Managing lower layer triggered cell switch and failure recovery

Abstract

A user equipment (UE) communicates with a radio access network (RAN) via a serving cell using a first configuration; receives, via the serving cell, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell; initiates an LTM cell switch procedure, including applying the LTM candidate configuration to access the candidate cell; and performs one of: (i) in response to determining that the UE successfully connected to the candidate cell, releasing the first configuration, or (ii) subsequently to determining that the UE failed to connect to the candidate cell, performing a connection reestablishment using the first configuration or the LTM candidate configuration.

Description

MANAGING LOWER LAYER TRIGGERED CELL SWITCH AND FAILURE RECOVERYREFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of the filing date of provisional U.S. Patent Application No. 63 / 618,891 entitled “Managing Lower-Layer Triggered Cell Switch and Failure Recovery,” filed on January 8, 2024. The entire content of the provisional application is hereby expressly incorporated herein by reference.FIELD OF THE DISCLOSURE

[0002] This disclosure relates to wireless communications and, more particularly, to lower- layer signaling triggered cell switch handling and failure recovery.BACKGROUND

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

[0004] In telecommunication systems, the Packet Data Convergence Protocol (PDCP) sublayer of the radio protocol stack provides services such as transfer of user-plane data, ciphering, integrity protection, etc. For example, the PDCP layer defined for the Evolved Universal Terrestrial Radio Access (EUTRA) radio interface (see 3GPP specification TS 36.323) and New Radio (NR) (see 3GPP specification TS 38.323) provides sequencing of protocol data units (PDUs) in the uplink direction (from a user device, also known as a user equipment (UE), to a base station) as well as in the downlink direction (from the base station to the UE). Further, the PDCP sublayer provides signaling radio bearers (SRBs) and data radio bearers (DRBs) to the Radio Resource Control (RRC) sublayer. Generally speaking, the UE and a base station can use SRBs to exchange RRC messages as well as non-access stratum (NAS) messages, and can use DRBs to transport data on a user plane.

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

[0006] The UE in some scenarios 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 determines that the UE should establish a radio connection with another base station. For example, one base station can determine to hand the UE over to the second base station, and initiate a handover procedure.

[0007] When the UE moves from coverage area of one cell to another cell in a RAN, the UE and the RAN at some point 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 ^ReconfigurationWithSync IE) for change of the serving cell (e.g., PCell or PSCell). In cases where the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN has to release the at least one SCell due to the change of the PCell or PSCell. The serving cell change involvescomplete L2 (and LI) resets, leading to longer latency, larger overhead and longer interruption time. To address some of these concerns, 3 GPP recently proposed to develop mobility procedures to reduce latency and overhead for fast serving cell change, described in the technical document RP-221799. These procedures provide fast serving cell changes and can be referred to as lower layer triggered mobility (LTM).

[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 in some cases 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 vian RRC signaling. In some implementations, the RAN includes the configuration parameters for the first radio bearer in the LTM configuration. At a later time, 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. The RAN in this case transmits an LTM cell switch command to the UE, so as to command (instruct) the UE to perform the LTM cell switch to the LTM candidate cell. The UE can perform a cell change from the serving cell to the LTM candidate cell in response to the LTM cell switch command as described in 3GPP R2-2313672.

[0009] According to this approach, the UE uses a certain MCG C-RNTI (i.e., a first C- RNTI) and then receives another C-RNTI (i.e., a second C-RNTI) as a part of the LTM candidate configuration (i.e., the Itm-CandidateConfig) . The UE performs an LTM cell switch upon receiving an LTM command or upon cell selection, while timer T311 is running. If the UE encounters a failure of the LTM cell switch, the UE initiates an RRC connection reestablishment procedure to recover from the failure. However, it is not clear which C-RNTI the UE should use to perform the RRC connection reestablishment procedure.

[0010] Moreover, the UE communicates with the RAN using a certain set of configurations included in the cell group configuration before performing the LTM cell switch. The UE releases this set of configurations upon completing the LTM cell switch. When the RAN receives, from the UE, an RRC reestablishment request message in the RRC connection reestablishment procedure, the RAN may not be able to determine that the UE released the set of configurations, which can cause communication errors after the RRC connection reestablishment procedure.SUMMARY

[0011] An example embodiment of the techniques of this disclosure is a configuration management method implemented in a user equipment (UE). The method comprises communicating with a radio access network (RAN) via a serving cell, using a first UE identity (ID); initiating a lower-layer triggered mobility (LTM) cell switch procedure using an LTM candidate configuration that includes a second UE ID, to access a candidate cell; and in response to expiration of a timer associated with the LTM cell switch procedure, initiating a connection reestablishment procedure with the RAN, using the first UE ID.

[0012] Another example embodiment of these techniques is a configuration management method implemented in a radio access network (RAN). The method comprises communicating with a user equipment (UE) via a serving cell using a first UE identity (ID); transmitting, to the UE via the serving cell, a command to initiate a lower-layer triggered mobility (LTM) cell switch procedure using an LTM candidate configuration that includes a second UE ID, to access a candidate cell; and performing a connection reestablishment with the UE, using the first UE identity.

[0013] Yet another example embodiment of the techniques of this disclosure is a configuration management method implemented in a user equipment (UE). The method comprises communicating with a radio access network (RAN) via a serving cell using a first configuration; receiving, via the serving cell, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell; initiating an LTM cell switch procedure, including applying the LTM candidate configuration to access the candidate cell; and performing one of (i) in response to determining that the UE successfully connected to the candidate cell, releasing the first configuration, or (ii) subsequently to determining that the UE failed to connect to the candidate cell, performing a connection reestablishment using the first configuration or the LTM candidate configuration.

[0014] Another example embodiment of these techniques is a configuration management method implemented in a radio access network (RAN). The method comprises communicating with a user equipment (UE) via a serving cell using a first configuration for the UE; transmitting, to the UE via the serving cell, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell; and performing one of: (i) subsequently to the UE initiating an LTM switch cell switch procedure, releasing the first configuration, or (ii)performing a connection reestablishment with the UE using the first configuration or the LTM candidate configuration.

[0015] Another example embodiment of these techniques is an apparatus comprising processing hardware and configured to implement one of the methods above.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Fig. 1 A is a block diagram of an example system in which a radio access network (RAN) and a user device can implement the techniques of this disclosure for managing LTM cell switching and failure recovery;

[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. 1 A communicates with base stations;

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

[0020] Fig. 3 is a messaging diagram of an example scenario in which a UE communicates with a distributed base station and performs an LTM cell switch in response to a command from the base station;

[0021] Fig. 4 is a messaging diagram of an example scenario generally similar to that of Fig. 3, but in which the base station includes a source DU and a target DU, and the candidate cell for an LTM cell switch is associated with the target DU;

[0022] Fig. 5 is a flow diagram of an example method in a UE for releasing a configuration the UE used to communicate with the RAN in a serving cell, after successfully completing an LTM cell switch;

[0023] Fig. 6A is a flow diagram of an example method in a UE for performing an RRC connection reestablishment procedure after expiration of a timer associated with an LTM cell switch procedure;

[0024] Fig. 6B is a flow diagram of a method similar to that of Fig. 6A, but in which the UE uses a different user identity;

[0025] Fig. 6C is a flow diagram of a method similar to that of Fig. 6A, but in which the UE performs an additional LTM cell switch procedure;

[0026] Fig. 7 is a flow diagram of an example method in a UE for initiating an LTM cell switch procedure after a radio link failure;

[0027] Figs. 8A and 8B are further examples of methods that include portions of the methods of Figs. 5, 6A or 6B, and 7;

[0028] Fig. 9 is a flow diagram of an example method in a UE for determining whether to revers back to a prior configuration or initiate an RRC connection reestablishment procedure, upon expiration of a timer related to a reconfiguration with sync procedure;

[0029] Fig. 10 is a flow diagram of an example method in a RAN for managing configurations in view of an LTM cell switch;

[0030] Figs. 11 A and 1 IB are flow diagrams of further example methods in a RAN for performing an RRC connection reestablishment procedure;

[0031] Fig. 12 is a flow diagram of an example method similar to that of Fig. 10, but with the RAN applying an LTM configuration after the UE accesses the candidate cell;

[0032] Fig. 13 A is a flow diagram of an example method in a CU for managing LTM execution;

[0033] Fig. 13B is a flow diagram of an example method similar to that of Fig. 13 A, but with the CU releasing configurations and a user identity in response to a different message; and

[0034] Figs. 14A-14D are flow diagrams of example methods in a CU similar to that of Fig. 13 A, but including the checking of MAC-I.DETAILED DESCRIPTION OF THE DRAWINGS

[0035] Fig. 1 A 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.

[0036] 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 thebase 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.

[0037] 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.

[0038] 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. 1 A) 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 the handover. The base stations 104 and 106 in this case operate as a source MN (S-MN) and a target MN (T-MN), respectively.

[0039] 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. 1 A. 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 packetdata 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.

[0040] As illustrated in Fig. 1 A, 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. 1 A). 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.

[0041] 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 (5GNR 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 5GNR-6G DC.

[0042] 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. UE102) via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The PHY controller 132 is also configured to receive data and control signal on physical uplink (UL) channels and / or UL reference signals with the one or more user devices via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The processing hardware 130 in an example implementation includes a MAC controller 134 configured to perform MAC functions with one or more user devices. The MAC functions include a random access (RA) procedure, managing UL timing advance (TA) for the one or more user devices, and / or communicating UL / DL MAC PDUs with the one or more 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 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.

[0043] The UE 102 is equipped with processing hardware 150 that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. The PHY controller 152 is also configured to receive data and control signal on physical DL channels and / or DL reference signals with the base station 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 anRRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack.

[0044] 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.

[0045] 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 some examples, the processing hardware in an example implementation includes a medium access control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure) and a radio link control (RLC) controller configured to manage or control one or more RLC operations or procedures when the base station 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.

[0046] 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).

[0047] In the example stack 200, a physical layer (PHY) 202 A of EUTRA provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logicalchannels 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.

[0048] 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.”

[0049] 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. 2 A) to exchange RRC messages or non-access-stratum (NAS) messages, for example. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide Data Radio Bearers (DRBs) to support data exchange. Data exchanged on the NR PDCP sublayer 210 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0050] 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.

[0051] Next, several example scenarios in which the base station operating in the system of Fig. 1 A 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- 14D that are similar are labeled with similar reference numbers (e.g., event 304 in Fig. 3 is similar to event 404 of Fig. 3, block 672 in Figs. 6A and 6B is similar to block 872 in Fig. 8A, block 1002 in Fig. 10 is similar to block 1202 in Fig. 12), with the 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.

[0052] 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 124 A. The UE 102 initially communicates 302 with the DU 174 on the cell 124 A 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 124 A and other cell(s) (e.g., cell 124D not shown in Fig. 1 A) 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 other implementations, the UE 102 in communicates with the DU 174 on the cell 124A only. In some implementations, the UE 102 communicates with the DU 174 on the cell 124A and / or other cell(s) via one or multiple TRPs. In some implementations, the cell 124A can be a PCell. In such cases, the other cell(s) include SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In other implementations, the cell 124A can be a SCell, and one of the other cell(s) is a PCell. In such cases, the rest includes SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In the following description, the base station 104 can be the DU 174, the CU 172 or the DU 174 and CU 172.

[0053] In the event 302, the UE 102 can transmit 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 can include SRBs and / or DRB(s). The base station 104 can configure the radio bearers to the UE 102. In some implementations, UL control signals include UL control information, channel state information, hybrid automatic repeat request (HARQ) acknowledgements (ACKs), HARQ negative ACKs, scheduling request(s) and / orsounding reference signal(s). Similarly, the UE 102 can receive 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)). The base station 104 can transmit the DCIs on physical downlink control channel(s) (PDCCH(s)) monitored by the UE 102, on the cell 124A and / or other cell(s) via one or multiple TRPs.

[0054] In some implementations, the serving DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some implementations, the serving DU configuration includes at least one first non-LTM TCI state configuration for the serving cell(s). In some implementations, the DU 174 can transmit these configuration parameters and / or the first non-LTM TCI state configuration(s) to the CU 172. The CU 172 generates one or more messages (e.g., RRC reconfiguration message(s)) including the configuration parameters and / or the first non-LTM TCI state configuration(s) and transmits the one or more messages to the UE 102 via the DU 174. In other implementations, the DU 174 transmits the configuration parameters and / or the first non-LTM TCI state configuration(s) to the UE 102 directly. In some implementations, the serving DU configuration is CellGroupConfig ^E defined in 3GPP specification 38.331. In other implementations, the serving DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the serving CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the serving CU configuration includes a MeasConfig IE and / or a RadioBearerConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some implementations, the serving DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and reporting. In other implementations, the serving CU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and reporting. In some implementations, the UE 102 receives the serving CU configuration or the configuration parameters in the serving CU configuration from the CU 172 via the DU 174. In other implementations, the UE 102 receives a portion of the serving CU 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.

[0055] In some implementations, the UE 102 and DU 174 communicates 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 communicates 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.

[0056] In some implementations, each of the first non-LTM TCI States Activation / Deactivation command(s) is a MAC CE. The MAC CE(s) may 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 States Activation / Deactivation for UE-specific PDSCH MAC CEs, one or more Enhanced PUCCH Spatial 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.

