leading to longer latency, larger overhead and longer interruption time.

[0008] To address some of these concerns, the 3rd Generation Partnership Project (3GPP) proposed mobility procedures, referred to as lower layer triggered mobility (LTM), to provide fast serving cell changes by reducing latency and overhead.

[0009] A base station can use LTM when communicating with a UE via a serving cell and after receiving one or more layer 3 (e.g., RRC) measurement results from the UE. Based on the layer 3 (L3) measurement result(s), the base station can determine to configure an LTM candidate cell for an LTM cell switch. To configure the LTM candidate cell for the UE, the base station transmits, to the UE via RRC signaling, an LTM candidate configuration for the LTM candidate cell. At a later time, the base station receives one or more measurement results from the UE. Based on the one or more measurement result(s), the base station determines that the LTM candidate cell qualifies to be a serving cell for the UE. The base station accordingly transmits, to the UE, an LTM cell switch command to instruct the UE to perform the LTM cell switch to the LTM candidate cell. The UE performs a cell change from the serving cell to the LTM candidate cell in response to the LTM cell switch command.

[0010] The base station can be distributed base station that consists of a central unit (CU) and one or more distributed units (DUs). One of the DU(s) operating the serving cell is a serving DU. If the LTM candidate cell is operated by the serving DU, the LTM cell switch is an intra-CU intra-DU LTM cell switch. If the LTM candidate cell is operated by a candidate DU in the DU(s), the LTM cell switch is an intra-CU inter-DU LTM cell switch. 3 GPP has described some of the intra-CU intra-DU LTM cell switch and intra-CU inter-DU LTN cell switch procedures.

[0011] Although 3GPP has started to specify inter-CU LTM cell switch procedures, multiple scenarios that involve inter-CU LTM with MR-DC or non-MR-DC remain unclear. One such issue is handling, at a serving base station (e.g., MN or SN), a request to set up a new serving configuration or modify an existing serving configuration for a UE when anPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 LTM cell switch is necessary for the UE. Another issue is updating, at a serving base station, the LTM candidate configuration for a UE.SUMMARY

[0012] An example embodiment of the techniques of this disclosure is a method implemented in a serving radio access network (RAN) node, the method comprising: communicating, with a user equipment (UE), according to a serving configuration; configuring the UE with for a lower-layer triggered mobility (LTM) switch to a target cell associated with a target RAN node; determining, after the configuring but prior to initiating the LTM switch, that a change in the serving configuration is required; and in response to the determining, performing one of: (i) initiating a procedure to add or modify radio resources configured for the UE, or (ii) transmitting, to the UE, a command to initiate the LTM switch.

[0013] Another example embodiment of these techniques is a method implemented in a RAN node, the method comprising: communicating, with a user equipment UE according to a serving configuration; performing, with a core network (CN), a resource management procedure for the UE; during the performing of the resource management procedure, determining to perform a mobility preparation procedure for the UE; and determining whether to perform a mobility preparation procedure while the resource management procedure is ongoing based on whether the mobility preparation procedure relates to immediate mobility or LTM mobility.

[0014] Another example method of these techniques is a RAN node comprising processing hardware and configured to implement one of the methods above.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Fig. 1 A is a block diagram of an example system in which a radio access network (RAN) and a user device can implement the techniques of this disclosure for managing LTM procedures related to a secondary node (SN);

[0016] Fig. IB is another block diagram of an example system in which a radio access network (RAN) and a user device can implement the techniques of this disclosure for managing LTM procedures related to an MN or an SN;

[0017] 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;PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0018] Fig. 2A is a block diagram of an example protocol stack according to which the UE of Fig. 1A communicates with base stations;

[0019] Fig. 2B is a block diagram of an example protocol stack according to which the UE of Fig. 1A communicates with a CU and a DU;

[0020] Fig. 3 is a signaling diagram for an intra-DU LTM.

[0021] Fig. 4 is a signaling diagram for an inter-DU LTM.

[0022] Fig. 5 A is a signaling diagram of a first example illustrating an inter-CU LTM between a user equipment (UE) and a base station (BS).

[0023] Fig. 5B is a signaling diagram of a second example illustrating an inter-CU LTM between a UE and a BS.

[0024] Fig. 5C is a signaling diagram of a third example illustrating an inter-CU LTM between a UE and a BS.

[0025] Fig. 6A is signaling diagram of a first example illustrating communications between a UE, a master node (MN) and a serving secondary node (S-SN) of a multi-radio dual-connectivity (MR-DC) configuration, and a candidate secondary node (C-SN) for inter-CU LTM cell switch.

[0026] Fig. 6B is signaling diagram of a second example illustrating communications between a UE, an MN and a S-SN of a MR-DC configuration, and a C-SN for inter-CU LTM cell switch.

[0027] Fig. 6C is signaling diagram of a third example illustrating communications between a UE, an MN and a S-SN of a MR-DC configuration, and a C-SN for inter-CU LTM cell switch.

[0028] Fig. 7A is a flow diagram of an example method at a first BS for inter-CU LTM cell switch;

[0029] Fig. 7B is a flow diagram of another method at a first BS for inter-CU LTM cell switch;

[0030] Fig. 8A is a flow diagram of an example method at a first BS for an inter-CU LTM in MR-DC cell switch;

[0031] Fig. 8B is a flow diagram of another exmaple method at a first BS for an inter-CU LTM in MR-DC cell switch;PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0032]

[0033] Fig. 9A is a flow diagram of a first method at a first BS for inter-CU LTM cell switch, according to one embodiment;

[0034] Fig. 9B is a flow diagram of a second method at a first BS for inter-CU LTM cell switch, according to one embodiment;

[0035] Fig. 10A is a flow diagram of a first method at a S-SN for inter-CU LTM cell switch, according to one embodiment; and

[0036] Fig. 10B is a flow diagram of a second method at a S-SN for inter-CU LTM cell switch, according to one embodiment.DETAILED DESCRIPTION

[0037] Fig. 1A depicts an example wireless communication system 100 in which communication devices can implement these techniques. The wireless communication system 100 includes a UE 102, a base station (BS) 104A, a base station 106A, and a core network (CN) 110. The base stations 104 A and 106 A operate in a radio access network (RAN) 105. The UE 102 initially connects to the base station 104A. In some scenarios, the base station 104A can perform an SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104A and the base station 106A. The base stations 104A and 106A operate as an MN and an SN for the UE 102, respectively.

[0038] In various configurations of the wireless communication system 100, the base station 104A can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station 106A can be implemented as a secondary gNB (SgNB). The UE 102 can communicate with the base station 104A and the base station 106A via the same RAT such as EUTRA or NR, or different RATs. When the base station 104 A is an MeNB and the base station 106A is a SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0039] In some cases, an MeNB or an SeNB is implemented as an ng-eNB rather than an eNB. When the base station 104A is a Master ng-eNB (Mng-eNB) and the base station 106A is a SgNB, the UE 102 can be in next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. When the base station 104A is an MgNB and the base station 106A is an SgNB, the UE 102 may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the base station 104A is an MgNB and the base station 106A is a SecondaryPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 ng-eNB (Sng-eNB), the UE 102 may be in NR-EUTRA DC (NE-DC) with the MgNB and the Sng-eNB.

[0040] In the scenarios where the UE 102 hands over from the base station 104A to the base station 106A, the base stations 104A and 106A operate as the source base station (S-BS) and a target base station (T-BS), respectively. The UE 102 can operate in DC with the base station 104A and an additional base station (not shown in Fig. 1A) for example prior to the handover. The UE 102 can continue to operate in DC with the base station 106A and the additional base station or operate in single connectivity (SC) with the base station 106A, after completing the handover. The base stations 104A and 106A in this case operate as a source MN (S-MN) and a target MN (T-MN), respectively.

[0041] A core network (CN) 110 can be an evolved packet core (EPC) 111 or a fifthgeneration core (5GC) 160, both of which are depicted in Fig. 1A. The base station 104A can be an eNB supporting an S 1 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 104A and 106A can support an X2 or Xn interface. Among other components, the EPC 111 can include a Serving Gateway (SGW) 112, a Mobility Management Entity (MME) 114, 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, etc., and 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 (AMF) 164, 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, etc., the AMF 164 is configured to manage authentication, registration, paging, and other related functions, and the SMF 166 is configured to manage PDU sessions.

[0042] As illustrated in Fig. 1A, the base station 104A supports cell 124A, and the base station 106A 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 104A and the base station 106A,PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 where one of the base stations 104A and 106A is an MN and the other is an SN. The base station 104A can support additional cell(s) such as cells 124B and 124C, and the base station 106 A can support additional cell(s) such as cell 126B. The cells 124 A, 124B and 124C can partially overlap, so that the UE 102 can communicate in carrier aggregation (CA) with the base station 104 A. The base station 104 A can operate the cells 124 A, 124B and 124C via one or more transmit and receive points (TRPs). More particularly, when the UE 102 is in DC with the base station 104A and the base station 106A, one of the base stations 104A and 106A operates as an MeNB, an Mng-eNB or an MgNB, and the other operates as an SgNB or an Sng-eNB.

[0043] In general, the wireless communication system 100 can include any suitable number of base stations supporting NR cells and / or EUTRA cells. More particularly, the EPC 111 or the 5GC 160 can 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 can apply to other suitable radio access and / or core network technologies such as sixth generation (6G) radio access and / or 6G core network or 5G NR-6G DC.

[0044] With continued reference to Fig. 1A, the base station 104A 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 MAC controller 134 configured to perform MAC functions with 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 userPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 devices. The MAC functions include lower triggered mobility (LTM) related functions as described below. The processing hardware 130 can further include an 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 104A operates as an MN relative to an SN or as an SN relative to an MN. An LTM controller 138 is configured to support LTM operations and interactions between LTM operations and changes in serving configurations.

[0045] The base station 106 A can include processing hardware 140 that is similar to processing hardware 130. In particular, components 142, 144, 146, and 148 can be similar to the components 132, 134, 136, and 138, respectively.

[0046] 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 also configured to receive data and control signal on physical DL channels and / or DL reference signals with the base station 104A or 106A via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126A) and / or one or more TRPs. The PHY controller 152 is also configured to transmit data and control signal on physical UL channels and / or UL reference signals with the base station 104A or 106A 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 A or 106 A. For example, the MAC functions includes 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 104A or 106A. In another example, the MAC functions includes LTM related functions as described below. The processing hardware 150 can further include an RRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack.

[0047] In operation, the UE 102 in DC can use a radio bearer (e.g., a DRB or an SRB) that at different times terminates at the MN 104B or the SN 106A. The UE 102 can apply one or more security keys when communicating on the radio bearer, in the uplink (UL) (from the UE 102 to a base station) and / or downlink (from a base station to the UE 102) direction.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0048] Fig. 1C depicts an example distributed implementation of a base station such as the base station 104A or 106 A. The base station in this implementation can include a centralized unit (CU) 172 and one or more distributed units (DUs) 174A, 174B. The functionality of the CU 172 can be split between one or more instances of a CU control plane function (CU-CP) 172A and one or more instances of a CU user plane function (CU-UP) 172B, interconnected via an El interface for example.

[0049] 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. The DU 174A 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 medium access control (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 106A 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.

[0050] Fig. 2A illustrates, in a simplified manner, an example protocol stack 200 according to which the UE 102 can communicate with an eNB / ng-eNB and / or a gNB (e.g., one or more of the base stations 104 A, 106A).

[0051] In the example stack 200, a physical layer (PHY) 202A of EUTRA provides transport channels to the EUTRA MAC sublayer 204A, 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 PDCP sublayer 208 and, in some cases, to an NR PDCP sublayer 210. 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 NR PDCP sublayer 210 in turn can provide data transfer services to Service DataPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 Adaptation Protocol (SDAP) sublayer 212 or a radio resource control (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.

[0052] The EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 receive packets (e.g., from an Internet Protocol (IP) layer, layered directly or indirectly over the PDCP sublayer 208 or 210) that can be referred to as service data units (SDUs), and output packets (e.g., to the RLC sublayer 206A or 206B) that can be referred to as protocol data units (PDUs). Except where the difference between SDUs and PDUs is relevant, this disclosure for simplicity refers to both SDUs and PDUs as “packets.”

[0053] On a control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide signaling radio bearers (SRBs) or RRC sublayer (not shown in Fig. 2A) to exchange RRC messages or non-access-stratum (NAS) messages, for example. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide Data Radio Bearers (DRBs) to support data exchange. Data exchanged on the NR PDCP sublayer 210 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0054] Fig. 2B illustrates, in a simplified manner, an example protocol stack 250, which the UE 102 can communicate with a DU (e.g., DU 174) and a CU (e.g., CU 172). The radio protocol stack 200 is functionally split as shown by the radio protocol stack 250 in Fig. 2B. The CU at any of the base stations 104A or 106A can hold all the control and upper layer functionalities (e.g., RRC 214, SDAP sublayer 212, NR PDCP 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 sublayer 212 and SRBs to RRC 214.

[0055] Next, several example scenarios in which the base station operating in the system of Fig. 1A transmits a configuration to the UE 102 and later activates a configuration for communication between the UE 102 and base station. Generally speaking, events in Figs. 3-10B that are similar are labeled with similar reference numbers (e.g., event 302 is similar to event 402 of Fig. 4, event 502 of Figs. 5A-5C, event 602 of Figs. 6A and 6B, and block 702PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 of Figs. 7-10B, event 390 is similar to event 490 of Fig. 4, event 590 of Fig. 5A, and event 690 of Fig. 6A), with differences discussed below where appropriate. With the exception of the differences shown 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.

[0056] Referring first to Fig. 3, in a scenario 300, the base station 104A includes a CU 172 and DU 174A and the DU 174A operates the cell 124A. The UE 102 initially communicates 302 with the DU 174A 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 serving DU configuration includes configuration parameters provided by the DU 174, and the serving CU configuration includes configuration parameters provided by the CU 172. The DU 174A is a serving or a source DU (S-DU) for the UE 102. In other words, the DU 174 A is a serving DU (S-DU) that is communicating with the UE 102. In some implementations, the UE 102 in carrier aggregation (CA) communicates with the DU 174A on the cell 124A and other cell(s) using the serving DU configuration. The DU 174A operates the other cell(s). The cell 124 A and / or the other cell(s) are serving cell(s) for the UE 102. In other implementations, the UE 102 in communicates with the DU 174A on the cell 124A only. In some implementations, the UE 102 communicates with the DU 174A on the cell 124A and / or other cell(s) (i.e., serving cell(s)) via one or multiple TRPs. In the following description, events 394, 324, 350, 352, 354, and 326 occur 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 additional cell(s) associated with the PCell or a SCell. In other implementations, the cell 124A can be a SCell, and one of the other cell(s) is a PCell. In such cases, the rest includes SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In the following description, the base station 104A can be the DU 174, the CU 172 or the DU 174A and CU 172.

[0057] As a part of the event 302, the UE 102 can transmit UL PDUs and / or UL control signals to the base station 104A 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 104A via radio bearers which can include SRBs and / or DRB(s). The base station 104 A can configure the radio bearers to the UE 102. In some implementations, UL control signals include UL control information, channel state information, hybrid automatic repeat request (HARQ) acknowledgements (ACKs), HARQ negative ACKs, schedulingPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 request(s) and / or sounding reference signal(s). Similarly, the UE 102 can receive DL PDUs and / or DL control signals from the base station 104 A on the cell 124 A and / or other cell(s) via one or multiple TRPs. In some implementations, the DL control signals include downlink control information (DCIs) and reference signals (e.g., synchronization signal block, channel state information reference signal(s) (CSI-RS(s)), and / or tracking reference signal(s)). The base station 104A can transmit the DCIs on physical downlink control channel(s) (PDCCH(s)) monitored by the UE 102, on the cell 124A and / or other cell(s) via one or multiple TRPs.

[0058] In some implementations, the serving DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or REC configuration parameters. In some implementations, the serving DU configuration includes at least one first non-LTM TCI state configuration for the serving cell(s). In some implementations, the DU 174A can transmit these configuration parameters and / or the first non-LTM TCI state configuration(s) to the CU 172. The CU 172 generates one or more messages (e.g., RRC reconfiguration message(s)) including the configuration parameters and / or the first non-LTM TCI state configuration(s) and transmits the one or more messages to the UE 102 via the DU 174. In other implementations, the DU 174A transmits the configuration parameters and / or the first non-LTM TCI state configuration(s) to the UE 102 directly. In some implementations, the serving DU configuration is CellGroupConfighE defined in 3GPP specification 38.331. In other implementations, the serving DU configuration includes configuration parameters in the CellGroupConfighE. 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 aMeasConfig IE and / or a RadioBear erConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. The radio configuration parameters or the RadioBearerConfig IE configures one or more DRBs. In some implementations, the serving DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (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 receives 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 receives a portion of the serving CU configurationPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 and / or a portion of the serving DU configuration from a base station other than the base station 104A and the remaining portion of these configuration parameters from the base station 104A.

[0059] In some implementations, the DU 174A and the UE 102 communicate with each other using first non-LTM TCI state configuration(s), e.g., during the events 302, 318, 320, 324, 350, 354, and / or 326. In some implementations, the DU 174A transmits at least one first non-LTM TCI States Activation / D eactivation command (e.g., MAC control element (CE)) to the UE 102 to activate the first non-LTM TCI state configuration(s). The UE 102 activates the first non-LTM TCI state configuration(s) in response to the first non-LTM TCI States Activation / Deactivation command(s). In some implementations, the DU 174A includes a serving cell ID (e.g., a serving cell index) in each of the first non-LTM TCI States Activation / Deactivation command(s) to identify the first non-LTM TCI state configuration(s). Each of the serving cell ID(s) indicates a respective serving cell of the serving cell(s). In some implementations, the serving DU configuration includes the serving cell ID(s) and configures association(s) between the serving cell ID(s) and the first non-LTM TCI state configuration(s).

