Configuring measurements for inter-central unit lower layer triggered mobility

Abstract

This disclosure provides systems, devices, apparatus, and methods, including computer programs encoded on storage media, for configuring measurements for inter-central unit lower layer triggered mobility. A RAN node (104) transmits, to a candidate RAN node (106), a handover request message. The RAN node receives, from the candidate RAN node (106) in response to the handover request message, a handover request acknowledgement message indicating a LTM candidate cell configuration. The RAN node receives a reference signal resource configuration associated with a LTM candidate cell. The RAN node transmits, to a UE (102), a CSI report configuration, the reference signal resource configuration, and the LTM candidate cell configuration.

Description

CONFIGURING MEASUREMENTS FOR INTER-CENTRAL UNIT LOWERLAYER TRIGGERED MOBILITYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 562.982, filed 8 March 2024 the disclosure of which is incorporated herein by reference in its entirety.FIELD OF THE DISCLOSURE

[0002] This disclosure relates to wireless communications and, more particularly, to configuring lower-layer measurement (e.g., Layer 1 measuremenet) for inter-central unit lower layer triggered mobility.SUMMARY

[0003] This 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 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 ty pes of SRBs and DRBs. When operating in dual connectivity (DC), the cells associated with the base station operating the master node (MN) define a master cell group (MCG), and the cells associated with the base station operating as the secondary node (SN) define the secondary cell group (SCG). So-called SRB1 resources carry RRC messages, which in some cases include NAS messages over the dedicated control channel(DCCH), and SRB2 resources support RRC messages that include logged measurement information or NAS messages, also over the DCCH but with lower priority’ than SRB1 resources. More generally, SRB1 and SRB2 resources allow the UE and the MN to exchange RRC messages related to the MN and embed RRC messages related to the SN, and also can be referred to as MCG SRBs. SRB3 resources allow the UE and the SN to exchange RRC messages related to the SN, and can be referred to as SCG SRBs. Split SRBs allow the UE to exchange RRC messages directly with the MN via lower lay er 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 can concurrently utilize resources of multiple radio access network (RAN) nodes (e.g., base stations or components of a distributed base station), interconnected by a backhaul. When these network nodes support different radio access technologies (RATs), this type of connectivity is referred to as Multi-Radio Dual Connectivity (MR-DC). When a UE operates in MR-DC. one base station operates as a master node (MN) that covers a primary7cell (PCell), and the other base station operates as a secondary7node (SN) that covers a primary7secondary7cell (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, at some point a serving cell change has to be performed 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 a RRC reconfiguration message configuring Reconfiguration with Synchronization (e.g., the RRC reconfiguration message includes a ReconfigurationWithSync information element (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 involves complete L2 (and LI) resets, leading to longer latency, larger overhead and longer interruption time.

[0008] While a base station of the RAN communicates with the UE via a serving cell, the base station receives one or more layer 3 (e.g., RRC) measurement results from the UE. Thebase station consists of a central unit (CU) and one or more distributed units (DUs). One of the DU(s) operating the serving cell is a serving DU. Based on the layer 3 (L3) measurement result(s), the base station determines to configure a LTM candidate cell for LTM cell switch. To configure the LTM candidate cell for the UE, the base station transmits a LTM candidate configuration configuring the LTM candidate cell to the UE via RRC signaling. Later on, the base station receives one or more layer 1 (LI) measurement results from the UE. Based on the one or more L I measurement result(s). the base station determines that the LTM candidate cell qualifies to be a serving cell for the UE. Therefore, the base station transmits a LTM cell switch command to the UE to command the UE to perform the LTM cell switch to the LTM candidate cell. The UE performs a cell change from the serving cell to the LTM candidate cell in response to the LTM cell switch command. If the LTM candidate cell is operated by the serving DU. the LTM cell switch is an intra-CU intra-DU LTM cell switch. If the LTM candidate cell is operated by a candidate DU in the DU(s), the LTM cell switch is an intra-CU inter-DU LTM cell switch. 3GPP has enabled the intra-CU intra-DU LTM cell switch and intra-CU inter-DU LTN cell switch in Release 18 specifications. However, 3GPP has not specified inter-CU LTM cell switch yet.

[0009] In some aspects, a RAN node transmits, to a candidate RAN node, a handover request message. The RAN node receives, from the candidate RAN node in response to the handover request message, a handover request acknowledgement message indicating a LTM candidate cell configuration. The RAN node receives a reference signal resource configuration associated with a LTM candidate cell. The RAN node transmits, to a UE, a CSI report configuration, the reference signal resource configuration, and the LTM configuration.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1A is a block diagram of an example system in which a radio access network (RAN) and a UE can implement the techniques of this disclosure for managing conditional procedures related to a secondary node (SN) according to some embodiments.

[0011] 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. 1A according to some embodiments.

[0012] Fig. 2A is a block diagram of an example protocol stack according to which the UE of Fig. 1A communicates with base stations according to some embodiments.

[0013] Fig. 2B is a block diagram of an example protocol stack according to which the UE of Fig. 1A communicates with a CU and a DU according to some embodiments.

[0014] Figs. 3-5 are signal flow diagrams for configuring measurements for inter-CU LTM according to some embodiments.

[0015] Figs. 6A, 6B, 7 A, 7B, 8, 9, 10A, 10B, 11, and 12 illustrate flowcharts of methods for configuring measurements for inter-CU LTM according to some embodiments.DETAILED DESCRIPTION

[0016] Fig. 1A depicts an example wireless communication system 100 in which communication devices can implement these techniques. The wireless communication system 100 includes a UE 102, a base station (BS) 104, a base station 106 and a core network (CN) 110. The UE 102 initially connects to the base station 104. In some scenarios, the base station 104 can perform an SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104 and the base station 106. The base stations 104 and 106 operate as an MN and an SN for the UE 102, respectively.

[0017] In various configurations of the wireless communication system 100, the base station 104 can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station 106 can be implemented as a secondary gNB (SgNB). The UE 102 can communicate with the base station 104 and the base station 106 via the same RAT such as EUTRA or NR, or different RATs. When the base station 104 is an MeNB and the base station 106 is a SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0018] 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.

[0019] In the scenarios where the UE 102 hands over from the base station 104 to the base station 106, the base stations 104 and 106 operate as the source base station (S-BS) and a target base station (T-BS), respectively. The UE 102 can operate in DC with the base station 104 and an additional base station (not shown in Fig. 1A) for example prior to the handover. The UE 102 can continue to operate in DC with the base station 106 and the additional base station or operate in single connectivity (SC) with the base station 106, after completing 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.

[0020] A core network (CN) 110 can be an evolved packet core (EPC) 111 or a fifthgeneration core (5GC) 160, both of which are depicted in Fig. 1A. The base station 104 can be an eNB supporting an S 1 interface for communicating with the EPC 111 , an ng-eNB supporting an NG interface for communicating with the 5GC 160, or a gNB that supports an NR radio interface as well as an NG interface for communicating with the 5GC 160. To directly exchange messages with each other during the scenarios discussed below, the base stations 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 configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME 114 is configured to manage authentication, registration, paging, and other related functions. The PGW 116 provides connectivity from the UE to one or more external packet data networks, e.g., an Internet network and / or an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The 5GC 160 includes a User Plane Function (UPF) 162 and an Access and Mobility Management (AMF) 164, and / or Session Management Function (SMF) 166. The UPF 162 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF 164 is configured to manage authentication, registration, paging, and other related functions, and the SMF 166 is configured to manage PDU sessions.

[0021] 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 125 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 cell 126, and the base station 106 can support additional cell(s) (not shown in Fig. 1A). The cells 124A, and 125 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 and 125 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.

[0022] 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 disclosurealso can apply to other suitable radio access and / or core network technologies such as sixth generation (6G) radio access and / or 6G core network or 5G NR-6G DC.

[0023] 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 anon- transitory computer-readable memory7storing instructions that the one or more general-purpose processors execute. Additionally or alternatively, the processing hardware 130 can include special-purpose processing units. The processing hardware 130 can include a PHY controller 132 configured to transmit data and control signal on physical downlink (DL) channels and DL reference signals with one or more user devices (e.g. UE 102) via one or more cells (e.g., the cell(s) 124A and / or 125) 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 and / or 125) 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 mobility7(LTM) related functions as described below. The processing hardware 130 can further include an RRC controller 136 to implement procedures and messaging at the RRC sublayer of the protocol communication stack. For example, the RRC controller 136 may be configured to support RRC messaging associated with handover procedures, and / or to support the necessary operations when the base station 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.

[0024] The UE 102 is equipped with processing hardw are 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, 125 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, 125 and / or 126) and / or one or more TRPs. Theprocessing 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 include a random access procedure, managing UL timing advance for the one or more user devices, and communicating UL / DL MAC PDUs with the base station 104 or 106. In another example, the MAC functions includes LTM related functions as described below. The processing hardware 150 can further include an RRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack.

[0025] 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.

[0026] 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 hardw are 140. The processing hardw are 140 in an example implementation includes an SN RRC controller 146 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 174A is also equipped with processing hardw are 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 hardw are may include further a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0027] 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).

[0028] In the example stack 200, a physical layer (PHY) 202A of EUTRA provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logical channels to the EUTRA RLC sublayer 206 A. 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 206A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

[0029] 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.’'

[0030] On a control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide signaling radio bearers (SRBs) or RRC sublayer (not shown in Fig. 2A) to exchange RRC messages or non-access-stratum (NAS) messages, for example. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide Data Radio Bearers (DRBs) to support data exchange. Data exchanged on the NR PDCP sublayer 210 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0031] 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 of Fig. 2A 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.

[0032] Next, several example scenarios in which the base station operating in the system of Fig. 1A transmits a configuration to the UE 102 and later activates a configuration for communication between the UE 102 and base station. Generally speaking, events in Figs. 3-5 that are similar are labeled with similar reference numbers (e. g. , event 302 is similar to event 402 of Fig. 4 and event 502 of Fig. 5, event 390 is similar to event 490 of Fig. 4 and event 590 of Fig. 5), with differences discussed below where appropriate. With the exception of the differences shown in the figures and discussed below, any of the alternative implementations discussed with respect to a particular event (e.g., for messaging and processing) may apply to events labeled with similar reference numbers in other figures.

[0033] Referring first to Fig. 3, in a scenario 300, the base station 104 includes a CU 172 and DU 174 and the DU 174 operates the cell 124A. The UE 102 initially communicates 302 with the DU 174 on a serving cell (e.g., the cell 124A), using a serving DU configuration, and communicates with the CU 172 via the DU 174, using a serving CU configuration. The DU 174 is a serving or a source DU (S-DU) for the UE 102. In other words, the DU 174 is a serving DU (S-DU) that is communicating with the UE 102. In some implementations, the UE 102 in carrier aggregation (CA) mode communicates with the DU 174 on the cell 124A 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 124 A and / or the other cell(s) are serving cell(s) for the UE 102. In other implementations, the UE 102 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) (i.e., serving cell(s)) via one or multiple TRPs. In the following description, events 394, 324, 350, 352, 354, and 326 occur on the serving cell(s). In some implementations, the cell 124A can be a PCell. In such cases, the other cell(s) include SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In other implementations, the cell 124A can be a SCell, and one of the other cell(s) is a PCell. In such cases, the rest includes SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In the following description, the base station 104 can be the DU 174, the CU 172 or the DU 174 and CU 172.

[0034] 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 / or soundingreference 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.

[0035] 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 IE 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. The radio configuration parameters or the RadioBearerConfig IE configures one or more DRBs. In some implementations, the serving DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and reporting. In other implementations, the serving CU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and reporting. In some implementations, the UE 102 receives the serving CU configuration or the configuration parameters in the serving CU configuration from the CU 172 via the DU 174. In other implementations, the UE 102 receives a portion of the serving CU 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.

[0036] In some implementations, the DU 174 and the UE 102 communicate with each other using first non-LTM TCI state configuration(s), (e.g., in the events 302, 318, 320, 324,350, 354, and / or 326). In some implementations, the DU 174 transmits at least one first non-LTM TCI States Activation / Deactivation command (e.g., MAC control element (CE)) to the UE 102 to activate the first non-LTM TCI state configuration(s). The UE 102 activates the first non- LTM TCI state configuration(s) in response to the first non-LTM TCI States Activation / Deactivation command(s). In some implementations, the DU 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).

[0037] 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 measurement report(s) includes measurement results for a serving cell (e.g., the cell 124A) of the UE 102 and / or at least one non-serving cell. For each of the measurement report(s), the DU 174 transmits 306 a DU-to-CU message including the measurement report to the CU 172. In some implementations, the DU-to-CU message(s) of the event 306 is / are Fl application protocol (F1AP) message(s) (e.g.. UL RRC Message Transfer message(s)). The at least one serving cell includes the cell 124A and / or other cell(s), and the at least one non-serving cell includes the cell 125 and / or additional cell(s). In some implementations, the serving CU configuration includes at least one measurement configuration. In accordance with the measurement configuration(s), the UE 102 performs measurements and transmits 304 the measurement report(s) to the DU 174. In some implementations, the measurement configuration(s) includes Layer 3 (L3) measurement configuration(s) (e.g., MeasConfig IE(s)) and the measurement report(s) include L3 measurement report(s).

[0038] After (e.g., in response to) receiving one or some of the measurement report(s) from the UE 102, the CU 172 determines to prepare a first cell (e g., cell 1 such as the cell 125) as a LTM candidate cell for the UE 102. In some implementations, the base station 104 determines to prepare the first cell for the UE 102 because the measurement report(s) indicates that the first cell could be used by the base station 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 measurement report(s) indicates that the first cell qualifies to be a LTM candidate cell that could be used for communication with the UE 102. In some implementations, if theL3 measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than strength and / or quality of the serving cell (e.g., cell 124 A), and / or is better than strength and / or quality of the serving cell by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. Alternatively, the CU 172 determines to prepare the first cell for the UE 102 regardless of whether a measure report is received from the UE 102 or not.

[0039] In response to determining to prepare the first cell for LTM. the CU 172 transmits 308 a first CU-to-DU message to the DU 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 a LTM indicator in the first CU-to-DU message to indicate to the DU 174 to prepare the first cell for LTM. In some implementations, the CU 172 includes the LTM indicator in a LTM Information Setup IE and includes the LTM Information Setup IE in the first CU-to-DU message. In yet other implementations, the CU 172 includes the LTM indicator in a LTM Information Modify IE and includes the LTM Information Modify IE in the first CU-to-DU message.

[0040] 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. In some implementations, the CU 172 includes a first LTM configuration ID (i.e., referred to herein after as LTM ID 1) in the first CU-to-DU message and the DU 174 associates the LTM ID 1 and / or the cell ID 1 with the LTM DU configuration 1. 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.