[0057] 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).

[0058] 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 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 the event 302. 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). The LI measurement configuration(s) (e.g., CSI-MeasConfig IE(s)) can include LI measurement resource configuration(s) and / or LI measurement reporting configuration(s). The LI measurement resource configuration(s) can configure reference signal(s) and / or resources of the reference signal(s) for the UE 102 to measure and obtain LI measurement results. In some implementations, the reference signal(s) includes CSLRS(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 CSI-ResourceConfig IE(s). In another example, the LI measurement reporting configuration(s) configures way(s) the UE 102 uses to transmit LI measurement results / reports. For example, the LI measurement report configuration(s) is / are CSI- ReportConfig IE(s). For 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 one implementations, the DU 174 does not transmit the LI measurement report(s) to the CU 172.

[0059] In some implementations, the LI measurement configuration(s) are new RRC IE(s) defined in 3GPP specification 38.331 vl8.0.0 and / or later version for a lower layer triggered mobility (LTM). In some implementations, the LI measurement resource configuration(s) are new RRC IE(s) defined in 3GPP specification 38.331 vl8.0.0 and / or later version for the LTM. In some implementations, the LI measurement reporting configuration(s) are newRRC IE(s) defined in 3GPP specification 38.331 vl8.0.0 and / or later version for the LTM. In some implementations, each of the LI measurement reporting configuration(s) can include a trigger event configuration configuring a trigger event to trigger the UE 102 to transmit a LI measurement report. If the UE 102 detects the trigger event, the UE 102 transmits a LI measurement report to the DU 174.

[0060] In some implementations, (each of) the LI measurement report(s) can include 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 LI- Signal to Interference Noise Ratio (Ll-SINR) value. For each of the LI measurement report(s), the UE 102 transmits a PUCCH transmission including the LI measurement report to the DU 174, in some implementations. That is, the UE 102 transmits the each of the LI measurement report(s) on a PUCCH to the DU 174. In other 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 other 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 portion 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 CSI (i.e., a CSI component) or CSI. In some implementations, the UE 102 can include other CSI component(s) in (each of) the PUCCH transmission(s) and / or PUSCH transmission(s) described above. In one implementation, the other CSI component(s) include such as 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) in format of RRC message(s) to the DU 174.

[0061] In some implementations, each of the L3 measurement report(s) can include at least one L3 measurement result. In some implementations, the at least one L3 measurement result includes at least one RSRP (value) and / or at least one SINR (value). In one implementation, the UE 102 transmits each of the L3 measurement report(s) on a PUSCH to the CU 172 viathe DU 174. In some implementations, each of the L3 measurement report(s) can be 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. 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 can determine that the L3 measurement report is associated to a L3 measurement configuration identified by the measurement identity.

[0062] In some alternative implementations, for each of the at least one measurement report (e.g., LI measurement report(s)), the UE 102 transmits a MAC control element (CE) including the measurement report to the DU 174 in the event 304. To transmit the MAC CE(s), the UE 102 generate one or more MAC PDUs each including one or more of the MAC CE(s) to the DU 174 in the event 304.

[0063] In some implementations, the UE 102 performs measurements on one or more reference signals in accordance with the at least one measurement configuration. The one or more reference signals can include one or more Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Blocks (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. 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. 1 A).

[0064] 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 first cell could be used by the base station 104 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 that could be used for communication with the UE 102. In some implementations, if the L3 measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than strength and / or quality of the cell 124A, and / or is better than strength and / or quality of the cell 124 A by a first predetermined threshold, the CU 172 determines to prepare the first cellfor the UE 102. In other implementations, if the LI 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 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.

[0065] In the case that 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 cell global identity (CGI). In another example, the cell ID is a portion of the CGI. In yet another example, the cell ID is a physical cell ID (PCI). In some implementations, the CU 172 includes an LTM indicator in the first CU-to-DU message to indicate the DU 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 other implementations, the CU 172 includes the LTM indicator 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 other implementations, the CU 172 includes the LTM indicator in an 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 herein after 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 can include 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 the case that 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.

[0066] 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 identifiesthe LTM DU configuration 1 is configured for or associated with the first cell. In some scenarios and implementations, the CU 172 can include 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 that which LTM DU configuration is associated to which cell (ID). The cell(s) 1 and / or 2, . . . , N are candidate cell(s).

[0067] In some 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 a reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, . . ., N (i.e., nonreference 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 other 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 augment the reference LTM DU configuration. In yet other 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.

[0068] 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 CellGroupConfig IE defined in 3 GPP specification 38.331. In other implementations, the reference LTM DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the reference LTM DU configuration includes a CSI- MeasConfig IE or configuration parameters for channel state information (CSI) measurement and / or reporting.

[0069] 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 other implementations, the reference LTM DU configuration is the same as the serving DU configuration.

[0070] 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 316. In other implementations, the CU 172 does not include a / 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 316. In other 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 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 316.

[0071] 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 of the events 316 and 318. In such cases, the CU 172 generates the first container. The first container is to indicate the UE 102 not to apply the LTM DU configuration 1 and / or the LTM CU configuration 1 immediately. In some scenarios or 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). If the configuration is included in the first container, the UE 102 refrains from immediately applying the configuration. Otherwise, if the configuration is not included in the first container, the UE 102 can apply the configuration immediately. 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 theLTM CU configuration 1 in a first element (referred to herein after 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). When the UE 102 receives the first addition or modification list, the UE 102 can store the first addition or modification list, e.g., in a variable in its random access memory (RAM). In other alternative implementations, the DU 174 generates the first container and includes the first container in the first DU-to-CU message. In yet other alternative implementations, the DU 174 generates the element 1 and includes the element 1 in the first DU-to-CU message.

[0072] In some implementations, the CU 172 includes an LTM CU configuration 1 in the RRC reconfiguration message 316, the first container or the element 1, where the LTM CU configuration 1 associated with the LTM DU configuration 1. To associate the LTM CU configuration 1 with the LTM DU configuration 1, the CU 172 can include 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 316 or the second container, where the LTM CU configuration(s) 2, . . . , N associated with the LTM DU configuration(s) 2, . . . , N, respectively. To associate the LTM CU configuration(s) 2, . . . , N with the LTM DU configuration(s) 2, . . . , N , the CU 172 can include the LTM CU configuration(s) 2, . . . , N and the LTM DU configuration(s) in the element(s) 2, . . . , N, respectively. In other 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 316, LTM CU configuration(s) for some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, . . . , N.

[0073] After receiving the RRC reconfiguration message 316, the DU 174 transmits 318 the RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320 an 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 RRCreconfiguration message. For 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 a PDCP PDU including the encrypted RRC reconfiguration message and encrypted MAC-I to the UE 102 via the DU 174 in the events 316 and 318. When the UE 102 receives the PDCP PDU from the CU 172 via the DU 174 (i.e., 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 the MAC-I is valid. If the UE 102 verifies the MAC-I is invalid, the UE 102 discards or ignores the RRC reconfiguration message. In some implementations, the UE 102 can perform an RRC connection reestablishment procedure in response to the invalid MAC-I. Otherwise, if the UE 102 verifies the MAC-I is valid, the UE 102 can process 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 with reference to events 330, 350.

[0074] 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.

[0075] 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 can transmit 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 DL RRC Message Transfer message. In other implementations, the second CU-to-DU message is a UE Context Modification Request message. In some implementations, the second DU-to-CU message is a UL RRC Message Transfer message. In other implementations, the second DU-to-CU message is a UE Context Modification Response message.

[0076] In some implementations, the CU 172 can include a reference LTM CU configuration in the RRC reconfiguration message 316 or the first container. In someimplementations, the CU 172 can generate the LTM CU configuration 1 (i.e., non-reference LTM CU configuration) as a delta configuration to augment the reference LTM CU configuration. Similarly, the CU 172 can generate some or all of the LTM CU configuration(s) 2, . . . , N as delta configuration(s) to augment the reference LTM CU configuration. Alternatively, in the RRC reconfiguration message 316 or the first container, the CU 172 includes the reference LTM CU configuration and does not include a nonreference LTM CU configuration. 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 316.

[0077] In some implementations, the reference LTM CU configuration is different from the serving CU configuration. In some 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 yet other implementations, the reference LTM CU configuration is the same as the serving LTM CU configuration.

[0078] In some implementations, the CU 172 includes, in the RRC reconfiguration message, a first LTM ID (referred to herein after 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.

[0079] In some implementations, the CU 172 can transmit 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 other 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 can include the LTM DU configuration 1 and the ID 1 and indicate the association between the ID 1 and LTM DU configuration 1. Thus, the DU 174 can directly associate the ID 1 with the LTM DU configuration 1. In other implementations, in the third CU-to-DU message, the CU 172 can include the cell ID 1 and the ID 1 (i.e., the first LTM ID) and indicate the association between the cell ID 1 and the ID 1. Thus, the DU 174 can associate the ID 1 with the LTM DU configuration 1, based on the association between the cell ID 1and the ID 1 and the association between the cell ID 1 and the LTM DU configuration 1. In yet other implementations, in the third CU-to-DU message, the CU 172 can include the LTM DU configuration 1, the cell ID 1 and / or the ID 1 and indicate the association between the ID 1, LTM DU configuration 1 and / or the cell ID 1. In some implementations, the DU 174 can transmit 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 message and UE Context Modification Response message. In some implementations, the CU 172 can include 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 can be omitted. In some 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.

[0080] 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.

[0081] In the case that the CU 172 includes the ID 1 in the first CU-to-DU message, the DU 174 can include the ID 1 in the LTM DU configuration 1, first container or element 1. Alternatively, the DU 174 does not include the ID 1 in the LTM DU configuration 1, first container and / or element 1.

[0082] 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 other implementations, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316 and outside 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 316. In yet other 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 other 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 thefirst DU-to-CU message 310. In such cases, the CU 172 includes the fourth container in the RRC reconfiguration message 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.

[0083] 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.

[0084] 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 include physical layer configuration parameters (e.g., PhysicalCellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE) and / or RLC configuration parameters (e.g., RLC-BearerConfig IE(s)). In some further implementations, the plurality of configuration parameters include a special cell configuration (e.g., SpCellConfig E) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some implementations, the LTM DU configuration 1 is CellGroupConfig ^E defined in 3GPP specification 38.331. In other implementations, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0085] 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 defined in 3GPP specification 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 CSI-MeasConfig IE) and / or at least one configuration indicator (TCI) state configuration. In other 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 CSI-RS(s). The RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In someimplementations, each of the RS resource configuration(s) 1 includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) 1 is / are (similar to) CSI-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.

[0086] 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 other 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 316, 318. In other implementations, the CU 172 transmits another RRC reconfiguration message including the serving DU configuration to the UE 102 via the DU 174.

[0087] In some implementations, the DU 174 includes a random access configuration in the LTM DU configuration 1. In other implementations, the DU 174 does not include a random access configuration in the LTM DU configuration 1. In some implementations, if the cell 124 A 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 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 random access 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 random access configuration in the LTM DU configuration 1. If the LTM DU configuration 1 includes the random access configuration, the UE 102 performs the random access procedure in the event 332 in accordance with therandom 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 the random access procedure of the event 332 in response to the LTM DU configuration 1 excluding the random access configuration.

[0088] 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 124 A and first cell are synchronized or not. The UE 102 performs the random access procedure in the event 332 in accordance with the random access configuration parameters, as described below. In some implementations, the random access configuration parameters configure physical random access channel (PRACH) resources, an association between SSB and PRACH resources, and / or one or more PRACH occasions.

[0089] In some implementations, if the cell 124 A and 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 124 A and first cell are not synchronized, the DU 174 determines to not include the first indication in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has 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 has 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 the random access procedure of the event 332 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 the random access procedure in accordance with the random access configuration in the event 332, in response to the LTM DU configuration 1 excluding the first indication, as described below.

[0090] 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 other 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 cellswitch information in the first LTM DU configuration 1. In some implementations, the DU 174 includes the random access configuration (parameters) in the LTM cell switch information (e.g., Itm-CellSw itchinfo field or LTM-CellSw itchinfo IE). In some implementations, if the cell 124 A and 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 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 the random access procedure in the event 332 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 the random access procedure of the event 332. In some implementations, the DU 174 includes a cell ID (i.e., cell ID 1) of cell 1 (i.e., the first cell) in the LTM DU configuration 1. In one implementation, the cell ID 1 can be a PCI. In another implementation, the cell ID 1 is a CGI. In some implementations, the cell ID 1 included in the LTM DU configuration l is a PCI, while the cell ID 1 included in the first CU-to-DU message is a CGI. In some 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.

[0091] In some implementations, after (e.g., in response to) receiving one or some of the at least one measurement report of the event 304, 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 one implementation, 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 additional cell(s) could be used by the base station 104 to communicate with the UE 102. The additional cell(s) can include the cell 124C and / or cell(s) other than thecells 124A, 124B and 124C. In some implementations, if the L3 measurement report(s) indicates that signal strength and / or 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 other implementations, if the LI measurement report(s) indicates that 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 one implementation, the respective predetermined threshold(s) for the additional cells can be different from the first predetermined threshold. In another implementation, the respective predetermined threshold(s) for the additional cell(s) can be the same as the first predetermined threshold. In some implementations, the respective predetermined thresholds for the additional cells can be 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.