[0060] While communicating with the base station 104 A, the UE 102 transmits 304 at least one measurement report to the DU 174. In some implementations, the measurement report(s) includes measurement results for a serving cell (e.g., the cell 124A) of the UE 102 and / or at least one non-serving cell. For each of the measurement report(s), the DU 174A transmits 306 a DU-to-CU message including the measurement report to the CU 172. In some implementations, the DU-to-CU message(s) of the event 306 is / are Fl application protocol (F1AP) message(s) (e.g., UL RRC Message Transfer message(s)). The at least one 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 measurement configuration(s), the UE 102 performs measurements and transmits 304 the measurement report(s) to the DU 174. In some implementations, the measurement configuration(s) includes Layer 3 (L3) measurement configuration(s) (Q.g.,MeasConfig IE(s)) and the measurement report(s) include L3 measurement report(s).

[0061] After (e.g., in response to) receiving one or some of the measurement report(s) from the UE 102, the CU 172 determines to prepare a first cell (e.g., cell 1 such as the cell 124B)PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 as an LTM candidate cell for the UE 102. In some implementations, the base station 104 A determines to prepare the first cell for the UE 102 because the measurement report(s) indicates that the first cell could be used by the base station 104A to communicate with the UE 102. In some implementations, the base station 104 A determines to prepare the first cell for the UE 102 because the measurement report(s) indicates that the first cell qualifies to be an LTM candidate cell that could be used for communication with the UE 102. In some implementations, if the L3 measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than strength and / or quality of the serving cell (e.g., cell 124A), and / or is better than strength and / or quality of the serving cell by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. Alternatively, the CU 172 determines to prepare the first cell for the UE 102 regardless of whether a measure report is received from the UE 102 or not.

[0062] In response to determining to prepare the first cell for LTM, the CU 172 transmits 308 a first CU-to-DU message to the DU 174A to prepare the first 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 174A to prepare the first cell for LTM for the UE 102. For example, the cell ID 1 is cell global identity (CGI). In another example, the cell ID is a portion of the CGI. In yet another example, the cell ID is a physical cell ID (PCI). In some implementations, the CU 172 includes an LTM indicator in the first CU-to-DU message to indicate the DU 174A 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 yet 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.

[0063] In response to the first CU-to-DU message, the DU 174A generates a first LTM DU configuration (referred to herein after 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 (i.e., referred to herein after as LTM ID 1) in the first CU-to-DU message and the DU 174A associates the LTM ID 1 and / or the cell ID 1 with the LTM DU configuration 1. The DU 174A then transmits 310 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.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0064] The events 308 and 310 are collectively referred to in Fig. 3 as an LTM preparation procedure 390.

[0065] In some implementations, the DU 174A 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 procedure 2, ..., N described below) with the DU 174A to prepare multiple LTM candidate cells, the CU 172 can 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.

[0066] 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 174A generates an LTM reference DU configuration and includes the LTM reference DU configuration in the first DU-to-CU message. In some implementations, the DU 174A generates the LTM DU configuration 1 as a delta configuration to augment the LTM reference DU configuration. In other implementations, the DU 174A generates the LTM DU configuration 1 as a complete configuration, i.e., not on top of the LTM reference DU configuration.

[0067] In some implementations, the CU 172 includes an LTM reference DU configuration request in the first CU-to-DU message, and the DU 174A generates 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 174A includes the LTM reference DU configuration in the first DU-to-CU message in response to the LTM reference DU configuration request. Otherwise, if the CU 172 determines that the UE 102 does not support an LTM reference configuration, the CU 172 does not include the LTM reference DU configuration request in the first CU-to-DU message. In this case, the DU 174A may generate the LTM DU configuration 1 as a complete configuration and may not include a / the 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 174A instead of the first CU-to-DU message.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 In response, the DU 174 A includes an additional DU-to-CU message including the LTM reference DU configuration to the CU 172. In yet other implementations, the DU 174A determines whether the UE 102 supports an LTM reference configuration. If the DU 174A determines that the UE 102 supports an LTM reference configuration, the DU 174A includes the LTM reference DU configuration in the first DU-to-CU message. Otherwise, if the DU 174A determines that the UE 102 does not support an LTM reference configuration, the DU 174A does not include a / the LTM reference DU configuration in the first DU-to-CU message.

[0068] 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 receives the LTM reference DU configuration from an additional DU during an LTM preparation procedure as described above and for Fig. 4. In other implementations, the CU 172 is preconfigured with the LTM reference DU configuration. In some implementations, the DU 174A generates the LTM DU configuration 1 as a delta configuration to augment the LTM reference DU configuration. In other implementations, the DU 174A ignores the LTM reference DU configuration and generates the LTM DU configuration 1 as a complete configuration, i.e., not on top of the LTM reference DU configuration.

[0069] If the DU 174A generates the LTM DU configuration 1 as a complete configuration, the DU 174A 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 a / the LTM reference DU configuration, the CU 172 may determine that the LTM DU configuration 1 as a complete configuration. Otherwise, if the first CU-to-DU message includes a / the LTM reference DU configuration, the CU 172 may determine that the LTM DU configuration 1 is a delta configuration.

[0070] 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 RLCPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 configuration parameters. In some implementations, the LTM reference DU configuration is the CellGroupConfig IE defined in 3GPP specification 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-or configuration parameters for channel state information (CSI) measurement and / or reporting.

[0071] 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 other implementations, the LTM reference DU configuration is the same as the serving DU configuration.

[0072] To prepare the first cell as an LTM candidate cell for the UE 102, the CU 172 may transmit 312 a second CU-to-DU message to the DU 174, including a CSI resource configuration (e.g., CSI resource configuration 1) and / or an LTM SSB configuration (i.e., LTM SSB configuration 1) to request the DU 174A to generate one or more CSI report configurations (e.g., (LTM) CSI report configuration(s) 1). The CSI resource configuration (e.g., (LTM) CSI resource configuration(s) 1) include configuration parameters configuring at least one reference signal (RS) transmitted on the first cell. The RS(s) include SSB(s) and / or CSI-RS(s). The LTM SSB configuration include SSB configuration parameters configuring a SSB frequency, a subcarrier spacing, a SSB periodicity, SSB positions (e.g., SSB Positions In Burst IE) and / or SSB power for SSB(s) transmitted on the first cell.

[0073] After (e.g., in response to) receiving the CSI resource configuration, the DU 174A generates one or more CSI report configurations based on the CSI resource configuration and includes the CSI report configuration(s) 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 CSI report configuration(s) configures the UE 102 to transmit CSI reports based on measurements of the RS(s). The DU 174A transmits 314 a second DU-to-CU message including the second serving DU configuration to the CU 172. In some implementations, the CSI resource configuration comprises (e.g., is or includes) one or more LTM-CSI-ResourceConfig-r 18 IES. In other implementations, the CSI resourcePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 configuration comprises an Itm-C Si-Re sour ceConfigToAddModList field / IE. In some implementations, the second serving DU configuration is a CellGroupConfig IE.

[0074] 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 / are associated with the first cell. In another implementation, the CU 172 does so for the DU 174A to associate the LTM ID 1 with the first cell, the cell ID 1, the LTM DU configuration 1, and / or the CSI report configuration(s). Based on the above implementation(s), the DU 174A 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 CSI report configuration(s)) 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.

[0075] In some alternative implementations, the CU 172 includes the CSI resource configuration in the first CU-to-DU message and the DU 174A includes the CSI report configuration(s) in the first DU-to-CU message.

[0076] In some implementations, the DU 174A transmits 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 174A transmits 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 174A transmits 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.

[0077] 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.

[0078] After receiving the first DU-to-CU message, the CU 172 generates a first LTM candidate configuration (i.e., LTM candidate configuration 1) including the LTM DU configuration 1 and generates 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. The CU 172 transmits 316 a third CU-to-DU message including the first RRC reconfiguration message to the DU 174. In turn, the DU 174A transmits 318 the first RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320 a first RRCPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 reconfiguration complete message to the DU 174. The DU 174A then transmits 322 a third DU-to-CU message including the first RRC reconfiguration complete message to the CU 172.

[0079] If the first DU-to-CU message includes the LTM reference DU configuration, the CU 172 generates 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. 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 configuration. Alternatively, the CU 172 transmits a second RRC reconfiguration message including the LTM reference configuration to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a second RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. 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.

[0080] 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 as a complete configuration. Otherwise, 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 generates the LTM candidate configuration 1 as a complete configuration. Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU 172 generates 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 completePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 configuration indication from the first RRC reconfiguration message to indicate that the LTM candidate configuration 1 is a delta configuration.

[0081] 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. Alternatively, the CU 172 transmits a third RRC reconfiguration message including the second serving DU configuration to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a third RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322.

[0082] 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 transmits a fourth RRC reconfiguration message including the CSI resource configuration to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a fourth RRC reconfiguration complete message to the UE 102 via the DU 174, similar to the events 320 and 322.

[0083] In some implementations, the DU 174A transmits a DU-to-CU message to the CU 172, including 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 174A transmits 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 174A transmits 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 one implementation, the DU 174A does so, if the DU 174A determines that the UE 102 supports (i.e., is capable of) early UL synchronization with an LTM candidate cell (e.g., early TA acquisition with an LTM candidate cell, early RA on an LTM candidate cell, or UE measured TA). Otherwise, if the DU 174A determines that the UE 102 does not support the early UL synchronization with an LTM candidate cell, the DU 174A does not transmit the early synchronization information to the CU 172. In other implementations, the CU 172 transmits a CU-to-DU message including an early synchronization information request (e.g., an IE) to the DU 174, and the DU 174A 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-DUPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 message, the second CU-to-DU message or the fourth CU-to-DU message. In one implementation, the CU 172 does so if the CU 172 determines that the UE 102 supports the early UL synchronization with an LTM candidate cell. Otherwise, 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 174A 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. Alternatively, the CU 172 transmits 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. In response, the UE 102 transmits a fifth RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322.

[0084] In some implementations, the early synchronization information includes a random access channel (RACH) configuration (i.e., RACH configuration 1) and / or one or more TCI state configurations (i.e., TCI state configuration(s) 1). In some implementations, the early synchronization request may include a request for a RACH configuration. If the early synchronization request includes the request for a RACH configuration, the DU 174A includes the RACH configuration in the early synchronization information or in the DU-to-CU message (e.g., be the first, second or fourth DU-to-CU message). Otherwise, if the early synchronization request does not include the request for a RACH configuration, the DU 174A neither includes the RACH configuration in the early synchronization information or in the DU-to-CU message.

[0085] In some implementations, the CU 172 includes, 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.

[0086] The events 316, 318, 320, 322 are collectively referred to in Fig. 3 as an LTM configuration delivery procedure 394. The second, third, fourth and / or fifth RRC reconfiguration message(s)) and the second, third, fourth and / or fifth RRC reconfiguration complete message(s), the related CU-to-DU message(s) and / or the related DU-to-CU message(s) are also considered as part of the LTM configuration delivery procedure 394. In some implementations, the RRC reconfiguration message and the RRC reconfigurationPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 complete message described above are an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively.

[0087] In some implementations, the first CU-to-DU message is a UE Context Modification Request message, and the first DU-to-CU message is a UE Context Modification Response message. In some implementations, the second CU-to-DU message is a UE Context Modification Request message, and the second DU-to-CU message is 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 can transmit a UE Context Modification Confirm message to the DU 174A in response to UE Context Modification Required message. In some implementations, the third CU-to-DU message is a DL RRC Message Transfer message. In other implementations, the third CU-to-DU message is a UE Context Modification Request message. In some implementations, the third DU-to-CU message is a UL RRC Message Transfer message. In other implementations, the third DU-to-CU message is a UE Context Modification Response message.

[0088] In some implementations, the LTM reference CU configuration is different from the serving CU configuration. In some implementations, a portion of the LTM reference CU configuration is the same as a portion of the serving CU configuration and the rest of the LTM reference CU configuration is different from the rest of the serving CU configuration. In yet other implementations, the LTM reference CU configuration is the same as the serving CU configuration.

[0089] 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 RadioBearerConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE.

[0090] In some implementations, the LTM CU configuration 1 and / or the LTM reference CU configuration 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 includes a. MeasConfig and / or a RadioBearerConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0091] In some implementations, the LTM DU configuration 1 includes a plurality of configuration parameters for the UE 102 to communicate with the DU 174 A on the first cell. In some implementations, the plurality of configuration parameters include physical layer configuration parameters (e.g., PhysicalCellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE) and / or RLC configuration parameters (e.g., RLC-BearerConfigIE(s)). In some further implementations, the plurality of configuration parameters 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 is CellGroupConfig defined in 3GPP specification 38.331. In other implementations, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0092] In some implementations, the LTM DU configuration 1 includes a first LI measurement configuration (e.g., a CSI-MeasConfig IE) and / or at least one first transmission configuration indicator (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) configures one or more RSs or one or more RS resources associated with the cell 1. The RS(s) includes SSB(s) and / or CSLRS(s). The RS resource(s) includes SSB resource(s) and / or CSLRS resource(s). In some implementations, each of the first RS resource configuration(s) includes 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., PUCCH resources or 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) includes 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 quasicolocation (QCL) type. The DL RS(s) are associated with the cell 1.

[0093] 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 performs measurements on at least one first RS, generates at least one first LIPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 measurement result based on the measurements, and transmits 324 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 pattern(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 performs 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.

[0094] 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 performs measurements on at least one second RS, generates at least one second LI measurement result based on the measurements, and transmits at least one second LI measurement 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 pattern(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 (event 302) and / or the second serving DU configuration. The UE 102 performs 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).

[0095] After transmitting the RACH configuration to the UE 102 via the CU 172, the DU 174A may transmit 350 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 transmits a RA preamble on the first cell. The DU 174A includes PDCCH order information in the PDCCH order. The PDCCH order information includes a RA preamble index, an UL or a supplemental UL indicator, a SSB index and / or a physical RACH mask index. In some implementations, the DU 174A includes the LTM ID 1 in the PDCCH order to indicate the first cell. The UE 102 identifies the first cell based on the LTM ID 1 in the PDCCH order and transmits 352 the RA preamble on the first cell to the DU 174, using the PDCCH order information. Correspondingly, the DU 174A receives 352 the RA preamble in accordance with the PDCCH order information. In some implementations, the DU 174A may determine the SSB index, based on receiving 324 the LI measurement report(s), and / or the CSI resourcePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 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) include a SS / PBCH Block Resource Indicator (SSBRI) corresponding to the SSB index. Thus, the DU 174A determines the SSB index based on the SSBRI.

[0096] In some implementations, the DU 174A determines whether to transmit the PDCCH order based on the LI measurement result(s) (event 324). In some implementations, if the LI measurement result(s) indicate that the first cell qualifies for the UE 102 to perform RA for early UL synchronization, the DU 174A transmits the PDCCH order. Otherwise, if the LI measurement result(s) indicate that the first cell does not qualify for the UE 102 to perform RA for early UL synchronization, the DU 174A 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 174A transmits the PDCCH order.Otherwise, if the LI measurement result(s) indicate that the first cell does not qualify for the UE 102 to access, the DU 174A refrains from transmitting the PDCCH order. In yet other implementations, the DU 174A transmits the PDCCH order after receiving 320 the RRC reconfiguration complete message, regardless of the LI measurement result(s) 324.

[0097] After transmitting 324 the LI measurement report(s) or 352 the RA preamble, the UE 102 may transmit 354 additional LI measurement report(s) to the DU 174, similar to the event 324. The DU 174A 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) 324. In response to the determination, the DU 174A generates an LTM Cell Switch Command (e.g., a MAC CE) including the LTM ID 1 and transmits 326 the LTM Cell Switch Command to the UE 102. In response to the determination, the DU 174A may transmit 328 a DU-CU Cell Switch Notification message to the CU 172. In response to the LTM Cell Switch Command, the UE 102 performs an LTM cell switch to the first cell. In the LTM cell switch, the UE 102 accesses 332 the first cell and transmits 336 an RRC reconfiguration complete message to the DU 174A via the first cell. The DU 174A transmits 338 a DU-to-CU message (e.g., UL RRC Message Transfer message) including the RRC reconfiguration complete message to the CU 172. When the UE 102 receives the LTM Cell Switch Command, the UE 102 identifies the LTM candidate configuration 1 from the LTM ID 1 and accesses 332 the first cell using the LTM candidate configuration 1. Depending on implementations, the UE 102 may stop communicating on the serving cell(s) in response to the LTM Cell SwitchPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 Command. In turn, the DU 174A transmits a fifth DU-to-CU message including the RRC reconfiguration complete message to the CU 172. When the DU 174A detects that the UE 102 accesses the first cell during the event 332, the DU 174A may transmit 334 an Access Success message to the CU 172 to indicate that the UE 102 has accessed the first cell.

