Managing lower-layer triggered mobility

Abstract

Techniques for performing lower-layer triggered mobility (LTM) cell switches when a UE is in DC with a master node (MN) using a master cell group (MCG) and a secondary node (SN) using a secondary cell group (SCG) are disclosed. The RAN may transmit, to the UE, an LTM candidate configuration that includes both an MCG-LTM configuration and an SCG- LTM configuration. The LTM cell switch may be initiated by the UE responsive to an LTM cell switch command received from the radio access network (RAN) or responsive to a failure detected by the UE, and the LTM cell switch may include using the received LTM candidate configuration to for a PCell switch and / or for a PSCell switch.

Description

MANAGING LOWER-LAYER TRIGGERED MOBILITY CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 754,360, filed February 5, 2025 and entitled “MANAGING LOWER-LAYER TRIGGERED MOBILITIY,” which is hereby incorporated herein by reference in its entirety.FIELD OF THE DISCLOSURE

[0002] This disclosure relates to wireless communications and, more particularly, to managing (e.g., coordinating, administrating, or otherwise conducting) a serving cell change triggered by a lower layer triggered mobility command.BACKGROUND

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

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

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

[0006] The UE in some scenarios concurrently utilizes resources of multiple radio access network (RAN) nodes (e.g., base stations or components of a distributed base station), interconnected by a backhaul. When the network nodes support different radio access technologies (RATs), such a type of connectivity is referred to as Multi-Radio Dual Connectivity (MR-DC). When a UE operates in MR-DC, one base station operates as a master node (MN) that covers a primary cell (PCell), and the other base station operates as a secondary node (SN) that covers a primary secondary cell (PSCell). The UE communicates with the MN (via the PCell) and the SN (via the PSCell). In other scenarios, the UE utilizes resources of one base station at a time. One base station and / or the UE determines that the UE should establish a radio connection with another base station. For example, one base station can determines 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 an RRC reconfiguration message configuring Reconfiguration with Synchronization (e.g., the RRC reconfiguration message includes a ReconfigurationWithSync IE) for change of the serving cell (e.g., PCell or PSCell). In cases where the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN releases the at least one SCell dueto 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. The base 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 Lower-Layer Triggered Mobility (LTM) candidate cell for LTM cell switch. To configure the LTM candidate cell for the UE, the base station transmits an LTM candidate configuration configuring the LTM candidate cell to the UE via RRC signaling. Later on, the base station receives one or more measurement results from the UE. Based on the one or more measurement result(s), the base station determines that the LTM candidate cell qualifies to be a serving cell for the UE. Therefore, the base station transmits an LTM cell switch command to the UE to command the UE to perform the LTM cell switch to the LTM candidate cell. 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 LTM cell switch in Release 18 specifications. Although 3GPP has started to specify inter-CU LTM cell switch, there are still remaining issues for the inter-CU LTM involving MR-DC or non-MR-DC scenarios.SUMMARY

[0009] Methods, systems, and techniques for performing lower-layer triggered mobility (LTM) cell switches when a User Equipment UE is in dual connectivity (DC) with a master node (MN) using a master cell group (MCG) and a secondary node (SN) using a secondary cell group (SCG) include transmitting, by the radio access network (RAN) and to the UE, a an LTM candidate configuration that includes both an MCG-LTM configuration and an SCG-LTM configuration. For example, the RAN may transmit a single (e.g., only one) message (such as a reconfiguration message) which includes both the MCG-LTM configuration and the SCG-LTM configuration. That is, both the MCG-LTM configuration and the SCG-LTM configuration may be included in a same or common message, such as a (single) RRC reconfiguration message, in embodiments. The reconfiguration message may additionally oralternatively include other types of configurations, such as random access channel (RACH) configurations, transmission configuration indication (TCI) state configurations, LTM synchronization signaling block (SSB) configurations, channel state information (CSI) report configurations, serving distributed unit (DU) configurations, etc., and / or may include various types of identifications (IDs) such as LTM configuration IDs, LTM candidate PCell and / or PSCell TA IDs, serving PCell and / lor PSCell timing advance (TA) IDs, etc.

[0010] The UE may initiate the performing of an LTM cell switch responsive to an LTM cell switch command received from the radio access network (RAN) or responsive to a failure detected by the UE. The initiated LTM cell switch may utilize the received LTM candidate configuration including the MCG-LTM configuration and SCG-LTM configuration for switching to a PCell and / or a PSCell.

[0011] In an embodiment, a method implemented in a user equipment (UE) includes first communicating, by the UE, with a radio access network (RAN) in dual connectivity (DC) with a master node (MN) using a master cell group (MCG) and a secondary node (SN) using a secondary cell group (SCG); receiving, from the MN, a lower-layer triggered mobility (LTM) candidate configuration, the LTM candidate configuration including an MCG-LTM candidate configuration and an SCG-LTM candidate configuration; initiating an LTM cell switch; and subsequent to the initiating of the LTM cell switch, second communicating with the RAN in accordance with at least one of the MCG-LTM candidate configuration or the SCG-LTM candidate configuration.

[0012] In an embodiment, a method implemented in a radio access network (RAN includes communicating, by the RAN, with a user equipment (UE) in dual connectivity (DC) with the RAN via a master node (MN) using a master cell group (MCG) and a secondary node (SN) using a secondary cell group (SCG); and transmitting, to the UE, a lower-layer triggered mobility (LTM) candidate configuration for the UE to utilize for an LTM cell switch, the LTM candidate configuration including an MCG-LTM candidate configuration and an SCG-LTM candidate configuration.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1A is a block diagram of an example system in which a radio access network (RAN) and a user device can implement the techniques of this disclosure for managing (e.g.,coordinating, administrating, or otherwise conducting) LTM procedures related to a secondary node (SN);

[0014] Fig. IB is another block diagram of an example system in which a radio access network (RAN) and a user device can implement the techniques of this disclosure for managing (e.g., coordinating, administrating, or otherwise conducting) LTM procedures related to an MN or an SN;

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

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

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

[0018] Fig. 3 is a signaling diagram for an intra-DU LTM.

[0019] Fig. 4 is a signaling diagram for an inter-DU LTM.

[0020] Fig. 5 is a signaling diagram of an example illustrating an inter-CU LTM between a user equipment (UE) and a base station (BS).

[0021] Fig. 6 is a signaling diagram of an example illustrating communications between a UE, a master node (MN) and a serving secondary node (S-SN) of a multi-radio dualconnectivity (MR-DC) configuration, and a candidate secondary node (C-SN) for inter-CU LTM cell switch.

[0022] Fig. 7 is a signaling diagram of an example illustrating communications between a UE, a master node (MN) and a serving secondary node (S-SN) of a multi-radio dualconnectivity (MR-DC) configuration, and a candidate secondary node (C-SN) for inter-CU LTM primary secondary cell (PSCell) switch.

[0023] Fig. 8 is a signaling diagram of an example illustrating communications between a UE, a serving master node (S-MN) and a serving secondary node (S-SN) of a multi-radio dual-connectivity (MR-DC) configuration, a candidate master node (C-MN), and a candidate secondary node (C-SN) for inter-MN secondary cell (PSCell) switch.

[0024] Fig. 9 is a block diagram of an example method in a UE in DC for an LTM cell switch, responsive to an MN command, to an LTM candidate cell of a C-SN, which may include a PCell and / or a PSCell.

[0025] Fig. 10 a block diagram of an example method in a UE for an LTM cell switch, responsive to an MN command, to an LTM candidate cell of a C-SN, which may include a PCell and / or a PSCell.

[0026] Fig. 11 is a block diagram of an example method in a UE for an LTM cell switch, responsive to a failure detected by the UE, to an LTM candidate cell of a C-SN, which may include a PCell and / or a PSCell.

[0027] Fig. 12 is a block diagram of an example method in a UE for an LTM cell switch, responsive to a failure detected by the UE, to an LTM candidate cell of a C-SN, which may include a PCell and / or a PSCell.

[0028] Fig. 13 a block diagram of an example method in a UE for an LTM cell switch, responsive to an SN command, to an LTM candidate cell of a C-SN, which may include a PCell and / or a PSCell.

[0029] Fig. 14 is a block diagram of an example method in a UE for an LTM cell switch, initiated by the UE for an SCG, to an LTM candidate cell of a C-SN, which may include a PCell and / or a PSCell.

[0030] Fig. 15 is a block diagram of an example method in a UE for an LTM cell switch, initiated by the UE for an MCG, to an LTM candidate cell of a C-SN, which may include a PCell and / or a PSCell.

[0031] Fig. 16 is a block diagram of an example method in a RAN for an LTM cell switch, as commanded by an MN, to an LTM candidate cell of a C-SN.

[0032] Fig. 17 is a block diagram of an example method in a RAN for an LTM cell switch, as initiated by the UE, to an LTM candidate cell of a C-SN.DETAILED DESCRIPTION OF THE DRAWINGS

[0033] Fig. 1A depicts an example wireless communication system 100 in which communication devices can implement these techniques. The wireless communication system 100 includes a UE 102, a base station (BS) 104A, a base station 106A and a core network (CN) 110. The UE 102 initially connects to the base station 104A. In somescenarios, the base station 104A can perform an SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104A and the base station 106 A. The base stations 104A and 106A operate as an MN and an SN for the UE 102, respectively.

[0034] In various configurations of the wireless communication system 100, the base station 104A can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station 106A can be implemented as a secondary eNB (SeNB) or a secondary gNB (SgNB). The UE 102 can communicate with the base station 104A and the base station 106A via the same RAT such as EUTRA or NR, or different RATs. When the base station 104A is an MeNB and the base station 106A is a SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0035] In some cases, an MeNB or an SeNB is implemented as an ng-eNB rather than an eNB. When the base station 104A is a Master ng-eNB (Mng-eNB) and the base station 106A is a SgNB, the UE 102 can be in next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. When the base station 104A is an MgNB and the base station 106A is an SgNB, the UE 102 may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the base station 104A is an MgNB and the base station 106 A 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.

[0036] In the scenarios where the UE 102 hands over from the base station 104A to the base station 106A, the base stations 104A and 106A operate as the source base station (S-BS) and a target base station (T-BS), respectively. The UE 102 can operate in DC with the base station 104A and an additional base station (not shown in Fig. 1A) for example prior to the handover. The UE 102 can continue to operate in DC with the base station 106A and the additional base station or operate in single connectivity (SC) with the base station 106A, after completing the handover. The base stations 104A and 106 A in this case operate as a source MN (S-MN) and a target MN (T-MN), respectively.

[0037] A core network (CN) 110 can be an evolved packet core (EPC) 111 or a fifthgeneration core (5GC) 160, both of which are depicted in Fig. 1A. The base station 104A can be an eNB supporting an SI interface for communicating with the EPC 111, an ng-eNB supporting an NG interface for communicating with the 5GC 160, or a gNB that supports an NR radio interface as well as an NG interface for communicating with the 5GC 160. Todirectly exchange messages with each other during the scenarios discussed below, the base stations 104A and 106A can support an X2 or Xn interface. Among other components, the EPC 111 can include a Serving Gateway (SGW) 112, a Mobility Management Entity (MME) 114, and a Packet Data Network Gateway (PGW) 116. The SGW 112 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME 114 is configured to manage authentication, registration, paging, and other related functions. The PGW 116 provides connectivity from the UE to one or more external packet data networks, e.g., an Internet network and / or an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The 5GC 160 includes a User Plane Function (UPF) 162 and an Access and Mobility Management (AMF) 164, and / or Session Management Function (SMF) 166. The UPF 162 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF 164 is configured to manage authentication, registration, paging, and other related functions, and the SMF 166 is configured to manage PDU sessions.

[0038] As illustrated in Fig. 1A, the base station 104A supports cell 124A, and the base station 106A supports a cell 126A. The cells 124A and 126A can partially overlap, so that the UE 102 can communicate in DC with the base station 104A and the base station 106 A, where one of the base stations 104A and 106A is an MN and the other is an SN. The base station 104A can support additional cell(s) such as cells 124B and 124C, and the base station 106A can support additional cell(s) (not shown in Fig. 1A). The cells 124A, 124B and 124C can partially overlap, so that the UE 102 can communicate in carrier aggregation (CA) with the base station 104A. The base station 104A can operate the cells 124A, 124B and 124C via one or more transmit and receive points (TRPs). More particularly, when the UE 102 is in DC with the base station 104A and the base station 106A, one of the base stations 104A and 106 A operates as an MeNB, an Mng-eNB or an MgNB, and the other operates as an SgNB or an Sng-eNB.

[0039] 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. An example configuration in which the CN 110 is connected to additional base stations is discussed below with reference to Fig. IB. Although the examples below refer specifically to specific CN types (EPC, 5GC) and RAT types (5G NRand EUTRA), in general the techniques of this disclosure also can apply to other suitable radio access and / or core network technologies such as sixth generation (6G) radio access and / or 6G core network or 5G NR-6G DC.

[0040] With continued reference to Fig. 1A, the base station 104A is equipped with processing hardware 130 that can include one or more general-purpose processors (e.g., CPUs) and a non-transitory computer-readable memory storing instructions that the one or more general-purpose processors execute. Additionally or alternatively, the processing hardware 130 can include special-purpose processing units. The processing hardware 130 can include a PHY controller 132 configured to transmit data and control signal on physical downlink (DL) channels and DL reference signals with one or more user devices (e.g. UE 102) via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The PHY controller 132 is also configured to receive data and control signal on physical uplink (UL) channels and / or UL reference signals with the one or more user devices via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The processing hardware 130 in an example implementation includes a MAC controller 134 configured to perform MAC functions with one or more user devices. The MAC functions include a random access (RA) procedure, managing UL timing advance (TA) for the one or more user devices, and / or communicating UL / DL MAC PDUs with the one or more user devices. The MAC functions include lower triggered mobility (LTM) related functions as described below. The processing hardware 130 can further include an RRC controller 136 to implement procedures and messaging at the RRC sublayer of the protocol communication stack. For example, the RRC controller 132 may be configured to support RRC messaging associated with handover procedures, and / or to support the necessary operations when the base station 104A operates as an MN relative to an SN or as an SN relative to an MN. The base station 106A 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.

[0041] The UE 102 is equipped with processing hardware 150 that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. The PHY controller 152 is also configured to receive data and control signal on physical DL channels and / or DL referencesignals with the base station 104A or 106A via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126A) and / or one or more TRPs. The PHY controller 152 is also configured to transmit data and control signal on physical UL channels and / or UL reference signals with the base station 104A or 106A via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126A) and / or one or more TRPs. The processing hardware 150 in an example implementation includes a MAC controller 154 configured to perform MAC functions with base station 104A or 106 A. For example, the MAC functions includes a random access procedure, managing UL timing advance for the one or more user devices, and communicating UL / DL MAC PDUs with the base station 104A or 106 A. 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.

[0042] 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 104A or the SN 106 A. 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.

[0043] Fig. IB depicts additional base stations 104B and 106B, which may be included in the wireless communication system 100. The UE 102 initially connects to the base station 104A. The BSs 104B and 106B may have similar processing hardware as the base station 106 A. The UE 102 initially connects to the base station 104A.

[0044] In some scenarios, the base station 104A can perform immediate SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104A (via a PCell) and the base station 106 A (via a PSCell other than cell 126A). The base stations 104A and 106A operate as an MN and an SN for the UE 102, respectively. The UE 102 in some cases can operate using the MR-DC connectivity mode, e.g., communicate with the base station 104A using 5G NR and communicate with the base station 106 A using EUTRA, or communicate with the base station 104A using EUTRA and communicate with the base station 106 A using 5G NR. Multi-connectivity coordination can help the two base stations coordinate shared UE capabilities including operational frequencies (e.g., band combinations, frequency ranges), UE measurements and reporting (e.g., intra-frequency measurements, inter-frequency measurements, inter-RAT measurements, measurement gaps), receptiontiming (e.g., DRX configurations, offset timing), and uplink power control (e.g., power headroom, maximum transmit power).

[0045] At some point, the MN 104A can perform an immediate SN change to change the SN of the UE 102 from the base station 106A (source SN, or “S-SN”) to the base station 104B (target SN, or “T-SN”) while the UE 102 is communicating in DC with the MN 104A and the S-SN 106A. In another scenario, the SN 106A can perform an immediate PSCell change to change the PSCell of the UE 102 to the cell 126A. In one implementation, the SN 106 A can transmit a configuration changing the PSCell to cell 126 A to the UE 102 via a signaling radio bearer (SRB) (e.g., SRB3) for the immediate PSCell change. In another implementation, the SN 106 A can transmit a configuration changing the PSCell to the cell 126 A to the UE 102 via the MN 104A for the immediate PSCell change. The MN 104A may transmit the configuration immediately changing the PSCell to the cell 126 A to the UE 102 via SRB1. Extending multi-connectivity coordination can help the newly-added base station coordinate shared UE capabilities.

[0046] Fig. 1C depicts an example distributed implementation of a base station such as the base station 104A or 106 A. The base station in this implementation can include a centralized unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 is equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In one example, the CU 172 is equipped with the processing hardware 130. In another example, the CU 172 is equipped with the processing hardware 140. The processing hardware 140 in an example implementation includes an SN RRC controller 142 configured to manage or control one or more RRC configurations and / or RRC procedures when the base station 106A operates as an SN. The DU 174A is also equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In some examples, the processing hardware in an example implementation includes a medium access control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure) and a radio link control (RLC) controller configured to manage or control one or more RLC operations or procedures when the basestation 106 A operates as an MN or an SN. The processing hardware may include further a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0047] Fig. 2A illustrates, in a simplified manner, an example protocol stack 200 according to which the UE 102 can communicate with an eNB / ng-eNB and / or a gNB (e.g., one or more of the base stations 104A, 106A).

[0048] In the example stack 200, a physical layer (PHY) 202 A of EUTRA provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logical channels to the EUTRA RLC sublayer 206A. The EUTRA RLC sublayer 206A in turn provides RLC channels to an EUTRA PDCP sublayer 208 and, in some cases, to an NR PDCP sublayer 210. Similarly, the NR PHY 202B provides transport channels to the NR MAC sublayer 204B, which in turn provides logical channels to the NR RLC sublayer 206B. The NR RLC sublayer 206B in turn provides data transfer services to the NR PDCP sublayer 210. The NR PDCP sublayer 210 in turn can provide data transfer services to Service Data Adaptation Protocol (SDAP) 212 or a radio resource control (RRC) sublayer (not shown in Fig. 2A). The UE 102, in some implementations, supports both the EUTRA and the NR stack as shown in Fig. 2A, to support handover between EUTRA and NR base stations and / or to support DC over EUTRA and NR interfaces. Further, as illustrated in Fig. 2A, the UE 102 can support layering of NR PDCP 210 over EUTRA RLC 206 A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

[0049] 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.”