[0092] In the case that the CU 172 determines to prepare the additional cell(s), the CU 172 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the DU 174 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390. In the case that the DU 174 determines to prepare the additional cell(s), the DU 174 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the CU 172 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390.

[0093] In some implementations, the CU 172 and DU 174 perform LTM preparation procedure(s) 2, . . . , N to prepare the cell(s) 2, . . . , N, respectively, similar to the procedure 390. The CU 172 can include 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 with reference to the LTM DU configuration 1. In the case that 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 numberof “N” is 4, 8, 16 or 32. At least some of the example implementations and other details discussed with reference to the LTM DU configuration 1 can apply to the LTM DU configured on(s) 2, . . . , N.

[0094] In other 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 configured on(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, the DU 174 can include the cell ID(s) 1, 2, . . ., N respectively associated with the LTM DU configured on(s) 1, 2, . . . , N to indicate that the LTM DU configured on(s) 1, 2, . . . , N are configured for the cell ID(s) 1, 2, . . ., N, respectively. In the case that 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.

[0095] After receiving the LTM DU configured on(s) 2, . . . , N from the DU 174, the CU 172 can include the LTM DU configured on(s) 2, . . ., N in the first container. In some implementations, the CU 172 can include the LTM DU configured on(s) 2, . . ., N in element(s) 2, . . . , N, respectively, and includes the element(s) 2, . . . , N in the first container. In some implementations, the CU 172 includes, in the RRC reconfiguration message, LTM ID(s) (i.e., ID(s) 2, . . . , N) for identifying the LTM DU configured on(s) 2, . . . , N, respectively. In some implementations, the CU 172 includes the ID(s) 2, . . ., N in the first container. For example, the CU 172 can include 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.

[0096] In some implementations, the CU 172 assigns the ID(s) 2, . . . , N for the LTM DU configured on(s) 2, . . ., N, respectively. In other 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 yet other 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.

[0097] In some implementations, the CU 172 can perform an LTM ID assignment procedure with the DU 174 for each of the LTM DU configured on(s) 2, . . ., N, similar to the procedure 392. In other implementations, the CU 172 can include the ID(s) 2, . . ., N and the LTM DU configuration(s) 2, . . ., N in the third CU-to-DU message and indicate the association between the ID(s) 2, . . . , N and the LTM DU configured on(s) 2, . . . , N,respectively. Thus, the DU 174 can associate the LTM DU configuration(s) 2, . . . , N with the ID(s) 2, . . ., N, respectively. In yet other implementations, the CU 172 can include the cell ID(s) 2, . . . , N and the ID(s) 2, . . . , N in the third CU-to-DU message and indicate the association between the cell ID(s) 2, . . . , N and the ID(s) 2, . . . , N, respectively. Thus, the DU 174 can associate 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 other implementations, the CU 172 can include 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, the third CU-to-DU message can be omitted. In yet other implementations, the CU 172 can include the ID(s) 2, . . ., N in the first CU-to-DU message and indicate the ID(s) 2, . . . , N is / are respectively associated with the cell ID(s) 2, . . . , N. In one implementation, 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, first container and / or element(s) 2, . . ., N.

[0098] In some alternative implementations, the DU 174 assigns the ID(s) 2, . . ., N. In some implementations, the DU 174 includes the ID(s) 2, . . ., N in the first DU-to-CU message of the procedure 390. In yet other 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. The CU 172 can include the ID(s) 2, . . ., N in the RRC reconfiguration message. In other 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.

[0099] In some alternative implementations, the CU 172 can generate 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 can be a second addition or modification list (e.g., Itm- ConfigToAddModList field, LTM-ConfigToAddModList IE, Itm-CandidateConfigToAddModList field, or LTM-CandidateConfigToAddModList ^E), and eachof the element(s) 2, . . N can be an addition or modification IE (e.g., Itm-ConfigToAddMod field, LTM-ConfigToAddMod IE, Itm-CandidateConfigToAddMod field, or LTM- CandidateConfigToAddMod IE). When the UE 102 receives the second addition or modification list, the UE 102 can store the second addition or modification list together with the first addition or modification list, e.g., in a variable in its random access memory (RAM).

[0100] 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 one implementation, each of the cell ID(s) 2, . . . , N is a PCI. In some 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 the case that the CU 172 prepares the cell(s) 2, . . . , N for LTM in the procedure 390, the CU 172 can set 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 the case that the CU 172 prepares the cell(s) 2, . . . , N in the additional LTM preparation procedure(s), the CU 172 can set the cell index(es) 2, . . ., N to different values and include 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 different values. 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.

[0101] 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 some implementations, each of the LTM DU configuration(s) 1, . . ., N can be a CellGroupConfig IE as defined in 3GPP specification 38.331. In other implementations, each of the LTM DU configuration(s) 1, . . . , N include configuration parameters included in a CellGroupConfig IE as defined in 3 GPP specification 38.331. In some further implementations, the plurality of configuration parameters in each of the LTM DU configuration(s) include a particular special cell configuration (e.g., SpCellConfig E) 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) defined in 3GPP specification 38.331. In other implementations, the LTM DU configuration(s) 1, . . ., N include configuration parameters in the CellGroupConfig IE.

[0102] In some implementations, the CU 172 can include 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. At least some of the example implementations and other details discussed with reference to the additional LTM CU configurations are similar to the LTM CU configuration 1.

[0103] 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 an 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 one implementation, 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 the DU 174 to release the LTM DU configuration M. To indicate the DU 174 to release the LTM DU configuration M, the CU 172 can include 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.

[0104] In other implementations, the DU 174 determines to release the LTM DU configuration K. 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. To indicate the LTM DU configuration K is released, the DU 174 can include 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. 1 < K < N. 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. The CU 172 cantransmit 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.

[0105] After receiving the RRC reconfiguration in the event 318 or transmitting the RRC reconfiguration complete message in the event 320, 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 may transmit 326 a DU-to-CU message including the at least one measurement report to the CU 172, similar to the event 306. In other implementations, the DU 174 does not transmit the at least one measurement report to the CU 172. In some implementations, the at least one measurement report of the event 324 include LI measurement report(s) or L3 measurement repot(s), as described with reference to the event 304. In some 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 other 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 some implementations, the UE 102 does not transmit the LI measurement report(s) in format of RRC message(s) to the DU 174.

[0106] 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. For example, the CU 172 can transmit 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. The one or more RRC messages may or may not 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. The one or more reference signals can 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 ormore reference signals on the cell 124A, the cell 1 and / or the cell(s) 2, . . N. The one or more reference signals can be CSI-RS(s) or SSB(s).

[0107] In some implementations, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)), as described with reference to the event 304. In other implementations, the at least one measurement configuration includes or is LI measurement configuration(s), as described above. In yet other implementations, the LI measurement configuration(s) can be CSI-MeasConfig IE(s) defined in 3GPP specification 38.331 V18.0.0 and / or later versions. The LI measurement configuration(s) can 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 CSI-ReportConfig IE(s). In other implementations, each of the report configuration(s) is a new RRC IE. In some implementations, (each of) the report configuration(s) configures periodically reporting and / or event-triggered reporting of the LI measurement result(s).

[0108] In some implementations, the LI measurement report(s) is / are CSI report(s). In other implementations, the LI measurement report(s) is / are MAC CE(s). In some 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) indicates the RS(s) or a 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)). The quantized measurement values can include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0109] In yet other implementations, the at least one measurement configuration includes new-type measurement configuration(s) (e.g., LTM measurement configuration(s)). The new-type measurement configuration can be newly defined in a 3GPP specification vl 8.0.0 and / or later versions. In some implementations, the new-type measurement configuration(s)includes 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 one implementation, the reference signal resource configuration(s) is / are CSI-ResourceConfig IE(s). In another implementation, the new-type 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 such cases, the measurement report(s) can be LI measurement report(s) or new-type measurement report(s) (e.g., LTM measurement report(s)). In some implementations, the new-type measurement configuration includes configuration parameters newly defined in a 3GPP specification vl 8.0.0 and / or later versions.

[0110] After (e.g., in response to) receiving the measurement report(s) in the event 324, 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 the cell 124A to the UE 102. In other implementations, the DU 174 transmits the first LTM command on the cell 124D to the UE 102. In some implementations, the DU 174 can include 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.[OHl] In other implementations, the DU 174 can include 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 thecell 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.

[0112] In yet other 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 other implementations, the DU 174 determines the cell ID 1 (e.g., PCI) included in the first LTM command from 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 (received in the first LTM command) and the association 1. Before receiving the first LTM command, the UE 102 retrieves the cell ID(es) 2, . . . , N from the LTM DU configuration(s) or element(s) 2, . . . , N and establishes association(s) 2, . . . , N between the cell ID(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 ID(es) 2, . . . , N, before receiving the first LTM command. In some implementations, the DU 174 has 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.

[0113] In yet other implementations, the DU 174 can include 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 one implementation, 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, the UE 102 can determine 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 another implementation, 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, the UE 102 can determine the cell index 1, the ID 1 LTM DU configuration 1 or 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 other 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 can set the corresponding bit (e.g., bit L or bit Z-7) in the bit map to the first value and set 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.

[0114] 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.

[0115] In some implementations, the at least one measurement report (e.g., LI measurement report(s) or new-type 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. The reference signal(s) can be CSI-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 other implementations, the at least one measurement result includes RSRP value(s), RSRQ value(s) and / or SINR value(s) for the new-type measurement report(s). In some implementations, the second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is larger than the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell is suitable for communication with the UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell has been continuously above the second predetermined threshold or the first predeterminedthreshold. This indicates 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 that signal strength or quality of the first cell is above the second predetermined threshold for the UE 102.

[0116] 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 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 one implementation, the second predetermined threshold is larger than the first predetermined threshold. In such an implementation, 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 another implementation, the second predetermined threshold is equal to the first predetermined threshold. In such an implementation, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This also indicates 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 that signal strength or quality of the first cell is above the second predetermined threshold. 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 other 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, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the cell index 1. In other implementations, the CU 172 can include 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 yet other implementations, the CU 172 can include the ID 1 in the fourth CU-to-DU message. Thus, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the ID 1. In someimplementations, 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 other implementations, the fourth CU-to-DU message and / or fourth DU-to- CU message are new interface messages, e.g., Fl application protocol (F1AP) messages defined in 3GPP specification 38.473 vl8.0.0 and / or later versions.

[0117] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 330, the DU 174 can transmit 329 to the CU 172 a DU-to- CU message indicating LTM (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 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). The DU can transmit the DU-to-CU message 329 to the CU 172 before or after transmitting the LTM command 330.

[0118] 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. The MAC CE can be a new MAC CE defined in 3GPP specification 38.321 vl8.0.0 and / or later versions. In one implementation, the DU 174 includes a subheader identifying the new MAC CE in the MAC PDU and the UE 102 identifies the new MAC CE in the MAC PDU in accordance with the subheader. The subheader can include a logical channel ID or extended logical channel ID defined in a 3GPP specification to identify the new MAC CE. For example, the logical channel ID or extended logical channel ID are newly defined in 3GPP specification 38.321 vl 8.0.0 and / or later versions. In other implementations, the first LTM command is a DCI that the UE 102 receives on a PDCCH from the DU 174 in the event 330. The DU 174 generates a cyclic redundancy check (CRC) for the DCI, scrambles the CRC with a first C- RNTI of the UE 102, and transmits the DCI and scrambled CRC on the PDCCH in the event 330. In one implementation, a format of the DCI can be an existing DCI format defined in a 3GPP specification (e.g., 38.212). In another implementation, the format of the DCI can be a new DCI format defined in a 3GPP specification (e.g., 38.212 V18.0.0 or later versions).

[0119] In some implementations, the DU 174 does not perform security protection (e.g., integrity protection and / or encryption) on the first LTM command. This speeds up processing the first LTM command in the UE 102 because the UE 102 does not perform security check (e.g., decryption and / or integrity check) on the first LTM command.

[0120] In some implementations, after receiving the first LTM command, the UE 102 may transmit 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 other implementations, the acknowledgement is a MAC CE. For example, the MAC CE is an existing MAC CE defined in 3GPP specification 38.321 vl7.2.0 and / or later versions. In another example, the MAC CE is a new MAC CE defined in 3GPP specification 38.321 vl8.0.0 and / or later versions. In yet other implementations, the acknowledgement is a PUCCH transmission.

[0121] In some implementations, the CU 172 transmits 316 the RRC reconfiguration message in response to the L3 measurement report 306 for the first cell. To configure the UE 102 to transmit the L3 measurement report 306, the CU 172 can transmit a first RRC reconfiguration message including the L3 measurement configuration (e.g., a M easConfig 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) 324 for the first cell. To configure the UE 102 to transmit the LI or new-type measurement report(s) 324, the CU 172 can transmit a second RRC reconfiguration message including the LI or new-type measurement configuration(s) to the UE 102. In some implementations, the first and second RRC reconfiguration messages can be the same message (i.e., the same instance). In other 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 other implementations, the second RRC reconfiguration message is different from the RRC reconfiguration message of the event 316.

[0122] After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 the first cell. In some implementations, the UE 102, starts a timer. In one implementations, the timer is an RRC timer (e.g., T304 or a new timer). In another implementations, the timer is a MAC timer. 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 the first LTM command or after transmitting 331 the acknowledgement. In some implementations, the UE 102 stops communicating on the cell 124 A 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 byperforming a random access procedure on the first cell with the DU 174, in response to receiving the first LTM command. In other implementations, the UE 102 skips a 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, after (e.g., in response to) receiving the first LTM command.