[0041] The events 308 and 310 are collectively referred to in Fig. 3 as a LTM preparation procedure 390.

[0042] In some implementations, the DU 174 includes, in the first DU-to-CU message, the cell ID 1 of the first cell associated with the LTM DU configuration 1 to indicate that the LTM DU configuration 1 is configured for or associated with the first cell. In cases where the CU 172 performs multiple LTM preparation procedures (e.g., the procedure 390 and the LTM preparation procedure 2. .... N described below) with the DU 174 to prepare multiple LTM candidate cells, the CU 172 can determine that the LTM DU configuration 1 is configured for or associated with the first cell, based on the cell ID 1 in the first DU-to-CU message.

[0043] In some implementations, the CU 172 does not include a LTM reference DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates a LTM reference DU configuration and includes the LTM reference DU configuration in the first DU- to-CU message. In some implementations, the DU 174 generates the LTM DU configuration 1 as a delta configuration to augment the LTM reference DU configuration. In other implementations, the DU 174 generates the LTM DU configuration 1 as a complete configuration, i.e., not on top of the LTM reference DU configuration.

[0044] In some implementations, the CU 172 includes a LTM reference DU configuration request in the first CU-to-DU message, and the DU 174 generates the LTM reference DU configuration and includes the LTM reference DU configuration in the first DU-to-CU message in response to the request. In some implementations, the CU 172 determines whether the UE 102 supports a LTM reference configuration. If the CU 172 determines that the UE 102 supports a LTM reference configuration, the CU 172 includes the LTM reference DU configuration request in the first CU-to-DU message. The DU 174 includes the LTM reference DU configuration in the first DU-to-CU message in response to the LTM reference DU configuration request. Otherwise, if the CU 172 determines that the UE 102 does not support a LTM reference configuration, the CU 172 does not include the LTM reference DU configuration request in the first CU-to-DU message. In this case, the DU 174 may generate the LTM DU configuration 1 as a complete configuration and may not include a / the LTM reference DU configuration in the first DU-to-CU message. In other implementations, the CU 172 transmits an additional CU-to-DU message including the LTM reference DU configuration request to the DU 174 instead of the first CU-to-DU message. In response, the DU 174 includes an additional DU-to-CU message including the LTM reference DU configuration to the CU 172. In yet other implementations, the DU 174 determines whether the UE 102 supports a LTM reference configuration. If the DU 174 determines that the UE 102 supports a LTM reference configuration, the DU 174 includes the LTM reference DU configuration in the first DU-to- CU message. Otherwise, if the DU 174 determines that the UE 102 does not support a LTM reference configuration, the DU 174 does not include a / the LTM reference DU configuration in the first DU-to-CU message.

[0045] In some implementations, the CU 172 includes a LTM reference DU configuration in the first CU-to-DU message. In some implementations, the CU 172 receives the LTM reference DU configuration from an additional DU during a LTM preparation procedure as described above and for Fig. 4. In other implementations, the CU 172 is preconfigured with the LTM reference DU configuration. In some implementations, the DU 174 generates the LTMDU configuration 1 as a delta configuration to augment the LTM reference DU configuration. In other implementations, the DU 174 ignores the LTM reference DU configuration and generates the LTM DU configuration 1 as a complete configuration, i.e., not on top of the LTM reference DU configuration.

[0046] If the DU 174 generates the LTM DU configuration 1 as a complete configuration, the DU 174 may include a complete configuration indication in the first DU-to-CU message to indicate that the LTM DU configuration 1 is a complete configuration. In some implementations, if the first CU-to-DU message does not include a / the LTM reference DU configuration, the CU 172 may determine that the LTM DU configuration 1 as a complete configuration. Otherwise, if the first CU-to-DU message includes a / the LTM reference DU configuration, the CU 172 may determine that the LTM DU configuration 1 is a delta configuration.

[0047] In some implementations, the LTM reference DU configuration is different from the serving DU configuration. In some implementations, a portion of the LTM reference DU configuration is the same as a portion of the serving DU configuration and the rest of the LTM reference DU configuration is different from the rest of the serving DU configuration. In yet other implementations, the LTM reference DU configuration is the same as the serving DU configuration. In some implementations, the LTM reference DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some implementations, the LTM reference DU configuration is the CellGroupConfig IE defined in 3GPP specification 38.331 . In other implementations, the LTM reference DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the LTM reference DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and / or reporting.

[0048] To prepare the first cell as a LTM candidate cell for the UE 102, the CU 172 may transmit 312 a second CU-to-DU message to the DU 174, including a CSI resource configuration (e.g.. CSI resource configuration 1) and / or a LTM SSB configuration (i.e., LTM SSB configuration 1) to request the DU 174 to generate one or more CSI report configurations (e.g., (LTM) CSI report configuration(s) 1). The CSI resource configuration (e g., (LTM) CSI resource configuration(s) 1) include configuration parameters configuring at least one reference signal (RS) transmitted on the first cell. The RS(s) include SSB(s) and / or CSI-RS(s). The LTM SSB configuration include SSB configuration parameters configuring a SSBfrequency, a subcarrier spacing, a SSB periodicity, SSB positions and / or SSB power for SSB(s) transmitted on the first cell.

[0049] After (e.g., in response to) receiving the CSI resource configuration, the DU 174 generates one or more CSI report configurations based on the CSI resource configuration and includes the CSI report configuration(s) in a serving DU configuration (referred to as a second serving DU configuration to distinguish from the serving DU configuration in event 302). In some implementations, the CSI report configuration(s) configures the UE 102 to transmit CSI reports based on measurements of the RS(s). The DU 174 transmits 314 a second DU-to-CU message including the second serving DU configuration to the CU 172. In some implementations, the CSI resource configuration comprises (e.g., is or includes) one or more LTM-CSI-ResourceConfig-rl8 IES. In other implementations, the CSI resource configuration comprises an Itm-CSI-ResourceConflgToAddModList field / IE. In some implementations, the second serving DU configuration is a CellGroupConfig IE.

[0050] In some implementations, the CU 172 includes the cell ID 1 and / or the LTM ID 1 in the second CU-to-DU message. In one implementation, the CU 172 does so to indicate that the CSI resource configuration is / are associated with the first cell. In another implementation, the CU 172 does so for the DU 174 to associate the LTM ID 1 with the first cell, the cell ID 1, the LTM DU configuration 1, and / or the CSI report configuration(s). Based on the above implementation(s). the DU 174 can associate the LTM ID 1 and / or the cell ID 1 with configurations (e.g., LTM DU configuration 1, the CSI resource configuration, and / or the CSI report configuration(s)) related to the first cell. In such implementations, the CU 172 may or may not include the LTM ID 1 in the first CU-to-DU message.

[0051] In some alternative implementations, the CU 172 includes the CSI resource configuration in the first CU-to-DU message and the DU 174 includes the CSI report configuration(s) in the first DU-to-CU message.

[0052] In some implementations, the DU 174 transmits the LTM SSB configuration or the SSB configuration parameters to the CU 172, e.g., in the first DU-to-CU message, the second DU-to-CU message or an additional DU-to-CU message. In some implementations, the DU 174 transmits the additional DU-to-CU message in response to receiving an additional CU-to- DU message from the CU 172. In other implementations, the DU 174 transmits the fourth DU- to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message or the second CU-to-DU message.

[0053] The events 312 and 314 are collectively referred to in Fig. 3 as a LTM CSI report configuration and / or LTM ID configuration procedure 392.

[0054] After receiving the first DU-to-CU message, the CU 172 generates a first LTM candidate configuration (i.e.. LTM candidate configuration 1) including the LTM DU configuration 1 and generates a first RRC reconfiguration message including the LTM candidate configuration 1 and the LTM ID 1. In some implementations, the CU 172 includes LTM CU configuration 1 in the LTM candidate configuration 1. In other implementations, the CU 172 does not include a LTM CU configuration in the LTM candidate configuration 1. The CU 172 transmits 316 a third CU-to-DU message including the first RRC reconfiguration message to the DU 174. In turn, the DU 174 transmits 318 the first RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320 a first RRC reconfiguration complete message to the DU 174. The DU 174 then transmits 322 a third DU-to-CU message including the first RRC reconfiguration complete message to the CU 172.

[0055] If the first DU-to-CU message includes the LTM reference DU configuration, the CU 172 generates a LTM reference configuration including the LTM reference DU configuration. In such cases, the CU 172 may include the LTM reference configuration in the first RRC reconfiguration message. In some implementations, the CU 172 includes a LTM reference CU configuration in the LTM reference configuration. In such cases, the CU 172 may generate the LTM CU configuration 1 as a delta configuration based on the LTM reference CU configuration. In other implementations, the CU 172 does not include a LTM reference CU configuration in the LTM reference configuration. In such cases, the CU 172 may generate the LTM CU configuration 1 as a complete configuration. Alternatively, the CU 172 transmits a second RRC reconfiguration message including the LTM reference configuration to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a second RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. In some implementations, if the CU 172 does not receive a LTM reference DU configuration, the CU 172 may generate a LTM reference configuration including only the LTM reference CU configuration. In other implementations, if the CU 172 does not receive a LTM reference DU configuration, the CU 172 may not generate a LTM reference configuration.

[0056] In some implementations, if the first DU-to-CU message includes the complete configuration indication, the CU 172 may determine that the LTM DU configuration 1 as a complete configuration. Otherwise, if the first DU-to-CU message does not include the complete configuration indication, the CU 172 may determine that the LTM DU configuration 1 is a delta configuration. In some implementations, if the LTM DU configuration 1 is a complete configuration, the CU 172 generates the LTM candidate configuration 1 as acomplete configuration. Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU 172 generates the LTM candidate configuration 1 as a delta configuration. If the LTM candidate configuration 1 is a complete configuration, the CU 172 includes, in the first RRC reconfiguration message, a complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration. If the LTM candidate configuration 1 is a delta configuration, the CU 172 excludes the complete configuration indication from the first RRC reconfiguration message to indicate that the LTM candidate configuration 1 is a delta configuration.

[0057] In the case that the CU 172 performs the procedure 392, the CU 172 may include the second serving DU configuration in the first RRC reconfiguration message. Alternatively, the CU 172 transmits a third RRC reconfiguration message including the second serving DU configuration to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a third RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322.

[0058] In some implementations, the CU 172 includes the CSI resource configuration in the first RRC reconfiguration message, the second RRC reconfiguration message, or the third RRC reconfiguration message. In other implementations, the CU 172 transmits a fourth RRC reconfiguration message including the CSI resource configuration to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a fourth RRC reconfiguration complete message to the UE 102 via the DU 174, similar to the events 320 and 322.

[0059] In some implementations, the DU 174 transmits a DU-to-CU message to the CU 172, including early synchronization information for the UE 102. The DU-to-CU message may be the first DU-to-CU message, the second DU-to-CU message or a fourth DU-to-CU message. In some implementations, the DU 174 transmits the fourth DU-to-CU message in response to receiving a fourth CU-to-DU message from the CU 172. In other implementations, the DU 174 transmits the fourth DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message or the second CU-to-DU message. In one implementation, the DU 174 does so, if the DU 174 determines that the UE 102 supports (i.e.. is capable ol) early UL synchronization with a LTM candidate cell (e.g., early TA acquisition wi th a LTM candidate cell, early RA on a LTM candidate cell, or UE measured TA). Otherwise, if the DU 174 detenwines that the UE 102 does not support the early UL synchronization with a LTM candidate cell, the DU 174 does not transmit the early synchronization information to the CU 172. In other implementations, the CU 172 transmits a CU-to-DU message includingan early synchronization information request (e.g.. an IE) to the DU 174, and the DU 174 includes the early synchronization information in the DU-to-CU message in response to the early synchronization information request. The CU-to-DU message may be the first CU-to-DU message, the second CU-to-DU message or the fourth CU-to-DU message. In one implementation, the CU 172 does so if the CU 172 determines that the UE 102 supports the early UL synchronization with aLTM candidate cell. Otherwise, if the CU 172 determines that the UE 102 does not support the early UL synchronization with a LTM candidate cell, the CU 172 does not request the DU 174 to provide the early synchronization information for the UE 102. If the CU 172 receives the early synchronization information, the CU 172 includes the early synchronization information in the first, second, third or fourth RRC reconfiguration message. Alternatively, the CU 172 transmits a fifth RRC reconfiguration message including the early synchronization information to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a fifth RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322.

[0060] In some implementations, the early synchronization information includes a random access channel (RACH) configuration (i.e.. RACH configuration 1) and / or one or more TCI state configurations (i.e., TCI state configuration(s) 1). In some implementations, the early synchronization request may include a request for a RACH configuration. If the early synchronization request includes the request for a RACH configuration, the DU 174 includes the RACH configuration in the early synchronization information or in the DU-to-CU message (e.g., be the first, second or fourth DU-to-CU message). Otherwise, if the early synchronization request does not include the request for a RACH configuration, the DU 174 neither includes the RACH configuration in the early sy nchronization information or in the DU-to-CU message.

[0061] In some implementations, the CU 172 includes, in the first, second, third, fourth and / or fifth RRC reconfiguration messages, one or more other LTM related configurations for the first cell. For example, the other LTM related configuration(s) include a PCI of the first cell and / or the LTM SSB configuration.

[0062] The events 316. 318, 320, 322 are collectively referred to in Fig. 3 as a LTM configuration delivery procedure 394. The second, third, fourth and / or fifth RRC reconfiguration message(s)) and the second, third, fourth and / or fifth RRC reconfiguration complete message(s), the related CU-to-DU message(s) and / or the related DU-to-CU message(s) are also considered as part of the LTM configuration delivery procedure 394. In some implementations, the RRC reconfiguration message and the RRC reconfigurationcomplete message described above are an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively.

[0063] In some implementations, the first CU-to-DU message is a UE Context Modification Request message, and the first DU-to-CU message is a UE Context Modification Response message. In some implementations, the second CU-to-DU message is a UE Context Modification Request message, and the second DU-to-CU message is a UE Context Modification Response message or a UE Context Modification Required message. In the case of the UE Context Modification Required message, the CU 172 can transmit a UE Context Modification Confirm message to the DU 174 in response to UE Context Modification Required message. In some implementations, the third CU-to-DU message is a DL RRC Message Transfer message. In other implementations, the third CU-to-DU message is a UE Context Modification Request message. In some implementations, the third DU-to-CU message is a UL RRC Message Transfer message. In other implementations, the third DU-to-CU message is a UE Context Modification Response message.

[0064] In some implementations, the LTM reference CU configuration is different from the serving CU configuration. In some implementations, a portion of the LTM reference CU configuration is the same as a portion of the serving CU configuration and the rest of the LTM reference CU configuration is different from the rest of the serving CU configuration. In yet other implementations, the LTM reference CU configuration is the same as the serving CU configuration.

