Managing carrier aggregation for lower layer triggered mobility

Abstract

A user equipment (UE) can implement a method for configuring carrier aggregation for mobility triggered by lower layer signaling. The method includes: receiving, from a radio access network (RAN) node and when the UE operates in a currently serving cell, a lower- layer triggered mobility (LTM) candidate configuration associated with an LTM identifier corresponding to a first candidate cell and a second candidate cell; receiving, from the RAN node, a command to perform an LTM switch to the first candidate cell; and accessing the first candidate cell in response to the command.

Description

MANAGING CARRIER AGGREGATION FOR LOWER LAYER TRIGGERED MOBILITYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of the filing date of provisional U.S. Patent Application No. 63 / 680,546, titled “MANAGING CARRIER AGGREGATION FOR LOWER LAYER TRIGGERED MOBILITY,” filed on August 7, 2024 and provisional U.S. Patent Application No. 63 / 603,635, titled “MANAGING CARRIER AGGREGATION FOR LOWER LAYER TRIGGERED MOBILITY,” filed on November 28, 2023. The entire contents of the provisional applications are hereby expressly incorporated herein by reference.FIELD OF THE DISCLOSURE

[0002] This disclosure relates to wireless communications and, more particularly, to configuring carrier aggregation for mobility triggered by lower layer signaling.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 technical specification (TS) 36.323) and New Radio (NR) (see 3GPP 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. The UE and the base station can further use DRBs to transport data on a user plane.

[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). SRB1 resources carry RRC messages, which in some cases include NAS messages, over the dedicated control channel (DCCH), and SRB2 resources support RRC messages, which 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. The SRB 1 and SRB2 resources 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 to as MCG DRBs, DRBs using the lower-layer resources of only the SN can be referred to 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] In some scenarios, the UE concurrently utilizes 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 determine that the UE should establish a radio connection with another base station. For example, one base station determines to hand the UE over to the second base station and initiates a handover procedure.

[0007] When the UE moves from coverage area of one cell to another cell in a RAN, at some point the RAN performs a serving cell change for the UE. To perform the serving cell change, 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 configuring Reconfiguration with Synchronization (e.g., the RRC reconfiguration message includes a ReconfigurationWithSync Information Element (IE)) for change of theserving cell (e.g., PCell or PSCell). In cases where the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN releases the at least one SCell due to the change of the PCell or PSCell. The serving cell change involves complete L2 (and LI) resets, leading to longer latency, larger overhead, and longer interruption time. Thus, it is desirable to develop new mobility techniques for serving cell changes. These techniques, aiming to reduce latency and overhead, are called low-layer triggered mobility (LTM) (also referred to as lower layer triggered mobility) cell switch or faster serving cell switching.

[0008] While the RAN communicates with the UE via the serving cell, the RAN receives one or more layer 3 (e.g., RRC) measurement results from the UE. Based on the layer 3 (L3) measurement result(s), the RAN determines to configure an LTM candidate cell for LTM cell switch. To configure the LTM candidate cell for the UE, the RAN transmits an LTM configuration configuring the LTM candidate cell to the UE via RRC signaling. In some implementations, the RAN includes the configuration parameters for the first radio bearer in the LTM configuration. Later on, the RAN receives one or more layer 1 (LI) measurement results from the UE. Based on the one or more LI measurement result(s), the RAN determines that the LTM candidate cell qualifies to be a serving cell for the UE. Therefore, the RAN transmits an LTM cell switch command to the UE to command 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. In response to the cell change, the UE disconnects from the serving cell and accesses the LTM candidate cell. After the UE successfully accesses the LTM candidate cell, the UE communicates with the RAN via the LTM candidate cell, and the LTM candidate cell becomes a new serving cell for the UE.

[0009] In some cases, before switching to the LTM candidate cell, the UE obtains a timing advance (TA) value for synchronization with the target cell. When performing the LTM cell switch to the LTM candidate cell, the UE applies the TA value to communicate on the LTM candidate cell directly without performing a random access procedure for uplink synchronization with the RAN on the LTM candidate cell. It is not clear whether the RAN can configure multiple LTM candidate cells (i.e., one LTM candidate PCell and one or more LTM candidate SCell) for the UE. In cases where the RAN configures multiple LTM candidate cells (i.e., one LTM candidate PCell and one or more LTM candidate SCell) in anLTM configuration (e.g., an LTM DU configuration as described below), it is not clear how the UE obtain uplink synchronization with the multiple LTM candidate cells.SUMMARY

[0010] An example embodiment of the techniques of this disclosure is a method implemented in a user equipment (UE). The method comprises receiving, from a radio access network (RAN) and when the UE operates in a currently serving cell, a lower- lay er triggered mobility (LTM) candidate configuration associated with an LTM identifier corresponding to a first candidate cell and a second candidate cell; receiving, from the RAN, a command to perform an LTM switch to the first candidate cell; and accessing the first candidate cell in response to the command.

[0011] Another example embodiment of these techniques is a user equipment (UE) comprising a transceiver and / or processing hardware configured to implement the method above.

[0012] Another example embodiment of these techniques is a method implemented in a radio access network (RAN) node. The method comprises transmitting, to a user equipment (UE), a lower-layer triggered mobility (LTM) candidate configuration associated with an LTM identifier corresponding to a first candidate cell and a second candidate cell; transmitting, to the UE, a command to perform an LTM switch to the first candidate cell; and communicating with the UE responsive to detecting that the UE accesses the first candidate cell in response to the command.

[0013] Another example embodiment of these techniques is a method implemented in a centralized unit (CU) of a radio access network (RAN) node. The method comprises communicating, via a first distributed unit (DU), with a user equipment (UE); receiving, from a second DU, a lower-layer triggered mobility (LTM) DU configuration that configures a single candidate cell; and transmitting, to the UE, the LTM DU configuration.

[0014] Another example embodiment of these techniques is a method implemented in a distributed unit (DU) of a radio access network (RAN) node including a centralized unit (CU). The method comprises receiving, from the CU, a message for configuring lower-layer triggered mobility (LTM) for a user equipment (UE); transmitting, to the CU, an LTM DU configuration that configures a single candidate cell responsive to the receiving the message; and communicating with the UE via the single candidate cell in accordance with the LTM DU configuration.

[0015] Another example embodiment of these techniques is a radio access network (RAN) node comprising a transceiver and / or processing hardware configured to implement the methods above.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Fig. 1A 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 conditional procedures related to a secondary node (SN);

[0017] Fig. IB is a block diagram of an example base station including a centralized unit (CU) and a distributed unit (DU) that can operate in the system of Fig. 1 A;

[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 messaging diagram of an example scenario for managing lower layer triggered mobility configuration and reconfiguration.

[0021] Fig. 4 is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the UE transmits measurement reports to a target DU;

[0022] Fig. 5A is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the UE communicates in DC with an MN and an SN;

[0023] Fig. 5B is a messaging diagram of an example scenario similar to that of Fig. 5A, but in which the SN provides configuration information to the UE via the MN;

[0024] Fig. 6A is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the UE communicates with a target DU using an LTM configuration;

[0025] Fig. 6B is a messaging diagram of an example scenario similar to that of Fig. 6A, but in which the SN provides configuration information to the UE via the MN;

[0026] Fig. 7A is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the UE communicates in with a combined MN / SN;

[0027] Fig. 7B is a messaging diagram of an example scenario similar to that of Fig. 7A, but in which an S-DU provides configuration information to the UE via an M-DU;

[0028] Fig. 8A is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the UE communicates with a combined MN / SN including a target DU;

[0029] Fig. 8B is a messaging diagram of an example scenario similar to that of Fig. 8A, but in which the S-DU provides configuration information to the UE via an M-DU;

[0030] Fig. 9A is a flow diagram of an example method, implemented in a UE, for receiving an LTM command from a RAN, including a TA value, accessing a first candidate cell, receiving an activation command from the RAN, and activating communication via a second candidate cell in response to the activation command;

[0031] Fig. 9B is a flow diagram of an example method similar to that of Fig. 9A, but in which the UE activates communication with the RAN via the second candidate cell in response to the LTM command;

[0032] Fig. 9C is a flow diagram of an example method similar to that of Fig. 9A, but in which the UE access the first and second candidate cells in response to the LTM command;

[0033] Fig. 9D is a flow diagram of an example method similar to that of Fig. 9A, but in which the UE determines whether to activate communication in response to the activation command or the LTM command based on whether the LTM candidate configuration configures the second candidate cell as active;

[0034] Fig. 9E is a flow diagram of an example method similar to that of Fig. 9D, but in which the determination is whether to activate communication with the second candidate cell in response to the activation command or access the first and second candidate cells in response to the LTM command;

[0035] Fig. 9F is a flow diagram of an example method similar to that of Fig. 9D, but in which the determination is based on whether the LTM command indicates that the TA value is applied to the second candidate cell;

[0036] Fig. 9G is a flow diagram of an example method similar to that of Fig. 9F, but in which the determination is whether to activate communication with the second candidate cell in response to the activation command or access the first and second candidate cells in response to the LTM command;

[0037] Fig. 10A is a flow diagram of an example method, implemented in a RAN, for transmitting an LTM command to a UE, detecting that the UE accesses a first candidate cell, transmitting an activation command to the UE, and activating communication with the UE via a second candidate cell in response to the activation command;

[0038] Fig. 10B is a flow diagram of an example method similar to that of Fig. 10A, but in which the RAN activates communication with the UE via the second candidate cell while communicating via the first candidate cell;

[0039] Fig. 10C is a flow diagram of an example method similar to that of Fig. 10A, but in which the RAN detects that the UE access the first and second candidate cells after transmitting the LTM command;

[0040] Fig. 10D is a flow diagram of an example method similar to that of Fig. 10A, but in which the RAN determines whether to activate the second candidate cell in response to the LTM command or the activation command based on whether the LTM candidate configuration configures the second cell as active;

[0041] Fig. 10E is a flow diagram of an example method similar to that of Fig. 10D, but in which the RAN activates the second candidate cell in response to the activation command or detects that the UE access both the first and second candidate cell;

[0042] Fig. 10F is a flow diagram of an example method similar to that of Fig. 10D, but in which the determination is based on whether the LTM command indicates that the TA value is applied to the second candidate cell;

[0043] Fig. 10G is a flow diagram of an example method similar to that of Fig. 10F, but in which the RAN activates the second candidate cell in response to the activation command or detects that the UE access both the first and second candidate cell;

[0044] Fig. 11 is a flow diagram of an example method, implemented in a CU, for transmitting a message for configuring LTM for the UE to a second DU, receiving an LTM DU configuration, and transmitting the LTM DU configuration to a UE;

[0045] Fig. 12 is a flow diagram of an example method, implemented in a DU, for transmitting an LTM DU configuration to a CU and transmitting an LTM command to a UE;

[0046] Fig. 13 is a flow diagram of an example method, implemented in a DU, for determining whether to replace at least one serving cell with a candidate cell based on whether a message requests configuration or reconfiguration of a candidate cell; and

[0047] Fig. 14 is a flow diagram of an example method, implemented in a DU, for determining whether to replace a first candidate cell with a second candidate cell based on whether a received ID is an ID for the first candidate cell.DETAILED DESCRIPTION OF THE DRAWINGS

[0048] 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) 104, a base station 106 and a core network (CN) 110. The UE 102 initially connects to the base station 104. In some scenarios, the base station 104 can perform an SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104 and the base station 106. The base stations 104 and 106 operate as an MN and an SN for the UE 102, respectively.

[0049] In various configurations of the wireless communication system 100, the base station 104 can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station 106 can be implemented as a secondary gNB (SgNB). The UE 102 can communicate with the base station 104 and the base station 106 via the same RAT such as EUTRA or NR, or different RATs. When the base station 104 is an MeNB and the base station 106 is a SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0050] In some cases, an MeNB or an SeNB is implemented as an ng-eNB rather than an eNB. When the base station 104 is a Master ng-eNB (Mng-eNB) and the base station 106 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 104 is an MgNB and the base station 106 is an SgNB, the UE 102 may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the base station 104 is an MgNB and the base station 106 is a Secondary ng-eNB (Sng-eNB), the UE 102 may be in NR-EUTRA DC (NE-DC) with the MgNB and the Sng-eNB.

[0051] In the scenarios where the UE 102 hands over from the base station 104 to the base station 106, the base stations 104 and 106 operate as 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 104 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 106 and the additional base station or operate in single connectivity (SC) with the base station 106, after completing thehandover. The base stations 104 and 106 in this case operate as a source MN (S-MN) and a target MN (T-MN), respectively.

[0052] 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 104 can be an eNB supporting an SI interface for communicating with the EPC 111, an ng-eNB supporting an NG interface for communicating with the 5GC 160, or a gNB that supports an NR radio interface as well as an NG interface for communicating with the 5GC 160. To directly exchange messages with each other during the scenarios discussed below, the base stations 104 and 106 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.

[0053] As illustrated in Fig. 1A, the base station 104 supports cell 124A, and the base station 106 supports a cell 126. The cells 124A and 126 can partially overlap, so that the UE 102 can communicate in DC with the base station 104 and the base station 106, where one of the base stations 104 and 106 is an MN and the other is an SN. The base station 104 can support additional cell(s) such as cells 124B and 124C, and the base station 106 can support additional cell(s) (not shown in Fig. 1A). The cells 124A, 124B and 124C can partially overlap, so that the UE 102 can communicate in carrier aggregation (CA) with the base station 104. The base station 104 can operate the cells 124A, 124B and 124C via one or more transmit and receive points (TRPs). More particularly, when the UE 102 is in DC with the base station 104 and the base station 106, one of the base stations 104 and 106 operates as an MeNB, an Mng-eNB or an MgNB, and the other operates as an SgNB or an Sng-eNB.

[0054] In general, the wireless communication network 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. 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.

[0055] With continued reference to Fig. 1A, the base station 104 is equipped with processing hardware 130 that can include one or more general-purpose processors (e.g., CPUs) and a non-transitory computer-readable memory storing instructions that the one or more general-purpose processors execute. Additionally or alternatively, the processing hardware 130 can include special-purpose processing units. The processing hardware 130 can include a PHY controller 132 configured to transmit data and control signal on physical downlink (DL) channels and DL reference signals with one or more user devices (e.g. UE 102) via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The PHY controller 132 is also configured to receive data and control signal on physical uplink (UL) channels and / or UL reference signals with the one or more user devices via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The processing hardware 130 in an example implementation includes a 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 for the one or more user devices, and / or communicating UL / DL MAC PDUs with the one or more user 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 132 may be configured to support RRC messaging associated with LTM configuration procedures, handover procedures, and / or to support the necessary operations when the base station 104 operates as an MN relative to an SN or as an SN relative to an MN. The base station 106 can include processing hardware 140 that is similar to processing hardware 130. In particular, components 142, 144, and 146 can be similar to the components 132, 134, and 136, respectively.

[0056] 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 memorystoring 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 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126) 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 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126) and / or one or more TRPs. The processing hardware 150 in an example implementation includes a MAC controller 154 configured to perform MAC functions with base station 104 or 106. For example, the MAC functions 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 104 or 106. 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.

[0057] 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 104 or the SN 106. 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.

[0058] Fig. IB depicts an example distributed implementation of a base station such as the base station 104 or 106. The base station in this implementation can include a centralized unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 is equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In one example, the CU 172 is equipped with the processing hardware 130. In another example, the CU 172 is equipped with the processing hardware 140. The processing hardware 140 in an example implementation includes an SN RRC controller 142 configured to manage or control one or more RRC configurations and / or RRC procedures when the base station 106 operates as an SN. The DU 174 is also equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In someexamples, 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 106 operates as an MN or an SN. The process hardware may include further a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0059] Fig. 2A illustrates, in a simplified manner, an example protocol stack 200 according to which the UE 102 can communicate with an eNB / ng-eNB or a gNB (e.g., one or more of the base stations 104, 106).

[0060] 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 Data Adaptation Protocol (SDAP) 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 210 over EUTRA RLC 206 A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

[0061] 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 layer 208 or 210) that can be referred to as service data units (SDUs), and output packets (e.g., to the RLC layer 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.”

[0062] 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) toexchange 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.

[0063] 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 104 or 106 can hold all the control and upper layer functionalities (e.g., RRC 214, SDAP 212, NR PDCP 210), while the lower layer operations (e.g., NR RLC 206B, NR MAC 204B, and NR PHY 202B) are delegated to the DU. To support connection to a 5GC, NR PDCP 210 provides SRBs to RRC 214, and NR PDCP 210 provides DRBs to SDAP 212 and SRBs to RRC 214.

[0064] 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- 7B that are similar are labeled with similar reference numbers e.g., event 316 is similar to event 416 of Figs 4A and 4B, event 516 of Fig. 5A, event 517 of Fig. 5B, event 616 of Fig. 6A, event 617 of Fig. 6B, event 716 of Fig. 7A, and event 717 of Fig. 7B), 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.

[0065] Referring first to Fig. 3, in a scenario 300, the base station 104 includes a CU 172 and a DU 174 and the DU 174 operates the cell 124A. The UE 102 initially communicates 302 with the DU 174 on the cell 124A using a serving DU configuration, and communicates with the CU 172 via the DU 174 (e.g., using a serving CU configuration). In other words, the DU 174 is a serving DU that is communicating with the UE 102. In some implementations, the UE 102 in carrier aggregation (CA) communicates with the DU 174 on the cell 124A and other cell(s) (e.g., cell 124D not shown in Fig. 1A) using the serving DU configuration. The DU 174 operates the other cell(s). The cell 124A and / or the other cell(s) are serving cell(s) for the UE 102. In further implementations, the UE 102 only communicates with the DU 174 on the cell 124A. In some implementations, the UE 102 communicates with the DU 174 onthe cell 124A and / or other cell(s) via one or multiple TRPs. In some implementations, the cell 124A is a PCell. In such cases, the other cell(s) include SCell(s) and / or additional cell(s) associated with the PCell or an SCell. In further implementations, the cell 124A is an SCell, and one of the other cell(s) is a PCell. In such cases, the remaining cells include SCell(s) and / or additional cell(s) associated with the PCell or an SCell. In some implementations, for the following description, the base station 104 is the DU 174, the CU 172, or the DU 174 and CU 172.

[0066] In further implementations, the UE 102 transmits 302 UL PDUs and / or UL control signals to the base station 104 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 104 via radio bearers which include SRBs and / or DRB(s). In further implementations, the base station 104 configures 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, scheduling request(s), and / or sounding reference signal(s). In further implementations, similarly the UE 102 receives DL PDUs and / or DL control signals from the base station 104 on the cell 124A 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)). In further implementations, the base station 104 transmits 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.

[0067] In some implementations, the serving DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In further implementations, the serving DU configuration includes at least one first non-LTM TCI state configuration for the serving cell(s). In still further implementations, the DU 174 transmits 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 some implementations, the DU 174 transmits the configuration parameters and / or the first non-LTM TCI state configuration(s) to the UE 102 directly. In further implementations, the serving DU configuration is a CellGroupConfig IE (e.g., definedin 3GPP TS 38.331). In still further implementations, the serving DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the serving CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In further implementations, the serving CU configuration includes a MeasConfig IE and / or a RadioBearerConfig IE (e.g., defined in 3GPP TS 38.331), or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some implementations, the serving DU configuration includes a CSl-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and reporting. In further implementations, the serving CU configuration includes a CSl-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 further implementations, the UE 102 receives a portion of the serving CU configuration and / or a portion of the serving DU configuration from a base station other than the base station 104 and the remaining portion of these configuration parameters from the base station 104.

[0068] In some implementations, the UE 102 and DU 174 communicate with each other using the first non-LTM TCI state configuration(s) (e.g., in the events 302, 318, 320, 324, 325, 330, and / or 331). In some implementations, the DU 174 transmits at least one first non- LTM TCI States Activation / Deactivation command to the UE 102 to activate some of the first non-LTM TCI state configuration(s). The UE 102 activates the some of 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 174 indicates deactivation of some of the first non-LTM TCI state configuration(s) in some of the first non- LTM TCI States Activation / Deactivation command(s). The UE 102 and DU 174 communicate with each other using the activated non-LTM TCI state configuration(s) (e.g., in the events 302, 318, 320, 324, 325, 330, and / or 331).

[0069] In some implementations, the first non-LTM TCI States Activation / Deactivation command(s) are MAC CE(s). In further implementations, the MAC CE(s) include one or more TCI States Activation / Deactivation for UE-specific PDSCH MAC CEs, one or more TCI State Indication for UE-specific PDCCH MAC CEs, one or more PUCCH spatial relation Activation / Deactivation MAC CEs, one or more Enhanced TCI StatesActivation / Deactivation for UE-specific PDSCH MAC CEs, one or more Enhanced PUCCHSpatial Relation Activation / Deactivation MAC CEs, one or more Enhanced TCI States Indication for UE-specific PDCCH MAC CEs, one or more PUCCH spatial relation Activation / Deactivation for multiple TRP PUCCH repetition MAC CEs, and / or one or more Unified TCI States Activation / Deactivation MAC CEs.

[0070] In some implementations, the DU 174 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).

[0071] While communicating with the base station 104, the UE 102 transmits 304 at least one measurement report to the DU 174. In some implementations, the at least one measurement report includes Layer 1 (LI) measurement report(s) and / or Layer 3 (L3) measurement report(s) for at least one serving cell of the UE 102 and / or at least one nonserving cell. For each of the L3 measurement report(s), the DU 174 transmits 306 a DU-to- CU message including the L3 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)). In some implementations, the DU 174 does not transmit or refrains from transmitting the LI measurement report(s) to the CU 172. The at least one serving cell includes the cell 124A and / or other cell(s), and the at least one nonserving cell includes the cell 124B and / or cell 124C. In some implementations, the serving DU configuration or the serving CU configuration includes at least one measurement configuration. In some implementations, the UE 102 receives 302 one or more RRC messages (e.g., RRCReconfiguration message(s)) including the at least one measurement configuration from the CU 172 via the DU 174. In accordance with the at least one measurement configuration, the UE 102 performs measurements and transmits 304 the at least one measurement report to the DU 174. In some implementations, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)) and / or LI measurement configuration(s). In further implementations, the LI measurement configuration(s) (e.g., CSl-MeasConfig IE(s)) includes LI measurement resource configuration(s) and / or LI measurement reporting configuration(s). In yet further implementations, the LI measurement resource configuration(s) configure reference signal(s) and / or resources of the reference signal(s) for the UE 102 to measure and obtain LImeasurement results. In some implementations, the reference signal(s) includes CSI-RS(s) and / or Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Block(s) (SSB(s)). For example, the LI measurement resource configuration(s) is / are CS1- ResourceConfig IE(s). In another example, the LI measurement reporting configuration(s) configure way(s) the UE 102 uses to transmit LI measurement results / reports. For example, the LI measurement report configuration(s) is / are CSl-ReportConfig IE(s). As another example, the UE 102 transmits the L3 measurement report(s) to the CU 172 via the DU 174 in accordance with the L3 measurement configuration(s). The UE 102 transmits the LI measurement report(s) to the DU 174 in accordance with the LI measurement configuration(s) or LI measurement reporting configuration(s). In some implementations, the DU 174 does not transmit the LI measurement report(s) to the CU 172.

[0072] In some implementations, the LI measurement configuration(s) are specifically defined RRC IE(s) (e.g., as defined in 3GPP TS 38.331) for a lower layer triggered mobility (LTM). In some implementations, the LI measurement resource configuration(s) are specifically defined RRC IE(s) (e.g., as defined in 3GPP TS 38.331) for the LTM. In some implementations, the LI measurement reporting configuration(s) are specifically defined RRC IE(s) (e.g., as defined in 3GPP TS 38.331) for the LTM. In some implementations, each of the LI measurement reporting configuration(s) includes a trigger event configuration configuring a trigger event to trigger the UE 102 to transmit an LI measurement report. If the UE 102 detects the trigger event, the UE 102 transmits an LI measurement report to the DU 174.

[0073] In some implementations, each of the LI measurement report(s) includes at least one LI measurement result. In some implementations, the at least LI measurement result includes at least one LI -reference signal received power (Ll-RSRP) value and / or at least one Ll-Signal to Interference Noise Ratio (Ll-SINR) value. In some implementations, for each of the LI measurement report(s), the UE 102 transmits a PUCCH transmission, including the LI measurement report, to the DU 174. That is, the UE 102 transmits the each of the LI measurement report(s) on a PUCCH to the DU 174. In further implementations, for each of the LI measurement report(s), the UE 102 transmits a PUSCH transmission, including the LI measurement report, to the DU 174. That is, the UE 102 transmits the each of the LI measurement report(s) on a PUSCH to the DU 174. In yet further implementations, the UE 102 transmits a portion of the LI measurement report(s) on PUCCH(s) and the rest of the LI measurement report(s) on physical UL shared channel(s) (PUSCH(s)) to the DU 174. That is,for each of the portions of the LI measurement report(s), the UE 102 transmits a PUCCH transmission including the LI measurement report to the DU 174, and for each of the rest of the LI measurement report(s), the UE 102 transmits a PUSCH transmission including the LI measurement report to the DU 174. In some implementations, each of the LI measurement report(s) is a part of a CSI report (i.e., a CSI component) or a CSI report. In some implementations, the UE 102 includes other CSI components in the PUCCH transmission(s) and / or PUSCH transmission(s) described above. In further implementations, the other CSI component(s) include a channel quality indicator (CQI), a Precoding Matrix Indicator (PMI), a CSLRS Resource Indicator (CRI), a SSB Resource Indicator (SSBRI), a Layer Indicator (LI), and / or a Rank Indicator (RI). In some implementations, the UE 102 does not transmit the LI measurement report(s) formatted as RRC message(s) to the DU 174.

[0074] In some implementations, each of the L3 measurement report(s) includes at least one L3 measurement result. In further implementations, the at least one L3 measurement result includes at least one RSRP value and / or at least one SINR value. In some implementations, the UE 102 transmits each of the L3 measurement report(s) on a PUSCH to the CU 172 via the DU 174. In some implementations, each of the L3 measurement report(s) is an RRC message (e.g., MeasurementReport message). In some implementations, each of the L3 measurement configuration(s) includes a particular measurement identity (e.g., measld) and each of the L3 measurement report(s) includes a particular measurement identity in a particular L3 measurement configuration. In some implementations, when the CU 172 receives a L3 measurement report including a measurement identity and a L3 measurement result from the UE 102 via the DU 174, the CU 172 determines that the L3 measurement report is associated with an L3 measurement configuration identified by the measurement identity.

[0075] In further implementations, for each of the at least one measurement report (e.g., LI measurement report(s)), the UE 102 transmits 304 a MAC control element (CE), including the measurement report, to the DU 174. To transmit the MAC CE(s), the UE 102 generates one or more MAC PDUs each including one or more of the MAC CE(s) to the DU 174.

[0076] In some implementations, the UE 102 performs measurements on one or more reference signals in accordance with the at least one measurement configuration. In further implementations, the one or more reference signals includes one or more Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Blocks (SSBs) and / or one or more CSLRSs.The UE 102 obtains the at least one LI measurement result and / or at least one L3 measurement result from the measurements. The DU 174 transmits the one or more reference signals on the cell 124A and other cell(s) (e.g., the cell 124B, the cell 124C, and / or cell(s) not shown in Fig. 1A).

[0077] After (e.g., in response to) receiving one or some of the at least one measurement report from the UE 102, the base station 104 (i.e., the CU 172 or DU 174) determines to prepare a first cell (e.g., the cell 124B) for LTM for the UE 102. In some implementations, the base station 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the base station 104 can use the first cell to communicate with the UE 102. In some implementations, the base station 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the first cell qualifies to be a candidate cell for communications 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 signal strength and / or quality of the cell 124A, and / or is better than signal strength and / or quality of the cell 124A by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. In further implementations, if the LI measurement report(s) indicate that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than signal strength and / or quality of the cell 124A, and / or is better than signal strength and / or quality of the cell 124A by a first predetermined threshold, the DU 174 determines to prepare the first cell for the UE 102. Alternatively, the base station 104 determines to prepare the first cell for the UE 102 regardless of whether a measure report is received from the UE 102 or not.