[0123] 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 (e.g., 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 a random access procedure on the first cell in the event 332, in order to connect to the first cell. For example, the LTM DU configuration 1 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) to configure that the UE 102 performs a random access procedure when the UE 102 receives an LTM command for the first cell. In other implementations, in the LTM DU configuration 1, the DU 174 configures the UE 102 to skip the random access procedure for an 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 skipping a random access procedure for an LTM serving cell change to the first cell.

[0124] In other 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 332 whether to perform the random access procedure in 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) indicating skipping 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 other implementations, the DU 174 excludes the indication in the first LTM command to configure the UE 102 to perform arandom 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 some other implementations, the DU 174 includes a timing advance value in the first LTM command to indicate skipping 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 yet other 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.

[0125] In some implementations, the random access procedure is a four-step random access procedure. In other 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 other 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 or completes the LTM serving cell change). In response to the determination, the UE 102 stops the timer. In one implementation, the MAC 204B of the UE 102 transmits an indication to the RRC 214 of the UE 102 to indicate success of the LTM serving cell change. The RRC 214 stops the timer in response to the indication. 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 other implementations, the LTM DU configuration 1 does not includea C-RNTI, 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 other implementations, the DU 174 includes the second C-RNTI in the LTM cell switch information.

[0126] 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).

[0127] If the DU 174 configures the UE 102 to perform a random access procedure on the first cell as described above, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives Message 3, Message A, or the dedicated preamble in the random access procedure. If the DU 174 configures the UE 102 to skip a random access procedure, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives the first transmission. In some implementations, once the DU 174 detects that the UE 102 has accessed the first cell, the DU 174 may determine success of the LTM serving cell change for the UE 102.

[0128] 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 LTM DU configuration 1 includes a configured configuration to configure the UL grant. In other implementations, the first LTM command includes the UL grant. In other 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 the case that the LTM DU configuration 1 includes the second C-RNTI, the UE 102 determines that the first DCI wassent for the UE 102, using the first DCI, the CRC and the second C-RNTI. In the case that the LTM DU configuration 1 does not include the second C-RNTI, the UE 102 determines that the first DCI was sent for the UE 102, using the first DU, the CRC and the first C-RNTI.

[0129] In some implementations, after transmitting the first transmission, the UE 102 monitors one or more PDCCHs on the first cell using the LTM DU configuration 1 as described above. If the UE 102 receives a second DCI and a CRC of the second DCI on a PDCCH after transmitting the first transmission and the UE 102 determines that the second DCI was sent for the UE 102 using the second C-RNTI or the first C-RNTI as described for the first DCI, the UE 102 determines that UE 102 successfully completes the LTM serving cell change. Upon successfully completing the LTM serving cell change, the UE stops the timer. In one implementation, the MAC 204B of the UE 102 transmits an indication to the RRC 214 of the UE 102 to indicate success of the LTM serving cell change. The RRC 214 stops the timer in response to the indication.

[0130] 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. Each TCI state associates or includes one or two DL RSs with a corresponding QCL type and the DL RS(s) can be 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 further implementations, the DU 174 includes the first TCI state configuration(s) in a serving DU configuration (e.g., CellGroupConfig ^E) 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 310 or the DU-to-CU message 314. In other implementations, the DU-to-CU message is a message different from the messages 310, 314. For example, the DU-to-CU message is a UE Context Modification Response message or a UE Context Modification Required message.

[0131] 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 310, and includes the serving DU configuration in a second interface protocol lE / field in the DU-to-CU message 314. In someimplementations, the events 312 (optional) and / or 314 (optional) are collectively referred to in Fig. 3 as an LTM TCI state configuration procedure 392.

[0132] In some implementations, the CU 172 includes the serving DU configuration in the RRC message. In some implementations, the CU 172 refrains from including the serving DU configuration in a container for LTM (e.g., the first container). In some 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 316, 318. In such cases, the CU 172 may include the first LTM TCI state configuration(s) in the element 1. In other 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 other implementations, the DU 174 refrains from including the first TCI state configuration(s) in the LTM DU configuration 1.

[0133] 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 Fl AP 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 Fl AP lE / field in a DU to CU RRC Information IE in the message 314 and includes the second F1AP lE / field in the DU to CU RRC Information IE in the DU-to-CU message. In other implementations, neither the first F1AP lE / field nor the second F1AP IE is a F1AP CellGroupConfig lE / field. In other implementations, the second Fl AP lE / field is the DU to CU RRC Information IE and the first F1AP lE / field is a new IE specific for including an LTM DU configuration.

[0134] 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 state configuration(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 StatesActivation / 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). The DL RS(s) may 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). The UE 102 may obtain LI measurement results from the received DL RS(s) and transmits the LI measurement results to the DU 174. The UE 102 may obtain 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).

[0135] 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 other 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) may include 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 some alternative 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.

[0136] In some implementations, after (e.g., in response to) receiving the first LTM command or accessing 332 the first cell, the UE 102 performs 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 the event 336. In other implementations, after (e.g., in response to) receiving the first LTM command or accessing 332 the first cell, the UE 102 performs 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) in the event 336.

[0137] In some implementations, each of the first LTM TCI state configuration(s) includes a TCI state ID identifying the corresponding TCI state configuration. For example, the first LTM TCI state configuration(s) includes 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 332 on the first cell using the (activated) LTM TCI state configuration 1. In other implementations, the UE 102 accesses 332 on the first cell without using the first LTM TCI state configuration(s). In some implementations, the UE 102 communicates 336 on the first cell using the (activated) LTM TCI state configuration 1. In some implementations, the DU 174 communicates 336 with the UE 102 on the first cell, using the activated LTM TCI state configurations 1.

[0138] In some implementations, in the 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 332 that the UE 102 accesses the first cell and / or communicates 336 with the UE 102 on the first cell, based on the LTM TCI state configuration 1. In some implementations, the DU 174 receives 332 the first transmission and / or 336 the additional transmission(s) from the UE 102 on the first cell, based on the TCI state configuration 1. In other implementations, in the 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.

[0139] 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 state configuration 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 332 and / or communicates 336 on the first cell using the activated LTM TCI state configurations 1 and 2. After (e.g., in response to) transmitting the first LTM commandor receiving the acknowledgement 331, the DU 174 communicates with the UE 102 on the first cell in the events 332 and / or 336, using the activated LTM TCI state configurations 1 and 2.

[0140] 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 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 the first LTM command or receiving 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.

[0141] 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.

[0142] In other 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 state configuration 2. Each of the control signal(s) includes a DCI and a scrambled CRC for the DCI. 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 firsttransmission 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 other implementations, the UE 102 may transmit 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.

[0143] In yet other 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 such implementations, the DU 174 transmits one or more control signals on one or more PDCCHs 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 signal(s) includes a DCI and a scrambled CRC for the DCI.

[0144] 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 a NG application protocol (NGAP) message. In other 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 yet other 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.

[0145] 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 an LTM TCI state configuration in the RRC reconfiguration message 316, 318.

[0146] In other 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 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 316, 318.

[0147] In yet other 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 does not include an LTM TCI state configuration in the RRC reconfiguration message 316, 318.

[0148] In yet other 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 316, 318.

[0149] In yet other implementations, the DU 174 does not determine whether to provide an 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 316, 318.

[0150] In other 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 316, 318.

[0151] In yet other 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. For example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message 316, 318.

[0152] In yet other 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 asdescribed 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. For example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message 316, 318.

[0153] In some alternative implementations, the DU 174 may not activate or may determine 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.

[0154] 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.

[0155] In other 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.

[0156] In yet other 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.

[0157] In yet other 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 capabilityindicates 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.

[0158] In yet other 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.

[0159] In some implementations, the UE 102 stops using or deactivates the first non-LTM TCI configuration(s) upon receiving the first LTM command.

[0160] After successfully accessing the first cell, the UE 102 communicates 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 336 with the UE 102 on the first cell using the LTM DU configuration 1. In some scenarios or implementations, the UE 102 communicates 336 PUSCH transmissions, PDSCH transmissions, PUCCH transmissions, PDCCH transmissions, and / or sounding reference signal (SRS) transmissions with the DU 174 on the first cell.

[0161] In the case that the UE 102 receives the reference LTM DU configuration as described above, the UE 102 communicates 336 with and 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 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 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 336 with the UE 102 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration.

[0162] In the case that the UE 102 receives neither the LTM CU configuration 1 nor a / the reference LTM CU configuration, the UE 102 communicates 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 / the reference CU configuration to the UE 102, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving CU configuration. In the case that the UE 102 receives the LTM CU configuration 1 and thereference LTM CU configuration from the CU 172, the UE 102 communicates 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 this case, the CU 172 communicates 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.

[0163] In the case that 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 336 with the CU 172 via the DU 174 using the LTM CU configuration 1. In this case, the CU 172 communicates 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 communicates 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 / the 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 / the 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 316 to indicate that the LTM CU configuration l is a full configuration. If the LTM CU configuration l is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 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 / the reference LTM CU configuration from the base station 104, the UE 102 determines that the LTM CU configuration l 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 316. Alternatively, the CU 172 includes a second indication (e.g., afield or IE) in the LTM CU configuration 1, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration l 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 316.

[0164] In the case that 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 336 with the CU 172 via the DU 174 using the reference LTM CU configuration. In this case, the CU 172 communicates 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 communicates 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 as specified in a 3GPP specification (e.g., 3GPP specification 38.331 vl8.0.0 or later version). 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 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 communicates 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 RRC reconfiguration message 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 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 316.

[0165] In the case that 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 336 with the CU 172 via the DU 174 using the serving LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving LTM CU configuration.

[0166] 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. While communicating with the UE 102 at event 332 or 336, the DU 174 may transmit 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. The MAC CE may be 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, an PUCCH spatial relation Activation / Deactivation for multiple TRP PUCCH repetition MAC CE, or an Unified TCI States Activation / Deactivation MAC CE.

[0167] In some implementations, the second non-LTM state configuration(s) may be Rel- 15 / 16 TCI state configuration(s) (i.e., not a unified joint / DL / UL TCI state). This imply that the BS 104 may configure Rel-15 / 16 beam indication framework for the first cell. Non- LTM TCI state configurations activated / indicated by the second non-LTM TCI States Activation / Deactivation command(s) may be 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 would stop or use 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 Indicationfor UE-specific PDCCH MAC CE, the UE 102 would stop or use the first LTM TCI state for at least one of other channels or RSs applicable to share / follow / apply unified TCI states as well (e.g., PDSCH, PUSCH, PUCCH, CSI-RS or SRS). If the UE 102 receives a second non- LTM TCI States Activation / Deactivation command, the UE 102 may deactivate the activated first LTM TCI state configuration(s).

[0168] 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 other implementations, 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 some other implementations, 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). The BS 104 / CU 172 / DU 174 may notify the UE 102 in an RRC message or signal, whether first LTM TCI state configuration(s) is identical or different or a subset of the second non-LTM TCI state configuration(s).

[0169] 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. This may imply 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 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 ranges from #000 to #007; TCI state IDs of the second non- LTM TCI state configurations for the first cell ranges from #008 to #015. In such 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 catenate 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 someimplementations, 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.

[0170] In some implementations, the DU 174 may 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. This may imply 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.

[0171] In some implementations, if a first LTM TCI state configuration associates or includes a SSB corresponding to QCL type A, the UE 102 refrains from using such TCI state configuration for non-LTM purpose or communication in the first cell. In some implementations, the UE 102 may consider or determine 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.

[0172] In some implementations, when or while the DU 174 communicates 332, 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 other implementations, when or while the DU 174 communicates 332, 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 the second LTM TCI States Activation / Deactivation command, the DU 174 may deactivate the LTM TCI state configuration(s) activated in the first LTM command, in some implementations. Insuch cases, the UE 102 deactivate the LTM TCI state configuration(s) activated in the first LTM command, in response. 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.

[0173] In some implementations, the UE 102 transmits an RRC message (e.g., 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 the case that the UE 102 performs the random access procedure 332, the UE 102 can include 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 the case that the UE 102 skip the random access procedure 332, the UE 102 includes the RRC message in a PUSCH transmission of the at least one PUSCH transmission. For example, the PUSCH transmission is the first transmission described above. In some implementations, if the UE 102 maintains communication on the cell 124 A with the base station 104 (i.e., the UE 102 does not disconnect from the cell 124A), the UE 102 can transmit the RRC message to the base station 104 via the cell 124 A. When the DU 174 receives the RRC message, the DU 174 transmits the RRC message to the CU 172.

[0174] In other 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 such cases, the UE 102 can include or transmit data in the Message 3, Message A or PUSCH transmission as described above. The UE 102 can generate a MAC PDU and / or a RLC PDU including the data and transmits or includes the MAC PDU and / or RLC PDU in the PUSCH transmission. For example, the data can be a PDCP PDU, a SDAP PDU, a 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. The MM message can be a 5G MM message or a 6G MM message, and the SM message can be 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.