[0098] In some alternative implementations, the UE 102 may transmit at least one L3 measurement result to the CU 172 via the DU 174A after event 320. Based on the at least one L3 measurement result, the CU 172 may send a CU-to-DU message to the DU 174, requesting or indicating to the DU 174A to trigger the LTM Cell Switch to the first cell for the UE 102. In some implementations, the CU-to-DU message includes a field or IE for the requesting or indicating. In response to the CU-to-DU message or the field or IE, the DU 174A transmits 350 the PDCCH order and / or 326 the LTM Cell Switch Command to the UE 102. In some implementations, the CU-to-DU message includes the at least one L3 measurement result. In some implementations, the DU 174A determine to send 350 the PDCCH order and / or 326 the LTM Cell Switch Command based on the at least one L3 measurement result. In some implementations, the CU-to-DU message is an existing message defined in 3GPP specification 38.473. For example, the CU-to-DU message is a UE Context Modification Request message or a CU-DU Cell Switch Notification message. In yet other implementations, the CU-to-DU message is a new CU-to-DU message that is newly defined in 3 GPP specification 38.473 vl 8.4.0 or a later release / version.

[0099] In some implementations, the DU 174A includes, in the LTM Cell Switch Command, a TA value for UL synchronization with the first cell. In one implementation, the DU 174A derives the TA value based on the RA preamble (e.g., reception timing of the RA preamble). In another implementation, the DU 174A derives the TA value from an UL transmission on the serving cell (e.g., the cell 124A) from the UE 102. The UE 102 applies the TA value to synchronize with the first cell in UL transmission. After applying the TA value, the UE 102 transmits 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 transmits 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 transmitting 336 the RRC reconfiguration complete message. 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,PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 the UL grant is a dynamic grant that the UE 102 receives on a PDCCH on the first cell. After transmitting the first UL transmission, the UE 102 receives a PDCCH transmission addresses 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.

[0100] The PDCCH transmission may include a UL grant or a DL assignment. In the case of the UL grant, the UE 102 transmits a PUSCH transmission to the DU 174A on the first cell using the UL grant. In the case of the DL assignment, the DU 174A transmits a PDSCH transmission to the UE 102 on the first cell in accordance with the DL assignment. The DU 174A may transmit 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 PUSH transmission or transmitting the PDSCH transmission.

[0101] In other implementations, the DU 174A does not include a TA value in the LTM Cell Switch Command. If the LTM Cell Switch Command does not include a / the TA value, the UE 102 performs 332 a 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 or the LTM DU configuration 1. In some implementations, the RA configuration parameters configure 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, 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. During the four-step RA procedure, the UE 102 transmits a Message 3 on the first cell and the DU 174A transmits a Message 4 on the first cell to the UE 102 in response. During the two-step RA procedure, the UE 102 transmits a Message A on the first cell and the DU 174 A transmits a Message B to the UE 102 on the first cell in response. The UE 102 may include the RRC reconfiguration complete message (event 336) in the Message 3 or Message A. Alternatively, the UE 102 transmits 336 the RRC reconfiguration complete message after completing the RA procedure. The DU 174A may transmit 334 the Access Success message to the CU 172, after receiving the Message 3, Message A, or the RRC reconfiguration complete message (event 336) or transmitting the Message 4 or Message B.

[0102] After successfully completing the LTM cell switch to the first cell as described above, the UE 102 communicates 340 with the DU 174A and the CU 172 via the first cell,PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 using the LTM candidate configuration 1. In the case of the LTM reference configuration, the UE 102 applies the LTM reference configuration first and then apply the LTM candidate configuration 1 to augment the LTM reference configuration.

[0103] In some implementations, each of the TCI state configuration(s) include a TCI state ID. In some implementations, the DU 174A includes, in the LTM Cell Switch Command, a first TCI state ID indicating a first one of the TCI state configuration(s). The UE 102 identifies the first one of the TC state configuration(s) based on the first TCI state ID and applies the first TCI state configuration to communicate UL transmissions and / or DL transmissions with the DU 174A during the events 332, 336 and / or 340. The DU 174A applies the first TCI state configuration to communicate UL transmissions and / or DL transmissions with the UE 102 during the events 332, 336 and / or 340

[0104] 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 the LTM Cell Switch Command or during, before or after the procedure 390 or 392, as described above. N is an integer and larger than 1. For example, the CU 172 performs additional LTM preparation procedure(s) 2, ..., N with the DU 174A 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 receives LTM DU configuration(s) 2, ..., N configuring the cell(s) 2, ..., N for LTM, respectively. The CU 172 generates 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 CSI resource configuration 2, ,..., N and perform CSI report configuration and / or LTM ID configuration procedure(s) 2, ..., N with the DU 174A to obtain the CSI report configuration(s) 2, ..., N, respectively, as discussed with respect to 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 discussed with respect to the RACH configuration 1. The CU 172 may obtain TCI state configuration(s) 2, ..., N for the cell(s) 2, ..., N respectively, as discussed with respect to 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 discussed with respect to the LTM SSB configuration 1. In some implementations, the CU 172 may perform LTM configuration delivery procedure 2,PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 .. 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 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 2, ..., N is similar to the procedure 394. In other implementations, the CU 172 includes the list in the first RRC reconfiguration message.

[0105] In some implementations, after receiving 334 the Access Success message or 338 the DU-to-CU message, the CU 172 may transmit 342 a CU-to-DU message to the DU 174. In one implementation, the CU 172 transmits 342 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 transmits 342 the CU-to-DU message to release some of the LTM candidate cell(s) 2, ..., N. In this case, in response to receiving 342 the CU-to-DU the DU 174A transmits 344 a DU-to-CU message to the CU 172. In some implementations, the CU-to-DU message (event 342) and the DU-to-CU message (event 344) are a UE Context Modification Request message and a UE Context Modification Response message, respectively

[0106] In some implementations, an LTM ID in a PDCCH order, an LTM Cell Switch Command and an RRC reconfiguration message is represented in different formats. For example, the PDCCH order or the LTM Cell Switch Command includes a first field to include the LTM ID 1 and the first RRC reconfiguration message includes 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 uses a binary format (i.e., 3 bits) with a value range of 0, ..., 7 and the second field uses 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 11 lb is equivalent to the second field with integer value 8.

[0107] The events 304, 306, 390, 392, 394, and 324 are collectively referred to in Fig. 3 as an intra-CU intra-DU LTM configuration procedure 396. The events 304, 306, 390, 392, 394,PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 324, 350, 352, 354, 326, 328, 332, 334, 336, 338, and 340 are collectively referred to in Fig.3 as an intra-CU intra-DU LTM procedure 380.

[0108] Referring next to Fig. 4, in a scenario 400, the base station 104A includes a CU 172, a S-DU 174A and a candidate DU (C-DU) 174B. The S-DU 174A operates the cell 124A and optionally additional cell(s), while the C-DU 174B operates a first cell (e.g., cell 124C). The scenario 400 is an intra-CU inter-DU scenario, similar to the scenario 300. Thus, the discussion of scenario 300 can generally apply to the scenario 400. At least some of the discussion of the DU 174A in Fig. 3 may apply to the S-DU 174A in Fig. 4, and at least some of the discussion of the DU 174A in Fig. 3 may apply to the C-DU 174B. The differences between the scenarios 300 and 400 are described below.

[0109] Initially, the UE 102 communicates 402 with the S-DU 174A on one or more serving cells (e.g., the cell 124A and / or other cell(s)) using a serving DU configuration and communicates with the CU 172 via the S-DU 174 A using a serving CU configuration. In some implementations, the CU 172 and S-DU 174A might perform the LTM configuration procedure 396 or the LTM procedure 380 with the UE 102, as discussed with 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 discussed with respect to Fig. 3. Upon successfully completing the LTM cell switch, the first cell becomes a serving cell and cell 124 A 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. During the communication 402, the UE 102 transmits 404, 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 performs 490 an LTM preparation procedure 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 transmits 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 transmits 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 discussed with respect to Fig. 3. The C-PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 DU 174B may or may not include an LTM reference DU configuration in the first DU-to-CU message, as discussed with respect to Fig. 3.

[0110] In some implementations, if the CU 172 receives an LTM reference DU configuration from the S-DU 174A as discussed 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 receives 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 discussed 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.

[0111] To prepare the cell 1 for LTM, the CU 172 may performs 492 an LTM CSI report configuration and / or LTM ID configuration procedure with the S-DU 174A. In the procedure 492, the CU 172 transmits a second CU-to-DU message including a CSI resource configuration (e.g., CSI resource configuration 1) and / or an LTM SSB configuration (i.e., LTM SSB configuration 1) to the S-DU 174A, similar to the event 312. In response, the S-DU 174A transmits 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 generates 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 discussed with respect to Fig. 3. In some implementations, the CU 172 includes {the LTM ID 1, the cell ID 1} as a tuple in the second CU-to-DU message.

[0112] To prepare the cell 1 as an LTM candidate cell for the UE 102, the CU 172 may receive 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 transmits 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 transmits 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 earlyPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 synchronization information includes a RACH configuration (e.g., RACH configuration 1) and / or at least one TCI state configuration (e.g., TCI state configuration(s) 1), as discussed 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 (PDCCH order information 1) for early UL synchronization with the first cell.

[0113] 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 transmits 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 transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message.

[0114] As discussed with respect to Fig. 3, the CU 172 performs 494 LTM configuration delivery procedure with the UE 102 to transmit the LTM ID 1 and the LTM candidate configuration to the UE 102. In some implementations, the CU 172 transmits {LTM ID, the LTM candidate configuration} as a tuple in a first RRC reconfiguration message in the 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 discussed with respect to Fig. 3. The CU 172 includes 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 includes 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 includes {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 in the other RRC reconfiguration message(s). In response to each of the other RRC reconfigurationPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 message(s), the UE 102 transmits an RRC reconfiguration complete message to the CU 172 via the S-DU 174A.

[0115] 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 includes 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 includes {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. The S-DU 174A transmits 450 a PDCCH order to the UE 102, based on the PDCCH order information. For example, The S-DU 174A transmits 450 a PDCCH order to the UE 102, including the PDCCH order information. In some implementations, the S-DU 174A may determine a SSB index included in the PDCCH order, based on LI measurement report(s) 424, and / or the CSI resource configuration, the CSI report configuration and / or the LTM SSB configuration. In some implementations, the S-DU 174A includes 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. The UE 102 transmits 452 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 derives a TA value based on the RA preamble. The C-DU 174B transmits 456 a DU-CU TA Information Transfer message including the TA value to the CU 172. The CU 172 in turn transmits 458 a CU-DU TA Information Transfer message including the TA value to the S-DU 174A. In some implementations, the C-DU 174B includes 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 message 456. In such cases, the CU 172 includes the cell ID 1, the RA preamble index, the RA-RNTI, and / or the DU ID of the S-DU 174A in the message 458. In response to determining to command the UE 102 to perform an LTM cell switch to the cell 1, the S-DU 174A transmits 456 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 firstPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 TCI state ID in the LTM Cell Switch Command. The first TCI state ID indicates a first one of the TCI state configuration(s).

[0116] In some implementations, the C-DU 174B determines the RA-RNTI based on a PRACH occasion in which the C-DU 174B receives 452 the RA preamble. In some implementations, the C-DU 174B calculates the RA-RNTI as:RA-RNTI = 1 + s_id + 14 x t_id + 14 x 80 x f_id + 14 x 80x8 x ul_carrier_id where s_id is the index of the first 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 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 for NUL carrier, and 1 for SUL carrier).

[0117] In response to determining to command the UE 102 to perform an LTM cell switch or transmitting 456 the LTM Cell Switch Command, the S-DU 174A transmits 428 aDU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 performs an LTM cell switch to the cell 1. In response, the CU 172 transmits 430 a CU-DU Cell Switch Notification message to the C-DU 174B to indicate that the UE 102 performs an LTM cell switch to the cell 1. In some implementations, the S-DU 174A includes the first TCI state ID in the DU-CU Cell Switch Notification message and the CU 172 in turn includes 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 TC 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 during the events 432, 436 and / or 440.

[0118] In some implementations, each of the TCI state configuration(s) includes or is 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 includes 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 includes {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-PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 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 includes, in the LTM Cell Switch Command 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 fist TCI state ID. The UE 102 identifies the one of the TCI state configuration(s) based on the first TCI state ID and applies the first TCI state configuration in UL transmissions and / or DL receptions during the events 432, 436 and / or 440.

[0119] 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 procedure 490 or 492, as discussed with respect to Fig. 3.

[0120] In some implementations, the first CU-to-DU message and the first DU-to-CU message are a UE Context Setup Request message and a UE Context Setup Response message. In some implementations, the first CU-to-DU message and the first DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message. In some implementations, the LTM preparation procedure 490 is a UE Context Setup procedure and the additional LTM preparation procedure is a UE Context Modification procedure. In other implementations, the LTM procedure 490 and the addition LTM preparation procedures are UE Context Setup procedures. In yet other implementations, the LTM procedure 490 and the addition LTM preparation procedures are UE Context Modification procedures.

[0121] The events 404, 406, 490, 492, 494, 494, and 424 are collectively referred to in Fig.4 as an intra-CU inter-DU LTM configuration procedure 496. The events 404, 406, 490, 492, 494, 494, 424, 450, 452, 454456, 458, 426, 428, 430, 432, 434, 436, 438, 440, 442, and 444 are collectively referred to in Fig. 4 as an intra-CU inter-DU LTM procedure 480.

[0122] Referring next to Fig. 5A, in a scenario 500A, the base station 104A operates as a serving or source base station (S-BS), and the base station 106A operates as a candidate base station (C-BS). The C-BS 106A includes a CU 172 and a DU 174. The scenario 500A is similar to the scenarios 300 and 400, except that the scenario 500A is an inter-CU scenario (i.e., inter-base station scenario) while the scenarios 300 and 400 are intra-CU (i.e., intra-base station) scenarios. The S-BS 104A can include a CU and a DU (not shown in Fig. 5 A), similar to the base station 104 A of Figs. 3 and 4. Initially, the UE 102 communicates 502PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 with the S-BS 104A via serving cell(s) using a serving configuration (a first serving configuration). In some implementations, the S-BS 104A includes a S-DU and a CU and the serving configuration may include a serving CU configuration and a serving DU configuration, as discussed with respect to Figs. 3 and 4. While the communicating 502 with the UE 102, the S-BS 104A might perform 580 intra-CU LTM procedure(s) with the UE 102, similar to the procedures 380 and / or 480. Alternatively, while the communicating 502 with the UE 102, the S-BS 104A might perform 596 intra-CU LTM configuration procedure(s) with the UE 102, similar to the procedures 396 and / or 496.

[0123] While communicating with the S-BS 104 A, the UE 102 transmits 504 at least one measurement report to the S-BS 104A. The measurement report(s) include measurement results for a serving cell of the UE 102 and / or at least one non-serving cell (e.g., cell 126A). The S-BS 104A 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) include a PCI of the first cell and measurement result(s) of the cell 126A. The S-BS 104A identifies that the first cell is operated by the base station 106A based on the PCI, and determines that the first cell qualifies for LTM preparation based on the measurement result(s).

[0124] After (e.g., in response to) determining to prepare the first cell as an LTM candidate cell for the UE 102, the S-BS 104A (e.g., the CU of the S-BS 104A) generates a Handover Request message including a first cell ID (i.e., cell ID 1) of the first cell (i.e., cell 1). The S-BS 104A transmits 505 the Handover Request message to the CU 172. In some implementations, the Handover Request message includes 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 performs an LTM preparation procedure 590 with the DU 174A to prepare the first cell as an LTM candidate cell for the UE 102, similar to the procedure 390 or 490. In the procedure 590, the CU 172 transmits a first CU-to-DU message including the first cell ID to the DU 174A to request preparing the first cell, similar to the event 308. 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. The CU 172 generates a first LTM candidate configuration (LTM candidate configuration 1). In response to the Handover Request message, the CU 172 transmits 507 a Handover Request Acknowledge message including the first LTM candidate configuration to the S-BS 104A. In some implementations, the CU 172 includes the first cell ID in he Handover RequestPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 Acknowledge message to indicate that the first LTM candidate configuration is provided for or associated with the first cell (ID).

[0125] The events 505, 590, 507 are collectively referred to in Fig. 5A as an inter-CU LTM preparation procedure (or called inter-MN LTM preparation procedure) 598.

[0126] In some implementations, the Handover Request message includes a DU ID of the S-DU of the S-BS 104A. In such cases, the CU 172 includes the DU ID in the first CU-to-DU message. In some implementations, the Handover Request message includes a BS ID of the S-BS 104A. 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 is a gNB ID.

[0127] The CU 172 may or may not request an LTM reference DU configuration in the procedure 590, as discussed with respect to Figs. 3 and 4. The DU 174A may or may not transmit an LTM reference DU configuration to the CU 172 in the procedure 590, as discussed with respect to Figs. 3 and 4. In some implementations, the S-BS 104A (e.g., the CU of the S-BS 104A) may obtain an LTM reference configuration, as discussed with respect to Figs. 3 and 4. In other implementations, the S-BS 104A may receive an LTM reference configuration from another BS (not shown in Fig. 5A) in another inter-CU LTM preparation procedure as described above and below. If the S-BS 104A obtains an LTM reference configuration, the S-BS 104A may include the LTM reference configuration (S-BS generated LTM reference configuration) in he Handover Request, message. In some implementations, the S-BS 104 A includes the LTM reference configuration in the inter-node RRC message HandoverPreparationlnformation or as an Xn Application Protocol (XnAP) IE or field and includes the inter-node RRC message or the XnAP IE in the Handover Request message. Alternatively, the S-BS 104A determines to request or cause the C-BS 106A to provide a complete LTM candidate configuration so that the S-BS 104A does not include the LTM reference configuration in the Handover Request message. If the S-BS 104A does not obtain an LTM reference configuration, the S-BS 104 A 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 174A may extract an LTM reference DU configuration from the LTM reference configuration. Alternatively, the CU 172 extracts an LTM reference DU configuration from the LTM reference configuration and includes the LTM reference DU configuration in the first CU-to-DU message. The DU 174A mayPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 generate an LTM DU configuration as a delta configuration based on the LTM reference DU configuration, as discussed with respect to Fig. 3. Alternatively, the DU 174A may ignore the LTM reference (DU) configuration and generate an LTM DU configuration as a complete configuration, as discussed with respect to Fig. 3.