[0078] In cases where the CU 172 determines to prepare the first cell for LTM, the CU 172 transmits 308 a first CU-to-DU message to the DU 174 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 174 to prepare the first cell for LTM for the UE 102. For example, the cell ID 1 is a 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 a LTM indicator in the first CU-to-DU message to indicate to the DU 174 to prepare the first cell for LTM. In some implementations, the LTM indicator is an LTM Information to be Setup IE or LTM Information to be Modified IE. In further implementations, the CU 172 includes the LTMindicator in an LTM Information to be Setup IE and includes the LTM Information to be Setup IE in the first CU-to-DU message. In yet further implementations, the CU 172 includes the LTM indicator in a LTM Information to be Modified IE and includes the LTM Information to be Modified IE in the first CU-to-DU message. In response to the first CU-to-DU message, the DU 174 generates a first LTM DU configuration (referred to hereinafter as LTM DU configuration 1) for the UE 102, which configures the first cell for LTM. The DU 174 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. In some implementations, the DU 174 includes the cell ID 1 together with the LTM DU configuration 1 in an IE of the first DU-to- CU message to indicate that the LTM DU configuration 1 is associated with the first cell (i.e., the cell ID 1). In cases where the DU 174 determines to prepare the first cell, the DU 174 initiates transmission of the first DU-to-CU message to the CU 172 instead of in response to a CU-to-DU message received from the CU 172.

[0079] In some implementations, the DU 174 includes, in the first DU-to-CU message, the cell ID 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. The CU 172 identifies the LTM DU configuration 1 is configured for or associated with the first cell. In some implementations, the CU 172 includes additional cell ID(s) (e.g., cell ID(s) 2, ..., N) in the first CU-to-DU message to prepare additional cell(s) (e.g., cell(s) 2, ..., N) for LTM for the UE 102, and the DU 174 includes additional LTM DU configuration(s) (e.g., LTM DU configuration(s) 2, ..., N), each configuring a particular cell of the additional cell(s), as described below. In such cases, the DU 174 includes, in the first DU-to-CU message, the additional cell ID(s) respectively associated with the additional LTM DU configuration(s) to indicate which LTM DU configuration is associated to which cell (ID). The cell(s) 1 and / or 2, ..., N are candidate cell(s).

[0080] In some implementations, the CU 172 does not include an LTM DU configuration and / or a reference LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, ..., N (i.e., non-reference LTM DU configuration(s)) based on the reference LTM DU configuration, and includes the reference LTM DU configuration in the first DU-to-CU message. In further implementations, the CU 172 includes a reference LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates the LTM DU configuration(s) 1 and / or 2, ..., N, which are delta configuration(s) to augmentthe reference LTM DU configuration. In yet further implementations, the CU 172 includes a reference LTM DU configuration (e.g., a first reference LTM DU configuration) in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration (e.g., a second reference LTM DU configuration) replacing the first reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, ..., N based on the second reference LTM DU configuration, and includes the second reference LTM DU configuration in the first DU-to-CU message. In additional implementations, the CU 172 does not include a reference LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates the LTM DU configuration(s) 1 and / or 2, ..., N (i.e., non-reference LTM DU configuration(s)) as complete LTM DU configuration(s).

[0081] In some implementations, the reference LTM DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some implementations, the reference LTM DU configuration is a CellGroupConfig IE (e.g., defined in 3GPP TS 38.331). In further implementations, the reference LTM DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the reference LTM DU configuration includes a CS1- MeasConfig IE or configuration parameters for channel state information (CSI) measurement and / or reporting.

[0082] In some implementations, the reference LTM DU configuration is different from the serving DU configuration. In some implementations, a portion of the reference LTM DU configuration is the same as a portion of the serving DU configuration and the rest of the reference LTM DU configuration is different from the rest of the serving DU configuration. In further implementations, the reference LTM DU configuration is the same as the serving DU configuration.

[0083] After receiving the first DU-to-CU message, the CU 172 generates an RRC reconfiguration message (e.g., an RRCReconfiguration message), including the LTM DU configuration 1, and transmits 316 a second CU-to-DU message, including the RRC reconfiguration message, to the DU 174. In some implementations, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message that the CU 172 transmits 316. In further implementations, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message 316. In some implementations, if the CU 172 transmits the reference LTM DU configuration to the UE 102 during the event 302,the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message during the event 316. In further implementations, if the CU 172 receives the reference LTM DU configuration from the DU 174, the CU 172 includes the LTM DU configuration in the RRC reconfiguration message of event 316. Otherwise, if the CU 172 does not receive a reference LTM DU configuration from the DU 174, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message of event 316.

[0084] In some implementations, the CU 172 includes the LTM DU configuration 1 and / or the LTM CU configuration 1 in a first container (e.g., a field / IE) and includes the first container (e.g., LTM configuration 1) in the RRC reconfiguration message in events 316 and 318. In such cases, the CU 172 generates the first container. The first container indicates to the UE 102 not to apply the LTM DU configuration 1 and / or the LTM CU configuration 1 immediately. In some implementations, the UE 102 receives an RRC reconfiguration message (e.g., the RRC reconfiguration message of the event 318) including a configuration (e.g., the LTM DU configuration 1 and / or the LTM CU configuration 1). If the first container includes the configuration and the RRC reconfiguration message includes the first container, the UE 102 refrains from immediately applying the configuration. Otherwise, in some implementations if the configuration is not included in the first container, the UE 102 applies the configuration immediately.

[0085] In some implementations, the first container includes or is a first addition or modification list (e.g., Itm-CandidateToAddModList field or LTM-CandidateToAddModList IE). The CU 172 includes the LTM DU configuration 1 and / or the LTM CU configuration 1 in a first element (referred to hereinafter as element 1) of the first addition or modification list. In some implementations, the CU 172 generates an RRC message (e.g., RRCRecconfiguration message), including the LTM DU configuration 1 and / or the LTM CU configuration 1, and includes the RRC message in the element 1. In some implementations, the element 1 is an addition or modification IE (e.g., LTM-ConfigToAddMod IE, LTM- Candidate IE, LTM-CandidateToAddMod IE or LTM-CandidateConfigToAddMod IE). In some implementations, when the UE 102 receives the first addition or modification list, the UE 102 stores the first addition or modification list (e.g., in a variable in the random access memory (RAM)). In further implementations, the DU 174 generates the first container and includes the first container in the first DU-to-CU message. In yet further implementations,the DU 174 generates the element 1 and includes the element 1 in the first DU-to-CU message.

[0086] In some implementations, the CU 172 includes an LTM CU configuration 1 in the RRC reconfiguration message in event 316, the first container, or the element 1, where the LTM CU configuration 1 is associated with the LTM DU configuration 1. In further implementations, to associate the LTM CU configuration 1 with the LTM DU configuration 1, the CU 172 includes the LTM CU configuration 1 and the LTM DU configuration in the element 1. In some implementations, the CU 172 includes LTM CU configuration(s) 2, ..., N in the RRC reconfiguration message of event 316 or the second container, where the LTM CU configuration(s) 2, ..., N are associated with the LTM DU configuration(s) 2, ..., N, respectively. In some implementations, to associate the LTM CU configuration(s) 2, ..., N with the LTM DU configuration(s) 2, ..., N, the CU 172 includes the LTM CU configuration(s) 2, ..., N and the LTM DU configuration(s) in element(s) 2, ..., N, respectively. In further implementations, the CU 172 includes, in the element(s) 2, ..., N, the LTM CU configuration(s) 2, ..., N associated with the LTM DU configuration(s) 2, ..., N, respectively. Alternatively, the CU 172 does not include, in the RRC reconfiguration message of event 316, LTM CU configuration(s) for some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ..., N.

[0087] After receiving 316 the RRC reconfiguration message, the DU 174 transmits 318 the RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320 a RRC reconfiguration complete message (e.g., an RRCReconfigurationComplete message) to the DU 174, which in turn transmits 322 a second DU-to-CU message, including the RRC reconfiguration complete message, to the CU 172. In some implementations, the CU 172 performs security protection (e.g., integrity protection and / or encryption) on the RRC reconfiguration message. Lor example, the CU 172 generates a message authentication code for integrity (MAC-I) for the RRC reconfiguration message, encrypts the RRC reconfiguration message and the MAC-I to obtain an encrypted RRC reconfiguration message and an encrypted MAC-I, and transmits 316 and 318 a PDCP PDU including the encrypted RRC reconfiguration message and encrypted MAC-I to the UE 102 via the DU 174. When the UE 102 receives the PDCP PDU from the CU 172 via the DU 174 (i.e., at events 316 and 318), the UE 102 decrypts the encrypted RRC reconfiguration and encrypted MAC-I to obtain the RRC reconfiguration message and MAC-I and verifies whether theMAC-I is valid. If the UE 102 verifies the MAC-I is invalid, the UE 102 discards or ignoresthe RRC reconfiguration message. In some implementations, the UE 102 performs an RRC connection reestablishment procedure in response to the invalid MAC-I. In further implementations, if the UE 102 verifies the MAC-I is valid, the UE 102 processes the RRC reconfiguration. The UE 102 refrains from applying (i.e., executing) the LTM DU configuration 1 until receiving an LTM command activating the LTM DU configuration 1 as described for events 330, 350.

[0088] The events 308 (optional) and 310 are collectively referred to in Fig. 3 as an LTM preparation procedure 390. The events 316, 318, 320, 322 are collectively referred to in Fig.3 as an LTM configuration delivery procedure 394.

[0089] In some implementations, the first CU-to-DU message is a UE Context Setup Request message, and the first DU-to-CU message is a UE Context Setup Response message. 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 or UE Context Modification Required message. In the case of the UE Context Modification Required message, the CU 172 transmits a UE Context Modification Confirm message to the DU 174 in response to UE Context Modification Required message. In some implementations, the second CU-to-DU message is a DE RRC Message Transfer message. In further implementations, the second CU-to-DU message is a UE Context Modification Request message. In still further implementations, the second DU-to-CU message is a UE RRC Message Transfer message. In yet still further implementations, the second DU-to-CU message is a UE Context Modification Response message.

[0090] In some implementations, the UE Context Modification Request and UE Context Modification Response (collectively referred to as a “UE context modification procedure”) is performed to modify the established UE Context (e.g., establishing, modifying, and / or releasing radio resources or sidelink resources). In some implementations, the UE context modification procedure is also used to command the DU 174 to stop data transmission for the UE 102 for mobility (see 3GPP TS 38.401). In further implementations, the procedure uses UE-associated signaling.

[0091] In some implementations, the UE Context Modification Request message is initiated by the CU 172. In further implementations, upon receipt of the UE Context Modification Request message, the DU 174 performs the modifications, and, if successful, reports the update in the UE Context Modification Response message.

[0092] In some implementations, if the SpCell ID IE is included in the UE Context Modification Request message, the DU 174 replaces any previously received value and regards it as a reconfiguration with sync (e.g., as defined in 3GPP TS 38.331). In further implementations, if the ServCelllndex IE is included in the UE Context Modification Request message, the DU 174 considers the ServCelllndex IE for the indicated SpCell. In still further implementations, if the SpCell UE Configured IE is included in the UE Context Modification Request message, the DU 174 configures UL for the indicated SpCell accordingly. In yet further implementations, if the servingCellMO IE is included in the UE Context Modification Request message, the DU 174 configures servingCellMO for the indicated SpCell accordingly. In yet still further implementations, if the servingCellMO List IE is included in the UE Context Modification Request message, the DU 174, if supported, configures servingCellMO after determining the list of BWPs for the UE and includes the list of servingCellMOs that have been encoded in CellGroupConfig IE as a ServingCellMO- encoded-in-CGC List IE in the UE Context Modification Response message.

[0093] In some implementations, if the Configured BWP List IE is included in the UE Context Modification Response message, the CU 172, if supported, considers the Configured BWP List IE when requesting the DU 174 for generating preconfigured measurement GAP for the indicated BWPs.

[0094] In further implementations, if the Preconfigured Measurement GAP Request IE is present in the CU-to-DU RRC Information IE in the UE Context Modification Request message, the DU 174, if supported, considers that the content of the previous CellGroupConfig IE was not sent to the UE 102 and generates the pre-configured measurement GAP for the indicated BWPs in the MeasConfig IE. In further implementations, if the DU 174 successfully generates pre-configured measurement GAP for the indicated BWPs, the DU 174 updates the CellGroupConfig IE with the content of the previous CellGroupConfig IE and the preconfigured measurement GAP configuration in the UE Context Modification Response message.

[0095] In some implementations, if the SCell To Be Setup List IE is included in the UE Context Modification Request message, the DU 174 considers the SCell To Be Setup List IE as a list of candidate SCells to be set up. In further implementations, if (i) the SCell To Be Setup List IE is included in the UE Context Modification Request message not concerning conditional handover, conditional PSCell addition, conditional PSCell change, LTM, and / orsubsequent CPAC, and (ii) the indicated SCell(s) are already setup, the DU 174 replaces any previously received value. In further implementations, if (i) the SCell To Be Setup List IE is included in the UE Context Modification Request message, (ii) the UE Context Modification Request message concerns LTM, and (iii) the indicated SCell(s) are already setup, the DU 174 replaces any previously received value associated with the SpCell ID indicated in the UE Context Modification Request message. In still further implementations, if the SCell UL Configured IE is included in the UE Context Modification Request message, the DU 174 configures UL for the indicated SCell accordingly. In yet further implementations, if the servingCellMO IE is included in the UE Context Modification Request message, the DU 174 configures servingCellMO for the indicated SCell accordingly.

[0096] In some implementations, the CU 172 include a reference LTM CU configuration in the RRC reconfiguration message or the first container in the event 316. In further implementations, the CU 172 generates the LTM CU configuration 1 (i.e., non-reference LTM CU configuration) as a delta configuration to augment the reference LTM CU configuration. Similarly, in still further implementations, the CU 172 generates some or all of the LTM CU configuration(s) 2, ..., N as delta configuration(s) to augment the reference LTM CU configuration. Alternatively, the CU 172 includes the reference LTM CU configuration and does not include a non-reference LTM CU configuration in the RRC reconfiguration message or the first container of event 316. In some implementations, the CU 172 includes the reference LTM CU configuration and / or the reference LTM DU configuration in an additional container (e.g., reference LTM configuration) and include the additional container in the RRC reconfiguration message of event 316.

[0097] In some implementations, the reference LTM CU configuration is different from the serving CU configuration. In further implementations, a portion of the reference LTM CU configuration is the same as a portion of the serving CU configuration and the rest of the reference LTM CU configuration is different from the rest of the serving CU configuration. In still further implementations, the reference LTM CU configuration is the same as the serving CU configuration.

[0098] In some implementations, the CU 172 includes, in the RRC reconfiguration message, a first LTM ID (referred to hereinafter as ID 1) for identifying the LTM DU configuration 1 or the element 1. In some implementations, the CU 172 includes the ID 1 in the first container or element 1. In some implementations, the CU 172 assigns the ID 1.

[0099] In some implementations, the CU 172 transmits the ID 1 to the DU 174, and the DU 174 associates the ID 1 with the LTM DU configuration 1 and / or the cell ID 1. In some implementations, the CU 172 includes the ID 1 in the first CU-to-DU message. In further implementations, after receiving the first DU-to-CU message, the CU 172 transmits 312 a third CU-to-DU message including the ID 1 to the DU 174 instead of including the ID 1 in the first CU-to-DU message. In some implementations, in the third CU-to-DU message, the CU 172 includes the LTM DU configuration 1 and the ID 1 and indicates the association between the ID 1 and LTM DU configuration 1. Thus, in some implementations, the DU 174 directly associates the ID 1 with the LTM DU configuration 1. In further implementations, in the third CU-to-DU message, the CU 172 includes the cell ID 1 and the ID 1 (i.e., the first LTM ID) and indicates the association between the cell ID 1 and the ID 1. Thus, in some such implementations, the DU 174 associates the ID 1 with the LTM DU configuration 1, based on the association between the cell ID 1 and the ID 1 and the association between the cell ID 1 and the LTM DU configuration 1. In yet still further implementations, in the third CU-to-DU message, the CU 172 includes the LTM DU configuration 1, the cell ID 1 and / or the ID 1 and indicates the association between the ID 1, LTM DU configuration 1 and / or the cell ID 1. In some implementations, the DU 174 transmits 314 a third DU-to-CU message to the CU 172 in response to the third CU-to-DU message. In some implementations, the third CU-to-DU message and third DU-to-CU message are UE Context Modification Request messages and UE Context Modification Response messages. In some implementations, the CU 172 includes the ID 1, the cell ID 1 and / or the LTM DU configuration 1 in the second CU-to-DU message as described above. Thus, the third CU-to-DU message is omitted. In further implementations, the third DU-to-CU message is a UE Context Modification Required message. In such cases, the CU 172 transmits a UE Context Modification Confirm message to the DU 174 in response to the UE Context Modification Required message.

[0100] In some implementations, the events 312 (optional) and / or 314 (optional) are collectively referred to in Fig. 3 as an LTM ID assignment procedure 392.

[0101] In some implementations, in cases where the CU 172 includes the ID 1 in the first CU-to-DU message, the DU 174 includes the ID 1 in the LTM DU configuration 1, the first container, or element 1. Alternatively, in some implementations, the DU 174 does not include the ID 1 in the LTM DU configuration 1, the first container, and / or element 1. 1

[0102] In some implementations, the CU 172 includes the reference LTM DU configuration in the first container. For example, the CU 172 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1. In further implementations, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message of event 316 and outside of the first container. For example, the CU 172 generates a third container (e.g., a field / IE) to include the first container and the reference LTM DU configuration and includes the third container in the RRC reconfiguration message of the event 316. In yet further implementations, the DU 174 includes the reference LTM DU configuration in the first container. For example, the DU 174 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1. In yet still further implementations, the DU 174 generates a fourth container (e.g., a field / IE) to include the first container and the reference LTM DU configuration and includes the fourth container in the first DU-to-CU message of the event 310. In such cases, the CU 172 includes the fourth container in the RRC reconfiguration message of the event 316. Alternatively, the CU 172 retrieves the reference LTM DU configuration and the LTM DU configuration 1 from the fourth container and includes the reference LTM DU configuration and the LTM DU configuration 1 as described above.

[0103] In some implementations, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM DU configuration. In some implementations, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM CU configuration.

[0104] In some implementations, the LTM DU configuration 1 includes a plurality of configuration parameters for the UE 102 to communicate with the DU 174 on the first cell. In some implementations, the plurality of configuration parameters includes 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-BearerConfig IE(s)). In 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 a CellGroupConfig IE (e.g., defined in 3GPP TS 38.331. In other implementations, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0105] In some implementations, the LTM CU configuration 1 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 (e.g., defined in 3GPP TS 38.331) or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some implementations, the LTM DU configuration 1 includes LI measurement configuration 1 (e.g., a CSl-MeasConfig IE) and / or at least one configuration indicator (TCI) state configuration. In some implementations, the LTM CU configuration 1 includes the LI measurement configuration and / or the TCI state configuration(s) 1. In some implementations, the LI measurement configuration includes at least one reference signal (RS) resource configuration 1 and / or at least one report configuration 1. In some implementations, the RS resource configuration(s) 1 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 RS resource configuration(s) 1 includes an RS resource configuration ID. In some implementations, the RS resource configuration(s) 1 is / are (or are similar to) CSl-ResourceConfig IE(s). In some implementations, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configuration(s) 1. In some implementations, each of the TCI state configuration(s) 1 configures a TCI state that associates one or two DL RSs with a corresponding quasi-colocation (QCL) type. The DL RS(s) are associated with the cell 1.

[0106] In some implementations, the DU 174 includes the LI measurement configuration 1 and / or the TCI state configuration(s) 1 in a serving DU configuration 1 (e.g., non-LTM DU configuration). In some implementations, the DU 174 includes the serving DU configuration in the first DU-to-CU message. In further implementations, the DU 174 transmits an additional DU-to-CU message including the serving DU configuration to the CU 172. In some implementations, the additional DU-to-CU message is a UE Context Modification Required message. In some implementations, the CU 172 includes the serving DU configuration 1 in the RRC reconfiguration message of event(s) 316, 318. In furtherimplementations, the CU 172 transmits another RRC reconfiguration message including the serving DU configuration to the UE 102 via the DU 174.

[0107] In some implementations, the DU 174 includes a random access configuration in the LTM DU configuration 1. In further implementations, the DU 174 does not include a random-access configuration in the LTM DU configuration 1. In some implementations, if the cell 124A and first cell are not synchronized, the DU 174 determines to include the random access configuration in the LTM DU configuration 1. Otherwise, if the cell 124A and first cell are synchronized, the DU 174 determines to not include the random access configuration in the LTM DU configuration 1. In some implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the random-access configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 is synchronized in UL with the first cell, the DU 174 determines to not include the random access configuration in the LTM DU configuration 1. If the LTM DU configuration 1 includes the random access configuration, the UE 102 performs 332 the random access procedure in accordance with the random-access configuration, as described below. Otherwise, if the LTM DU configuration 1 does not include the random-access configuration or indicates the UE 102 to skip a random-access procedure in LTM, the UE 102 skips or refrains from performing 322 the random-access procedure in response to the LTM DU configuration 1 excluding the random-access configuration.

[0108] In some implementations, the DU 174 includes random-access configuration parameters in the LTM DU configuration 1 and / or the reference LTM DU configuration regardless of whether the cell 124A and the first cell are synchronized. The UE 102 performs 332 the random access procedure in accordance with the random access configuration parameters, as described below. In some implementations, the random access configuration parameters configure the physical random-access channel (PRACH) resources, an association between SSB and PRACH resources, and / or one or more PRACH occasions.

[0109] In some implementations, if the cell 124A and the first cell are synchronized, the DU 174 determines to include, in the LTM DU configuration 1, a first indication configuring the UE 102 not to perform a random-access procedure on the first cell. Otherwise, if the cell 124A and the first cell are not synchronized, the DU 174 determines to not include the first indication in the LTM DU configuration 1. In further implementations, if the DU 174determines that the UE 102 is synchronized in UL with the first cell, the DU 174 determines to include the first indication in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 is not synchronized in UL with the first cell, the DU 174 determines to not include the first indication in the LTM DU configuration 1. If the LTM DU configuration 1 includes the first indication, the UE 102 skips or refrains from performing 332 the random access procedure in accordance with or in response to the first indication. Otherwise, if the LTM DU configuration 1 does not include the first indication, the UE 102 performs 332 the random access procedure in accordance with the random-access configuration, in response to the LTM DU configuration 1 excluding the first indication, as described below.

[0110] In some implementations, the DU 174 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In further implementations, the DU 174 does not include a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In some implementations, the DU 174 includes an LTM cell switch information in the first LTM DU configuration 1. In further implementations, the DU 174 includes the random access configuration (parameters) in the LTM cell switch information (e.g., Itm-CellSwitchlnfo field or LTM-CellSwitchlnfo IE). In some implementations, if the cell 124A and the first cell are not synchronized, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the cell 124A and the first cell are synchronized, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1. In some implementations, if the LTM DU configuration 1 includes the reconfiguration with sync configuration, the UE 102 performs 332 the random access procedure as described below, in response to or in accordance with the reconfiguration with sync configuration. Otherwise, if the LTM DU configuration 1 does not include the reconfiguration with sync configuration, the UE 102 skips or refrains from performing 332 the random access procedure. In some implementations, the DU 174 includes a cell ID (i.e., cell ID 1) of thecell 1 (i.e., the first cell) in the LTM DU configuration 1. In further implementations, the cell ID 1 is a PCI. In still further implementations, the cell ID 1 is a CGI. In some implementations, the cell ID 1 included in the LTM DU configuration 1 is a PCI, while the cell ID 1 included in the first CU-to-DU message is a CGI. In further implementations, the LTM DU configuration 1 includes a cell index 1 indexing the cell ID 1 or the first cell. The cell index 1 is not a cell ID. The cell index takes fewer bits than the cell ID. In some implementations, the CU 172 sets the cell index 1 to a value and includes the cell index 1 in the first CU-to-DU message of the event 308.

[0111] In some implementations, after (e.g., in response to) receiving 304 one or some of the at least one measurement report, the base station 104 (i.e., the CU 172 or DU 174) determines to prepare additional cell(s) (i.e., cell(s) 2, ..., N) of the base station 104 for LTM for the UE 102. In further implementations, the base station 104 determines to prepare the additional cell(s) for LTM for the UE 102 because the at least one measurement report indicates that the base station 104 uses the additional cell(s) to communicate with the UE 102. In still further implementations, the additional cell(s) include the cell 124C and / or cell(s) other than the cells 124A, 124B and 124C. In some implementations, if the L3 measurement report(s) indicate that the signal strength and / or the quality of a particular cell of the additional cell(s) is above a respective predetermined threshold and / or is better than the cell 124A, the CU 172 determines to prepare the particular cell for LTM for the UE 102. In yet still further implementations, if the LI measurement report(s) indicates that the signal strength and / or quality of a particular cell of the additional cell(s) is above a first predetermined threshold and / or is better than the cell 124A, the DU 174 determines to prepare the particular cell for LTM for the UE 102. In some implementations, the respective predetermined threshold(s) for the additional cells are different from the first predetermined threshold. In further implementations, the respective predetermined threshold(s) for the additional cell(s) are the same as the first predetermined threshold. In still further implementations, the respective predetermined thresholds for the additional cells are the same or different. Alternatively, the base station 104 determines to prepare the additional cell(s) for the UE 102 regardless of whether a measurement report is received from the UE 102 or not.

[0112] In cases where the CU 172 determines to prepare the additional cell(s), the CU 172 initiates and performs at least one additional LTM preparation procedure with the DU 174 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) issimilar to the procedure 390. In cases where the DU 174 determines to prepare the additional cell(s), the DU 174 initiates and performs at least one additional LTM preparation procedure with the CU 172 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) are similar to the procedure 390.

[0113] In some implementations, the CU 172 and DU 174 perform the LTM preparation procedure(s) 2, ..., N to prepare the cell(s) 2, ..., N, respectively, similar to the procedure 390. In further implementations, the CU 172 includes the cell ID(s) 2, ..., N in CU-to-DU message(s) 2, ..., N in the LTM preparation procedure(s) 2, ..., N, respectively, similar to the first CU-to-DU message. In the LTM preparation procedure(s) 2, ..., N, the DU 174 generates LTM DU configuration(s) 2, ..., N configuring the cell(s) 2, ..., N and includes the LTM DU configuration(s) 2, ..., N in DU-to-CU message(s) 2, .., N, respectively, as described for the LTM DU configuration 1. In cases where the DU 174 receives the CU-to- DU message(s) 2, ..., N, the DU-to-CU message(s) 2, ..., N responds to the CU-to-DU message(s) 2, ..., N, respectively. “N” is an integer and larger than one. For example, “N” is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 14, 15, or 16. In another example, the maximum number of “N” is 4, 8, 16, or 32. Examples and implementations regarding the LTM DU configuration 1 can apply to the LTM DU configuration(s) 2, ..., N.

[0114] In further implementations, the CU 172 and DU 174 performs a single LTM preparation procedure (i.e., the LTM preparation procedure 390) to prepare the cell(s) 1, 2, ..., N. In such cases, the DU 174 includes the LTM DU configuration(s) 1, 2, ..., N for the cell(s) 1, 2, ..., N, respectively in the first DU-to-CU message. In the first DU-to-CU message, in still further implementations, the DU 174 includes the cell ID(s) 1, 2, ..., N respectively associated with the LTM DU configuration(s) 1, 2, ..., N to indicate that the LTM DU configuration(s) 1, 2, ..., N are configured for the cell ID(s) 1, 2, ..., N, respectively. In cases where the CU 172 determines to perform the LTM preparation procedure 390, the CU 172 includes the cell ID(s) 1, 2, ..., N in the first CU-to-DU message to request the DU 174 to prepare the cell(s) 1, 2, ..., N, respectively, for LTM.

[0115] In some implementations, after receiving the LTM DU configuration(s) 2, ..., N from the DU 174, the CU 172 includes the LTM DU configuration(s) 2, ..., N in the first container. In further implementations, the CU 172 includes the LTM DU configuration(s) 2, ..., N in element(s) 2, ..., N, respectively, and includes the element(s) 2, ..., N in the first container. In still further implementations, the CU 172 includes, in the RRC reconfigurationmessage, LTM ID(s) (i.e., ID(s) 2, N) for identifying the LTM DU configuration(s) 2, N, respectively. In yet still further implementations, the CU 172 includes the ID(s) 2, ..., N in the first container. For example, the CU 172 includes the ID(s) 2, ..., N and LTM DU configuration(s) 2, ..., N in the element(s) 2, ..., N in the first addition or modification list.