[0050] 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 sublayer210 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets. In some implementations, the “EUTRA PDCP”, “EUTRA RLC”, “EUTRA MAC”, and “EUTRA PHY” can be replaced with “6G PDCP”, “6G RLC”, “6G MAC” and “6G PHY”, respectively.

[0051] Fig. 2B illustrates, in a simplified manner, an example protocol stack 250, which the UE 102 can communicate with a DU (e.g., DU 174) and a CU (e.g., CU 172). The radio protocol stack 200 is functionally split as shown by the radio protocol stack 250 in Fig. 2B. The CU at any of the base stations 104A or 106A can hold all the control and upper layer functionalities (e.g., RRC 214, SDAP 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.

[0052] Next, several example scenarios in which the base station operating in the system of Fig. 1A transmits a configuration to the UE 102 and later activates a configuration for communication between the UE 102 and base station. Generally speaking, events in Figs. 3-10B that are similar are labeled with similar reference numbers (e.g., event 302 is similar to event 402 of Fig. 4, event 502 of Figs. 5A-5C, event 602 of Fig. 6, event 702 of Figs. 7-10B, event 802 of Fig. 8, event 902 of Fig. 9, etc.; event 390 is similar to event 490 of Fig. 4, event 590 of Fig. 5, and event 690 of Fig. 6, etc.), 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.

[0053] Referring first to Fig. 3, in a scenario 300, the base station 104A 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 serving DU configuration includes configuration parameters provided by the DU 174, and the serving CU configuration includes configuration parameters provided by the CU 172. The DU 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) communicates with the DU 174 onthe cell 124A and other cell(s) (e.g., cell 124D not shown in Fig. 1A) using the serving DU configuration. The DU 174 operates the other cell(s). The cell 124A and / or the other cell(s) are serving cell(s) for the UE 102. In 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 at least some embodiments of the following description, events 394, 324, 350, 352, 354, and 326 occur on the serving cell(s). In some implementations, the cell 124A is a PCell. In such cases, the other cell(s) include SCell(s) and / or additional cell(s) associated with the PCell or an SCell. In other implementations, the cell 124A is an SCell, and one of the other cell(s) is a PCell. In such cases, the remaining cells include SCell(s) and / or additional cell(s) associated with the PCell or an SCell. In at least some implementations of the following description, the base station 104A is the DU 174, the CU 172, or the DU 174 and CU 172.

[0054] In some implementations, in the event 302, the UE 102 transmits UL PDUs and / or UL control signals to the base station 104A on the cell 124A and / or other cell(s) via one or multiple TRPs. In some implementations, the UE 102 communicates UL PDUs and / or DL PDUs with the base station 104A via radio bearers which can include SRBs and / or DRB(s). In some implementations, the base station 104A configures the radio bearers to the UE 102. In some implementations, UL control signals include UL control information, channel state information, hybrid automatic repeat request (HARQ) acknowledgements (ACKs), HARQ negative ACKs, scheduling request(s) and / or sounding reference signal(s). Similarly, in further implementations, the UE 102 receives DL PDUs and / or DL control signals from the base station 104A on the cell 124A and / or other cell(s) via one or multiple TRPs. In some implementations, the DL control signals include downlink control information (DCIs) and reference signals (e.g., synchronization signal block, channel state information reference signal(s) (CSI-RS(s)), and / or tracking reference signal(s)). In some implementations, the base station 104A transmits the DCIs on physical downlink control channel(s) (PDCCH(s)) monitored by the UE 102, on the cell 124A and / or other cell(s) via one or multiple TRPs.

[0055] 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 transmits these configuration parameters and / or the first non-LTM TCI stateconfiguration(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 a CellGroupConfig IE (e.g., as 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 MeasConfiig IE and / or a RadioBearerConfig IE (e.g., as defined in 3GPP specification 38.331) or includes configuration parameters in the MeasConfiig 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 CSl-MeasConfitg IE or configuration parameters for channel state information (CSI) measurement and reporting. In other implementations, the serving CU configuration includes a CSl-MeasConfitg 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 A and the remaining portion of these configuration parameters from the base station 104A.

[0056] 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 stateconfiguration(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).

[0057] While communicating with the base station 104A, 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 are Fl application protocol (F1AP) message(s) (e.g., ULRRC Message Transfer message(s)). The at least one serving cell includes the cell 124A and / or other cell(s), and the at least one non-serving cell includes the cell 124B and / or additional cell(s). In some implementations, the serving CU configuration includes at least one measurement configuration. In accordance with the measurement configuration(s), the UE 102 performs measurements and transmits 304 the measurement report(s) to the DU 174. In some implementations, the measurement configuration(s) includes Layer 3 (L3) measurement configuration(s) (e.g., MeasConfig IE(s)) and the measurement report(s) include L3 measurement report(s).

[0058] After (e.g., in response to) receiving one or some of the measurement report(s) from the UE 102, the CU 172 determines to prepare a first cell (e.g., cell 1 such as the cell 124B) as an LTM candidate cell for the UE 102. In some implementations, the base station 104A determines to prepare the first cell for the UE 102 because the measurement report(s) indicates that the first cell could be used by the base station 104A to communicate with the UE 102. In some implementations, the base station 104A determines to prepare the first cell for the UE 102 because the measurement report(s) indicates that the first cell qualifies to be an LTM candidate cell that could be used for communication with the UE 102. In some implementations, if the L3 measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than strength and / or quality of the serving cell (e.g., cell 124A), and / or is better than strength and / or quality of the serving cell by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. Alternatively, the CU 172 determines to prepare the first cell for the UE 102 regardless of whether a measure report is received from the UE 102 or not.

[0059] 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 an 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 an LTM Information Setup IE and includes the LTM Information Setup IE in the first CU-to-DU message. In yet other implementations, the CU 172 includes the LTM indicator in an LTM Information Modify IE and includes the LTM Information Modify IE in the first CU-to-DU message.

[0060] In response to the first CU-to-DU message, the DU 174 generates a first LTM DU configuration (also referred to herein 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., also referred to herein 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.

[0061] The events 308 and 310 are collectively referred to in Fig. 3 as an LTM preparation procedure 390.

[0062] 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 some 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 determines 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.

[0063] In some implementations, the CU 172 does not include an LTM reference DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates an LTMreference 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).

[0064] In some implementations, the CU 172 includes an 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 an LTM reference configuration. If the CU 172 determines that the UE 102 supports an LTM reference configuration, the CU 172 includes the LTM reference DU configuration request in the first CU-to-DU message. The DU 174 includes the LTM reference DU configuration in the first DU-to-CU message in response to the LTM reference DU configuration request. Otherwise, if the CU 172 determines that the UE 102 does not support an LTM reference configuration, the CU 172 does not include the LTM reference DU configuration request in the first CU-to-DU message. In some such implementations,, the DU 174 generates the LTM DU configuration 1 as a complete configuration and does not include an LTM reference DU configuration in the first DU-to-CU message. In other implementations, the CU 172 transmits an additional CU-to-DU message including the LTM reference DU configuration request to the DU 174 instead of the first CU-to-DU message. In response, the DU 174 includes an additional DU-to-CU message, including the LTM reference DU configuration, to the CU 172. In yet other implementations, the DU 174 determines whether the UE 102 supports an LTM reference configuration. If the DU 174 determines that the UE 102 supports an LTM reference configuration, the DU 174 includes the LTM reference DU configuration in the first DU-to-CU message. Otherwise, if the DU 174 determines that the UE 102 does not support an LTM reference configuration, the DU 174 does not include an LTM reference DU configuration in the first DU-to-CU message.

[0065] In some implementations, the CU 172 includes an LTM reference DU configuration in the first CU-to-DU message. In some implementations, the CU 172 receives the LTM reference DU configuration from an additional DU during an LTM preparation procedure as described above and for Fig. 4. In other implementations, the CU 172 is preconfigured withthe LTM reference DU configuration. 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 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).

[0066] In some implementations, if the DU 174 generates the LTM DU configuration 1 as a complete configuration, the DU 174 includes 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 the LTM reference DU configuration, the CU 172 determines that the LTM DU configuration 1 as a complete configuration. Otherwise, in further implementations, if the first CU-to-DU message includes the LTM reference DU configuration, the CU 172 determines that the LTM DU configuration 1 is a delta configuration.

[0067] 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 a CellGroupConfig IE (e.g., 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 CSl-MeasConfiig IE or configuration parameters for LTM or non-LTM channel state information (CSI) measurement and / or reporting.

[0068] In some implementations, the LTM reference DU configuration is different from the serving DU configuration. In some implementations, a portion of the LTM reference DU configuration is the same as a portion of the serving DU configuration and the rest of the LTM reference DU configuration is different from the rest of the serving DU configuration. In other implementations, the LTM reference DU configuration is the same as the serving DU configuration.

[0069] In some implementations, to prepare the first cell as an LTM candidate cell for the UE 102, the CU 172 transmits 312 a second CU-to-DU message to the DU 174, including a CSI resource configuration (e.g., CSI resource configuration 1) and / or an LTM SSB configuration (i.e., LTM SSB configuration 1), to request the DU 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 CSLRS(s). The LTM SSB configuration include SSB configuration parameters configuring an SSB frequency, a subcarrier spacing, an SSB periodicity, SSB positions (e.g., SSB Positions In Burst IE) and / or SSB power for SSB(s) transmitted on the first cell.

[0070] 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-ResourceConfigToAddModList field / IE. In some implementations, the second serving DU configuration is a CellGroupConfig IE.

[0071] 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 some implementations, the CU 172 does so to indicate that the CSI resource configuration is / are associated with the first cell. In further implementations, 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). In some such implementations, (e.g., based on the above implementation(s)) the DU 174 associates 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 some various such implementations, the CU 172 does or does not include the LTM ID 1 in the first CU-to-DU message.

[0072] In some alternative implementations, the CU 172 includes the CSI resource configuration and / or the LTM SSB 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.

[0073] 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.

[0074] The events 312 and 314 are collectively referred to in Fig. 3 as an LTM CSI report configuration and / or LTM ID configuration procedure 392.

[0075] After receiving the first DU-to-CU message, the CU 172 generates a first LTM candidate configuration (i.e., LTM candidate configuration 1), including the LTM DU configuration 1, and generates a first RRC reconfiguration message including the LTM candidate configuration 1 and the LTM ID 1. In some implementations, the CU 172 includes LTM CU configuration 1 in the LTM candidate configuration 1. In other implementations, the CU 172 does not include an LTM CU configuration in the LTM candidate configuration 1. The CU 172 transmits 316 a third CU-to-DU message, including the first RRC reconfiguration message, to the DU 174. In turn, the DU 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.

[0076] If the first DU-to-CU message includes the LTM reference DU configuration, the CU 172 generates an LTM reference configuration including the LTM reference DU configuration. In some such cases, the CU 172 includes the LTM reference configuration in the first RRC reconfiguration message. In some implementations, the CU 172 includes an LTM reference CU configuration in the LTM reference configuration. In some such cases, the CU 172 generates the LTM CU configuration 1 as a delta configuration based on the LTM reference CU configuration. In other implementations, the CU 172 does not include an LTM reference CU configuration in the LTM reference configuration. In some such cases, the CU 172 generates the LTM CU configuration 1 as a complete configuration.Alternatively, the CU 172 transmits a second RRC reconfiguration message, including the LTM reference configuration, to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a second RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. In some implementations, if the CU 172 does not receive an LTM reference DU configuration, the CU 172 generates an LTM reference configuration including only the LTM reference CU configuration. In other implementations, if the CU 172 does not receive an LTM reference DU configuration, the CU 172 does not generate an LTM reference configuration.

[0077] In some implementations, if the first DU-to-CU message includes the complete configuration indication, the CU 172 determines that the LTM DU configuration 1 is a complete configuration. Otherwise, in further implementations, if the first DU-to-CU message does not include the complete configuration indication, the CU 172 determines that the LTM DU configuration 1 is a delta configuration. In some implementations, if the LTM DU configuration 1 is a complete configuration, the CU 172 generates the LTM candidate configuration 1 as a complete configuration. Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU 172 generates the LTM candidate configuration 1 as a delta configuration. If the LTM candidate configuration 1 is a complete configuration, the CU 172 includes, in the first RRC reconfiguration message, a complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration. If the LTM candidate configuration 1 is a delta configuration, the CU 172 excludes the complete configuration indication from the first RRC reconfiguration message to indicate that the LTM candidate configuration 1 is a delta configuration.

[0078] In some cases in which the CU 172 performs the procedure 392, the CU 172 includes 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.

[0079] 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 DU174, 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.

[0080] In some implementations, the DU 174 transmits a DU-to-CU message to the CU 172, including early synchronization information for the UE 102. Depending on the implementation, the DU-to-CU message is 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 some implementations, the DU 174 transmits such if the DU 174 determines that the UE 102 supports (i.e., is capable of) early UL synchronization with an LTM candidate cell (e.g., early TA acquisition with an LTM candidate cell, early RA on an LTM candidate cell, or UE measured TA). Otherwise, if the DU 174 determines that the UE 102 does not support the early UL synchronization with an LTM candidate cell, the DU 174 does not transmit the early synchronization information to the CU 172. In other implementations, the CU 172 transmits a CU-to-DU message, including an early synchronization information request (e.g., an IE), to the DU 174, and the DU 174 includes the early synchronization information in the DU-to-CU message in response to the early synchronization information request. Depending on the implementation, the CU-to-DU message is the first CU-to-DU message, the second CU-to-DU message or the fourth CU-to-DU message. In some implementations, the CU 172 transmits such a request if the CU 172 determines that the UE 102 supports the early UL synchronization with an LTM candidate cell. Otherwise, if the CU 172 determines that the UE 102 does not support the early UL synchronization with an LTM candidate cell, the CU 172 does not request the DU 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.

[0081] 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) for LTM. In some implementations, the early synchronization request includes 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 synchronization information nor in the DU-to-CU message.

[0082] 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.

[0083] In some implementations, the CU 172 includes, in the RRC reconfiguration message(s) described above, an LTM candidate cell TA ID for the UE 102 to determine whether to perform a UE-based TA measurement for an LTM cell switch to the LTM candidate cell. In some implementations, the CU 172 includes a serving cell TA ID for the serving cell in the RRC reconfiguration message(s). In some implementations, if the LTM candidate cell TA ID and the serving cell TA ID have the same value, the UE 102 performs a UE-based TA measurement to obtain a TA for the LTM candidate cell after receiving the RRC reconfiguration message(s). In further implementations, upon receiving 326 the LTM Cell Switch Command, the UE 102 applies the obtained TA value to access 332 the LTM candidate cell without performing a random access procedure on the LTM candidate cell as described above for the case where the LTM Cell Switch Command including a TA value. If the LTM candidate TA ID and the serving cell TA ID have different values, the UE 102 accesses 332 the LTM candidate cell with or without a random access procedure as described above.

[0084] In some implementations, the CU 172 includes {the LTM ID 1, the LTM candidate configuration 1, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration, and / or the PCI of the cell 1 } as or in a tuple (e.g., LTM-Candidate IE) in the first RRC reconfiguration message. In some implementations, the CU 172 includes the LTMcandidate cell TA ID in the tuple. In some implementations, the CU 172 includes the CSI resource configuration in the tuple. In other implementations, the CU 172 includes, in the first RRC reconfiguration message, the CSI resource configuration outside the tuple. In some implementations, the CU 172 includes, in the first RRC reconfiguration message, the serving cell TA ID outside the tuple.

[0085] The events 316, 318, 320, and / or 322 are collectively referred to in Fig. 3 as an LTM configuration delivery procedure 394. The second, third, fourth, and / or fifth RRC reconfiguration message(s)) and the second, third, fourth, and / or fifth RRC reconfiguration complete message(s); the related CU-to-DU message(s); and / or the related DU-to-CU message(s) are also considered as part of the LTM configuration delivery procedure 394. In some implementations, the RRC reconfiguration message and the RRC reconfiguration complete message described above are an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively.

[0086] 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 some cases in which the message(s) include the UE Context Modification Required message, the CU 172 transmits a UE Context Modification Confirm message to the DU 174 in response to UE Context Modification Required message. In some implementations, the 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.

[0087] 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.

[0088] In some implementations, the LTM reference CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 includes a MeasConfig IE and / or a RadioBearerConfig IE (e.g., as defined in 3GPP specification 38.331) or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE.

[0089] In some implementations, the LTM CU configuration 1 and / or the LTM reference CU configuration include PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 or the LTM reference CU configuration includes a MeasConfig IE and / or a RadioBearerConfig IE (e.g., as defined in 3GPP specification 38.331) or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE.

[0090] In some implementations, the LTM DU configuration 1 includes a plurality of configuration parameters for the UE 102 to communicate with the DU 174 on the first cell. In some implementations, the plurality of configuration parameters include physical layer configuration parameters (e.g., PhysicalCellGroupConfiig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfiig IE), and / or RLC configuration parameters (e.g., RLC-BearerConfiig IE(s)). In some further implementations, the plurality of configuration parameters includes a special cell configuration (e.g., SpCellConfiig IE) and / or one or more SCell configurations (e.g., SCellConfiig IE(s)). In some implementations, the LTM DU configuration 1 is CellGroupConfiig IE (e.g., as defined in 3GPP specification 38.331). In other implementations, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0091] In some implementations, the LTM DU configuration 1 includes a first LI measurement configuration (e.g., a CSl-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) include SSB(s) and / or CSLRS(s). The RS resource(s) include SSB resource(s) and / or CSLRS resource(s). In some implementations, each of the first RSresource configuration(s) includes an RS resource configuration ID. In some implementations, the first RS resource configuration(s) are and / or 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.

[0092] 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 LI 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. In some implementations, the first RS(s) comprise SSB(s) and / or CSLRS(s). In some implementations, the first RS(s) and / or transmission pattem(s) of the first RS(s) are configured in the CSI report configuration(s), the LTM SSB configuration, and / or the CSI resource configuration. The UE 102 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.

[0093] After receiving the LTM-related configurations and the second serving DU configuration, or after receiving the RRC reconfiguration message(s) described above, the UE 102 performs measurements on at least one 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. In some implementations, the second RS(s) comprise SSB(s) and / or CSLRS(s). In some implementations, the second RS(s) and / or transmission pattern(s) of the second RS(s) are configured in one or more second CSI report configurations and / or one or more second CSI resource configuration that are included in the serving DU configuration 302 and / or the second serving DU configuration. The UE 102 performs the measurements on the second RS(s) in accordance with the second CSI report configuration(s) and / or the second CSIresource configuration(s). In some implementations, the second CSI report configuration(s) include non-LTM CSI report configuration(s) and / or LTM CSI report configuration(s). In further implementations, the second CSI resource configuration(s) include non-LTM CSI resource configuration(s) and / or LTM CSI resource configuration(s).