[0065] In some implementations, the LTM reference CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 includes a MeasConflg IE and / or a RadioBearerConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConflg IE and / or RadioBearerConfig IE.

[0066] In some implementations, the LTM CU configuration 1 and / or the LTM reference CU configuration include PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 or the LTM reference CU configuration includes a MeasConflg IE and / or a RadioBearerConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConflg IE and / or RadioBearerConfig IE.

[0067] 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 layerconfiguration parameters (e.g., PhysicalCellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE) and / or RLC configuration parameters (e.g., RLC- BearerConflg IE(s)). In some further implementations, the plurality of configuration parameters include a special cell configuration (e.g., SpCellConfig IE) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some implementations, the LTM DU configuration 1 is CellGroupConfig IE defined in 3GPP specification 38.331. In other implementations, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0068] In some implementations, the LTM DU configuration 1 includes a first LI measurement configuration (e g., a CSI-MeasConfig IE) and / or at least one first transmission configuration indicator (TCI) state configuration. In other implementations, the LTM CU configuration 1 includes the first TCI state configuration(s). In some implementations, the first LI measurement configuration includes at least one first RS resource configuration and / or at least one first report configuration. In some implementations, the first RS resource configuration(s) configures one or more RSs or one or more RS resources associated with the cell 1. The RS(s) includes SSB(s) and / or CSLRS(s). The RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some implementations, each of the first RS resource configuration(s) includes a RS resource configuration ID. In some implementations, the first RS resource configuration(s) is / are (similar to) CSI-ResourceConfig IE(s). In some implementations, the first report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the first cell for the UE 102 to transmit measurement results (e.g., CSI reports or LTM CSI reports). In some implementations, each of the first report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the first RS resource configuration(s). In some implementations, each of the first TCI state configuration(s) configures a TCI state that associates one or two DL RSs with a corresponding quasi-colocation (QCL) type. The DL RS(s) are associated with the cell 1.

[0069] After receiving the LTM-related configurations and the second serving DU configuration or after receiving the RRC reconfiguration message(s) described above, the UE 102 performs measurements on at least one first RS, generates at least one first L 1 measurement result based on the measurements, and transmits 324 at least one first LI measurement report including the first LI measurement result(s) to the DU 174. The first RS(s) may comprise SSB(s) and / or CSI-RS(s). In some implementations, the first RS(s) and / or transmission pattem(s) of the first RS(s) are configured in the CSI report configuration(s), the LTM SSBconfiguration, and / or the CSI resource configuration. The UE 102 performs the measurements on the first RS(s) in accordance with the CSI report configuration(s). the LTM SSB configuration, and / or the CSI resource configuration.

[0070] After receiving the LTM-related configurations and the second serving DU configuration or after receiving the RRC reconfiguration message(s) described above, the UE 102 performs measurements on at least one second RS, generates at least one second LI measurement result based on the measurements, and transmits at least one second LI measurement report including the first LI measurement result(s) to the DU 174. The second RS(s) may comprise SSB(s) and / or CSI-RS(s). In some implementations, the second RS(s) and / or transmission pattem(s) of the second RS(s) are configured in one or more second CSI report configurations and / or one or more second CSI resource configuration that are included in the serving DU configuration and / or the second serving DU configuration. The UE 102 performs the measurements on the second RS(s) in accordance with the second CSI report configuration(s) and / or the second CSI resource configuration(s). The second CSI report configuration(s) may include non-LTM CSI report configuration(s) and / or LTM CSI report configuration(s). The second CSI resource configuration s) may include non-LTM CSI resource configuration(s) and / or LTM CSI resource configuration(s).

[0071] After transmitting the RACH configuration to the UE 102 via the CU 172, the DU 174 may transmit 350 a PDCCH order to the UE 102 to command the UE 102 to transmit a RA preamble on the first cell. In response to the PDCCH order, the UE 102 transmits a RA preamble on the first cell. The DU 174 includes PDCCH order information in the PDCCH order. The PDCCH order information includes a RA preamble index, an UL or a supplemental UL indicator, a SSB index and / or a physical RACH mask index. In some implementations, the DU 174 includes the LTM ID 1 in the PDCCH order to indicate the first cell. The UE 102 identifies the first cell based on the LTM ID 1 in the PDCCH order and transmits 352 the RA preamble on the first cell to the DU 174, using the PDCCH order information. Correspondingly, the DU 174 receives 352 the RA preamble in accordance with the PDCCH order information. In some implementations, the DU 174 may determine the SSB index, based on LI measurement report(s). and / or the CSI resource configuration, the CSI report configuration and / or the LTM SSB configuration. In some implementations, the LI measurement report(s) may include the SSB index. In other implementations, the LI measurement report(s) include a SS / PBCH Block Resource Indicator (SSBRI) corresponding to the SSB index. Thus, the DU 174 determines the SSB index based on the SSBRI.

[0072] In some implementations, the DU 174 determines whether to transmit the PDCCH order based on the LI measurement result(s). In some implementations, if the LI measurement result(s) indicate that the first cell qualifies for the UE 102 to perform RA for early UL synchronization, the DU 174 transmits the PDCCH order. Otherwise, if the LI measurement result(s) indicate that the first cell does not qualify for the UE 102 to perform RA for early UL synchronization, the DU 174 refrains from transmitting the PDCCH order. In other implementations, if the LI measurement result(s) indicate that the first cell qualifies for the UE 102 to access, the DU 174 transmits the PDCCH order. Otherwise, if the LI measurement result(s) indicate that the first cell does not qualify for the UE 102 to access, the DU 174 refrains from transmitting the PDCCH order. In yet other implementations, the DU 174 transmits the PDCCH order after receiving 320 the RRC reconfiguration complete message, regardless of the LI measurement result(s).

[0073] After transmitting 324 the LI measurement report(s) or 352 the RA preamble, the UE 102 may transmit 354 additional LI measurement report(s) to the DU 174, similar to the event 324. The DU 174 determines to command the UE 102 to perform a LTM cell switch to the first cell based on the additional LI measurement report(s) and / or the LI measurement report(s). In response to the determination, the DU 174 generates a LTM Cell Switch Command (e.g., a MAC CE) including the LTM ID 1 and transmits 326 the LTM Cell Switch Command to the UE 102. In response to the determination, the DU 174 may transmit 328 a DU-CU Cell Switch Notification message to the CU 172. In response to the LTM Cell Switch Command, the UE 1 2 performs a LTM cell switch to the first cell. In the LTM cell switch, the UE 102 accesses 332 the first cell and transmits 336 a RRC reconfiguration complete message to the DU 174 via the first cell. The DU 174 transmits 338 a DU-to-CU message (e.g., UL RRC Message Transfer message) including the RRC reconfiguration complete message to the CU 172. When the UE 102 receives the LTM Cell Switch Command, the UE 102 identifies the LTM candidate configuration 1 from the LTM ID 1 and accesses 332 the first cell using the LTM candidate configuration 1. Depending on implementations, the UE 102 may stop communicating on the serving cell(s) in response to the LTM Cell Switch Command. In turn, the DU 174 transmits a fifth DU-to-CU message including the RRC reconfiguration complete message to the CU 172. When the DU 174 detects the UE 102 accesses the first cell in the event 332, the DU 174 may transmit 334 an Access Success message to the CU 172 to indicate that the UE 102 has accessed the first cell.

[0074] In some implementations, the DU 174 includes, in the LTM Cell Switch Command, a TA value for UL synchronization with the first cell. In one implementation, the DU 174derives the TA value based on the RA preamble (e.g., reception timing of the RA preamble). In another implementation, the DU 174 derives the TA value from an UL transmission on the serving cell (e.g., the cell 124A) from the UE 102. The UE 102 applies the TA value to synchronize with the first cell in UL transmission. After applying the TA value, the UE 102 transmits the first UL transmission on the first cell based on the LTM candidate configuration 1 without performing a RA procedure on the first cell. In some implementations, the UE 102 transmits the first UL transmission on the first cell using a UL grant. In such cases, the first UL transmission is a PUSCH transmission. In some implementations, the PUSCH transmission includes the RRC reconfiguration complete message 336. In some implementations, the UL grant is a configured grant and the LTM candidate configuration 1 or the LTM DU configuration 1 includes the configured grant configuration configuring the configured grant. In other implementations, the UL grant is a dynamic grant that the UE 102 receives on a PDCCH on the first cell. After transmitting the first UL transmission, the UE 102 receives a PDCCH transmission addresses to a C-RNTI of the UE 102 and determines that the LTM cell switch is completed successfully in response to receiving the PDCCH transmission.

[0075] The PDCCH transmission may include a UL grant or a DL assignment. In the case of the UL grant, the UE 102 transmits a PUSCH transmission to the DU 174 on the first cell using the UL grant. In the case of the DL assignment, the DU 174 transmits a PDSCH transmission to the UE 102 on the first cell in accordance with the DL assignment. The DU 174 may transmit 334 the Access Success message to the CU 172 after receiving (e.g., in response to) the first UL transmission, transmitting the PDCCH transmission, receiving the PUSH transmission or transmitting the PDSCH transmission.

[0076] In other implementations, the DU 174 does not include a TA value in the LTM Cell Switch Command. If the LTM Cell Switch Command does not include a / the TA value, the UE 102 performs a RA procedure on the first cell in accordance with the RA configuration parameters. In some implementations, the RA configuration parameters are included in the LTM candidate configuration 1 or the LTM DU configuration 1. In some implementations, the RA configuration parameters configure PRACH resources, an association between SSB and PRACH resources, and / or one or more PRACH occasions. If the UE 102 successfully completes the RA procedure, the UE 102 determines the LTM cell switch to the first cell is completed successfully. Depending on implementations and / or the RA configuration parameters, the RA procedure can be a four-step RA procedure or a two-step RA procedure. During the four-step RA procedure, the UE 102 transmits a Message 3 on the first cell and the DU 174 transmits a Message 4 on the first cell to the UE 102 in response. During the two-stepRA procedure, the UE 102 transmits a Message A on the first cell and the DU 174 transmits a Message B to the UE 102 on the first cell in response. The UE 102 may include the RRC reconfiguration complete message 336 in the Message 3 or Message A. Alternatively, the UE 102 transmits the RRC reconfiguration complete message 336 after completing the RA procedure. The DU 174 may transmit 334 the Access Success message to the CU 172, after receiving the Message 3, Message A or the RRC reconfiguration complete message 336 or transmitting the Message 4 or Message B.

[0077] After successfully completing the LTM cell switch to the first cell as described above, the UE 102 communicates 340 with the DU 174 and the CU 172 via the first cell, using the LTM candidate configuration 1. In the case of the LTM reference configuration, the UE 102 applies the LTM reference configuration first and then apply the LTM candidate configuration 1 to augment the LTM reference configuration.

[0078] In some implementations, each of the TCI state configuration(s) include a TCI state ID. In some implementations, the DU 174 includes, in the LTM Cell Switch Command, a first TCI state ID indicating a first one of the TCI state configuration(s). The UE 102 identifies the first one of the TC state configuration(s) based on the first TCI state ID and applies the first TCI state configuration to communicate UL transmissions and / or DL transmissions with the DU 174 in the events 332, 336 and / or 340. The DU 174 applies the first TCI state configuration to communicate UL transmissions and / or DL transmissions with the UE 102 in the events 332, 336 and / or 340.

[0079] In some implementations, the CU 172 may prepare additional cell(s) (i.e., cell(s) 2, ... , N) as LTM candidate cell(s) for the UE 102 with the DU 174, before or after transmitting the LTM Cell Switch Command or during, before or after the procedure 390 or 392, as described above. N is an integer and larger than 1. For example, the CU 172 performs additional LTM preparation procedure(s) 2, ... , N with the DU 174 to prepare the cell(s) 2, ...N respectively. Each of the LTM preparation procedure(s) 2, ... , N is similar to the procedure 390. In the LTM preparation procedure(s) 2, ... , N, the CU 172 receives LTM DU configuration(s) 2, ... , N configuring the cell(s) 2, ... , N for LTM. respectively. The CU 172 generates LTM candidate configuration(s) 2, .. . , N including the LTM DU configuration(s) 2. ...N, respectively. The CU 172 assigns LTM ID(s) 2, ... , N to identify the LTM DU configuration(s) 2, ... , N and the LTM candidate configuration(s) 2, ... , N, respectively. The CU 172 may obtain CSI resource configuration 2, ,... , N and perform CSI report configuration and / or LTM ID configuration procedure(s) 2, ... , N with the DU 174 to obtain the CSI report configuration(s) 2, ... , N, respectively, as described for the CSI resource configuration 1 andthe CSI report configuration(s) 1. The CU 172 may obtain RACH configuration 2, N for the cell(s) 2, . . . , N respectively, as described for the RACH configuration 1. The CU 172 may obtain TCI state configuration(s) 2, . . . , N for the cell(s) 2, .. . , N respectively, as described for the TCI state configuration(s) 1. Each of the CSI report configuration and / or LTM ID configuration procedure(s) 2, ... , N is similar to the procedure 392. The CU 172 may obtain LTM SSB configuration 2, . .. , N for the cell(s) 2, .. . , N, respectively, as described for the LTM SSB configuration 1. In some implementations, the CU 172 may perform LTM configuration delivery procedure 2, . . . , N with the UE 102 to transmit a list of the {LTM ID 2, the LTM candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained)}. ... , {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained)} to the UE 102, respectively. Each of the LTM configuration delivery procedure 2, ... , N is similar to the procedure 394. In other implementations, the CU 172 includes the list in the first RRC reconfiguration message.

[0080] In some implementations, after receiving 334 the Access Success message or 338 the DU-to-CU message, the CU 172 may transmit 342 a CU-to-DU message to the DU 174. In one implementation, the CU 172 transmits 342 the CU-to-DU message to release radio resources and / or configurations of the serving cell(s) configured for the UE 102. In another implementation, the CU 172 transmits 342 the CU-to-DU message to release some of the LTM candidate cell(s) 2, . .. , N. In this case, the CU 172 . In response to the CU-to-DU message, the DU 174 transmits 344 a DU-to-CU message to the CU 172. In some implementations, the CU- to-DU message and the DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0081] In some implementations, a LTM ID in a PDCCH order, a LTM Cell Switch Command and a RRC reconfiguration message is represented in different formats. For example, the PDCCH order or the LTM Cell Switch Command includes a first field to include the LTM ID 1 and the first RRC reconfiguration message includes a second field to include the LTM ID 1. In some implementations, the first field and the second field have different formats or coding schemes. For example, the first field uses a binary7format (i.e., 3 bits) with a value range of 0, . .. , 7 and the second field uses an integer format with a value range of 1. . . . , 8. In this example, the first field with binary value 000b is equivalent to the second field with integer value 1, the first field with binary' value 001b is equivalent to the second field with integervalue 2, .. . , the first field with binary' value 11 lb is equivalent to the second field with integer value 8.