[0116] In some implementations, the CU 172 assigns the ID(s) 2, ..., N for the LTM DU configuration(s) 2, ..., N, respectively. In further implementations, the CU 172 receives the ID(s) 2, ..., N from the DU 174 in the first DU-to-CU message of the procedure 390. In still further implementations, the CU 172 receives, from the DU 174, the ID(s) 2, ..., N in the DU-to-CU message(s) 2, ..., N of the LTM preparation procedure(s) 2, ..., N, respectively.

[0117] In some implementations, the CU 172 performs an LTM ID assignment procedure with the DU 174 for each of the LTM DU configuration(s) 2, ..., N, similar to the procedure 392. In further implementations, the CU 172 includes the ID(s) 2, ..., N and the LTM DU configuration(s) 2, ..., N in the third CU-to-DU message and indicates the association between the ID(s) 2, ..., N and the LTM DU configuration(s) 2, ..., N, respectively. Thus, in some such implementations, the DU 174 associates the LTM DU configuration(s) 2, ..., N with the ID(s) 2, ..., N, respectively. In yet further implementations, the CU 172 includes the cell ID(s) 2, ..., N and the ID(s) 2, ..., N in the third CU-to-DU message and indicates the association between the cell ID(s) 2, ..., N and the ID(s) 2, ..., N, respectively. Thus, in some such implementations, the DU 174 associates the LTM DU configuration(s) 2, ..., N with the ID(s) 2, ..., N, respectively, based on the association between the cell ID(s) 2, ..., N and the ID(s) 2, ..., N and the association between the cell ID(s) 2, ..., N and the LTM DU configuration(s) 2, ..., N, respectively. In some implementations, the CU 172 includes the ID(s) 2, ..., N, the cell ID(s) 2, ..., N and / or the LTM DU configuration(s) 2, ..., N in the second CU-to-DU message as described above. Thus, in further implementations, the CU 172 omits the third CU-to-DU message. In yet further implementations, the CU 172 includes the ID(s) 2, ..., N in the first CU-to-DU message and indicates that the ID(s) 2, ..., N is / are respectively associated with the cell ID(s) 2, ..., N. In some implementations, the DU 174 includes the ID(s) 2, ..., N in the LTM DU configuration(s) 2, ..., N. Thus, the CU 172 does not include the ID(s) 2, ..., N in the RRC reconfiguration message, the first container, and / or the element(s) 2, ... , N.

[0118] In some implementations, the DU 174 assigns the ID(s) 2, ..., N. In further implementations, the DU 174 includes the ID(s) 2, ..., N in the first DU-to-CU message ofthe procedure 390. In still further implementations, the DU 174 includes the ID(s) 2, .. N in the DU-to-CU message(s) 2, .. N of the LTM preparation procedure(s) 2, .. ,,N. In some implementations, the CU 172 includes the ID(s) 2, ..., N in the RRC reconfiguration message. In some implementations, the DU 174 includes the ID(s) 2, ..., N in the LTM DU configuration(s) 2, ..., N. Thus, the CU 172 does not include an ID (e.g., LTM ID) identifying each of the LTM DU configuration(s) 2, ..., N in the RRC reconfiguration message, first container, and / or element 1.

[0119] In some implementations, the CU 172 generates a second container including the LTM DU configuration(s) 2, ..., N or element(s) 2, ..., N instead of using the first container. The CU 172 then transmits an additional RRC reconfiguration message, including the second container, to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits an additional RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. In some implementations, the second container includes or is a second addition or modification list (e.g., Itm-ConfigToAddModList field, LTM-ConfigToAddModList IE, Itm-CandidateConfigToAddModList field, or LTM- CandidateConfigToAddModList IE), and each of the element(s) 2, ..., N is an addition or modification IE (e.g., Itm-ConfigToAddMod field, LTM-ConfigToAddMod l , Itm- CandidateConfigToAddMod field, or LTM-CandidateConfigToAddMod IE). In some implementations, when the UE 102 receives the second addition or modification list, the UE 102 stores the second addition or modification list together with the first addition or modification list (e.g., as a variable in RAM).

[0120] In some implementations, the DU 174 includes cell ID(s) 2, ..., N in the LTM DU configuration(s) 2, ..., N to identify the cell(s) 2, ..., N, respectively. In some implementations, each of the cell ID(s) 2, ..., N is a PCI. In further implementations, the LTM DU configuration(s) 2, ..., N includes cell index(es) 2 , ..., N indexing the cell ID(s) 2, ..., N or the cell(s) 2, ..., N, respectively. In some cases where the CU 172 prepares the cell(s) 2, ..., N for LTM in the procedure 390, the CU 172 sets the cell index(es) 2, ..., N to different value(s) and include the cell index(es) 2, ..., N in the first CU-to CU-to-DU message of the event 308. In some cases where the CU 172 prepares the cell(s) 2, ..., N in the additional LTM preparation procedure(s), sets the cell index(es) 2, ..., N to different values, and includes the cell index(es) 2, ..., N in CU-to-DU message(s) of the additional LTM preparation procedure(s). The CU 172 sets the cell index(es) 1, ..., N to differentvalues. In some implementations, the cell ID(s) 1, N in the LTM DU configuration(s) 1, .. N are different from the cell ID(s) 1, .. N in the CU-to-DU message(s) described above.

[0121] In some implementations, each of the LTM DU configuration(s) 1, ..., N includes physical configuration parameters, MAC configuration parameters, RLC configuration parameters, and / or LI measurement configuration(s). In further implementations, each of the LTM DU configuration(s) 1, ..., N is a CellGroupConfig IE (e.g., as defined in 3GPP TS 38.331). In still further implementations, each of the LTM DU configuration(s) 1, ..., N includes configuration parameters included in a CellGroupConfig IE (e.g., as defined in 3GPP TS 38.331). In still further implementations, the plurality of configuration parameters in each of the LTM DU configuration(s) include a particular 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(s) 1, ..., N are CellGroupConfig IE(s) (e.g., defined in 3GPP TS 38.331). In yet still further implementations, the LTM DU configuration(s) 1, ..., N include configuration parameters in the CellGroupConfig IE.

[0122] In some implementations, the CU 172 includes one or more additional LTM CU configurations in at least one of the element(s) 2, ..., N, the first container, or the second container. Each of the additional LTM CU configurations are associated with a particular LTM DU configuration of the LTM DU configuration(s) 2, ..., N. Examples and implementations of the additional LTM CU configurations are similar to the LTM CU configuration 1.

[0123] In some implementations, the CU 172 determines to release the LTM DU configuration M of the LTM DU configuration(s) 1, ..., N (or the element M of the element(s) 1, ..., M). 1 < M < N. In response to the determination, the CU 172 transmits a RRC reconfiguration message to the UE 102 via the DU 174 to indicate the UE 102 to release the LTM DU configuration M or element M. In some implementations, the CU 172 generates a release list, including the ID (i.e., LTM ID) M for releasing the LTM DU configuration M or element M, and includes the release list in the RRC reconfiguration message. In response to the RRC reconfiguration message, the UE 102 releases the LTM DU configuration M or element M and transmits an RRC reconfiguration complete message to the CU 172 via the DU 174. In response to the determination, the CU 172 transmits a CU-to- DU message to the DU 174 to indicate to the DU 174 to release the LTM DU configuration M. In some implementations, to indicate to the DU 174 to release the LTM DU configurationM, the CU 172 includes the cell ID M or the ID (i.e., LTM ID) M in a release indication (e.g., a field or IE) in the CU-to-DU message. In response, the DU 174 releases the LTM DU configuration M and transmits a DU-to-CU message to the CU 172. In some implementations, the CU-to-DU message and DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0124] In other implementations, the DU 174 determines to release the LTM DU configuration K, where 1 < K < N. In response to the determination, the DU 174 transmits a DU-to-CU message to the CU 172 to release the LTM DU configuration K. In some implementations, to indicate the LTM DU configuration K is released, the DU 174 includes the cell ID K or the ID (i.e., LTM ID) K in a release indication (e.g., a field or IE) in the DU- to-CU message. After (e.g., in response to) receiving the DU-to-CU message, the CU 172 generates a release list, including the ID (i.e., LTM ID) K to release the LTM DU configuration K or element K, and transmits an RRC reconfiguration message including the release list to the UE 102 via the DU 174. In response, the UE 102 releases the LTM DU configuration K or element K and transmits an RRC reconfiguration complete message to the UE 102 via the DU 174. In some implementations, the CU 172 transmits a CU-to-DU message to the DU 174 in response to the DU-to-CU message. In some implementations, the DU-to-CU message and CU-to-DU message are a UE Context Modification Required message and a UE Context Modification Confirm message, respectively.

[0125] After receiving 318 the RRC reconfiguration or transmitting 320 the RRC reconfiguration complete message, the UE 102 transmits 324 at least one measurement report to the DU 174, similar to the event 304. In some implementations, the DU 174 transmits 326 a DU-to-CU message, including the at least one measurement report, to the CU 172, similar to the event 306. In further implementations, the DU 174 does not transmit the at least one measurement report to the CU 172. In some implementations, the UE 102 transmits 324 the at least one measurement report including LI measurement report(s) or L3 measurement report(s) as described for the event 304. In further implementations, the UE 102 transmits 324 the at least one measurement report on PUCCH(s) and / or PUSCH(s) to the DU 174, similar to the event 304. In still further implementations, the UE 102 transmits 324 at least one MAC CE including the at least one measurement report to the DU 174, similar to the event 304. In yet still further implementations, the UE 102 does not transmit the LI measurement report(s) in the format of the RRC message(s) to the DU 174.

[0126] In some implementations, the UE 102 transmits 324 the at least one measurement report to the DU 174 in accordance with at least one measurement configuration. The at least one measurement configuration configures the UE 102 to perform measurements and report measurement results. The CU 172 transmits the at least one measurement configuration to the UE 102 via the DU 174. In some implementations, the CU 172 transmits one or more RRC messages (e.g., RRCReconfiguration message(s)), including the at least one measurement configuration, to the UE 102 via the DU 174 in the event 302 and / or 316 and / or after the event 306 or 316. In some implementations, the one or more RRC messages include the RRC reconfiguration message of the event 316. In accordance with the at least one measurement configuration, the UE 102 performs measurements on one or more reference signals. In some implementations, the one or more reference signals include one or more SSBs and / or one or more CSI-RSs. The UE 102 obtains the at least one LI measurement result and / or at least one L3 measurement result from the measurements and includes the at least one LI measurement result and / or at least one L3 measurement result in the at least measurement report of the event 324. The DU 174 transmits the one or more reference signals on the cell 124A, the cell 1 and / or the cell(s) 2, ..., N. In some implementations, the one or more reference signals are CSI-RS(s) or SSB(s).

[0127] In some implementations, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)), as described for the event 304. In further implementations, the at least one measurement configuration includes or is one or more LI measurement configuration(s), as described above. In still further implementations, the LI measurement configuration(s) are or include CSl-MeasConfig IE(s) (e.g., defined in 3GPP TS 38.331). In yet still further implementations, the LI measurement configuration(s) include RS resource configuration(s) and / or report configuration(s). The UE 102 transmits 324 the LI measurement report(s) on UL resources (e.g., PUCCH resources or PUSCH resources) to the DU 174 in accordance with the report configuration(s). The DU 174 receives the LI measurement report(s) on the UL resources in accordance with the report configuration(s). In some implementations, the report configuration(s) are or are similar to CSl-ReportConfig IE(s). In further implementations, each of the report configuration(s) is a specifically defined RRC IE (e.g., as defined in 3GPP TS 38.331). In some implementations, (each of) the report configuration(s) configures periodically reporting and / or event-triggered reporting of the LI measurement result(s).

[0128] In some implementations, the LI measurement report(s) is / are CSI report(s). In further implementations, the LI measurement report(s) is / are MAC CE(s). In still further implementations, each of the measurement report(s) includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) and / or the report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicate the RS(s) or RS resource(s) where the UE 102 performs measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) include one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). In some implementations, the quantized measurement values include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0129] In further implementations, the at least one measurement configuration includes specifically defined measurement configuration(s) (e.g., LTM measurement configuration(s) as defined in 3GPP TS 38.331)). In some implementations, the specifically defined measurement configuration(s) include reference signal resource configuration(s) configuring resources where the DU 174 transmits reference signal(s). For example, the reference signal resource configuration(s) include CSI-RS(s) and / or SSB(s). In some implementations, the reference signal resource configuration(s) is / are CSl-ResourceConfig IE(s). In further implementations, the specifically defined measurement configuration(s) include measurement report configuration(s), as described above. The UE 102 transmits the measurement report(s) on PUCCH(s) or MAC CE(s) to the DU 174 in accordance with the measurement report configuration(s). The DU 174 receives the measurement report(s) on PUCCH(s) or MAC CE(s) in accordance with the measurement report configuration(s). In some implementations, the measurement report(s) are LI measurement report(s) or specifically defined measurement report(s) (e.g., LTM measurement report(s)). In some implementations, the specifically defined measurement configuration includes specifically defined configuration parameters (e.g., specifically defined in 3GPP TS 38.331).

[0130] After (e.g., in response to) receiving 324 the measurement report(s), the DU 174 generates a first LTM command to activate the LTM DU configuration 1 (i.e., the first LTM command commands the UE 102 to apply the LTM DU configuration 1 or to perform a serving cell change to the cell 1). The DU 174 then transmits 330 the first LTM command to the UE 102. In some implementations, the DU 174 transmits the first LTM command on thecell 124A to the UE 102. In further implementations, the DU 174 transmits the first LTM command on the cell 124D to the UE 102. In some implementations, the DU 174 includes the ID 1 in the first LTM command to indicate the LTM DU configuration 1 or element 1, and the UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 in accordance with the ID 1.

[0131] In further implementations, the DU 174 includes the cell index 1 indexing the cell ID 1 in the first LTM command. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 based on the cell index 1. Before receiving the first LTM command, the UE 102 retrieves the cell index 1 from the LTM DU configuration 1 or element 1 and establishes an association 1 between the cell index 1 and the LTM DU configuration 1 or element 1. In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell index 1, before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell index 1 and the association 1. Before receiving the first LTM command, the UE 102 retrieves the cell index(es) 2, ..., N from the LTM DU configuration(s) or element(s) 2, ..., N and establishes association(s) 2, ..., N between the cell index(es) 2, ..., N and the LTM DU configuration(s) or element(s) 2, ..., N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, ..., N to obtain the cell index(es) 2, ..., N, before receiving the first LTM command.

[0132] In further implementations, the DU 174 includes cell ID 1 in the first LTM command, where the cell ID 1 identifies the cell 1. In some implementations, the cell ID 1 included in the first LTM command is the same as the cell ID 1 included in the first CU-to- DU message. In further implementations, the DU 174 determines the cell ID 1 (e.g., PCI) included in the first LTM command using the cell ID 1 (e.g., CGI) received in the first CU- to-DU message. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 based on the cell ID 1. Before receiving the first LTM command, the UE 102 retrieves the cell ID 1 from the LTM DU configuration 1 or element 1 and establishes an association 1 between the cell ID 1 and the LTM DU configuration 1 or element 1. In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell ID 1, before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell ID 1 (e.g., received in the first LTM command) and the association 1. Before receiving the first LTM command, the UE 102 retrieves the cell ID(s) 2, .. N from the LTM DU configuration(s) or element(s) 2, .. N andestablishes association(s) 2, .. N between the cell ID(s) 2, .. N and the LTM DU configuration(s) or element(s) 2, .. N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, .. N to obtain the cell ID(s) 2, .. N, before receiving the first LTM command. In some implementations, the DU 174 stores a mapping table to store mappings between the PCI(s) 1, ..., N and the CGI(s) 1, ..., N for the cell(s) 1, ..., N, respectively.

[0133] In yet further implementations, the DU 174 includes a bit map in the first LTM command to activate the LTM DU configuration 1 instead of the ID 1 or cell index 1. The number of bits in the bit map is larger than or equal to “N”. In some implementations, bit 1, ..., N corresponds to the cell index(es) 1, ..., N, the ID(s) 1, ..., N, the LTM DU configuration(s) 1, ..., N, or the element(s) 1, ..., N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 1) in the bit map to a first value to indicate the cell index 1, the ID 1, the LTM DU configuration 1, or the element 1. Thus, in some such implementations, the UE 102 determines the cell index 1, the ID 1, LTM DU configuration 1, or element 1 in accordance with the bit 1 set to the first value in the bit map. In further implementations, bit 0, ..., N-l corresponds to the cell index(es) 1, ..., N, the ID(s) 1, ..., N, the LTM DU configuration(s) 1, ..., N, or the element (s) 1, ..., N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 0) in the bit map to a first value to indicate the cell index 1, the ID 1, the LTM DU configuration 1, or the element 1. Thus, in some such implementations, the UE 102 determines the cell index 1, the ID 1, the LTM DU configuration 1, or the element 1 in accordance with the bit 0 set to the first value in the bit map. In such implementations, the DU 174 sets the remaining bits in the bit map to a second value to indicate that the rest of the LTM DU configuration(s) 1, ..., N is / are not activated. In some implementations, the first value is one and the second value is zero. In further implementations, the first value is zero and the second value is one. Generally, if the DU 174 determines to activate the LTM DU configuration L or change a serving cell to the cell L for the UE 102, the DU 174 sets the corresponding bit (e.g., bit L or bit L-7) in the bit map to the first value and sets the remaining bits to the second value, where 1 < L < N. In some implementations, the DU 174 sets at most one bit in the bit map to the first value.

[0134] After determining or identifying the LTM DU configuration 1 or element 1, the UE 102 then applies the LTM DU configuration 1 and / or LTM CU configuration after (e.g., in response to) receiving the first LTM command.

[0135] In some implementations, the at least one measurement report (e.g., LI measurement report(s) or specifically defined measurement report(s)) of the event 324 includes at least one measurement result for the first cell, TRP(s) of the first cell or reference signal(s) transmitted on the first cell. In some implementations, the reference signal(s) are CS RS(s) or SSB(s). The DU 174 determines to activate the LTM DU configuration 1 or transmit the first LTM command, based on the at least one measurement result. In some implementations, the DU 174 determines to activate the LTM DU configuration 1 because, when, or if the at least one measurement result is above a second predetermined threshold. In some implementations, the at least one measurement result includes Ll-RSRP value(s), Ll- RSRQ value(s), and / or Ll-SINR value(s). In further implementations, the at least one measurement result includes RSRP value(s), RSRQ value(s), and / or SINR value(s) for the specifically defined measurement report(s). In some implementations, the second predetermined threshold is different from the first predetermined threshold. In some implementations, the second predetermined threshold is larger than the first predetermined threshold. In such cases, the at least one measurement result indicates that the first cell is suitable for communication with the UE 102. In further implementations, the second predetermined threshold is equal to the first predetermined threshold. In such cases, the at least one measurement result indicates that the first cell has been continuously above the second predetermined threshold or the first predetermined threshold, indicating that the first cell is suitable for communication with the UE 102. Thus, the DU 174 determines to activate the LTM DU configuration 1 in response to the signal strength or the quality of the first cell exceeding the second predetermined threshold for the UE 102.

[0136] In some implementations, the at least one measurement report (e.g., L3 measurement report(s)) of the events 324 and 326 includes at least one measurement result for the first cell. The CU 172 determines to activate the LTM DU configuration 1 or transmit the first LTM command because the at least one measurement result indicates that the signal strength or quality of the first cell is above a second predetermined threshold. The second predetermined threshold is different from the first predetermined threshold. In some implementations, the second predetermined threshold is larger than the first predetermined threshold. In such implementations, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell is suitable for communication with the UE 102. In still further implementations, the second predetermined threshold is equal to the first predetermined threshold. In such implementations, the at least one measurement reportof the event 326 indicates that the signal strength or the quality of the first cell has been continuously above the second predetermined threshold or the first predetermined threshold, further indicating that the first cell is suitable for communication with the UE 102. Thus, the CU 172 determines to activate the LTM DU configuration 1 in response to the signal strength or the quality of the first cell exceeding the second predetermined threshold.

[0137] In response to the determination, the CU 172 transmits 328 a fourth CU-to-DU message to the DU 174 to activate the LTM DU configuration 1 or trigger a serving cell change to the cell 1 for the UE 102. In some implementations, the CU 172 includes the ID 1 in the fourth CU-to-DU message. In further implementations, the CU 172 includes the cell index 1 in the fourth CU-to-DU message. In response to the fourth CU-to-DU message, the DU 174 transmits 330 the first LTM command to the UE 102 and optionally transmits a fourth DU-to-CU message to the CU 172. In some implementations, the CU 172 includes the cell index 1 in the fourth CU-to-DU message. Thus, in some further implementations, the DU 174 determines to activate the LTM DU configuration 1 in accordance with the cell index 1. In further implementations, the CU 172 includes the cell ID 1 in the fourth CU-to-DU message. Thus, the DU 174 determines to activate the LTM DU configuration 1 in accordance with the cell ID 1. In still further implementations, the CU 172 includes the ID 1 in the fourth CU-to-DU message. Thus in some implementations, the DU 174 determines to activate the LTM DU configuration 1 in accordance with the ID 1. In some implementations, the fourth CU-to-DU message and fourth DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In further implementations, the fourth CU-to-DU message and / or fourth DU-to-CU message are specifically defined interface messages (e.g., El application protocol (E1AP) messages as defined in 3GPP TS 38.473).

[0138] In some implementations, when or in response to determining to activate the LTM DU configuration 1 or transmit 330 the first LTM command, the DU 174 transmits 329, to the CU 172, a DU-to-CU message indicating that LTM is or is being executed. In some implementations, the DU-to-CU message is an LTM Cell Change Notification message. In some implementations, the DU 174 includes the cell ID 1 or the ID 1 (i.e., LTM ID) in the DU-to-CU message of event 329 to indicate that the DU 174 is to activate the LTM DU configuration 1 or trigger a fast serving cell change (i.e., an LTM serving cell change). In further implementations, the DU 174 transmits 329 the DU-to-CU message to the CU 172 before or after transmitting 330 the LTM command.

[0139] In some implementations, the first LTM command is a MAC CE included in a MAC PDU that the UE 102 receives from the DU 174 in the event 330. In some implementations, the MAC CE is a specifically defined MAC CE (e.g., as defined in 3GPP TS 38.321). In some implementations, the DU 174 includes a subheader identifying the specifically defined MAC CE in the MAC PDU, and the UE 102 identifies the specifically defined MAC CE in the MAC PDU in accordance with the subheader. In some implementations, the subheader includes a logical channel ID or extended logical channel ID (e.g., as defined in 3GPP TS 38.321) to identify the new MAC CE. In further implementations, the first LTM command is a DO that the UE 102 receives 330 on a PDCCH from the DU 174. The DU 174 generates a cyclic redundancy check (CRC) for the DO, scrambles the CRC with a first C-RNTI of the UE 102, and transmits 330 the DCI and scrambled CRC on the PDCCH. In some implementations, a format of the DCI is an existing DCI format (e.g., defined in 3GPP TS 38.212). In further implementations, the format of the DCI is a specifically defined DCI format (e.g., as defined in 3GPP TS 38.212.

[0140] In some implementations, the DU 174 does not perform security protection (e.g., integrity protection and / or encryption) on the first LTM command, which speeds up processing the first LTM command in the UE 102 because the UE 102 does not perform a security check (e.g., decryption and / or integrity check) on the first LTM command.

[0141] In some implementations, after receiving the first LTM command, the UE 102 transmits 331 an acknowledgement to the DU 174 on the cell 124A or cell 124D to indicate that the UE 102 receives the first LTM command. In some implementations, the acknowledgement is a HARQ ACK. In further implementations, the acknowledgement is a MAC CE. For example, the MAC CE is an existing MAC CE (e.g., as defined in 3GPP TS 38.321). In another example, the MAC CE is a specifically defined MAC CE (e.g., as defined in 3GPP TS 38.321). In yet further implementations, the acknowledgement is a PUCCH transmission.

[0142] In some implementations, the CU 172 transmits 316 the RRC reconfiguration message in response to the L3 measurement report of event 306 for the first cell. To configure the UE 102 to transmit the L3 measurement report of event 306, the CU 172 transmits a first RRC reconfiguration message, including the L3 measurement configuration (e.g., a MeasConfig IE), to the UE 102 before the event 306. In some implementations, the DU 174 transmits 330 the first LTM command in response to the LI measurement report(s)of event 324 for the first cell. In some implementations, to configure the UE 102 to transmit the LI or a specifically defined measurement report(s) of event 324, the CU 172 transmits a second RRC reconfiguration message including the LI or a specifically defined measurement configuration(s) to the UE 102. In some implementations, the first and second RRC reconfiguration messages are the same message (i.e., the same instance). In further implementations, the first and second RRC reconfiguration messages are different messages. In some implementations, the second RRC reconfiguration message is the RRC reconfiguration message of the event 316. In further implementations, the second RRC reconfiguration message is different from the RRC reconfiguration message of the event 316.

[0143] After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 the first cell. The UE 102 identifies the LTM DU configuration 1 in accordance with the ID 1, the cell ID 1, or the cell index 1 received in the first LTM command and applies the LTM DU configuration 1 to communicate with the DU 174 on the first cell. In some implementations, the UE 102 disconnects from the cell 124A after (e.g., in response to) receiving 330 the first LTM command or after transmitting 331 the acknowledgement. In some implementations, the UE 102 stops communicating on the cell 124A after (e.g., in response to) receiving 330 the first LTM command or transmitting 331 the acknowledgement. In some implementations, the UE 102 accesses the first cell by performing a random-access procedure on the first cell with the DU 174, in response to receiving the first LTM command. In further implementations, the UE 102 skips a randomaccess procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174, after (e.g., in response to) receiving the first LTM command.

[0144] In some implementations, the DU 174 configures the access of the UE 102 to the first cell, including whether or not the UE 102 performs a random-access procedure, in the LTM DU configuration 1. When receiving the first LTM command, the UE 102 determines whether to perform a random-access procedure on the first cell in accordance with the LTM DU configuration 1. If the LTM DU configuration 1 configures the UE 102 to perform a random-access procedure, the UE 102 performs 332 a random-access procedure on the first cell to connect to the first cell. Lor example, the LTM DU configuration 1 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) to configure the UE 102 to perform a random-access procedure when the UE 102 receives an LTM command for the first cell. In some implementations, in the LTM DU configuration 1, the DU 174configures the UE 102 to skip the random-access procedure for a LTM serving cell change to the first cell. In such cases, after receiving the first LTM command, the UE 102 skips the random-access procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174 in the event 332. In some implementations, the DU 174 excludes a reconfiguration with sync configuration in the LTM DU configuration 1 to configure the UE 102 to skip a random-access procedure for an LTM serving cell change to the first cell.

[0145] In some implementations, the LTM DU configuration 1 includes the reconfiguration with sync configuration or the random-access configuration. In such cases, the DU 174 configures whether the UE 102 performs a random-access procedure on the first cell in an LTM command. Thus, the UE 102 determines whether to perform 332 the randomaccess procedure on the first cell in accordance with the first LTM command. In some implementations, the DU 174 includes, in the first LTM command, an indication (e.g., a field) to skip a random-access procedure. In response to the indication or the first LTM command including the indication, the UE 102 skips a random-access procedure and directly transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to access the first cell. In some implementations, the DU 174 excludes the indication in the first LTM command to configure the UE 102 to perform a random-access procedure. In response to the first LTM command excluding the indication, the UE 102 performs a random-access procedure on the first cell to access the first cell. In further implementations, the DU 174 includes a timing advance value in the first LTM command to indicate to skip a random-access procedure. In response to receiving the timing advance value or the first LTM command including the timing advance value, the UE 102 skips a random-access procedure and transmits the first transmission on the first cell to access the first cell, using the timing advance value. In still further implementations, the DU 174 excludes, in the first LTM command, a timing advance value to configure the UE 102 to perform a random-access procedure. In response to the first LTM command excluding a timing advance command, the UE 102 performs a random access procedure on the first cell to access the first cell.