[0094] In some implementations, after transmitting the RACH configuration to the UE 102 via the CU 172, the DU 174 transmits 350 a PDCCH order to the UE 102 to command the UE 102 to transmit an RA preamble on the first cell. In response to the PDCCH order, the UE 102 transmits an RA preamble on the first cell. The DU 174 includes PDCCH order information in the PDCCH order. The PDCCH order information includes an RA preamble index, a UL or a supplemental UL indicator, an SSB index, and / or a physical RACH mask index. In some implementations, the DU 174 includes the LTM ID 1 in the PDCCH order to indicate the first cell. 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 and 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 determines the SSB index based on LI measurement report(s) 324 and / or the CSI resource configuration, the CSI report configuration, and / or the LTM SSB configuration. In some implementations, the LI measurement report(s) include the SSB index. In other implementations, the LI measurement report(s) include an SS / PBCH Block Resource Indicator (SSBRI) corresponding to the SSB index. Thus, the DU 174 determines the SSB index based on the SSBRI.

[0095] In some implementations, the DU 174 determines whether to transmit the PDCCH order based on the LI measurement result(s) 324. In some implementations, if the LI measurement result(s) indicate that the first cell qualifies for the UE 102 to perform RA for early UL synchronization, the DU 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 DU174 transmits the PDCCH order after receiving 320 the RRC reconfiguration complete message, regardless of the LI measurement result(s) 324.

[0096] In some implementations, after transmitting 324 the LI measurement report(s) or 352 the RA preamble, the UE 102 transmits 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 an LTM cell switch to the first cell based on the additional LI measurement report(s) and / or the LI measurement report(s) 324. In response to the determination, the DU 174 generates an LTM Cell Switch Command (e.g., a MAC CE) including the LTM ID 1 and transmits 326 the LTM Cell Switch Command to the UE 102. In further implementations, in response to the determination, the DU 174 transmits 328 a DU-CU Cell Switch Notification message to the CU 172. In response to the LTM Cell Switch Command, the UE 102 performs an LTM cell switch to the first cell. In the LTM cell switch, the UE 102 accesses 332 the first cell and transmits 336 an RRC reconfiguration complete message to the DU 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 the implementation, the UE 102 stops communicating via 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. In some implementations, when the DU 174 detects the UE 102 accesses the first cell in the event 332, the DU 174 transmits 334 an Access Success message to the CU 172 to indicate that the UE 102 has accessed the first cell.

[0097] In some alternative implementations, the UE 102 transmits at least one L3 measurement result to the CU 172 via the DU 174 after event 320. In some implementations, based on the at least one L3 measurement result, the CU 172 sends a CU-to-DU message to the DU 174, requesting or indicating to the DU 174 to trigger the LTM Cell Switch to the first cell for the UE 102. In some implementations, the CU-to-DU message includes a field or IE for the requesting or indicating. In response to the CU-to-DU message or the field or IE, the DU 174 transmits 350 the PDCCH order and / or 326 the LTM Cell Switch Command to the UE 102. In some implementations, the CU-to-DU message includes the at least one L3 measurement result. In some implementations, the DU 174 determines to send 350 thePDCCH order and / or 326 the LTM Cell Switch Command based on the at least one L3 measurement result. In some implementations, the CU-to-DU message is an existing message (e.g., as defined in 3GPP specification 38.473). For example, the CU-to-DU message is a UE Context Modification Request message or a CU-DU Cell Switch Notification message. In yet other implementations, the CU-to-DU message is a specifically defined CU-to-DU message (e.g., defined in 3GPP specification 38.473).

[0098] In some implementations, the DU 174 includes, in the LTM Cell Switch Command, a TA value for UL synchronization with the first cell. In some implementations, the DU 174 derives the TA value based on the RA preamble (e.g., reception timing of the RA preamble). In further implementations, the DU 174 derives the TA value from a 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 an 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 cell radio network temporary identifier (C-RNTI) of the UE 102 and determines that the LTM cell switch is completed successfully in response to receiving the PDCCH transmission.

[0099] In some implementations, the PDCCH transmission includes 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. When the PDCCH transmission includes a DL assignment, the DU 174 transmits a PDSCH transmission to the UE 102 on the first cell in accordance with the DL assignment. In some implementations, the DU 174 transmits 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.

[0100] In other implementations, the DU 174 does not include a TA value in the LTM Cell Switch Command. In some implementations, if the LTM Cell Switch Command does not include the TA value, the UE 102 performs 332 an RA procedure on the first cell in accordance with the RA configuration parameters. In some implementations, the RA configuration parameters are included in the LTM candidate configuration 1 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 that the LTM cell switch to the first cell is completed successfully. Depending on the implementation 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-step RA 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. In some implementations, the UE 102 includes 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. In some implementations, the DU 174 transmits 334 the Access Success message to the CU 172 after receiving the Message 3, Message A, or the RRC reconfiguration complete message 336, or after transmitting the Message 4 or Message B.

[0101] The events 324, 350, and 352 are collectively referred to in Fig. 3 as an early TA acquisition procedure 382.

[0102] 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. With regard to the LTM reference configuration, the UE 102 applies the LTM reference configuration first and then applies the LTM candidate configuration 1 to augment the LTM reference configuration.

[0103] In some implementations, each of the TCI state configuration(s) includes 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 TCI state configuration(s) based on the first TCI state ID and applies the first TCI state configuration to communicate UL transmissions and / or DLtransmissions 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

[0104] In some implementations, the CU 172 prepares additional cell(s) (i.e., cell(s) 2, N) as LTM candidate cell(s) for the UE 102 with the DU 174 (i) before or after transmitting the LTM Cell Switch Command or (ii) 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. In some implementations, the CU 172 obtains the CSI resource configuration(s) 2, ,..., N and performs CSI report configuration and / or LTM ID configuration procedure(s) 2, ..., N with the DU 174 to obtain the CSI report configuration(s) 2, ..., N, respectively, as described for the CSI resource configuration 1 and the CSI report configuration(s) 1. In some implementations, the CU 172 obtains RACH configuration(s) 2, ..., N for the cell(s) 2, ..., N respectively, as described for the RACH configuration 1. In further implementations, the CU 172 obtains 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. In some implementations, the CU 172 obtains 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 performs 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 configurationdelivery procedure(s) 2, .. N is similar to the procedure 394. In other implementations, the CU 172 includes the list in the first RRC reconfiguration message.

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

[0106] In some implementations, an LTM ID in a PDCCH order, an LTM Cell Switch Command, and an RRC reconfiguration message are represented in different formats. For example, the PDCCH order and / or the LTM Cell Switch Command includes a first field to include the LTM ID 1, and the first RRC reconfiguration message includes a second field to include the LTM ID 1. In some implementations, the first field and the second field have different formats or coding schemes. For example, the first field uses a binary format (i.e., 3 bits) with a value range of 0, ..., 7 and the second field uses an integer format with a value range of 1, ..., 8. In this example, the first field with binary value 000b is equivalent to the second field with integer value 1, the first field with binary value 001b is equivalent to the second field with integer value 2, ..., the first field with binary value 11 lb is equivalent to the second field with integer value 8.

[0107] The events 304, 306, 390, 392, and 394 are collectively referred to in Fig. 3 as an intra-CU intra-DU LTM configuration procedure 396. The events 354, 326, 328, 332, 334, 336, 338, and 340 are collectively referred to in Fig. 3 as an LTM cell switch execution procedure 397. 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.

[0108] Referring next to Fig. 4, in a scenario 400, the base station 104A includes a CU 172, an 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., cell124C). 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 apply to the S-DU 174A in Fig. 4, and some descriptions for the DU 174 in Fig. 3 apply to the C-DU 174B. The differences between the scenarios 300 and 400 are described below.

[0109] Initially, the UE 102 communicates 402 with the S-DU 174A on one or more serving cells (e.g., the cell 124A and / or other cell(s)) using a serving DU configuration and communicates with the CU 172 via the S-DU 174A using a serving CU configuration. In some implementations, the CU 172 and S-DU 174A perform the LTM configuration procedure 396 or the LTM procedure 380 with the UE 102, as described for Fig. 3. In some implementations, with regard to the procedure 380, the UE 102 performs an LTM cell switch to the first cell (e.g. Cell 124B) 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) are no longer serving cell(s) for the UE 102. With regard to the procedure 396, the UE 102 does not perform an LTM cell switch. During the communication 402, the UE 102 transmits 404, 406 at least one measurement report (e.g., L3 measurement report(s)) to the CU 172 via the S-DU 174A. Based on the measurement report(s), the CU 172 determines to prepare cell 1 (e.g., cell 124C operated by the C-DU 174B) for LTM for the UE 102. The cell 1 is identified by a cell ID (i.e., cell ID 1). In response to the determination, the CU 172 performs 490 an LTM preparation procedure with the C-DU 174B to and / or to request the C-DU 174B to prepare the cell 1 as an LTM candidate cell for the UE 102. In the LTM preparation procedure 490, the CU 172 transmits a first CU-to-DU message, including a cell ID 1 of the cell 1, to the C-DU 174B to request the C-DU 174B to prepare the cell 1 as an LTM candidate cell for the UE 102, similar to the event 308. In response, the C-DU 174B transmits a first DU-to-CU message including an LTM DU configuration (e.g., LTM DU configuration 1) to the CU 172, similar to the event 310. Depending on the implementation, the CU 172 does or does not request an LTM reference DU configuration in the first CU-to-DU message, as described for Fig. 3. Depending on the implementation, the C-DU 174B does or does not include an LTM reference DU configuration in the first DU-to-CU message, as described for Fig. 3.

[0110] In some implementations, if the CU 172 receives an LTM reference DU configuration from the S-DU 174A as described for Fig. 3, the CU 172 includes the LTMreference DU configuration in the first CU-to-DU message, and the C-DU 174B generates the LTM DU configuration as a delta configuration based on the LTM reference DU configuration. In such cases, the C-DU 174B does not transmit an LTM reference DU configuration for the UE 102 to the CU 172. In other implementations, the CU 172 receives an LTM reference DU configuration from the C-DU 174B (e.g., in the first DU-to-CU message or an additional DU-to-CU message), as described for Fig. 3. In some such cases, the CU 172 generates an LTM reference configuration including the LTM reference DU configuration. Depending on the implementation, the CU 172 does or does not include an LTM reference CU configuration in the LTM reference configuration.

[0111] In some implementations, to prepare the cell 1 for LTM, the CU 172 performs 492 an LTM CSI report configuration and / or LTM ID configuration procedure with the S-DU 174A. In the procedure 492, the CU 172 transmits a second CU-to-DU message including a CSI resource configuration (e.g., CSI resource configuration 1) and / or an LTM SSB configuration (i.e., LTM SSB configuration 1) to the S-DU 174A, similar to the event 312. In response, the S-DU 174A transmits a second DU-to-CU message including one or more CSI report configurations (e.g., CSI report configuration(s) 1) to the CU 172. In some implementations, the CU 172 generates an LTM candidate configuration (e.g., LTM candidate configuration 1) including the LTM DU configuration and assigns an LTM ID (e.g., LTM ID 1) for identifying the LTM DU configuration and / or the LTM candidate configuration as 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.

[0112] To prepare the cell 1 as an LTM candidate cell for the UE 102, the CU 172 may receive early synchronization information for the cell 1 in a DU-to-CU message (e.g., the first DU-to-CU message or an additional DU-to-CU message) from the C-DU 174B. In some implementations, the C-DU 174B transmits the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other implementations, the C-DU 174B transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message. The 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 for Fig. 3. In some implementations, the C-DU 174B includes, in the early synchronizationinformation or in the DU-to-CU message, the PDCCH order information (PDCCH order information 1) for early UL synchronization with the first cell.

[0113] In some implementations, the CU 172 receives 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 receives a PCI of the cell 1 from the C-DU 174B in the first DU-to-CU message or the additional DU-to-CU message. In some implementations, the C-DU 174B transmits the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other implementations, the C-DU 174B transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message.

[0114] As 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 {the LTM ID, the LTM candidate configuration] as a tuple in a first RRC reconfiguration message in the procedure 494. Depending on the implementation, the CU 172 includes 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 some implementations, the CU 172 includes an LTM candidate cell TA ID for the LTM candidate cell in the tuple in the first or other RRC reconfiguration message. In other implementations, the CU 172 includes, in the first or other RRC reconfiguration message, the CSI resource configuration outside the tuple. In some implementations, the CU172 includes, in the first RRC or other reconfiguration message, a serving cell TA ID for the serving cell outside the tuple. In response to each of the other RRC reconfiguration message(s), the UE 102 transmits an RRC reconfiguration complete message to the CU 172 via the S-DU 174A.

[0115] In some implementations, the PDCCH order information includes a frequency domain resource assignment, an RA preamble index, a UL or a supplemental UL indicator, an SSB index and / or a physical RACH mask index. In some implementations, the CU 172 transmits a CU-to-DU message (e.g., the second CU-to-DU message or an additional CU-to-DU message), including the PDCCH order information, to the S-DU 174A. In some implementations, the CU 172 includes the LTM ID 1 or the cell ID 1 in the CU-to-DU message to indicate that the PDCCH order information is associated with the LTM ID 1 or the cell ID 1. For example, the CU 172 includes {the cell ID 1, the PDCCH order information} as a tuple in the CU-to-DU message. In some implementations, with regard to the additional CU-to-DU message, the S-DU 174A transmits 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 determines an 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 some implementations, with regard to the additional CU-to-DU message, the S-DU 174A transmits an additional DU-to-CU message to the CU 172 in response. The UE 102 transmits 452 an 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, an 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 102to perform an LTM cell switch to the cell 1, the S-DU 174A transmits 456 the LTM Cell Switch Command, including the LTM ID 1, to the UE 102. In some implementations, if the S-DU 174A receives a TA value as described above, the S-DU 174A includes the TA value in the LTM Cell Switch Command. In further implementations, the S-DU 174A 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).

[0116] 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 452. In some implementations, the C-DU 174B calculates the RA-RNTI as:RA-RNTI = 1 + s_id + 14 x t_id + 14 x 80 x f_id + 14 x 80 x 8 x ul_carrier_id where s_id is the index of the first OFDM symbol of the PRACH occasion (0 < s_id < 14), t_id is the index of the first slot of the PRACH occasion in a system frame (0 < t_id < 80), the subcarrier spacing to determine t_id is based on a previously defined value of p (e.g., as specified in clause 5.3.2 in 3GPP TS 38.211) for p = {0, 1, 2, 3}, and for p = {5, 6}, t_id is the index of the 120 kHz slot in a system frame that contains the PRACH occasion (0 < t_id < 80), f_id is the index of the PRACH occasion in the frequency domain (0 < f_id < 8), and ul_carrier_id is the UL carrier used for the RA Preamble transmission (0 for NUL carrier, and 1 for SUL carrier).

[0117] The events 424, 450, 452, 456, and 458 are collectively referred to in Fig. 4 as an early TA acquisition procedure 482.

[0118] In response to determining to command the UE 102 to perform an LTM cell switch or transmitting 456 the LTM Cell Switch Command, the S-DU 174A transmits 428 DU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 performs an LTM cell switch to the cell 1. In response, the CU 172 transmits 430 a CU-DU Cell Switch Notification message to the C-DU 174B to indicate that the UE 102 performs an LTM cell switch to the cell 1. In some implementations, the S-DU 174A includes the first TCI state ID in the DU-CU Cell Switch Notification message and the CU 172 in turn includes the first TCI state ID in the CU-DU Cell Switch Notification message. The UE 102 and the C-DU 174B identify the first one of the TC state configuration(s) based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in the events 432, 436, and / or 440.

[0119] 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 transmits 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 some implementations, with regard to the additional CU-to-DU message, the S-DU 174A transmits 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.

[0120] In some implementations, the CU 172 prepares additional cell(s) (i.e., cell(s) 2, ..., N) as LTM candidate cell(s) for the UE 102 with the C-DU 174B (i) before or after transmitting the LTM Cell Switch Command or (ii) during, before, or after the procedure 490 or 492, as described for Fig. 3.

[0121] 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.

[0122] The events 404, 406, 490, 492, and 494 are collectively referred to in Fig. 4 as an intra-CU inter-DU LTM configuration procedure 496. The events 454456, 458, 426, 428, 430, 432, 434, 436, 438, 440, 442, and 444 are collectively referred to in Fig. 4 as an LTMcell switch execution procedure 497. The events 404, 406, 490, 492, 494, 494, 424, 450, 452, 454456, 458, 426, 428, 430, 432, 434, 436, 438, 440, 442, and 444 are collectively referred to in Fig. 4 as an intra-CU inter-DU LTM procedure 480.

[0123] Referring next to Fig. 5, in a scenario 500, the base station 104A operates as a serving or source base station (S-BS), and the base station 106A operates as a candidate base station (C-BS). The C-BS 106A includes a CU 172 and a DU 174. The scenario 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 104A can include a CU and a DU (not shown in Fig. 5), similar to the base station 104A of Figs. 3 and 4. Initially, the UE 102 communicates 502 with the S-BS 104A via serving cell(s) using a serving configuration (a first serving configuration). In some implementations, the S-BS 104A includes an S-DU and a CU, and the serving configuration includes a serving CU configuration and a serving DU configuration, as described for Figs. 3 and 4. In some implementations, while communicating 502 with the UE 102, the S-BS 104A performs 580 intra-CU LTM procedure(s) with the UE 102, similar to the procedures 380 and / or 480. Alternatively, while the communicating 502 with the UE 102, the S-BS 104A performs 596 intra-CU LTM configuration procedure(s) with the UE 102, similar to the procedures 396 and / or 496.

[0124] While communicating with the S-BS 104A, the UE 102 transmits 504 at least one measurement report to the S-BS 104A. The measurement report(s) include measurement results for a serving cell of the UE 102 and / or at least one non-serving cell (e.g., cell 126A). The S-BS 104A determines to prepare a first cell (e.g., the cell 126A) as an LTM candidate cell (i.e., an LTM candidate PSCell) for the UE 102, based on the measurement report(s). For example, the measurement report(s) include a PCI of the first cell and measurement result(s) of the cell 126A. The S-BS 104A identifies that the first cell is operated by the base station 106 A based on the PCI, and determines that the first cell qualifies for LTM preparation based on the measurement result(s).

[0125] After (e.g., in response to) determining to prepare the first cell as an LTM candidate cell for the UE 102, the S-BS 104A (e.g., the CU of the S-BS 104A) generates a Handover Request message including a first cell ID (i.e., cell ID 1) of the first cell (i.e., cell 1). The S-BS 104A transmits 505 the Handover Request message to the CU 172. In some implementations, the Handover Request message includes an LTM indicator indicating theHandover Request message concerns LTM for the first cell ID. After (e.g., in response to) receiving the Handover Request message, the CU 172 performs an LTM preparation procedure 590 with the DU 174 to prepare the first cell as an LTM candidate cell for the UE 102, similar to the procedure 390 or 490. In the procedure 590, the CU 172 transmits a first CU-to-DU message, including the first cell ID, to the DU 174 to request preparation of the first cell, similar to the event 308. In some implementations, in response, the CU 172 receives a first DU-to-CU message, including an LTM DU configuration 1, from the DU 174, similar to the event 310. The CU 172 generates a first LTM candidate configuration (LTM candidate configuration 1). In response to the Handover Request message, the CU 172 transmits 507 a Handover Request Acknowledge message, including the first LTM candidate configuration, to the S-BS 104A. In some implementations, the CU 172 includes the first cell ID in the Handover Request Acknowledge message to indicate that the first LTM candidate configuration is provided for or associated with the first cell (ID). In some implementations, the CU 172 includes the first LTM candidate configuration in an RRC container (e.g., HandoverCommand message) and includes the RRC container in the Handover Request Acknowledge message.