[0175] When the DU 174 determines that the UE 102 successfully connects to the first cell in the event 332 or 336, the DU 174 can transmit 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 can include the cell ID 1 of the first cell in the DU-to-CU message of the event 334.The cell ID can be 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. When the DU 174 determines that the UE 102 successfully connect to the first cell in the event 332 or 336, the DU 174 can transmit 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 the DU-to-CU message 329, the CU 172 can stop or suspend transmitting DL data for the UE 102 to the DU 174 until receiving the DU-to-CU message 334. The CU 172 can do so because the DU 174 cannot buffer DL data for the UE 102 during the LTM execution in the events 330 and / or 332. After receiving the DU-to-CU message 334, the CU 172 continues or resumes transmitting DL data for the UE 102 to the DU 174. In other implementations, when the CU 172 receives the DU-to-CU message 329, the CU 172 can continue transmitting DL data for the UE 102 to the DU 174. The CU 172 can do so because the DU 174 can buffer 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.

[0176] 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, the DU 174 can stop communicating with the UE 102 on the cell 124A and / or release resources of the cell 124 A configured for the UE 102.

[0177] In some implementations, the DU 174 can generate some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ..., N as full configuration(s) to replace the serving DU configuration. If the LTM DU configuration l is a full configuration, the UE 102 and DU 174 communicate 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 each of the LTM DU configured on(s) 2, . . . , N, the DU 174 can include an indication to indicate that the corresponding DU configuration is a full configuration. Each of the indication(s) in the LTM DU configured on(s) 1, . . ., N can be a field or IE (i.e., the same field or IE). In other implementations, the CU 172 can include, 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 the case of the second container, the CU 172 can include, in the additional RRC reconfiguration message, a single indication indicating that the LTM DU configuration(s) 2, . . ., N is / are fullconfiguration(s). In yet other implementations, the CU 172 can include, 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 yet other implementations, for each of the LTM DU configuration(s) 2, . . ., N, the CU 172 can include, in the first container, a particular indication indicating the corresponding LTM DU configuration is a full configuration. In the case of the second container, the CU 172 can include, in the second container, a single indication indicating that the LTM DU configuration(s) 2, . . ., N is / are full configuration(s). In yet other implementations, the CU 172 can include, in the element 1, includes an indication indicating that the LTM DU configuration 1 is a full configuration. In each of the element(s) 2, . . ., N, the CU 172 can include an indication indicating that the corresponding LTM DU configuration is a full configuration. The UE 102 can determine 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 a fullConfig field defined in the current 3GPP specification. In some implementations, each of the indication(s) above is a fullConfig field defined in the current 3GPP specification. In the case that the LTM DU configuration l is a full configuration, the UE 102 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, the DU 174 can not include a / the reference LTM DU configuration in the first DU-to-CU message 310.

[0178] In other implementations, the DU 174 can generate the LTM DU configuration 1 and / or LTM DU configuration(s) 2, . . ., N as delta configuration(s) that augment (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. For example, if the LTM DU configuration 1 is a delta configuration, the UE 102 and DU 174 augment (the portion of) the reference LTM DU configuration with the LTM DU configuration 1. Thus, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM DU configuration 1 and unaugment 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). The UE 102 can determine that each of the LTM DU configuration(s) 1 and / or 2, . . ., N is a delta configuration based onthat the indication is excluded in the LTM DU configuration(s) 1 and / or 2,first container, second container or element(s) 1 and / or 2, . . N.

[0179] 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).

[0180] In other 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 delta configuration(s) to augment the serving DU configuration. In such cases, the UE 102 communicates 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 336 with the UE 102 in accordance with the LTM DU configuration 1 and the at least a portion of the serving DU configuration.

[0181] After or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351, 352, 354 and / or 356 can 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 secondLTM 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.

[0182] When or in response to determining to activate the LTM DU configuration 2 or transmit the second LTM command, the DU 174 can transmit 349 to the CU 172 a DU-to-CU message indicating LTM (being) 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. The DU can transmit the DU-to-CU message 349 to the CU 172 before or after transmitting the LTM command 350.

[0183] 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. For example, “ cell 124 A”, “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.

[0184] The events 344, 346, 348, 350, 351, 352, 354 are collectively referred to in Fig. 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, 356 are collectively referred to in Fig. 3 as an LTM DU configuration and / or activation procedure 380.

[0185] Referring next to Fig. 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 124 A and optionally additional cell(s), while the T-DU 174B operates a first cell (e.g., cell 124C). 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.

[0186] 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 174 A. The S-DU 174A is a serving DU similar to the DU 174 in Fig. 3. During the communication 402, the UE 102 transmits 404, 406 at least one measurement report (e.g., L3 measurement report(s)) to the CU 172 via the S-DU 174 A. 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 anLTM preparation procedure with the T-DU 174B to (request the T-DU 174B to) prepare cell(s) 1, . . . , N for LTM for the UE 102. N can be 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 can include cell index(es) 1, . . ., N in the LTM DU configuration(s) 1, . . ., N, respectively. In some implementations, the CU 172 can set 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.

[0187] After performing the LTM preparation procedure 490, the CU 172 can perform an 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. The CU 172 can determine to do so based on one or more measurement reports received from the UE 102 via the S-DU 174A, similar to the events 404, 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.

[0188] In some implementations, the LTM preparation procedure 490 is a UE Context Setup procedure and the additional LTM preparation procedure is a UE Context Modification procedure. In other implementations, the LTM procedure 490 and the addition LTM preparation procedures are UE Context Setup procedures. In yet other implementations, the LTM procedure 490 and the addition LTM preparation procedures are UE Context Modification procedures.

[0189] In some implementations, the CU 172 and S-DU 174 A can perform the procedure 380 with the UE 102, as described with reference to Fig. 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, the value N in the procedure 380 or described with reference to Fig. 3 can be the same as or different from the value N described with reference to Fig. 4. In the procedure 390, the CU 172 can receive the first DU-to-CU message including the reference LTM DU configuration from the S-DU 174A in the event 310. In other implementations, the CU 172 and S-DU 174 A does not perform the procedure 380 with the UE 102. In such cases, the CU 172 can perform 488 a reference LTM DU configuration query procedure with the S-DU 174 A 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 can include 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-DU message 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 other implementations, the indication is an LTM indication, and the CU 172 can include 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 (received from the S-DU 174 A) 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. The CU 172 can not include the reference LTM DU configuration inCU-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.

[0190] 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 this case, the T-DU 174B can 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 other 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 174 A.

[0191] 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.

[0192] 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 CSI-RS(s). The RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some implementations, each of the RS resource configuration(s) X includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) X is / are (similar to) CSI-ResourceConfig IE(s). In some implementations, the LTM DU configuration X includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI-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 is / are (similar to) CSI-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 other 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 a RS resource configuration ID to a value for each of the RS resource configuration(s) 1 (including the RS resource configuration(s) X) and includes the RS resource configuration ID in the corresponding RS resource configuration.

[0193] 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 an LTM serving cell change to the cell 1 from the cell 124 A, the UE 102 communicates with the S-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 a 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-RSresource indicators (CRI(s)). The quantized measurement values can include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0194] 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) is / are (similar to) CSI-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) is / are (similar to) CSI-ReportConfig IE(s).

[0195] In some implementations, the additional report configuration(s) 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 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 124 A, the UE 102 communicates 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 a 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 SSBresource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values can include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0196] Similarly, the T-DU 174B can generate 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, and include 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.

[0197] In other 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) can be associated with the cell X operated by the S-DU 174 A. In some implementations, each of the TCI state configuration(s) X includes a TCI state ID. In some implementations, each of the TCI state configuration(s) X is a TCI-State IE. In some implementations, the TCI state configuration(s) X includes / is / are an ul-TCI-ToAddModList-r 17 field, one or more TCI-UL-State-r 17 IES, a dl-OrJointTCI-StateToAddModList-rl7 field, one or more TCI-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 includes the 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 other 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 (including the TCI state configuration(s) X) and includes the TCI state ID in the corresponding TCI state configuration. While the UE 102 and the S-DU 174B communicate 436 with one another, the S-DU 174B can transmit 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, wherethe TCI state configuration is one of the TCI state configuration(s) X or includes configurations of one of the TCI state configuration(s) X.

[0198] Similarly, the T-DU 174B can generate TCI state configuration(s) 2, . . N, considering or based on the RS resource configuration(s) X, and include the TCI state configuration(s) 2, . . . , N, and / or N+l, . . . , N+M in the LTM DU configured on(s) 2, . . . , N, and / or N+l, N+M, respectively, as described above.

[0199] 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 configured on(s) 1, . . ., N of the procedure 490 in the CU-to-DU message of the procedure 380, and the S-DU 174 A generates the LTM DU configured on(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.

[0200] In some implementations, the CU 172 assigns ID(s) 1, . . ., N identifying the LTM DU configured on(s) 1, . . ., N (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 configured on(s) 1, . . . , N and / or the cell ID(s) 1, . . . , N, respectively. In other implementations, the T-DU 174B assigns ID(s) 1, . . ., N identifying the LTM DU configuration(s) 1, . . ., N (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 (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 other implementations, the T-DU 174B assigns ID(s) N+l, . . . , N+M identifying the LTM DU configured on(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.

[0201] 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 412 and DU-to-CU message 414 arecollectively 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 412 and message 414 can be UE Context Modification Request message and 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 412. In one implementation, the CU 172 includes the ID(s) 1, . . ., N in the CU-to-DU message 412. In another implementation, the CU 172 includes the cell index(es) 1, . . ., N in the CU-to-DU message 412. In some alternative implementations, the CU 172 can perform 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 174 A. In each of the procedures, the CU 172 includes 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 configured on(s) 1, . . ., N and / or the cell ID(s) 1, . . ., N, respectively. In other alternative implementations, the CU 172 can perform multiple LTM cell index transfer procedures to transmit the cell index(es) 1, . . . , N, cell ID(s) 1, . . . , N and / or LTM DU configured on(s) 1, . . ., N to the S-DU 174A. In each of the procedures, the CU 172 includes 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 174A associates the cell index(es) 1, . . ., N with the LTM DU configured on(s) 1, . . ., N and / or the cell ID(s) 1, . . ., N, respectively.

[0202] In some implementations, the S-DU 174 A 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 414. In some implementations, the first serving DU configuration including configurations updating (e.g., augmenting, modifying or replacing) the serving DU configuration 402. In other implementations, the first serving DU configuration includes configurations that are not included in the serving DU configuration 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 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 174 A using configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. The following areexample implementations of generating the first serving DU configuration based on the LTM DU configuration 1, . . . , N.

[0203] 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 CSI-RS(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 a RS resource configuration ID. In some implementations, the RS resource configuration(s) Y is / are (similar to) CSI-ResourceConfig IE(s). In some implementations, the LTM DU configuration Y includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI-ResourceConfig IE(s). The S-DU 174A generates at least one serving report configuration for reporting, on the cell 124 A, 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 (similar to) CSI-ReportConfig IE(s). In some implementations, the S-DU 174 A 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, the S-DU 174 A includes the RS resource configuration(s) Y in the serving RS resource configuration(s). In other 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 174 A assigns a RS resource configuration ID to a value for each of the serving RS resource configuration(s) (including the RS resource configuration(s) Y) and includes the RS resource configuration ID in the corresponding serving RS resource configuration.

[0204] 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 some 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 174 A, the UE 102 transmits measurement results on the UL resource(s) via the cell 124 A to the S-DU 174 A, in accordance with the serving report configuration(s) (e.g., event 424). Correspondingly, the S-DU 174A receives themeasurement results on the UL resource (s) via the cell 124 A 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 a 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)). The quantized measurement values can include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0205] 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) can be 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 state configuration(s) Y is a TCI-State IE. In some implementations, the TCI state configuration(s) Y includes / is / are an ul-TCI-ToAddModList-r 17 field, one or more TCI-UL-State-r 17 IES, a dl-OrJointTCI-StateToAddModList-rl7 field, one or more TCI-State IEs, TCI- 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 configured on(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 configured on(s) Y. In other implementations, the S-DU 174 A 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 configured on(s) Y. The S-DU 174A assigns a TCI state ID to a value for each of the serving TCI state configuration(s) (including the TCI state configuration(s) Y) and includes the TCI state ID in the corresponding serving TCI state configuration. While the S- DU 174 A communicate 436 with the UE 102, the S-DU 174 A can transmit an LTMcommand 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.

[0206] 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 174 A in response, similar to the CU-to-DU message 412 and the DU-to-CU message 414, 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 some alternative implementations, the CU 172 can perform 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 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 412. Thus, the S-DU 174 A associates the ID(s) N+l, . . . , N+M with the LTM DU configured on(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 the LTM DU configured on(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 including configurations updating (e.g., augmenting, modifying or replacing) the first serving DU configuration and / or updating configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. In other 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 174 A. 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 174 A using configurations included in the serving DU configuration 402 and / or the first serving DU configuration and not updated by the second serving DU configuration. In some implementations, the S-DU 174 A generates one or more new LI measurement configurations, based on LI measurement configuration(s) in the LTMDU 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 174 A generates one or more new TCI state configuration, 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.

[0207] In some implementations, in the case that the CU 172 and S-DU 174 A 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 in connection with the scenario 400. In some implementations, in the case that the CU 172 and S-DU 174 A 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 in connection with the scenario 400. In some implementations, in the case that the CU 172 and S-DU 174 A 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 in connection with the scenario 400.