[0146] In some implementations, the random-access procedure is a four-step randomaccess procedure. In further implementations, the random-access procedure is a two-step random-access procedure. In some implementations, the random-access procedure is a contention-free random-access procedure. In still further implementations, the random-access procedure is a contention-based random-access procedure. In cases where the random-access procedure is a four-step random-access procedure, the UE 102 transmits a Message 3 including a UE identity to the DU 174 via the first cell in the random-access procedure. The DU 174 transmits a contention resolution message (e.g., a Message 4) to the UE 102 in response to the Message 3. In cases where the random-access procedure is a two- step random-access procedure, the UE 102 transmits a Message A including the UE identity to the DU 174 via the first cell in the random-access procedure. The DU 174 transmits a contention resolution message (e.g., Message B) to the UE 102 in response to the Message A. In some implementations, when the UE 102 receives the contention resolution message from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the random-access procedure (i.e., the UE 102 successfully accesses the first cell). In some implementations, the LTM DU configuration 1 includes a second C-RNTI and the UE identity is the second C-RNTI of the UE 102. In such implementations, the contention resolution message is a PDCCH transmission addressed to the second C-RNTI. In further implementations, the LTM DU configuration 1 does not include a C-RNTI and the UE identity is the first C-RNTI. In such implementations, the contention resolution message is a PDCCH transmission addressed to the first C-RNTI. In some implementations, the DU 174 includes the second C-RNTI in the reconfiguration with sync configuration. In further implementations, the DU 174 includes the second C-RNTI in the LTM cell switch information.

[0147] In cases where the LTM DU configuration 1 includes a dedicated random-access preamble, the random-access procedure is a contention free random access procedure. In such cases, the UE 102 transmits the dedicated random-access preamble to the DU 174 via the first cell. When the UE 102 receives a random-access response, including an ID of the dedicated random-access preamble, from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the random access procedure (i.e., the UE 102 successfully accesses the first cell).

[0148] If the DU 174 configures the UE 102 to perform a random-access procedure on the first cell as described above, the DU 174 detects that the UE 102 has accessed the first cell when the DU 174 receives Message 3, Message A, or the dedicated preamble in the randomaccess procedure. If the DU 174 configures the UE 102 to skip a random-access procedure, the DU 174 detects that the UE 102 has accessed the first cell when the DU 174 receives the first transmission.

[0149] In some implementations, the UE 102 transmits the first transmission (e.g., the PUSCH transmission) on the first cell using a UL grant. In some implementations, the first LTM command includes the UL grant. In further implementations, when the UE 102 performs an LTM serving cell change to the first cell in response to the first LTM command, the UE 102 receives a first DCI including the UL grant on a PDCCH on the first cell. In some implementations, the UE 102 attempts to receive the first DCI or the UL grant by monitoring one or more PDCCHs on the first cell in accordance with the LTM DU configuration 1 when the UE 102 switches to the first cell in response to the first LTM command. While monitoring one or more PDCCHs on the first cell, the UE 102 receives the first DCI and a CRC of the first DCI on the PDCCH. In cases where the LTM DU configuration 1 includes the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the second C-RNTI. In cases where the LTM DU configuration 1 does not include the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the first C-RNTI.

[0150] In some implementations, the CU 172 transmits at least one first TCI state configuration (e.g., LTM TCI state configuration) for the first cell to the UE 102 via the DU 174. In some implementations, each of the first TCI state configuration(s) configures a TCI state for the UE 102 to transmit and / or receive data and / or control signal on the first cell. In some implementations, each TCI state associates or includes one or two DL RSs with a corresponding QCL type, and the DL RS(s) are associated with a particular cell of the cell(s) 1, ..., N. The DL RS(s) include SSB(s) and / or tracking reference signal(s) (TRS(s)). In some implementations, the CU 172 receives a DU-to-CU message including the first TCI state configuration(s) from the DU 174 and transmits an RRC message including the first TCI state configuration(s) to the UE 102 via the DU 174. In some implementations, the DU 174 includes the first TCI state configuration(s) in a serving DU configuration (e.g., CellGroupConfig IE) and includes the serving DU configuration in the DU-to-CU message. In some implementations, the DU-to-CU message is the DU-to-CU message of event 310 or the DU-to-CU message of event 314. In further implementations, the DU-to-CU message is a message different from the messages of events 310 and 314. For example, the DU-to-CU message is a UE Context Modification Response message or a UE Context Modification Required message.

[0151] In some implementations, the DU 174 includes the LTM DU configuration 1 in a first interface protocol lE / field in the DU-to-CU message of event 310 and includes theserving DU configuration in a second interface protocol lE / field in the DU-to-CU message of event 314. In some implementations, in cases where the DU 174 includes the first TCI state configuration(s) in the DU-to-CU message of event 314, the events 312 (optional) and / or 314 (optional) are collectively referred to in Fig. 3 as an LTM TCI state configuration procedure 392.

[0152] In some implementations, the CU 172 includes the serving DU configuration in the RRC message. In further implementations, the CU 172 refrains from including the serving DU configuration in a container for LTM (e.g., the first container). In still further implementations, the CU 172 includes the LTM ID 1 and the first LTM TCI state configuration(s) in an element for LTM, an addition or modification list for LTM, or a container, and the CU 172 includes the element, addition or modification list for LTM, or the container in the RRC message, similar to the element 1, the first addition or modification list, or the first container respectively. In some implementations, the RRC message is the RRC reconfiguration message of events 316 and / or 318. In some such cases, the CU 172 includes the first LTM TCI state configuration(s) in the element 1. In further implementations, the RRC reconfiguration is another RRC reconfiguration message (not shown in Fig. 3). In some implementations, the DU 174 also includes the first TCI state configuration(s) in the LTM DU configuration 1. In further implementations, the DU 174 refrains from including the first TCI state configuration(s) in the LTM DU configuration 1.

[0153] In some implementations, the first interface protocol lE / field is a first F1AP lE / field, and the second interface protocol lE / field is a second F1AP lE / field. In some implementations, one of the first F1AP lE / field and the second F1AP lE / field is a F1AP CellGroupConfig lE / field, and the other is not the F1AP CellGroupConfig lE / field. In some implementations, the DU 174 includes the first F1AP lE / field in a DU-to-CU RRC Information IE in the message (e.g., of the event 314) and includes the second F1AP lE / field in the DU-to-CU RRC Information IE in the DU-to-CU message. In further implementations, neither the first F1AP lE / field nor the second F1AP IE is a F1AP CellGroupConfig lE / field. In still further implementations, the second F1AP lE / field is the DU-to-CU RRC Information IE and the first F1AP lE / field is a new IE specific for including a LTM DU configuration.

[0154] In some implementations, the DU 174 transmits 325 at least one first LTM TCI states Activation / Deactivation command to the UE 102 to activate some of the first LTM TCI state configuration(s). The UE 102 activates the some of the first LTM TCI stateconfiguration(s) in response to the first LTM TCI States Activation / Deactivation command(s). In some implementations, the DU 174 indicates deactivation of some of the first LTM TCI state configuration(s) in some of the first LTM TCI States Activation / Deactivation command(s). In some implementations, the DU 174 transmits one or more DL RSs on the candidate cell(s) using the activated LTM TCI state configuration(s) or the first LTM TCI state configuration(s). In some implementations, the DL RS(s) include one or more SSBs and / or one or more TRSs. In some implementations, the UE 102 receives the DL RS(s) using the activated LTM TCI state configuration(s). In further implementations, the UE 102 obtains the LI measurement results from the received DL RS(s) and transmits the LI measurement results to the DU 174. In still further implementations, the UE 102 obtains the L3 measurement results from the received DL RS(s) and transmits the L3 measurement results to the CU 172 via the DU 174. In some implementations, the DU 174 refrains from using the first LTM TCI state configuration(s) to communicate with the UE 102 on the serving cell(s). In some implementations, the UE 102 refrains from using the first LTM TCI state configuration(s) to communicate with the DU 174 on the serving cell(s).

[0155] In some implementations, each of the first LTM TCI States Activation / Deactivation command(s) is a MAC CE (e.g., Candidate Cell TCI States Activation / Deactivation command). In some implementations, the DU 174 includes the LTM ID 1 in each of the first LTM TCI States Activation / Deactivation command(s) to identify the first LTM TCI state configuration(s). In further implementations, the DU 174 includes a candidate cell index (e.g., the cell index 1) in each of the first LTM TCI States Activation / Deactivation command(s) to identify the first LTM TCI state configuration(s). In such cases, the candidate cell index is different from the LTM ID 1. In some implementations, each of the first LTM TCI state configuration(s) includes the candidate cell index. Alternatively, the CU 172 includes the candidate cell index in the RRC message including the first LTM TCI state configuration(s). For example, the CU 172 includes the candidate cell index in the element 1. In further implementations, the UE 102 and the DU 174 determines the candidate cell index from the PCI of the first cell. In such cases, the base station 104 does not transmit the candidate cell index to the UE 102.

[0156] In some implementations, after (e.g., in response to) receiving the first LTM command or accessing 332 the first cell, the UE 102 performs 336 DL reception (e.g., monitors one or more PDCCHs) or UL transmission on the first cell using some or all of the first LTM TCI state configuration(s). In further implementations, after (e.g., in response to)receiving the first LTM command or accessing 332 the first cell, the UE 102 performs 336 DL reception (e.g., monitors one or more PDCCHs) or UL transmission on the first cell without using the first LTM TCI state configuration(s).

[0157] In some implementations, each of the first LTM TCI state configuration(s) includes a TCI state ID identifying the corresponding TCI state configuration. Lor example, the first LTM TCI state configuration(s) include LTM TCI state configuration(s) 1, ..., L, where L is a positive integer larger than zero. The LTM TCI state configuration(s) 1, ..., L include TCI state ID(s) 1, ..., L identifying the LTM TCI state configuration(s) 1, ..., L, respectively. In some implementations, the DU 174 includes the TCI state ID 1 in the first LTM command to indicate to the UE 102 to activate the LTM TCI state configuration 1 to communicate on the first cell. The UE 102 activates the LTM TCI state configuration 1 in response to receiving the TCI state ID 1 in the first LTM command. In some implementations, the UE 102 accesses, at event 332, on the first cell using the (activated) LTM TCI state configuration 1. In further implementations, the UE 102 accesses, at event 332, on the first cell without using the first LTM TCI state configuration(s). In some implementations, the UE 102 communicates, at event 336, on the first cell using the (activated) LTM TCI state configuration 1. In some implementations, the DU 174 communicates, at event 336, with the UE 102 on the first cell, using the activated LTM TCI state configurations 1.

[0158] In some implementations, at events 332 and / or 336, the UE 102 monitors one or more PDCCHs, receives one or more DL RSs, receives one or more PDSCH transmissions, and / or transmits the first transmission and / or one or more additional transmissions using the LTM TCI state configuration 1. In some implementations, the DU 174 detects, at event 332, that the UE 102 accesses the first cell and / or communicates, at event 336, with the UE 102 on the first cell, based on the LTM TCI state configuration 1. In further implementations, the DU 174 receives, at events 332 and / or 336, the first transmission and / or the additional transmission(s) from the UE 102 on the first cell, based on the TCI state configuration 1. In still further implementations, at events 332 and / or 336, the DU 174 transmits one or more PDCCHs, one or more PDSCH transmissions, and / or one or more DL RSs, based on the LTM TCI state configuration 1.

[0159] In some implementations, the DU 174 includes the TCI state ID 2 in the first LTM command to indicate to the UE 102 to activate the TCI state configuration 2 to communicate on the first cell, in addition to the TCI state ID 1. The UE 102 activates the LTM TCI stateconfiguration 1 in response to receiving the TCI state ID 1 in the first LTM command and activates the LTM TCI state configuration 2 in response to receiving the TCI state ID 2 in the first LTM command. After (e.g., in response to) receiving the first LTM command, the UE 102 accesses and / or communicates (e.g., at events 332 and / or 336, respectively) on the first cell using the activated LTM TCI state configurations 1 and 2. After (e.g., in response to) transmitting 330 the first LTM command or receiving 331 the acknowledgement, the DU 174 communicates with the UE 102 on the first cell, at events 332 and / or 336, using the activated LTM TCI state configurations 1 and 2.

[0160] In some implementations, after applying one or more TCI state configurations (e.g., the TCI state configuration(s) 1 and / or 2) indicated in an LTM command (e.g., the first LTM command), the UE 102 takes time (e.g., beam application time or cell switch delay) to acquire TCI state(s) configured in the TCI state configuration(s) (e.g., synchronize and / or receive DL RS(s) configured in the TCI state configuration(s)). The time to acquire the TCI state(s) is considered as a switch delay. In such cases, the DU 174 takes the switch delay into account when communicating with the UE 102 on the first cell in the events 332 and / or 336. For example, after transmitting 330 the first LTM command or receiving 331 the acknowledgement 331, the DU 174 starts to communicate with the UE 102 on the first cell in the events 332 and / or 336 after the switch delay using the activated LTM TCI state configuration(s) 1 and / or 2.

[0161] In some implementations, the UE 102 monitors one or more PDCCHs, receives one or more DL RSs, and / or receives one or more PDSCH transmissions from the DU 174 on the first cell using the LTM TCI state configuration 1 and transmits the first transmission and / or one or more additional transmissions on the first cell to the DU 174 using the LTM TCI state configuration 2. In such implementations, the DU 174 transmits one or more control signals one or more PDCCHs, one or more DL RSs, and / or one or more PDSCH transmissions to the UE 102 on the first cell using the LTM TCI state configuration 1 and receives the first transmission and / or one or more additional transmissions on the first cell from the UE 102 using the LTM TCI state configuration 2. Each of the control signal(s) includes a DCI and a scrambled CRC for the DCI.

[0162] In further implementations, the UE 102 monitors one or more PDCCHs from the DU 174 on the first cell using the LTM TCI state configuration 1 and receives one or more PDSCH transmissions from the DU 174 on the first cell using the LTM TCI stateconfiguration 2. Each of the control signal(s) includes a DCI and a scrambled CRC for the DO. In such implementations, the DU 174 transmits one or more control signals on one or more PDCCHs on the first cell to the UE 102 using the LTM TCI state configuration 1 and transmits one or more PDSCH transmissions to the UE 102 on the first cell using the LTM TCI state configuration 2. In some implementations, the UE 102 transmits the first transmission and / or one or more additional transmissions to the DU 174 on the first cell using the LTM TCI state configuration 1. In such implementations, the DU 174 receives the first transmission and / or one or more additional transmissions from the UE 102 on the first cell, using the LTM TCI state configuration 1. In some further implementations, the UE 102 transmits the first transmission and / or one or more additional transmissions to the DU 174 on the first cell using the LTM TCI state configuration 2. In such implementations, the DU 174 receives the first transmission and / or one or more additional transmissions from the UE 102 on the first cell, using the LTM TCI state configuration 2.

[0163] In still further implementations, the UE 102 monitors one or more PDCCHs on the first cell using the TCI state configuration 1 and the TCI state configuration 2 and transmits the first transmission and / or one or more additional transmissions on the first cell using one of the TCI state configuration 1 and the TCI state configuration 2. In some such implementations, the DU 174 transmits one or more control signals on one or more PDCCHs and receives the first transmission and / or one or more additional transmissions from the UE 102 on the first cell using the LTM TCI state configuration 2. Each of the control signals includes a DCI and a scrambled CRC for the DCI.

[0164] In some implementations, the CU 172 receives a CN-to-BS message including a UE capability IE of the UE 102 from a CN (e.g., the CN 110 or the AMF 164) (e.g., during the event 302). For example, the CN-to-BS message is an NG application protocol (NGAP) message. In further implementations, the CU 172 receives a BS-to-BS message including the UE capability IE from another base station (e.g., the base station 106) (e.g., before the event 302). In still further implementations, the CU 172 receives a UE Capability Information message including the UE capability IE from the UE 102, via the DU 174 or another DU (e.g., during the event 302). In some implementations, the DU 174 receives the UE capability IE (e.g., UE-NR-Capability or UE-6G-Capability) of the UE 102 from the CU 172 (e.g., during the event 302).

[0165] In some implementations, the UE capability IE indicates that the UE 102 supports RACH-less LTM. Thus, based on the indication of supporting Random Access Channel-less (RACH-less) LTM, the DU 174 configures and / or activates one or more LTM TCI state configurations for the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support RACH-less LTM, the DU 174 refrains from configuring and / or activating an LTM TCI state configuration for the UE 102. For example, the DU 174 refrains from including an LTM TCI state configuration for the UE 102 in the DU-to-CU message(s) described above. Accordingly, the CU 712 does not transmit an LTM TCI state configuration to the UE 102. For example, the CU 172 does not include a LTM TCI state configuration in the RRC reconfiguration message of events 316 and / or 318.

[0166] In further implementations, the UE capability IE indicates that the UE supports early timing advance (TA) acquisition. Based on the indication of supporting early TA acquisition, the DU 174 configures and / or activates one or more LTM TCI state configurations for the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support the early TA acquisition, the DU 174 refrains from configuring and / or activating a LTM TCI state configuration for the UE 102. For example, the DU 174 refrains from including an LTM TCI state configuration for the UE 102 in the DU-to-CU message(s) described above. Accordingly, the CU 712 does not transmit an LTM TCI state configuration to the UE 102. For example, the CU 172 does not include an LTM TCI state configuration in the RRC reconfiguration message of events 316 and / or 318.

[0167] In still further implementations, the UE capability IE indicates that the UE supports a UE-based TA acquisition (e.g., the UE acquires UL synchronization based on reference signal time difference (RSTD) measurements). Based on the indication of supporting the UE-based TA acquisition, the DU 174 configures and / or activates one or more LTM TCI state configurations for the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support the UE-based TA acquisition, the DU 174 refrains from configuring and / or activating an LTM TCI state configurations for the UE 102. For example, the DU 174 refrains from including an LTM TCI state configuration for the UE 102 in the DU-to-CU message(s) described above. Accordingly, the CU 712 does not transmit an LTM TCI state configuration to the UE 102. For example, the CU 172 doesnot include an LTM TCI state configuration in the RRC reconfiguration message of the events 316 and / or 318.

[0168] In yet still further implementations, the UE capability IE indicates that the UE supports LTM TCI states. Based on the indication of supporting LTM TCI states, the DU 174 configures and / or activates one or more LTM TCI state configurations for the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support LTM TCI states, the DU 174 refrains from configuring and / or activating an LTM TCI state configuration for the UE 102. For example, the DU 174 refrains from including an LTM TCI state configuration for the UE 102 in the DU-to-CU message(s) described above. Accordingly, the CU 712 does not transmit an LTM TCI state configuration to the UE 102. For example, the CU 172 does not include an LTM TCI state configuration in the RRC reconfiguration message of events 316 and / or 318.

[0169] In some implementations, the DU 174 does not determine whether to provide a LTM TCI state configuration for the UE 102. The DU 174 provides the LTM TCI state configuration(s) for the UE 102 to the CU 172 as described above. The CU 172 determines whether to transmit the first LTM TCI state configuration(s) to the UE 102. In some implementations, based on the indication of supporting RACH-less LTM, the CU 172 transmits the first LTM TCI state configuration(s) to the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support RACH- less LTM, the CU 172 refrains from transmitting an LTM TCI state configuration to the UE 102. For example, the CU 172 refrains from transmitting the first LTM TCI state configuration(s) to the UE 102. For example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message of events 316 and / or 318.

[0170] In further implementations, based on the indication of supporting the early TA acquisition, the CU 172 transmits the first LTM TCI state configuration(s) to the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support the early TA acquisition, the CU 172 refrains from transmitting an LTM TCI state configuration to the UE 102. For example, the CU 172 refrains from transmitting the first LTM TCI state configuration(s) to the UE 102. For example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message of events 316 and / or 318.

[0171] In further implementations, based on the indication of supporting the UE-based TA acquisition, the CU 172 transmits the first LTM TCI state configuration(s) to the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support the UE-based TA acquisition, the CU 172 refrains from transmitting an LTM TCI state configuration to the UE 102. For example, the CU 172 refrains from transmitting the first LTM TCI state configuration(s) to the UE 102. As a further example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message of events 316 and / or 318.

[0172] In still further implementations, based on the indication of supporting the LTM TCI states, the CU 172 transmits the first LTM TCI state configuration(s) to the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support LTM TCI states, the CU 172 refrains from transmitting an LTM TCI state configuration to the UE 102. For example, the CU 172 refrains from transmitting the first LTM TCI state configuration(s) to the UE 102. As a further example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message of events 316 and / or 318.

[0173] In some alternative implementations, the DU 174 does not activate or determines to not activate a (LTM) TCI state configuration in the first LTM command. In such cases, the DU 174 does not include a TCI state ID in the first LTM command. Thus, when the UE 102 receives the first LTM command not including a TCI state configuration, the UE 102 refrains from using the first LTM TCI configuration(s) to access and / or communicate on the first cell.

[0174] In some implementations, if the UE capability IE indicates that the UE 102 does not support the RACH-less LTM, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the UE capability IE indicates that the UE 102 supports the RACH-less LTM, the DU 174 includes the one or more TCI state IDs (e.g., the TCI state ID 1 and / or the TCI state ID 2) in the first LTM command as described above.

[0175] In further implementations, if the DU 174 does not configure LTM TCI state configurations for the first cell for the UE 102, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the DU 174 configures one or more LTM TCI state configurations (e.g., the first LTM TCI state configuration(s)), the DU 174 includes one or more LTM TCI state IDs (e.g., the TCI state ID 1 and / or the TCI state ID 2) in the first LTM command.

[0176] In yet further implementations, if the UE capability IE indicates that the UE 102 does not support the early TA acquisition, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the UE capability indicates that the UE 102 supports the early TA acquisition, the DU 174 includes the TCI state ID 1 and / or the TCI state ID 2 in the first LTM command as described above.

[0177] In still further implementations, if the UE capability IE indicates that the UE 102 does not support the UE-based TA acquisition, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the UE capability indicates that the UE 102 supports the early TA acquisition, the DU 174 includes the TCI state ID 1 and / or the TCI state ID 2 in the first LTM command as described above.

[0178] In still yet further implementations, if the UE capability IE indicates that the UE 102 does not support LTM TCI states, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the UE capability indicates that the UE 102 supports LTM TCI states, the DU 174 includes the TCI state ID 1 and / or the TCI state ID 2 in the first LTM command as described above.

[0179] In some implementations, the UE 102 stops using or deactivates the first non-LTM TCI configuration(s) upon receiving the first LTM command.

[0180] After successfully accessing the first cell, the UE 102 communicates, at event 336, with the DU 174 on the first cell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the DU 174. In such cases, the DU 174 communicates, at event 336, with the UE 102 on the first cell using the LTM DU configuration 1. In some implementations, the UE 102 communicates, at event 336, PUSCH transmissions, PDSCH transmissions, PUCCH transmissions, PDCCH transmissions, and / or sounding reference signal (SRS) transmissions with the DU 174 on the first cell.

[0181] In cases where the UE 102 receives the reference LTM DU configuration as described above, the UE 102 communicates, at event 336, with the DU 174 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the UE 102 communicates, at event 336, with the DU 174 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration. Similarly, the DU 174 communicates, at event 336, with the UE 102 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the DU 174 communicates, at event 336,with the UE 102 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration.

[0182] In cases where the UE 102 receives neither the LTM CU configuration 1 nor a / the reference LTM CU configuration, the UE 102 communicates, at event 336, with the CU 172 via the DU 174 using the serving CU configuration. Correspondingly, if the CU 172 neither transmits the LTM CU configuration 1 nor a reference CU configuration to the UE 102, the CU 172 communicates, at event 336, with the UE 102 via the DU 174 using the serving CU configuration. In cases where the UE 102 receives the LTM CU configuration 1 and the reference LTM CU configuration from the CU 172, the UE 102 communicates, at event 336, with the CU 172 via the DU 174 using the LTM CU configuration 1 and at least a portion of the reference LTM CU configuration not augmented by the LTM CU configuration 1. In such cases, the CU 172 communicates, at event 336, with the UE 102 via the DU 174 using the LTM CU configuration 1 and at least a portion of the reference LTM CU configuration not augmented by the LTM CU configuration 1.

[0183] In cases where the UE 102 receives the LTM CU configuration 1 and does not receive the reference LTM CU configuration from the CU 172, the UE 102 communicates, at event 336, with the CU 172 via the DU 174 using the LTM CU configuration 1. In such cases, the CU 172 communicates, at event 336, with the UE 102 via the DU 174 using the LTM CU configuration 1. If the LTM CU configuration 1 is a full configuration, the UE 102 and CU 172 communicate, at event 336, with each other via the DU 174 using the LTM CU configuration 1 instead of the serving CU configuration. In some implementations, if the UE 102 does not receive a reference LTM CU configuration from the base station 104, the UE 102 determines that the LTM CU configuration 1 is a full configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a full configuration, the CU 172 does not transmit a reference LTM CU configuration to the UE 102. In other implementations, the CU 172 includes a first indication (e.g., a field or IE) in the LTM CU configuration 1, the first container, the element 1, or the RRC reconfiguration message (e.g., at event 316) to indicate that the LTM CU configuration 1 is a full configuration. If the LTM CU configuration 1 is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicate, at event 336, with each other via the DU 174 using the LTM CU configuration 1 and at least a portion of the serving CU configuration not augmented by the LTM CU configuration 1. In some implementations, if the UE 102 does not receive a reference LTM CU configuration from the base station 104,the UE 102 determines that the LTM CU configuration 1 is a delta configuration to augment the serving CU configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a delta configuration to augment the serving CU configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In some implementations, the CU 172 indicates that the LTM CU configuration 1 is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the LTM CU configuration 1, the first container, the element 1, and / or the RRC reconfiguration message (e.g., of event 316). Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the LTM CU configuration 1, the first container, the element 1, or the RRC reconfiguration message (e.g., of event 316) to indicate that the LTM CU configuration 1 is a delta configuration to augment the serving CU configuration. In some implementations, the CU 172 indicates that the LTM CU configuration 1 is a full configuration, by excluding the second indication in the LTM CU configuration 1, the first container, the element 1, and / or the RRC reconfiguration message (e.g., of event 316).

[0184] In cases where the UE 102 receives the reference LTM CU configuration and does not receive the LTM CU configuration 1 from the CU 172, the UE 102 communicates, at event 336, with the CU 172 via the DU 174 using the reference LTM CU configuration. In this case, the CU 172 communicates, at event 336, with the UE 102 via the DU 174 using the reference LTM CU configuration. If the reference LTM CU configuration is a full configuration, the UE 102 and CU 172 communicate, at event 336, with each other via the DU 174 using the reference LTM CU configuration instead of the serving CU configuration. In some implementations, the UE 102 and CU 172 determine that the reference LTM CU configuration 1 is a full configuration (e.g., as specified in 3GPP TS 38.331). In other implementations, the CU 172 includes a first indication (e.g., a field or IE) in the reference LTM CU configuration, the first container, or the RRC reconfiguration message (e.g., of event 316) to indicate that the reference LTM CU configuration is a full configuration. If the reference LTM CU configuration is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicate, at event 336, with each other via the DU 174 using the reference LTM CU configuration and at least a portion of the serving CU configuration not augmented by the reference LTM CU configuration. In some implementations, the CU 172 indicates that the reference LTM CU configuration is a delta configuration to augment to the serving CU configuration by excluding the first indication in the reference LTM CU configuration, the first container, the element 1, and / or the RRCreconfiguration message (e.g., of event 316). Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the reference LTM CU configuration, the first container, the element 1, or the RRC reconfiguration message (e.g., of event 316) to indicate that the reference LTM CU configuration is a delta configuration to augment the serving CU configuration. In some implementations, the CU 172 indicates that the reference LTM CU configuration is a full configuration by excluding the second indication in the reference LTM CU configuration, the first container, the element 1, and / or the RRC reconfiguration message (e.g., of event 316).

[0185] In cases where the UE 102 neither receives the reference LTM CU configuration and nor the LTM CU configuration 1 from the CU 172, the UE 102 communicates, at event 336, with the CU 172 via the DU 174 using the serving CU configuration. In this case, the CU 172 communicates, at event 336, with the UE 102 via the DU 174 using the serving CU configuration.