[0126] The events 505, 590, 507 are collectively referred to in Fig. 5 as an inter-CU MCG LTM preparation procedure or inter-MN LTM preparation procedure 598.

[0127] In some implementations, the Handover Request message includes a DU ID of the S-DU of the S-BS 104A. In such cases, the CU 172 includes the DU ID in the first CU-to-DU message. In some implementations, the Handover Request message includes a BS ID of the S-BS 104A. In further implementations, when receiving the BS ID, the CU 172 includes the BS ID in the first CU-to-DU message. For example, the BS ID is a gNB ID.

[0128] Depending on the implementation, the CU 172 does or does not request an LTM reference DU configuration in the procedure 590, as described for Figs. 3 and 4. Depending on the implementation, the DU 174 does or does not transmit an 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 104A (e.g., the CU of the S-BS 104A) obtains an LTM reference configuration, as described for Figs. 3 and 4. In other implementations, the S-BS 104A receives an LTM reference configuration from another BS (not shown in Fig. 5) in another inter-CU LTM preparation procedure as described above and below. In some implementations, if the S-BS 104A obtains an LTM reference configuration generated by theS-BS 104A or received from another BS, the S-BS 104A includes the LTM reference configuration in the Handover Request message. In some implementations, the S-BS 104A includes the LTM reference configuration in the inter-node RRC message HandoverPreparationlnformation or as an Xn Application Protocol (XnAP) IE or field and includes the inter-node RRC message or the XnAP IE in the Handover Request message. Alternatively, the S-BS 104A determines to request or cause the C-BS 106A to provide a complete LTM candidate configuration so that the S-BS 104A does not include the LTM reference configuration in the Handover Request message. If the S-BS 104A does not obtain an LTM reference configuration, the S-BS 104A does not include an LTM reference configuration in the Handover Request message. In some implementations, if the Handover Request message includes an LTM reference configuration, the CU 172 includes the LTM reference configuration in the first CU-to-DU message. In some implementations, the DU 174 extracts an LTM reference DU configuration from the LTM reference configuration. Alternatively, the CU 172 extracts an LTM reference DU configuration from the LTM reference configuration and includes the LTM reference DU configuration in the first CU-to-DU message. In some implementations, the DU 174 generates an LTM DU configuration as a delta configuration based on the LTM reference DU configuration, as described for Fig. 3. Alternatively, the DU 174 ignores the LTM reference (DU) configuration and generate an LTM DU configuration as a complete configuration, as described for Fig. 3.

[0129] Otherwise, in some implementations, if the Handover Request message does not include an LTM reference configuration, the CU 172 does or does not receive an LTM reference DU configuration from the DU 174 as described for Fig. 3. If the CU 172 receives an LTM reference DU configuration (e.g., in the first DU-to-CU message), the CU 172 generates an LTM reference configuration (C-BS generated LTM reference configuration) including the LTM reference DU configuration. In some implementations, the CU 172 includes an LTM reference CU configuration (candidate CU (C-CU) generated LTM reference CU configuration). Otherwise, if the CU 172 does not receive an LTM reference DU configuration from the DU 174 as described for Fig. 3, the CU 172 does not generate an LTM reference configuration. Alternatively, the CU 172 generates an LTM reference configuration (C-BS generated LTM reference configuration) only including a C-CU generated LTM reference CU configuration. In cases where the CU 172 generates an LTM reference configuration (C-BS generated LTM reference configuration), the CU 172 includesthe C-BS generated LTM reference configuration in the Handover Request Acknowledge message.

[0130] 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. In further implementations, the CU 172 includes a complete configuration indication (e.g., a BS-to-BS interface protocol field / IE) in the Handover Request Acknowledge message to indicate that the LTM candidate configuration 1 is a complete configuration. In some implementations, the BS-to-BS interface protocol is an Xn application protocol (e.g., as defined in 3GPP specification 38.423). In some implementations, the complete configuration indication is a specifically defined 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 (e.g., as defined in 3GPP specification 38.423). Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU 172 generates the LTM candidate configuration 1 as a delta configuration. In some implementations, the CU 172 excludes 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 includes 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 (e.g., as 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 (e.g., as 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.

[0131] In some implementations, the S-BS 104A is preconfigured with a CSI resource configuration (e.g., (LTM) CSI resource configuration 1) and / or an LTM SSB configuration (LTM SSB configuration 1) for the first cell. In other implementations, the S-BS 104A receives the CSI resource configuration and / or the LTM SSB configuration from anOperations, Administration, and Maintenance (OAM) node. In yet other implementations, the S-BS 104A receives the CSI resource configuration and / or the LTM SSB configuration from the CU 172. For example, the CU 172 includes the CSI resource configuration and / or the LTM SSB configuration in the Handover Request Acknowledge message. In some implementations, the CU 172 includes a PCI (PCI 1) of the first cell in 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 104A performs an LTM CSI report configuration and / or LTM ID configuration procedure (not shown in Fig. 5) with an S-DU of the S-BS 104A, similar to the procedure 392. In the LTM CSI report configuration and / or LTM ID configuration procedure, the CU of the S-BS 104A transmits the CSI resource configuration and / or the LTM SSB configuration to the S-DU of the S-BS 104A. In response, the CU of the S-BS 104A receives one or more CSI report configurations for the UE 102 from the S-DU of the S-BS 104A. In some implementations, the CU of the S-BS 104A receives the CSI report configuration(s) in a second serving DU configuration from the S-DU.

[0132] In some implementations, to prepare the first cell as an LTM candidate cell for the UE 102, the CU 172 receives 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.

[0133] In some implementations, the CU 172 assigns an LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration and includes the LTM ID in the Handover Request Acknowledge message. In other implementations, the S-BS 104A assigns an LTM ID (e.g., LTM ID 1) for identifying the first LTM candidate configuration.

[0134] After (e.g., in response to) receiving the Handover Request Acknowledge message, the S-BS 104A (e.g., the CU of the S-BS 104A) transmits 518 a first RRC reconfiguration message to the UE 102, including {the LTM ID 1, the LTM candidate configuration 1 } as a tuple, similar to the event 318. In some implementations, if the Handover Request Acknowledge message includes the LTM reference configuration, the S-BS 104A includes the LTM reference configuration in the first RRC reconfiguration message. In further implementations, the S-BS 104A includes the CSI resource configuration 1, the TCI state configuration(s) 1, the RACH configuration 1, and / or the LTM SSB configuration 1 in the tuple, if received in the Handover Request Acknowledge message. Alternatively, the S-BS 104A transmits one or more additional RRC reconfiguration messages to the UE 102, including the CSI resource configuration 1, the TCI state configuration(s) 1, the RACH configuration 1, the LTM SSB configuration 1, and / or the PCI of the first cell. In each of the additional RRC reconfiguration message(s), the S-BS 104A includes the LTM ID 1 to indicate that the CSI resource configuration 1, the TCI state configuration(s) 1, the RACH configuration 1, the LTM SSB configuration 1, and / or the PCI of the first cell are associated with the first cell or configured for the first cell. The UE 102 transmits 520 a first RRC reconfiguration complete message to the S-BS 104A in response to the first RRC reconfiguration message. The UE 102 transmits an additional RRC reconfiguration complete message to the S-BS 104A in response to each of the additional RRC reconfiguration complete message(s). The RRC reconfiguration message(s) (i.e., the first RRC reconfiguration message and / or the additional RRC reconfiguration message(s)) and the RRC reconfiguration complete message(s) (i.e., the first RRC reconfiguration complete message and / or the additional RRC reconfiguration complete message(s)) form an LTM configuration delivery procedure. In some implementations, the S-BS 104A includes the second serving DU configuration in the first RRC reconfiguration message or one or the additional RRC reconfiguration message(s).

[0135] In some implementations, if the Handover Request Acknowledge message includes the complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration, the S-BS 104A includes, in the first RRC reconfiguration message, a complete configuration indication (e.g., an RRC field / IE) to indicate that the LTM candidate configuration 1 is a complete configuration. Otherwise, if the Handover Request Acknowledge message does not include the complete configuration indication or includes thedelta configuration indication to indicate that the LTM candidate configuration 1 is a delta configuration, the S-BS 104A excludes or does not include, in the first RRC reconfiguration message, the complete configuration indication (e.g., an RRC field / IE) to indicate that the LTM candidate configuration 1 is a delta configuration.

[0136] If the Handover Request Acknowledge message includes the PDCCH order information (PDCCH order information 1), the S-BS 104A transmits 550 a PDCCH order, based on the PDCCH order information. In some implementations, if the S-BS 104A is a distributed base station, the CU of the S-BS 104A transmits the PDCCH order information to the S-DU of the S-BS 104A. For example, the S-BS 104A or the S-DU of the S-BS 104A transmits 550 a PDCCH order to the UE 102, including the PDCCH order information. In some implementations, the S-BS 104A or the S-DU of the S-BS 104A determines an SSB index included in the PDCCH order, based on LI or L3 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 104A includes the LTM ID 1 in the PDCCH order to indicate the first cell. The UE 102 transmits 552 an RA preamble to the DU 174 on the first cell, using the RACH configuration and / or the PDCCH order information. The S-DU or the S-BS 104A derives a TA value based on the RA preamble. The DU 174 transmits 556 a DU-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 104A (e.g., the CU of the S-BS 104A). 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 104A, and / or the BS ID of the S-BS 104A 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 104A in the message 558. In some implementations, the CU 172 does not include the BS ID in the message 558. The CU of the S-BS 104A transmits a CU-DU TA Information Transfer message, including the TA value, the cell ID 1, the RA preamble index, the RA-RNTI, and / or the DU ID of the S-DU, and / or the BS ID of the S-BS 104A, to the S-DU of the S-BS 104A. In some implementations, the CU of the S-BS 104A does not include the BS ID in the CU-DU TA Information Transfer message.

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

[0138] In response to determining to command the UE 102 to perform an LTM cell switch to the first cell (e.g., based on the measurement report(s) 524 and / or 554), the S-DU or the S-BS 104A transmits 526 the LTM Cell Switch Command, including the LTM ID 1, to the UE 102. In some implementations, the S-DU transmits 528 a Cell Switch Notification message to the CU, indicating that the LTM cell switch to the first cell is triggered for the UE 102. In some implementations, in response to the LTM Cell Switch Command, the UE 102 stops communication on the serving cell(s). In response to the LTM Cell Switch Command, the UE 102 accesses 532 the first cell and transmits 536 an 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 106A communicates 540 with the UE 102 in accordance with the first LTM candidate configuration and / or the LTM reference configuration. In some implementations, the UE 102 includes 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 first cell 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.

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

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

[0141] In response to determining to command the UE 102 to perform the LTM cell switch or transmitting 526 the LTM Cell Switch Command, the S-DU of the S-BS 104A transmits a DU-CU Cell Switch Notification message to the CU of the S-BS 104A to indicate that the UE 102 performs or is performing an LTM cell switch to the first cell. In response to receiving the DU-CU Cell Switch Notification message, the CU of the S-BS 104A transmits 527 a CU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 performs an 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 an LTM cell switch to the first cell. In some implementations, the S-BS 104A includes the first TCI state ID in the CU-CU Cell Switch Notification message, and the CU 172 then includes the first TCI state ID in the CU-DU Cell Switch Notification message. The UE 102 and the DU 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.

[0142] In some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting 526 the LTM Cell Switch Command, or receiving 527 the DU-CU Cell Switch Notification message, the S-BS 104A (e.g., the CU ofthe S-BS 104A) transmits 531 one or more Early Status Transfer messages to the CU 172, each including a DL COUNT value or a DISCARD DL COUNT value for a DRB over which the UE 102 and the S-BS 104A communicate 502 data with each other. In some implementations, after receiving 534 the Access Success message or receiving 538 the DU-to-CU message or the RRC reconfiguration complete message, the CU 172 transmits 539 an LTM Success message to the S-BS 104A (e.g., the CU of the S-BS 104A) to indicate that the LTM cell switch is completed successfully. In some implementations, the LTM Success message is a Handover Success message. In some implementations, the CU 172 includes the first cell ID in the LTM Success message. In other implementations, the CU 172 does not transmit a BS-to-BS message to the S-BS 104A (e.g., the CU of the S-BS 104A) to indicate that the LTM cell switch is completed successfully.

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

[0144] In some implementations, after (e.g., in response to) receiving 534 the Access Success message, receiving 538 the DU-to-CU message or the RRC reconfiguration complete message, or receiving 541 the SN Status Transfer message, the CU 172 transmits 543 a UE Context Release message to the S-BS 104A. In response to the UE Context Release message, the S-BS 104A releases a UE context of the UE 102.

[0145] The events 505, 590, and 507 are collectively referred to in Fig. 5 as an inter-CU MCG LTM preparation procedure 598. The events 504, 598, 518, and 520 are collectively referred to in Fig. 5 as an inter-CU MCG LTM configuration procedure 581. The events 524, 550, 552, 556, and 558 are collectively referred to in Fig. 5 as an early TA acquisition procedure 582. The events 554, 526, 528, 527, 530, 531, 532, 534, 536, 538, 539, 541, 540, and 543 are collectively referred to in Fig. 5 as an LTM cell switch execution procedure 597.

[0146] In some implementations, the S-BS 104A (e.g., the CU of the S-BS 104A) performs additional inter-CU MCG LTM preparation procedure(s) to prepare additional cell(s) (i.e.,cell(s) 2, .. N) as LTM candidate cell(s) for the UE 102 with the CU 172. 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 106A. N is an integer and larger than 1. For example, the S-BS 104A performs additional inter-CU LTM preparation procedure(s) 2, N with the CU 172 to prepare the cell(s) 2, .. N, respectively. Each of the inter-CU LTM preparation procedure(s) 2, ..., N is similar to the procedure 598. In the inter-CU LTM preparation procedure(s) 2, ..., N, the S-BS 104A receives LTM candidate configuration(s) 2, ..., N configuring the cell(s) 2, .. ., N for LTM, respectively. As described above, the S-BS 104A or the C-BS 106A assigns LTM ID(s) 2, ..., N to identify the LTM candidate configuration(s) 2, ..., N, respectively. In some implementations, the S-BS 104A obtains CSI resource configuration 2, ,..., N for the cell(s) 2, ..., N respectively, as described for the CSI resource configuration 1. In further implementations, the S-BS 104A obtains CSI report configuration(s) 2, ..., N or the cell(s) 2, .. ., N, respectively, as described for the CSI report configuration(s) 1. In some implementations, the S-BS 104A obtains RACH configuration 2, ..., N for the cell(s) 2, ..., N respectively, as described for the RACH configuration 1. In further implementations, the S-BS 104A obtains TCI state configuration(s) 2, ..., N for the cell(s) 2, ..., N respectively, as described for the TCI state configuration(s) 1. In some implementations, the S-BS 104A obtains LTM SSB configuration 2, ..., N for the cell(s) 2, ..., N, respectively, as described for LTM SSB configuration 1. In further implementations, the S-BS 104A obtains PCI(s) 2, .. ., N for the cell(s) 2, ..., N respectively, as described for the PCI 1. In some implementations, the S-BS 104A performs LTM configuration delivery procedure 2, ..., N with the UE 102 to transmit a list of the {LTM ID 2, the LTM candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained), the PCI 2 (if obtained)}, ..., {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained), the PCI N (if obtained)} to the UE 102, respectively. Each of the LTM configuration delivery procedure(s) 2, ..., N is similar to the procedures 394, 494, and / or 518 and 520. In other implementations, the S-BS 104A includes the list in the first RRC reconfiguration message.

[0147] In other implementations, the S-BS 104A performs the procedure 598 with the CU 172 to prepare one or more of the cell(s) 1, ..., N as LTM candidate cell(s) for the UE 102.In such implementations, the S-BS 104A includes the cell ID(s) 1, N in the Handover Request message 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 in the Handover Request message. The CU 172 performs LTM preparation procedure(s) 2, ..., M with the DU 174 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. In some implementations, the C-BS 106A generates 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 104A 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 configuration(s) 1, ..., M, respectively in the Handover Request Acknowledge message, as described for the LTM ID 1 and the LTM candidate configuration 1.

[0148] 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 104A 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.

[0149] In some implementations, the CU 172 or the S-BS 104A obtains LTM SSB configuration(s) 2, ..., M for the cell(s) 2, ..., M, respectively, as described for the LTM SSB configuration 1. In cases where the CU 172 obtains the LTM SSB configuration(s) 2, ..., M,the CU 172 includes the LTM SSB configuration(s) 2, M in the Handover Request Acknowledge message. In some implementations, the CU 172 or the S-BS 104A obtains PCI(s) 2, .. M for the cell(s) 2, .. M, respectively, as described for the PCI 1. In cases where the CU 172 obtains the PCI(s) 2, ..., M, the CU 172 includes the PCI(s) 2, ..., M in the Handover Request Acknowledge message.

[0150] In some implementations, the CU 172 includes a list of {the cell ID 1, the LTM ID 1 (if obtained or optional), the LTM candidate configuration 1, the CSI resource configuration 1 (if obtained or optional), the TCI state configuration 1 (if obtained or optional), the early synchronization information 1 (if obtained or optional), the LTM SSB configuration 1 (if obtained or optional), PCI 1 (if obtained or optional)}, , {the cell ID M, the LTM ID M (if obtained or optional), the LTM candidate configuration M, the CSI resource configuration M (if obtained or optional), the TCI state configuration M (if obtained or optional), the early synchronization information M (if obtained or optional), the LTM SSB configuration M (if obtained or optional), the PCI M (if obtained or optional) } in the Handover Request Acknowledge message.

[0151] 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 some implementations, the CU 172 includes the PDCCH order information 2, ..., M in the Handover Request Acknowledge message. In further implementations, the CU 172 includes the PDCCH order information 2, ..., M in the early synchronization information 2, ..., M, respectively. In some implementations, the S-BS 104A obtains RACH configuration 2, TCI state configuration(s) 2, and / or the PDCCH order information 2, ...., RACH configuration M, TCI state configuration(s) M, and / or the PDCCH order information M from the early synchronization information 2, ..., M, respectively or from the Handover Request Acknowledge message.

[0152] In some implementations, the S-BS 104A performs 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 (ifobtained)} to the UE 102, respectively. Each of the LTM configuration delivery procedure 2, .. M is similar to the procedures 394, 494, and / or 518 and 520. In other implementations, the S-BS 104A includes the list in the first RRC reconfiguration message.