[0082] The events 304, 306, 390, 392, 394, and 324 are collectively referred to in Fig. 3 as an intra-CU intra-DU LTM configuration procedure 396. The events 304, 306, 390, 392, 394, 324, 350, 352, 354, 326, 328, 332, 334, 336, 338, and 340 are collectively referred to in Fig. 3 as an intra-CU intra-DU LTM procedure 380.

[0083] Referring next to Fig. 4, in a scenario 400, the base station 104 includes a CU 172. a S-DU 174A and a candidate DU (C-DU) 174B. The S-DU 174A operates the cell 124A and optionally additional cell(s), while the C-DU 174B operates a first cell (e.g., cell 125). The scenario 400 is an intra-CU inter-DU scenario, similar to the scenario 300. Thus, the descriptions for the scenario 300 can generally apply to the scenario 400. Some descriptions for the DU 174 in Fig. 3 may apply to the S-DU 174A in Fig. 4, and some descriptions for the DU 174 in Fig. 3 may apply to the C-DU 174B. The differences between the scenarios 300 and 400 are described below.

[0084] Initially, the UE 102 communicates 402 with the S-DU 174A on one or more serving cells (e.g.. the cell 124A and / or other cell(s)) using a serving DU configuration and communicates with the CU 172 via the S-DU 174A using a serving CU configuration. In some implementations, the CU 172 and S-DU 174A might perform the LTM configuration procedure 396 or the LTM procedure 380 with the UE 102, as described for Fig. 3. In the case of the procedure 380. the UE 102 may perform a LTM cell switch to the first cell (e.g. cell 125) as described for Fig. 3. Upon successfully completing the LTM cell switch, the first cell becomes a serving cell and cell 124A and / or the other cell(s) is / are no longer serving cell(s) for the UE 102. In the case of the procedure 396, the UE 102 does not perform a LTM cell switch. During the communication 402, the UE 102 transmits 404, 406 at least one measurement report (e.g., L3 measurement report(s)) to the CU 172 via the S-DU 174A. Based on the measurement report(s), the CU 172 determines to prepare cell 1 (e.g., cell 125 operated by the C-DU 174B) for LTM for the UE 102. The cell 1 is identified by a cell ID (i.e., cell ID 1). In response to the determination, the CU 172 performs 490 a LTM preparation procedure with the C-DU 174B to (request the C-DU 174B to) prepare the cell 1 as a LTM candidate cell for the UE 102. In the LTM preparation procedure 490, the CU 172 transmits a first CU-to-DU message including a cell ID 1 of the cell 1 to the C-DU 174B to request the C-DU 174B to prepare the cell 1 as a LTM candidate cell for the UE 102, similar to the event 308. In response, the C-DU 174B transmits a first DU-to-CU message including a LTM DU configuration (e.g.. LTM DU configuration 1) to the CU 172, similar to the event 310. The CU 172 may or may not requestaLTM reference DU configuration in the first CU-to-DU message, as described for Fig. 3. The C-DU 174B may or may not include a LTM reference DU configuration in the first DU-to-CU message, as described for Fig. 3.

[0085] In some implementations, if the CU 172 receives a LTM reference DU configuration from the S-DU 174A as described for Fig. 3, the CU 172 may include the LTM reference DU configuration in the first CU-to-DU message and the C-DU 174B may generate the LTM DU configuration as a delta configuration based on the LTM reference DU configuration. In such cases, the C-DU 174B does not transmit a LTM reference DU configuration for the UE 102 to the CU 172. In other implementations, the CU 172 receives aLTM reference DU configuration from the C-DU 174B, e.g., in the first DU-to-CU message or an additional DU-to-CU message as described for Fig. 3. In such cases, the CU 172 may generate a LTM reference configuration including the LTM reference DU configuration. The CU 172 may or may not include a LTM reference CU configuration in the LTM reference configuration.

[0086] To prepare the cell 1 for LTM, the CU 172 may perform 492 a LTM CSI report configuration and / or LTM ID configuration procedure with the S-DU 174A. In the procedure 492, the CU 172 transmits a second CU-to-DU message including a CSI resource configuration (e g., CSI resource configuration 1) and / or a LTM SSB configuration (i.e., LTM SSB configuration 1) to the S-DU 174A, similar to the event 312. In response, the S-DU 174A transmits a second DU-to-CU message including one or more CSI report configurations (e.g., CSI report configuration(s) 1) to the CU 172. In some implementations, the CU 172 generates a LTM candidate configuration (e.g., LTM candidate configuration 1 ) including the LTM DU configuration and assigns a LTM ID (e.g., LTM ID 1) for identifying the LTM DU configuration and / or the LTM candidate configuration as described for Fig. 3. In some implementations, the CU 172 includes {the LTM ID 1, the cell ID 1 } as a tuple in the second CU-to-DU message.

[0087] To prepare the cell 1 as aLTM candidate cell forthe UE 102, the CU 172 may receive early synchronization information for the cell 1 in a DU-to-CU message (e.g., the first DU-to- CU message or an additional DU-to-CU message) from the C-DU 174B. In some implementations, the C-DU 174B transmits the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other implementations, the C- DU 174B transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message. The early synchronization information includes a RACH configuration (e.g., RACH configuration 1) and / or at least one TCI state configuration (e.g., TCI state configuration(s) 1), as described forFig. 3. In some implementations, the C-DU 174B includes, in the early synchronization information or in the DU-to-CU message, the PDCCH order information (PDCCH order information 1) for early UL synchronization with the first cell.

[0088] In some implementations, the CU 172 may receive the LTM SSB configuration or SSB configuration parameters in the LTM SSB configuration from the C-DU 174B, e.g., in the first DU-to-CU message or an additional DU-to-CU message. In some implementations, the CU 172 may receive a PCI of the cell 1 from the C-DU 174B in the first DU-to-CU message or the additional DU-to-CU message. In some implementations, the C-DU 174B transmits the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other implementations, the C-DU 174B transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message.

[0089] As described for Fig. 3, the CU 172 performs 494 LTM configuration delivery procedure with the UE 102 to transmit the LTM ID 1 and the LTM candidate configuration to the UE 102. In some implementations, the CU 172 transmits {LTM ID, the LTM candidate configuration} as a tuple in a first RRC reconfiguration message in the procedure 494. Depending on the implementations, the CU 172 may include the LTM reference configuration, the CSI report configuration(s), the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1 to the UE 102 in the first RRC reconfiguration message and / or other RRC reconfiguration message(s) transmitted to the UE 102, as described for Fig. 3. The CU 172 includes the LTM ID in the first RRC reconfiguration or the other RRC reconfiguration message(s) to indicate the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1 are associated with the cell 1. For example, the CU 172 includes the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1 in the tuple. In another example, the CU 172 includes {LTM ID, the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1 } as a tuple in the other RRC reconfiguration message(s). In response to each of the other RRC reconfiguration message(s), the UE 102 transmits a RRC reconfiguration complete message to the CU 172 via the S-DU 174A.

[0090] In some implementations, the PDCCH order information includes a frequency domain resource assignment, a RA preamble index, an UL or a supplemental UL indicator, a SSB index and / or a physical RACH mask index. The CU 172 may transmit a CU-to-DUmessage (e.g., the second CU-to-DU message or an additional CU-to-DU message) including the PDCCH order information to the S-DU 174A. In some implementations, the CU 172 includes the LTM ID 1 or the cell ID 1 in the CU-to-DU message to indicate that the PDCCH order information is associated with the LTM ID 1 or the cell ID 1. For example, the CU 172 includes {the cell ID 1, the PDCCH order information} as a tuple in the CU-to-DU message. In the case of the additional CU-to-DU message, the S-DU 174A may transmit an additional DU-to-CU message to the CU 172 in response. The S-DU 174A transmits 450 a PDCCH order to the UE 102, based on the PDCCH order information. For example. The S-DU 174A transmits 450 a PDCCH order to the UE 102, including the PDCCH order information. In some implementations, the S-DU 174A may determine a SSB index included in the PDCCH order, based on LI measurement report(s) 424. and / or the CSI resource configuration, the CSI report configuration and / or the LTM SSB configuration. In some implementations, the S-DU 174A includes the LTM ID 1 in the PDCCH order to indicate the cell 1. In the case of the additional CU-to-DU message, the S-DU 174A may transmit an additional DU-to-CU message to the CU 172 in response. The UE 102 transmits 452 a RA preamble to the C-DU 174B on the cell 1, using the RACH configuration and / or the PDCCH order information. The C-DU 174B derives a TA value based on the RA preamble. The C-DU 174B transmits 456 a DU-CU TA Information Transfer message including the TA value to the CU 172. The CU 172 in turn transmits 458 a CU-DU TA Information Transfer message including the TA value to the S-DU 174A. In some implementations, the C-DU 174B includes the cell ID 1, the RA preamble index, a RA radio network temporary identifier (RA-RNTI) and / or a DU ID of the S-DU 174A in the message 456. In such cases, the CU 172 includes the cell ID 1, the RA preamble index, the RA-RNTI, and / or the DU ID of the S-DU 174A in the message 458. In response to determining to command the UE 102 to perform a LTM cell switch to the cell 1, the S-DU 174A transmits 456 the LTM Cell Switch Command including the LTM ID 1 to the UE 102. If the S-DU 174A receives a TA value as described above, the S-DU 174A may include the TA value in the LTM Cell Switch Command. The S-DU 174A may include a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID indicates a first one of the TCI state configuration(s).

[0091] In some implementations, the C-DU 174B determines the RA-RNTI based on a PRACH occasion in which the C-DU 174B receives the RA preamble. In some implementations, the C-DU 174B calculates the RA-RNTI as:RA-RNTI = 1 + s_id + 14 t_id + 14 * 80 * f id + 14 * 80 * 8 * ul_carrier_id where s id is the index of the first OFDM symbol of the PRACH occasion (0 < s id < 14), t id is the index of the first slot of the PRACH occasion in a system frame (0 < t_id < 80), wherethe subcarrier spacing to determine t_id is based on the value of p specified in clause 5.3.2 in 3GPP TS 38.211 for p = {0. 1, 2, 3}, and for p = {5, 6}, t_id is the index of the 120 kHz slot in a system frame that contains the PRACH occasion (0 < t_id < 80), f id is the index of the PRACH occasion in the frequency domain (0 < f id < 8), and ul carrier id is the UL carrier used for the RA Preamble transmission (0 for NUL carrier, and 1 for SUL carrier).

[0092] In response to determining to command the UE 102 to perform a LTM cell switch or transmitting 456 the LTM Cell Switch Command, the S-DU 174A transmits 428 aDU-CUCell Switch Notification message to the CU 172 to indicate that the UE 102 performs a LTM cell switch to the cell 1. In response, the CU 172 transmits 430 a CU-DU Cell Switch Notification message to the C-DU 174B to indicate that the UE 102 performs a LTM cell switch to the cell 1. In some implementations, the S-DU 174A includes the first TCI state ID in the DU-CU Cell Switch Notification message and the CU 172 in turn includes the first TCI state ID in the CU- DU Cell Switch Notification message. The UE 102 and the C-DU 174B identify the first one of the TC state configuration(s) based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in the events 432, 436 and / or 440.

[0093] In some implementations, each of the TCI state configuration(s) includes or is associated with a TCI state ID. In some implementations, the CU 172 may transmit a CU-to- DU message (e.g., the second CU-to-DU message or an additional CU-to-DU message) including the TCI state configuration(s) and / or the associated TCI state ID(s) to the S-DU 174A. In some implementations, the CU 172 includes the LTM ID 1 or the cell ID 1 in the CU- to-DU message to indicate that the TCI state configuration(s) is associated with the LTM ID 1 or the cell ID 1. For example, the CU 172 includes {the cell ID 1, the TCI state configuration(s)} as a tuple in the CU-to-DU message. In the case of the additional CU-to-DU message, the S-DU 174A may transmit an additional DU-to-CU message to the CU 172 in response. In some implementations, the S-DU 174A includes, in the LTM Cell Switch Command 426, a first TCI state ID indicating a first one of the TCI state configuration(s). In some implementations, the S-DU 174A determines the first TCI state configuration or the fist TCI state ID. The UE 102 identifies the one of the TCI state configuration(s) based on the first TCI state ID and applies the first TCI state configuration in UL transmissions and / or DL receptions in the events 432, 436 and / or 440.

[0094] In some implementations, the CU 172 may prepare additional cell(s) (i.e., cell(s) 2, ... , N) as LTM candidate cell(s) for the UE 102 with the C-DU 174B, before or aftertransmitting the LTM Cell Switch Command or during, before or after the procedure 490 or 492, as described for Fig. 3.

[0095] In some implementations, the first CU-to-DU message and the first DU-to-CU message are a UE Context Setup Request message and a UE Context Setup Response message. In some implementations, the first CU-to-DU message and the first DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message. In some implementations, the LTM preparation procedure 490 is a UE Context Setup procedure and the additional LTM preparation procedure is a UE Context Modification procedure. In other implementations, the LTM procedure 490 and the addition LTM preparation procedures are UE Context Setup procedures. In yet other implementations, the LTM procedure 490 and the addition LTM preparation procedures are UE Context Modification procedures.

[0096] The events 404, 406, 490, 492, 494, 494, and 424 are collectively referred to in Fig. 4 as an intra-CU inter-DU LTM configuration procedure 496. The events 404, 406, 490, 492, 494, 494, 424, 450, 452, 454 456, 458, 426, 428, 430, 432, 434, 436, 438, 440, 442, and 444 are collectively referred to in Fig. 4 as an intra-CU inter-DU LTM procedure 480.

[0097] Referring next to Fig. 5. in a scenario 500, the base station 104 operates as a serving or source base station (S-BS), and the base station 106 operates as a candidate base station (C- BS). The C-BS 106 includes a CU 172 and a DU 174. The scenario 500 is similar to the scenarios 300 and 400, except that the scenario 500 is an inter-CU scenario (i.e., inter-base station scenario) while the scenarios 300 and 400 are intra-CU (i.e., intra-base station) scenarios. The S-BS 104 can include a CU and a DU (not shown in Fig. 5), similar to the base station 104 of Figs. 3 and 4. Initially, the UE 102 communicates 502 with the S-BS 104 via serving cell(s) using a serving configuration. In some implementations, the S-BS 104 includes a S-DU and a CU and the serving configuration may include a serving CU configuration and a serving DU configuration, as described for Figs. 3 and 4. While the communicating 502 with the UE 102, the S-BS 104 might perform 580 intra-CU LTM procedure(s) with the UE 102, similar to the procedures 380 and / or 480. Alternatively, while the communicating 502 with the UE 102, the S-BS 104 might perform 596 intra-CU LTM configuration procedure(s) with the UE 102, similar to the procedures 396 and / or 496.