[0186] In some implementations, the DU 174 includes or configures at least one second non-LTM TCI state configuration for the first cell in the LTM DU configuration 1. In some implementations, while communicating with the UE 102 (e.g., at event 332 or 336), the DU 174 transmits a second non-LTM TCI States Activation / Deactivation command on the first cell to the UE 102 to activate the second non-LTM TCI state configuration(s) and / or deactivate the activated LTM TCI state configuration(s). In some implementations, the DU 174 includes a serving cell index for the first cell in the second non-LTM TCI States Activation / Deactivation command. The DU 174 includes the serving cell index in the LTM DU configuration 1. In some implementations, the UE 102 stops using or deactivates the (activated) LTM TCI state configuration(s) in response to receiving the second non-LTM TCI States Activation / Deactivation command. In some implementations, the second non-LTM TCI States Activation / Deactivation command(s) is a MAC CE. In further implementations, the MAC CE is a TCI States Activation / Deactivation for UE-specific PDSCH MAC CE, a TCI State Indication for UE-specific PDCCH MAC CEs, a PUCCH spatial relation Activation / Deactivation MAC CEs, an Enhanced TCI States Activation / Deactivation for UE- specific PDSCH MAC CE, an Enhanced PUCCH Spatial Relation Activation / Deactivation MAC CE, an Enhanced TCI States Indication for UE-specific PDCCH MAC CE, a PUCCH spatial relation Activation / Deactivation for multiple TRP PUCCH repetition MAC CE, or a Unified TCI States Activation / Deactivation MAC CE.

[0187] In some implementations, the second non-LTM state configuration(s) are Rel-15 / 16 TCI state configuration(s) (i.e., not a unified joint / DL / UL TCI state) which, in some implementations, implies that the BS 104 configures the Rel-15 / 16 beam indication framework for the first cell. In some implementations, non-LTM TCI state configurations activated / indicated by the second non-LTM TCI States Activation / Deactivation command(s) are only applicable to a channel or RS (PDSCH / PDCCH / CSI-RS / PUCCH / SRS). In such implementations, if the UE 102 receives a second non-LTM TCI States Activation / Deactivation command, the UE stops or uses the first LTM TCI state for channels or RSs, which are applicable to share / follow / apply unified TCI states. For example, if the UE 102 receives an Enhanced TCI States Indication for UE- specific PDCCH MAC CE, the UE 102 stops or uses the first LTM TCI state for at least one of the other channels or RSs applicable to share / follow / apply unified TCI states as well (e.g., PDSCH, PUSCH, PUCCH, CSLRS or SRS). In some implementations, if the UE 102 receives a second non-LTM TCI States Activation / Deactivation command, the UE 102 deactivates the activated first LTM TCI state configuration(s).

[0188] In some implementations, the second non-LTM TCI state configuration(s) includes at least one TCI state configured in the first LTM TCI state configuration(s). In further implementations, the TCI state(s) in the second non-LTM TCI state configuration(s) is / are different from the TCI(s) in the first LTM TCI state configuration(s). In some implementations, the second non-LTM TCI state configuration(s) configure more TCI states than the first LTM TCI state configurations(s). In further implementations, the TCI state(s) in the second non-LTM TCI state configuration(s) is / are identical with the TCI(s) in the first LTM TCI state configuration(s). In some implementations, the BS 104 / CU 172 / DU 174 notifies the UE 102 in a RRC message or signal whether the first LTM TCI state configuration(s) is identical or different or a subset of the second non-LTM TCI state configuration(s).

[0189] In some implementations, the first LTM TCI state configuration(s) for the first cell is a subset of the second non-LTM TCI state configuration(s) for the first cell. In some implementations, TCI state IDs of the first LTM TCI state configuration(s) for the first cell are not overlapped or identical with those of the second non-LTM TCI state configuration(s) for the first cell which, in some implementations, implies that, when the UE 102 receives the second non-LTM TCI States Activation / Deactivation command(s), the UE 102 considers / determines that the TCI state ID(s) indicated in the second non-LTM TCI StatesActivation / Deactivation command(s) refer to the first LTM TCI state configuration(s) for the first cell or the second non-LTM TCI state configurations for the first cell. For example, TCI state IDs of the first LTM TCI state configuration(s) for the first cell range from #000 to #007; TCI state IDs of the second non-LTM TCI state configurations for the first cell range from #008 to #015. In such an example, if the second non-LTM TCI States Activation / Deactivation command indicates TCI state ID #001, the UE 102 activates the first LTM TCI state configuration identified by TCI state ID #001; if the second non-LTM TCI States Activation / Deactivation command indicates TCI state ID #012, the UE 102 activates the second non-LTM TCI state configuration identified by TCI state ID #012. In some implementations, the UE 102 combines or concatenates the first LTM TCI state configuration(s) for the first cell and the second non-LTM TCI state configurations for the first cell for non-LTM TCI state activation / indicate purpose. In some implementations, the UE 102 considers or determines the first LTM TCI state configuration(s) for the first cell as the non-LTM TCI state configurations for the first cell.

[0190] In some implementations, the DU 174 does not include or configure the at least one second non-LTM TCI state configuration for the first cell in the LTM DU configuration 1. In such cases, the UE 102 considers or determines the at least one first TCI state configuration(s) (e.g., LTM TCI state configuration) for the first cell as the non-LTM TCI state configurations for the first cell, which, in some such implementations, implies that, when the UE 102 receives the second non-LTM TCI States Activation / Deactivation command(s), the UE 102 considers / determines that the TCI state ID(s) indicated in the second non-LTM TCI States Activation / Deactivation command(s) refer to the first LTM TCI state configuration(s) for the first cell. For example, if the second non-LTM TCI States Activation / Deactivation command indicates TCI state ID #000, the UE 102 activates and / or applies the first TCI state configuration (e.g., LTM TCI state configuration) identified by TCI state ID #000 and performs non-LTM communication in the first cell.

[0191] In some implementations, if a first LTM TCI state configuration associates or includes an SSB corresponding to QCL type A, the UE 102 refrains from using such TCI state configuration for non-LTM purposes or communications in the first cell. In some implementations, the UE 102 considers or determines a first LTM TCI state configuration(s) for the first cell as a non-LTM TCI state configurations for the first cell, unless it includes or associates a SSB corresponding to QCL type A.

[0192] In some implementations, when or while the DU 174 communicates (e.g., at events 332 and / or 336) with the UE 102 on the first cell, the DU 174 refrains from transmitting an LTM TCI States Activation / Deactivation command to the UE 102 to activate an LTM TCI state configuration for the first cell or associated with the LTM ID 1. In further implementations, when or while the DU 174 communicates (e.g., at events 332 and / or 336) with the UE 102 on the first cell, the DU 174 transmits a second LTM TCI States Activation / Deactivation command to the UE 102 to activate at least one LTM TCI state configuration in the first LTM TCI state configuration(s) that is / are not activated by the first LTM command. In response to the second LTM TCI States Activation / Deactivation command, the UE 102 activates the LTM TCI state configuration(s) indicated in the second LTM TCI States Activation / Deactivation command. In some implementations, in the second LTM TCI States Activation / Deactivation command, the DU 174 deactivates the LTM TCI state configuration(s) activated in the first LTM command. In such cases, in response, the UE 102 deactivates the LTM TCI state configuration(s) activated in the first LTM command. The UE 102 and the DU 174 communicate with each other on the first cell using the LTM TCI state configuration(s) activated by the second LTM TCI States Activation / Deactivation command, as described above.

[0193] In some implementations, the UE 102 transmits an RRC message (e.g., an RRC reconfiguration complete message) to the CU 172 via the DU 174 and the first cell to indicate that the UE 102 applies the LTM DU configuration 1. In some implementations, in cases where the UE 102 performs 332 the random-access procedure, the UE 102 includes the RRC message in the Message 3 or Message A. Alternatively, the UE 102 transmits the RRC message after completing the random-access procedure. In cases where the UE 102 skips performing 332 the random-access procedure, the UE 102 includes the RRC message in a PUSCH transmission of the at least one PUSCH transmission. In some implementations, if the UE 102 maintains communication on the cell 124A with the base station 104 (i.e., the UE 102 does not disconnect from the cell 124A), the UE 102 transmits the RRC message to the base station 104 via the cell 124A. When the DU 174 receives the RRC message, the DU 174 transmits the RRC message to the CU 172.

[0194] In further implementations, the UE 102 refrains from transmitting the RRC message to the base station 104 in response to applying the LTM DU configuration 1 or receiving the first LTM command. In some such implementations, the UE 102 includes or transmits data in the Message 3, Message A, or PUSCH transmission as described above. Insome implementations, the UE 102 generates a MAC PDU and / or an RLC PDU including the data and transmits or includes the MAC PDU and / or RLC PDU in the PUSCH transmission. For example, in some implementations the data is a PDCP PDU, an SDAP PDU, an LTE Positioning Protocol (LPP) PDU, an RRC PDU, and / or a NAS PDU. The RRC PDU includes a UL-DCCH-Message excluding an RRC reconfiguration complete message. The NAS PDU includes a Mobility Management (MM) message or a Session Management (SM) message. In some implementations, the MM message is a 5G MM message or a 6G MM message, and the SM message is a 5G SM message or a 6G SM message. When the DU 174 receives the data, the DU 174 transmits the data to the CU 172.

[0195] In some implementations, when the DU 174 determines that the UE 102 successfully connects to the first cell in the event 332 or 336, the DU 174 transmits 334 a DU-to-CU message (e.g., Access Success message) to the CU 172 (e.g., a CP of the CU 172). In some implementations, the DU 174 includes the cell ID 1 of the first cell in the DU-to-CU message of the event 334. In some implementations, the cell ID is a PCI or a CGI. Thus, the CU 172 determines that the UE 102 connects to the first cell upon receiving the DU-to-CU message of the event 334. In some implementations, when the DU 174 determines that the UE 102 successfully connect to the first cell in the event 332 or 336, the DU 174 transmits a DL Data Delivery Status message or frame to the CU 172 (e.g., a UP of the CU 172). In some implementations, when or after the CU 172 receives 329 the DU-to-CU message, the CU 172 stops or suspends transmitting DL data for the UE 102 to the DU 174 until receiving 334 the DU-to-CU message. In further implementations, the CU 172 stops or suspends transmitting because the DU 174 is not capable of buffering the DL data for the UE 102 during the LTM execution in the events 330 and / or 332. After receiving 334 the DU-to-CU message, the CU 172 continues or resumes transmitting the DL data for the UE 102 to the DU 174. In some implementations, when the CU 172 receives the DU-to-CU message 329, the CU 172 continues transmitting the DL data for the UE 102 to the DU 174. In some implementations, the CU 172 continues transmitting because the DU 174 is capable of buffering the DL data for the UE 102 during the LTM execution in the events 330 and / or 332. When or after the DU 174 detects that UE 102 accesses the cell 1, the DU 174 transmits the DL data to the UE 102 via the cell 1.

[0196] In some implementations, when determining that the UE 102 connects to the first cell, transmitting 330 the first LTM command, or receiving 331 the acknowledgement, theDU 174 stops communicating with the UE 102 on the cell 124A and / or releases resources of the cell 124 A configured for the UE 102.

[0197] In some implementations, the DU 174 generates some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, N as full configuration(s) (i.e., complete configuration(s) without referring to a reference LTM DU configuration). If the LTM DU configuration 1 is a full configuration, the UE 102 and DU 174 communicate, at event 336, with each other in accordance with the LTM DU configuration 1 instead of the serving DU configuration. In some implementations, the DU 174 includes an indication indicating that the LTM DU configuration 1 is a full configuration in the LTM DU configuration 1. In some implementations, in each of the LTM DU configuration(s) 2, ..., N, the DU 174 includes an indication to indicate that the corresponding DU configuration is a full configuration. In some implementations, each of the indication(s) in the LTM DU configuration(s) 1, ..., N is a field or IE (i.e., the same field or IE). In some implementations, the CU 172 includes, in the RRC reconfiguration message of the events 316, 318, a single indication indicating that the LTM DU configuration(s) 1 and / or 2, ..., N is / are full configuration(s). In some implementations, in the case of the second container, the CU 172 includes, in the additional RRC reconfiguration message, a single indication indicating that the LTM DU configuration(s) 2, ..., N is / are full configuration(s). In further implementations, the CU 172 includes, in the first container, a single indication indicating that the LTM DU configuration(s) 1 and / or 2, ..., N is / are full configuration(s). In still further implementations, for each of the LTM DU configuration(s) 2, ..., N, the CU 172 includes, in the first container, a particular indication indicating the corresponding LTM DU configuration is a full configuration. In the case of the second container, in some implementations the CU 172 includes, in the second container, a single indication indicating that the LTM DU configuration(s) 2, ..., N is / are full configuration(s). In further implementations, the CU 172 includes, in the element 1, an indication indicating that the LTM DU configuration 1 is a full configuration. In some implementations, in each of the element(s) 2, ..., N, the CU 172 includes an indication indicating that the corresponding LTM DU configuration is a full configuration. In some implementations, the UE 102 determines that the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ..., N is / are full configuration(s) based on the indication(s) above. In some implementations, each of the indication(s) above is different from fullConfig field defined in the current 3GPP specification. In some implementations, each of the indication(s) above is fullConfig fielddefined in the current 3GPP specification. In cases where the LTM DU configuration 1 is a full configuration, the UE 102 (e.g., in the event 336) does not apply the reference LTM DU configuration if received from the base station 104 (e.g., in the RRC reconfiguration message 318). In such cases, in some implementations the DU 174 does not include a / the reference LTM DU configuration in the first DU-to-CU message of event 310.

[0198] In some implementations, the DU 174 generates the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ..., N as delta configuration(s) that augment at least a portion of the reference LTM DU configuration. In other words, the DU 174 generates the LTM DU configuration(s) 1, .. ,N based on the reference LTM DU configuration. Lor example, if the LTM DU configuration 1 is a delta configuration, the UE 102 and DU 174 augment the at least a portion of the reference LTM DU configuration with the LTM DU configuration 1. Thus, the UE 102 and DU 174 communicate, at event 336, with each other in accordance with the LTM DU configuration 1 and an unaugmented portion of the reference LTM DU configuration. In some implementations, the LTM DU configuration(s) 1, and / or 2..., N, first container, second container, or element(s) 1, ..., N exclude indication(s) indicating that the LTM DU configuration(s) 1, and / or 2..., N is / are full configuration(s) to indicate that the LTM DU configuration(s) 1 and / or 2, ..., N is / are delta configuration(s). In some implementations, the UE 102 determines that each of the LTM DU configuration(s) 1 and / or 2, ..., N is a delta configuration based on the LTM DU configuration(s) 1 and / or 2, ...,N, first container, second container, or element(s) 1 and / or 2, ..., N excluding the indication.

[0199] In some implementations, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and / or the LTM DU configuration(s) 2, ..., N, the UE 102 determines that the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, ..., N are full configuration(s). Correspondingly, if the DU 174 does not obtain a reference LTM DU configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM DU configuration for the UE 102 and / or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, ..., N as full configuration(s).

[0200] In further implementations, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and / or the LTM DU configuration(s) 2, ..., N, the UE 102 determines that the LTM DU configuration 1 and / or the LTM DUconfiguration(s) 2, ..., N are delta configuration(s) to augment the serving DU configuration. In such cases, the UE 102 communicates, at event 336, with the DU 174 in accordance with the LTM DU configuration 1 and at least a portion of the serving DU configuration not augmented by LTM DU configuration 1. Correspondingly, if the DU 174 does not obtain a reference LTM DU configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM DU configuration for the UE 102 and / or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, ..., N as delta configuration(s) to augment the serving DU configuration. In such cases, the DU 174 communicates, at event 336, with the UE 102 in accordance with the LTM DU configuration 1 and the at least a portion of the serving DU configuration.

[0201] In some implementations, the UE 102 uses a UE MAC entity (e.g., MAC 204B) to communicate with a DU MAC entity (e.g., MAC 204B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330, and / or 331). In some implementations, the UE 102 resets the UE MAC entity, after or in response to receiving the first LTM command and before performing 332 the random-access procedure or performing 336 communication with the DU 174 via the first cell. In some implementations, the DU 174 resets the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving 331 the acknowledgement or determining that the UE 102 connects to the first cell.

[0202] In some implementations, when the UE 102 resets the UE MAC entity, the UE 102 performs at least one of the following actions for the UE MAC entity (i.e., UE MAC reset or full UE MAC reset): (i) initialize Bj for configured logical channel(s) to zero; (ii) stop one or more timers; (iii) consider timeAlignmentTimeris) as expired if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1); (iv) set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0; (v) set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in sidelink resource allocation mode 1; (vi) flush Message (Msg3) buffer; (vii) flush Message A(MSGA) buffer; (viii) cancel, if any, a triggered Scheduling Request procedure; (ix) cancel, if any, a triggered Buffer Status Reporting procedure; (x) cancel, if any, a triggered Power Headroom Reporting procedure; (xi) cancel, if any, a triggered consistent LBT failure; (xii) cancel, if any, a triggered BFR; (xiii) cancel, if any, a triggered Sidelink Buffer Status Reporting procedure; (xiv) cancel, if any, a triggered Pre-emptive Buffer Status Reporting procedure;(xv) cancel, if any, a triggered Timing Advance Reporting procedure; (xvi) cancel, if any, atriggered Recommended bit rate query procedure; (xvii) cancel, if any, a triggered configured uplink grant confirmation; (xviii) cancel, if any, a triggered configured sidelink grant confirmation; (xix) cancel, if any, a triggered Desired Guard Symbol query; (xx) cancel, if any, a triggered Positioning Measurement Gap Activation / Deactivation Request procedure; (xxi) flush soft buffers for DL HARQ process(es); (xxii) for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission; (xxiii) release, if any, a Temporary C-RNTI; and / or (xxiv) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0203] In some implementations, when the DU 174 resets the DU MAC entity, the DU 174 performs at least one of the following actions for the DU MAC entity (i.e., DU MAC reset or full DU MAC reset): (i) stop one or more timers; (ii) consider timeAlignmentTimer(s), that the DU 174 starts and / or maintains for the UE 102, as expired if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1); (iii) set NDI(s) for DL HARQ process(es) to value 0; (iv) flush soft buffers for UL HARQ process(es); (v) for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission; and (vi) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0204] Depending on implementation, the UE 102 determines to partially or fully reset the UE MAC entity. In some implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 fully resets the UE MAC entity (i.e., a full UE MAC reset). In the full UE MAC reset, the UE 102 performs some or all of the actions described above. In further implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 partially resets the UE MAC entity (i.e., a partial UE MAC reset). In the partial UE MAC reset, the UE 102 performs a subset or portion of the some or all of the actions in the full UE MAC reset.

[0205] In further implementations, the partial UE MAC reset includes at least one of the following actions: (i) consider timeAlignmentTimeris) of the UE 102 as expired if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1); (ii) flush Msg3 buffer; (iii) flush MSGA buffer; (iv) release, if any, a Temporary C-RNTI; and / or (v) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0206] In still further implementations, the partial UE MAC reset further includes at least one of the following actions: (i) cancel, if any, a triggered Scheduling Request procedure; (ii) cancel, if any, a triggered Buffer Status Reporting procedure; (iii) cancel, if any, a triggered Power Headroom Reporting procedure; (iv) cancel, if any, a triggered consistent LBT failure; (v) cancel, if any, a triggered BFR; (vi) cancel, if any, a triggered Sidelink Buffer Status Reporting procedure; (vii) cancel, if any, a triggered Pre-emptive Buffer Status Reporting procedure; (viii) cancel, if any, a triggered Timing Advance Reporting procedure; (ix) cancel, if any, a triggered Recommended bit rate query procedure; (x) cancel, if any, a triggered configured uplink grant confirmation; (xi) cancel, if any, a triggered configured sidelink grant confirmation; (xii) cancel, if any, a triggered Desired Guard Symbol query; and / or (xiii) cancel, if any, a triggered Positioning Measurement Gap Activation / Deactivation Request procedure.

[0207] In yet still further implementations, the partial UE MAC reset further includes at least one of the following actions: (i) stop a first portion of the one or more timers and retain the rest of the one or more timers; (ii) set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0; (iii) set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1 ; (iv) flush soft buffers for DL HARQ process(es); and / or (v) for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission.

[0208] Depending on the implementation, the DU 174 determines to partially or fully reset the DU MAC entity. In some implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 fully resets the DU MAC entity (i.e., a full DU MAC reset). In the full DU MAC reset, the DU 174 performs some or all of the actions described above. In further implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 partially resets the DU MAC entity (i.e., a partial DU MAC reset). In the partial DU MAC reset, the DU 174 performs a subset or portion of the some or all of the actions in the full DU MAC reset.

[0209] In still further implementations, the partial DU MAC reset includes at least one of the following actions in the partial MAC reset: (i) consider limeAlignmenlTimer( ) that the DU 174 starts and / or maintains for the UE 102 as expired if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., theconfiguration 1) and / or (ii) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0210] In yet still further implementations, the partial DU MAC reset includes at least one of the following actions for the MAC entity (i.e., DU MAC reset): (i) stop a first portion of the one or more timers and retain the rest of the one or more timers; (ii) set NDI(s) for DL HARQ process(es) to value 0; (iii) flush soft buffers for UL HARQ process(es); (iv) for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission; and (v) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0211] In some implementations, the UE 102 refrains from resetting the UE MAC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from resetting the DU MAC entity after (e.g., in response to) transmitting 330 the first LTM command, receiving 331 the acknowledgement, or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the UE MAC entity (e.g., not reset). Similarly, the DU 174 communicates with the UE 102 using the DU MAC entity (e.g., not reset) on the first cell during or after the random-access procedure of event 332 or after determining that the UE 102 connects to the first cell.

[0212] In some implementations, the UE 102 uses at least one UE RLC entity (e.g., RLC 206B) to communicate RLC PDUs with at least one DU RLC entity (e.g., RLC 206B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330, and / or 331). In some implementations, the UE 102 reestablishes some or all of the at least one UE RLC entity, after or in response to receiving the first LTM command and before performing 332 the random-access procedure or communicating 336 with the DU 174 via the first cell. In some implementations, the DU 174 reestablishes some or all of the at least one DU RLC entity after (e.g., in response to) transmitting 330 the first LTM command, receiving 331 the acknowledgement, or determining that the UE 102 connects to the first cell.

[0213] In some implementations, the LTM DU configuration 1 includes one or more RLC reestablishment indications (e.g., reestablishRLC field(s)) configuring the UE 102 to reestablish some or all of the at least one UE RLC entity. If the LTM DU configuration 1 includes an RLC reestablishment indication configuring the UE 102 to reestablish a first UE RLC entity, of the at least one UE RLC entity, that the UE 102 uses to communicate RLC PDU(s) with the DU 174, the UE 102 reestablishes the first UE RLC entity in response to theRLC reestablishment indication and the first LTM command. In some implementations, the UE 102 reestablishes the first UE RLC entity before performing 332 the random access procedure or performing 336 communication with the DU 174 via the first cell. In further implementations, the UE 102 reestablishes the first UE RLC entity while or after performing 332 the random-access procedure. Otherwise, if the LTM DU configuration 1 does not include the RLC reestablishment indication, the UE 102 refrains from reestablishing the first UE RLC entity in response to the first LTM command.

[0214] In some implementations, when the UE 102 reestablishes the first UE RLC entity, the UE 102 performs at least one of the following actions for the first UE RLC entity: (i) discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any; (ii) stop and reset timer(s), if running; and (iii) reset state variables to initial values. In some implementations, the state variables and timer(s) are pre-defined (e.g., defined in 3GPP TS 38.322).

[0215] Otherwise, if the LTM DU configuration 1 does not include the RLC reestablishment indication for the first UE RLC entity, the UE 102 refrains from reestablishing the first UE RLC entity upon or when receiving the first LTM command. In other words, the UE 102 refrains from performing the actions for reestablishing the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. In some implementations, if the LTM DU configuration 1 or element 1 does not include the RLC reestablishment indication and includes an indication that the configuration 1 is a full configuration, the UE 102 reestablishes the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. Otherwise, if the LTM DU configuration 1 or element 1 does not include the RLC reestablishment indication and the indication indicating that the configuration 1 is a full configuration, the UE 102 refrains from reestablishing the first UE RLC entity upon or when receiving the first LTM command.Similarly, the DU 174 reestablishes some or all of at least one DU RLC entity (e.g., NR RLC 206B) that the DU 174 uses to communicate with the at least one UE RLC entity of the UE 102 (e.g., the events 302, 304, 318, 320, 324, 330, and / or 331) in response to the RLC reestablishment indication. In some implementations, the DU 174 reestablishes a first DU RLC entity of the at least one DU RLC entity after transmitting the first LTM command, receiving an acknowledgement for the first LTM command from the UE 102, or determining that the UE 102 connects to the first cell. In some implementations, the acknowledgement is a HARQ ACK. In further implementations, the acknowledgement is a MAC CE. In someimplementations, the acknowledgement is a PUCCH transmission. In some implementations, when the base station 104 reestablishes the first DU RLC entity, the DU 174 performs at least one of the following actions for the first DU RLC entity: (i) discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any; (ii) stop and reset timer(s), if running; and / or (iii) reset state variables to initial values. In some implementations, the state variables and timer(s) are pre-defined (e.g., in 3GPP TS 38.322).

[0216] In some implementations, the UE 102 refrains from reestablishing some or all of the at least one UE RLC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from reestablishing some or more of the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving 331 the acknowledgement or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the some or all of the at least one UE RLC entity (e.g., not reestablished). For example, the some or all of the at least one UE RLC entity includes the first UE RLC entity and / or a second UE RLC entity. Similarly, the DU 174 communicates with the UE 102 using the some or all of the at least one DU RLC entity (e.g., not reestablished) on the first cell during or after the random-access procedure 332 or after determining that the UE 102 connects to the first cell. For example, the some or all of the at least one DU RLC entity includes the first DU RLC entity and / or a second DU RLC entity.

[0217] In some implementations, the UE 102 uses at least one UE PDCP entity (e.g., PDCP 210) to communicate UL PDCP PDUs and / or DL PDCP PDUs with at least one CU PDCP entity (e.g., PDCP 210) of the CU 172 in the event 302. In some implementations, the UE 102 performs a PDCP recovery procedure for some or all of the at least one UE PDCP entity, after or in response to receiving the first LTM command. For example, the UE 102 performs a PDCP recovery procedure for a first UE PDCP entity of the at least one UE PDCP entity after or in response to receiving the first LTM command. In the PDCP recovery procedure, the UE 102 may or may not reestablish the first UE PDCP entity. In some implementation, after or in response to performing the PDCP recovery procedure, the UE 102 retransmit at least a portion of the UL PDCP PDUs to the CU 172 via the DU 174 and the first cell in the event 336. Similarly, the CU 172 performs a PDCP recovery procedure for some or all of the at least one CU PDCP entity after or in response to transmitting the first LTM command. For example, the CU 172 performs a PDCP recovery procedure for a first CU PDCP entity of the at least one CU PDCP entity, after or in response to transmitting thefirst LTM command. In some implementations, the CU 172 performs 329 or 334 the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DU-to-CU message. In further implementations, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DL Data Delivery Status message. In some implementations, in the PDCP recovery procedure, the CU 172 reestablishes the first CU PDCP entity. In further implementations, after or in response to performing the PDCP recovery procedure, the CU 172 retransmit at least a portion of the DL PDCP PDUs to the UE 102 via the DU 174 and the first cell in the event 336.

[0218] In some implementations, the UE 102 refrains from reestablishing some or all of the at least one UE PDCP entity in response to receiving the first LTM command. For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and / or a second UE PDCP entity. Similarly, the CU 172 refrains from reestablishing 329 or 340 some or more of the at least one CU PDCP entity, after (e.g., in response to) receiving the DU-to-CU message or after (e.g., in response to) receiving the DL Data Delivery Status message. In other words, the UE 102 communicates with the CU 172 via the DU 174 and the first cell using the some or all of the at least one UE PDCP entity (e.g., not reestablished). For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and / or a second UE PDCP entity. Similarly, the CU 172 communicates with the UE 102 using the some or all of the at least one CU PDCP entity (e.g., not reestablished) via the DU 174 and the first cell. For example, the some or all of the at least one CU PDCP entity includes the first CU PDCP entity and / or a second CU PDCP entity.

[0219] In some implementations, after determining that the UE 102 connects to the first cell, receiving 329 the DU-to-CU message, or receiving 334 the Access Success message, the CU 172 transmits 338 a CU-to-DU message (e.g., a UE Context Modification Request message) to the DU 174 to indicate the DU 174 to stop communicating with the UE 102 and / or to release or suspend resources, of the cell 124A, configured for the UE 102. In some implementations, in response to the event 338, the DU 174 stops communicating on the cell 124A with the UE 102 and / or releases or suspends resources of the cell 124A, configured for the UE 102, and transmits 340 a DU-to-CU message (e.g., a UE Context Modification Response message) to the CU-172. The events 338 (optional) and 340 (optional) are collectively referred to in Fig. 3 as a resource release or modification procedure 396.