[0153] In some implementations, the S-BS 104A includes measurement result(s) 1, ..., N for the cell(s) 1, ..., N respectively in the Handover Request message. The S-BS 104A receives the measurement result(s) from the UE 102. In further implementations, the C-BS 106A selects or determines the cell(s) 1, ...M, based on the measurement result(s) 1, ..., N. In other implementations, the C-BS 106A selects or determines 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 some implementations, the maximum number is included in the Handover Request message. In further implementations, the maximum number is a predetermined number.

[0154] Referring next to Fig. 6, in a scenario 600, the base station 104B operates as an MN, the base station 106A operates as a candidate SN (C-SN), and the base station 104A operates as a serving or source SN (S-SN). The MN 104B includes a CU 172 and a DU 174. In some implementations, the C-SN 106A and the S-SN 104A include a CU and a DU (not shown in Fig. 6), similar to the C-BS 106A in the Fig. 5. The scenario 600 is similar to the scenario 500, except that the scenario 600 is a DC scenario and the scenario 500 is a single connectivity scenario.

[0155] Initially, the UE 102 in DC communicates 602 with the MN 104B and with S-SN 104A. In some implementations, the UE 102 communicates with the DU of the S-SN 104A on cell 124A (e.g., a PSCell) using a serving DU configuration and communicates with the CU of the S-SN 104A via the DU of the S-SN 104A using a serving CU configuration, similar to the event 302. In some implementations, the UE 102 in DC communicates 602 UL PDUs and / or DL PDUs with the MN 104B and / or S-SN 104A via radio bearers which, in some implementations, include SRBs and / or DRB(s). In further implementations, the MN 104B and / or the S-SN 104A configure the radio bearers to the UE 102. The UE 102 in DC communicates 602 UL PDUs and / or DL PDUs with the S-SN 104A on an SCG (i.e., SCG radio resources) that the S-SN 104A configures for communication with the UE 102. In event 602, the UE 102 and the DU 174 communicate UL PDUs and / or DL PDUs with each other on an MCG (i.e., MCG radio resources) in accordance with a (serving) MN configuration (i.e., first serving MCG configuration). In some implementations, the servingDU configuration is a first SN configuration (i.e., first serving SCG configuration). In the MN configuration, the MN 104B configures the MCG, which includes at least one serving cell (e.g., the cell 124B and / or other cell(s)) operated by the MN 104B. In some implementations, the cell 124B is a PCell. In the serving DU configuration, the S-SN 104A configures the SCG, which includes at least one serving cell (e.g., the cell 124A and / or other cell(s)) operated by the S-SN 104A. In some implementations, the MN configuration includes multiple configuration parameters, and the UE 102 receives the configuration parameters in one or more RRC messages from the MN 104B. As described for Fig. 3, the serving DU configuration includes multiple configuration parameters. In some implementations, the UE 102 receives the configuration parameters in one or more RRC messages from the S-SN 104A (e.g., via the MN 104B) and / or on an SRB (e.g., SRB3) that the MN 104B or S-SN 104A configures to exchange RRC messages between the UE 102 and the S-SN 104A.

[0156] In some implementations, while communicating with the UE 102 in DC with the MN 104B and S-SN 104A, the S-SN 104A performs 696 an intra-CU LTM configuration with the UE 102, similar to the procedures 396 and / or 496. In further implementations, while communicating with the UE 102 in DC with the MN 104B and S-SN 104A, the S-SN 104A performs 680 an intra-CU LTM procedure with the UE 102, similar to the procedures 380 and / or 480. In some implementations, in the procedure 696 or 680, the CU of the S-SN 104A transmits one or more RRC reconfiguration messages, each including one or more LTM candidate configurations, to the UE 102 via the SRB3, similar to the procedure 394 or 494. Alternatively, the CU of the S-SN 104A transmits one or more RRC reconfiguration messages, each including one or more LTM candidate configurations, to the UE 102 via the MN 104B and an SRB1. In response to each of the RRC reconfiguration message(s), the UE 102 transmits an RRC reconfiguration complete message to the S-SN 104A via the MN 104B and the SRB1.

[0157] In some implementations, while communicating in DC with the MN 104B and S-SN 104A, the UE 102 transmits 604-1 at least one measurement report to the S-SN 104A directly (e.g. Via the SRB3), similar to the events 304 / 306, the events 404 / 406, and the event 504. Alternatively, the UE 102 transmits 604-2 the measurement report(s) to the MN 104B. The measurement report(s) include one or more measurement results of the first cell. In some implementations, the MN 104B generates at least one SN message including themeasurement report(s) and transmits the SN message(s) to the CU 172. In some implementations, the SN message(s) include RRC Transfer message(s) and / or SN Modification Request message(s). The S-SN 104A (e.g., the CU of the S-SN 104A) generates a measurement configuration to configure the UE 102 to transmit the measurement report(s) and transmits the measurement configuration to the UE 102 directly (e.g., via the S-DU of the S-SN 104A) or via the MN 104B. Alternatively, the MN 104B generates a measurement configuration to configure the UE 102 to transmit the measurement report(s) and transmits the measurement configuration to the UE 102 directly (e.g., via the S-DU of the MN 104B)

[0158] In some implementations, based on the measurement report(s) received from the UE 102, the S-SN 104A (e.g., the CU of the S-SN 104A) determines to request the C-SN 106A preparing a first cell (e.g., the cell 126A) as an LTM candidate cell for the UE 102. In response to the determination, the S-SN 104A generates an SN Required message (a first SN Required message) including a first cell ID (i.e., cell ID 1) of the first cell. In some implementations, the S-SN 104A includes an LTM indicator in the SN Required message, indicating the SN Required message is sent for LTM. In some implementations, the S-SN 104A includes a C-SN ID (as a target SN ID) indicating the C-SN 106A in the SN Required message. In some implementations, the S-SN 104A includes the one or more measurement results in the SN Required message. The S-SN 104A transmits 603 the SN Required message to the MN 104B. In some implementations, the one or more measurement results (e.g., a candidateCelllnfoListSN field / IE or MeasResultList2NR IE) include measurement result(s) of the first cell. In some implementations, the one or more measurement results include measurement result(s) of other cell(s). After (e.g., in response to) receiving the SN Required message, the MN 104B transmits 605 an SN Request message (a first SN Request message) to the C-SN 106A to request preparation of the first cell as an LTM candidate cell for the UE 102. In some implementations, the MN 104B includes the one or more measurement results in the SN request message. In other implementations, the MN 104B transmits 605 the SN Request message based on the measurement report(s) that the MN 104B receives 604-2 from the UE 102. In some implementations, the MN 104B includes a CG-Confiiglnfo IE in the SN Request message and includes the one or more measurement results in the CG-Confiiglnfo IE. In some implementations, the CU 172 sends a request message (e.g., SN Modification Request message) to the S-SN 104A to request a SCG configuration for the UE 102. Inresponse, the S-SN 104A transmits a response message (e.g., SN Modification Request Acknowledge message) to the CU 172, including a SCG configuration for the UE 102. In some implementations, the CU 172 includes the SCG configuration in the SN Request message 605 or the CG-Configlnfo IE.

[0159] In response to the SN Request message 605, the C-SN 106A performs an LTM preparation procedure 690 to prepare the first cell as an LTM candidate cell for the UE 102, similar to the procedure 390, 490, or 590. In some implementations, if the one or more measurement results include measurement results of the first cell and other cell(s), the C-SN 106A determines to prepare the first cell for LTM. In the procedure 690, if the C-SN 106A consists of a CU and a DU, the CU of the C-SN 106A transmits a first CU-to-DU message, including the first cell ID, to the DU of the C-SN 106A to request preparation of the first cell, similar to the event 308. In some implementations, in response, the CU of the C-SN 106A receives a first DU-to-CU message, including an LTM DU configuration 1 from the DU of the C-SN 106A, similar to the event 310. The CU of the C-SN 106A generates a first SCG LTM candidate configuration (SCG LTM candidate configuration 1) including the LTM DU configuration 1. In response to the SN Request message, the (CU of the) C-SN 106A transmits 607 an SN Request Acknowledge message (e.g., a first SN Request Acknowledge message) including the first SCG LTM candidate configuration and the cell ID 1 to the MN 104B. In some implementations, the C-SN 106A includes an SCG LTM reference configuration in the SN Request Acknowledge message. In some implementations, the C-SN 106 A generates the SCG LTM reference configuration based on the SCG configuration received from the CU 172. In some implementations, the C-SN 106A so includes the SCG LTM reference configuration if the SN Request message includes a reference configuration request indicator. The reference configuration request indicator requests or indicates to the C-SN 106A to provide an SCG LTM reference configuration. If the C-SN 106A supports the reference configuration request indicator, the C-SN 106 A includes the SCG LTM reference configuration in the SN Request Acknowledge message. In such cases, the C-SN 106A generates the first SCG LTM candidate configuration augmenting the SCG LTM reference configuration. In some implementations, the C-SN 106 A includes a first indicator in the SN Request Acknowledge message, indicating that the first SCG LTM candidate configuration is a delta configuration. Alternatively, the C-SN 106A excludes the second indicator below in the SN Request Acknowledge message to indicate that the first SCG LTM candidateconfiguration is a delta configuration. Otherwise, if the C-SN 106 A does not support the reference configuration request indicator, the C-SN 106 A does not include the SCG LTM reference configuration in the SN Request Acknowledge message. In some such cases, the C-SN 106A generates the first SCG LTM candidate configuration as a complete configuration and includes a second indicator in the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is a complete configuration.Alternatively, the C-SN 106 A excludes the first indicator above in the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is a complete configuration. In some implementations, the MN 104B transmits 609 an SN Confirm message to the S-SN 104A in response to the SN Required message.

[0160] In some alternative implementations, the CU 172 includes an SCG LTM reference configuration in the first SN Request message instead of including the reference configuration request indicator. In some implementations, the CU 172 receives the SCG LTM reference configuration from the S-SN 104A. In other implementations, the CU 172 generates the SCG LTM reference configuration. In some implementations, the CU 172 generates the SCG LTM reference configuration based on the SCG configuration received from the S-SN 104A. If the C-SN 106A supports the SCG LTM reference configuration, the C-SN 106A generates the first SCG LTM candidate configuration augmenting the SCG LTM reference configuration. Otherwise, if the C-SN 106A does not support the SCG LTM reference configuration, the C-SN 106 A generates the first SCG LTM candidate configuration as a complete configuration. The C-SN 106A transmits the first SCG LTM candidate configuration to the CU 172 as described above.

[0161] In some implementations, the C-SN 106A includes one or more LTM CSI resource configuration(s) (the LTM CSI resource configuration 1) for the first cell in the SN Request Acknowledge message. In some implementations, the CU of the C-SN 106A is preconfigured with the LTM CSI resource configuration(s). In other implementations, the CU receives the LTM CSI resource configuration(s) from the DU of the C-SN 106A, where the DU operates the first cell. In yet other implementations, the CU receives the LTM CSI resource configuration(s) from an OAM node.

[0162] In some implementations, the SN Request message includes an SCG LTM reference configuration. If the C-SN 106A supports use of an SCG LTM reference configuration, the C-SN 106A generates the first SCG LTM candidate configurationaugmenting the SCG LTM reference configuration. In some implementations, the C-SN 106A includes a delta configuration indication in the SN Request Acknowledge message, indicating that the first SCG LTM candidate configuration is a delta configuration.Alternatively, the C-SN 106 A excludes a complete configuration indication in the SN Request Acknowledge message, indicating that the first SCG LTM candidate configuration is a delta configuration. In such cases, the C-SN 106A does not include an SCG LTM reference configuration in the SN Request Acknowledge message. Otherwise, if the C-SN 106A does not support to use an SCG LTM reference configuration, the C-SN 106A generates the first SCG LTM candidate configuration as a complete configuration. In some such cases, the C-SN 106A includes a complete configuration indication in the SN Request Acknowledge message, indicating that the first SCG LTM candidate configuration is a complete configuration.

[0163] In some implementation, the C-SN 106A includes the first SCG LTM candidate configuration, the cell ID 1, and / or the SCG LTM reference configuration in a CG-Config IE or a CG-Configlnfo IE and includes the CG-Config IE or CG-Confiiglnfo IE in the SN Request Acknowledge message. In some implementations, the CU 172 includes the cell ID 1 in the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is provided for or associated with the first cell (i.e., the cell ID 1).

[0164] In some implementations, after (e.g., in response to) receiving 607 the SN Request Acknowledge message, the CU 172 transmits 660, to the DU 174 of the MN 104B, a CU-to-DU message (e.g., a UE Context Modification Request message). In some implementations, the CU 172 includes an LTM indicator indicating ‘LTM-preparation’, the cell ID 1 indicating the prepared first PSCell, the CG-Config IE, the CG-Configlnfo IE, the first SCG LTM candidate configuration, and / or the SCG LTM reference configuration in the CU-to-DU message. In some implementations, the LTM indicator is an LTM Trigger lE / field. In some implementations, the LTM Trigger lE / filed is set to the value ‘LTM-preparation’. In further implementations, the CU 172 includes the LTM indicator in an Inter-SN LTM MCG Information IE or Inter-CU SCG LTM MCG Information IE included in the CU-to-DU message. In some implementations, based on the information provided in the CU-to-DU message, the DU 174 of the MN 104B generates an LTM MCG configuration for the UE 102 to perform an LTM cell switch to the first cell. In some implementations, the LTM MCG configuration concerns communication on the cell 124B (e.g., PCell). In furtherimplementations, the LTM MCG configuration includes configuration parameters for the cell 124B.

[0165] In response to the CU-to-DU message 660, the DU 174 then transmits 662 a DU-to-CU message (e.g., UE Context Modification Response message), including the LTM MCG configuration, to the CU 172. In some implementations, the DU 174 includes the cell ID 1 (e.g., in a Requested Target Cell ID field / IE) in the DU-to-CU message, indicating that the LTM MCG configuration is associated with the first cell. In some implementations, the DU 174 includes the LTM MCG configuration in an existing field / IE included in the DU-to-CU message, such as a CellGroupConfig IE or a DU to CU RRC Information IE (e.g., defined in 3GPP specification 38.473). In other implementations, the DU 174 includes the LTM MCG configuration in a specifically defined container field / IE. The DU 174 refrains from applying the LTM MCG configuration to communicate with the UE 102, until the DU 174 receives a further indication message (e.g., event 665 as described below) from the CU 172. The further indication message indicates to the DU 174 to apply the LTM MCG configuration. In some alternative implementations, the DU 174 determines not to generate an LTM MCG configuration based on the information included in the CU-to-DU message. In such cases, the DU 174 transmits 662 a DU-to-CU message excluding (i.e., not including) an LTM MCG configuration to the CU 172 in response to the CU-to-DU message.

[0166] In some implementations, the DU 174 of the MN 104B generates an MCG LTM reference configuration based on the information in the CU-to-DU message 660.Alternatively, the DU 174 generates an MCG LTM reference configuration based on the first serving MCG configuration. The DU 174 includes the MCG LTM reference configuration in the DU-to-CU message 662. In some implementations, the CU 172 includes a reference configuration request indicator in the CU-to-DU message 660 to request an MCG LTM reference configuration. If the DU 174 supports the reference configuration request indicator, the DU 174 includes the MCG LTM reference configuration in the DU-to-CU message 662. Otherwise, if the DU 174 does not support the reference configuration request indicator, the DU 174 refrains from including the MCG LTM reference configuration in the DU-to-CU message 662. In other implementations, the CU 172 includes an MCG LTM reference configuration in the CU-to-DU message 660.

[0167] In some implementations, when obtaining the MCG LTM reference configuration as described above, the DU 174 generates the LTM MCG configuration as a deltaconfiguration to augment the MCG LTM reference configuration. In some alternative implementations, the DU 174 does not obtain an MCG LTM reference configuration and generates the LTM MCG configuration as a complete configuration (i.e., no dependency to any configuration).

[0168] In some implementations, the UE 102 only applies the LTM MCG configuration and / or the MCG LTM reference configuration to communicate on the cell 124B (e.g., PCell) after (e.g., in response to) performing an LTM cell switch to the first cell as described for event 640. In some implementations, the DU 174 determines not to include a ReconfigurationWithSync configuration in the LTM MCG configuration and the MCG LTM reference configuration (if generated) to prevent the UE 102 from performing a random access procedure with the MN 104B upon performing the LTM cell switch to the first cell. As such, the system avoids interruption of communication between the UE 102 and the MN 104B while the UE 102 performs the LTM cell switch to the first cell as described below.

[0169] In some implementations, the MN 104B transmits 663 an SN Request message (e.g., SN Modification Request message) to the S-SN 104A, including (i) the LTM CSI resource configuration(s), (ii) the first SCG LTM candidate configuration, (iii) the SCG LTM reference configuration, (iv) a configuration ID (e.g., LTM ID 1), and / or (v) the cell ID 1. In response, the S-SN 104A transmits 664 an SN Request Acknowledge message (e.g., SN Modification Request Acknowledge message) to the MN 104B. In some implementations, the MN 104B assigns the configuration ID for the first cell (i.e., the configuration ID is associated with the cell ID 1). The MN 104B configures the configuration ID to identify the LTM candidate configuration as described for event 616. In other implementations, the S-SN 104A assigns the configuration ID for the first cell (i.e., the configuration ID is associated with the cell ID 1) and includes the configuration ID in the SN Required message. The S-SN 104A configures the configuration ID to identify the LTM candidate configuration as described for event 616. The MN 104B associates the configuration ID (received from the S-SN 104A) with the LTM candidate configuration. In some alternative implementations, the S-SN 104A is preconfigured with the LTM CSI resource configuration(s). In other alternative implementations, the S-SN 104A receives the LTM CSI resource configuration(s) from the OAM node.

[0170] In some implementations, the S-SN 104A (e.g., a DU of the S-SN 104A) generates a second SN configuration (e.g., a second SCG configuration or a second serving DUconfiguration) for the UE 102 based on the LTM CSI resource configuration(s) and includes the second SN configuration in the SN Request Acknowledge message 664. In some implementations, the S-SN 104A generates the second SN configuration as a delta configuration on top of the first SN configuration. In some implementations, the S-SN 104A generates one or more LTM CSI report configuration(s) for the UE 102 based on the LTM CSI resource configuration(s) and includes the LTM CSI report configuration(s) in the second SN configuration. In some implementations, the S-SN 104A (i) includes the configuration ID and the cell ID 1 and (ii) indicates the association of the configuration ID and the cell ID 1 in the SN Request Acknowledge message 664. In other implementations, the S-SN 104A transmits another SN message to the MN 104B, including the configuration ID and the cell ID 1 and indicating the association of the configuration ID and the cell ID 1. In some such cases, the S-SN 104A does or does not include the configuration ID and the cell ID 1 and indicate the association of the configuration ID and the cell ID 1 in the SN Required message.