[0098] While communicating with the S-BS 104, the UE 102 transmits 504 at least one measurement report to the S-BS 104. The measurement report(s) include measurement results for a serving cell of the UE 102 and / or at least one non-serving cell (e.g., cell 126). The S-BS 104 determines to prepare a first cell (e.g., the cell 126) as a LTM candidate cell for the UE 102, based on the measurement report(s). For example, the measurement report(s) include aPCI of the first cell and measurement result(s) of the cell 126. The S-BS 104 identifies that the first cell is operated by the base station 106 based on the PCI, and determines that the first cell qualifies for LTM preparation based on the measurement result(s).

[0099] After (e.g., in response to) determining to prepare the first cell as a LTM candidate cell for the UE 102, the S-BS 104 (e.g., the CU of the S-BS 104) generates a Handover Request message including a first cell ID (i.e., cell ID 1) of the first cell (i.e., cell 1). The S-BS 104 transmits 505 the Handover Request message to the CU 172. In some implementations, the Handover Request message includes a LTM indicator indicating the Handover Request message concerns LTM for the first cell ID. After (e.g., in response to) receiving the Handover Request message, the CU 172 performs a LTM preparation procedure 590 with the DU 174 to prepare the first cell as a LTM candidate cell for the UE 102, similar to the procedure 390 or 490. In the procedure 590, the CU 172 transmits a first CU-to-DU message including the first cell ID to the DU 174 to request preparing the first cell, similar to the event 308. In response, the CU 172 may receive a first DU-to-CU message including a LTM DU configuration 1 from the DU 174, similar to the event 310. The CU 172 generates a first LTM candidate configuration (LTM candidate configuration 1 ). In response to the Handover Request message, the CU 172 transmits 507 a Handover Request Acknowledge message including the first LTM candidate configuration to the S-BS 104. In some implementations, the CU 172 includes the first cell ID in the Handover Request Acknowledge message to indicate that the first LTM candidate configuration is provided for or associated with the first cell (ID).

[0100] The events 505, 590, 507 are collectively referred to in Fig. 5 as an inter-CU LTM preparation procedure (or called inter-MN LTM preparation procedure) 598.

[0101] In some implementations, the Handover Request message includes a DU ID of the S-DU of the S-BS 104. In such cases, the CU 172 includes the DU ID in the first CU-to-DU message. In some implementations, the Handover Request message includes a BS ID of the S- BS 104. When receiving the BS ID, the CU 172 may include the BS ID in the first CU-to-DU message. For example, the BS ID is a gNB ID.

[0102] The CU 172 may or may not request a LTM reference DU configuration in the procedure 590. as described for Figs. 3 and 4. The DU 174 may or may not transmit a LTM reference DU configuration to the CU 172 in the procedure 590, as described for Figs. 3 and 4. In some implementations, the S-BS 104 (e.g., the CU of the S-BS 104) may obtain a LTM reference configuration, as described for Figs. 3 and 4. In other implementations, the S-BS 104 may receive a LTM reference configuration from another BS (not shown in Fig. 5) in another inter-CU LTM preparation procedure as described above and below. If the S-BS 104 obtains aLTM reference configuration, the S-BS 104 may include the LTM reference configuration (S- BS generated LTM reference configuration) in the Handover Request message. In some implementations, the S-BS 104 includes the LTM reference configuration in the inter-node RRC message HandoverPreparationlnformation or as an Xn Application Protocol (XnAP) IE or field and includes the inter-node RRC message or the XnAP IE in the Handover Request message. Alternatively, the S-BS 104 determines to request or cause the C-BS 106 to provide a complete LTM candidate configuration so that the S-BS 104 does not include the LTM reference configuration in the Handover Request message. If the S-BS 104 does not obtain a LTM reference configuration, the S-BS 104 does not include a LTM reference configuration in the Handover Request message. If the Handover Request message includes a LTM reference configuration, the CU 172 may include the LTM reference configuration in the first CU-to-DU message. The DU 174 may extract a LTM reference DU configuration from the LTM reference configuration. Alternatively, the CU 172 extracts a LTM reference DU configuration from the LTM reference configuration and includes the LTM reference DU configuration in the first CU-to-DU message. The DU 174 may generate a LTM DU configuration as a delta configuration based on the LTM reference DU configuration, as described for Fig. 3. Alternatively, the DU 174 may ignore the LTM reference (DU) configuration and generate a LTM DU configuration as a complete configuration, as described for Fig. 3.

[0103] Otherwise, if the Handover Request message does not include a LTM reference configuration, the CU 172 may or may not receive a LTM reference DU configuration from the DU 174 as described for Fig. 3. If the CU 172 receives a LTM reference DU configuration (e.g., in the first DU-to-CU message), the CU 172 generates a LTM reference configuration (C-BS generated LTM reference configuration) including the LTM reference DU configuration. The CU 172 may include a LTM reference CU configuration (candidate CU (C-CU) generated LTM reference CU configuration). Otherwise, if the CU 172 does not receive a LTM reference DU configuration from the DU 174 as described for Fig. 3, the CU 172 does not generate a LTM reference configuration. Alternatively, the CU 172 generates a LTM reference configuration (C-BS generated LTM reference configuration) only including a C-CU generated LTM reference CU configuration. In cases where the CU 172 generates a LTM reference configuration (C-BS generated LTM reference configuration), the CU 172 includes the C-BS generated LTM reference configuration in the Handover Request Acknowledge message.

[0104] In some implementations, if the LTM DU configuration 1 is a complete configuration, the CU 172 generates the LTM candidate configuration 1 as a complete configuration. The CU 172 may include a complete configuration indication (e.g., a BS-to-BSinterface protocol field / IE) in the Handover Request Acknowledge message to indicate that the LTM candidate configuration 1 is a complete configuration. In some implementations, the BS- to-BS interface protocol is an Xn application protocol defined in 3GPP specification 38.423. In some implementations, the complete configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the complete configuration indication is an existing field / IE defined in 3 GPP specification 38.423. Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU 172 generates the LTM candidate configuration 1 as a delta configuration. The CU 172 may exclude the complete configuration indication from the Handover Request Acknowledge message to indicate that the LTM candidate configuration 1 is a delta configuration. Alternatively, the CU 172 may include a delta configuration indication (e.g., a BS-to-BS interface protocol field / IE) in the Handover Request Acknowledge message to indicate that the LTM candidate configuration 1 is a delta configuration. In some implementations, the BS-to-BS interface protocol is an Xn application protocol defined in 3GPP specification 38.423. In some implementations, the delta configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other implementations, the delta configuration indication is an existing field / IE defined in 3GPP specification 38.423. In some implementations, the BS-to-BS interface protocol field / IE have two values (i.e., a first value and a second value). The BS-to- BS interface protocol field / IE set to the first value is the complete configuration indication and the BS-to-BS interface protocol field / IE set to the second value is the delta configuration indication.

[0105] In some implementations, the S-BS 104 is preconfigured with a CSI resource configuration (e.g., (LTM) CSI resource configuration 1) and / or a LTM SSB configuration (LTM SSB configuration 1) for the first cell. In other implementations, the S-BS 104 receives the CSI resource configuration and / or the LTM SSB configuration from an 0AM (Operations, Administration and Maintenance) node. In yet other implementations, the S-BS 104 receives the CSI resource configuration and / or the LTM SSB configuration from the CU 172. For example, the CU 172 includes the CSI resource configuration and / or the LTM SSB configuration in the Handover Request Acknowledge message. In some implementations, the CU 172 includes a PCI (PCI 1) of the first cell in the Handover Request Acknowledge message. To prepare the first cell as a candidate LTM cell for the UE 102, the CU of the S-BS 104 performs a LTM CSI report configuration and / or LTM ID configuration procedure (not shown in Fig. 5) with a S-DU of the S-BS 104, similar to the procedure 392. In the LTM CSI report configuration and / or LTM ID configuration procedure, the CU of the S-BS 104 transmits theCSI resource configuration and / or the LTM SSB configuration to the S-DU of the S-BS 104. In response, the CU of the S-BS 104 receives one or more CSI report configurations for the UE 102 from the S-DU of the S-BS 104. In some implementations, the CU of the S-BS 104 receives the CSI report configuration(s) in a second serving DU configuration from the S-DU.

[0106] To prepare the first cell as a LTM candidate cell for the UE 102, the CU 172 may receive early synchronization information (early synchronization information 1) for the first cell from the DU 174 in a DU-to-CU message (e.g., the first DU-to-CU message or an additional DU-to-CU message). In some implementations, the DU 174 transmits the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other implementations, the DU 174 transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message. The CU 172 includes the early synchronization information in the Handover Request Acknowledge message. The early synchronization information includes a RACH configuration (RACH configuration 1) and / or at least one TCI state configuration (TCI state configuration(s) 1). In some implementations, the DU 174 includes, in the early synchronization information or in the DU-to-CU message, PDCCH order information for early UL synchronization with the first cell. The CU 172 includes the PDCCH order information in the Handover Request Acknowledge message.

[0107] In some implementations, the CU 172 assigns a LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration and includes the LTM ID in the Handover Request Acknowledge message. In other implementations, the S-BS 104 assigns a LTM ID (e.g., LTM ID 1) for identify ing the first LTM candidate configuration.

[0108] After (e.g., in response to) receiving the Handover Request Acknowledge message, the S-BS 104 (e.g., the CU of the S-BS 104) transmits 518 a first RRC reconfiguration message to the UE 102, including {the LTM ID 1, the LTM candidate configuration 1 } as a tuple, similar to the event 318. If the Handover Request Acknowledge message includes the LTM reference configuration, the S-BS 104 may include the LTM reference configuration in the first RRC reconfiguration message. The S-BS 104 may include the CSI resource configuration 1, the TCI state configuration(s) 1, the RACH configuration 1, and / or the LTM SSB configuration 1 in the tuple, if received in the Handover Request Acknowledge message. Alternatively, the S-BS 104 transmits one or more additional RRC reconfiguration messages to the UE 102, including the CSI resource configuration 1, the TCI state configuration(s) 1, the RACH configuration 1, the LTM SSB configuration 1, and / or the PCI of the first cell. In each of the additional RRC reconfiguration message(s), the S-BS 104 includes the LTM ID 1 to indicate that the CSIresource configuration 1, the TCI state configuration(s) 1, the RACH configuration 1, the LTM SSB configuration 1, and / or the PCI of the first cell are associated with the first cell or configured for the first cell. The UE 102 transmits 520 a first RRC reconfiguration complete message to the S-BS 104 in response to the first RRC reconfiguration message. The UE 102 transmits an additional RRC reconfiguration complete message to the S-BS 104 in response to each of the additional RRC reconfiguration complete message. The RRC reconfiguration message(s) (i.e., the first RRC reconfiguration message and / or the additional RRC reconfiguration message(s)) and the RRC reconfiguration complete message(s) (i.e., the first RRC reconfiguration complete message and / or the additional RRC reconfiguration complete message(s)) form a LTM configuration delivery procedure. The S-BS 104 may include the second serving DU configuration in the first RRC reconfiguration message or one or the additional RRC reconfiguration message(s).

[0109] In some implementations, if the Handover Request Acknowledge message includes the complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration, the S-BS 104 includes, in the first RRC reconfiguration message, a complete configuration indication (e.g.. a RRC field / IE) to indicate that the LTM candidate configuration 1 is a complete configuration. Otherwise, if the Handover Request Acknowledge message does not include the complete configuration indication or includes the delta configuration indication to indicate that the LTM candidate configuration 1 is a delta configuration, the S-BS 104 excludes or does not include, in the first RRC reconfiguration message, the complete configuration indication (e g., a RRC field / IE) to indicate that the LTM candidate configuration 1 is a delta configuration.

[0110] If the Handover Request Acknowledge message includes the PDCCH order information (PDCCH order information 1), the S-BS 104 transmits 550 a PDCCH order, based on the PDCCH order information. If the S-BS 104 is a distributed base station, the CU of the S-BS 104 may transmit the PDCCH order information to the S-DU of the S-BS 104. For example, the S-BS 104 or the S-DU of the S-BS 104 transmits 550 a PDCCH order to the UE 102, including the PDCCH order information. In some implementations, the S-BS 104 or the S-DU of the S-BS 104 may determine a SSB index included in the PDCCH order, based on LI measurement report(s) 524, and / or the CSI resource configuration, the CSI report configuration and / or the LTM SSB configuration. In some implementations, the S-DU or the S-BS 104 includes the LTM ID 1 in the PDCCH order to indicate the first cell. The UE 102 transmits 552 a RA preamble to the DU 174 on the first cell, using the RACH configuration and / or the PDCCH order information. The S-DU or the S-BS 104 derives a TA value based on the RApreamble. The DU 174 transmit 556 aDU-CU TA Information Transfer message including the TA value to the CU 172. The CU 172 transmits 558 a CU-CU TA Information Transfer message including the TA value to the S-SB 104 (e.g., the CU of the S-BS 104). In some implementations, the DU 174 includes the cell ID 1, the RA preamble index, a RA-RNTI, the DU ID of the S-DU of the S-BS 104, and / or the BS ID of the S-BS 104 in the message 556. In some implementations, the DU 174 does not include the BS ID in the message 556. In some implementations, the CU 172 includes the cell ID 1. the RA preamble index, the RA-RNTI. the DU ID of the S-DU, and / or the BS ID of the S-BS 104 in the message 558. In some implementations, the CU 172 does not include the BS ID in the message 558. The CU of the S-BS 104 transmits a CU-DU TA Information Transfer message including the TA value, the cell ID 1. the RA preamble index, the RA-RNTI, and / or the DU ID of the S-DU, and / or the BS ID of the S-BS 104 to the S-DU of the S-BS 104. In some implementations, the CU of the S- BS 104 does not include the BS ID in the CU-DU TA Information Transfer message.[OHl] In some implementations, the CU 172 determines an address (e.g., an IP address) of the S-BS 104 or the CU of the S-BS 104. based on the BS ID of the S-BS 104. In other implementations, the CU 172 determines an address (e.g., an IP address) of the S-BS 104 or the CU of the S-BS 104, based on the DU ID of the S-DU of the S-BS 104. With these implementations, the CU 172 sends the CU-CU TA Information Transfer message to the S-BS 104 or the CU of the S-BS 104 in accordance with the address.