[0128] Otherwise, if the Handover Reques message does not include an LTM reference configuration, the CU 172 may or may not receive an LTM reference DU configuration from the DU 174A as discussed 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 generates 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). Otherwise, if the CU 172 does not receive an LTM reference DU configuration from the DU 174A as discussed with respect to Fig. 3, the CU 172 does not generate an LTM reference configuration.Alternatively, the CU 172 generates an LTM reference configuration (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 (C-BS generated LTM reference configuration), the CU 172 includes the C-BS generated LTM reference configuration in the Handover Request Acknowledge message.

[0129] In some implementations, if the LTM DU configuration 1 is a complete configuration, the CU 172 generates 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 / 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 defined in 3GPP specification 38.423. In some implementations, the complete configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the complete configuration indication is an existing field / IE defined in 3GPP specification 38.423. Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU 172 generates 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, the CU 172 may include a delta configuration indication (e.g., a BS-to-BS interface protocol field / IE) in the Handover RequestPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 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 defined in 3GPP specification 38.423. In some implementations, the delta configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the delta configuration indication is an existing field / IE defined in 3GPP specification 38.423. In some implementations, the BS-to-BS interface protocol field / IE have two values (i.e., a first value and a second value). The BS-to-BS interface protocol field / IE set to the first value is the complete configuration indication and the BS-to-BS interface protocol field / IE set to the second value is the delta configuration indication.

[0130] In some implementations, the S-BS 104A is 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 104A receives 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 104A receives the CSI resource configuration and / or the LTM SSB configuration from the CU 172. For example, the CU 172 includes the CSI resource configuration and / or the LTM SSB configuration in the Handover Request Acknowledge message. In some implementations, the CU 172 includes a PCI (PCI 1) of the first cell in he Handover Request Acknowledge message. To prepare the first cell as a candidate LTM cell for the UE 102, the CU of the S-BS 104A performs an LTM CSI report configuration and / or LTM ID configuration procedure (not shown in Fig. 5 A) with a S-DU of the S-BS 104A, similar to the procedure 392. In the LTM CSI report configuration and / or LTM ID configuration procedure, the CU of the S-BS 104A transmits the CSI resource configuration and / or the LTM SSB configuration to the S-DU of the S-BS 104A. In response, the CU of the S-BS 104A receives one or more CSI report configurations for the UE 102 from the S-DU of the S-BS 104A. In some implementations, the CU of the S-BS 104A receives the CSI report configuration(s) in a second serving DU configuration from the S-DU.

[0131] To prepare the first cell as an LTM candidate cell for the UE 102, the CU 172 may receive early synchronization information (early synchronization information 1) for the first cell from the DU 174A 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 174A transmits the additional DU-to-CU message in response to receiving an additional CU-to-DU messagePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 from the CU 172. In other implementations, the DU 174A transmits 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 includes the early synchronization information in the Handover Request Acknowledge message. The early synchronization information includes a RACH configuration (RACH configuration 1) and / or at least one TCI state configuration (TCI state configuration(s) 1). In some implementations, the DU 174A includes, 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 includes the PDCCH order information in the Handover Request Acknowledge message.

[0132] In some implementations, the CU 172 assigns an LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration and includes the LTM ID in the Handover Request Acknowledge message. In other implementations, the S-BS 104A assigns an LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration.

[0133] After (e.g., in response to) receiving the Handover Request Acknowledge message, the S-BS 104A (e.g., the CU of the S-BS 104A) transmits 518 a first RRC reconfiguration message to the UE 102, including {the LTM ID 1, the LTM candidate configuration 1} as a tuple, similar to the event 318. If the Handover Request Acknowledge message includes the LTM reference configuration, the S-BS 104A may include the LTM reference configuration in the first RRC reconfiguration message. The S-BS 104A may include the CSI resource configuration 1, the TCI state configuration(s) 1, the RACH configuration 1, and / or the LTM SSB configuration 1 in the tuple, if received in the Handover Request Acknowledge message. Alternatively, the S-BS 104A transmits 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 104A includes 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. The UE 102 transmits 520 a first RRC reconfiguration complete message to the S-BS 104A in response to the first RRC reconfiguration message. The UE 102 transmits an additional RRC reconfiguration complete message to the S-BS 104 A in response to each of the additional RRC reconfiguration complete message. The RRC reconfiguration message(s) (i.e., the first RRC reconfiguration message and / or the additional RRC reconfiguration message(s)) and thePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 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 104A may include the second serving DU configuration in the first RRC reconfiguration message or one or the additional RRC reconfiguration message(s).

[0134] 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 104A includes, in the first RRC reconfiguration message, a complete configuration indication (e.g., an RRC field / IE) to indicate that the LTM candidate configuration 1 is a complete configuration. Otherwise, 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 delta configuration, the S-BS 104A excludes or does not include, in the first RRC reconfiguration message, the complete configuration indication (e.g., an RRC field / IE) to indicate that the LTM candidate configuration 1 is a delta configuration.

[0135] If the Handover Request Acknowledge message includes the PDCCH order information (PDCCH order information 1), the S-BS 104A transmits 550 a PDCCH order, based on the PDCCH order information. If the S-BS 104A is a distributed base station, the CU of the S-BS 104A may transmit the PDCCH order information to the S-DU of the S-BS 104A. For example, the S-BS 104A or the S-DU of the S-BS 104A transmits 550 a PDCCH order to the UE 102, including the PDCCH order information. In some implementations, the S-BS 104A or the S-DU of the S-BS 104A may determine a SSB index included in the PDCCH order, based on LI or L3 measurement report(s) (event 524), 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-BS 104A includes the LTM ID 1 in the PDCCH order to indicate the first cell. The UE 102 transmits 552 a RA preamble to the DU 174A on the first cell, using the RACH configuration and / or the PDCCH order information. The S-DU or the S-BS 104A derives a TA value based on the RA preamble. The DU 174A transmit 556 aDU-CU TA Information Transfer message including the TA value to the CU 172. The CU 172 transmits 558 a CU-CU TA Information Transfer message including the TA value to the S-BS 104A (e.g., the CU of the S-BS 104A). In some implementations, the DU 174A includes the cell ID 1, the RA preamble index, a RA-RNTI, the DU ID of the S-DU of the S-BS 104A, and / or the BS ID of the S-BS 104A in the message 556. In some implementations, the DUPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 174A does not include the BS ID in the message 556. In some implementations, the CU 172 includes 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 104A in the message 558. In some implementations, the CU 172 does not include the BS ID in the message 558. The CU of the S-BS 104A transmits 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 104A to the S-DU of the S-BS 104A. In some implementations, the CU of the S-BS 104A does not include the BS ID in the CU-DU TA Information Transfer message.

[0136] The events 524, 550, 552, 556, and 558 are collectively referred to in Fig. 5A as an early TA acquisition procedure 582.

[0137] In some implementations, the CU 172 determines an address (e.g., an IP address) of the S-BS 104A or the CU of the S-BS 104A, based on the BS ID of the S-BS 104A. In other implementations, the CU 172 determines an address (e.g., an IP address) of the S-BS 104A or the CU of the S-BS 104A, based on the DU ID of the S-DU of the S-BS 104A. With these implementations, the CU 172 sends the CU-CU TA Information Transfer message to the S-BS 104A or the CU of the S-BS 104A in accordance with the address.

[0138] 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) (event 524 and / or 554), the S-DU or the S-BS 104A transmits 526 the LTM Cell Switch Command including the LTM ID 1 to the UE 102. The S-DU may transmit 528 a Cell Switch Notification message to the CU, indicating that the LTM cell switch to the first cell is triggered for the UE 102. In response to the LTM Cell Switch Command, the UE 102 may stop communication on the serving cell(s). In response to the LTM Cell Switch Command, the UE 102 accesses 532 the first cell and transmits 536 an RRCreconfiguration complete message to DU 174. The DU 174A in turn transmits 538 a DU-to-CU message including the RRC reconfiguration complete message to the CU 172. After receiving 538 the DU-to-CU message or the RRC reconfiguration complete message, the C-BS 106A communicates 540 with the UE 102 in accordance with the first LTM candidate configuration and / or the LTM reference configuration. In some implementations, the UE 102 includes 536 the LTM ID 1 in the RRC reconfiguration complete message 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 172PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 identifies the first LTM candidate configuration and / or the LTM reference configuration based on the first cell ID included 534 in the Access Success message. 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.

[0139] In some implementations, after (e.g., in response to) event 532, 534, 538 and / or 541, the CU 172 performs a Path Switch procedure with the CN 110 (not shown in Fig. 5A). In the Path Switch procedure, the CU 172 sends a Path Switch Request message to the CN 110 (e.g., AMF). The Path Switch Request message is to establish a UE associated signaling connection for the UE 102 between the CU 172 and the AMF and request a switch of a downlink termination point of a UP transport bearer (e.g., NG-U transport bearer) from an old termination point (e.g., the S-BS 104A or the S-CU of the S-BS 104A) towards a new termination point (e.g., the CU 172). In response to the Path Switch Request message, the CN 110 (e.g., AMF) establishes a UE associated signaling connection for the UE 102 with the CU 172 and switches the downlink termination point of the UP transport bearer from the old termination point towards the new termination point. In response to the Path Switch Request message, the CN 110 (e.g., AMF) transmits a Path Switch Request Acknowledge message to the CU 172. After the Path Switch procedure, the CN 110 (e.g., UPF) communicates UP data with the UE 102 via the S-BS 106A and the UP transport bearer.

[0140] In some implementations, if the S-DU or the S-BS 104A receives a TA value as described above, the S-DU or the S-BS 104A may include the TA value in the LTM Cell Switch Command. In some implementations, the S-DU or the S-BS 104A includes a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID indicates a first one of the TCI state configuration(s).

[0141] In response to determining to command the UE 102 to perform the LTM cell switch or transmitting 526 the LTM Cell Switch Command, the S-DU of the S-BS 104A transmits a DU-CU Cell Switch Notification message to the CU of the S-BS 104A to indicate that the UE 102 performs or is performing an LTM cell switch to the first cell. In response to receiving the DU-CU Cell Switch Notification message, the CU of the S-BS 104A transmits 527 a CU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 performs anPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 LTM cell switch to the first cell. In response, the CU 172 transmits 530 a CU-DU Cell Switch Notification message to the DU 174A to indicate that the UE 102 performs an LTM cell switch to the first cell. In some implementations, the S-BS 104A includes the first TCI state ID in the CU-CU Cell Switch Notification message and the CU 172 then includes the first TCI state ID in the CU-DU Cell Switch Notification message. The UE 102 and the DU 174A identify the first one of the TC 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 during the events 532, 536 and / or 540.

[0142] In some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting 526 the LTM Cell Switch Command, or receiving 527 the DU-CU Cell Switch Notification message, the S-BS 104A (e.g., the CU of the S-BS 104A) transmits 531 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 104A communicate 502 data with each other. In some implementations, after receiving 534 the Access Success message or receiving 538 the DU-to-CU message or the RRC reconfiguration complete message, the CU 172 transmits 539 an LTM Success message to the S-BS 104A (e.g., the CU of the S-BS 104A) to indicate that the LTM cell switch is completed successfully. In some implementations, the LTM Success message is a Handover Success message. In some implementations, the CU 172 includes 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 104A (e.g., the CU of the S-BS 104A) to indicate that the LTM cell switch is completed successfully.

[0143] In some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting 526 the LTM Cell Switch Command, receiving 527 the DU-CU Cell Switch Notification message, or receiving 539 the LTM Success message, the S-BS 104A (e.g., the CU of the S-BS 104A) transmits 541 an SN Status Transfer message to the CU 172, including a DL COUNT value and / or a UL COUNT value for a / the DRB over which the UE 102 and the S-BS 104A communicate 502 data with each other.

[0144] In some implementations, after (e.g., in response to) receiving 534 the Access Success message, receiving 538 the DU-to-CU message or the RRC reconfiguration complete message or receiving 541 the SN Status Transfer message, the CU 172 transmits 543 a UEPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 Context Release message to the S-BS 104A. In response to the UE Context Release message, the S-BS 104 A releases a UE context of the UE 102.

[0145] In some implementations, the S-BS 104A (e.g., the CU of the S-BS 104A) 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 procedure 598, as described above. The cell(s) 2, ..., N are identified by cell ID(s) 2, ..., N, respectively and operated by the DU 174A and / or other DU(s) of the C-BS 106A. N is an integer and larger than 1. For example, the S-BS 104A performs 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 procedure 598. In the inter-CU LTM preparation procedure(s) 2, ..., N, the S-BS 104A receives LTM candidate configuration(s) 2, ..., N configuring the cell(s) 2, ..., N for LTM, respectively. As described above, the S-BS 104A or the C-BS 106A assigns LTM ID(s) 2, ..., N to identify the LTM candidate configuration(s) 2, ..., N, respectively. The S-BS 104A may obtain CSI resource configuration 2, ,..., N for the cell(s) 2, ..., N respectively, as discussed with respect to the CSI resource configuration 1. The S-BS 104A may obtain CSI report configuration(s) 2, ..., N or the cell(s) 2, ..., N, respectively, as discussed with respect to the CSI report configuration(s) 1. The S-BS 104A may obtain RACH configuration 2, ..., N for the cell(s) 2, ..., N respectively, as discussed with respect to the RACH configuration 1. The S-BS 104A may obtain TCI state configuration(s) 2, ..., N for the cell(s) 2, ..., N respectively, as discussed with respect to the TCI state configuration(s) 1. The S-BS 104A may obtain LTM SSB configuration 2, ..., N for the cell(s) 2, ..., N, respectively, as discussed with respect to LTM SSB configuration 1. The S-BS 104A may obtain PCI(s) 2, . .. , N for the cell(s) 2, ... , N respectively, as discussed with respect to the PCI 1. In some implementations, the S-BS 104A may perform LTM configuration delivery procedure 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 procedure 2, ..., N is similar to thePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 procedure 394 or 494. In other implementations, the S-BS 104A includes the list in the first RRC reconfiguration message.

[0146] In other implementations, the S-BS 104A performs the procedure 598 with the CU 172 to prepare one or more of the cell(s) 1, ..., N as LTM candidate cell(s) for the UE 102. In such implementations, the S-BS 104A includes the cell ID(s) 1, ..., N in the Handover Request message (event 505) for LTM, as discussed with respect to the cell ID 1. In some implementations, upon receiving the Handover 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 Handover Request message. The CU 172 performs LTM preparation procedure(s) 2, ..., M with the DU 174A 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 590 that the CU 172 performs with the DU 174A to prepare the cell 1. The CU 172 obtains 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-BS 106A 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 discussed with respect to the LTM candidate configuration 1. The CU 172 includes the LTM candidate configuration(s) 2, ..., M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 104A assigns LTM ID(s) 2, ..., M to identify the LTM preparation procedure(s) 2, ..., M respectively, as discussed with respect to the LTM ID 1. In the case the CU 172 assigns the LTM ID(s) 1, ..., M, the CU 172 includes the LTM ID(s) 1, ..., M with the LTM candidate configuration(s) 1, ..., M, respectively in he Handover Request Acknowledge message, as discussed with respect to the LTM ID 1 and the LTM candidate configuration 1.

[0147] In some implementations, the CU 172 obtains early synchronization information 2, ..., M for the cell(s) 2, ..., M, respectively, as discussed with respect to the early synchronization information 1. The CU 172 includes the early synchronization information 2, ..., M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 104A obtains CSI resource configuration(s) 2, ..., M for the cell(s) 2, ..., M, respectively, as discussed with respect to the CSI resource configuration 1. In the case that the CU 172 obtains the CSI resource configuration(s) 2, ..., M, the CU 172 includes the CSI resource configuration(s) 2, ..., M in the Handover Request Acknowledge message.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0148] In some implementations, the CU 172 or the S-BS 104A obtains LTM SSB configuration(s) 2, .. M for the cell(s) 2, .. M, respectively, as discussed with respect to the LTM SSB configuration 1. In the case that the CU 172 obtains the LTM SSB configuration(s) 2, ..., M, the CU 172 includes the LTM SSB configuration(s) 2, ..., M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 104A obtains PCI(s) 2, ..., M for the cell(s) 2, ..., M, respectively, as discussed with respect to the PCI 1. In the case that the CU 172 obtains the PCI(s) 2, ..., M, the CU 172 includes the PCI(s) 2, ..., M in the Handover Request Acknowledge message.

[0149] In some implementations, the CU 172 includes a list of {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 Handover Request Acknowledge message.

[0150] In some implementations, the CU 172 obtains PDCCH order information 2, ..., M for the cell(s) 2, ..., M, respectively, as discussed with respect to the PDCCH order information 1. In one implementation, the CU 172 includes the PDCCH order information 2, ..., M in the Handover Request Acknowledge message. In another implementation, the CU 172 includes the PDCCH order information 2, ..., M in the early synchronization information 2, ..., M, respectively. The S-BS 104A 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.