[0208] Later in time, the UE 102 can transmit 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) can be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 1. Likewise, the second measurement result(s) can be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 124 A. In some implementations, the event ID, RSRP, RSRQ and / or SINR are LI -event ID, LI -RSRP, LI -RSRQ and / or LI -SINR, respectively. Based on the first measurement result(s) and / or second measurement result(s), the S-DU 174A can transmit 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 other 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. After (e.g., in response to) receiving the first LTM command, the UE 102 can or can not perform 432 arandom access procedure with the T-DU 174B, similar to the event 332. After (e.g., in response to) receiving the first LTM command or completing the random access procedure 432, the UE 102 can communicates 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. If a serving cell change occurs in the procedure 380, the serving cell can be 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 the LTM ID 1, as described with reference to Fig. 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 the cell index 1, as described with reference to Fig. 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.

[0209] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 430, the S-DU 174 A can transmit 429 to the CU 172 a DU- to-CU message indicating LTM (being) executed. In some implementations, the S-DU 174 A includes the cell ID 1 or the LTM ID 1 in the DU-to-CU message 429 to indicate that the S- DU 174A is to activate the LTM DU configuration 1 or trigger an LTM serving cell change. The S-DU 174 A can transmit the DU-to-CU message 429 to the CU 172 before or after transmitting the LTM command 430. In some implementations, when or after the CU 172 receives the DU-to-CU message 429, the CU 172 can stop or suspend transmitting DL data for the UE 102 to the S-DU 174A until receiving the DU-to-CU message 434. After receiving the DU-to-CU message 434, 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.

[0210] The resource release procedure 496 can be similar to the procedure 396. Alternatively, in the resource release procedure 496, the CU 172 can transmit a CU-to-DU message (e.g., a UE Context Release Command message) to the S-DU 174 A to release a UE context of the UE 102. In response, the S-DU 174 A 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.

[0211] Next, several example methods, which can be implemented in a RAN (e.g., a base station, a DU or a CU) or a UE, for LTM, are discussed next with reference to Figs. 5-14B. At least some of the example implementations and other details discussed with reference to Figs. 3 and 4 can also apply to Figs. 5-14B. Similar steps are similarly labeled (e.g., 302, 402, 502, 1002, etc.) and individual descriptions are therefore omitted.

[0212] Fig. 5 is a flow diagram of an example method 500 for managing an LTM execution, which can be implemented by a UE (e.g., the UE 102). The method 500 begins at block 502, where the UE communicates with a RAN via a first serving cell using a first UE identifier (ID) and multiple configurations. The UE receives the first UE ID and the multiple configurations from the RAN. In some implementations, the first UE ID is a first C-RNTI. The UE uses the first C-RNTI to monitor a PDCCH on the first serving cell. For example, the UE receives a DCI and a CRC of the DCI on a PDCCH using the first C-RNTI. In some implementations, the DCI includes a DL assignment, and the UE receives a PDSCH transmission from the RAN in the first serving cell in accordance with the DL assignment. In other implementations, the DCI includes a UL grant, and the UE transmits a PUSCH transmission to the RAN in the first serving cell in accordance with the UL grant. In some implementations, the multiple configurations include a cell group configuration, a radio bearer configuration, a measurement configuration and / or a security configuration. In other implementations, the multiple configurations include a cell group configuration, one or more radio bearer configurations, one or more measurement configurations, and / or one or more security configurations. In some implementations, the cell group configuration includes physical layer configurations, MAC layer configurations and / or RLC layer configurations. In some implementations, the first serving cell is a PCell.

[0213] At block 518, the UE receives a first LTM candidate configuration from the RAN, where the first LTM candidate configuration configures a first candidate cell and includes a second UE ID (e.g., events 316, 318, 394, 494). In some implementations, the second UE ID is a second C-RNTI. At block 530, the UE receives an LTM command from the RAN via the first serving cell, where the LTM command instructs the UE to perform an LTM cell switch to the first candidate cell. In cases where the UE communicates with the RAN in the first serving cell and a second serving cell, the UE can receive the LTM command via the second serving cell instead of the first serving cell.

[0214] At block 556, the UE initiates an LTM cell switch execution to switch to the first candidate cell in response to the LTM command. At block 532, the UE applies the first LTM candidate configuration and accesses the first candidate cell in response to initiating the LTM cell switch execution. In some implementations, the UE accesses the first candidate cell in accordance with the configurations included in the first LTM candidate configuration. At block 560, the UE starts a timer (e.g., T304) in response to initiating the LTM cell switch execution. In some implementations, the UE starts the timer in response to applying the first LTM candidate configuration. At block 562, the UE retains the configurations after (e.g., in response to) initiating the LTM cell switch execution. At block 564, the UE determines that the UE successfully connected to the first candidate cell in the LTM cell switch execution. In some implementations, the UE determines that the first candidate cell is a new serving cell (e.g., a new PCell) when the UE successfully connects to the first candidate cell in the LTM cell switch execution (i.e., the UE successfully completes the LTM cell switch). At block 566, the UE stops the timer in response to the determination that the UE successfully connected to the first candidate cell. At block 536, the UE communicates with the RAN via the first candidate cell using the second UE ID and configurations in the first LTM candidate configuration. At block 568, the UE releases the first UE ID and the configurations after successfully connecting to the first candidate cell.

[0215] In some implementations, the UE releases the first UE ID and the plurality of configurations by discarding or deleting the first UE ID and the configurations. In one implementation, if the LTM candidate configuration does not include the first UE ID and the configurationsan LTM, the UE releases, deletes or discards the first UE ID and the configurations. In other alternative implementations, the UE retains the first UE ID and the configurations and stops using the configurations after (e.g., in response to) successfully connecting to the first candidate cell, instead of releasing 568 the first UE ID and the plurality of configurations. In one implementation, if the first UE ID and the plurality of configurations are included in an LTM candidate configuration (e.g., a second LTM candidate configuration), the UE retains the first UE ID and the plurality of configurations and stops using the first UE ID and the configurations after (e.g., in response to) successfully connecting to the first candidate cell.

[0216] In some implementations, the UE receives 518 an LTM ID identifying the first LTM candidate configuration from the RAN along the first LTM candidate configuration. In some implementations, the LTM command includes the LTM ID, and the UE identifies theLTM candidate configuration in accordance with the LTM ID. In other implementations, the LTM command includes an LTM configuration index derived or mapped from the LTM ID. In one example implementation, the LTM configuration index is the value of LTM ID decremented by one (i.e., LTM ID-1). For example, if the LTM ID is set to value N, the LTM configuration index is value N-l. Thus, the UE identifies the LTM candidate configuration in accordance with the LTM configuration index and the mapping between the LTM configuration index and the LTM ID.

[0217] In some implementations, the second UE ID is a second C-RNTI. The UE uses the second C-RNTI to monitor a PDCCH on the first candidate cell (i.e., the new serving cell) at block 536. For example, the UE receives a DCI and a CRC of the DCI on a PDCCH via the new serving cell using the second C-RNTI. In some implementations, the DCI includes a DL assignment and the UE receives a PDSCH transmission from the RAN on the new serving cell in accordance with the DL assignment. In other implementations, the DCI includes a UL grant and the UE transmits a PUSCH transmission to the RAN on the new serving cell in accordance with the UL grant.

[0218] Fig. 6A is a flow diagram of an example method 600A generally similar to the method 500, except that the method 600A includes blocks 672 and 676 instead of blocks 564, 566, 536 and 568. At block 672, the UE detects that the timer expires before the UE successfully completes the LTM cell switch. Because the timer expires, the UE determines failure of the LTM cell switch (i.e., LTM cell switch failure). At block 676, the UE initiates an RRC connection reestablishment procedure to recover the LTM cell switch failure using the first UE ID, in response to expiry (or “expiration”) of the timer. Although the UE applies the first LTM candidate configuration to perform the LTM cell switch execution, the UE uses the first UE ID to perform the RRC connection reestablishment procedure instead of the second UE ID.

[0219] At least some of the example implementations and other details discussed with reference to Fig. 5 can also apply to Fig. 6A. Example implementation of the RRC connection reestablishment procedure is described below.

[0220] In some implementations, the UE performs a cell selection after (e.g., in response to) initiating the RRC connection reestablishment procedure. The UE cancan select a cell (i.e., target cell) in the cell selection. In some implementations, the UE generates a message authentication code for integrity (MAC-I) based on an integrity algorithm, the first UE ID, acell ID of the selected cell and / or a PCI of the first serving cell. In some implementations, the MAC-I is a short MAC-I. In some implementations, a security configuration included in the multiple configurations is for the integrity algorithm. The UE generates an RRC reestablishment request message including the MAC-I, the first UE ID, and / or the PCI of the first serving cell, and transmits the RRC reestablishment request message to the RAN via the selected cell. In response, the UE cancan receive an RRC reestablishment message from the RAN via the selected cell and transmit an RRC reestablishment complete message to the RAN via the selected cell.

[0221] In some implementations, a base station (e.g., base station 104) of the RAN (e.g., the RAN 105) operates the first serving cell and the target cell. In such cases, the base station receives the RRC reestablishment request message and verifies whether the MAC-I is valid based on an integrity algorithm (e.g., the same as the integrity algorithm used by the UE to generate the MAC-I), the first UE ID, the PCI of the first serving cell and / or the cell ID of the target cell. In cases where the base station confirms the MAC-I is valid, the base station transmits the RRC reestablishment message to the UE via the target cell and receives the RRC reestablishment complete message from the UE via the target cell. After transmitting the RRC reestablishment message to the UE or receiving the RRC reestablishment complete message, the base station performs an RRC reconfiguration procedure with the UE. To perform the RRC reconfiguration procedure, the base station transmits an RRC reconfiguration message including a second plurality of configurations to the UE via the target cell. In response, the UE transmits an RRC reconfiguration complete message to the base station via the target cell. In some implementations, the base station generates the second set of configurations to augment at least a portion of the current configurations, and the UE augments the at least a portion of the current configurations with the second set of configurations. In such cases, the UE and the RAN communicate with each other in the target cell in accordance with the un-augmented portion of the current configurations, the augmented portion of the current configurations, and / or additional configurations of the second set of configurations (if one exists). In other implementations, the base station generates the second set of configurations to replace the current configurations, and the UE applies the second of configurations and releases or discards the current configurations. In such cases, the UE and the RAN communicate with each other on the target cell in accordance with the second configurations.

[0222] In some implementations, the second configurations include a cell group configuration, a radio bearer configuration, a measurement configuration and / or a security configuration. In other implementations, the second plurality of configurations include a cell group configuration, one or more radio bearer configurations, one or more measurement configurations, and / or one or more security configurations. In some implementations, the cell group configuration includes physical layer configurations, MAC layer configurations and / or RLC layer configurations.

[0223] In cases where the base station determines that the MAC -I is invalid, the base station cancan transmit an RRC reject message or an RRC setup message to the UE via the target cell instead of the RRC reestablishment message.

[0224] In other implementations, a first base station (i.e., source base station 104) of the RAN operates the first serving cell, and a second base station (i.e., target base station 106) of the RAN operates the target cell. The second base station retrieves the MAC-I, the first UE ID, and / or the PCI of the first serving cell from the RRC reestablishment request message and transmits a Retrieve UE Context Request message including the MAC-I, the MAC-I, the first UE ID, and / or the PCI of the first serving cell to the first base station. The first base station determines whether the MAC-I is valid based on an integrity algorithm (e.g., the same as the integrity algorithm used by the UE to generate the MAC-I), the first UE ID, the PCI of the first serving cell and / or the cell ID of the target cell. In cases where the first base station confirms the MAC-I is valid, the first base station transmits a Retrieve UE Context Response message to the second base station. In some implementations, the Retrieve UE Context Response message includes a UE context of the UE. In one implementation, the UE context includes some of the configurations. Upon receiving the Retrieve UE Context Response message, the second base station transmits the RRC reestablishment message to the UE via the target cell and receives the RRC reestablishment complete message from the UE via the target cell. After transmitting the RRC reestablishment message to the UE or receiving the RRC reestablishment complete message, the second base station performs an RRC reconfiguration procedure with the UE as described above.

[0225] In cases where the first base station verifies the MAC-I is invalid, the first base station can transmit a Retrieve UE Context Failure message to the second base station. Upon receiving the Retrieve UE Context Failure message, the second base station transmits the RRC reject message or the RRC setup message to the UE via the target cell.

[0226] Fig. 6B is a flow diagram of an example method 600B similar to the method 600A, except that the method 600B includes blocks 661 and 677 instead of blocks 672 and 676. At block 661, the UE releases the first UE ID and the configurations in response to initiating the LTM cell switch execution. At block 677, the UE initiates an RRC connection reestablishment procedure to recover the LTM cell switch failure using the second UE ID, in response to expiry of the timer.

[0227] In some implementations, the UE releases 661 the first UE ID and the configurations by discarding or deleting the first UE ID and the configurations. In one implementation, if the first UE ID and / or the configurations are not included in an LTM candidate configuration, the UE releases, deletes or discards the configurations. In other alternative implementations, the UE retains the first UE ID and the configurations and stops using the configurations after (e.g., in response to) initiating the LTM cell switch execution, instead of releasing 661 the first UE ID and the plurality of configurations. In one implementation, if the first UE ID and the configurations are included in an LTM candidate configuration, the UE retains the first UE ID and the configurations and stops using the first UE ID and the plurality of configurations after (e.g., in response to) initiating the LTM cell switch execution.