[0112] In response to determining to command the UE 102 to perform a LTM cell switch to the first cell, e.g., based on the measurement report(s) 524 and / or 554, the S-DU or the S-BS 104 transmits 526 the LTM Cell Switch Command including the LTM ID 1 to the UE 102. In response to the LTM Cell Switch Command, the UE 102 may stop communication on the serving cell(s). In response to the LTM Cell Switch Command, the UE 102 accesses 532 the first cell and transmits 536 a RRC reconfiguration complete message to DU 174. The DU 174 in turn transmits 538 a DU-to-CU message including the RRC reconfiguration complete message to the CU 172. After receiving 538 the DU-to-CU message or the RRC reconfiguration complete message, the C-BS 106 communicates 540 with the UE 102 in accordance with the first LTM candidate configuration and / or the LTM reference configuration. In some implementations, the UE 102 includes the LTM ID 1 in the RRC reconfiguration complete message 536 to indicate that the UE 102 applies the first LTM candidate configuration. In accordance with the LTM ID 1, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration. In other implementations, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration based on the firstcell ID included in the Access Success message 534. In such implementations, the CU 172 maintains or stores association information between the first cell ID. and the first LTM candidate configuration and / or the LTM reference configuration. When the CU 172 receives the first cell ID in the Access Success message, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration in accordance with the first cell ID and the association information.

[0113] In some implementations, if the S-DU or the S-BS 104 receives a TA value as described above, the S-DU or the S-BS 104 may include the TA value in the LTM Cell Switch Command. In some implementations, the S-DU or the S-BS 104 includes a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID indicates a first one of the TCI state configuration(s).

[0114] In response to determining to command the UE 102 to perform the LTM cell switch or transmitting 526 the LTM Cell Switch Command, the S-DU of the S-BS 104 transmits a DU-CU Cell Switch Notification message to the CU of the S-BS 104 to indicate that the UE 102 performs or is performing a LTM cell switch to the first cell. In response to receiving the DU-CU Cell Switch Notification message, the CU of the S-BS 104 transmits 527 a CU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 performs a LTM cell switch to the first cell. In response, the CU 172 transmits 530 a CU-DU Cell Switch Notification message to the DU 174 to indicate that the UE 102 performs a LTM cell switch to the first cell. In some implementations, the S-BS 104 includes the first TCI state ID in the CU- CU Cell Switch Notification message and the CU 172 then includes the first TCI state ID in the CU-DU Cell Switch Notification message. The UE 102 and the DU 174 identify the first one of the TC state configuration(s) based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in the events 532, 536 and / or 540.

[0115] In some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting 526 the LTM Cell Switch Command, or receiving 527 the DU-CU Cell Switch Notification message, the S-BS 104 (e.g., the CU of the S-BS 104) transmits 531 one or more Early Status Transfer messages to the CU 172. each including a DL COUNT value or a DISCARD DL COUNT value for a DRB over which the UE 102 and the S-BS 104 communicate 502 data. In some implementations, after receiving 534 the Access Success message or receiving 538 the DU-to-CU message or the RRC reconfiguration complete message, the CU 172 transmits 539 a LTM Success message to the S-BS 104 (e.g., the CU of the S-BS 104) to indicate that the LTM cell switch is completedsuccessfully. In some implementations, the LTM Success message is a Handover Success message. In some implementations, the CU 172 includes the first cell ID in the LTM Success message. In other implementations, the CU 172 does not transmit a BS-to-BS message to the S-BS 104 (e.g., the CU of the S-BS 104) to indicate that the LTM cell switch is completed successfully.

[0116] In some implementations, after (e.g.. in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting 526 the LTM Cell Switch Command, receiving 527 the DU-CU Cell Switch Notification message, or receiving 539 the LTM Success message, the S-BS 104 (e.g., the CU of the S-BS 104) transmits 541 a SN Status Transfer message to the CU 172, including a DL COUNT value and / or a UL COUNT value for a / the DRB over which the UE 102 and the S-BS 104 communicate 502 data.

[0117] In some implementations, after (e.g., in response to) receiving 534 theyicces.' Success message, receiving 538 the DU-to-CU message or the RRC reconfiguration complete message or receiving 541 the SN Status Transfer message, the CU 172 transmits 543 a UE Context Release message to the S-BS 104. In response to the UE Context Release message, the S-BS 104 releases a UE context of the UE 102.

[0118] In some implementations, the S-BS 104 (e.g., the CU of the S-BS 104) may prepare additional cell(s) (i.e., cell(s) 2, ... , N) as LTM candidate cell(s) for the UE 102 with the CU 172, before or after transmitting the LTM Cell Switch Command or during, before or after the procedure 598. as described above. The cell(s) 2. .... N are identified by cell ID(s) 2. .... N, respectively and operated by the DU 174 and / or other DU(s) of the C-BS 106. N is an integer and larger than 1. For example, the S-BS 104 performs additional inter-CU LTM preparation procedure(s) 2, ... , N with the CU 172 to prepare the cell(s) 2, ...N respectively. Each of the inter-CU LTM preparation procedure(s) 2, ... , N is similar to the procedure 598. In the inter- CU LTM preparation procedure(s) 2, ... , N, the S-BS 104 receives LTM candidate configuration(s) 2, ... , N configuring the cell(s) 2, ... , N for LTM, respectively. As described above, the S-BS 104 or the C-BS 106 assigns LTM ID(s) 2, . . . , N to identify the LTM candidate configuration(s) 2, ... , N, respectively. The S-BS 104 may obtain CSI resource configuration 2, .... , N for the cell(s) 2, ... , N respectively, as described for the CSI resource configuration 1. The S-BS 104 may obtain CSI report configuration(s) 2, ... , N or the cell(s) 2, ... , N, respectively, as described for the CSI report configuration(s) 1. The S-BS 104 may obtain RACH configuration 2, .. . , N for the cell(s) 2, .. . , N respectively, as described for the RACH configuration 1. The S-BS 104 may obtain TCI state configuration(s) 2. .... N for the cell(s) 2, ... , N respectively, as described for the TCI state configuration(s) 1. The S-BS 104 may obtainLTM SSB configuration 2, N for the cell(s) 2, ... , N, respectively, as described for LTM SSB configuration 1. The S-BS 104 may obtain PCI(s) 2. .... N for the cell(s) 2. ... , N respectively, as described for the PCI 1. In some implementations, the S-BS 104 may perform LTM configuration delivery procedure 2, .. . , N with the UE 102 to transmit a list of the {LTM ID 2, the LTM candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained), the PCI 2 (if obtained)}. .... {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configured on(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained), the PCI N (if obtained)} to the UE 102, respectively. Each of the LTM configuration delivery procedure 2. ... , N is similar to the procedures 394, 494 and / or 594. In other implementations, the S-BS 104 includes the list in the first RRC reconfiguration message.

[0119] In other implementations, the S-BS 104 performs the procedure 598 with the CU 172 to prepare one or more of the cell(s) 1 , . .. , N as LTM candidate cell(s) for the UE 102. In such implementations, the S-BS 104 includes the cell ID(s) 1, ... , N in the Handover Request message 505 for LTM. as described for the cell ID 1 . In some implementations, upon receiving the Handover Request message, the CU 172 determines or selects the cell(s) 1, ... , M from the cell(s) 1, ... , N as LTM candidate cell(s). M is a positive integer and M < N. In other implementations, CU 172 prepares the cell(s) 1, .... N for LTM as requested inHandover Request message. The CU 172 performs LTM preparation procedure(s) 2, . . . , M with the DU 172 to prepare the cell(s) 2, . . . , M as LTM candidate cell(s) for the UE 102, respectively. The LTM preparation procedure(s) 2, ... , M are similar to the procedure 590 that the CU 172 performs with the DU 174 to prepare the cell 1. The CU 172 obtains the LTM candidate configuration(s) 2, . . . , M for the cell(s) 2, .. . , M as a result of the LTM preparation procedure(s) 2, ... , M respectively, similar to obtaining the LTM candidate configuration 1. The C-BS 106 may generate the LTM candidate configuration(s) 2, ... , M as complete configuration(s) or generate delta configuration(s) based on the LTM reference configuration, as described for the LTM candidate configuration 1. The CU 172 includes the LTM candidate configuration(s) 2, .... M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 104 assigns LTM ID(s) 2, ... , M to identify the LTM preparation procedure(s) 2, ... , M respectively, as described for the LTM ID 1. In the case the CU 172 assigns the LTM ID(s) 1, ... , M, the CU 172 includes the LTM ID(s) 1, ... , M with the LTM candidate configured on(s) 1. ... , M. respectively in the Handover Request Acknowledge message, as described for the LTM ID 1 and the LTM candidate configuration 1.

[0120] In some implementations, the CU 172 obtains early synchronization information 2, M for the cell(s) 2, M, respectively, as described for the early synchronization information 1. The CU 172 includes the early synchronization information 2, M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 104 obtains CSI resource configuration(s) 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the CSI resource configuration 1. In the case that the CU 172 obtains the CSI resource configuration(s) 2, ... , M, the CU 172 includes the CSI resource configuration(s) 2. . .. , M in the Handover Request Acknowledge message.

[0121] In some implementations, the CU 172 or the S-BS 104 obtains LTM SSB configuration(s) 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the LTM SSB configuration 1. In the case that the CU 172 obtains the LTM SSB configuration(s) 2. ... . M, the CU 172 includes the LTM SSB configuration(s) 2, ... , M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 104 obtains PCI(s) 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the PCI 1. In the case that the CU 172 obtains the PCI(s) 2, .. . . M, the CU 172 includes the PCI(s) 2, . . . , M in the Handover Request Acknowledge message.

[0122] In some implementations, the CU 172 includes a list of {the cell ID 1, the LTM ID 1 (if obtained or optional), the LTM candidate configuration 1, the CSI resource configuration 1 (if obtained or optional), the TCI state configuration 1 (if obtained or optional), the early synchronization information 1 (if obtained or optional), the LTM SSB configuration 1 (if obtained or optional), PCI I (if obtained or optional)}, , {the cell ID M, the LTM ID M (if obtained or optional), the LTM candidate configuration M, the CSI resource configuration M (if obtained or optional), the TCI state configuration M (if obtained or optional), the early synchronization information M (if obtained or optional), the LTM SSB configuration M (if obtained or optional), the PCI M (if obtained or optional)} in the Handover Request Acknowledge message.

[0123] In some implementations, the CU 172 obtains PDCCH order information 2, ... , M for the cell(s) 2, . . . , M, respectively, as described for the PDCCH order information 1. In one implementation, the CU 172 includes the PDCCH order information 2, . . . , M in the Handover Request Acknowledge message. In another implementation, the CU 172 includes the PDCCH order information 2, . . . , M in the early synchronization information 2, . .. , M, respectively. The S-BS 104 may obtain RACH configuration 2, TCI state configuration(s) 2 and / or the PDCCH order information 2. ... ., RACH configuration M. TCI state configuration(s) M and / or thePDCCH order information M from the early synchronization information 2, . . . , M, respectively or from the Handover Request Acknowledge message.

[0124] In some implementations, the S-BS 104 may perform LTM configuration delivery procedure 2, , M with the UE 102 to transmit a list of the {LTM ID 2, the LTM candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained), the PCI 2 (if obtained)}, ... , {the LTM ID M, the LTM candidate configuration M. the CSI resource configuration M, the TCI state configuration(s) M (if obtained), the RACH configuration M (if obtained), the LTM SSB configuration M (if obtained), the PCI M (if obtained)} to the UE 102, respectively. Each of the LTM configuration delivery procedure 2, . .. , M is similar to the procedures 394. 494 and / or 594. In other implementations, the S-BS 104 includes the list in the first RRC reconfiguration message.

[0125] In some implementations, the S-BS 104 may include measurement result(s) 1, . . . , N for the cell(s) 1, ... , N respectively in the Handover Request message. The S-BS 104 receives the measurement result(s) from the UE 102. The C-BS 106 may select or determine the cell(s) 1, ... M, based on the measurement result(s) 1, ... , N. In other implementations, the C-BS 106 may select or determine the cell(s) 1, ... M, based on one or more other factors (e.g., capacity or load of the cell(s) 1, ... , N and / or a maximum number of LTM candidate cell(s)). In one implementation, the maximum number is included in the Handover Request message. In another implementation, the maximum number is a predetermined number.

[0126] Next, several example methods, which can be implemented in a RAN node (e.g., a base station, a DU or a CU) for inter-CU LTM, are discussed next with reference to Figs. 6A- 13. Descriptions described for Figs. 3-5 can apply to Figs. 6A-13. Similar steps are similarly labeled (e.g., 302, 402. 502, 602, etc.) and individual descriptions are therefore omitted.

[0127] Fig. 6A illustrates an example method 600A, which can be implemented by an S-BS (e.g., the S-BS 104 in Fig. 5). The method 600A begins at block 602, where the S-BS communicates with a UE. At block 680, the S-BS might perform at least one intra-CU LTM preparation and / or execution procedure with the UE (e.g., event 396, 496. 380, and / or 480). At block 660, the S-BS determines to prepare a first cell as a LTM candidate cell for the UE. At block 605, the S-BS transmits a Handover Request message to a C-BS (e.g., the C-BS 106 in Fig. 5) to request preparing the first cell as a LTM candidate cell for the UE. At block 607 A, the S-BS receives a Handover Request Acknowledge message from the C-BS, including a first LTM candidate configuration configuring the first cell as a LTM candidate cell for the UE. At block 662, the S-BS obtains a first LTM CSI resource configuration, configuring CSI resourcesfor the first cell. At block 664, the S-BS generates a first LTM CSI report configuration based on the first LTM CSI resource configuration. At block 618, the S-BS transmits the first LTM candidate configuration and the first LTM CSI report configuration to the UE. At block 624, the S-BS receives one or more LI measurement reports from the UE in accordance with the first LTM CSI report configuration.

[0128] In some implementations, the S-BS receives the first LTM CSI resource configuration from a network node (e.g., 0AM). In other implementations, the S-BS is preconfigured with the first LTM CSI resource configuration in a storage and obtains the first LTM CSI resource configuration from the storage. In some implementations, the first LTM CSI report configuration configures CSI report(ing) for CSI resources configured in the first LTM CSI resource configuration. In some implementations, the CSI resources include one or more reference signals, and / or time and frequency resources for the reference signal(s). The reference signal(s) might include SSB(s) and / or CSI-RS(s).