[0151] In some implementations, the S-BS 104A may perform LTM configuration delivery procedure 2, ..., M 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 (ifPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 obtained), the PCI 2 (if obtained)}, ..., {the LTM ID M, the LTM candidate configuration M, the CSI resource configuration M, the TCI state configuration(s) M (if obtained), the RACH configuration M (if obtained), the LTM SSB configuration M (if obtained), the PCI M (if obtained)} to the UE 102, respectively. Each of the LTM configuration delivery procedure 2, ..., M is similar to the procedure 394 or 494. In other implementations, the S-BS 104A includes the list in the first RRC reconfiguration message.

[0152] In some implementations, the S-BS 104A may include measurement result} s) 1, ..., N for the cell(s) 1 , ... , N respectively in the Handover Request message. The S-BS 104A receives the measurement result(s) from the UE 102. The C-BS 106A may select or determine the cell(s) 1, ...M, based on the measurement result(s) 1, ..., N. In other implementations, the C-BS 106A 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.

[0153] The events 527, 530, 531, 532, 534, 536, 538, 539, 541, 540, and 543 are collectively referred to in Fig. 5A as an LTM cell switch execution procedure 584.

[0154] Referring next to Fig. 5B which depicts a scenario 500B, similar to Fig. 5A. Before triggering an LTM cell switch to the first cell, the S-BS 104A receives 570 a PDU Session Resource Request message from the CN 110 (e.g., an AMF), requesting to manage (e.g., set up or modify) resources for the UE 102. The PDU Session Resource Request message may be a PDU Session Resource Setup Request message or a PDU Session Resource Modify Request message. In some implementations, the PDU Session Resource Request message includes PDU Session related information, e.g., PDU Session setup, modification or release information.

[0155] Based on the PDU Session Resource Request message, the S-BS 104A determines to set up new radio resources or modify radio resources configured for the UE 102 (e.g., determines to update the first serving configuration in event 502). In response to the determination, the S-BS 104A generates 574 a second serving configuration to update the first serving configuration. The S-BS 104A then transmits 576 an RRCreconfiguration message including the second serving configuration to the UE 102. In response, the UE 102 updates (e.g., replaces, modifies, or augments) the first serving configuration with the secondPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 serving configuration and transmits 578 an RRC reconfiguration complete message to the S-BS 104A. The UE 102 then communicates with the S-BS 104A using the updated serving configuration. The updated serving configuration includes the second serving configuration and optionally at least a portion of the first serving configuration (i.e., not augmented by the second serving configuration).

[0156] If the S-BS 104A includes a CU and a DU, the first serving configuration includes a first serving CU configuration and a first serving DU configuration. In this case, the CU may perform a UE Context Modification procedure with the DU to obtain a second serving DU configuration from the DU to update the first serving DU configuration. In the UE Context Modification procedure, the CU transmits a UE Context Modification Request message to the DU, including radio resource information (e.g., SRB setup or modification information, and / or DRB setup or modification information). In response, the DU generates the second serving DU configuration. In some implementations, the CU may generate a second CU configuration to update the first serving CU configuration. In such cases, the second serving configuration includes the second serving DU configuration and / or the second serving CU configuration. Examples and implementations described above for a DU configuration can apply to the first serving DU configuration and the second serving DU configuration.Examples and implementations described above for a CU configuration can apply to the first serving CU configuration and the second serving CU configuration. To simplify the following description, the “serving configuration” can represent the “serving DU configuration” and / or the “serving CU configuration).

[0157] In response to the PDU Session Resource Request message, the S-BS 104A transmits 572B a PDU Session Resource Response message to the CN 110, indicating success to set up or modify resources for the UE 102. In some implementations, the S-BS 104A transmits 572B the PDU Session Resource Response message after event 574, 576, or 578.

[0158] In some implementations, if the first serving configuration is updated, the S-BS 104A may suspend 585 triggering an LTM cell switch for the UE 102. In some implementations, the DU of the S-BS 104A suspends 585 triggering an LTM cell switch for the UE 102 in response to performing the UE Context Modification procedure. In some implementations, the CU of the S-BS 104A includes an LTM suspend indication in the UE Context Modification Request message to the DU, indicating suspension of an LTM cellPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 switch for the UE 102. The DU suspends 585 triggering an LTM cell switch for the UE 102 in response to the LTM suspend indication. In other implementations, in response to event 574 or 586, the CU transmits a CU-to-DU message to the DU, indicating to suspend an LTM cell switch for the UE 102. In some implementations, the CU-to-DU message may be a F1AP message defined in 3GPP specification 38.473 vl 8.5.0 or a later version. In other implementations, the CU-to-DU message is a UE Context Modification Request message including the LTM suspend indication.

[0159] In some implementations, if the first serving configuration is updated, (the CU of) the S-BS 104A may determine 586 to update the LTM candidate configuration(s) 1, ..., K configured for the UE 102 as described above. K is an integer and 0 < K < N. The S-BS 104A may determine to do so because the S-BS 104A needs to update the LTM candidate configuration(s) to align with the second serving configuration. For example, the second serving includes a SRB configuration configuring a new SRB, a DRB configuration configuring a new DRB, a REC configuration for the new SRB, and / or a RLC configuration for the new DRB, and the LTM candidate configuration(s) 1, ..., K do not include configurations for the new SRB and / or the new DRB. In another example, the LTM candidate configuration(s) 1, ..., K includes configurations for a SRB and / or a DRB, and the second serving configuration releases the SRB and / or DRB.

[0160] In response to the determination 586, the S-BS 104A performs 58 IB one or more LTM modification procedure(s) with the C-BS 106A and / or other C-BS(s) and the UE 102 to update the LTM candidate configuration(s) 1, ..., K, similar to the procedure 581 A. In the LTM modification procedure(s), the S-BS 104A obtains LTM candidate configuration(s) 1’, .. ., K’ and transmits the LTM candidate configuration(s) 1’, ..., K’ to the UE 102. The UE 102 updates (e.g., replaces, modifies, or augments) the LTM candidate configuration(s) 1, ..., K, with the LTM candidate configuration(s) 1’, ..., K’, respectively. After performing the LTM modification procedure(s), the S-BS 104A may resume 587 triggering an LTM cell switch for the UE 102. In some implementations, the CU of the S-BS 104A transmits a CU-to-DU message to the DU 174A of the S-BS 104A, indicating to resume an LTM cell switch for the UE 102. The DU resumes 587 triggering an LTM cell switch for the UE 102 in response to the LTM resume indication. In some implementations, the CU-to-DU message may be a F1AP message defined in 3GPP specification 38.473 vl8.5.0 or a later version. In other implementations, the CU-to-DU message is a UE Context Modification Request message including the LTM resume indication.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0161] In some implementations, events 576 and 578 can be combined into the LTM modification procedure(s) 58 IB. For example, the RRC reconfiguration message (event 576) can include the second serving configuration and at least one of the LTM candidate configuration(s) 1’, ..., K’.

[0162] After updating the LTM candidate configuration(s) 1, ..., K, the S-BS 104A may trigger an LTM cell switch for the UE 102 as discussed with respect to Fig. 5 A.

[0163] The events 570, 572B, 574, 576, 578, 585, 586, 58 IB, and 587 are collectively referred to in Fig. 5B as a PDU Session Resource management procedure 588B.

[0164] Referring next to Fig. 5C which depicts a scenario 500C, similar to Figs. 5A and 5B. Based on the LI or L3 measurement report, the S-BS 104A determines to trigger an LTM cell switch to the first cell as discussed with respect to Fig. 5 A. If the S-BS 104A includes a CU and a DU, the CU may receive 528 a DU-CU Cell Switch Notification message from the DU in response to the determination or event 526, similar to events 328 and 428. After the determination or event 526 or 528, or before completing the LTM cell switch execution procedure 584, the S-BS 104A receives 570 the PDU Session Resource Request message from the CN 110. In response, the S-BS 104A transmits 572C a PDU Session Resource Response message to the CN 110, indicating failure to set up or modify resources for the UE 102. In this case, the S-BS refrains from updating the first serving configuration. In some implementations, the S-BS 104A includes a cause in the PDU Session Resource Response message, indicating that the failure is due to an LTM triggered or an LTM cell switch triggered. In some implementations, the S-BS 104A includes a cause in the PDU Session Resource Response message, indicating that the failure is due to a handover triggered (e.g., Xn handover triggered). After S-BS 104A, the C-BS 106A and the UE 102 complete 584 the LTM cell switch execution procedure, the C-BS 106A becomes a S-BS for the UE 102 and the CN 110 may perform 588C another PDU Session Resource procedure with the S-BS 106A and the UE 102, similar to the procedure 588B.

[0165] Referring next to Fig. 6A, in a scenario 600A, the base station 104B operates as an MN, the base station 106 A operates as a candidate SN (C-SN) and the base station 104A operates as a serving or source SN (S-SN). The MN 104B includes a CU 172 and a DU 174. The C-SN 106A and the S-SN 104A might include a CU and a DU (not shown in Fig. 6A) similar to the C-BS 106A in the Fig. 5 A. The scenario 600A is similar to the scenario 500A,PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 except that the scenario 600A is a DC scenario and the scenario 500A is a single connectivity scenario.

[0166] Initially, the UE 102 in DC communicates 602 with the MN 104B and with S-SN 104A. In some implementations, the UE 102 communicates with the DU of the S-SN 104A on cell 124A using a serving DU configuration and communicates with the CU of the S-SN 104A via the DU of the S-SN 104A using a serving CU configuration, similar to the event 302. In some implementations, the UE 102 in DC can communicate 602 UL PDUs and / or DL PDUs with the MN 104B and / or S-SN 104A via radio bearers which can include SRBs and / or DRB(s). The MN 104B and / or the S-SN 104A can configure the radio bearers to the UE 102. The UE 102 in DC communicates 602 UL PDUs and / or DL PDUs with the S-SN 104A on an SCG (i.e., SCG radio resources) that the S-SN 104A configures for communication with the UE 102. The UE 102 in DC communicates UL PDUs and / or DL PDUs with the MN 104B on an MCG (i.e., MCG radio resources) in accordance with a (serving) MN configuration (i.e., first serving MCG configuration). In some implementations, the serving DU configuration is a first SN configuration (i.e., first serving SCG configuration). In the MN configuration, the MN 104B configures the MCG which includes at least one serving cell (e.g., the cell 124B and / or other cell(s)) operated by the MN 104B. In the serving DU configuration, the S-SN 104A 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 104A. In some implementations, the MN configuration includes multiple configuration parameters and the UE 102 receives the configuration parameters in one or more RRC messages from the MN 104B. As discussed with respect to Fig. 3, the serving DU configuration includes multiple configuration parameters. In some implementations, the UE 102 receives these configuration parameters in one or more RRC messages from the S-SN 104A, e.g., via the MN 104B and / or on an SRB (e.g, SRB3) that the MN 104B or S-SN 104A configures to exchange RRC messages between the UE 102 and the S-SN 104A.

[0167] While communicating with the UE 102 in DC with the MN 104B and S-SN 104A, the S-SN 104A can perform 696 an intra-CU LTM configuration with the UE 102, similar to the procedures 396 and / or 496. While communicating with the UE 102 in DC with the MN 104B and S-SN 104A, the S-SN 104A can perform 680 an intra-CU LTM procedure with the UE 102, similar to the procedures 380 and / or 480. In the procedure 696 or 680, the CU of the S-SN 104A 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 procedurePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 394 or 494. Alternatively, the CU of the S-SN 104A may transmit one or more RRC reconfiguration messages, each including one or more LTM candidate configurations, to the UE 102 via the MN 104B. In response to each of the RRC reconfiguration message(s), the UE 102 transmits an RRCreconfiguration complete message to the S-SN 104A via the MN 104B.

[0168] While communicating in DC with the MN 104B and S-SN 104A, the UE 102 can transmit 604-1 at least one measurement report to the S-SN 104A directly, e.g. via the SRB3, similar to the events 304 / 306, the events 404 / 406 and the event 504. Alternatively, the UE 102 can transmit 604-2 the measurement report(s) to the MN 104B. The measurement report(s) include one or more measurement results of the first cell. In some implementations, the MN 104B generates at least one SN message including the measurement report(s) and transmits 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 104A (e.g., the CU of the S-SN 104A) generates a measurement configuration to configure the UE 102 to transmit the measurement report(s) and transmits the measurement configuration to the UE 102 directly (e.g., via the S-DU of the S-SN 104A) or via the MN 104B. Alternatively, the MN 104B generates a measurement configuration to configure the UE 102 to transmit the measurement report(s) and transmits the measurement configuration to the UE 102 directly (e.g., via the S-DU of the MN 104B)

[0169] In some implementations, based on the measurement report(s) received from the UE 102, the S-SN 104A (e.g., the CU of the S-SN 104A) determines to request the C-SN 106A preparing a first cell (e.g., the cell 126A) as an LTM candidate cell for the UE 102. In response to the determination, the S-SN 104A generates an SN Required message (a first SN Required message) including a first cell ID (i.e., cell ID 1) of the first cell. In some implementations, the S-SN 104A includes an LTM indicator in the SN Required message, indicating the SN Required message is sent for LTM. In some implementations, the S-SN 104A includes a C-SN ID (as a target SN ID) indicating the C-SN 106A in the SN Required message. In some implementations, the S-SN 104A includes the one or more measurement results of the first cell in the SN Required message. The S-SN 104A transmits 603 the SN Required message to the MN 104B. In some implementation, the one or more measurement results include the cell ID 1 and its corresponding measurement quantity results (e.g., a candidateCelllnfoListSN fleld / IE or MeasResultList2NR IE). After (e.g., in response to) receiving the SN Required message, the MN 104B transmits 605 an SN Request message (aPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 first SN Request message) including the one or more measurement results of the first cell to the C-SN 106A to request preparing the first cell as an LTM candidate cell for the UE 102. In other implementations, the MN 104B transmits 605 the SN Request message based on the measurement report(s) that the MN 104B received 604-2 from the UE 102.

[0170] In response to the SN Request message 603, the C-SN 106A performs an LTM preparation procedure 690 to prepare the first cell as an LTM candidate cell for the UE 102, similar to the procedure 390, 490 or 590. In the procedure 690, if the C-SN 106A consists of a CU and a DU, the CU of the C-SN 106A transmits a first CU-to-DU message including the first cell ID to the DU of the C-SN 106A to request preparing the first cell, similar to the event 308. In response, the CU of the C-SN 106A may receive a first DU-to-CU message including an LTM DU configuration 1 from the DU of the C-SN 106A, similar to the event 310. The CU of the C-SN 106A generates a first SCG LTM candidate configuration (SCG LTM candidate configuration 1) including the LTM DU configuration 1. In response to the SN Request message, the (CU of the) C-SN 106A transmits 607 an SN Request Acknowledge message (a first SN Request Acknowledge message) including the first SCG LTM candidate configuration and the cell ID 1 to the MN 104B. In some implementations, the C-SN 106A includes a SCG LTM reference configuration in the SN Request Acknowledge message. The C-SN 106A may do so if the SN Request message includes a reference configuration request indicator. The reference configuration request indicator requests or indicates to the C-SN 106A to provide a SCG LTM reference configuration. If the C-SN 106A supports the reference configuration request indicator, the C-SN 106A includes the SCG LTM reference configuration in the SN Request Acknowledge message. In this case, the C-SN 106A generates the first SCG LTM candidate configuration augmenting the SCG LTM reference configuration. The C-SN 106A may include an indicator in the SN Request Acknowledge message, indicating that the first SCG LTM candidate configuration is a delta configuration. Otherwise, if the C-SN 106A does not support the reference configuration request indicator, the C-SN 106A does not include the SCG LTM reference configuration in the SN Request Acknowledge message. In this case, the C-SN 106A generates the first SCG LTM candidate configuration as a complete configuration and may include an indicator in the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is a complete configuration. In some implementations, the MN 104B transmits 609 an SN Confirm message to the S-SN 104A in response to the SN Required message.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0171] In some implementations, the C-SN 106A includes one or more LTM CSI resource configuration(s) (the LTM CSI resource configuration 1) for the first cell in the SN Request Acknowledge message. In some implementations, the CU of the C-SN 106A is preconfigured with the LTM CSI resource configuration(s). In other implementations, the CU receives the LTM CSI resource configuration(s) from the DU of the C-SN 106A, where the DU operates the first cell. In yet other implementations, the CU receives the LTM CSI resource configuration(s) from an 0AM node.

[0172] In some implementations, the SN Request message includes a SCG LTM reference configuration. If the C-SN 106A supports to use a SCG LTM reference configuration, the C-SN 106A generates the first SCG LTM candidate configuration augmenting the SCG LTM reference configuration. The C-SN 106A may include a delta configuration indication in the SN Request Acknowledge message, indicating that the first SCG LTM candidate configuration is a delta configuration. Alternatively, the C-SN 106A excludes a complete configuration indication in the SN Request Acknowledge message, indicating that the first SCG LTM candidate configuration is a delta configuration. In this case, the C-SN 106A does not include a SCG LTM reference configuration in the SN Request Acknowledge message. Otherwise, if the C-SN 106A does not support to use a SCG LTM reference configuration, the C-SN 106A generates the first SCG LTM candidate configuration as a complete configuration. In this case, may include a complete configuration indication in the SN Request Acknowledge message, indicating that the first SCG LTM candidate configuration is a complete configuration.

[0173] In some implementation, the C-SN 106A includes the first SCG LTM candidate configuration, the cell ID 1, and / or the SCG LTM reference configuration in a CG-Config IE or a CG-Configlnfo IE and includes the CG-Config IE or CG-Configlnfo IE in the SN Request Acknowledge message. In some implementations, the CU 172 includes the cell ID 1 in the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is provided for or associated with the first cell (i.e., the cell ID 1).