[0220] In some implementations, after or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351, 352, 354, and / or 356 occur, similar to the events 324, 326, 328, 330, 331, 332, 334, and / or 336, respectively. The UE 102 transmits 344 at least one measurement report to the DU 174. The at least one measurement report includes at least one measurement result for a second cell (i.e., the cell 2). The at least one measurement result indicates that the second cell is suitable for communication with UE 102 and / or the first cell is not suitable for communication with the UE 102. After (e.g., in response to) receiving the at least one measurement report, the DU 174 determines to activate the LTM DU configuration 2 and generates a second LTM command to activate the LTM DU configuration 2 (i.e., the second LTM command commands the UE 102 to apply the LTM DU configuration 2). The DU 174 then transmits 350 the second LTM command to the UE on the first cell to the UE 102.

[0221] In some implementations, when or in response to determining to activate the LTM DU configuration 2 or transmit the second LTM command, the DU 174 transmits 349, to the CU 172, a DU-to-CU message indicating that LTM is being and / or will be executed. In some implementations, the DU 174 includes the cell ID 2 or the ID 2 (i.e., LTM ID) in the DU-to- CU message 349 to indicate that the DU 174 is to activate the LTM DU configuration 2. In some implementations, the DU transmits 349 the DU-to-CU message to the CU 172 before or after transmitting 350 the LTM command.

[0222] The descriptions for the events 324, 326, 328, 330, 331, 332, 334 and / or 336 can be applied to the events 344, 346, 348, 350, 351, 352, 354 and / or 356 with simple changes. Lor example, “ cell 124A”, “first LTM command”, “first cell”, “ID 1”, “LTM DU configuration 1”, and / or “LTM CU configuration 1” are replaced with “first cell”, “second LTM command” and “second cell”, “ID 2”, “LTM DU configuration 2”, and / or “LTM CU configuration 2”, respectively.

[0223] The events 344, 346, 348, 350, 351, 352, and 354 are collectively referred to in Eig. 3 as an LTM execution procedure 398. The events 304, 306, 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, and 356 are collectively referred to in Eig. 3 as an LTM DU configuration and / or activation procedure 380.

[0224] Referring next to Eig. 4, in a scenario 400, the base station 104 includes a CU 172, a source DU (S-DU) 174A and a target DU (T-DU) 174B. The S-DU 174A operates the cell 124A and optionally additional cell(s), while the T-DU 174B operates a first cell (e.g., cell124C). The scenario 400 is similar to the scenario 300. Thus, the descriptions for the scenario 300 can generally apply to the scenario 400. The differences between the scenarios 300 and 400 are described below.

[0225] Initially, the UE 102 communicates 402 with the S-DU 174A on cell 124A using a serving DU configuration and communicates with the CU 172 via the S-DU 174A. The S- DU 174A is a serving DU similar to the DU 174 in Fig. 3A. During the communication at event 402, the UE 102 transmits 404 and 406 at least one measurement report (e.g., L3 measurement report(s)) to the CU 172 via the S-DU 174A. Based on the at least one measurement report, the CU 172 determines to prepare cell(s) 1, ..., N (operated by the T-DU 174B) for LTM for the UE 102, where N is a positive integer larger than 0 or 1. The cell(s) 1, ..., N are identified by cell ID(s) 1, ..., N, respectively. In response to the determination, the CU 172 performs 490 an LTM preparation procedure with the T-DU 174B to (e.g., request the T-DU 174B to) prepare cell(s) 1, ..., N for LTM for the UE 102. In some implementations, N is a positive integer larger than zero or 1. In the LTM preparation procedure 490, the CU 172 transmits a CU-to-DU message including the cell ID(s) 1, ..., N to the T-DU 174B to request the T-DU 174B to prepare the cell(s) 1, ..., N for LTM for the UE 102, similar to the event 308. In response, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) 1, ..., N to the CU 172, similar to the event 310. The LTM DU configuration(s) 1, ..., N configures the cell(s) 1, ..., N for LTM, respectively. In details, the LTM DU configuration(s) 1, ..., N include configuration parameters for communication on the cell(s) 1, ..., N, respectively. In some implementations, the CU-to-DU message and DU-to-CU message in the procedure 490 are UE Context Setup Request message and UE Context Setup Response message, respectively. The CU 172 then transmits the LTM DU configuration(s) 1, ..., N in an RRC reconfiguration message in an LTM configuration delivery procedure 494, similar to the LTM configuration delivery procedure 394. In some implementations, the T-DU 174B includes cell index(es) 1, ..., N in the LTM DU configuration(s) 1, ..., N, respectively. In some implementations, the CU 172 sets the cell index(es) 1, ..., N to different values and include the cell index(es) 1, ..., N in the CU-to-DU message of the procedure 490.

[0226] In some implementations, after performing the LTM preparation procedure 490, the CU 172 performs additional LTM preparation procedure(s) with the T-DU 174B to prepare cell(s) N+l, ..., N+M for LTM for the UE 102, similar to the procedure 490. M is a positive integer larger than zero. In further implementations, the CU 172 determines to do so basedon one or more measurement reports received from the UE 102 via the S-DU 174A, similar to the events 404 and 406. In the additional LTM preparation procedure, the CU 172 transmits a CU-to-DU message including cell ID(s) N+l, N+M to the T-DU 174B to request the T-DU 174B to prepare the cell(s) N+l, ..., N+M for LTM for the UE 102. The cell ID(s) N+l, ..., N+M identifies the cell ID(s) N+l, ..., N+M, respectively. In response to the CU-to-DU message, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) N+l, ..., N+M to the CU 172. The LTM DU configuration(s) N+l, ..., N+M configures the cell(s) N+l, ..., N+M for LTM, respectively. In details, the LTM DU configuration(s) N+l, ..., N+M include configuration parameters for communication on the cell(s) N+l, ..., N+M, respectively. The CU 172 then transmits the LTM DU configuration(s) N+l, ..., N+M in an RRC reconfiguration message in an additional LTM configuration delivery procedure, similar to the LTM configuration delivery procedure 394 or 494.

[0227] 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 further implementations, the LTM procedure 490 and the additional LTM preparation procedures are UE Context Setup procedures. In still further implementations, the LTM procedure 490 and the additional LTM preparation procedures are UE Context Modification procedures.

[0228] In some implementations, the CU 172 and S-DU 174A performs the procedure 380 with the UE 102, as described for Eig. 3. In the procedure 380, the CU 172 and S-DU 174A performs the procedure(s) 390 and / or 392 to prepare cell(s) of the S-DU 174A for LTM for the UE 102. Note, in some implementations, the value N in the procedure 380 or as described for Eig. 3 is the same as or different from the value N described for Eig. 4. In some implementations, in the procedure 390, the CU 172 receives 310 the first DU-to-CU message including the reference LTM DU configuration from the S-DU 174A. In further implementations, the CU 172 and S-DU 174A do not perform the procedure 380 with the UE 102. In some such implementations, the CU 172 performs 488 a reference LTM DU configuration query procedure with the S-DU 174A to obtain a reference LTM DU configuration. In the procedure 488, the CU 172 transmits 460 a CU-to-DU message to the S-DU 174A to request or query a reference LTM DU configuration. In some implementations, the CU 172 includes an indication in the CU-to-DU message to request or query a reference LTM DU configuration. In response to the indication or CU-to-DUmessage of event 460, the S-DU 174A transmits 462 a DU-to-CU message including a reference LTM DU configuration to the CU 172. In some implementations, the indication is a reference LTM DU configuration query indication. In further implementations, the indication is an LTM indication, and the CU 172 includes a query indication (e.g., GNB-DU Configuration Query IE) in the CU-to-DU message. After receiving the reference LTM DU configuration (i.e., either in the procedure 390 or in the procedure 488), the CU 172 includes the reference LTM DU configuration (e.g., received from the S-DU 174A) in the CU-to-DU message in the LTM preparation procedure 490. The T-DU 174B generates the LTM DU configuration(s) 1, ..., N based on the reference LTM DU configuration received from the CU 172. In such cases, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. In some implementations, the CU 172 does not include the reference LTM DU configuration in CU- to-DU message in the additional LTM preparation procedure with the T-DU 174B. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+l, ..., N+M based on the reference LTM DU configuration received from the CU 172.

[0229] In some implementations, the CU 172 does not provide a reference LTM DU configuration to the T-DU 174B in the LTM preparation procedure 490. In such cases, the T- DU 174B generates a reference LTM DU configuration and generates the LTM DU configuration(s) 1, ..., N based on the reference LTM DU configuration. In such cases, the T-DU 174B includes the reference LTM DU configuration in the DU-to-CU message in the procedure 490. The CU 172 transmits the reference LTM DU configuration in the RRC reconfiguration message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+l, ..., N+M based on the reference LTM DU configuration. In some such implementations, the T-DU 174B does not include the reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. In some implementations, the reference LTM DU configuration generated by the T-DU 174B is different from the reference LTM DU configuration generated by the S-DU 174A. In further implementations, the reference LTM DU configuration generated by the T-DU 174B is the same as the reference LTM DU configuration generated by the S-DU 174A.

[0230] In some implementations, the CU 172 includes the LTM DU configuration(s) 1, N of the procedure 380 in the CU-to-DU message of the procedure 490, and the T-DU 174B generates the LTM DU configuration(s) 1, ..., N and / or N+l, ..., N+M, considering or based on configuration(s) in the LTM DU configuration(s) of the procedure 380.

[0231] In some implementations, the LTM DU configuration X of the procedure 380 includes at least one reference signal (RS) resource configuration X, where 1 < X < N. Each of the RS resource configuration(s) X configures one or more RSs or one or more RS resources associated with the cell X of the S-DU 174A. 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 RS resource configuration(s) X includes an RS resource configuration ID. In some implementations, the RS resource configuration(s) X are and / or are similar to CSl-ResourceConfig IE(s). In some implementations, the LTM DU configuration X includes a CSl-MeasConfig IE and the CSl-MeasConfig IE includes the CSl- ResourceConfig IE(s). The T-DU 174B generates at least one report configuration 1 for reporting on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s), and includes the report configuration(s) 1 in the LTM DU configuration 1. In some implementations, the report configuration(s) 1 are and / or are similar to CS1- ReportConfig IE(s). In some implementations, the T-DU 174B generates at least one RS resource configuration 1 considering or based on the RS resource configuration(s) X and includes the RS resource configuration(s) 1 in the LTM DU configuration 1. In some implementations, the T-DU 174B includes the RS resource configuration(s) X in the RS resource configuration(s) 1. In further implementations, the T-DU 174B includes each of the RS resource configuration(s) X in the RS resource configuration(s) 1, except the RS resource configuration ID(s) in the RS resource configuration(s) X. The T-DU 174B assigns an RS resource configuration ID to a value for each of the RS resource configuration(s) 1 (e.g., including the RS resource configuration(s) X) and includes the RS resource configuration ID in the corresponding RS resource configuration.

[0232] In some implementations, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configuration(s) 1. After the UE 102 performs a LTM serving cell change to the cell 1 from the cell 124A, the UE 102 communicates with theS-DU 174B (i.e., the T-DU 17B becomes a S-DU for the UE 102) and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the report configuration(s) 1. Correspondingly, the S-DU 174B receives the measurement results on the UL resource(s) via the cell 1 from the UE 102 in accordance with the report configuration(s) 1. In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) 1 and / or the report configuration(s) 1 and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or RS resource(s) where the UE 102 performs measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). In some implementations, the quantized measurement values include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0233] In some implementations, the T-DU 174B also includes additional RS resource configuration(s) in the LTM DU configuration 1. Each of the additional RS resource configuration(s) configures one or more additional RSs or one or more additional RS resources associated with the cell 1. The additional RS(s) includes SSB(s) and / or CSI-RS(s). The additional RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some implementations, each of the additional RS resource configuration(s) includes a RS resource configuration ID. In some implementations, the additional RS resource configuration(s) are and / or are similar to CSl-ResourceConfig IE(s). In some implementations, the T-DU 174B includes the CSI-ResourceConfig IE(s) in the CSI-MeasConfig IE. The T-DU 174B generates at least one additional report configuration for reporting, on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s) and includes the additional report configuration(s) in the LTM DU configuration 1. In some implementations, the additional report configuration(s) are and / or are similar to CSl-ReportConfig IE(s).

[0234] In some implementations, the additional report configuration(s) configure one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the additional report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the additional RS resource configuration(s). After the UE 102 performs an LTM serving cell change to the cell 1 from the cell 124A, the UE 102communicates 436 with the S-DU 174B and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the additional report configuration(s). Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the additional report configuration(s). In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the additional RS(s) or the additional RS resource(s) in accordance with the additional RS resource configuration(s) and / or the additional report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the additional RS(s) or an RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). In some implementations, the quantized measurement values includes one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0235] Similarly, in some implementations, the T-DU 174B generates RS resource configuration(s) 2, ..., N, and / or N+l, ..., N+M and / or report configuration(s) 2, ..., N, and / or N+l, ..., N+M, considering or based on the RS resource configuration(s) X. In some such implementations, the T-DU 174B also includes the RS resource configuration(s) 2, ..., N, and / or N+l, ..., N+M and / or the report configuration(s) 2, ..., N, and / or N+l, ..., N+M in the LTM DU configuration(s) 2, ..., N, and / or N+l, ..., N+M, respectively, as described above.

[0236] In some implementations, the LTM DU configuration X of the procedure 380 includes at least one TCI state configuration X, where 1 < X < N. Each of the TCI state configuration(s) X configures a TCI state that associates or includes one or two DL RSs with a corresponding QCL type. In some implementations, the DL RS(s) are associated with the cell X operated by the S-DU 174A. In some implementations, each of the TCI state configuration(s) X includes a TCI state ID. In further implementations, each of the TCI state configuration(s) X is a TCl-State IE. In some implementations, the TCI state configuration(s) X includes / is / are an ul-TCl-ToAddModList-rl7 field, one or more TCl-UL-State-rl7 IES, a dl-OrJointTCl-StateToAddModList-rl7 field, one or more TCl-State IEs, TCI-ActivatedConfig IE, and / or a tci-StatesToAddModList field. In some implementations, the LTM DU configuration X includes a PDSCH-Config IE and the PDSCH-Config IE includesthe TCI state configuration(s) X. In some implementations, the T-DU 174B generates at least one TCI state configuration 1 considering or based on the TCI state configuration(s) X and includes the TCI state configuration(s) 1 in the LTM DU configuration 1. In some implementations, the TCI state configuration(s) 1 includes the TCI state configuration(s) X. In some implementations, the T-DU 174B includes each of the TCI state configuration(s) X in the TCI state configuration(s) 1, except the TCI state ID(s) in the TCI state configuration(s) X. The T-DU 174B assigns a TCI state ID to a value for each of the TCI state configuration(s) 1 (e.g., including the TCI state configuration(s) X) and includes the TCI state ID in the corresponding TCI state configuration. In some implementations, while the UE 102 and the S-DU 174B communicate 436 with one another, the S-DU 174B transmits an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell X. The S-DU 174B includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell X, where the TCI state configuration is one of the TCI state configuration(s) X or includes configurations of one of the TCI state configuration(s) X.

[0237] In some implementations, similarly the T-DU 174B generates TCI state configuration(s) 2, ..., N, considering or based on the RS resource configuration(s) X and includes the TCI state configuration(s) 2, ..., N and / or N+l, ..., N+M in the LTM DU configuration(s) 2, ..., N and / or N+l, ..., N+M, respectively, as described above.

[0238] In some implementations, in cases where the CU 172 performs the procedure 380 after performing the procedure 490, the CU 172 includes the LTM DU configuration(s) 1, ..., N of the procedure 490 in the CU-to-DU message of the procedure 380 and the S-DU 174A generates the LTM DU configuration(s) 1, ..., N of the procedure 380 considering or based on configurations in the LTM DU configuration(s) of the procedure 490 in a similar way as described above.

[0239] In some implementations, the CU 172 assigns ID(s) 1, ..., N identifying the LTM DU configuration(s) 1, ..., N (e.g., received from the T-DU 174B), respectively, and performs the procedure 492 with the T-DU 174B to provide the ID(s) 1, ..., N and / or cell ID(s) 1, ..., N to the T-DU 174B, similar to the procedure 392. Thus, the T-DU 174B associates the ID(s) 1, ..., N with the LTM DU configuration(s) 1, ..., N and / or the cell ID(s) 1, ..., N, respectively. In some implementations, the T-DU 174B assigns ID(s) 1, ..., N identifying the LTM DU configuration(s) 1, ..., N (e.g., generated by the T-DU 174B),respectively and includes the ID(s) 1, .. N in the DU-to-CU message of the procedure 490 similar to the event 310. In some implementations, the CU 172 assigns ID(s) N+l, N+M identifying the LTM DU configuration(s) N+l, ..., N+M, respectively, and performs a procedure (e.g., similar to the procedure 492) with the T-DU 174B to provide the ID(s) N+l, ..., N+M and / or cell ID(s) N+l, ..., N+M to the T-DU 174B, similar to the procedure 392. Thus, the T-DU 174B associates the ID(s) N+l, ..., N+M with the LTM DU configuration(s) N+l, ..., N+M and / or the cell ID(s) N+l, ..., N+M, respectively. In further implementations, the T-DU 174B assigns ID(s) N+l, ..., N+M identifying the LTM DU configuration(s) N+l, ..., N+M, respectively and includes the ID(s) 1, ..., N in the DU-to-CU message of the additional LTM preparation procedure, similar to the event 310.

[0240] In some implementations, the CU 172 transmits 412 a CU-to-DU message including the ID(s) 1, ..., N to the S-DU 174A and receives 414 a DU-to-CU message from the S-DU 174A in response. The CU-to-DU message of event 412 and DU-to-CU message of event 414 are collectively referred to in Fig. 4 as an LTM ID transfer procedure 493 or an LTM cell index transfer procedure 493. In some implementations, the message of event 412 and message of event414 are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In some implementations, the CU 172 includes the LTM DU configuration(s) 1, ..., N and / or cell ID(s) 1, ..., N in the CU-to-DU message of event 412. In some implementations, the CU 172 includes the ID(s) 1, ..., N in the CU-to-DU message of event 412. In further implementations, the CU 172 includes the cell index(es) 1, ..., N in the CU-to-DU message of event 412. In still further implementations, the CU 172 performs multiple LTM ID transfer procedures to transmit the ID(s) 1, ..., N, cell ID(s) 1, ..., N and / or LTM DU configuration(s) 1, ..., N to the S-DU 174A. In each of the procedures, the CU 172 includes a particular portion of the ID(s) 1, ..., N, cell ID(s) 1, ..., N and / or LTM DU configuration(s) 1, ..., N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associates the ID(s) 1, ..., N with the LTM DU configuration(s) 1, ..., N and / or the cell ID(s) 1, ..., N, respectively. In yet still further implementations, the CU 172 performs multiple LTM cell index transfer procedures to transmit the cell index(es) 1, ..., N, cell ID(s) 1, ..., N and / or LTM DU configuration(s) 1, ..., N to the S-DU 174A. In each of the procedures, the CU 172 includes a particular portion of the cell index(es) 1, ..., N, cell ID(s) 1, ..., N and / or LTM DU configuration(s) 1, ..., N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174Aassociates the cell index(es) 1, .. N with the LTM DU configuration(s) 1, .. N and / or the cell ID(s) 1, N, respectively.

[0241] In some implementations, the S-DU 174A generates a first serving DU configuration, based on the LTM DU configuration(s) 1, 2,... , and / or N, and includes the first serving DU configuration in the DU-to-CU message of event 414. In some implementations, the first serving DU configuration includes configurations updating (e.g., augmenting, modifying or replacing) the serving DU configuration of event 402. In further implementations, the first serving DU configuration includes configurations that are not included in the serving DU configuration of event 402. The CU 172 transmits an RRC reconfiguration message including the first serving DU configuration to the UE 102. The UE 102 applies the first serving DU configuration to communicate with the S-DU 174A upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on implementations, the UE 102 communicates with the S-DU 174A using configurations included in the serving DU configuration of event 402 and not updated by the first serving DU configuration. The following are example implementations of generating the first serving DU configuration based on the LTM DU configuration 1, ..., N.

[0242] In some implementations, the LTM DU configuration Y of the procedure 490 includes at least one RS resource configuration Y, where 1 < Y < N. Each of the RS resource configuration(s) Y configures one or more RSs or one or more RS resources associated with the cell Y of the T-DU 174B. 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 RS resource configuration(s) Y includes an RS resource configuration ID. In some implementations, the RS resource configuration(s) Y are and / or are similar to CS1- ResourceConfig IE(s). In some implementations, the LTM DU configuration Y includes a CSl-MeasConfig IE and the CSl-MeasConfig IE includes the CSl-ResourceConfig IE(s). The S-DU 174A generates at least one serving report configuration for reporting, on the cell 124A, measurement results of the RS(s) or RS resource(s) and includes the serving report configuration(s) in the first serving DU configuration. In some implementations, the serving report configuration(s) is / are (e.g., similar to) CSl-ReportConfig IE(s). In some implementations, the S-DU 174A generates at least one serving RS resource configuration considering or based on the RS resource configuration(s) Y and includes the serving RS resource configuration(s) in the first serving DU configuration. In some implementations, theS-DU 174A includes the RS resource configuration(s) Y in the serving RS resource configuration(s). In further implementations, the S-DU 174A includes each of the RS resource configuration(s) Y in the serving RS resource configuration(s) except the RS resource configuration ID(s) in the RS resource configuration(s) Y. The S-DU 174A assigns an RS resource configuration ID to a value for each of the serving RS resource configuration(s) (e.g., including the RS resource configuration(s) Y) and includes the RS resource configuration ID in the corresponding serving RS resource configuration.

[0243] In some implementations, the serving report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 124A for the UE 102 to transmit measurement results. In further implementations, each of the serving report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the serving RS resource configuration(s). While the UE 102 communicates with the S-DU 174A, the UE 102 transmits measurement results on the UL resource(s) via the cell 124A to the S-DU 174A, in accordance with the serving report configuration(s) (e.g., event 424). Correspondingly, the S-DU 174A receives the measurement results on the UL resource (s) via the cell 124A from the UE 102, in accordance with the serving report configuration(s). In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the serving RS resource configuration(s) and / or the serving report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or an RS resource(s) where the UE 102 performs measurements or obtains the quantized measurement values. In further implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). In some implementations, the quantized measurement values include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0244] In other implementations, the LTM DU configuration Y of the procedure 490 includes at least one TCI state configuration Y, where 1 < Y < N. Each of the TCI state configuration(s) Y configures a TCI state that associates or includes one or two DL RSs with a corresponding QCL type. In some implementations, the DL RS(s) are associated with the cell Y operated by the T-DU 174B. In some implementations, each of the TCI state configuration(s) Y includes a TCI state ID. In some implementations, each of the TCI stateconfiguration(s) Y is a TCl-State IE. In some implementations, the TCI state configuration(s) Y includes / is / are an ul-TCl-ToAddModList-rl7 field, one or more TCl-UL-State-rl7 IES, a dl-OrJointTCl-StateToAddModList-rl7 field, one or more TCl-State IEs, TC1- ActivatedConfig IE and / or a tci-StatesToAddModList field. In some implementations, the LTM DU configuration Y includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) Y. In some implementations, the S-DU 174A generates at least one serving TCI state configuration considering or based on the TCI state configuration(s) Y and includes the serving TCI state configuration(s) in the first serving DU configuration. In some implementations, the serving TCI state configuration(s) 1 includes the TCI state configuration(s) Y. In other implementations, the S-DU 174A includes each of the TCI state configuration(s) Y in the serving TCI state configuration(s), except the TCI state ID(s) in the TCI state configuration(s) Y. The S-DU 174A assigns a TCI state ID to a value for each of the serving TCI state configuration(s) (e.g., including the TCI state configuration(s) Y) and includes the TCI state ID in the corresponding serving TCI state configuration. In some implementations, while the S-DU 174A communicates at event 436 with the UE 102, the S- DU 174A transmits an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell Y. The S-DU 174A includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell Y, where the TCI state configuration is one of the TCI state configuration(s) Y or includes configurations of one of the TCI state configuration(s) Y.

[0245] In some implementations, the CU 172 transmits a CU-to-DU message, including the ID(s) N+l, ..., N+M, to the S-DU 174A and receives a DU-to-CU message from the S- DU 174A in response, similar to the CU-to-DU message of event 412 and the DU-to-CU message of event414, respectively. In some implementations, the CU 172 includes the LTM DU configuration(s) N+l, ..., N+M and / or cell ID(s) N+l, ..., N+M in the CU-to-DU message. In further implementations, the CU 172 performs multiple LTM ID transfer procedures to transmit the ID(s) N+l, ..., N+M, cell ID(s) N+l, ..., N+M and / or LTM DU configuration(s) N+l, ..., N+M to the S-DU 174A. In each of the procedures, the CU 172 includes a particular portion of the ID(s) N+l, ..., N+M, cell ID(s) N+l, ..., N+M and / or LTM DU configuration(s) 1, ..., N in a CU-to-DU message similar to the message of event 412. Thus, the S-DU 174A associates the ID(s) N+l, ..., N+M with the LTM DU configuration(s) N+l, ..., N+M and / or the cell ID(s) N+l, ..., N+M, respectively. In some implementations, the S-DU 174A generates a second serving DU configuration, based on theLTM DU configuration(s) N+l, N+2, and / or N+M, and includes the second serving DU configuration in the DU-to-CU message. In some implementations, the second serving DU configuration includes configurations updating (e.g., augmenting, modifying, or replacing) the first serving DU configuration and / or updating configurations included in the serving DU configuration of event 402 and not updated by the first serving DU configuration. In further implementations, the second serving DU configuration includes configurations that are not included in the first serving DU configuration. The CU 172 transmits an RRC reconfiguration message including the second serving DU configuration to the UE 102 via the S-DU 174A. The UE 102 applies the second serving DU configuration to communicate with the serving DU upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on implementations, the UE 102 communicates with the S-DU 174A using configurations included in the serving DU configuration of event 402 and / or the first serving DU configuration and not updated by the second serving DU configuration. In some implementations, the S-DU 174A generates one or more new LI measurement configurations based on LI measurement configuration(s) in the LTM DU configuration(s) N+l, N+2,... , and / or N+M and includes the new LI measurement configuration(s) in the second serving DU configuration. In some implementations, the S-DU 174A generates one or more new TCI state configurations based on TCI state configuration(s) in the LTM DU configuration(s) N+l, N+2,... , and / or N+M and includes the new TCI state configuration(s) in the second serving DU configuration.

[0246] In some implementations, in cases where the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the ID(s) 1, ..., N of the procedure 380 are different from value(s) of the ID(s) 1, ...., N, and the ID(s) N+l ,...., N+M described for the scenario 400. In further implementations, in cases where the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the cell ID(s) 1, ..., N of the procedure 380 are different from value(s) of the cell ID(s) 1, ...., N, and the cell ID(s) N+l ,...., N+M described for the scenario 400. In still further implementations, in cases where the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the cell index(es) 1, ..., N of the procedure 380 are different from value(s) of the cell index(es) 1, ...., N, and the cell index(es) N+l ,...., N+M described for the scenario 400.