[0129] In some implementations, the LI measurement report(s) include LI measurement results for the first cell. The LI measurement report(s) may include LI measurement result(s) for a serving cell where the S-BS receives the LI measurement report(s). The S-BS determines whether to command the UE to perform a LTM cell switch to the first cell, based on the LI measurement report(s). If the S-BS determines to command the UE to perform a LTM cell switch to the first cell, the S-BS transmits a LTM cell switch command to the UE, commanding the UE to perform a LTM cell switch to the first cell. In response to commanding the UE to perform the LTM cell switch, the S-BS might transmit a CU-to-CU Cell Switch Notification message to the C-BS, notifying that the S-BS initiates transmission of a LTM cell switch command to the UE for a LTM cell switch to the first cell. In response to commanding the UE to perform the LTM cell switch, the S-BS might transmit an Early Status Transfer message to the C-BS, including a DL COUNT value or a DISCARD DL COUNT value for a DRB over which the UE and the S-BS communicate data. After transmitting the LTM cell switch command, the S-BS might receive an LTM Success message from the C-BS, notifying the LTM cell switch is completed successfully. In response to commanding the UE to perform the LTM cell switch or after transmitting the LTM cell switch command or receiving the LTM Success message, the S-BS might transmit a SN Status Transfer message to the C-BS, including a UL COUNT value and / or a DL COUNT value for the DRB.

[0130] In some implementations, the S-BS generates at least one first RRC message including the first LTM candidate configuration, a first configuration ID identifying the first LTM candidate configuration, the first LTM CSI resource configuration and the first LTM CSIreport configuration to the UE. In some implementations, the S-BS generates a first LTM configuration, including the first LTM candidate configuration, the first configuration ID, and the first LTM CSI resource configuration. In some implementations, the first configuration ID is a LTM candidate ID. In some implementations, the S-BS generates a first serving configuration including the first LTM CSI report configuration. For example, the first serving configuration is a cell group configuration (e.g., CellGroupConfig IE). The S-BS transmits the first RRC message(s) including the first LTM configuration and the first serving configuration to the UE at block 618. In some implementations, the Handover Request Acknowledge message at block 607A includes a first cell ID of the first cell to indicate that the first LTM candidate configuration is associated with the first cell.

[0131] In some implementations, while or after preparing the first cell as a LTM candidate cell for the UE, the S-BS may prepare a second cell of the C-BS (i.e., a first C-BS) as a LTM candidate cell for the UE by transmitting a second Handover Request message to the C-BS, similar to block 605. In response, the S-BS receives a second Handover Request Acknowledge message from the C-BS, including a second LTM candidate configuration configuring the second cell for LTM, similar to block 607 A. The S-BS obtains a second LTM CSI resource configuration configuring CSI resources for the second cell and generates a second LTM CSI report configuration based on the second LTM CSI resource configuration, similar to blocks 662 and 664 respectively. In some implementations, the S-BS includes the second LTM candidate configuration, a second configuration ID identifying the second LTM candidate configuration, the second LTM CSI resource configuration in the first RRC message or the first LTM configuration. The S-BS might include the second LTM CSI report configuration in the first serving configuration or the first RRC message. In some implementations, the second configuration ID is a LTM candidate ID.

[0132] In other implementations, the S-BS transmits at least one second RRC message to the UE, including the second LTM candidate configuration, the second configuration ID, the second LTM CSI resource configuration and the second LTM CSI report configuration, similar to block 618. In some implementations, the S-BS generates a second LTM configuration, including the second LTM candidate configuration, the second configuration ID, and the second LTM CSI resource configuration. In some implementations, the S-BS might include the second LTM CSI report configuration in a second serving configuration, and includes the second serving configuration in the second RRC message(s). For example, the second serving configuration is a cell group configuration (e.g., CellGroupConfig IE). The S-BS includes the second LTM configuration and the second serving configuration in the second RRCmessage(s). In some implementations, the second Handover Request Acknowledge message includes a second cell ID of the second cell to indicate that the second LTM candidate configuration is associated with the second cell.

[0133] In some implementations, while or after preparing the first cell for LTM, the S-BS may prepare a third cell of another C-BS (i.e. second C-BS) as a LTM candidate cell for the UE by transmitting a third Handover Request message to the second C-BS. similar to block 605. In response, the S-BS receives a third Handover Request Acknowledge message from the second C-BS, including a third LTM candidate configuration configuring the third cell for LTM, similar to block 607A. The S-BS obtains a third LTM CSI resource configuration configuring CSI resources for the third cell and generates a third CSI report configuration based on the third LTM CSI resource configuration, similar to blocks 662 and 664 respectively. In some implementations, the S-BS includes the third LTM candidate configuration, a third configuration ID identifying the third LTM candidate configuration, the third LTM CSI resource configuration in the first LTM configuration, the second LTM configuration, the first RRC message(s) and / or the second RRC message(s). The S-BS might include the third LTM CSI report configuration in the first serving configuration, the first RRC message, the second serving configuration or the second RRC message. In some implementations, the third configuration ID is a LTM candidate ID.

[0134] In other implementations, the S-BS transmits at least one third RRC message to the UE, including the third LTM candidate configuration, the third configuration ID, the third LTM CSI resource configuration and the third LTM CSI report configuration, similar to block 618. In some implementations, the S-BS generates a third LTM configuration, including the third LTM candidate configuration, the third configuration ID, and the third LTM CSI resource configuration. In some implementations, the S-BS includes the third LTM CSI report configuration in a third serving configuration and includes the third serving configuration in the third RRC message(s). For example, the third serving configuration is a cell group configuration (e.g., CellGroupConfig IE). The S-BS includes the third LTM configuration and the third serving configuration in the third RRC message(s). In some implementations, the third Handover Request Acknowledge message includes a third cell ID of the third cell to indicate that the third LTM candidate configuration is associated with the third cell.

[0135] In some implementations, the first, second and third RRC message(s) are RRC reconfiguration messages.

[0136] Fig. 6B is a flow diagram of an example method 600B similar to the method 600A, except that the method 600B includes block 607B instead of blocks 607A and 662. At block607B, the S-BS receives a Handover Request Acknowledge message from the first C-BS, including a first LTM candidate configuration and a first LTM CSI resource configuration for the UE, where the first LTM candidate configuration configures the first cell for LTM and the first LTM CSI configuration configures CSI resources for the first cell.

[0137] Fig. 7A illustrates an example method 700A similar to the method 600 A, which can be implemented by a CU of an S-BS (e.g., the S-BS 104 of Fig. 5). The method 700A begins at block 702. where the CU communicates with a UE via an S-DU. At block 780-1, the CU might perform an intra-CU intra-DU LTM preparation and / or execution procedure with the S- DU (e.g., event 396 or 380). At block 780-2, the CU might perform an intra-CU inter-DU LTM preparation and / or execution procedure with a candidate DU (e.g., event 496 or 480). The flow proceeds to blocks 660, 605. 607 A, and 662. At block 712, the CU transmits a first CU-to-DU message to the S-DU, including the first LTM CSI resource configuration (e.g., event 312, 392, or 492). At block 714, the CU receives a DU-to-CU message from the S-DU, including a first LTM CSI report configuration. In some implementations, the first LTM CSI report configuration is generated by the S-DU based on the first CSI resource configuration. At block 718, the CU transmits a first RRC message to the UE via the S-DU. including the first LTM candidate configuration and the first configuration ID. At block 728, the CU receives a DU- CU Cell Switch Notification message from the S-DU.

[0138] Examples and implementations described for Fig. 6A can apply to the Fig. 7A. In some implementations, the CU includes the second configuration ID and the second cell ID in the first CU-to-DU message. In other implementations, the CU transmits a second CU-to-DU message to the S-DU, including second configuration ID and the second cell ID, similar to the event 312, 392, or 492. In some implementations, the CU includes the third configuration ID and the third cell ID in the first CU-to-DU message or the second CU-to-DU message. In other implementations, the CU transmits a third CU-to-DU message to the S-DU, including third configuration ID and the third cell ID, similar to the event 312, 392, or 492.

[0139] Fig. 7B is a flow diagram of an example method 700B similar to the methods 600B and 700 A, except that the method 700B includes block 607B instead of blocks 607A and 662.

[0140] Fig. 8 illustrates an example method 800, which can be implemented by a C-BS (e.g.. the C-BS 106 or the CU 172 in Fig. 5). The method 800 begins at block 805, where the C-BS receives a Handover Request message from an S-BS (e.g., the S-BS 104 in Fig. 5), requesting to prepare a first cell as a LTM candidate cell for a UE. At block 862, the C-BS obtains a first LTM CSI resource configuration configuring CSI resources for the first cell. At block 807. the C-BS transmits a Handover Request Acknowledge message to the S-BS, including a first LTMcandidate configuration and the first LTM CSI resource configuration, where the first LTM candidate configuration configures the first cell as a LTM candidate cell for the UE.

[0141] In some implementations, the C-BS receives the first LTM CSI resource configuration from a network node (e.g., 0AM). In other implementations, the C-BS is preconfigured with the first LTM CSI resource configuration in a storage and obtains the first LTM CSI resource configuration from the storage. Examples and implementations for the C- BS described for Fig. 6A can apply to Fig. 8.

[0142] Fig. 9 illustrates an example method 900 similar to the method 800, which can be implemented by a CU of a C-BS (e.g., the C-BS 106 of Fig. 5). The method 900 begins at block 805. At block 962, the CU receives a DU-to-CU message including a first LTM CSI resource configuration from a DU. where the first LTM CSI resource configuration configures CSI resources for the first cell. The flow proceeds to block 807.

[0143] The DU operates the first cell. In some implementations, the CU transmits a CU-to- DU message to the DU and receives the DU-to-CU message from the DU in response. For example, the CU-to-DU message and the DU-to-CU message are a UE Context Setup Request message and a UE Context Setup Response message, respectively. In other implementations, the CU-to-DU message and the DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In other implementations, the DU-to-CU message is a Fl Setup Request message and the CU transmits a F 1 Setup Response message to the DU in response. In yet other implementations, the DU-to- CU message is a GNB-DU Configuration Update message and the CU transmits a GNB-DU Configuration Update Acknowledge message to the DU in response. In yet other implementations, the DU-to-CU message is a GNB-CU Configuration Update Acknowledge message.

[0144] Fig. 10A is a flow diagram of an example method 1000A similar to the method 600A, except that the method 1000A includes blocks 1072, 1074, 1018, and 1024 instead of blocks 662, 664, 618, and 624. Blocks 1072, 1074, 1018, and 1024 are similar to blocks 662, 664, 618, and 624.

[0145] At block 1072, the S-BS obtains first SSB information for the first cell, where the first SSB information includes time and frequency configuration of one or more SSBs transmitted on the first cell. At block 1074, the S-BS generates a first LTM SSB configuration based on the first SSB information. The first LTM SSB configuration includes or configures the time and frequency configuration of the one or more SSBs. At block 1018, the S-BS transmits the first LTM candidate configuration and the first LTM SSB configuration to theUE. At block 1024, the S-BS receives, from the UE, one or more LI measurement reports each including a measurement result for a SSB configured in the first LTM SSB configuration. In some alternative implementations of block 1072, the S-BS obtains the first LTM SSB configuration instead of the first SSB information. In such cases, block 1074 is skipped.

[0146] In some implementations, the S-BS receives the first SSB information from a network node (e.g., 0AM). In other implementations, the S-BS is preconfigured with the first SSB information in a storage and obtains the first SSB information from the storage. In some implementations, the first SSB information is LTM SSB information.

[0147] In some implementations, the S-BS generates at least one first RRC message including the first LTM candidate configuration, a first configuration ID identifying the first LTM candidate configuration, and the first LTM SSB configuration to the UE. In some implementations, the S-BS generates a first LTM configuration, including the first LTM candidate configuration, the first configuration ID, and the first LTM SSB configuration. In some implementations, the first configuration ID is a LTM candidate ID. The S-BS transmits the first RRC message including the first LTM configuration to the UE at block 1018.

[0148] In some implementations, while or after preparing the first cell as a LTM candidate cell for the UE, the S-BS may prepare a second cell of the C-BS (i.e., a first C-BS) as a LTM candidate cell for the UE by transmitting a second Handover Request message to the C-BS, similar to block 605. In response, the S-BS receives a second Handover Request Acknowledge message from the C-BS, including a second LTM candidate configuration configuring the second cell for LTM, similar to block 607A. The S-BS obtains second SSB information for the UE, which includes time and frequency configuration of one or more SSBs transmitted on the second cell, similar to block 1072. The second SSB information might be LTM SSB information. The S-BS generates a second LTM SSB configuration based on the second SSB information, similar to block 1074. Alternatively, the S-BS obtains the second LTM SSB configuration, e.g., from the network node or the storage. In some implementations, the S-BS includes the second LTM candidate configuration, a second configuration ID identifying the second LTM candidate configuration, the second LTM SSB configuration in the first RRC message or the first LTM configuration. In some implementations, the second configuration ID is a LTM candidate ID.

[0149] In other implementations, the S-BS transmits at least one second RRC message to the UE, including the second LTM candidate configuration, the second configuration ID, and the second LTM SSB configuration, similar to block 1018. In some implementations, the S-BS generates a second LTM configuration, including the second LTM candidate configuration, thesecond configuration ID, and the second LTM SSB configuration. The S-BS includes the second LTM configuration in the second RRC message(s).

[0150] In some implementations, the second Handover Request message and the second Handover Request Acknowledge message can be combined with the first Handover Request message and the first Handover Request Acknowledge message as a single Handover Request message and a single Handover Request Acknowledge message, respectively.

[0151] In some implementations, while or after preparing the first cell for LTM, the S-BS may prepare a third cell of another C-BS (i.e. second C-BS) as a LTM candidate cell for the UE by transmitting a third Handover Request message to the second C-BS, similar to block 605. In response, the S-BS receives a third Handover Request Acknowledge message from the second C-BS, including a third LTM candidate configuration configuring the third cell for LTM, similar to block 607 A. The S-BS obtains third SSB information for the UE, which includes time and frequency configuration of one or more SSBs transmitted on the third cell, similar to block 1072. The third SSB information might be LTM SSB information. The S-BS generates a third LTM SSB configuration based on the third SSB information, similar to block 1074. Alternatively, the S-BS obtains the third LTM SSB configuration, e.g., from the network node or the storage. In some implementations, the S-BS includes the third LTM candidate configuration, a third configuration ID identifying the third LTM candidate configuration, the third LTM SSB configuration in the first LTM configuration, the second LTM configuration, the first RRC message(s) and / or the second RRC message(s). In some implementations, the second configuration ID is a LTM candidate ID.

[0152] In other implementations, the S-BS transmits at least one third RRC message to the UE, including the third LTM candidate configuration, the third configuration ID, and the third LTM SSB configuration, similar to block 1018. In some implementations, the S-BS generates a third LTM configuration, including the third LTM candidate configuration, the third configuration ID, and the third LTM SSB configuration. The S-BS includes the third LTM configuration in the third RRC message(s).