[0171] In some implementations, the SN Request message 663 additionally includes (vi) an LTM SSB configuration (e.g., an SSB Positions in Burst IE) for the first cell. In some implementations, the MN 104B receives the LTM SSB configuration in the SN Request Acknowledge message 607 from the C-SN 106A. In some alternative implementations, the SN Request message 663 does not include an LTM SSB configuration for the first cell. In such cases, the S-SN 104A obtains an SSB configuration (similar to the LTM SSB configuration) for the first cell from the OAM node. In yet other implementations, the S-SN 104A obtains the SSB configuration from the C-SN 106 in an Xn Setup procedure (i.e., the Xn Setup Request message and Xn Setup Response message) with the C-SN 106A. In yet other implementations, the S-SN 104A obtains the SSB configuration from the C-SN 106 in an NG-RAN node Configuration Update procedure (i.e., the NG-RAN node Configuration Update message and the NG-RAN node Configuration Update Acknowledge message) with the C-SN 106A. In some implementations, the S-SN 104A uses LTM SSB configuration or the SSB configuration to determine a TA value received for the UE 102 in the early TA acquisition procedure 682. In some implementations, the S-SN 104A uses the LTM SSB configuration to generate the LTM CSI report configuration(s).

[0172] In some implementations, the SN Request message 663 and SN Request Acknowledge message 664 are an LTM Configuration Update message and an LTM Configuration Update Acknowledge message, respectively.

[0173] In some alternative implementations, the MN 104B includes some or all of the above configurations (i) - (vi) in the SN Confirm message instead of the SN Request message 663. In some implementations, if the MN 104B includes the LTM CSI resource configuration(s) in the SN Confirm message, the S-SN 104A transmits an SN message, including the second SN configuration, to the MN 104B. In some implementations, the SN message is an SN Modification Required message. In some implementations, in response to the SN Modification Required message, the MN 104B transmits an SN Modification Confirm message to the S-SN 104A. In other implementations, the SN message is an RRC Transfer message.

[0174] In some implementations, the CU 172 generates an LTM candidate configuration (i.e., LTM candidate configuration 1), including the first SCG LTM candidate configuration and / or the LTM MCG configuration (if received from the DU 174 of the MN 104B in event 662), to configure the first cell for LTM. In some implementations, the LTM candidate configuration is a message (e.g., an RRC reconfiguration message). If the CU 172 receives the SCG LTM reference configuration and / or the MCG LTM reference configuration as described above, the CU 172 generates an LTM reference configuration (i.e., a container) including the SCG LTM reference configuration and / or the MCG LTM reference configuration. In some implementations, the LTM reference configuration is a message (e.g., an RRC reconfiguration message). The CU 172 generates at least one RRC reconfiguration message(s) for the UE 102, including the second SN configuration, a tuple of the LTM candidate configuration and a configuration ID, and / or the LTM reference configuration. The CU 172 transmits 616 the RRC reconfiguration message(s) to the UE 102 via the DU 174, similar to events 316 and 318. In response to each of the RRC reconfiguration message(s), the UE 102 transmits 620 an RRC reconfiguration complete message to the CU 172 via the DU 174, similar to events 320 and 322. In some implementations, after receiving 620 the RRC reconfiguration complete message, the CU 172 transmits 621 an SN Complete message (e.g., SN Reconfiguration Complete message) to the S-SN 104A, indicating that the UE 102 receives the second SN configuration. In further implementations, the UE 102 includes an SN configuration complete indication in the RRC reconfiguration complete message 620, andthe MN 104B includes the SN configuration complete indication in the SN Complete message. In some implementations, the second SN configuration and the SN configuration complete indication are an RRC reconfiguration message and an RRC reconfiguration complete message, respectively. In some implementations, the SN Confirm message and the SN Complete message can be combined as a single SN message, such as an SN Confirm message or an SN Complete message, as described above.

[0175] In some implementations, the MN 104B assigns the configuration ID (e.g., LTM ID 1) for identifying the LTM candidate configuration including the first SCG LTM candidate configuration and / or the LTM MCG configuration. In other implementations, the MN 104B receives the configuration ID from the S-SN 104A as described above and associates the configuration ID with the LTM candidate configuration.

[0176] The events 603, 604-1, 604-2, 605, 690, 607, 660, 662, 609, 663, 664, 616, 620, and 621 are collectively referred to in Fig. 6 as an inter-SN LTM preparation procedure 681. In some implementations, the events 663 and 664 form an LTM CSI report configuration and / or LTM ID configuration procedure.

[0177] In some implementations, the SN Required message and the SN Confirm message are an SN Change Required message and an SN Change Confirm message, respectively. In other implementations, the SN Required message and the SN Confirm message are an SN Modification Required message and an SN Modification Confirm message, respectively. In some implementations, the SN Request message and the SN Request Acknowledge message are an SN Addition Request message and an SN Addition Request Acknowledge message, respectively. In other implementations, the SN Request message and the SN Request Acknowledge message are an SN Modification Request message and an SN Modification Request Acknowledge message, respectively.

[0178] In some implementations, if the C-SN 106 A is a distributed base station, the CU of the C-SN 106A requests an SCG LTM reference DU configuration from the DU of the C-SN 106A in the procedure 690, as described for Figs. 3, 4, and 5. For example, the CU includes a reference configuration request indicator in the first CU-to-DU message for this request. In some implementations, if the DU supports the request (e.g., the reference configuration request indicator), the DU transmits an SCG LTM reference DU configuration to the CU in the first DU-to-CU message of the procedure 690, as described for Figs. 3, 4, and 5. The CUthen generates the SCG LTM reference configuration including the SCG LTM reference DU configuration.

[0179] In some implementations, the S-SN 104A (e.g., the CU of the S-SN 104A) obtains an SCG LTM reference configuration, as described for Figs. 3 and 4. In other implementations, the S-SN 104A receives an SCG LTM reference configuration from the MN 106B (not shown in Fig. 6) in another inter-SN LTM preparation procedure as described above and below. In some implementations, if the S-SN 104A obtains an SCG LTM reference configuration, the S-SN 104A includes the SCG LTM reference configuration (e.g., S-SN generated LTM reference configuration) in the SN Required message. In turn, the MN 104B includes the SCG LTM reference configuration in the SN Request message.Alternatively, the S-SN 104A determines to request or cause the C-SN 106A to provide a complete SCG LTM candidate configuration so that the S-SN 104A does not transmit the SCG LTM reference configuration to the C-SN 106A. If the S-SN 104A does not obtain an SCG LTM reference configuration, the S-SN 104A does not include an SCG LTM reference configuration in the SN Required message. If the SN Required message includes an SCG LTM reference configuration, the MN 104B includes the SCG LTM reference configuration in the SN Request message. Otherwise, if the SN Required message does not include an SCG LTM reference configuration, the MN 104B may not include the SCG LTM reference configuration in the SN Request message.

[0180] If the SN Request message 605 includes an SCG LTM reference configuration as described above, the CU of the C-SN 106A may include the SCG LTM reference configuration in the first CU-to-DU message. Alternatively, the CU 172 retrieves an SCG LTM reference DU configuration from the SCG LTM reference configuration and includes the SCG LTM reference DU configuration in the first CU-to-DU message. Otherwise, in some implementations, if the SN Request message does not include an SCG LTM reference configuration, the CU of the C-SN 106A does or does not receive an SCG LTM reference DU configuration from the DU of the C-SN 106A as described for Fig. 3. If the CU receives an SCG LTM reference DU configuration (e.g., in the first DU-to-CU message), the CU generates an SCG LTM reference configuration (C-SN generated LTM reference configuration) including the SCG LTM reference DU configuration. In some implementations, the CU of the C-SN 106A includes an SCG LTM reference CU configuration (e.g., candidate CU (C-CU) generated LTM reference CU configuration).Otherwise, if the CU of the C-SN 106A does not receive an SCG LTM reference DU configuration from the DU of the C-SN 106A as described for Fig. 3, the CU does not generate an SCG LTM reference configuration. Alternatively, the CU generates an SCG LTM reference configuration (e.g., C-SN generated SCG LTM reference configuration) only including a C-CU generated SCG LTM reference CU configuration. In cases where the CU generates an LTM reference configuration (e.g., C-SN generated LTM reference configuration), the CU includes the C-SN generated LTM reference configuration in the SN Request Acknowledge message 607.

[0181] In some implementations, if the LTM DU configuration 1 is a complete configuration, the CU of the C-SN 106A generates the first SCG LTM candidate configuration as a complete configuration. In some implementations, the CU includes a complete configuration indication (e.g., a BS-to-BS interface protocol field / IE) in the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is a complete configuration. In some implementations, the BS-to-BS interface protocol is an Xn application protocol (e.g., as defined in 3GPP specification 38.423). In some implementations, the complete configuration indication is a specifically defined 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 (e.g., as defined in 3GPP specification 38.423). Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU generates the first SCG LTM candidate configuration as a delta configuration. In some implementations, the CU excludes the complete configuration indication from the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is a delta configuration. Alternatively, the CU includes a delta configuration indication (e.g., a BS-to-BS interface protocol field / IE) in the SN Request Acknowledge message to indicate that the first SCG LTM candidate configuration is a delta configuration. In some implementations, the BS-to-BS interface protocol is an Xn application protocol (e.g., as defined in 3GPP specification 38.423). In some implementations, the delta configuration indication is a specifically defined 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 (e.g., as defined in 3GPP specification 38.423). In some implementations, the BS-to-BS interface protocol field / IE includes 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 completeconfiguration indication and the BS-to-BS interface protocol field / IE set to the second value is the delta configuration indication.

[0182] To prepare the first cell as a candidate LTM cell for the UE 102, the CU of the S-SN 104A performs an LTM CSI report configuration and / or LTM ID configuration procedure (not shown in Fig. 6) with an S-DU of the S-SN 104A, similar to the procedure 392 or 492. In the LTM CSI report configuration and / or LTM ID configuration procedure, the CU of the S-SN 104A transmits the LTM CSI resource configuration(s) and / or the LTM SSB configuration to the S-DU of the S-SN 104A. In response, the CU of the S-SN 104A receives the LTM CSI report configuration(s) for the UE 102 from the S-DU of the S-SN 104A.

[0183] In some implementations, the CU of the C-SN 106A receives early synchronization information for the first cell and / or PDCCH order information from the DU of the C-SN 106A, as described for Fig. 5. In some implementations, the early synchronization information includes a RACH configuration (e.g., RACH configuration 1) and / or at least one TCI state configurations (e.g., TCI state configuration(s) 1). The CU of the C-SN 106A includes the early synchronization information and / or the PDCCH order information in the SN Request Acknowledge message. The MN 104B includes the early synchronization information and / or the PDCCH order information in the SN Confirm message or in the SN Request to S-SN 104A.

[0184] In some implementations, if the SN Request message or the SN Confirm message includes the PDCCH order information (PDCCH order information 1), the S-SN 104A performs an early TA acquisition procedure 682 with the UE 102, the MN 104B, and the C-SN 106A. In the procedure 682, the S-SN 104A transmits a PDCCH order to the UE 102, based on the PDCCH order information. If the S-SN 104A is a distributed base station, the CU of the S-SN 104A transmits the PDCCH order information to the S-DU of the S-SN 104A and the S-DU transmits the PDCCH order to the UE 102. In some implementations, the S-SN 104A or the S-DU determines to transmit the PDCCH order, based on (e.g., in response to) the measurement report(s). In some implementations, the S-SN 104A or the S-DU determines an SSB index included in the PDCCH order, based on LI measurement report(s) and / or the CSI resource configuration, the CSI report configuration and / or the LTM SSB configuration. In some implementations, the S-DU or the S-SN 104A includes the LTM ID 1 in the PDCCH order to indicate the first cell. The UE 102 transmits an RA preamble to the DU of the C-SN 106A on the first cell, using the RACH configuration and / or the PDCCHorder information. The S-DU or the S-SN 104A derives a TA value based on the RA preamble. The DU of the C-SN 106A transmit a DU-CU TA Information Transfer message including the TA value to the CU of the C-SN 106A. The CU of the C-SN 106A transmits a CU-CU TA Information Transfer message (e.g., TA Information Transfer) including the TA value, the first cell ID, and the associated TA information for the UE 102 to the MN 104B (e.g., the CU 172 of the MN 104B). The MN 104B transmits a CU-CU TA Information Transfer message including the TA value, the first cell ID, and the associated TA information for the UE 102 to the S-SN 104A. In some implementations, the DU of the C-SN 106A includes the cell ID 1, the RA preamble index, an RA-RNTI, and / or the DU ID of the S-DU of the S-SN 104A in the DU-CU TA Information Transfer message. In some implementations, the CU of the C-SN 106A includes the cell ID 1, the RA preamble index, the RA-RNTI, and / or the DU ID of the S-DU in the CU-CU TA Information Transfer message to the MN 104B. The MN 104B then includes the cell ID 1, the RA preamble index, the RA-RNTI, and / or the DU ID of the S-DU in the CU-CU TA Information Transfer message.

[0185] In response to determining to command the UE 102 to perform an LTM cell switch to the first cell (e.g., based on the LI or L3 measurement report(s) 654 or other LI or L3 measurement report(s) received before the event 654), the S-DU or the S-SN 104A transmits 626 an LTM Cell Switch Command, including the configuration ID, to the UE 102. In some implementations, in response to the LTM Cell Switch Command, the UE 102 stops communication on the serving cell(s). The S-SN 104A also transmits 627, to the MN 104B, a CU-to-CU Cell Switch Notification message (e.g., Cell Switch Notification) including the first cell ID and / or the first TCI State ID. The MN 104B then transmits 628, to the C-SN 106A, a CU-to-CU Cell Switch Notification message including the first cell ID and / or the first TCI State ID. In some implementations, in response to receiving 627 the CU-to-CU Cell Switch Notification message, the CU 172 transmits a CU-DU Cell Switch Notification message to the DU 174, indicating that the LTM cell switch to the first cell is or is being initiated for the UE 102. The UE 102 and the DU of the C-SN 106A identify the first one of the TC state configuration(s) based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in events 632, 636, and / or 640.

[0186] In response to the LTM Cell Switch Command, the UE 102 accesses 632 the first cell and transmits 636 the RRC reconfiguration complete message to the CU 172 via the DU 174. In some implementations, the RRC reconfiguration complete message includes the configuration ID and / or an SN configuration complete indication. For example, the SN configuration indication is an RRCReconfiigurationComplete message. After receiving 636 the RRC reconfiguration complete message, the CU 172 transmits 638 an SN Complete message (e.g., SN Reconfiguration Complete message). In some implementations, the CU 172 includes the SN configuration complete message in the SN Complete message. In some implementations, the C-SN 106A transmits 639 an LTM Success message including the first cell ID or the configuration ID to the CU 172.

[0187] In some implementations, after (e.g., in response to) the event 627, 637, or 639, the CU 172 transmits 665 a CU-to-DU message (e.g., UE Context Modification Request message), including the cell ID 1 and / or the configuration ID, to the DU 174. In some implementations, the CU-to-DU message includes an LTM-executed indicator. The LTM-executed indicator, the cell ID 1, and / or the configuration ID indicate that an LTM cell switch to the first cell has been executed. In some implementations, the LTM-executed indicator is an LTM Trigger lE / field (e.g., under an Inter-SN LTM MCG Information IE or Inter-CU SCG LTM MCG Information IE) and the LTM Trigger lE / field is set to ‘LTM-executed’. In response to or based on the LTM-executed indicator, the cell ID 1, and / or the configuration ID, the DU 174 identifies the LTM MCG configuration and applies 656 the LTM MCG configuration to communicate with the UE 102 in event 640. In other implementations, instead of including the LTM executed indicator, the CU 172 includes, in the CU-to-DU message, a specifically defined container (e.g., F1AP IE, Inter-SN LTM MCG Information IE or Inter-CU SCG LTM MCG Information IE) to indicate that the LTM cell switch to the first cell has been executed. In some implementations, the specifically defined container includes the cell ID 1 and / or the configuration ID. Based on the specifically defined container, the cell ID 1 and / or the configuration ID, the DU 174 identifies the LTM MCG configuration and applies 656 the LTM MCG configuration in communication with the UE 102 in event 640. If the DU 174 transmits the MCG LTM reference configuration to the UE 102 as described above, the DU 174 applies the MCG LTM reference configuration at event 656. In some implementations, the DU 174, in response to the CU-to-DU message 665, transmits 666 a DU-to-CU message (e.g., UE Context Modification Response message) to the CU 172 of theMN 104B. In further implementations, after (e.g., in response to) the event 637, 639, or 665, the CU 172 transmits 644, to the S-SN 104A, an SN Request message (e.g., SN Modification Request message or an SN Release Request message) to inform the S-SN 104A to stop transmitting to the UE 102.

[0188] In some implementations, the DU 174 releases the first serving MCG configuration at event 656 (e.g., in response to receiving 665 the CU-to-DU message or the LTM-executed indication). In some such cases, the DU 174 replaces the first serving MCG configuration with the LTM MCG configuration and / or the MCG LTM reference configuration. Likewise, the UE 102 releases the first serving MCG configuration and applies the LTM MCG configuration and / or the MCG LTM reference configuration in response to performing the LTM cell switch to the first cell (e.g., in response to receiving 626 the LTM Cell Switch Command or accessing 632 the first cell).

[0189] In other implementations, the DU 174 releases a portion of the first serving MCG configuration and retains the remaining portion of the first serving MCG configuration at event 656 (e.g., in response to receiving 665 the CU-to-DU message or the LTM-executed indication). In some implementations, the remaining portion includes a C-RNTI and one or more logical channel identities. The UE 102 and DU 174 use the C-RNTI to communicate with each other before the LTM cell switch to the first cell. The one or more logical channel identities are associated with one or more RLC bearers associated with one or more RLC entities that the DU 174 uses to communicate with the UE 102 before the LTM cell switch to the first cell (e.g., event 656). In some implementations, the DU 174 retains (e.g., keeps or maintains) state variables, buffers, and / or timers for the one or more RLC entities. Likewise, the UE 102 releases a portion of the first serving MCG configuration and retains the remaining portion of the first serving MCG configuration in response to performing the LTM cell switch to the first cell (e.g., in response to receiving 626 the LTM Cell Switch Command or accessing 632 the first cell). In some implementations, the remaining portion includes the C-RNTI and the one or more logical channel identities. The one or more logical channel identities are associated with one or more RLC bearers associated with one or more RLC entities that the UE 102 uses to communicate with the DU 174 before the LTM cell switch to the first cell (e.g., event 632). In some implementations, the UE 102 retains (e.g., keeps or maintains) state variables, buffers, and / or timers for the one or more RLC entities.