[0247] In some implementations, the UE 102 later transmits 424 at least one measurement report to the S-DU 174A, similar to the event 324. The at least one measurement report (e.g.,LI measurement report(s)) includes an event ID, first measurement result(s) for the cell 1 of the T-DU 174B, and / or includes second measurement result(s) for the cell 124A. In some implementations, the first measurement result(s) are include RSRP, RSRQ, and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 1. In some implementations, likewise, the second measurement result(s) are include RSRP, RSRQ, and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 124A. In some implementations, the event ID, RSRP, RSRQ, and / or SINR are Ll-event ID, Ll- RSRP, LI -RSRQ, and / or LI -SINR, respectively. In some implementations, based on the first measurement result(s) and / or second measurement result(s), the S-DU 174A transmits 430 a first LTM command (i.e., LTM command 1) including the ID 1 to the UE 102 to order the UE 102 to perform a serving cell change to the cell 1 of the T-DU 174B. In some implementations, the first LTM command includes the ID 1 (i.e., LTM ID). In further implementations, the first LTM command includes the cell index 1. When the UE 102 receives the first LTM command, the UE 102 performs a serving cell change to the cell 1 from a serving cell in accordance with the LTM DU configuration 1. In some implementations, after (e.g., in response to) receiving the first LTM command, the UE 102 does or does not perform 432 a random-access procedure with the T-DU 174B, similar to the event 332. In some implementations, after (e.g., in response to) receiving the first LTM command or completing the random-access procedure 432, the UE 102 communicates at event 436 with the T-DU 174B on the first cell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the T-DU 174B, similar to the event 336. In some implementations, if a serving cell change occurs in the procedure 380, the serving cell is the cell 1 or cell 2 of the S-DU 174A. Otherwise, if no serving cell change occurs in the procedure 380 or the procedure 380 is not performed, the serving cell is the cell 124A. If the first LTM command includes the LTM ID 1, the UE 102 identifies the LTM DU configuration 1 and / or cell ID 1 (i.e., the cell 1), based on the LTM ID 1, as described for Eig. 3. If the first LTM command includes the cell index 1, the UE 102 identifies the LTM DU configuration 1, cell ID 1 (i.e., the cell 1), and / or LTM ID 1 based on the cell index 1, as described for Eig. 3. The UE 102 applies the LTM DU configuration 1 to communicate with the T-DU 174B, after (e.g., in response to) receiving the first LTM command or successfully accessing the cell 1.

[0248] In some implementations, when or in response to determining to activate the LTM DU configuration 1 or transmit 430 the first LTM command, the S-DU 174A transmits 429 tothe CU 172 a DU-to-CU message indicating that LTM is or is being executed. In some implementations, the S-DU 174A includes the cell ID 1 or the LTM ID 1 in the DU-to-CU message of event 429 to indicate that the S-DU 174A is to activate the LTM DU configuration 1 or trigger an LTM serving cell change. In further implementations, the S-DU 174A transmits 429 the DU-to-CU message to the CU 172 before or after transmitting 430 the LTM command. In some implementations, when or after the CU 172 receives 429 the DU-to-CU message, the CU 172 stops or suspends transmitting DL data for the UE 102 to the S-DU 174A until receiving 434 the DU-to-CU message. After receiving 434 the DU-to-CU message, the CU 172 starts, continues, or resumes transmitting DL data for the UE 102 to the T-DU 174B. When or after the T-DU 174B detects that UE 102 accesses the cell 1, the T- DU 174B transmits the DL data to the UE 102 via the cell 1.

[0249] In some implementations, the resource release procedure 496 is similar to the procedure 396. In further implementations, in the resource release procedure 496, the CU 172 transmits a CU-to-DU message (e.g., a UE Context Release Command message) to the S-DU 174A to release a UE context of the UE 102. In response, the S-DU 174A releases a UE context of the UE 102 and transmits 440 a DU-to-CU message (e.g., a UE Context Release Complete message) to the CU-172.

[0250] The events 380, 404, 406, 490, 492, 494, 494, 424, 426, 428, 429, 430, 431, 432, 434, 436, 496, 498, and 456 are collectively referred to in Fig. 4 as an LTM configuration and / or activation procedure 480.

[0251] Referring next to Fig. 5A, in a scenario 500A, the base station 106 operates as an MN, and the base station 104 operates as an SN. The SN 104 includes a CU 172 and a DU 174. The scenario 500A is similar to the scenario 300, except that the scenario 500A is a DC scenario, and the scenario 300 is a single connectivity (SC) scenario. In some implementations, the MN 106 includes a CU and a DU similar to the base station 104 of Fig. 3.

[0252] Initially, the UE 102 in DC communicates with the MN 106 and with SN 104. In the event 502, the UE 102 communicates with the DU 174 on cell 124A using a serving DU configuration and communicates with the CU 172 via the DU 174 using a serving CU configuration, similar to the event 302. In some alternative implementations, the UE 102 does not communicate with the CU 172 via the DU 174 in the event 302. In some implementations, the UE 102 in DC communicates, at event 502, UL PDUs and / or DL PDUswith the MN 106 and / or SN 104 via radio bearers, which include SRBs and / or DRB(s). In some implementations, the MN 106 and / or the SN 104 configure the radio bearers for the UE 102. The UE 102 in DC communicates, at event 502, UL PDUs and / or DL PDUs with the SN 104 on an SCG (i.e., SCG radio resources) that the SN 104 configures for communication with the UE 102. The UE 102 in DC communicates UL PDUs and / or DL PDUs with the MN 106 on an MCG (i.e., MCG radio resources) in accordance with an MN configuration (i.e., MCG configuration). In some implementations, the serving DU configuration is an SN configuration (i.e., SCG configuration). In the MN configuration, the MN 106 configures the MCG which includes at least one serving cell (e.g., the cell 126 and / or other cell(s)) operated by the MN 106. In the serving DU configuration, the SN 106 A configures the SCG which includes at least one serving cell (e.g., the cell 124A and / or other cell(s)) operated by the SN 104. 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 106. As described for 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 SN 104, (e.g., via the MN 106 and / or on an SRB (e.g., SRB3)) that the MN 106 or SN 104 configures to exchange RRC messages between the UE 102 and the SN 104.

[0253] In further implementations, while the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 performs 580 an LTM DU configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. In some implementations, while communicating in DC with the MN 106 and SN 104, the UE 102 transmits the at least one measurement report to the CU 172 via the DU 174 and cell 124A in the events 504 and 506, similar to the events 304 and 306, respectively. In further implementations, while communicating in DC with the MN 106 and SN 104, the UE 102 transmits 505 at least one measurement report to the MN 106 via the cell 126. The MN 106 in turn transmits 507 the at least one measurement report to the CU 172. In some implementations, the MN 106 generates at least one SN message including the at least one measurement report and transmits 507 the at least one SN message to the CU 172. In some implementations, the at least one SN message includes an RRC Transfer message(s) and / or an SN Modification Request message(s).

[0254] After (e.g., in response to) receiving the at least one measurement report or while the SN 104 communicates with the UE 102, the SN 104 determines to prepare the first cellfor the UE 102, as described for Fig. 3. The events 590, 592, 594, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, and 556 are similar to the events 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, and 356, respectively. After receiving 530 the first LTM command, transmitting 531 the acknowledgement, or determining that the UE 102 successfully connects to the first cell (e.g., at event 532 or 536), the UE 102 operating in DC with the MN 106 and SN 104 communicates, at event 536, with the DU 174 on the first cell in accordance with the LTM DU configuration 1 and communicates, at event 536, with the CU 172 via the DU 174, similar to the event 336. In some implementations, the DU 174 and / or CU 172 later perform the LTM execution procedure 598 with the UE 102 to command the UE 102 to perform a cell change from the first cell to the second cell, similar to the procedure 398 or 498. As a result of the procedure 598, the UE 102 operating in DC with the MN 106 and SN 104 communicates, at event 556, with the DU 174 on the second cell in accordance with the LTM DU configuration 2 and communicates, at event 556, with the CU 172 via the DU 174, similar to the event 356.

[0255] The events 504, 506, 505, 507, 590, 592, 594, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, and 556 are collectively referred to in Fig. 5A as an LTM DU configuration and / or activation procedure 581.

[0256] Referring next to Fig. 5B, a scenario 500B is generally similar to the scenario 500A, except that the SN 104 transmits 517 and 519 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 521 and 523 the RRC reconfiguration complete message from the UE 102 via the MN 106. The RRC reconfiguration message of events 517 and 519 is similar to the RRC reconfiguration message of events 316 and 318. The RRC reconfiguration complete message of events 521 and 523 is similar to the RRC reconfiguration message of events 320 and 322. In some implementations, the SN 104 generates a first SN message (e.g., SN Modification Required message, SN Modification Required message, or RRC Transfer message), including the RRC reconfiguration message, and transmits 517 the first SN message to the MN 106. The MN 106 generates an MN RRC message including the RRC reconfiguration message and transmits 519 the MN RRC message to the UE 102. In response, the UE 102 generates an MN RRC response message, including the RRC reconfiguration complete message, and transmits 521 the MN RRC response message to the MN 106. In some implementations, the MN 106 generates a second SN message (e.g., SN Reconfiguration Complete message or RRC Transfer message), including the RRC reconfiguration complete message, and transmits 523 the second SNmessage to the SN 104. In some implementations, the MN RRC message and the MN RRC response message are an RRC reconfiguration message and an RRC reconfiguration complete message, respectively.

[0257] The events 504, 506, 505, 507, 590, 592, 594, 517, 519, 521, 523, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, and 556 are collectively referred to in Fig. 5B as an LTM DU configuration and / or activation procedure 582.

[0258] Referring next to Fig. 6A, in a scenario 600A, the base station 106 operates as an MN, and the base station 104 operates as an SN, similar to the scenarios 300-500B. The SN 104 includes a CU 172, an S-DU 174A, and a T-DU 174B, similar to the base station 104 in the scenario 400. In some implementations, while the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 performs 680 an LTM DU configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. In further implementations, while the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 performs 681 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A or S-DU 174B, similar to the procedure 581 or 582.

[0259] Referring next to Fig. 6B, a scenario 600B is similar to the scenarios 300-500B and 600A except the SN 104 transmits 617 and 619 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 621 and 623 the RRC reconfiguration complete message from the UE 102 via the MN 106.

[0260] Referring next to Fig. 7A, in a scenario 700A, the base station 104 operates as an MN and an SN, similar to the scenarios 300-600B. The base station 104 includes a CU 172, a master DU (M-DU) 174A and a secondary DU (S-DU) 174B. The CU 172 operates with the M-DU 174A as an MN, similar to the base station 104 in Fig. 3 or the MN 106 in Figs. 5A-6B, and the CU 172 operates with the S-DU 174B as an SN similar to the SN 104 in Figs. 5A-6B.

[0261] In the scenario 700A, the UE 102 initially communicates at event 702 in DC with the M-DU 174A and S-DU 174B and communicates at event 702 with the CU 172 via the M- DU 174A and S-DU 174B. In the event 702, the UE 102 communicates with the S-DU 174B on cell 124A using a serving DU configuration and communicates with the CU 172 via the S- DU 174B using a serving CU configuration, similar to the event 302. Events 704 and 706 are similar to the events 304 and 306. In some implementations, the UE 102 transmits 705 at least one measurement report to the M-DU 174A, similar to the event 304. The M-DU 174Ain turn transmits 707 at least one DU-to-CU message including the at least one measurement report to the CU 172, similar to the event 306. In some implementations, while the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 performs 780 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380.

[0262] The events 704, 706, 705, 707, 790, 792, 794, 724, 726, 728, 729, 730, 731, 732, 734, 736, 796, 798, and 756 are collectively referred to in Fig. 7A as an LTM configuration and / or activation procedure 781.

[0263] Referring next to Fig. 7B, a scenario 700B is similar to the scenarios 300-600B and 700A except the CU 172 transmits 717 and 719 the RRC reconfiguration message to the UE 102 via the M-DU 174A and receives 721 and 723 the RRC reconfiguration complete message from the UE 102 via the M-DU 174A.

[0264] The events 704, 706, 705, 707, 790, 792, 794, 717, 719, 721, 723, 724, 726, 728, 729, 730, 731, 732, 734, 736, 796, 798, and 756 are collectively referred to in Fig. 7B as an LTM DU configuration and / or activation procedure 782.

[0265] Referring next to Fig. 8A in a scenario 800A, the base station 104 operates as an MN and an SN, similar to the scenarios 300-700B. The base station 104 includes a CU 172, a master DU (M-DU) 174A, a secondary DU (S-DU) 174B and a target secondary DU (T- DU) 174C. The CU 172 operates with the M-DU 174A as an MN and operates with the S- DU 174B as an SN. In some implementations, while the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 performs 880 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380. In further implementations, while the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 performs 881 an LTM DU configuration and / or activation procedure with the UE 102 via the S-DU 174A, similar to the procedure 581 or 582.

[0266] Referring next to Fig. 8B, a scenario 800B is similar to the scenarios 300-700B and 800A except the CU 172 transmits 817 and 819 the RRC reconfiguration message to the UE 102 via the M-DU 174A and receives 821 and 823 the RRC reconfiguration complete message from the UE 102 via the M-DU 174A.

[0267] Next, several example methods, which can be implemented in a RAN node (e.g., a base station, a DU, or a CU) or a UE, for LTM, are discussed next with reference to Figs. 9A- 12. Descriptions described for Figs. 3-8B can apply to Figs. 9A-12.

[0268] Fig. 9A illustrates an example method 900A, which can be implemented by a UE (e.g., the UE 102).

[0269] The method 900A begins at block 902, where the UE communicates with a RAN via a first serving cell (e.g., events 302, 402, 502, 602, 702, 802). At block 904, the UE receives an LTM ID and an LTM candidate configuration from the RAN, where the LTM ID identifies the LTM candidate configuration and the LTM candidate configuration configures a first candidate cell and a second candidate cell (e.g., event 316, 318, 394, 494, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, or 819). In some implementations, the LTM candidate configuration includes an LTM DU configuration configuring the first candidate cell and the second candidate cell. In some implementations, the first candidate cell is a candidate PCell or a candidate PSCell and the second candidate cell is a candidate SCell. In some implementations, the LTM candidate configuration is an LTM-Candidate IE. In other implementations, the LTM candidate configuration is an LTM-CandidateConfig IE.

[0270] At block 906, the UE receives an LTM command from the RAN via the first serving cell, including the LTM ID (e.g., event 330, 430, 530, 630, 730, or 830). In some implementations, the UE identifies the LTM candidate configuration in accordance with the LTM ID. At block 910, the UE accesses the first candidate cell in response to the LTM command (e.g., event 332, 432, 532, 632, 732, or 832). At block 912, the UE applies a timing advance (TA) value to UL synchronization with the RAN on the first candidate cell. After applying the TA value to UL transmission timing, the UE is UL synchronized on the first candidate cell with the RAN. At block 914, the UE refrains from communicating with the RAN via the second candidate cell in response to the LTM command. In some implementations, the UE refrains from attempting to receive DL transmissions (e.g., control signals and / or data signals) on and / or from the second candidate cell in response to the LTM command. In some implementations, the UE refrains from transmitting UL transmissions (e.g., control signals and / or data signals) on and / or to the second candidate cell in response to the LTM command.

[0271] At block 916, the UE communicates with the RAN via the first candidate cell in accordance with the LTM candidate configuration (e.g., event 336, 436, 536, 636, 736, or 836). In some implementations, the UE at block 916 transmits UL transmissions to the RAN in accordance with the UL transmission timing where the UE applies the TA value. In other implementations, the UE obtains or receives the TA value as described below. At block 918,the UE receives an activation command from the RAN via the first candidate cell to activate the second candidate cell, while communicating with the RAN at block 916. At block 920, the UE activates communication with the RAN via the second candidate cell in response to the activation command, while communicating with the RAN via the first candidate cell. At block 922, the UE communicates with the RAN via the first candidate cell and the second candidate cell in accordance with the LTM candidate configuration. For example, at block 922, the UE receives data (e.g., PDSCH transmissions) and control signals (e.g., DCIs) from the RAN via the first candidate cell and the second candidate cell and / or transmits data (e.g., PUSCH transmissions) and control signals (e.g., PUCCH related signals) to the RAN via the first candidate cell and / or the second candidate cell. Descriptions for events 336, 436, 536, 636, 736 or 836 can apply to block 922.

[0272] In some implementations, the UE performs measurements of at least one first reference signal in accordance with one or more configurations (e.g., reference signal resource configuration(s)). The first reference signal(s) include one or more SSBs and / or one or more CSI-RSs. The RAN transmits the first reference signal(s) on the first candidate cell. In some implementations, the RAN includes the configuration(s) in the LTM candidate configuration. The UE obtains measurement results from the measurements and transmits the measurement results to the RAN via the serving cell (e.g., event 324, 424, 524, 624, 724, or 824). In some implementations, the UE performs early DL synchronization with the first candidate cell when receiving the reference signal(s) before receiving the LTM command. With the early DL synchronization, the UE does not perform DL synchronization with the first candidate cell upon receiving the LTM command. In other implementations, the UE performs DL synchronization with the first candidate cell by receiving the reference signal(s), upon receiving the LTM command.

[0273] In some implementations, the UE performs measurements of at least one second reference signal in accordance with one or more configurations (e.g., reference signal resource configuration(s)). The second reference signal(s) include one or more SSBs and / or one or more CSI-RSs. The RAN transmits the second reference signal(s) on the second candidate cell. In some implementations, the RAN includes the configuration(s) in the LTM candidate configuration. The UE obtains measurement results from the measurements and transmits the measurement results to the RAN via the serving cell (e.g., event 324, 424, 524, 624, 724, or 824). In some implementations, the UE performs early DL synchronization with the second candidate cell when receiving the reference signal(s) before receiving the LTMcommand. With the early DL synchronization, the UE does not perform DL synchronization with the second candidate cell upon receiving the LTM command. In other implementations, the UE performs DL synchronization with the second candidate cell by receiving the reference signal(s) upon receiving the LTM command. In other implementations, the RAN refrains from configuring the UE to perform measurements of a reference signal that the RAN transmits on the second candidate cell. Thus, the UE does not perform measurements on the reference signal.

[0274] In some implementations, the UE at block 902 communicates with the RAN via the first serving cell and a second serving cell. In some such cases, the UE receives the LTM command from the RAN on the second serving cell instead of the first serving cell. In some implementations, one of the first serving cell and the second serving cell is a PCell, the other cell is an SCell, and the UE communicates with the RAN in carrier aggregation on the PCell and SCell. In other implementations, one of the first serving cell and the second serving cell is a PSCell, the other cell is an SCell, and the UE communicates with the RAN in carrier aggregation on the PSCell and the SCell. In yet other implementations, one of the first serving cell and the second serving cell is a PCell, the other cell is a PSCell, and the UE communicates with the RAN in dual connectivity on the PSCell and the PSCell.

[0275] In some implementations, before receiving the LTM command, the UE receives a first random access triggering command (e.g., a PDCCH order) from the RAN on the first serving cell or the second serving cell. The first random access triggering command commands the UE to transmit a random access preamble on the first candidate cell for early TA acquisition (i.e., early uplink synchronization with the first candidate cell). In response to the random access triggering command, the UE transmits a first random access preamble on the candidate cell while maintaining a connection with the RAN on the first serving cell. In some implementations, the first random access triggering command configures the first random access preamble. For example, the first random access triggering command includes a parameter (i.e., a first preamble index) identifying or indexing the first random access preamble. The UE selects the first random access preamble in accordance with the first preamble index. In some implementations, the first random access triggering command also includes other parameters such as a PRACH mask index, a UL / supplementary UL indicator, an SSB index, a DO format identifier, and / or a frequency domain resource assignment.

[0276] In some implementations, the UE performs UL synchronization with the first candidate cell before performing an LTM cell switch to the first candidate cell at block 906 or 910. In some such implementations, the UE transmits the first random access preamble on a physical random access channel (PRACH) occasion (e.g., a time and / or frequency resource) in accordance with the parameters in the first random access triggering command and / or a random access configuration for early TA acquisition. The RAN receives the first random access preamble on the PRACH occasion on the first candidate cell in accordance with the parameters and the random access configuration. The LTM candidate configuration includes the random access configuration for early TA acquisition. In some implementations, the first random access triggering command includes the LTM ID. In other alternative implementations, the first random access triggering command includes a value of the LTM ID - 1. In some implementations, the RAN derives the TA value based on the first random access preamble and includes the TA value in the LTM command. In some implementations, upon receiving the LTM command or the TA value, the UE starts or restarts a first time alignment timer for a validity period of the UL synchronization with the first candidate cell. In some implementations, the UE at block 902 maintains the first time alignment timer for a validity period of the UL synchronization with the first serving cell. Alternatively, the UE refrains from starting or restarting a time alignment timer (e.g., the first time alignment timer) for a validity period of the UL synchronization with the first candidate cell upon receiving the LTM command or the TA value.

[0277] In further implementations, the UE performs UE-based measurements of reference signals from the first candidate cell to obtain TA for UL synchronization with the first candidate cell before performing an LTM cell switch to the first candidate cell at block 906 or 910. In some such implementations, before receiving the LTM command, the UE performs measurements of reference signals transmitted by the RAN and derives the TA value based on the measurements. In such cases, the UE does not transmit a random access preamble for early TA acquisition on the first candidate cell to the RAN. In some implementations, the UE refrains from starting or restarting a time alignment timer (e.g., the first time alignment timer) for a validity period of the UL synchronization with the first candidate cell. In other implementations, the UE starts or restarts a time alignment timer (e.g., the first time alignment timer) for a validity period of the UL synchronization with the first candidate cell upon receiving the LTM command.

[0278] In yet further implementations, the UE performs UL synchronization with the first candidate cell upon performing the LTM cell switch at block 906 or 910. In some such implementations, the UE transmits a random access preamble on a PRACH occasion with the RAN on the first candidate cell in response to receiving the LTM command (e.g., event 332, 432, 532, 632, 732, or 832). The UE receives a random access response including the TA value on the first candidate cell from the RAN (e.g., event 332, 432, 532, 632, 732, or 832). Upon receiving the random access response, the UE applies the TA value to UL synchronization with the RAN on the first candidate cell as described above. Upon receiving the random access response or the TA value, the UE starts or restarts a first time alignment timer for a validity period of the UL synchronization with the first candidate cell. The RAN receives the random access preamble on the PRACH occasion on the first candidate cell. The RAN derives the TA value based on the random access preamble and includes the TA value and a preamble index in the random access response. The preamble index identifies the random access preamble. In some implementations, the LTM command includes the preamble index (i.e., a parameter), and the UE selects the random access preamble in accordance with the preamble index. In further implementations, the LTM candidate configuration or the LTM command also includes other parameters such as a PRACH mask index, a UL / supplementary UL indicator, an SSB index, a DCI format identifier, and / or a frequency domain resource assignment. The UE determines the PRACH occasion based on some or all of the other parameters. The UE transmits the random access preamble on the PRACH occasion to the RAN on the first candidate cell in accordance with the parameters and / or the random access configuration in the LTM candidate configuration. The RAN receives the random access preamble on the PRACH occasion on the first candidate cell in accordance with the parameters and / or the random access configuration. In other implementations, the LTM command does not include the preamble index, and the UE selects the random access preamble from a plurality of random access preambles that is configured in the random access configuration in the LTM candidate configuration.

[0279] In some implementations, the activation command is a MAC CE different from the LTM command. In some implementations, the activation command includes a cell index indicating the second candidate cell. In some implementations, the cell index is neither a cell ID nor a configuration ID. In further implementations, the cell index is neither a PCI nor a CGI. In some implementations, the cell index is in a 5-bit format while the LTM ID is in a 3- bit format. In some implementations, the LTM candidate configuration includes the cellindex. In some implementations, the LTM DU configuration includes a first configuration and a second configuration for the first candidate cell and the second candidate cell respectively. In some implementations, the second configuration includes the cell index. The UE and RAN communicate with one another on the first candidate cell and the second candidate cell using the first configuration and the second configuration respectively.

[0280] In some implementations, the UE transmits a second random access preamble on a PRACH occasion on the second candidate cell after the activation 920. In some implementations, after the activation 920, the UE attempts to receive a second random access triggering command (e.g., a PDCCH order) from the RAN on the first candidate cell and / or the second candidate cell. The UE transmits the second random access preamble on the PRACH occasion on the second candidate cell in response to the second random access triggering command. In other implementations, the UE transmits the second random access preamble on the PRACH occasion on the second candidate cell to the RAN in response to the activation command. In some implementations, the second random access triggering command includes a second preamble index (i.e., a parameter) identifying or indexing the second random access preamble, and the UE selects the second random access preamble in accordance with the second preamble index. In some implementations, the second random access triggering command includes other parameters such as a PRACH mask index, a UL / supplementary UL indicator, ab SSB index, a DCI format identifier, and / or a frequency domain resource assignment. In other implementations, the LTM candidate configuration or the second configuration includes the parameters. The UE determines the PRACH occasion based on some or all of the parameters. The UE transmits the second random access preamble to the RAN on the PRACH occasion on the second candidate cell in accordance with the parameters and / or the random access configuration in the second configuration or the LTM candidate configuration. In some implementations, the second random access triggering command neither includes an LTM ID nor a value based on the LTM ID.

[0281] The RAN receives the second random access preamble in accordance with the parameters and / or the random access configuration in the second configuration or the LTM candidate configuration. The RAN derives a TA value based on the second random access preamble. In response to the second random access preamble, the RAN transmits a random access response to the UE on the first candidate cell or the second candidate cell, including the TA value and the second preamble index. Upon receiving the random access response, the UE applies the TA value to UL synchronization with the RAN on the second candidatecell. Upon receiving the random access response or the TA value, the UE starts or restarts a second time alignment timer indicating a validity period of the UL synchronization with the second candidate cell. After applying the TA value to UL transmission timing, the UE is UL synchronization on the second candidate cell with the RAN and transmits UL transmissions to the RAN in accordance with the UL transmission timing. In some implementations, the RAN includes a C-RNTI in the random access response. In some implementations, the UE and the RAN communicate with each other on the second candidate cell using the C-RNTI. In other implementations, the UE and the RAN discard the C-RNTI. In such cases, the UE and the RAN communicate with each other on the second candidate cell using a C-RNTI included in the LTM candidate configuration, the first configuration or the second configuration.

[0282] In some other implementations, the UE applies the UL transmission timing with the first candidate cell to UL transmissions with the second candidate cell after or in response to the activation 920. In such cases, the UE does not perform a random access procedure on the second candidate cell to acquire UL synchronization with the second candidate cell.

[0283] In some implementations, if the LTM candidate configuration or the second configuration configures a UL configuration for the second candidate cell, the UE performs a random access procedure on the second candidate cell to acquire UL synchronization with the second candidate cell as described above. Otherwise, if the LTM candidate configuration or the second configuration does not configure a UL configuration for the second candidate cell, the UE does not perform a random access procedure on the second candidate cell to acquire UL synchronization with the second candidate cell. In such cases, the UE refrains from transmitting any UL transmissions on the second candidate cell.

[0284] Eig. 9B is a flow diagram of an example method 900B similar to the method 900A, except that the method 900B includes block 921 instead of blocks 914, 918, and 920. At block 921, the UE activates communication with the RAN via the second candidate cell in response to the LTM command while communicating with the RAN via the first candidate cell. In some implementations, the UE at block 921 activates communication with the RAN via the second candidate cell after accessing the first candidate cell at block 910.

[0285] In some implementations, after the activation at block 921, the UE transmits a second random access preamble on the second candidate cell, as described for Eig. 9A. In some implementations, after the activation at block 921, the UE attempts to receive a secondrandom access triggering command (e.g., a PDCCH order) from the RAN on the first candidate cell and / or the second candidate cell, as described for Fig. 9A.

[0286] In some other implementations, the UE applies the UL transmission timing with the first candidate cell to communication with the second candidate cell after or in response to the activation at block 921. In such cases, the UE does not perform a random access procedure on the second candidate cell to acquire UL synchronization with the second candidate cell.

[0287] Fig. 9C is a flow diagram of an example method 900C similar to the method 900A, except that the method 900C includes blocks 909 and 911 instead of blocks 912, 914, 918, and 920. At block 909, the UE accesses the first candidate cell and the second candidate cell in response to the LTM command. In some implementations, the UE accesses the first candidate cell, similar to Figs. 3-8B (e.g., event 332, 432, 532, 632, 732, or 832). In further implementations, the UE accesses the second candidate cell, similar to Figs. 3-8B (e.g., event 332, 432, 532, 632, 732, or 832). In some implementations, the UE accesses the first candidate cell and the second cell simultaneously or in parallel.

[0288] At block 911, the UE applies a first TA value to UL synchronization on the first candidate cell with the RAN and applies a second TA value to UL synchronization on the second candidate cell with the RAN. In some implementations, the first TA value and the second TA value are the same. In such cases, the UE applies the same UL transmission timing with the first candidate cell and the second candidate cell. That is, the UE applies a single TA value to UL synchronization with the RAN on the first candidate cell. In other implementations, the first TA value and the second TA value are different. In some implementations, the UE receives or obtains the first TA value as described for Fig. 9A. In some implementations, the UE receives or obtains the second TA value as described for Fig. 9A.