[0228] Unlike the method of Fig. 6A, here the UE generates a MAC-I value based on an integrity algorithm, the second UE ID, the cell ID of the selected cell and / or the PCI of the first serving cell. The UE generates an RRC reestablishment request message including the MAC-I, the UE ID and / or the PCI of the first serving cell and transmits the RRC reestablishment request message to the RAN via the selected cell. In some implementations, a security configuration in the first LTM candidate configuration configures the integrity algorithm. At least some of the example implementations and other details discussed with reference to Fig. 6A can apply to Fig. 6B, except that for the RRC connection reestablishment procedure, the first UE ID is replaced with the second UE ID.

[0229] Fig. 6C is a flow diagram of an example method 600C similar to the method 600A, except that the method 600C includes blocks 618, 682, 684, 656, 632, 660, 662 and 673. Before the UE receives the LTM command at block 530, the UE receives a third LTM candidate configuration from the RAN, where the third LTM candidate configuration configures a third candidate cell and a third UE ID at block 618. At block 682, the UE performs a cell selection procedure in response to expiry of the timer. At block 684, the UEselects the third candidate cell in the cell selection procedure. At block 656, the UE initiates an additional LTM cell switch execution to switch to the third candidate cell in response to selecting the third candidate cell. At block 632, the UE applies the third LTM candidate configuration and access the third candidate cell in response to initiating the additional LTM cell switch execution. At block 660, the UE starts the timer in response to initiating the additional LTM cell switch execution. At block 662, the UE retains the first UE ID and the plurality of configurations after (e.g., in response to) initiating the additional LTM cell switch execution. At block 673, the UE detects expiry of the timer for the additional LTM cell switch execution.

[0230] Fig. 7 is a flow diagram illustrating an example method 700 similar to the method 500, except that the method 700 includes blocks 781, 782, 784 and 756 instead of blocks 530 and 556. At block 781, the UE detects a radio link failure while communicating with the RAN via the first serving cell. At block 782, the UE performs a cell selection procedure in response to the radio link failure. At block 784, the UE selects the first candidate cell in the cell selection procedure. At block 756, the UE initiates an LTM cell switch execution to switch to the first candidate cell in response to selecting the first candidate cell.

[0231] At least some of the discussion of the examples and implementations in connection with Fig. 5 also can apply to Fig. 7.

[0232] Fig. 8A is a flow diagram illustrating an example method 800A that combines blocks from Figs. 5, 6A and 7 (thus, blocks 872, 874 and 876 are similar to blocks 672, 674, and 676, respectively). At least some of the discussion of the examples and implementations in connection with Figs. 5, 6A, and 7 also can apply to Fig. 8A.

[0233] Fig. 8B is a flow diagram illustrating an example method 800B that combines blocks from Figs. 5, 6B and 7 (thus, blocks 861, 871, 872, and 877 are similar to blocks 661, 671, 672, and 677, respectively). At least some of the discussion of the examples and implementations in connection with Figs. 5, 6B, and 7 also can apply to Fig. 8B.

[0234] Fig. 9 is a flow diagram illustrating an example method 900 for managing a reconfiguration with sync procedure, which can be implemented by a UE (e.g., the UE 102). The method 900 begins at block 902. At block 986, the UE performs a reconfiguration with sync procedure while communicating with the RAN via the first serving cell. At block 962, the UE starts a timer in response to performing the reconfiguration with sync procedure. The flow proceeds to block 972 from block 962 and then proceeds to block 979 from block 972.At block 979, the UE determines whether the UE performed the reconfiguration with sync procedure for an LTM cell switch. If the UE performed the reconfiguration with sync procedure not for an LTM cell switch (i.e., No branch of block 979), the flow proceeds to block 974 and block 976. At block 974, the UE reverts back to the plurality of configurations in response to expiry of the timer. At block 976, the UE initiates an RRC connection reestablishment procedure in response to expiry of the timer.

[0235] Fig. 10 is a flow diagram illustrating an example method 1000 for managing an LTM switch execution, which can be implemented by a RAN (e.g., the RAN 105 or the base station 104 or 106). The method 1000 begins at block 1002, where the RAN communicates with a UE via a first serving cell using a plurality of configurations (i.e., current configurations). In some implementations, the plurality of configurations includes a first UE identifier (ID) for the UE to communicate with the RAN on the first serving cell. In some implementations, the first UE ID is a first C-RNTI. The UE uses the first C-RNTI to monitor a PDCCH on the first serving cell. For example, the RAN transmits a DCI and a CRC of the DCI on a PDCCH to the UE using the first C-RNTI. In some implementations, the DCI includes a DL assignment and the RAN transmits a PDSCH transmission to the UE on the first serving cell in accordance with the DL assignment. In other implementations, the DCI includes a UL grant and the RAN receives a PUSCH transmission from the UE on the first serving cell in accordance with the UL grant.

[0236] At block 1018, the RAN transmits a first LTM candidate configuration to the UE, where the first LTM candidate configuration configures a first candidate cell (e.g., events 316, 318, 394, 494). At block 1030, the RAN transmits an LTM command to the UE via the first serving cell, where the LTM command commands the UE to perform an LTM cell switch to the first candidate cell. In cases where the RAN communicates with the UE on the first serving cell and a second serving cell, the RAN cancan transmit the LTM command via the second serving cell instead of the first serving cell.

[0237] At block 1060, the RAN retains the plurality of configurations after (e.g., in response to) transmitting the LTM command. At block 1057, the RAN applies the first LTM candidate configuration after transmitting the LTM command. At block 1032, the RAN detects that the UE accesses the first candidate cell after transmitting the LTM command (e.g., events 332, 432). At block 1036, the RAN communicates with the UE via the first candidate cell using configurations (i.e., current configurations) in the first LTM candidateconfiguration (e.g., events 336, 436). At block 1068, the RAN releases the plurality of configurations after detecting that the UE accesses the first candidate cell or communicating with the UE via the first candidate cell.

[0238] In some implementations, the RAN is the RAN described in connection with Fig. 5. At least some of the example implementations discussed with reference to Fig. 5 can apply to Fig. 10.

[0239] Fig. 11 A is a flow diagram illustrating an example method 1100A similar to the method 1000, except that the method 1100A includes block 1176 instead of blocks 1032, 1036 and 1068. At block 1076, the RAN performs an RRC connection reestablishment procedure with the UE using at least one of the plurality of configurations. In some implementations, the RAN is the RAN described in connection with Figs. 5 and 6A. At least some of the example implementations and other details discussed with reference to Figs. 5 and 6A can also apply to Fig. 11 A.

[0240] Fig. 1 IB is a flow diagram illustrating an example method 1100B similar to the method 1100A, except that the method 1100B includes blocks 1161 and 1177 instead of blocks 1060 and 1176. At block 1161, the RAN releases the first plurality of configurations in response to initiating the LTM cell switch. At block 1177, the RAN performs an RRC connection reestablishment procedure with the UE using at least one configuration in the first LTM cell switch. In some implementations, the RAN is the RAN described in connection with Figs. 5 and 6B. At least some of the example implementations and other details discussed with reference to Figs. 5 and 6B can also apply to Fig. 1 IB.

[0241] In some implementations, the RAN releases the plurality of configurations by discarding or deleting the plurality of configurations. In one implementation, if the plurality of configurations are not included in an LTM candidate configuration, the RAN releases, deletes or discards the plurality of configurations. In other alternative implementations, the RAN retains the plurality of configurations and stops using the plurality of configurations after (e.g., in response to) initiating the LTM cell switch, instead of releasing 1161 the plurality of configurations. In one implementation, if the plurality of configurations are included in an LTM candidate configuration (e.g., a second LTM candidate configuration), the RAN retains the plurality of configurations and stops using the plurality of configurations after (e.g., in response to) initiating the LTM cell switch.

[0242] Fig. 12 is a flow diagram illustrating an example method 1200 similar to the method 1000, except that the method 1200 includes blocks 1232 and 1259 instead of block 1057 and 1032. At block 1232, the RAN detects that the UE accesses the first candidate cell after transmitting the first LTM candidate configuration. At block 1259, the RAN applies configurations in the first LTM candidate configuration after detecting that the UE accessed the first candidate cell. Because the RAN has not applied the LTM candidate configuration before detecting that the UE accesses the first candidate cell, the RAN considers the plurality of configurations as the current configurations. Thus, when the RAN receives an RRC reestablishment request from the UE, the RAN uses at least one of the plurality of configurations to identify the UE and perform an RRC connection reestablishment procedure with the UE as described in connection Fig. 5. At least some of the example implementations and other details discussed with reference to Fig. 10 can apply to Fig. 12.

[0243] In some implementations, the RAN detects 1232 the UE as block 1032. In other implementations, the RAN detects 1232 the UE because the UE detects a radio link failure and initiates an LTM cell switch execution as described with reference to Fig. 7.

[0244] Fig. 13A is a flow diagram illustrating an example method 1300A for managing an LTM execution, which can be implemented by a CU (e.g., the CU 172). The method 1300A begins at block 1301, where the CU receives a first DU-to-CU message including a first UE ID (e.g., a first C-RNTI). At block 1302, the CU communicates with a UE via first DU and a first serving cell, using a plurality of configurations (i.e., current configurations). At block 1310, the CU receives a second DU-to-CU message including a second UE ID (e.g., a second C-RNTI) for the UE from a second DU. At block 1316, the CU transmits a first LTM candidate configuration to the UE, where the first LTM candidate configuration configures a first candidate cell. At block 1329, the CU receives a third DU-to-CU message from the first DU, notifying initiation of an LTM cell switch to the first candidate cell for the UE. At block 1360, the CU retains the plurality of configurations and the first UE ID, after (e.g., in response to) receiving the third DU-to-CU message. At block 1334, the CU receives a fourth DU-to-CU message from the second DU, notifying that the UE has successfully accessed the first candidate cell. At block 1336, the CU communicates with the UE via the second DU and the first candidate cell using configurations in the first LTM candidate configuration. At block 1368, the CU releases the plurality of configurations and the first UE ID in response to receiving the fourth DU-to-CU message.

[0245] In some implementations, the first DU and the second DU are the same DU. In other implementations, the first DU and the second DU are different DUs. In some implementations, the CU releases the plurality of configurations and the first UE ID by discarding or deleting the plurality of configurations and the first UE ID. In one implementation, if the plurality of configurations and the first UE ID are not included in an LTM candidate configuration, the CU releases, deletes or discards the plurality of configurations. In other alternative implementations, the CU retains the plurality of configurations and the first UE ID and stops using the plurality of configurations and the first UE ID after (e.g., in response to) receiving the fourth DU-to-CU message, instead of releasing 1368 the plurality of configurations. In one implementation, if the plurality of configurations and the first UE ID are included in an LTM candidate configuration (e.g., a second LTM candidate configuration), the CU retains the plurality of configurations and the first UE ID and stops using the plurality of configurations and the first UE ID after (e.g., in response to) receiving the fourth DU-to-CU message.

[0246] As described above, the CU retains the plurality of configurations and the first UE ID before receiving the fourth DU-to-CU message. In cases where the CU receives an RRC reestablishment request message including a MAC-I, the first UE ID and / or the PCI of the first serving cell before receiving the fourth DU-to-CU message as described above, the CU verifies whether the MAC-I is valid based on an integrity algorithm, the first UE ID, the PCI of the first serving cell and / or the cell ID of the target cell as described above and in Fig.14 A.

[0247] Fig. 13B is a flow diagram illustrating an example method BOOB similar to the method 1300 A, except that the method BOOB includes block 1369 instead of blocks 1360 and 1368. At block 1369, the CU releases the plurality of configurations and the first UE ID in response to receiving the third DU-to-CU message.

[0248] In some implementations, the CU releases the plurality of configurations by discarding or deleting the plurality of configurations. In one implementation, if the plurality of configurations are not included in an LTM candidate configuration, the CU releases, deletes or discards the plurality of configurations. In other alternative implementations, the CU retains the plurality of configurations and stops using the plurality of configurations after (e.g., in response to) receiving the third DU-to-CU message, instead of releasing 1369 the plurality of configurations. In one implementation, if the plurality of configurations areincluded in an LTM candidate configuration (e.g., a second LTM candidate configuration), the CU retains the plurality of configurations and stops using the plurality of configurations after (e.g., in response to) receiving the third DU-to-CU message.

[0249] Fig. 14A is a flow diagram illustrating an example method 1400A similar to the method 1300A, except that the method 1400 A includes blocks 1481A, 1483 A, 1485A and 1487A instead of blocks 1334, 1336 and 1368. At block 1481A, the CU receives an RRC reestablishment request message that includes the first UE ID and a MAC-I. At block 1483 A, the CU determines whether the MAC-I is valid based on the first UE ID. If the CU determines that the MAC-I is valid based on the first UE ID, the CU transmits an RRC reestablishment message to the UE at block 1485A. Otherwise, if the CU determines that the MAC-I is invalid based on the first UE ID, the CU transmits an RRC reject message to the UE at block 1487A. Alternatively, if the CU determines that the MAC-I is invalid based on the first UE ID, the CU transmits an RRC setup message to the UE. In some implementations, the CU communicates the RRC reestablishment request message, the RRC reestablishment message, the RRC reject message and / or the RRC setup message via the first DU, the second DU or a third DU.