[0190] In some implementations, the UE 102 and the CU 172 communicate with each other using a security configuration and a security key (e.g., a master key) before the LTM cell switch (e.g., event 627, 628, 632, 636, 638, or 639). In further implementations, the security key is associated with the security configuration. For example, the UE 102 and the CU 172 apply the security configuration and the security key to communication in events 602, 604-1, 616, and / or 620. In some implementations, the CU 172 retains (e.g., keeps or maintains) the security configuration and / or the security key in response to the LTM cell switch (e.g., event 627, 628, 636, 638, or 639). Likewise, the UE 102 retains (e.g., keeps or maintains) the security configurations and / or the security key in response to performing the LTM cell switch (e.g., event 626 or 632). Thus, the UE 102 and the CU 172 communicate the RRC reconfiguration complete message and perform communication in events 636 and 640 respectively, using the security configuration and security key.

[0191] After event 632 or 638, the C-SN 106A communicates 640 with the UE 102 operating in DC with the MN 104B and the C-SN 106 A. If the MN 104B transmits the LTM MCG configuration and / or the MCG LTM reference configuration to the UE 102, the MN 104B communicates 640 with the UE 102 on the cell 124B in accordance with the LTM MCG configuration and / or the MCG LTM reference configuration. The C-SN 106A communicates with the UE 102 on the first cell in accordance with the first SCG LTM candidate configuration and / or the SCG LTM reference configuration. After (e.g., in response to) event 632 or 638, the UE 102 and / or C-SN 106A determine the serving PSCell changes from the cell 124A to the cell 126A, and the C-SN 106A becomes an S-SN for the UE 102.

[0192] In some implementations, after (e.g., in response to) event 632, event 638, or receiving the SN Status Transfer message as described below or an Access Success message indicating the UE 102 successfully accesses the first cell, the (CU of the) C-SN 106A performs a PDU Session path update procedure with the CN 110 (not shown in Fig. 6). The CU receives the Access Success message from the DU of the C-SN 106A, similar to event 334 or 434. In the PDU Session path update procedure, the (CU of the) C-SN 106A sends a PDU Session Resource Modify Indication message to the CN 110 (e.g., AMF). The PDU Session Resource Modify Indication message is to request a switch of a downlink termination point of a UP transport bearer (e.g., NG-U transport bearer) from an old termination point (e.g., the S-SN 104A or the S-CU of the S-SN 104A) toward a new termination point (e.g.,the C-SN 106A or the CU of the C-SN 106A). In response to the PDU Session Resource Modify Indication message, the CN 110 (e.g., AMF) switches the downlink termination point of the UP transport bearer from the old termination point toward the new termination point. In response to the PDU Session Resource Modify Indication message, the CN 110 (e.g., AMF) transmits a PDU Session Resource Modify Confirm message to the CU 172. After the PDU Session path update procedure, the CN 110 (e.g., UPF) communicates UP data with the UE 102 via the S-BS 106A and the UP transport bearer.

[0193] In some implementations, if the S-DU or the S-SN 104A receives a TA value as described above, the S-DU or the S-SN 104A includes the TA value in the LTM Cell Switch Command. In some implementations, the S-DU or the S-SN 104A includes a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID indicates a first one of the TCI state configuration(s).

[0194] In some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch or transmitting 626 the LTM Cell Switch Command, the S-SN 104A transmits one or more Early Status Transfer messages to the MN 104B, each including a DL COUNT value or a DISCARD DL COUNT value for a DRB over which the UE 102 and the S-SN 104A communicate 602 data with each other. The MN 104B transmits one or more Early Status Transfer messages to C-SN 106A, each including the DL COUNT value or the DISCARD DL COUNT value for the DRB over which the UE 102 and the S-SN 104A communicate 602 data with each other.

[0195] In some implementations, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting 626 the LTM Cell Switch Command, receiving the DU-CU Cell Switch Notification message from the S-DU, or receiving 644 the SN Request message, the S-SN 104A (e.g., the CU of the S-SN 104A) transmits an SN Status Transfer message to the MN 104B, including a DL COUNT value and / or a UL COUNT value for the DRB over which the UE 102 and the S-SN 104A communicate 602 data with each other. After (e.g., in response to) receiving the SN Status Transfer message from the S-SN 104A, the MN 104B transmits an SN Status Transfer message to the CU 172, including the DL COUNT value and / or the UL COUNT value.

[0196] In some implementations, before or after transmitting the LTM Cell Switch Command as described above, the S-SN 104A, the MN 104B, and / or one or more C-SNs(including the C-SN 106A) perform additional inter-SN LTM preparation procedure(s) 2, N to prepare cell(s) 2, .. N for LTM, respectively. The cell(s) 2, .. N are identified by cell ID(s) 2, .. N respectively. N is an integer larger than 1. Each of the inter-SN LTM preparation procedure(s) 2, ..., N is similar to the procedure 681. In some implementations, the procedure(s) 2, ..., N, the MN 104B obtains tuple(s) {LTM ID 2, the LTM candidate configuration 2, the LTM CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained)}, ..., {the LTM ID N, the LTM candidate configuration N, the LTM CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained)} for the cell(s) 2, .. ., N respectively. In some implementations, the MN 104B transmits the tuple(s) to the UE 102 in LTM configuration delivery procedure(s) 2, ..., N, similarly to events 616 and 620. In other implementations, the MN 104B includes the tuple(s) in the RRC reconfiguration message(s) 616.

[0197] In some implementations, the S-SN 104A includes the cell ID(s) 2, ..., N in the SN Required message 603. In some implementations, the MN 104B includes the cell ID(s) 2, ..., N in the SN Request message 605. In some implementations, the S-SN 104A includes one or more measurement results of the cell(s) 2, ..., N in the SN Required message as described for the first cell. In some implementations, the MN 104B includes the one or more measurement results of the cell(s) 2, ..., N in the SN Request message as described for the first cell. In some implementations, the C-SN 106A determines to prepare the first cell for LTM and not to prepare the cell(s) 2, ..., N for LTM. In some implementations, the C-SN 106A makes the determination based on capacity of the C-SN 106A and / or the measurement results of the first cell and the cell(s) 2, ..., N.

[0198] In some implementations, the CU 172 and the CU of the SN 104A are the same CU (i.e., the CU 172). In some such implementations, events 603, 609, 621, 627, and / or 644 can be omitted. In some such cases, the SN Request message 663 and the SN Request Acknowledge message 664 can be replaced by a CU-to-DU message (e.g., a UE Context Modification Request message) and a DU-to-CU message (e.g., a UE Context Modification Response message), respectively. Examples and implementations described for the message 663 and the message 664 can apply to the CU-to-DU message and the DU-to-CU message, respectively. Examples and implementations described for the procedures 392 and / or 492can apply to the CU-to-DU message and the DU-to-CU message. In other implementations, the CU 172 and the CU of the SN 104A are different CUs.

[0199] In some implementations, the CU 172 and the CU of the C-SN 106 A are the same CU (i.e., the CU 172). In some such implementations, events 605 and 607 can be replaced by a CU-to-DU message (e.g., a UE Context Modification Request message) and a DU-to-CU message (e.g., a UE Context Modification Response message), respectively. Examples and implementations described for the procedures 390 and / or 490 can apply to the CU-to-DU message and the DU-to-CU message. In other implementations, the CU 172 and the CU of the C-SN 106A are different CUs.

[0200] Fig. 7 depicts a scenario 700 for an intra-CU / MN MCG LTM with SCG configuration, similar to the scenario 600. The differences between the scenarios 600 and 700 are described below. In the following description, a base station (i.e., the MN 104B, the C-SN 106A, or the S-SN 104A) can be replaced by a CU and a DU of the base station, the DU of the base station, or the CU of the base station. Initially, the UE 102 communicates 702 with the MN 104B or communicates 702 with the MN 104B and the S-SN 104A. Event 702 is similar to event 602, except that, in some implementations, the UE 102 communicates with the MN 104B in single connectivity. In some implementations, the MN 104B and the UE 102 perform 796 at least one intra-CU MCG LTM configuration procedure similar to the procedure(s) 396 and / or 496. In some implementations, the MN 104B and the UE 102 perform 780 at least one intra-CU MCG LTM procedure similar to the procedure(s) 396, 380, 496, or 480.

[0201] While communicating with the MN 104B, the UE 102 transmits 704 at least one measurement report to the MN 104B, similar to events 304, 404, and / or 604-2. The at least one measurement report includes at least one first measurement result for a first cell of the MN 104B. Based on the at least one first measurement result, the MN 104B determines to configure the first cell of the MN 104B as an LTM candidate PCell for the UE 102. In response to the determination, the MN 104B performs 790 A an LTM preparation procedure to prepare the first cell of the MN 104B as an LTM candidate PCell for the UE 102, similar to the procedure 390 or 490. In the procedure 790A, the MN 104B obtains an LTM DU configuration (i.e., an MCG LTM DU configuration) for the UE 102. The LTM DU configuration configures the LTM candidate PCell and includes configuration parameters for communication on the LTM candidate PCell. The MN 104B performs 792 an LTM CSIreport configuration and / or LTM ID configuration procedure for the UE 102 and the LTM candidate PCell, similar to the procedure 392 or 492.

[0202] When (i) determining to configure or (ii) configuring the LTM candidate PCell for the UE 102, the MN 104B determines to configure a first cell of the C-SN 106A as a PSCell associated with the LTM candidate PCell. That is, the MN 104B determines to configure MCG LTM with SCG configuration for the UE 102. To simplify the following description, the first cell of the C-SN 106A is referred to as an LTM candidate PSCell. The “LTM candidate PSCell” can be replaced with the “PSCell associated with the LTM candidate PCell”. In some implementations, the at least one measurement report includes at least one second measurement result for the first cell of the C-SN 106A. The MN 104 determines to configure the first cell of the C-SN 106 A as an LTM candidate PSCell for the UE 102 based on the at least one second measurement result. In some implementations, the at least one measurement report includes measurement result(s) for other cell(s) of the C-SN 106A (e.g., other LTM candidate PSCell(s)). In other implementations, the at least one measurement report does not include a measurement result for any other LTM candidate PSCell(s).

[0203] In response to determining to configure the LTM candidate PSCell for the UE 102, the MN 104B transmits 705 an SN Request message to the C-SN 106 A to request or indicate preparation of the LTM candidate PSCell for the UE 102, similar to event 605. The MN 104B includes, in the SN Request message, a cell ID (i.e., PSCell ID 1) indicating the LTM candidate PSCell (i.e.., LTM candidate PSCell 1). In some implementations, the MN 104B includes an LTM indicator in the SN Request message so that the C-SN 106A determines that the SN Request message is for LTM based on the LTM indicator, as described above. In some implementations, the MN 104B includes, in the SN Request message, a cell ID (i.e., a PCell ID 1) indicating the LTM candidate PCell. In response to the SN Request message 705, the C-SN 106A performs an LTM preparation procedure 790B to prepare the LTM candidate PSCell for the UE 102, similar to the procedure 390, 490, or 690. In the procedure 790B, the C-SN 106A obtains an LTM DU configuration (i.e., an SCG LTM DU configuration) for the UE 102. The SCG LTM DU configuration configures the LTM candidate PSCell and includes configuration parameters for communication on the LTM candidate PSCell (LTM candidate PSCell 1). In some implementations, the CU of the C-SN 106A transmits a CU-to-DU message to the DU of the C-SN 106A and receives a DU-to-CU message, including SCG LTM DU configuration, from the DU, similar to event 308 andevent 310 respectively. In some implementations, the CU includes an LTM indicator in the CU-to-DU message as described for event 308. In some implementations, the CU includes LTM information (e.g., MCG LTM information) in the CU-to-DU message, indicating that the CU-to-DU message is sent for an MCG LTM with SCG configuration. Thus, the DU considers that LTM preparation procedure has been initiated or triggered as part of an MCG LTM preparation procedure. In some such cases, the CU does or does not include the LTM indicator in the CU-to-DU message. In some implementations, the LTM information (e.g., MCG LTM information) is an LTM information SN Addition IE (e.g., an MCG LTM information SN Addition IE) or an LTM information SN Modification IE (e.g., an MCG LTM information SN Modification IE). In other implementations, the LTM information is an IE of SCG configuration for MCG LTM.

[0204] In some implementations, the SN Request includes other cell ID(s) indicating the other LTM candidate PSCell(s). In some such cases, the MN 104B indicates, to the C-SN 106A, that the first cell and other cell(s) of the C-SN 106A are considered as LTM candidate PSCells. In some implementations, the C-SN 106A determines to configure the LTM candidate PSCell 1 for the UE 102 based on the at least one second measurement result. In some implementations, the C-SN 106A determines not to configure the other cell(s) as LTM candidate PSCell(s) for the UE 102, based on the at least second measurement result for the first cell and the measurement result(s) for the other cell(s). In other implementations, the C-SN 106 A determines to configure at least one of the other cell(s) as at least one LTM candidate PSCell for the UE 102 as described below for the LTM candidate PSCell 1.

[0205] In some implementations, the MN 104B refrains from performing, with the S-SN 104A, an LTM CSI report configuration and / or LTM ID configuration procedure (e.g., similar to events 663 and 664) for preparing the LTM candidate PSCell 1. The MN 104B (e.g., the CU or an S-DU) determines whether to trigger an LTM cell switch to the LTM candidate PCell (and the LTM candidate PSCell 1) for the UE 102 based on one or more LI or L3 measurement reports that the MN 104 received from the UE 102 similar to event 524 or 554. Thus, the MN 104B does not perform such a procedure to obtain an LTM CSI report configuration for the UE 102 from the S-SN 104A.

[0206] In some implementations, the CU of the C-SN 106A generates an LTM SCG configuration (e.g., an RRC reconfiguration message) including the SCG LTM DU configuration. In some implementations, the C-SN 106 A does or does not include a radiobearer configuration and / or a measurement configuration in the LTM SCG configuration. In some implementations, the radio bearer configuration configures SRB(s) and / or DRB(s). Alternatively, in further implementations, the radio bearer configuration does not configure DRB(s). In other implementations, the CU uses the SCG LTM DU configuration as an LTM SCG configuration. The C-SN 106 A transmits 707 an SN Request Acknowledge message, including the LTM SCG configuration, to the MN 104B. In some implementations, the C-SN 106A includes the PCell ID 1 in the SN Request Acknowledge message, indicating that the LTM SCG configuration is associated with the LTM candidate PCell. In some implementations, the C-SN 106A includes the PSCell ID 1 in the SN Request Acknowledge message, indicating that the LTM SCG configuration is provided for the LTM candidate PSCell 1.

[0207] The MN 104B then generates a first LTM candidate configuration (e.g., LTM candidate configuration 1) including the MCG LTM DU configuration and the LTM SCG configuration. In some implementations, the MN 104B includes an LTM CU configuration in the first LTM candidate configuration. In some implementations, the MN 104B assigns an LTM ID 1 (i.e., a configuration ID) to identify the first LTM candidate configuration (i.e., the MCG LTM DU configuration and the LTM SCG configuration), as described for Fig. 3 and Fig. 4. In some implementations, the MN 104B associates the configuration ID with the LTM candidate PCell. In the procedure 790A or 792, the CU of the MN 104B transmits the configuration ID, the PCell ID 1, and the association to the S-DU of the MN 104B. The MN 104B then transmits 716 an RRC reconfiguration message, including the configuration ID and the first LTM candidate configuration, to the UE 102. In some implementations, the MN 104B includes the LTM ID 1, the LTM candidate configuration 1, a first RACH configuration, first TCI state configuration(s), a first LTM SSB configuration, and / or a PCI of the LTM candidate PCell in the RRC reconfiguration message and / or other RRC reconfiguration message(s), as described above. The MN 104B configures the first RACH configuration, the first TCI state configuration(s) and / or the first LTM SSB configuration for the LTM candidate PCell. In some implementations, the MN 104B includes an LTM candidate PCell TA ID for the LTM candidate PCell in the RRC reconfiguration message or the other RRC reconfiguration message. In some implementations, the MN 104B includes a first CSI resource configuration (e.g., a first LTM CSI resource configuration) in the RRC reconfiguration message. In some implementations, the MN 104B includes a serving PCellTA ID for the serving PCell in the RRC reconfiguration message. In some implementations, in the procedure 792, the MN 104B generates a first (LTM) CSI report configuration based on the first CSI resource configuration and / or the first LTM SSB configuration. In such cases, the MN 104B includes the first CSI report configuration in a serving DU configuration and includes the serving DU configuration in the RRC reconfiguration message 716, similar to events 316 and / or 494.

[0208] In some implementations, the MN 104B includes a second RACH configuration, second TCI state configuration(s), a second LTM SSB configuration, and / or a PCI of the LTM candidate PSCell in the RRC reconfiguration message and / or other RRC reconfiguration message(s), as described above. In some implementations, the MN 104B receives the second RACH configuration, the second TCI state configuration(s) and / or the second LTM SSB configuration for the LTM candidate PSCell from the C-SN 106A (e.g., in the SN Request Acknowledge message 707 or another SN message). In some implementations, the MN 104B includes an LTM candidate PSCell TA ID for the LTM candidate PSCell in the RRC reconfiguration message or the other RRRC reconfiguration message. In some implementations, the MN 104B includes a second CSI resource configuration (e.g., a second LTM CSI resource configuration) in the RRC reconfiguration message. In some implementations, the MN 104B includes a serving PSCell TA ID for the serving PSCell in the RRC reconfiguration message. In some implementations, in the procedure 792, the MN 104B generates a second (LTM) CSI report configuration based on the second CSI resource configuration and / or the second LTM SSB configuration. In such cases, the MN 104B includes the second CSI report configuration in the serving DU configuration, similar to events 316 and / or 494. In other implementations, the MN 104B does transmit, to the UE 102, LTM-related configurations (i.e., the second RACH configuration, the second TCI state configuration(s), the second LTM SSB configuration, the PCI of the LTM candidate PSCell, the second LTM CSI resource configuration, second LTM CSI report configuration, and / or the second LTM CSI resource configuration) for the LTM candidate PSCell.

[0209] In response to the RRC reconfiguration message, the UE 102 transmits 720 an RRC reconfiguration complete message to the MN 104B, similar to event 620. In some implementations, after receiving the RRC reconfiguration complete message, the MN 104Btransmits 721 an SN Complete message to the C-SN 106A, similar to event 621. Alternatively, the MN 104B does not transmit the SN Complete message to the C-SN 106A.

[0210] In some implementations, the serving DU configuration includes a first LTM CSI report configuration. In the procedure 792, the MN 104B generates the first LTM CSI report configuration based on a first LTM CSI resource configuration for the LTM candidate PCell. In some implementations, the MN 104B obtains the first LTM CSI resource configuration as described above. The UE 102 transmits one or more first LI measurement reports (e.g., LTM CSI reports) to (the DU of) the MN 104B in accordance with the first LTM CSI report configuration, similar to events 324, 354, 382, 397, 424, 454, 482, and / or 497. The one or more first LI measurement reports include first LI measurement result(s) for the LTM candidate PCell. The MN 104B (e.g., an S-DU of the MN 104B) receives the one or more first LI measurement reports from the UE 102 in accordance with the first LTM CSI report configuration. In some implementations, the (S-DU of the) MN 104B determines to trigger the procedure 782A and / or the procedure 797 based on the first LI measurement result(s).