[0153] Fig. 10B is a flow diagram of an example method 1000B similar to the methods 600 A, 600B. and 1000A. except that the method 1000B includes block 1007B instead of blocks 607A and 1072. At block 1007B, the S-BS receives a Handover Request Acknowledge message from the C-BS, including a first LTM candidate configuration and first SSB information for the UE, where the first LTM candidate configuration configures the first cell for LTM, and the first SSB information includes time and frequency configuration of one or more SSBs transmitted on the first cell. In some alternative implementations in block 1007B, the HandoverRequest Acknowledge message includes the first LTM SSB configuration instead of the first SSB information. In such cases, block 1074 is skipped.

[0154] Examples and implementations described for Fig. 6A can apply to Figs. 10A and 10B. Fig. 10A or 10B can be combined with Fig. 6 A or 6B.

[0155] Fig. 11 illustrates an example method 1100 similar to the method 800. The method 1100 begins at block 805 and proceed to blocks 1172 and 1174 similar to blocks 1072 and 1074 respectively. At block 1107. the C-BS transmits a Handover Request Acknowledge message to the S-BS, including a first LTM candidate configuration and the first LTM SSB configuration, where the first LTM candidate configuration configures the first cell for LTM.

[0156] In some implementations, the C-BS receives the first SSB information from a network node (e.g., 0AM). In other implementations, the C-BS is preconfigured with the first SSB information in a storage and obtains the first SSB information from the storage. In some alternative implementations, the C-BS obtains the first LTM SSB configuration instead of the first SSB information. In such cases, block 1174 is skipped.

[0157] Examples and implementations described for Figs. 6A. 6B, and 8 can apply to Fig. 11. Fig. 11 can be combined with Fig. 8. Examples and implementations described for the S- BS in Figs. 10A and 10B can apply to the C-BS in Fig. 11. For example, while preparing the second cell with the S-BS as described for Fig. 10A, the C-BS obtains the second SSB information and generates the second LTM SSB configuration based on the second SSB information instead of the S-BS. Alternatively, the C-BS obtains the second LTM SSB configuration, e g., from the network node or the storage. The C-BS includes the second LTM SSB configuration in the second Handover Request Acknowledge message.

[0158] Fig. 12 illustrates an example method 1200 similar to the methods 800, 900, and 1100, which can be implemented by a CU of a C-BS (e.g., the C-BS 106 of Fig. 5). The method 1200 begins at blocks 805 and proceeds to blocks 1272 and 1174. At block 1272, the CU receives a DU-to-CU message including first SSB information from a DU, where the first SSB information includes time and frequency configuration of one or more SSBs transmitted on the first cell. The flow proceeds to block 1174 from block 1272.

[0159] Examples and implementations described for Figs. 6A, 6B. 8. 9, and 11 can apply to Fig. 12. Fig. 12 can be combined with Fig. 9. Examples and implementations described for the S-BS in Figs. 10A and 10B can apply to the CU in Fig. 12. For example, while preparing the second cell with the S-BS as described for Fig. 10A, the CU of the C-BS receives the second SSB information in a DU-to-CU message from the DU and generates the second LTM SSB configuration based on the second SSB information. Alternatively, the CU of the C-BS obtainsthe second LTM SSB configuration in a DU-to-CU message from the DU instead of the second SSB information. The C-BS includes the second LTM SSB configuration in the second Handover Request Acknowledge message.

[0160] The following description may be applied to the description above.

[0161] 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.

[0162] 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 “DU configuration” can be replaced by “cell group configuration”. 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”. "Handover Request” and “Handover Request Acknowledge" described above are for illustration of the invention and can be replaced by messages with general names. For example, “Handover Request” and “Handover Request Acknowledge” can be replaced by a first CU-to-CU message and a second CU-to-CU message, respectively. In another example, “Handover Request” and “Handover Request Acknowledge” can be replaced by a first interface message and a second interface message, respectively. In yet another example, “Handover Request” and “Handover Request Acknowledge” can be replaced by a first BS-to-BS message and a second BS-to-BS message, respectively. In some implementations, “include” can be replaced by “comprise”. In some implementations, “exclude” can be replaced by “refrain from including”.

[0163] 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 intemet-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.

[0164] Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules may can be software modules (e.g., code, or machine- readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module can comprise dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g.. as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry', or in temporarily configured circuitry (e.g... configured by software) may be driven by cost and time considerations.

[0165] 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.

[0166] 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 theart, 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.

[0167] The following examples are illustrative only and may be combined with other examples or teachings described herein, without limitation.

[0168] Example 1 is a method of wireless communication performed by a radio access network, RAN, node, the method including transmitting, to a candidate RAN node, a handover request message; receiving, from the candidate RAN node in response to the handover request message, a handover request acknowledgement message including a lower-layer triggered mobility, LTM, candidate cell configuration; obtaining a reference signal resource configuration associated with a LTM candidate cell; generating a channel state information, CSI, report configuration based on the reference signal resource configuration; and transmitting, to a user equipment, UE, the CSI report configuration, the reference signal resource configuration, and the LTM candidate cell configuration.

[0169] Example 2 may be combined with example 1 and further includes that the obtaining the reference signal resource configuration including receiving the reference signal resource configuration in the handover request acknowledgement message.

[0170] Example 3 may be combined with any examples 1 to 2 and further includes that the reference signal resource configuration indicates resources for at least one of: a CSI reference signal, CSI-RS: or a synchronization signal block. SSB.

[0171] Example 4 may be combined with any examples 1 to 3 and further includes receiving, from the UE, a CSI report based on the CSI report configuration and the reference signal resource configuration.

[0172] Example 5 may be combined with any examples 1 to 4 and further includes transmitting, to the UE, an LTM cell switch command for switching to the LTM candidate cell; transmitting, to the candidate RAN node, at least one of: a cell switch notification message; or an early status transfer message; receiving, from the candidate RAN node, an LTM success message; and transmitting, to the candidate RAN node, a sequence number. SN, status transfer message.

[0173] Example 6 may be combined with any examples 1 to 5 and further includes that the transmitting the CSI report configuration, the reference signal resource configuration, and the LTM candidate cell configuration including transmitting the CSI report configuration, thereference signal resource configuration, and the LTM configuration in a radio resource control, RRC, reconfiguration message.

[0174] Example 7 may be combined with any examples 1 to 6 and further includes that the RAN node including a serving base station and further includes that the candidate RAN node including a candidate base station.

[0175] Example 8 is a method of wireless communication performed by a radio access network, RAN, node, the method including transmitting, to a candidate RAN node, a handover request message; receiving, from the candidate RAN node in response to the handover request message, a handover request acknowledgement message indicating a lower-layer triggered mobility. LTM. candidate cell configuration; obtaining a reference signal resource configuration associated with a LTM candidate cell; transmitting, by a central unit, CU, of the RAN node, to a distributed unit, DU, of the RAN node, a CU-to-DU message including the reference signal resource configuration; receiving, by the CU from the DU, a DU-to-CU message including a channel state information, CSI, report configuration; and transmitting, to a user equipment, UE, the CSI report configuration, the reference signal resource configuration, and the LTM candidate cell configuration.

[0176] Example 9 may be combined with example 8 and further includes that the obtaining the reference signal resource configuration including receiving the reference signal resource configuration in the handover request acknowledgement message.

[0177] Example 10 may be combined with any examples 8 to 9 and further includes that the reference signal resource configuration indicates resources for at least one of: a CSI reference signal, CSI-RS; or a synchronization signal block. SSB.

[0178] Example 11 may be combined with any examples 8 to 10 and further includes receiving, from the UE, a CSI report based on the CSI report configuration and the reference signal resource configuration.

[0179] Example 12 may be combined with any examples 8 to 1 1 and further includes transmitting, to the UE, an LTM cell switch command to switch to the LTM candidate cell; transmitting, to the candidate RAN node, at least one of: a cell switch notification message; or an early status transfer message; and receiving, from the candidate RAN node, an LTM success message.

[0180] Example 13 may be combined with any examples 8 to 12 and further includes that the transmitting the CSI report configuration, the reference signal resource configuration, andthe LTM candidate cell configuration including transmitting the CSI report configuration, the reference signal resource configuration, and the LTM candidate cell configuration in a radio resource control, RRC, reconfiguration message.

[0181] Example 14 may be combined with any examples 8 to 13 and further includes that the RAN node including a serving base station and further includes that the candidate RAN node including a candidate base station.

[0182] Example 15 is a method of wireless communication performed by a radio access network, RAN, node, the method including receiving, from a serving RAN node, a handover request message; and transmitting, to the serving RAN node, a handover request acknowledgement message including a lower-layer triggered mobility, LTM. candidate cell configuration and a reference signal resource configuration associated with a LTM candidate cell.

[0183] Example 16 may be combined with example 15 and further includes receiving, from an operations, administration and maintenance, 0AM, node, the reference signal resource configuration associated with the LTM candidate cell.

[0184] Example 17 may be combined with any examples 15 to 16 and further includes retrieving, from a memory of the RAN node, the reference signal resource configuration associated with the LTM candidate cell.

[0185] Example 18 may be combined with any examples 15 to 17 and further includes that the reference signal resource configuration indicates resources for at least one of: a CSI reference signal, CSI-RS; or a synchronization signal block, SSB.

[0186] Example 19 may be combined with any examples 15 to 18 and further includes that the RAN node including a candidate base station and further includes that the serving RAN node including a serving base station.

[0187] Example 20 is a method of wireless communication performed by a radio access network, RAN, node, the method including receiving, from a serving RAN node, a handover request message; receiving, by a central unit, CU, of the RAN node, from a distributed unit, DU, of the RAN node, a DU-to-CU message including a reference signal resource configuration associated with a LTM candidate cell; and transmitting, to the serving RAN node, a handover request acknowledgement message including a lower-layer triggered mobility, LTM, candidate cell configuration associated with the LTM candidate cell and the reference signal resource configuration.

[0188] Example 21 may be combined with example 20 and further includes that the reference signal resource configuration indicates resources for at least one of a CSI reference signal, CSI-RS; or a synchronization signal block, SSB.

[0189] Example 22 may be combined with any examples 20 to 21 and further includes transmitting, by the CU to the DU, a user equipment, UE, context setup request message; and transmitting, by the DU to the CU, a UE context setup response message.

[0190] Example 23 may be combined with any examples 20 to 21 and further includes transmitting, by the CU to the DU, a user equipment, UE, context modification request message; and transmitting, by the DU to the CU, a UE context modification response message.

[0191] Example 24 may be combined with any examples 20 to 21 and further includes transmitting, by the DU to the CU, a next generation node B. GNB,-DU configuration update message; and transmitting, by the CU to the DU, a GNB-DU configuration update acknowledge message.

[0192] Example 25 may be combined with any examples 20 to 24 and further includes that the RAN node including a candidate base station and further includes that the serving RAN node including a serving base station.

[0193] Example 26 is an apparatus for wireless communication for implementing a method as in any of Examples 1-25.

[0194] Example 27 is an apparatus for wireless communication including means for implementing a method as in any of Examples 1-25.

[0195] Example 28 is a non-transitory computer-readable medium storing computer executable code, the code when executed by a processor causes the processor to implement a method as in any of Examples 1-25.

[0196] Example 29 is a computer program product for implementing a method as in any of Examples 1-25.

Claims

CLAIMSWhat is claimed is:

1. A method of wireless communication performed by a radio access network, RAN, node (104), the method comprising: transmitting, to a candidate RAN node (106), a handover request message; receiving, from the candidate RAN node (106) in response to the handover request message, a handover request acknowledgement message including a lower-layer triggered mobility, LTM, candidate cell configuration; obtaining a reference signal resource configuration associated with a LTM candidate cell; and transmitting, to a user equipment, UE (102), a channel state information, CSI, report configuration, the reference signal resource configuration, and the LTM candidate cell configuration.

2. The method of claim 1, further comprising: generating the CSI report configuration based on the reference signal resource configuration.

3. The method of claim 1, wherein the obtaining the reference signal resource configuration comprises receiving the reference signal resource configuration in the handover request acknowledgement message.

4. The method of any of claims 1 to 3, wherein the reference signal resource configuration indicates resources for at least one of: a CSI reference signal, CSI-RS: or a synchronization signal block, SSB.

5. The method of any of claims 1 to 4, further comprising: receiving, from the UE (102), a CSI report based on the CSI report configuration and the reference signal resource configuration.

6. The method of any of claims 1 to 5, further comprising: transmitting to the UE (102), an LTM cell switch command for switching to the LTM candidate cell;transmitting, to the candidate RAN node (106), at least one of: a cell switch notification message; or an early status transfer message; and receiving, from the candidate RAN node (106), an LTM success message.

7. The method of any of claims 1 to 6, further comprising: transmitting, to the candidate RAN node (106). a sequence number, SN, status transfer message, and wherein the transmitting the CSI report configuration, the reference signal resource configuration, and the LTM candidate cell configuration comprises transmitting the CSI report configuration, the reference signal resource configuration, and the LTM configuration in a radio resource control, RRC, reconfiguration message.

8. The method of any of claims 1 to 7, wherein the RAN node (104) comprises a serving base station and wherein the candidate RAN node (106) comprises a candidate base station.

9. The method of claim 1, further comprising: transmitting, by a central unit, CU, of the RAN node (104), to a distributed unit, DU, of the RAN node (104), a CU-to-DU message including the reference signal resource configuration; and receiving, by the CU from the DU. a DU-to-CU message including a channel state information, CSI, report configuration.

10. A method of wireless communication performed by a radio access network, RAN, node (106), the method comprising: receiving, from a serving RAN node (104), a handover request message; and transmitting, to the serving RAN node (104), a handover request acknowledgement message including a lower-layer triggered mobility, LTM, candidate cell configuration and a reference signal resource configuration associated wi th a LTM candidate cell.

11. The method of claim 10, further comprising: retrieving, from a memory of the RAN node (106), the reference signal resource configuration associated with the LTM candidate cell.

12. The method of any of claims 10 to 11. wherein the reference signal resource configuration indicates resources for at least one of a CSI reference signal, CSI-RS; or a synchronization signal block, SSB.

13. The method of claim 10, further comprising: receiving, by a central unit, CU. of the RAN node (106). from a distributed unit, DU. of the RAN node (106), a DU-to-CU message including a reference signal resource configuration associated with a LTM candidate cell.

14. The method of any of claims 10 to 13, further comprising: transmitting by the DU to the CU, a DU configuration update message; and transmitting by the CU to the DU, a DU configuration update acknowledge message.

15. An apparatus for wireless communication comprising a transceiver, a memory’, and a processor coupled to the memory and the transceiver, the apparatus being configured to implement a method as in any of claims 1-14.

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