[0250] Examples and implementations about generating and verifying MAC-I as described in connection with Figs. 5 and 6A can apply to Fig. 14A.

[0251] Fig. 14B is a flow diagram illustrating an example method 1400B similar to the method 1400A, except that the method 1400B includes blocks 1369, 1481B, and 1483B instead of blocks 1360, 1481A, and 1483A. At block 1481B, the CU receives an RRC reestablishment request message that includes the second UE ID and a MAC-I. At block 1483B, the CU determines whether the MAC-I is valid based on the second UE ID. If the CU determines that the MAC-I is valid based on the second UE ID, the CU transmits an RRC reestablishment message to the UE at block 1485A. Otherwise, if the CU determines that the MAC-I is invalid based on the second UE ID, the CU transmits an RRC reject message to the UE at block 1487A. Alternatively, if the CU determines that the MAC-I is invalid based on the second UE ID, the CU transmits an RRC setup message to the UE.

[0252] Examples and implementations about generating and verifying MAC-I as described in connection with Figs. 5 and 6B can apply to Fig. 14B.

[0253] Fig. 14C is a flow diagram illustrating an example method 1400C similar to the method 1400A, except that the method 1400C includes blocks 1481C, 1485C and 1487Cinstead of blocks 1481 A, 1485A and 1487A. At block 1481C, the CU receives a Retrieve UE Context Request message from a RAN node (e.g., a base station or another CU), including the first UE ID and a MAC-I. If the CU determines that the MAC-I is valid based on the first UE ID, the CU transmits a Retrieve UE Context Response message to the RAN node at block 1485C. Otherwise, if the CU determines that the MAC-I is invalid based on the first UE ID, the CU transmits a Retrieve UE Context Failure message to the RAN node at block 1487C.

[0254] Examples and implementations for generating and verifying MAC-I as described with reference to Figs. 5 and 6A can apply to Fig. 14C.

[0255] Fig. 14D is a flow diagram illustrating an example method MOOD similar to the methods 1400B and 1400C, except that the method MOOD includes blocks 148 ID instead of blocks 1481C. At block 1481D, the CU receives a Retrieve UE Context Request message from a RAN node (e.g., a base station or another CU), including the second UE ID and a MAC-I. If the CU determines that the MAC-I is valid based on the first UE ID, the CU transmits a Retrieve UE Context Response message to the RAN node at block 1485C. Otherwise, if the CU determines that the MAC-I is invalid based on the first UE ID, the CU transmits a Retrieve UE Context Failure message to the RAN node at block 1487C.

[0256] At least some of the example implementations and other details related to generating and verifying MAC-I, as described with reference to Figs. 5 and 6B, can also apply to Fig. 14D.

[0257] The following list of examples reflects a variety of the embodiments explicitly contemplated by the present disclosure.

[0258] Example 1. A configuration management method implemented in a user equipment(UE), the method comprising: communicating with a radio access network (RAN) via a serving cell using a first configuration; receiving, via the serving cell, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell; initiating an LTM cell switch procedure, including applying the LTM candidate configuration to access the candidate cell; and performing one of: in response to determining that the UE successfully connected to the candidate cell, releasing the first configuration, or subsequently to determining that the UE failed to connect to the candidate cell, performing a connection reestablishment using the first configuration or the LTM candidate configuration.

[0259] Example 2. The method of example 1, wherein: the first configuration includes a first UE identity; and the LTM candidate configuration includes a second UE identity.

[0260] Example 3. The method of example 2, wherein each of the first UE identity and the second UE identity is a respective cell Radio Network Temporary Identifier (C-RNTI).

[0261] Example 4. The method of example 2 or 3, further comprising: retaining the first configuration subsequent to the initiating of the LTM switch procedure; and performing the connection reestablishment using the first UE identity.

[0262] Example 5. The method of example 4, wherein: the candidate cell is a first candidate cell; the method further comprising: subsequently to the determining that the UE failed to connect to the candidate cell, initiating a second LTM cell switch procedure to a second candidate cell; and retaining the first configuration subsequent to the initiating of the second LTM switch procedure.

[0263] Example 6. The method of example 4, further comprising: subsequently to the determining that the UE failed to connect to the candidate cell, using the first configuration as a current configuration for initiating the connection reestablishment.

[0264] Example 7. The method of example 1 or 2, further comprising: releasing the first configuration in response to the initiating of the LTM cell switch procedure; and performing the connection reestablishment using the second UE identity.

[0265] Example 8. The method of example 7, further comprising: subsequent to the releasing of the first configuration, using the LTM candidate configuration as a current configuration for initiating the connection reestablishment.

[0266] Example 9. The method of any of examples 4-8, further comprising: determining that the UE failed a reconfiguration with sync procedure; and performing the connection reestablishment procedure in response to determining that the failed reconfiguration procedure was associated with the LTM cell switch procedure.

[0267] Example 10. The method of any of the preceding examples, further comprising: receiving, from the RAN, a command to initiate the LTM cell switch procedure.

[0268] Example 11. The method of any of examples 1-9, further comprising: detecting a radio link failure (RLF) during the communicating in the serving cell; and wherein the initiating of the LTM cell switch procedure in response to the detecting of the RLF.

[0269] Example 12. The method of any of examples 1-3 or 9-11, wherein the determining that the UE successfully connected to the candidate cell includes: successfully completing a random access procedure on the target cell.

[0270] Example 13. The method of any of examples 1-3 or 9-11, wherein the determining that the UE successfully connected to the target cell includes: transmitting an uplink transmission on a Physical Uplink Shared Channel (PUSCH) or a Physical Uplink Control Channel (PUCCH) of the target cell using a timing advance (TA) value received from the RAN, including omitting a random access procedure; and receiving a downlink transmission on a Physical Downlink Control Channel (PDCCH) of the target cell, subsequent to the transmitting of the uplink transmission.

[0271] Example 14. The method of any of examples 1-3 or 9-13, further comprising: starting a timer in response to the initiating an LTM cell switch procedure, and stopping the timer in response to the determining that the UE successfully connected to the target cell.

[0272] Example 15. The method of example 14, wherein the timer is a medium access control (MAC) timer.

[0273] Example 16. The method of example 14, wherein the timer is a radio resource control (RRC) timer.

[0274] Example 17. The method of example 14, wherein the timer is a T304 timer.

[0275] Example 18. The method of any of the preceding examples, wherein the first configuration includes one or more of: a cell group configuration, a radio bearer configuration, a measurement configuration, or a security configuration.

[0276] 19. A configuration management method implemented in a radio access network(RAN), the method comprising: communicating with a user equipment (UE) via a serving cell using a first configuration for the UE; transmitting, to the UE via the serving cell, a low- layer triggered mobility (LTM) candidate configuration for a candidate cell; and performing one of: subsequently to the UE initiating an LTM switch cell switch procedure, releasing the first configuration, or performing a connection reestablishment with the UE using the first configuration or the LTM candidate configuration.

[0277] 20. The method of example 19, further comprising: transmitting, to the UE via the serving cell, an LTM command for initiating an LTM cell switch procedure.

[0278] Example 21. The method of example 19 or 20, wherein: the releasing of the first configuration is in response to determining that the UE successfully connected to the candidate cell.

[0279] Example 22. The method of example 19 or 20, wherein: the releasing of the first configuration is in response to determining that the UE initiated the LTM switch cell switch procedure, prior to determining that the UE successfully connected to the candidate cell.

[0280] Example 23. The method of example 19 implemented in a central unit (CU) of a distributed base station, the method comprising: receiving, from a distributed unit (DU), an indication that the UE successfully connected to the candidate cell; wherein the releasing of the first configuration is in response to the indication from the DU.

[0281] Example 24. The method of example 23, wherein: the serving cell and the candidate cell are associated with different respective DUs.

[0282] Example 25. The method of any of examples 19-24, wherein: the first configuration includes a first UE identity; and the LTM candidate configuration includes a second UE identity.

[0283] Example 26. The method of example 25, wherein each of the first UE identity and the second UE identity is a respective cell Radio Network Temporary Identifier (C-RNTI).

[0284] Example 27. An apparatus comprising processing hardware and configured to implement a method of any of the preceding examples.

[0285] The following description may be applied to the description above.

[0286] Generally speaking, description for one of the above figures can apply to another of the above figures. Examples, implementations and methods described above can be combined, if there is no conflict. An event or block described above can be optional or omitted. For example, an event or block with dashed lines in the figures can be optional. The description described from the perspective of the receiving node also applies to the sending node. For example, a description that a receiving node (e.g., DU) receives a message from a sending node (e.g., CU) may be replaced by the sending node sending a message to the receiving node. Similarly, a description that a receiving node (e.g., CU) receives a message from a sending node (e.g., DU) may be replaced by the sending node sending a message to the receiving node.

[0287] In some implementations, “message” is used and can be replaced by “information element (IE)”, and vice versa. In some implementations, “IE” is used and can be replaced by “field”, and vice versa. In some implementations, “configuration” can be replaced by “configurations” or “configuration parameters”, and vice versa. In some implementations,the “LTM command” can be replaced by “serving cell change command”, “Layer 1 / Layer 2 LTM cell switch command”, “lower layer switching command” or “lower layer serving cell change command”. In some implementations, “some” means “one or more”. In some implementations, “at least one” means “one or more”. In some implementations, the “DU configuration” can be replaced by “cell group configuration”. In some implementations, the “cell index” can be replaced with “serving cell index”, “LTM cell index”, “special cell (SpCell) index”, “PCell index” or “PSCell index”. In some implementations, the “serving” can be replaced by “source”. In some implementations, the “measurement report” can be replaced by “measurement result(s)” or “CSI report”. In some implementations, the “early TA acquisition” can be replaced by “early UL timing synchronization” or “early UL synchronization”. In some implementations, the “early TA acquisition on a / the candidate cell” can be replaced by “early UL timing synchronization with a / the candidate cell” or “early UL synchronization with a / the candidate cell”.

[0288] A user device in which the techniques of this disclosure can be implemented (e.g., the UE 102) can be any suitable device capable of wireless communications such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media-streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an internet-of-things (loT) device or a mobile-internet device (MID). Depending on the type, the user device can include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0289] Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules may can be software modules (e.g., code, or machine- readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module can comprise dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g., asencompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

[0290] The term “or” as used herein is to be interpreted as an inclusive or meaning any one or any combination, unless expressly indicated otherwise, mutually exclusive, or indicated otherwise by context. Therefore, herein, the expression “A or B” means “A, B, or both A and B.”

[0291] When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software can be executed by one or more general-purpose processors or one or more special-purpose processors.

[0292] Upon reading this disclosure, those of skill in the art will appreciate still additional and alternative structural and functional designs for handling mobility between base stations through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

Claims

What is claimed is:

1. A configuration management method implemented in a user equipment (UE), the method comprising: communicating with a radio access network (RAN) via a serving cell, using a first UE identity (ID); initiating a lower-layer triggered mobility (LTM) cell switch procedure using an LTM candidate configuration that includes a second UE ID, to access a candidate cell; and in response to expiration of a timer associated with the LTM cell switch procedure, initiating a connection reestablishment procedure with the RAN, using the first UE ID.

2. The method of claim 1, wherein each of the first UE ID and the second UE ID is a respective cell Radio Network Temporary Identifier (C-RNTI).

3. The method of claim 1 or 2, further comprising: starting the timer in response to the initiating an LTM cell switch procedure, wherein stopping of the timer occurs in response to the UE successfully connecting to the candidate cell.

4. The method of claim 3, wherein the timer is a T304 timer.

5. The method of claim 3, wherein the timer is a radio resource control (RRC) timer.

6. The method of any of the preceding claims, further comprising: retaining, subsequent to the initiating of the LTM switch procedure, a configuration that includes the first UE ID.

7. The method of claim 6, wherein: the configuration that includes the first UE ID includes a radio bearer configuration.

8. The method of any of the preceding claims, further comprising: receiving, from the RAN, a command to initiate the LTM cell switch procedure;wherein the initiating of the LTM cell switch procedure is in response to the receiving of the command.

9. The method of any of the preceding claims, further comprising: retaining, subsequent to the initiating of the LTM switch procedure, a security configuration.

10. The method of any of claims 1-8, further comprising: detecting a radio link failure (RLF) during the communicating in the serving cell; wherein the initiating of the LTM cell switch procedure is in response to the detecting of the RLF.

11. A configuration management method implemented in a radio access network (RAN), the method comprising: communicating with a user equipment (UE) via a serving cell using a first UE identity (ID); transmitting, to the UE via the serving cell, a command to initiate a lower-layer triggered mobility (LTM) cell switch procedure using an LTM candidate configuration that includes a second UE ID, to access a candidate cell; and performing a connection reestablishment with the UE, using the first UE identity.

12. The method of claim 11, further comprising: transmitting, to the UE, the LTM candidate configuration.

13. The method of claim 11 or 12, wherein each of the first UE ID and the second UE ID is a respective cell Radio Network Temporary Identifier (C-RNTI).

14. The method of any of claims 11-13, wherein: a configuration that includes the first UE ID also includes a radio bearer configuration.

15. An apparatus comprising: processing hardware; and a transceiver; the apparatus configured to implement a method of any of the preceding claims.

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