[0174] In some implementations, after (e.g., in response to) receiving 607 the SN Request Acknowledge message, the CU 172 transmits 660, to the DU 174A of the MN 104B, a CU-to-DU message (e.g., a UE Context Modification Request message). In some implementations, the CU 172 includes an LTM indicator indicating ‘LTM-preparation’, the cell ID 1 indicating the prepared first PSCell, the CG-Config IE, the CG-Configlnfo IE, thePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 first SCG LTM candidate configuration, and / or the SCG LTM reference configuration in the CU-to-DU message. In some implementations, the LTM indicator is an LTM Trigger lE / field. In some implementations, the LTM Trigger lE / filed is set to the value ‘LTM-preparation’. The CU 172 may include the LTM indicator in an Inter -SN LTM MCG Information IE or Inter-CU SCG LTM MCG Information IE included in the CU-to-DU message. Based on the information provided in the CU-to-DU message, the DU 174A of the MN 104B may generate an LTM MCG configuration for the UE 102 and the first cell. The DU 174A then transmits 662 a DU-to-CU message (e.g., UE Context Modification Response message) including the LTM MCG configuration to the CU 172. In some implementations, the DU 174A includes the cell ID 1 (e.g., in a Requested Target Cell ID field / IE) in the DU-to-CU message, indicating the LTM MCG configuration is associated with the first cell. In some implementations, the DU 174A includes the LTM MCG configuration in an existing field / IE included in the DU-to-CU message. The existing field / IE may be a CellGroupConfig IE or a DU to CU RRC Information IE defined in 3GPP specification 38.473 vl9.0.0 or later version. In other implementations, the DU 174A includes the LTM MCG configuration in a new container field / IE specifically for this purpose. The DU 174 A refrains from applying the LTM MCG configuration to communicate with the UE 102, until the DU 174A receives a further indication message (e.g., event 665 as described below) from the CU 172. The further indication message indicates the DU 174A to apply the LTM MCG configuration. In some alternative implementations, the DU 174A determines not to generate an LTM MCG configuration based on the information included in the CU-to-DU message. In such cases, the DU 174A transmits 662 a DU-to-CU message excluding (i.e., not including) an LTM MCG configuration to the CU 172 in response to the CU-to-DU message.

[0175] In some implementations, the DU 174A of the MN 104B generates a MCG LTM reference configuration based on the information in the CU-to-DU message (event 660) and includes the MCG LTM reference configuration in the DU-to-CU message (event 662). In some implementations, the CU 172 includes a reference configuration request indicator in the CU-to-DU message 660 to request a MCG LTM reference configuration. If the DU 174A supports the reference configuration request indicator, the DU 174A includes 662 the MCG LTM reference configuration in the DU-to-CU message. Otherwise, if the DU 174A does not support the reference configuration request indicator, the DU 174A refrains from including 662 a / the MCG LTM reference configuration in the DU-to-CU message.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0176] In some implementations, the MN 104B transmits 663 an SN Request message (e.g., SN Modification Request message) to the S-SN 104A, including 1) the LTM CSI resource configuration(s), 2) the first SCG LTM candidate configuration, 3) the SCG LTM reference configuration, 4) a configuration ID (e.g., LTM ID 1), and / or 5) the cell ID 1. In response, the S-SN 104A transmits 664 an SN Request Acknowledge message (e.g., SN Modification Request Acknowledge message) to the MN 104B. In some implementations, the MN 104B assigns the configuration ID for the first cell (i.e., the configuration ID is associated with the cell ID 1). The MN 104B configures the configuration ID to identify the LTM candidate configuration as discussed with respect to event 616. In other implementations, the S-SN 104A assigns the configuration ID for the first cell (i.e., the configuration ID is associated with the cell ID 1) and includes the configuration ID in the SN Required message. The S-SN 104A configures the configuration ID to identify the LTM candidate configuration as discussed with respect to event 616. The MN 104B associates the configuration ID (received from the S-SN 104A) with the LTM candidate configuration. In some alternative implementations, the S-SN 104A is preconfigured with the LTM CSI resource configuration(s). In other alternative implementations, the S-SN 104A receives the LTM CSI resource configuration(s) from the 0AM node.

[0177] In some implementations, the S-SN 104A (e.g., a DU of the S-SN 104A) generates a second SN configuration (e.g., a second SCG configuration or a second serving DU configuration) for the UE 102 based on the LTM CSI resource configuration(s) and includes the second SN configuration in the SN Request Acknowledge message. In some implementations, the S-SN 104A generates the second SN configuration as a delta configuration on top of the first SN configuration. In some implementations, the S-SN 104A generates one or more LTM CSI report configuration(s) for the UE 102 based on the LTM CSI resource configuration(s) and includes the LTM CSI report configuration(s) in the second SN configuration.

[0178] In some implementations, the SN Request message (event 663) includes 6) an LTM SSB configuration (e.g., a SSB Positions in Burst IE) for the first cell. In some implementations, the MN 104B receives 607 the LTM SSB configuration in the SN Request Acknowledge message from the C-SN 106A. In some alternative implementations, the SN Request message (event 663) does not include an LTM SSB configuration for the first cell. In this case, the S-SN 104A obtains a SSB configuration (similar to the LTM SSB configuration) for the first cell from the 0AM node. In yet other implementations, the S-SNPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 104A obtains the SSB configuration from the C-SN 106A in an Xn Setup procedure (i.e., the Xn Setup Request message and Xn Setup Response message) with the C-SN 106A. In yet other implementations, the S-SN 104A obtains the SSB configuration from the C-SN 106A in an NG-RAN node Configuration Update procedure (i.e., the NG-RAN node Configuration Update message and the NG-RAN node Configuration Update Acknowledge message) with the C-SN 106A. In some implementations, the S-SN 104A uses LTM SSB configuration or the SSB configuration to determine a TA value received for the UE 102 in the early TA acquisition procedure 682. In some implementations, the S-SN 104A uses the LTM SSB configuration to generate the LTM CSI report configuration(s).

[0179] In some implementations, the SN Request message (event 663) and SN Request Acknowledge message (event 664) are an LTM Configuration Update message and an LTM Configuration Update Acknowledge message, respectively.

[0180] In some alternative implementations, the MN 104B includes some or all of the above configurations 1) - 6) in the SN Confirm message instead of the SN Request message (event 663). If the MN 104B includes the LTM CSI resource configuration(s) in the SN Confirm message, the S-SN 104A may transmit an SN message including the second SN configuration to the MN 104B. In some implementations, the SN message is an SN Modification Required message. In response to the SN Modification Required message, the MN 104B may transmit an SN Modification Confirm message to the S-SN 104A. In other implementations, the SN message is an C JMransfer message.

[0181] In some implementations, the CU 172 generates an LTM candidate configuration (i.e., LTM candidate configuration 1) including the first SCG LTM candidate configuration and / or the LTM MCG configuration (if received from the DU 174A of the MN 104B in event 662) to configure the first cell for LTM. In some implementations, the LTM candidate configuration is a message (e.g., an RRCreconfiguration message). If the CU 172 receives the SCG LTM reference configuration and / or the MCG LTM reference configuration as described above, the CU 172 generates an LTM reference configuration (i.e., a container) including the SCG LTM reference configuration and / or the MCG LTM reference configuration. In some implementations, the LTM reference configuration is a message (e.g., an RRCreconfiguration message). The CU 172 generates at least one RRC reconfiguration message(s) for the UE 102, including the second SN configuration, a tuple of the LTM candidate configuration and a configuration ID, and / or the LTM reference configuration. ThePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 CU 172 transmits 616 the RRC reconfiguration message(s) to the UE 102 via the DU 174, similar to events 316 and 318. In response to each of the RRC reconfiguration message(s), the UE 102 transmits 620 an RRC reconfiguration complete message to the CU 172 via the DU 174, similar to events 320 and 322. After receiving 620 the RRC reconfiguration complete message, the CU 172 may transmit 621 an SN Complete message (e.g., SN Reconfiguration Complete message) to the S-SN 104A, indicating that the UE 102 receives the second SN configuration. The UE 102 may include 620 an SN configuration complete indication in the RRC reconfiguration complete message and the MN 104B may include the SN configuration complete indication in the SN Complete message. In some implementations, the second SN configuration and the SN configuration complete indication are an RRCreconfiguration message and an RRCreconfiguration complete message, respectively. In some implementations, the SN Confirm message and the SN Complete message can be combined as a single SN message which can be an SN Confirm message or an SN Complete message as described above.

[0182] In some implementations, the MN 104B assigns the configuration ID (e.g., LTM ID 1) for identifying the LTM candidate configuration including the first SCG LTM candidate configuration and / or the LTM MCG configuration. In other implementations, the MN 104B receives the configuration ID from the S-SN 104A as described above and associates the configuration ID with the LTM candidate configuration.

[0183] The events 603, 604-1, 604-2, 605, 690, 607, 660, 662,609, 663, 664, 616, 620, and 621 are collectively referred to in Fig. 6A as an inter-SN LTM preparation procedure 681 A.

[0184] In some implementations, the SN Required message and the SN Confirm message are an SN Change Required message and an SN Change Confirm message, respectively. In other implementations, the SN Required message and the SN Confirm message are 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 are 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 are an SN Modification Request message and an SN Modification Request Acknowledge message, respectively.

[0185] In some implementations, if the C-SN 106A is a distributed base station, the CU of the C-SN 106A might request a SCG LTM reference DU configuration from the DU of thePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 C-SN 106A in the procedure 690, as discussed with respect to Figs. 3, 4 and 5. For example, the CU includes a reference configuration request indicator in the first CU-to-DU message for this request. If the DU supports the request (e.g., the reference configuration request indicator), the DU might transmit a SCG LTM reference DU configuration to the CU in the first DU-to-CU message of the procedure 690, as discussed with respect to Figs. 3, 4 and 5. The CU then generates the SCG LTM reference configuration including the SCG LTM reference DU configuration.

[0186] In some implementations, the S-SN 104A (e.g., the CU of the S-SN 104A) may obtain a SCG LTM reference configuration, as discussed with respect to Figs. 3 and 4. In other implementations, the S-SN 104A may receive a SCG LTM reference configuration from the MN 106B (not shown in Fig. 6A) in another inter-SN LTM preparation procedure as described above and below. If the S-SN 104A obtains a SCG LTM reference configuration, the S-SN 104A may include the SCG LTM reference configuration (S-SN generated LTM reference configuration) in the SN Required message. In turn, the MN 104B includes the SCG LTM reference configuration in the SN Request message. Alternatively, the S-SN 104A determines to request or cause the C-SN 106A to provide a complete SCG LTM candidate configuration so that the S-SN 104A does not transmit the SCG LTM reference configuration to the C-SN 106A. If the S-SN 104A does not obtain a SCG LTM reference configuration, the S-SN 104A does not include a SCG LTM reference configuration in the SN Required message. If the SN Required message includes a SCG LTM reference configuration, the MN 104B includes the SCG LTM reference configuration in the SN Request message. Otherwise, if the SN Required message does not include a SCG LTM reference configuration, the MN 104B may not include the SCG LTM reference configuration in the SN Request message.

[0187] If the SN Request message (event 605) includes a SCG LTM reference configuration as described above, the CU of the C-SN 106A may include the SCG LTM reference configuration in the first CU-to-DU message. Alternatively, the CU 172 may retrieve a SCG LTM reference DU configuration from the SCG LTM reference configuration and includes the SCG LTM reference DU configuration in the first CU-to-DU message. Otherwise, if the SN Request message does not include a SCG LTM reference configuration, the CU of the C-SN 106A may or may not receive a SCG LTM reference DU configuration from the DU of the C-SN 106A as discussed with respect to Fig. 3. If the CU receives a SCG LTM reference DU configuration (e.g., in the first DU-to-CU message), the CU generates a SCG LTM reference configuration (C-SN generated LTM reference configuration) includingPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 the SCG LTM reference DU configuration. The CU of the C-SN 106A may include a SCG LTM reference CU configuration (candidate CU (C-CU) generated LTM reference CU configuration). Otherwise, if the CU of the C-SN 106A does not receive a SCG LTM reference DU configuration from the DU of the C-SN 106A as discussed with respect to Fig.3, the CU does not generate a SCG LTM reference configuration. Alternatively, the CU generates a SCG LTM reference configuration (C-SN generated SCG LTM reference configuration) only including a C-CU generated SCG LTM reference CU configuration. In cases where the CU generates an LTM reference configuration (C-SN generated LTM reference configuration), the CU includes 607 the C-SN generated LTM reference configuration in the SN Request Acknowledge message.

[0188] In some implementations, if the LTM DU configuration 1 is a complete configuration, the CU of the C-SN 106A generates the first SCG LTM candidate configuration as a complete configuration. The CU may include a complete configuration indication (e.g., a BS-to-BS interface protocol field / IE) in the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is a complete configuration. In some implementations, the BS-to-BS interface protocol is an Xn application protocol defined in 3GPP specification 38.423. In some implementations, the complete configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the complete configuration indication is an existing field / IE defined in 3GPP specification 38.423. Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU generates the first SCG LTM candidate configuration as a delta configuration. The CU may exclude the complete configuration indication from the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is a delta configuration. Alternatively, the CU may include a delta configuration indication (e.g., a BS-to-BS interface protocol field / IE) in the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is a delta configuration. In some implementations, the BS-to-BS interface protocol is an Xn application protocol defined in 3GPP specification 38.423. In some implementations, the delta configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the delta configuration indication is an existing field / IE defined in 3GPP specification 38.423. In some implementations, the BS-to-BS interface protocol field / IE have two values (i.e., a first value and a second value). The BS-to-BS interface protocol field / IE set to the first value is the complete configuration indicationPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 and the BS-to-BS interface protocol field / IE set to the second value is the delta configuration indication.

[0189] To prepare the first cell as a candidate LTM cell for the UE 102, the CU of the S-SN 104A performs an LTM CSI report configuration and / or LTM ID configuration procedure (not shown in Fig. 6A) with an S-DU of the S-SN 104A, similar to the procedure 392 or 492. In the LTM CSI report configuration and / or LTM ID configuration procedure, the CU of the S-SN 104A transmits the LTM CSI resource configuration(s) and / or the LTM SSB configuration to the S-DU of the S-SN 104A. In response, the CU of the S-SN 104A receives the LTM CSI report configuration(s) for the UE 102 from the S-DU of the S-SN 104A.

[0190] In some implementations, the CU of the C-SN 106A receives early synchronization information for the first cell and / or PDCCH order information from the DU of the C-SN 106A, as discussed with respect to Fig. 5 A. In some implementations, the early synchronization information includes a RACH configuration (e.g., RACH configuration 1) and / or at least one TCI state configurations (e.g., TCI state configuration(s) 1). The CU of the C-SN 106A includes the early synchronization information and / or the PDCCH order information in the SN Request Acknowledge message. The MN 104B includes the early synchronization information and / or the PDCCH order information in the SN Confirm message or in the SN Request to S-SN 104A.

[0191] If the SN Request message or the SN Confirm message includes the PDCCH order information (PDCCH order information 1), the S-SN 104A may perform an early TA acquisition procedure 682 with the UE 102, the MN 104B, and the C-SN 106A. In the procedure 682, the S-SN 104A transmits a PDCCH order to the UE 102, based on the PDCCH order information. If the S-SN 104A is a distributed base station, the CU of the S-SN 104A transmits the PDCCH order information to the S-DU of the S-SN 104A and the S-DU transmits the PDCCH order to the UE 102. In some implementations, the S-SN 104A or the S-DU may determine to transmit the PDCCH order, based on (e.g., in response to) the measurement report(s). In some implementations, the S-SN 104A or the S-DU may determine a SSB index included in the PDCCH order, based on LI measurement report(s), 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 104A includes the LTM ID 1 in the PDCCH order to indicate the first cell. The UE 102 transmits a RA preamble to the DU of the C-SN 106A on the first cell, using the RACH configuration and / or the PDCCH order information.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 The S-DU or the S-SN 104A derives a TA value based on the RA preamble. The DU of the C-SN 106A transmit aDU-CU TA Information Transfer message including the TA value to the CU of the C-SN 106A. The CU of the C-SN 106A transmits a CU-CU TA Information Transfer message (e.g., TA Information Transfer) including the TA value, the first cell ID, and the associated TA information for the UE 102 to the MN 104B (e.g., the CU 172 of the MN 104B). The MN 104B transmits a CU-CU TA Information Transfer message including the TA value, the first cell ID, and the associated TA information for the UE 102 to the S-SN 104A. In some implementations, the DU of the C-SN 106A includes the cell ID 1, the RA preamble index, a RA-RNTI, and / or the DU ID of the S-DU of the S-SN 104A in the DU-CU TA Information Transfer message. In some implementations, the CU of the C-SN 106A includes 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 to the MN 104B. The MN 104B then includes 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.

[0192] 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 or L3 measurement report(s) 654 or other LI or L3 measurement report(s) received before the event 654, the S-DU or the S-SN 104A transmits 626 an LTM Cell Switch Command including the configuration ID to the UE 102. In response to the LTM Cell Switch Command, the UE 102 may stop communication on the serving cell(s). The S-SN 104A also transmits 627 to the MN 104B a CU-to-CU Cell Switch Notification message (e.g., Cell Switch Notification) including the first cell ID and / or the first TCI State ID. The MN 104B then transmits 628 to the C-SN 106A a CU-to-CU Cell Switch Notification message including the first cell ID and / or the first TCI State ID. The UE 102 and the DU of the C-SN 106 A identify the first one of the TC 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 events 632, 636 and / or 640.