[0289] Fig. 9D is a flow diagram of an example method 900D similar to the methods 900A and 900B, except that the method 900D includes block 913. The flow begins with blocks 902, 904, 906, 910, 912 (optional), and 916 as described for Fig. 9A, and proceeds to block 913. At block 913, the UE determines whether the LTM candidate configuration configures the second candidate cell as active. If the UE determines at block 913 that the LTM candidate configuration configures the second candidate cell as inactive (“No” branch of block 913), the UE performs actions described for blocks 914, 918 (optional), 920 (optional),and 922 (optional). Otherwise, if the UE determines at block 913 that the LTM candidate configuration configures the second candidate cell as active (“Yes” branch of block 913), the UE performs actions described for blocks 921 and 922.

[0290] Fig. 9E is a flow diagram of an example method 900E similar to the methods 900A, 900C, and 900D. The flow begins with blocks 902, 904, and 906 as described for Fig. 9A, and proceeds to block 913. If the UE determines at block 913 that the LTM candidate configuration configures the second candidate cell as inactive (“No” branch of block 913), the UE performs actions described for blocks 910, 912, 914, 916, 918 (optional), 920 (optional), and 922 (optional). Otherwise, if the UE determines at block 913 that the LTM candidate configuration configures the second candidate cell as active (“Yes” branch of block 913), the UE performs actions described for blocks 909, 911, and 922.

[0291] Fig. 9F is a flow diagram of an example method 900F similar to the methods 900A, 900B, and 900D, except that the method 900F includes block 923 instead of block 913. The LTM command at block 906 includes a TA value, and the UE applies the TA value at block 912. At block 923, the UE determines whether the LTM command indicates that the TA value is applied to the second candidate cell. If the UE determines at block 923 that the LTM command does not indicate that the TA value is applied to the second candidate cell (“No” branch of block 923), the UE performs actions described for blocks 914, 918 (optional), 920 (optional), and 922 (optional). Otherwise, if the UE determines at block 923 that the LTM command indicates the TA value is applied to the second candidate cell (“Yes” branch of block 923), the UE performs actions described for blocks 921 and 922.

[0292] Fig. 9G is a flow diagram of an example method 900E similar to the methods 900A, 900C, 900E, and 900F, except that the method 900G includes block 925 instead of block 923. If the UE determines at block 925 that the LTM command indicates that a first TA value is applied to the first candidate cell and a second TA value is applied to the second candidate cell (“Yes” branch of block 925), then the UE performs actions described for blocks 909, 911, and 922. Otherwise, if the UE determines at block 925 that the LTM command does not indicate that the first TA value is applied to the first candidate cell and the second TA value is applied to the second candidate cell (“No” branch of block 925), the UE performs actions described for blocks 910, 912 (optional), 914, 916, 918 (optional), 920 (optional), and 922 (optional). In some implementations, if the LTM command includes asingle TA value, the UE performs block 912. Otherwise, if the LTM command does not include a TA value, the UE skips block 912.

[0293] Fig. 10A illustrates an example method 1000A, which can be implemented by a RAN (e.g., the RAN 105, the base station 104 or 106, the DU 174).

[0294] The method 1000A begins at block 1002, where the RAN communicates with a UE via a first serving cell (e.g., events 302, 402, 502, 602, 702, 802). At block 1004, the RAN transmits an LTM ID and an LTM candidate configuration to the UE, where the LTM ID identifies the LTM candidate configuration, and the LTM candidate configuration configures a first candidate cell and a second candidate cell (e.g., event 316, 318, 394, 494, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, or 819). At block 1006, the RAN transmits an LTM command to the UE via the first serving cell, including the LTM ID (e.g., event 330, 430, 530, 630, 730, or 830). At block 1008, the RAN detects that the UE accesses the first candidate cell (e.g., event 332, 334, 432, 434, 532, 534, 632, 634, 732, 734, 832, or 834). At block 1010, the RAN communicates with the UE via the first candidate cell in accordance with the LTM candidate configuration (e.g., event 336, 436, 536, 636, 736, or 836). At block 1012, the RAN refrains from communicating with the UE via the second candidate cell in response to transmitting the LTM command. At block 1014, the RAN transmits an activation command to the UE via the first candidate cell to activate the second candidate cell. At block 1016, the RAN activates communication with the UE via the second candidate cell in response to the activation command, while communicating with the RAN via the first candidate cell. At block 1018, the RAN communicates with the UE via the first candidate cell and the second candidate cell in accordance with the LTM candidate configuration.

[0295] Examples and implementations described for Fig. 9A can apply to Fig. 10A.

[0296] Fig. 10B is a flow diagram of an example method 1000B similar to the method 1000A, except that the method 1000B includes block 1017 instead of blocks 1012, 1014, and 1016. At block 1017, the RAN activates communication with the UE via the second candidate cell in response to the LTM command, while communicating with the UE via the first candidate cell. In some implementations, the RAN at block 1017 activates communication with the UE via the second candidate cell after detecting that the UE accesses the first candidate cell at block 1008.

[0297] In some implementations, after the activation 1017, the RAN transmits a second random access triggering command (e.g., a PDCCH order) on the second candidate cell to theUE, as described for Figs. 9 A and 9B. In other implementations, after the activation 1017, the RAN transmits a second random access triggering command (e.g., a PDCCH order) on the first candidate cell to the UE, as described for Figs. 9A and 9B. After transmitting the second random access triggering command, the RAN attempts to receive and / or receives a second random access preamble from the UE, as described for Figs. 9A and 9B.

[0298] Examples and implementations described for Figs. 9A and 9B can apply to Fig. 10B.

[0299] Fig. 10C is a flow diagram of an example method 1000C similar to the method 1000A, except that the method 1000C includes block 1009 instead of blocks 1008, 1010, 1012, 1014, and 1016. At block 1009, the RAN detects that the UE accesses the first candidate cell and the second candidate cell (e.g., event 332, 334, 432, 434 532, 534 632, 634, 732, 734, 832, or 834).

[0300] Examples and implementations described for Figs. 9A-9C can apply to Fig. 10C.

[0301] Fig. 10D is a flow diagram of an example method WOOD similar to the methods 1000A and 1000B, except that the method WOOD includes block 1011. The flow begins with blocks 1002, 1004, 1006, 1008, 1010, and 1014 as described for Fig. 10A, and proceeds to block 1011. At block 1011, the RAN determines whether the ETM candidate configuration configures the second candidate cell as active. If the RAN determines at block 1011 that the ETM candidate configuration configures the second candidate cell as inactive (“No” branch of block 1011), the RAN performs actions described for blocks 1012, 1014 (optional), 1016 (optional), and 1018 (optional). Otherwise, if the RAN determines at block 1011 that the ETM candidate configuration configures the second candidate cell as active (“Yes” branch of block 1011), the RAN performs actions described for blocks 1017 and 1018.

[0302] Examples and implementations described for Figs. 9A-9D can apply to Fig. 10D.

[0303] Fig. 10E is a flow diagram of an example method 1000E similar to the methods 1000A, 1000B, and WOOD. The flow begins with blocks 1002, 1004, and 1006 as described for Fig. 10A, and proceeds to block 1011. At block 1011, the RAN determines whether the ETM candidate configuration configures the second candidate cell as active. If the RAN determines at block 1011 that the ETM candidate configuration configures the second candidate cell as inactive (“No” branch of block 1011), the RAN performs actions described for blocks 1008, 1010, 1012, 1014 (optional), 1016 (optional), and 1018 (optional).Otherwise, if the RAN determines at block 1011 that the ETM candidate configurationconfigures the second candidate cell as active (“Yes” branch of block 1011), the RAN performs actions described for blocks 1009 and 1018.

[0304] Examples and implementations described for Figs. 9A-9E can apply to Fig. 10E.

[0305] Fig. 10F is a flow diagram of an example method 1000F similar to the methods 1000A, 1000B, and WOOD, except that the method 1000F includes block 1021 instead of block 1011. The LTM command at block 1006 includes a TA value. At block 1021, the RAN determines whether the LTM command indicates that the TA value is applied to the second candidate cell. If the RAN determines at block 1021 that the LTM command does not indicate that the TA value is applied to the second candidate cell (“No” branch of block 1021), the RAN performs actions described for blocks 1012, 1014 (optional), 1016 (optional), and 1018 (optional). Otherwise, if the RAN determines at block 1021 that the LTM command indicates the TA value is applied to the second candidate cell (“Yes” branch of block 1021), the RAN performs actions described for blocks 1017 and 1018.

[0306] Examples and implementations described for Figs. 9A-9F can apply to Fig. 10F.

[0307] Fig. 10G is a flow diagram of an example method 1000G similar to the methods1000A, 1000C, 1000E, and lOOOF, except that the method 1000G includes block 1025 instead of block 1021. If the RAN determines at block 1025 that the LTM command does not indicate that a first TA value is applied to the first candidate cell and a second TA value is applied to the second candidate cell (“No” branch of block 1025), the RAN performs actions described for blocks 1008, 1010, 1012, 1014 (optional), 1016 (optional), and 1018 (optional). Otherwise, if the RAN determines at block 1025 that the LTM command indicates that the first TA value is applied to the first candidate cell and the second TA value is applied to the second candidate cell (“Yes” branch of block 1025), the RAN performs actions described for blocks 1009 and 1018.

[0308] Examples and implementations described for Figs. 9A-9G can apply to Fig. 10G.

[0309] Fig. 11 illustrates an example method 1100, which can be implemented by a CU (e.g., the CU 172).

[0310] The method 1100 begins at block 1102, where the CU communicates with a UE via a first DU, a first serving cell and a second serving cell (e.g., events 302, 402, 502, 602, 702, 802). The first DU operates the first serving cell and the second serving cell. At block 1104, the CU transmits a CU-to-DU message for configuring LTM for the UE to a second DU (e.g.,events 308, 312, 390, 392, 490, 492, 590, 592. 690, 692, 790, 792, 890, 892). At block 1106, the CU receives a DU-to-CU message from the second DU, including an LTM DU configuration, where the LTM DU configuration configures a single candidate cell (e.g., events 310, 314, 390, 392, 490, 492, 590, 592. 690, 692, 790, 792, 890, 892). At block 1108, the CU transmits an LTM ID and the LTM DU configuration to the UE (e.g., event 316, 318, 394, 494, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, or 819).

[0311] In some implementations, the first DU and the second DU are the same DU (i.e., a serving DU). In other implementations, the first DU is a serving DU and the second DU is a candidate DU. For example, the first DU and the second DU are S-DU 174A and T-DU 174B, respectively, as shown in Figs. 4 and 6A-6B. In another example, the first DU and the second DU are S-DU 174B and T-DU 174C, respectively, as shown in Figs 8A-8B.

[0312] In some implementations, the CU includes ETM information in the CU-to-DU message to configure ETM for the UE. In some implementations, the CU always excludes SCell information from the CU-to-DU message to prevent the second DU from configuring an additional candidate cell that is not expected by the CU. In other implementations, the CU always includes SCell information in the CU-to-DU message to prevent the second DU from configuring an additional candidate cell that is not expected by the CU. In some implementations, the SCell information is an SCell To Be Setup List that includes information for setup of one or more SCells. In some implementations, the SCell information includes one or more tuples of an SCell ID (e.g., CGI) and / or an SCell index.

[0313] In some implementations, the single candidate cell is a candidate special cell (SpCell). In one implementation, the candidate SpCell is a candidate PCell. In another implementation, the candidate SpCell is a candidate PSCell. In some implementations, if the CU determines to configure one or more candidate SCell(s) associated with the candidate SpCell, the CU includes SCell information (e.g., an SCell To Be Setup List) for setup of the candidate SCell(s) in the CU-to-DU message. Based on the SCell information, the DU may generate one or more SCell configuration(s) configuring the candidate SCell(s) and include the SCell configuration(s) in the ETM DU configuration. If the CU determines not to configure any candidate SCell associated with the candidate SpCell, the CU refrains from including SCell information (e.g., an SCell To Be Setup List) in the CU-to-DU message. Thus, the DU does not include a SCell configuration in the LTM DU configuration inresponse to the CU-to-DU message excluding SCell information (e.g., an SCell To Be Setup List).

[0314] In some implementations, the CU at block 1108 generates an LTM candidate configuration including the LTM DU configuration and / or an LTM CU configuration and transmits the LTM candidate configuration to the UE.

[0315] Examples and implementations described for Figs. 9A-10G can apply to Fig. 11.

[0316] Fig. 12 illustrates an example method 1200, which can be implemented by a DU (e.g., the DU 174, 174A, 174B, or 174C in Figs. 3-8B).

[0317] The method 1200 begins at block 1202, where the DU communicates with a UE via a first serving cell and a second serving cell (e.g., event 302, 402, 502, 602, 702, or 802). At block 1204, the DU receives a CU-to-DU message for configuring ETM for the UE from the CU (e.g., events 308, 312, 390, 392, 490, 492, 590, 592. 690, 692, 790, 792, 890, 892). At block 1206, the DU transmits a DU-to-CU message to the CU, including an ETM DU configuration, where the LTM DU configuration configures a single candidate cell (e.g., events 310, 314, 390, 392, 490, 492, 590, 592, 690, 692, 790, 792, 890, 892). In some implementations, when receiving a CU-to-DU message for configuring LTM, the DU always configures a single candidate cell in an LTM DU configuration, regardless of the number of serving cells where the DU communicates with the UE.

[0318] At block 1208, the DU transmits an LTM command to the UE, including an LTM ID (e.g., event 330, 430, 530, 630, 730, or 830). At block 1210, the DU detects that the UE accesses the candidate cell (e.g., event 332, 334, 432, 434 532, 534 632, 634, 732, 734, 832, or 834). At block 1212, the DU communicates with the RAN via the candidate cell in accordance with the LTM DU configuration (e.g., event 336, 436, 536, 636, 736, or 836).

[0319] In some implementations, the DU at block 1202 communicates with the UE using a plurality of configurations. The DU releases the plurality of configuration parameters in response to transmitting the LTM command, receiving an acknowledgement for the LTM command, or detecting the UE accesses the candidate cell. In some implementations, the single candidate cell is a candidate special cell (SpCell). In further implementations, the candidate SpCell is a candidate PCell. In further implementations, the candidate SpCell is a candidate PSCell. In some implementations, the plurality of configuration parameters include configuration parameters for the first serving cell and the second serving cell. In other implementations, the plurality of configuration parameters include configurationparameters for the second serving cell and do not include configuration parameters for the first serving cell. In some implementations, the DU stops communicating with the UE via the first serving cell and the second serving cell after transmitting the LTM command.

[0320] In some implementations, the first serving cell is a serving SpCell, and the second serving cell is a serving SCell. In some implementations, the CU-to-DU message does not include SCell information (e.g., SCell To Be Setup List) for setup of a candidate SCell. In such implementations, the DU refrains from including a SCell configuration in the LTM DU configuration in response to the CU-to-DU message excluding (the) SCell information (e.g., SCell To Be Setup List).

[0321] In some implementations, if the CU-to-DU message includes SCell information (e.g., SCell To Be Setup List) for setup of one or more candidate SCell(s) associated with the candidate SpCell, the DU generates one or more SCell configuration(s) for the candidate SCell(s), includes the SCell configuration(s) in the LTM DU configuration, and includes the LTM DU configuration in the DU-to-CU message. Upon receiving the CU-to-DU message including the SCell information, the DU refrains from replacing the second serving cell with the candidate SCell(s). In other words, the DU continues communicating with the UE via the first serving cell and the second serving cell after transmitting the DU-to-CU message, including the LTM DU configuration, to the CU. In some such implementations, the DU activates the candidate SCell(s) for the UE and / or communicate with the UE via the candidate SCell(s) as described for Eigs. 10A-10G.

[0322] Examples and implementations described for Figs. 9A-11 can apply to Fig. 12.

[0323] Fig. 13 illustrates an example method 1300, which can be implemented by a DU (e.g., the DU 174, 174A, 174B, or 174C in Figs. 3-8B).

[0324] The method 1300 begins at block 1302, where the DU communicates with a UE via a serving SpCell and at least one serving SCell (e.g., event 302, 402, 502, 602, 702, or 802). At block 1304, the DU receives a CU-to-DU message for the UE from the CU, including SCell information indicating at least one candidate SCell (e.g., event 308, 390, 490, 590, 690, 790, or 890). At block 1306, the DU generates a DU configuration configuring the at least one candidate SCell for the UE. At block 1308, the DU transmits a DU-to-CU message, including the DU configuration, to the CU (e.g., event 310, 390, 490, 590, 690, 790, or 890). At block 1310, the DU determines whether the CU-to-DU message requests configuration or reconfiguration of a candidate SpCell. If the CU-to-DU message does not requestconfiguration or reconfiguration of a candidate SpCell (i.e., “No” branch of block 1310), the flow proceeds to block 1312. At block 1312, the DU replaces the at least one serving SCell with the at least one candidate SCell for the UE. In such cases, the DU configuration is a serving DU configuration, and examples and implementations described above for a serving DU configuration can apply to the DU configuration of block 1306. In some implementations, if the CU-to-DU message does not request configuration or reconfiguration of a candidate SpCell (i.e., “No” branch of block 1310), the DU releases resources of the at least one serving SCell configured for the UE. In some implementations, the DU releases the resources after transmitting the DU configuration to the UE or the CU.

[0325] Otherwise, if the CU-to-DU message requests configuration or reconfiguration of a candidate SpCell (i.e., “Yes” branch of block 1310), the flow proceeds to block 1314. For example, the CU-to-DU message includes an SpCell ID and an indicator to request configuration of a candidate SpCell. The SpCell ID identifies an SpCell and the indicator indicates the SpCell is a candidate SpCell. At block 1314, the DU refrains from replacing the at least one serving SCell with the at least one candidate SCell. Thus, the DU refrains from releasing resources of the at least one serving SCell configured for the UE, and continues communicating with the UE via the at least one serving SCell. In some such cases, the DU configuration of block 1306 is a candidate DU configuration. In some implementations, the “candidate SpCell” in block 1310 may be replaced with a “LTM cell” or a “LTM SpCell”. In other implementations, the “candidate SpCell” in block 1310 may be replaced with a “candidate PCell” for a conditional handover (CHO) (e.g., as described for 3GPP TS 38.300, 38.401, 37.340, and / or 38.473). In yet other implementations, the “candidate cell” in block 1510 may be replaced with a “candidate PSCell” for a conditional PSCell addition or change (CP AC) (e.g., as described for 3GPP TS 38.300, 38.401, 37.340, and / or 38.473). In some implementations, the CP AC includes a conditional PSCell addition (CPA), a conditional PSCell change (CPC), or a subsequent CPAC. In some implementations, the candidate DU configuration is an LTM DU configuration, as described above. In some implementations, when or after transmitting or determining to transmit an LTM command to the UE via the serving SpCell or one of the at least one serving SCell, the DU replaces the at least one serving SCell with the at least one candidate SCell. In other implementations, when or after detecting that the UE accesses the candidate SpCell, the DU replaces the at least one serving SCell with the at least one candidate SCell. In other implementations, the candidate DU configuration is a DU configuration (e.g., CellGroupConfig IE) for a CHO or a CPAC. Insuch implementations, when or after detecting that the UE accesses the candidate SpCell, the DU replaces the at least one serving SCell with the at least one candidate SCell.

[0326] Descriptions for Figs. 3-12 above may apply to Fig. 13.

[0327] Fig. 14 illustrates an example method 1400, which can be implemented by a DU (e.g., the DU 174, 174A, 174B, or 174C in Figs. 3-8B).

[0328] The method 1400 begins at block 1402, where the DU transmits a first candidate DU configuration for a UE to a CU, where the first candidate DU configuration configures a first candidate SpCell and at least one first candidate SCell (e.g., event 310, 390, 490, 590, 690, 790, or 890). At block 1404, the DU receives a CU-to-DU message for the UE from the CU, including a SpCell ID and SCell information, where the SCell information indicates at least one second candidate SCell (e.g., event 308, 390, 490, 590, 690, 790, or 890). At block 1406, the DU generates a second candidate DU configuration for the UE, configuring the at least one second candidate SCell. At block 1408, the DU transmits a DU-to-CU message for the UE to the CU (e.g., event 310, 390, 490, 590, 690, 790, or 890), where the DU-to-CU message includes the second candidate DU configuration. At block 1410, the DU determines whether the SpCell ID in the CU-to-DU message is an SpCell ID of the first candidate SpCell. If the SpCell ID in the CU-to-DU message is an SpCell ID of the first candidate SpCell (i.e., “Yes” branch of block 1410), the flow proceeds to block 1412. At block 1412, the DU replaces the at least first candidate SCell with the at least one second candidate SCell. In such cases, the second candidate DU configuration updates (e.g., modifies or replaces) the first candidate DU configuration.

[0329] Otherwise, if the SpCell ID in the CU-to-DU message is not an SpCell ID of the first candidate SpCell (i.e., “No” branch of block 1410), the flow proceeds to block 1414. At block 1414, the DU refrains from replacing the at least one first candidate SCell with the at least one second candidate SCell. In such cases, the second candidate DU configuration does not update the first candidate DU configuration. The DU maintains or stores the first candidate DU configuration and the second candidate DU configuration.

[0330] In some implementations, the first and second candidate DU configurations are LTM DU configurations as described above. In other implementations, the first and second candidate DU configurations are DU configurations (e.g., CellGroupConfig IES) for a CHO or a CPAC. Descriptions for Figs. 3-13 may apply to Fig. 14.

[0331] The following list of examples reflects a variety of the embodiments explicitly contemplated by the present disclosure:

[0332] Example 1. A method implemented in a user equipment (UE), the method comprising: receiving, from a radio access network (RAN) node and when the UE operates in a current serving cell, a lower-layer triggered mobility (LTM) candidate configuration associated with an LTM identifier corresponding to a first candidate cell and a second candidate cell; receiving, from the RAN node, a command to perform an LTM switch to the first candidate cell; and accessing the first candidate cell in response to the command.

[0333] Example 2. The method of example 1, wherein: the first candidate cell includes a primary cell (PCell) or a primary secondary cell (PSCell); and the second candidate cell includes a secondary cell (SCell).

[0334] Example 3. The method of either one of examples 1 or 2, further comprising: receiving, from the RAN node, a command to activate the second candidate cell; and accessing the second candidate cell in response to the command to activate the second candidate cell.

[0335] Example 4. The method of example 3, further comprising: communicating with the RAN node via the first candidate cell and the second candidate cell using carrier aggregation (CA).

[0336] Example 5. The method of either one of examples 3 or 4, wherein the command to activate the second candidate cell is received in the first candidate cell.

[0337] Example 6. The method of either one of examples 1 or 2, further comprising: accessing the second candidate cell in response to the command to perform the LTM switch.

[0338] Example 7. The method of example 6, further comprising: communicating with the RAN node via the first candidate cell and the second candidate cell using carrier aggregation (CA).

[0339] Example 8. The method of example 7, further comprising: applying a first timing advance (TA) value for uplink (UL) synchronization in the first candidate cell; and applying a second TA value for UL synchronization in the second candidate cell.

[0340] Example 9. The method of example 8, further comprising: receiving the first TA value and the second TA value in the command to perform the LTM switch.

[0341] Example 10. The method of example 8, further comprising: receiving at least one of the first TA value or the second TA value prior to the command to perform the LTM switch.

[0342] Example 11. The method of any one of examples 1-6, further comprising: applying a timing advance (TA) value for uplink (UL) synchronization in the first candidate cell.

[0343] Example 12. The method of example 11, further comprising: receiving the TA value in the command to perform the LTM switch.

[0344] Example 13. The method of example 11, further comprising: receiving the TA value prior to the command to perform the LTM switch.

[0345] Example 14. The method of any of examples 3-10, wherein the accessing of the second candidate cell is further in response to determining that the LTM candidate configuration indicates that the second candidate cell is active.

[0346] Example 15. The method of any one of the examples 3-10 or 14, wherein the accessing of the first candidate cell is further in response to determining that the LTM candidate configuration indicates that the second candidate cell is active.

[0347] Example 16. The method of example 7, further comprising: when the command to perform the LTM switch indicates that a first TA value applies to the first candidate cell and a second TA value applies to the second candidate cell, activating communication via the first candidate cell and the second candidate cell in accordance with the first TA value and the second TA value.

[0348] Example 17. The method of example 7, further comprising: when the command to perform the LTM switch indicates that a TA value applies to the second candidate cell, activating communication via the second candidate cell in accordance with the second TA value.

[0349] Example 18. The method of any one of the preceding examples, wherein: when the UE receives the LTM configuration, the UE operates in a first serving cell.

[0350] Example 19. The method of any one of examples 1-17, wherein when the UE receives the LTM configuration, the UE operates in the first serving cell and a second serving cell using carrier aggregation (CA).I l l

[0351] Example 20. The method of any one of the preceding examples, further comprising: receiving the LTM identifier along with the LTM configuration, and receiving the LTM identifier with the command to the perform an LTM switch.

[0352] Example 21. A user equipment (UE) comprising: a transceiver; and processing hardware configured to implement a method of any of the preceding examples.

[0353] Example 22. A me...

Claims

What is claimed is:

1. A method implemented in a user equipment (UE), the method comprising: receiving, from a radio access network (RAN) node and when the UE operates in a current serving cell, a lower-layer triggered mobility (LTM) candidate configuration associated with an LTM identifier corresponding to a first candidate cell and a second candidate cell; receiving, from the RAN node, a command to perform an LTM switch to the first candidate cell; and accessing the first candidate cell in response to the command.

2. The method of claim 1, wherein: the first candidate cell includes a primary cell (PCell) or a primary secondary cell (PSCell); and the second candidate cell includes a secondary cell (SCell).

3. The method of either one of claims 1 or 2, further comprising: receiving, from the RAN node, a command to activate the second candidate cell; and accessing the second candidate cell in response to the command to activate the second candidate cell.

4. The method of either one of claims 1 or 2, further comprising: accessing the second candidate cell in response to the command to perform the LTM switch.

5. The method of either one of claims 3 or 4, further comprising: communicating with the RAN node via the first candidate cell and the second candidate cell using carrier aggregation (CA).

6. The method of any one of claims 1-5, further comprising: applying a timing advance (TA) value for uplink (UL) synchronization in the first candidate cell.

7. The method of any one of the preceding claims, further comprising: receiving the LTM identifier along with the LTM configuration, and receiving the LTM identifier with the command to the perform an LTM switch.

8. A user equipment (UE) comprising: a transceiver; and processing hardware configured to implement a method of any of the preceding claims.

9. A method implemented in a radio access network (RAN) node, the method comprising: transmitting, to a user equipment (UE), a lower-layer triggered mobility (LTM) candidate configuration associated with an LTM identifier corresponding to a first candidate cell and a second candidate cell; transmitting, to the UE, a command to perform an LTM switch to the first candidate cell; and communicating with the UE responsive to detecting that the UE accesses the first candidate cell in response to the command.

10. The method of claim 9, wherein: the first candidate cell includes a primary cell (PCell) or a primary secondary cell (PSCell); and the second candidate cell includes a secondary cell (SCell).

11. The method of either one of claims 9 or 10, further comprising: transmitting, to the UE, a command to activate the second candidate cell; and activating communication with the UE via the second candidate cell after the transmitting the command to activate the second candidate cell.

12. The method of either one of claims 9 or 10, further comprising: detecting that the UE accesses the second candidate cell, in response to the command to perform the LTM switch, to communicate with the UE via the first candidate cell and the second candidate cell using carrier aggregation (CA).

13. The method of any one of claims 9-12, further comprising: transmitting, to the UE, a first timing advance (TA) value for uplink (UL) synchronization in the first candidate cell and a second TA value for UL synchronization in the second candidate cell.

14. The method of any one of claims 9-12, further comprising: transmitting, to the UE, a timing advance (TA) value for uplink (UL) synchronization in the first candidate cell.

15. The method of any one of claims 9-14, wherein: when the RAN node transmits the LTM configuration, the RAN node communicates with the UE via a first serving cell.

16. The method of any one of claims 9-15, further comprising: transmitting an LTM identifier along with the LTM configuration, and transmitting the LTM identifier with the command to the perform an LTM switch.

17. A radio access network (RAN) node comprising: a transceiver; and processing hardware configured to implement a method of any of claims 9-16.

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