[0193] In response to the LTM Cell Switch Command, the UE 102 accesses 632 the first cell and transmits 636 the RRC reconfiguration complete message to the CU 172 via the DU 174. In some implementations, the RRC reconfiguration complete message includes the configuration ID and / or an SN configuration complete indication. For example, the SN configuration indication is an RRCReconfigurationComplete message. After receiving 636 the RRC reconfiguration complete message, the CU 172 transmits 638 an SN Complete message (e.g., SN Reconfiguration Complete message). In some implementations, the CU 172PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 includes the SN configuration complete message in the SN Complete message. The C-SN 106 A might transmit 639 an LTM Success message including the first cell ID or the configuration ID to the CU 172.

[0194] After (e.g., in response to) the event 627, 637, or 639, the CU 172 may transmit 665 a CU-to-DU message (e.g., UE Context Modification Request message) including the cell ID 1 and / or the configuration ID to the DU 174. In some implementations, the CU-to-DU message includes an LTM-executed indicator. The LTM-executed indicator, the cell ID 1 , and / or the configuration ID indicates that an LTM cell switch to the first cell has been executed. In some implementations, the LTM-executed indicator is an LTM Trigger lE / field (e.g., under an Inter-SN LTM MCG Information IE or Inter-CU SCG LTM MCG Information IE) and the LTM Trigger lE / filed is set to ‘LTM-executed’. In response to or based on the LTM-executed indicator, the cell ID 1, and / or the configuration ID, the DU 174A identifies the LTM MCG configuration and applies 656 the LTM MCG configuration to communicate with the UE 102 in event 640. In other implementations, instead of including the LTM executed indicator, the CU 172 includes, in the CU-to-DU message, a newly defined container (e.g., F1AP IE, Inter-SN LTM MCG Information IE o Inter-CU SCG LTM MCG Information IE) to indicate that the LTM cell switch to the first cell has been executed. The newly defined container may include the cell ID 1 and / or the configuration ID. Based on the newly defined container, the cell ID 1 and / or the configuration ID, the DU 174A identifies the LTM MCG configuration and applies 656 the LTM MCG configuration in communication with the UE 102 in event 640. The DU 174, in response to receiving 665 the CU-to-DU message, might transmit 666 a DU-to-CU message (e.g., UE Context Modification Response message) to the CU 172 of the MN 104B. After (e.g., in response to) the event 637, 639 or 665, the CU 172 might transmit 644 to the S-SN 104A an SN Request message (e.g., SN Modification Request message or an SN Release Request message) to inform the S-SN 104 A to stop transmitting to the UE 102.

[0195] After event 632 or 638, the C-SN 106A communicates 640 with the UE 102 operating in DC with the MN 104B and the C-SN 106A. If the MN 104B transmits the LTM MCG configuration and / or the MCG LTM reference configuration, the MN 104B communicates 640 with the UE 102 on the same serving cell in accordance with the LTM MCG configuration and / or the MCG LTM reference configuration. The C-SN 106A communicates with the UE 102 on the first cell in accordance with the first SCG LTM candidate configuration and / or the SCG LTM reference configuration.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0196] In some implementations, after (e.g., in response to) event 632, 638, or receiving the SN Status Transfer message as described below or an Access Success message indicating the UE 102 successfully accesses the first cell, the (CU of the) C-SN 106A performs a PDU Session path update procedure with the CN 110 (not shown in Fig. 6A. The CU receives the Access Success message from the DU of the C-SN 106A, similar to event 334 or 434. In the PDU Session path update procedure, the (CU of the) C-SN 106A sends a PDU Session Resource Modify Indication message to the CN 110 (e.g., AMF). The PDU Session Resource Modify Indication message is to request a switch of a downlink termination point of a UP transport bearer (e.g., NG-U transport bearer) from an old termination point (e.g., the S-SN 104A or the S-CU of the S-SN 104A) towards a new termination point (e.g., the C-SN 106A or the CU of the C-SN 106A). In response to the PDU Session Resource Modify Indication message, the CN 110 (e.g., AMF) switches the downlink termination point of the UP transport bearer from the old termination point towards the new termination point. In response to the PDU Session Resource Modify Indication message, the CN 110 (e.g., AMF) transmits a PDU Session Resource Modify Confirm message to the CU 172. After the PDU Session path update procedure, the CN 110 (e.g., UPF) communicates UP data with the UE 102 via the S-BS 106A and the UP transport bearer.

[0197] In some implementations, if the S-DU or the S-SN 104A receives a TA value as described above, the S-DU or the S-SN 104A may include the TA value in the LTM Cell Switch Command. In some implementations, the S-DU or the S-SN 104A includes a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID indicates a first one of the TCI state configuration(s).

[0198] In some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch or transmitting 626 the LTM Cell Switch Command, the S-SN 104A transmits one or more Early Status Transfer messages to the MN 104B, each including a DL COUNT value or a DISCARD DL COUNT value for a DRB over which the UE 102 and the S-SN 104A communicate 602 data with each other. The MN 104B transmits one or more Early Status Transfer messages to C-SN 106A, each including the DL COUNT value or the DISCARD DL COUNT value for the DRB over which the UE 102 and the S-SN 104A communicate 602 data with each other.

[0199] In some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting 626 the LTM Cell Switch Command,PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 receiving the DU-CU Cell Switch Notification message from the S-DU, or receiving 644 the SN Request message, the S-SN 104A (e.g., the CU of the S-SN 104A) transmits an SN Status Transfer message to the MN 104B, including a DL COUNT value and / or a UL COUNT value for a / the DRB over which the UE 102 and the S-SN 104A communicate 602 data with each other. After (e.g., in response to) receiving the SN Status Transfer message from the S-SN 104A, the MN 104B transmits an SN Status Transfer message to the CU 172, including the DL COUNT value and / or the UL COUNT value.

[0200] In some implementations, before or after transmitting the LTM Cell Switch Command as described above, the S-SN 104A, the MN 104B, and / or one or more C-SNs (including the C-SN 106A) perform additional inter-SN LTM preparation procedure(s) 2, ..., N to prepare cell(s) 2, .. ,N for LTM, respectively. The cell(s) 2, ..., N are identified by cell ID(s) 2, ... , N respectively. N is an integer larger than 1. Each of the inter-SN LTM preparation procedure(s) 2, ..., N is similar to the procedure 681 A. In the procedure(s) 2, .., N, the MN 104B may obtain tuple(s) {LTM ID 2, the LTM candidate configuration 2, the LTM 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 LTM 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)} for the cell(s) 2, ..., N respectively. In some implementations, the MN 104B transmits the tuple(s) to the UE 102 in LTM configuration delivery procedure(s) 2, ..., N, each is similar to events 616 and 620. In other implementations, the MN 104B includes 616 the tuple(s) in the RRC reconfiguration message(s).

[0201] In some implementations, the S-SN 104A may include the cell ID(s) 2, ..., N in the SN Required message 603. In some implementations, the MN 104B may include 605 the cell ID(s) 2, ..., N in the SN Request message. In some implementations, the S-SN 104A includes one or more measurement results of the cell(s) 2, ..., N in the SN Required message as discussed with respect to the first cell. In some implementations, the MN 104B includes the one or more measurement results of the cell(s) 2, ..., N in the SN Request message as discussed with respect to the first cell. In some implementations, the C-SN 106A may determine to prepare the first cell for LTM and not to prepare the cell(s) 2, ..., N for LTM. In some implementations, the C-SN 106A makes the determination based on capacity of the C-SN 106A and / or the measurement results of the first cell and the cell(s) 2, ..., N.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0202] The events 627, 628, 632, 636, 638, 639, 665, 656, 666, 644, and 640 are collectively referred to in Fig. 6A as an LTM cell switch execution procedure 684.

[0203] Referring next to Fig. 6B which depicts a scenario 600B, similar to Fig. 6A. Before triggering an LTM cell switch to the first cell, the S-BS 104A receives 670 a PDU Session Resource Request message from the CN 110 (e.g., an AMF), requesting to manage (e.g., set up or modify) resources for the UE 102. The PDU Session Resource Request message may be a PDU Session Resource Setup Request message or a PDU Session Resource Modify Request message. In some implementations, the PDU Session Resource Request message includes PDU Session related information, e.g., PDU Session setup, modification or release information.

[0204] Based on the PDU Session Resource Request message, the MN 104B determines to perform an SN Modification procedure with the S-SN 104A to set up new radio resources or modify radio resources configured for the UE 102. In response to the determination, the MN 104B transmits 675 an SN Modification Request message to the S-SN 104A. In some implementations, the MN 104B includes the PDU Session related information in the SN Modification Request message. Based on the SN Modification Request message or the PDU Session related information, the S-SN 104A generates a second SCG configuration for the UE 102, updating the first SCG configuration. The S-SN 10A transmits 677B an SN Modification Request Acknowledge message including the second SCG configuration to the MN 104B.

[0205] In some implementations, the CU 172 may obtain 674 a second serving MCG configuration from the DU 174, e.g., via a UE Context Modification procedure as described above. The second serving MCG configuration updates the first serving MCG configuration. In the UE Context Modification procedure, the CU 172 t. the DU 174A generates the second MCG configuration based on the PDU Session Resource Request message or the PDU Session related information, as discussed with respect to event 574 in Fig. 5B. The CU 172 may transmit (at least a portion of) the second MCG configuration to the S-SN 104A in the SN Modification Request message. The S-SN 104 A may generate the second SCG configuration based on (the at least a portion of) the second MCG configuration. In other implementations, the CU 172 obtains 674 the second serving MCG configuration after receiving the second serving SCG configuration. In such cases, the CU 172 may transmit (at least a portion of) the second serving SCG configuration to the DU 174. The DU 174A mayPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 generate the second MCG configuration based on the (at least a portion of) the second serving SCG configuration.

[0206] The CU 172 then transmits 676 an RRCreconfiguration message including the second serving MCG configuration and / or the second serving SCG configuration to the UE 102 via the DU 174, similar to event 616. In response, the UE 102 updates (e.g., replaces, modifies, or augments) the first serving MCG configuration and / or the first serving SCG configuration with the second serving MCG configuration and / or the second serving SCG configuration respectively and transmits 678 an RRCreconfiguration complete message to the MN 104B via the DU 174. If the RRC reconfiguration message includes the second MCG configuration, the UE 102 then communicates with the MN 104B using the second MCG serving configuration and optionally at least a portion of the first serving MCG configuration (i.e., not augmented by the second MCG configuration). The UE 102 then communicates with the S-SN 104A using the second SCG serving configuration and optionally at least a portion of the first serving MCG configuration (i.e., not augmented by the second SCG configuration). After receiving 678 the RRC reconfiguration complete message, the MN 104B transmits 679 an SN Complete message to the S-SN 104A. In some implementations, the UE 102 includes an SN configuration complete indication in the RRC reconfiguration complete message and the MN 104B includes the SN configuration complete indication in the SN Complete message. Events 676, 678, and 679 are similar to events 616, 620, and 621, respectively.

[0207] In some implementations, if the first serving SCG configuration is updated, the S-SN 104A may suspend 685 triggering an LTM cell switch for the UE 102. In some implementations, the DU of the S-SN 104A suspends 585 triggering an LTM cell switch for the UE 102 in response to performing the UE Context Modification procedure. In some implementations, the CU of the S-SN 104A includes an LTM suspend indication in the UE Context Modification Request message to the DU, indicating suspension of an LTM cell switch for the UE 102. The DU suspends 685 triggering an LTM cell switch for the UE 102 in response to the LTM suspend indication. In other implementations, in response to receiving the second serving SCG configuration from the DU, the CU transmits a CU-to-DU message to the DU, indicating to suspend an LTM cell switch for the UE 102. In some implementations, the CU-to-DU message may be a F1AP message defined in 3GPP specification 38.473 vl8.5.0 or a later version. In other implementations, the CU-to-DUPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 message is a UE Context Modification Request message including the LTM suspend indication.

[0208] After event 678 or 679, the MN 104B, the S-SN 014A and the UE 102 perform 681B one or more LTM modification procedure(s) with the C-SN 106A and / or other C-SN(s) to update the LTM candidate configuration(s) 1, ..., K, similar to the procedure 681 A. K is an integer and 0 < K < N. In some implementations, the MN 104B may initiate the LTM modification procedure(s) as discussed with respect to the procedure 681 A. In other implementations, the S-SN 104A may initiate the LTM modification procedure(s) as discussed with respect to the procedure 681 A. In the LTM modification procedure(s), the MN 104B obtains LTM candidate configuration(s) 1’, ..., K’ and transmits the LTM candidate configuration(s) 1’, ..., K’ to the UE 102. The UE 102 updates (e.g., replaces, modifies, or augments) the LTM candidate configuration(s) 1 , ... , K, with the LTM candidate configuration(s) 1’, ..., K’, respectively. After performing the LTM modification procedure(s), the S-SN 104A may resume 687 triggering an LTM cell switch for the UE 102. In some implementations, the CU of the C-SN 106A transmits a CU-to-DU message to the DU 174A of the S-SN 104A, indicating to resume an LTM cell switch for the UE 102. The DU resumes 687 triggering an LTM cell switch for the UE 102 in response to the LTM resume indication. In some implementations, the CU-to-DU message may be a F1AP message defined in 3GPP specification 38.473 vl 8.5.0 or a later version. In other implementations, the CU-to-DU message is a UE Context Modification Request message including the LTM resume indication. At least some of the discussion of events 586 and 58 IB can apply to the procedure 68 IB. Descriptions with respect to the first serving configuration and the second serving configuration can apply to the first serving MCG configuration and the second serving MCG configuration. Descriptions with respect to the first serving configuration and the second serving configuration can apply to the first serving SCG configuration and the second serving SCG configuration.

[0209] In some implementations, events 676 and 678 can be combined into the LTM modification procedure(s) 68 IB. For example, the RRC reconfiguration message (event 676) can include the second serving configuration and at least one of the LTM candidate configuration(s) 1’, ..., K’.

[0210] After updating the LTM candidate configuration(s) 1, ..., K, the S-SN 104A may trigger an LTM cell switch for the UE 102 as discussed with respect to Fig. 6A.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0211] The events 670, 672B, 674, 675, 677B, 676, 678, 685, 681B, 679, and 687 are collectively referred to in Fig. 6B as a PDU Session Resource management procedure 688B.

[0212] Referring next to Fig. 6C which depicts a scenario 600C, similar to Figs. 6A and 6B. Based on the LI or L3 measurement report, the S-SN 104A determines to trigger an LTM cell switch to the first cell as discussed with respect to Fig. 6A. If the S-SN 104A includes a CU and a DU, the CU may receive a DU-CU Cell Switch Notification message from the DU in response to the determination or event 626, similar to events 328 and 428. After the determination or event 626 or before completing the LTM cell switch execution procedure 684, the S-SN 104A receives 675 the SN Modification Request message. In response, the S-SN 104A transmits 677C an SN Modification Request Acknowledge message to the MN 104B, indicating failure to set up or modify resources for the UE 102. In this case, the S-SN 104A refrains from updating the first serving SCG configuration. In some implementations, the S-SN 104A includes a cause in the SN Modification Request Acknowledge message, indicating that the failure is due to an LTM triggered or an LTM cell switch triggered. In some implementations, the S-SN 104A includes a cause in the SN Modification Request Acknowledge message, indicating that the failure is due to an SN change triggered. After receiving the 677C the message, the MN 104B transmits 672C a PDU Session Resource Response message to the CN 110, indicating failure to set up or modify resources for the UE 102, similar to event 572C. The MN 104B may include, in the PDU Session Resource Response message, the cause received in the SN Modification Request Acknowledge message.

[0213] After S-SN 104A, the MN 104B, the C-SN 106A and the UE 102 complete 684 the LTM cell switch execution procedure, the C-SN 106A becomes a S-SN for the UE 102 and the CN 110 may perform 688C another PDU Session Resource procedure with the S-BS 106A and the UE 102, similar to the procedure 588B.

[0214] Next, several example methods, which can be implemented in a RAN node (e.g., a base station, an MN, an SN, a DU or a CU as described above) or a UE (e.g., the UE 102), for LTM, are discussed next with reference to Figs. 7-10B. Descriptions and example implementations discussed with respect to Figs. 3-6B can apply to Figs. 7-10B.

[0215] Fig. 7A illustrates an example method 700A, which can be implemented by a first RAN node. The method 700A begins at block 702, where the first RAN node communicates with a UE using a first serving configuration. At block 781 A, the first RAN node performs anPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 LTM setup or modification procedure for the UE with a second RAN node. At block 707, the first RAN node receives a first LTM candidate configuration from the second RAN node in the LTM setup or modification procedure. At block 736, the first RAN node transmits the first LTM candidate configuration to the UE. At block 774, the first RAN node determines to update, or updates, the first serving configuration. At block 78 IB, the first RAN node performs an LTM modification procedure for the UE with the second RAN node in response to the determining or updating. At block 773, the first RAN node may receive a second LTM candidate configuration from the second RAN node in the LTM modification procedure. At block 786, the first RAN node may transmit the second LTM candidate configuration to the UE to update the first LTM candidate configuration.

[0216] In some implementations, the LTM setup or modification procedure at block 781 A is a handover preparation procedure similar to events 505 and 507. In other implementations, the LTM setup or modification procedure at block 781 A is an SN addition preparation procedure similar to events 607 and 607). In some implementations, the LTM modification procedure at block 78 IB is a handover preparation procedure similar to events 505 and 507. In other implementations, the LTM modification procedure at block 78 IB is an SN addition preparation procedure similar to events 607 and 607. In some implementations, the first RAN node transmits a second serving configuration to the UE to update the first serving configuration. In some implementations, the first RAN node (e.g., first BS or a CU of the first BS) determines to update the first serving configuration in response to receiving a CN-to-BS message from a CN node (e.g., an AMF). The CN-to-BS message requests to set up or modify resources for the UE. For example, the CN-to-BS message is a PDU Session Resource Setup Request message or a PDU Session Resource Modify Request message. In other implementations, the first BS determines to update the first serving configuration in response to receiving a BS-to-BS message from the second RAN node (e.g., a second BS). For example, the first BS and the second BS are an S-SN and an MN respectively and the BS-to-BS message is an SN Modification Request message. In other implementations, the first BS determines to update the first serving configuration in response to receiving a BS-to-BS message from a third BS. For example, the first BS and the third BS are an MN and an S-SN respectively and the BS-to-BS message is an SN Modification Request message.

[0217] In some implementations, the first BS and the second BS are an S-BS and a C-BS, respectively. In such implementations, the first serving configuration and the second serving configuration are serving MN configurations or serving MCG configurations as describedPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 above. In other implementations, the first BS and the second BS are an S-SN and an MN, respectively. In yet other implementations, one of the first BS and the second BS are an S-SN and the other is a C-SN. In such cases, the first serving and second serving configurations are serving SN configurations or serving SCG configurations as described above. In such case, the first BS (e.g., S-SN) performs 781 A the procedure and transmits the second serving configuration to the UE via an MN. In some implementations, the first BS and the second BS can be a first CU of the first BS and a second CU of the second BS, respectively.

[0218] In some implementations, the RAN node and the second RAN node are a CU and a DU, respectively. In such cases, the mobility preparation procedure may be a UE Context Modification procedure or a UE Context Setup procedure similar to events 390, 392, 490 or 492.

[0219] Fig. 7B is a flow diagram of an example method 700B similar to the method 700A, except that the method 700B includes blocks 755 and 757. At block 755, the first RAN node determines whether the first LTM candidate configuration is invalid after the first serving configuration is updated. If the first LTM candidate configuration is invalid after the first serving configuration is updated (i.e., “Yes” branch of block 755), the flow proceeds to block 78 IB and may proceeds to blocks 773 and 786. Otherwise, if the first LTM candidate configuration is valid after the first serving configuration is updated (i.e., “No” branch of block 755), the flow proceeds to block 757 where the flow ends.

[0220] Fig. 8 A illustrates an example method 800A, which can be implemented by a first RAN node. The method 800A begins at block 702 as discussed with respect to Fig. 7A. At block 871, the first RAN node performs a resource management procedure for the UE with a CN. At block 881 A, the first RAN node determines to perform a mobility preparation procedure for the UE while performing the resource management procedure (e.g., event 581 A or 58 IB). At block 847, the first RAN node determines whether the mobility preparation procedure is for LTM or immediate mobility. If the mobility preparation procedure is for LTM (i.e., “Yes” branch of block 847), the flow proceeds to block 848. At block 848, the first RAN node stops performing the mobility preparation procedure. Otherwise, if the mobility preparation procedure is for immediate mobility (i.e., “No” branch of block 847), the flow proceeds to block 849. At block 849, the first RAN node performs the mobility preparation procedure.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0221] In some implementations, the first RAN node and the second RAN node are base stations. In other implementations, the first RAN node and the second RAN node are a CU and a DU respectively. In some implementations, the resource management procedure is a PDU Session Resource Setup procedure. In other implementations, the resource management procedure is a PDU Session Resource Modify procedure. In some implementations, if the first RAN node supports a conditional mobility and the mobility preparation procedure is performed for the conditional mobility, the first RAN node stops performing the mobility preparation procedure.

[0222] In some implementations, the immediate mobility is an immediate handover. In other implementations, the immediate mobility is an immediate SN change or immediate PSCell change. In some implementations, the mobility preparation procedure is a handover preparation procedure, e.g., as described in 3GPP specification 38.423. In other implementations, the mobility preparation procedure is an S-NG-RAN node addition preparation procedure or an S-NG-RAN node modification preparation, e.g., as described in 3GPP specification 38.423. In yet other implementations, the mobility preparation procedure is a UE Context Modification procedure a UE Context Setup procedure, e.g., as described in 3GPP specification 38.473.

[0223] Fig. 8B is a flow diagram of an example method 800B similar to the method 800 A, except that the method 800B includes blocks 869 and 845 instead of blocks 871 and 881 A. At block 869, the first RAN node performs a mobility preparation procedure for the UE with a second RAN node (e.g., event 581 A or 58 IB). At block 845, while performing the mobility preparation procedure, the first RAN node receives a CN-to-BS message from a CN node, requesting to set up or modify resources for the UE.

[0224] Fig. 9A illustrates an example method 900A, which can be implemented by a first BS. The method 900A begins at block 970, where the first BS receives a CN-to-BS message from a CN node after transmitting a first LTM candidate configuration to a UE, where the CN-to-BS message requests to set up or modify resources for the UE. In some implementations, the first BS transmits the first LTM candidate configuration to the UE as discussed with respect to blocks 702, 781 A, 707 and 736 in Fig. 7A. At block 997, the first BS determines whether an LTM cell switch is being triggered. If an LTM cell switch is triggered (i.e., “Yes” branch of block 997), the flow proceeds to blocks 999 and 972A. In this case, the LTM cell switch has been triggered and not completed yet. At block 999, the firstPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 BS indicates failure to set up or modify resources for the UE in a BS-to-CN message (e.g., event 572C). Otherwise, if an LTM cell switch is not triggered (i.e., “No” branch of block 997), the flow skips block 999 and proceeds to block 972A. That is, the first BS does not indicate the failure in the BS-to-CN message. At block 972A, the first BS transmits the BS-to-CN message to the CN node.

[0225] In some implementations, the CN-to-BS message and the BS-to-CN message are a PDU Session Resource Setup Request message and a PDU Session Resource Setup Response message, respectively. In other implementations, the CN-to-BS message and the BS-to-CN message are a PDU Session Resource Modify Request message and a PDU Session Resource Modify Response message, respectively.

[0226] Fig. 9B is a flow diagram of an example method 900B similar to the method 900 A, except that the method 900B includes blocks 972B and 972C instead of blocks 999 and 972A. If an LTM cell switch is triggered (i.e., “Yes” branch of block 997), the flow proceeds to block 972C. At block 972C, the first BS transmits a BS-to-CN message to the CN node, indicating that the BS fails to set up or modify resources for the UE (e.g., event 572C).Otherwise, if an LTM cell switch is not triggered (i.e., “No” branch of block 997), the flow proceeds to block 972B. At block 972B, the first BS transmits a BS-to-CN message to the CN node, indicating that the BS successfully sets up or modifies resources for the UE (e.g., event 572B).

[0227] Fig. 10A illustrates an example method 1000A, which can be implemented by an SN. The method 1000A begins at block 1075, where the SN receives an MN-to-SN message from an MN, requesting to set up or modify resources for the UE. In some implementations, the SN transmits the first LTM candidate configuration to the UE as discussed with respect to blocks 702, 781 A, 707 and 736 in Fig. 7A. At block 997, the SN determines whether an LTM cell switch is triggered. If an LTM cell switch is triggered (i.e., “Yes” branch of block 997), the flow proceeds to blocks 1059 A and 1077 A. At block 1059 A, the SN indicates failure to set up or modify resources for the UE in an SN-to-MN message. Otherwise, if an LTM cell switch is not triggered (i.e., “No” branch of block 997), the flow skips block 1059A and proceeds to block 1077A. That is, the SN does not indicate the failure in the SN-to-MN message. At block 1077A, the SN transmits the SN-to-MN message to the MN.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00

[0228] In some implementations, the MN-to-SN message and the SN-to-MN message are an SN Modification Request message and an SN Modification Request Acknowledge message, respectively.

[0229] Fig. 1 OB is a flow diagram of an example method 1000B similar to the method 1000 A, except that the method 1000B includes blocks 1059B and 1077B instead of blocks 1059 A and 1077 A. If an LTM cell switch is triggered, the flow proceeds to block 1059B. At block 1059B, the SN transmits an SN-to-MN message to the MN, indicating that the SN fails to set up or modify resources for the UE. Otherwise, if an LTM cell switch is not triggered, the flow proceeds to block 1077B. At block 1077B, the SN transmits an SN-to-MN message to the MN, indicating that the SN successfully sets up or modifies resources for the UE.

[0230] Examples and implementations discussed with respect to Fig. 7A can apply to Figs.8A-10B.

[0231] The following illustrates an example manner in which the techniques above may be incorporated into the 3GPP specification TS 38.413. Section 8.2.1 (“PDU Session Resource Setup”) can be modified so that, in section 8.2.1.2 (“Successful Operation”) and under the subheading “Interactions with Handover Preparation procedure,” the text can specify that “if an immediate handover or LTM cell switch triggering becomes necessary during the PDU Session Resource Setup procedure, the NG-RAN node may interrupt the ongoing PDU Session Resource Setup procedure and initiate the Handover Preparation procedure as follows: 1. The NG-RAN node shall send the PDU SESSION RESOURCE SETUP RESPONSE message in which the NG-RAN node shall indicate, if necessary, all the PDU session resources which failed to be setup with an appropriate cause value, e.g. "NG intrasystem handover triggered", "NG inter-system handover triggered" or "Xn handover triggered". 2. The NG-RAN node shall trigger the handover procedure.”

[0232] Further, Section 8.2.3 (“PDU Session Resource Modify”) can be modified so that, in section 8.2.3.2 (“Successful Operation”) and under the subheading “Interactions with Handover Preparation procedure,” the text can specify that “If an immediate handover or LTM cell switch triggering becomes necessary during the PDU Session Resource Modify procedure, the NG-RAN node may interrupt the ongoing PDU Session Resource Modify procedure and initiate the Handover Preparation procedure as follows: 1.The NG-RAN node shall send the PDU SESSION RESOURCE MODIFY RESPONSE message in which the NG-RAN node shall indicate, if necessary, all the PDU sessions failed with an appropriatePATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 cause value, e.g. "NG intra-system handover triggered", "NG inter-system handover triggered" or "Xn handover triggered. 2. The NG-RAN node shall trigger the handover procedure.”

[0233] The following list of examples reflects a variety of the embodiments explicitly contemplated by the present disclosure.

[0234] Example 1. A method implemented in a serving radio access network (RAN) comprises communicating, with a user equipment (UE), according to a serving configuration; configuring the UE with for a lower-layer triggered mobility (LTM) switch to a target cell associated with a target RAN node; determining, after the configuring but prior to initiating the LTM switch, that a change in the serving configuration is required; and in response to the determining, performing one of: initiating a procedure to add or modify radio resources configured for the UE, or transmitting, to the UE, a command to initiate the LTM switch.

[0235] Example 2. The method of example 1, wherein the determining that the change in the serving configuration is required includes receiving, from a core network (CN), a request related to a packet data unit (PDU) session.

[0236] Example 3. The method of example 2, wherein the request includes a PDU Session Resource Setup Request message.

[0237] Example 4. The method of example 2, wherein the request includes a PDU Session Resource Modify Request message.

[0238] Example 5. A method implemented in a RAN node comprises communicating, with a user equipment UE according to a serving configuration; performing, with a core network (CN), a resource management procedure for the UE; during the performing of the resource management procedure, determining to perform a mobility preparation procedure for the UE; and determining whether to perform a mobility preparation procedure while the resource management procedure is ongoing based on whether the mobility preparation procedure relates to immediate mobility or LTM mobility.

[0239] The following description may be applied to the description above.

[0240] Generally speaking, the discussion of one of the above figures can apply to another of the above figures. Examples, implementations and methods described above can be combined, if there is no conflict. An event or block described above can be optional or omitted. For example, an event or block with dashed lines in the figures can be optional.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 The description described from the perspective of the receiving node also applies to the sending node. For example, a description that a receiving node (e.g., DU) receives a message from a sending node (e.g., CU) may be replaced by the sending node sending a message to the receiving node. Similarly, a description that a receiving node (e.g., CU) receives a message from a sending node (e.g., DU) may be replaced by the sending node sending a message to the receiving node.

[0241] In some implementations, “message” is used and can be replaced by “information element (IE)”, and vice versa. In some implementations, “IE” is used and can be replaced by “field”, and vice versa. In some implementations, “configuration” can be replaced by “configurations” or “configuration parameters”, and vice versa. In some implementations, the “LTM command” can be replaced by “serving cell change command”, “Layer 1 / Layer 2 LTM cell switch command”, “lower layer switching command” or “lower layer serving cell change command”. In some implementations, “some” means “one or more”. In some implementations, “at least one” means “one or more”. In some implementations, the “DU configuration” can be replaced by “cell group configuration”. In some implementations, the “cell index” can be replaced with “serving cell index”, “LTM cell index”, “special cell (SpCell) index”, “PCell index” or “PSCell index”. In some implementations, the “serving” can be replaced by “source”. In some implementations, the “measurement report” can be replaced by “measurement result(s)” or “CSI report”. In some implementations, the “early TA acquisition” can be replaced by “early UL timing synchronization” or “early UL synchronization”. In some implementations, the “early TA acquisition on a / the candidate cell” can be replaced by “early UL timing synchronization with a / the candidate cell” or “early UL synchronization with a / the candidate cell”. In some implementations, “include” can be replaced by “comprise”. In some implementations, “exclude” can be replaced by “refrain from including”. In some implementations, “Handover Request” and “Handover Request Acknowledge” described above are for illustration of the techniques and can be replaced by messages with general names. For example, “Handover Request” and “Handover Request Acknowledge” can be replaced by a first CU-to-CU message and a second CU-to-CU message, respectively. In another example, “Handover Request” and “Handover Request Acknowledge” can be replaced by a first interface message and a second interface message, respectively. In yet another example, “Handover Request” and “Handover Request Acknowledge” can be replaced by a first BS-to-BS message and a second BS-to-BS message, respectively. In some implementations, “SN Request”, “SN Confirm”, “SN Request” andPATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 “SN Request Acknowledge” described above are for illustration of the techniques and can be replaced by messages with general names. For example, the “SN Required message” can be replaced by an SN-to-MN message. In another example, the “SN Confirm message” can be replaced by an MN-to-SN message.

[0242] A user device in which the techniques of this disclosure can be implemented (e.g., the UE 102) can be any suitable device capable of wireless communications such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media-streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an interne t-of-things (loT) device or a mobile-internet device (MID). Depending on the type, the user device can include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0243] Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules may can be software modules (e.g., code, or machine-readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module can comprise dedicated circuitry or logic that is permanently configured (e.g. , as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g., as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g. , configured by software) may be driven by cost and time considerations.

[0244] When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular software application,PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 etc. The software can be executed by one or more general-purpose processors or one or more special-purpose processors.

[0245] Upon reading this disclosure, those of skill in the art will appreciate still additional and alternative structural and functional designs for handling mobility between base stations through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

Claims

PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 What is claimed is:

1. A method implemented in a serving radio access network (RAN) node, the method comprising:communicating, with a user equipment (UE), according to a serving configuration; configuring the UE with for a lower-layer triggered mobility (LTM) switch to a target cell associated with a target RAN node;determining, after the configuring but prior to initiating the LTM switch, that a change in the serving configuration is required; andin response to the determining, performing one of:initiating a procedure to add or modify radio resources configured for the UE, ortransmitting, to the UE, a command to initiate the LTM switch.

2. The method of claim 1, wherein the performing includes:configuring the UE with an updated serving configuration.

3. The method of claim 2, wherein the configuring the UE with the updated serving configuration includes:transmitting, to the UE via a radio interface, a radio resource configuration (RRC) message.

4. The method of claim 2 or 3, further comprising:in response to the configuring the UE with the updated serving configuration, suspending triggering of the LTM switch.

5. The method of claim 4, further comprising:performing an LTM modification procedure with at least one of the target RAN node and the UE.

6. The method of claim 5, further comprising:subsequently to the performing of the LTM modification procedure with the target RAN node, resuming the triggering of the LTM switch.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 7. The method of any of claims 2-6, wherein:the communicating with the UE according to the serving configuration includes communicating with the UE in single connectivity.

8. The method of any of claims 2-7, wherein:the communicating with the UE according to the serving configuration includes communicating with the UE in dual connectivity; andthe updated serving configuration pertains to at least one of a master cell group (MCG) or a secondary cell group (SCG).

9. The method of any of claim 8, wherein:the initiating of the procedure to add or modify the radio resources for the UE includes transmitting, to the target RAN node, a secondary node (SN) modification request message.

10. The method of any of claims 2-4, further comprising:performing an LTM modification procedure with the target RAN node.

11. The method of claim 10, wherein the performing of the LTM modification procedure includes:receiving, from the target RAN node, an updated LTM configuration; and transmitting, to the UE, the updated LTM configuration.

12. The method of claim 10 or 11, wherein the performing of the LTM modification procedure with the target RAN node is response to:determining that the updated serving configuration makes an initial LTM configuration, according to which the UE was configured for the LTM switch to the target cell, invalid.

13. The method of claim 1, wherein the performing includes: transmitting, to the UE, the command to initiate the LTM switch; and refraining from updating the serving configuration.PATENT APPLICATION Attorney Docket No.: 31730 / 308797-00 14. The method of claim 13, wherein:the determining that the change in the serving configuration is required includes receiving, from a core network (CN), a request related to a packet data unit (PDU) session; andthe refraining from updating the serving configuration includes transmitting, to the CN and in response to the request related to the PDU session, an indication of a failure.

15. A RAN node comprising processing hardware and configured to perform a method of any of the preceding claims.

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