[0211] In some implementations, the serving DU configuration includes a second LTM CSI report configuration. In the procedure 792, the MN 104B generates the second LTM CSI report configuration based on a second LTM CSI resource configuration for the LTM candidate PSCell 1. The UE 102 transmits one or more second LI measurement reports (e.g., LTM CSI reports) to the MN 104B (e.g., an S-DU of the MN 104B) in accordance with the second LTM CSI report configuration, similar to events 324, 354, 382, 397, 424, 454, 482, and / or 497. The one or more second LI measurement reports include second LI measurement result(s) for the LTM candidate PSCell 1. The (S-DU of the) MN 104B receives the one or more second LI measurement reports from the UE 102 in accordance with the second LTM CSI report configuration. In some implementations, the S-MN 104B obtains the second LTM CSI resource configuration as described above. In further implementations, the MN 104B receives the second LTM CSI resource configuration from the C-SN 106A in an interface message. In some implementations, the interface message is the SN Request Acknowledge message, an XnAP message, or a 6G interface message. In some implementations, the (S-DU of the) MN 104B determines to trigger the procedure 782A and / or the procedure 797, based on the first LI measurement result(s) and the second LI measurement result(s). In other implementations, the MN 104B performs another LTM CSI report configuration procedure for the UE 102 and the LTM candidate PSCell 1 to obtain thesecond CSI report configuration and / or an additional serving DU configuration for the UE 102, similar to the procedure 792 and as described above. In some such cases, the MN 104B transmits an additional RRC reconfiguration message to the UE 102, including additional serving DU configuration or the second CSI report configuration, similar to the message 716.

[0212] In some other implementations, the UE 102 transmits one or more first L3 measurement reports (e.g., RRC measurement reports) to the MN 104B (e.g., the CU of the MN 104B via the S-DU), similar to events 304 and / or 404. The one or more first L3 measurement reports include first L3 measurement result(s) for the LTM candidate PCell. In some implementations, the (CU of the) MN 104B determines to trigger the procedure 782A and / or the procedure 797 based on the first L3 measurement result(s). In some implementations, the UE 102 transmits one or more second L3 measurement reports (e.g., RRC measurement reports) to the MN 104B (e.g., the CU of the MN 104B via the S-DU), similar to events 304 and / or 404. The one or more second L3 measurement reports include second L3 measurement result(s) for the LTM candidate PSCell 1. In some implementations, the (CU of the) MN 104B determines to trigger the procedure 782A and / or the procedure 797, based on the first L3 measurement result(s) and the second L3 measurement result(s). In response to determining to trigger the procedure 782A and / or the procedure 797, the CU transmits a CU-to-DU message to the S-DU to cause the S-DU to trigger the procedure 782A and / or the procedure 797. In some implementations, the CU-to-DU message is a UE Context Modification Request message. In further implementations, the CU-to-DU message is an F1AP message or a 6G interface message.

[0213] The events 704, 790A, 792, 705, 790B, 707, 716, 720, and 721 are collectively referred to in Fig. 7 as an MCG LTM with SCG configuration preparation procedure 781.

[0214] In some implementations, the MN 104B includes a RACH configuration for early UL synchronization on the LTM candidate PCell in the RRC reconfiguration message. In some implementations, the MN 104B receives a RACH configuration for early UL synchronization on the LTM candidate PSCell 1 from the C-SN 106A (e.g., in the SN Request Acknowledge message 607 or 664) and includes the RACH configuration in the RRC reconfiguration message or the first LTM candidate configuration.

[0215] In some implementations, the MN 104B later performs 782A an early TA acquisition procedure with the UE 102, similar to the procedure 382 or 482. In someimplementations, the MN 104B, the C-SN 106A, and the UE 102 perform 782B an early TA acquisition procedure, similar to the procedure 682. In the procedure 782 A, the MN 104B obtains a first TA value for early UL synchronization on the LTM candidate PCell for the UE 102. In the procedure 782B, the MN 104B obtains a second TA value for early UL synchronization on the LTM candidate PSCell 1 for the UE 102. Alternatively, the procedure 782B is skipped and the MN 104B does not obtain a TA value for early UL synchronization on the LTM candidate PSCell for the UE 102.

[0216] In some implementations, the MN 104B includes LTM information (e.g., MCG LTM information) in the SN Request message 705, indicating that the SN Request message is sent for an MCG LTM with SCG configuration. Thus, the C-SN 106A considers that the SN Addition Preparation procedure (i.e., events 705 and 707) has been triggered as part of an LTM preparation procedure (e.g., an MCG LTM preparation procedure) (e.g., event 790). In some implementations, the (MCG) LTM information is an LTM information SN Addition IE (e.g., an MCG LTM information SN Addition IE) or an LTM information SN Modification IE (e.g., an MCG LTM information SN Modification IE). In some such cases, the MN 104B does or does not include the LTM indicator in the SN Request message. Based on the (MCG) LTM information, the C-SN 106A determines not to send the RACH configuration for early UL synchronization on the LTM candidate PSCell 1 to the MN 104B. In other implementations, the LTM indicator is defined specifically for an MCG LTM with SCG configuration. Based on the LTM indicator, the C-SN 106A determines not to send the RACH configuration for early UL synchronization on the LTM candidate PSCell 1 to the MN 104B. Thus, the MN 104B does not transmit a RACH configuration for early UL synchronization on the LTM candidate PSCell 1 in the RRC reconfiguration. In some implementations, the MN 104B includes a source node ID (e.g., a Source M-NG-RAN node ID IE) and a source node UE interface ID (e.g., a Source M-NG-RAN node UE XnAP ID IE) in the SN Request message in the LTM information. In some implementations, the C-SN 106 A uses the source node ID and the source node UE interface ID to identity other active SN preparation procedure(s) for MCG LTM with SCG configuration and related to this UE. In some implementations, the other active SN preparation procedure(s) are SN Addition Preparation procedure(s) or SN Modification Preparation procedure(s) to prepare LTM candidate PSCell(s) for MCG LTM with SCG configuration. Each of the SN preparation procedure(s) is similar to events 705, 790B, and / or 707.

[0217] In some implementations, the MN 104B then determines to command the UE 102 to perform an LTM cell switch in accordance with the first LTM candidate configuration. In response to the determination, the MN 104B initiates an LTM cell switch execution procedure 797 with the UE 102 by transmitting an LTM Cell Switch Command to the UE 102 via a serving cell. The LTM Cell Switch Command indicates the configuration ID. If the MN 104B obtains the first TA value, the MN 104B includes the first TA value in the LTM Cell Switch Command. In some implementations, the MN 104B includes the second TA value in the LTM Cell Switch Command. Alternatively, the MN 104B does not include a TA value for the LTM candidate PSCell 1 in the LTM Cell Switch Command. In response to the LTM Cell Switch Command, the UE 102 performs an LTM cell switch to the LTM candidate PCell with SCG configuration. The UE 102 identifies the first LTM candidate configuration with the configuration ID. In some implementations, the UE 102 initiates an LTM cell switch to the LTM candidate PCell in response to the LTM Cell Switch Command and in accordance with the MCG LTM DU configuration. In some implementations, after performing or completing the LTM cell switch to the LTM candidate PCell, the UE 102 accesses 732 the LTM candidate PSCell 1 in accordance with the LTM SCG configuration. In further implementations, while performing the LTM cell switch to the LTM candidate PCell, the UE 102 accesses 732 the LTM candidate PSCell 1 in accordance with the LTM SCG configuration. If the LTM Cell Switch Command includes the first TA value, the UE 102 in the procedure 797 applies the first TA value to access the LTM candidate PCell 1 without performing a random access procedure. Otherwise, if the LTM Cell Switch Command does not include a TA value for the LTM candidate PCell, the UE 102 in the procedure 797 performs a random access procedure on the LTM candidate PCell with the MN 104B. In some implementations, the UE 102 performs a UE-based TA measurement to obtain a TA for the LTM candidate PCell and applies the obtained TA to access the LTM candidate PCell without performing a random access procedure in the procedure 797, as described above.

[0218] In some implementations, the LTM Cell Switch Command includes the second TA value for the LTM candidate PSCell. If the LTM Cell Switch Command includes the second TA value, the UE 102 applies the second TA value to access 732 the LTM candidate PSCell 1 without performing a random access procedure. Otherwise, if the LTM Cell Switch Command does not include a TA value for the LTM candidate PSCell 1, the UE 102performs 732 a random access procedure on the LTM candidate PSCell 1 with the C-SN 106A. In some implementations, the UE 102 performs a UE-based TA measurement to obtain a TA for the LTM candidate PSCell and applies the obtained TA to access 732 the LTM candidate PSCell without performing a random access procedure, as described above. In other implementations, the UE 102 does not perform a UE-based TA measurement for the LTM candidate PSCell. In some such cases, the UE 102 performs a random access procedure on the LTM candidate PSCell in event 732 as described above.

[0219] In some implementations, the UE 102 accesses the LTM candidate PCell first. After successfully accessing the LTM candidate PCell, the UE 102 starts accessing 732 the LTM candidate PSCell 1. In other implementations, the UE 102 simultaneously accesses the LTM candidate PCell and the LTM candidate PSCell 1.

[0220] In some implementations, in response to determining to trigger or triggering the LTM cell switch for the UE 102 as described above, the MN 104B sends 728 a CU-to-CU Cell Switch Notification message to the C-SN 106A to notify initiation of an LTM cell switch to the LTM candidate PSCell 1 for the UE 102. In some implementations, the MN 104B includes the cell ID 1 of the LTM candidate PSCell 1 in the CU-to-CU Cell Switch Notification message. Alternatively, the MN 104B sends an SN Modification Request message to notify initiation of an LTM cell switch to the LTM candidate PSCell 1 for the UE 102. In some implementations, the MN 104B includes the cell ID 1 of the LTM candidate PSCell 1 in the SN Modification Request message. In some implementations, the MN 104B includes, in the SN Modification Request message, an indication indicating initiation of an LTM cell switch to the LTM candidate PSCell 1 for the UE 102.

[0221] In some implementations, in response to determining to trigger or triggering the LTM cell switch for the UE 102 as described above, the MN 104B sends 729 an SN Request message to the S-SN 104A to indicate the S-SN 104A to release resources for the UE 102 and / or stop communication with the UE 102. In response, the S-SN 104A releases resources for the UE 102 and / or stops communication with the UE 102 and transmits an SN Request Acknowledge message to the MN 104B. In some implementations, the SN Request message and the SN Request Acknowledge message are an SN Modification Request message and an SN Modification Request Acknowledge message, respectively. In other implementations, the SN Request message and the SN Request Acknowledge message are an SN Release Request message and an SN Release Request Acknowledge message, respectively.

[0222] In some implementations, in the procedure 797, the MN 104 receives an RRC reconfiguration complete message from the UE 102, similar to event 636. In further implementations, after (e.g., in response to) receiving the RRC reconfiguration complete message, the MN 104B transmits 738 an SN Complete message to the C-SN 106A, similar to event 638. After successfully accessing the LTM candidate PCell, the UE 102 communicates 740 on the LTM candidate PCell (i.e., LTM candidate PCell 1) with the MN 104B using the MCG LTM DU configuration (i.e., MCG LTM DU configuration 1). After successfully accessing the LTM candidate PSCell 1, the UE 102 communicates 740 on the LTM candidate PSCell 1 with the C-SN 106A using the LTM SCG configuration (i.e., LTM SCG configuration 1). In some implementations, the UE 102 and the MN 104B communicate with each other via SRB(s) and / or DRB(s) configured in the LTM CU configuration. In some implementations, the UE 102 and the C-SN 106A communicate with each other via DRB(s) configured in the LTM CU configuration.

[0223] In some implementations, the MN 104B transmits an MCG LTM reference configuration to the UE 102, as described for Figs. 3-6. In some such cases, the UE 102 and the MN 104B communicate with each other in event 740 using the MCG LTM reference configuration. In some implementations, the MN 104B transmits an SCG LTM reference configuration to the UE 102, as described for Fig. 6. In some such cases, the UE 102 and the C-SN 106A communicate with each other in event 740 using the SCG LTM reference configuration.

[0224] In some implementations, the MN 104B includes one or more TCI state configuration(s) for an LTM cell switch to the LTM candidate PCell (and the LTM candidate PSCell 1) in the RRC reconfiguration message or in the first LTM candidate configuration. In some such cases, the MN 104B includes, in the LTM Cell Switch Command, a first TCI state ID indicating one of the TCI state configuration(s) and uses the indicated TCI state configuration to communicate with the UE 102 via the LTM candidate PCell during and / or after the LTM cell switch (e.g., access procedure in event 797 and / or communication in event 740). Based on the first TCI state ID, the UE 102 uses the indicated TCI state configuration to communicate with the MN 104B via the LTM candidate PCell during and / or after the LTM cell switch (e.g., access procedure in event 797 and / or communication in event 740).

[0225] In some implementations, the MN 104B receives, from the C-SN 106A (e.g., in the SN Request Acknowledge message 607 or 664), one or more TCI state configuration(s) forthe LTM cell switch and includes the TCI state configuration(s) in the RRC reconfiguration message or the first LTM candidate configuration. In some such cases, the MN 104B includes, in the LTM Cell Switch Command, a second TCI state ID indicating one of the TCI state configuration(s). In some implementations, when determining to trigger the LTM cell switch for the UE 102, the MN 104B transmits an SN Request message to the C-SN 106A to request a TCI state ID and receives the second TCI sate ID in an SN Request Acknowledge message in response. In other implementations, the C-SN 106A includes the second TCI state ID in the SN Request Acknowledge message 707. The C-SN 106A uses the indicated TCI state configuration to communicate with the UE 102 via the LTM candidate PSCell in event 732 and / or event 740. Based on the second TCI state ID, the UE 102 uses the indicated TCI state configuration to communicate with the C-SN 106A via the LTM candidate PSCell in event 732 and / or event 740.

[0226] In other implementations, based on the LTM indicator or the LTM information, the C-SN 106A determines not to send, to the MN 104B, a TCI state configuration for the LTM cell switch and the UE 102. In some such cases, the UE 102 and the C-SN 106A use beam(s) or a TCI state configuration corresponding to an SSB in event 732 and / or event 740. In some implementations, the C-SN 106A includes one or more TCI state configuration(s) in the LTM SCG configuration or the SCG LTM DU configuration. In further implementations, the C-SN 106A transmits, to the UE, a TCI state activation command (e.g., a DCI or a MAC CE) including a third TCI state ID to activate one of the TCI state configuration(s) in event 740. The C-SN 106 A uses the activated TCI state configuration to communicate with the UE 102 via the LTM candidate PSCell 1 in event 740. Based on the third TCI state ID, the UE 102 activates the TCI state configuration indicated by the third TCI state ID to communicate with the C-SN 106A via the LTM candidate PSCell 1 in event 740.

[0227] In some implementations, the C-SN 106A and the S-SN 104A are the same SN. In other implementations, the C-SN 106A and the S-SN 104A are different SNs.

[0228] In some implementations, the C-SN 106A includes LTM SCG configuration(s) 2 ..., N in the SN Request Acknowledge message 707 as described for the LTM SCG configuration 1, where N is an integer larger than 1. The LTM SCG configuration(s) 2, ..., N are configured for LTM candidate PSCell(s) 2, ..., N of the C-SN 106A, respectively. In some implementations, the LTM candidate PSCell(s) 2, ..., N belong to the other cell(s) of the C-SN 106A. In some implementations, the MN 104B generates LTM candidateconfiguration(s) 2, N including the LTM SCG configuration(s) 2 N, respectively. In some implementations, the MN 104B includes the MCG LTM DU configuration 1 in the each of the LTM candidate configuration(s) 2, .. N. In other implementations, the MN 104B obtains MCG LTM DU configuration(s) 2, ..., N for LTM candidate PCell(s) 2, ..., N, respectively, as described for the LTM candidate PCell 1, and includes the MCG LTM DU configuration(s) 2, ..., N in the LTM candidate configuration(s) 2 ..., N, respectively. In some implementations, some or all of the LTM candidate PCell(s) 1, ...,N are the same cell. In other implementations, the LTM candidate PCell(s) 1, ..., N are different cells. In some implementations, the MN 104B includes the LTM candidate configuration(s) 2, ..., N in the RRC reconfiguration message 716. In other implementations, the MN 10B transmits one or more additional RRC reconfiguration message(s) including the LTM candidate configuration(s) 2, ..., N to the UE 102, similar to event 716. The UE 102 transmits an RRC reconfiguration complete message to the MN 104B in response to each of the additional RRC reconfiguration message(s), similar to event 720.

[0229] In some implementations, the MN 104B performs one or more additional MCG LTM with SCG configuration preparation procedure(s) to prepare additional LTM candidate PCell(s) and additional LTM candidate PSCell(s), similar to the procedure 781. In some implementations, in the additional MCG LTM with SCG configuration preparation procedure(s), the MN 104B obtains additional LTM candidate configuration(s) as described for the procedure 781. Each of the additional LTM candidate configuration(s) is similar to the first LTM candidate configuration described for Fig. 7. In some implementations, the MN 104B includes at least a portion of the additional LTM candidate configuration(s) in the RRC reconfiguration message 716. In some implementations, the MN 104B transmits one or more additional RRC reconfiguration message(s), including the rest portion of the additional LTM candidate configuration(s), to the UE 102, similar to event 716. The UE 102 transmits an RRC reconfiguration complete message to the MN 104B in response to each of the additional RRC reconfiguration message(s), similar to event 720. In other implementations, the MN 104B transmits one or more additional RRC reconfiguration message(s), including the additional LTM candidate configuration(s), to the UE 102, similar to event 716. The UE 102 transmits an RRC reconfiguration complete message to the MN 104B in response to each of the additional RRC reconfiguration message(s), similar to event 720.

[0230] Descriptions for Figs. 3-6 can apply to Fig. 7.

[0231] Fig. 8 depicts a scenario 800 for an inter-CU / MN MCG LTM with SCG configuration, similar to the scenario 700. The differences between the scenarios 800 and 700 are described below. The S-MN 104B receives 804 at least one measurement report from the UE 102. The at least one measurement report includes at least one first measurement result for a first cell of the MN 104B. Based on the at least one first measurement result 804, the S-MN 104B determines to configure the first cell of the candidate MN (C-MN) 106B as an LTM candidate PCell for the UE 102. Unlike Fig. 7, the LTM candidate PCell is operated by the C-MN 106B instead of the MN 104B. Descriptions for the LTM candidate PCell and the MN 104B in Fig. 7 can apply to the LTM candidate PCell and the C-MN 106B. Fig. 8. In response to the determination, the S-MN 104B performs 898 an LTM preparation procedure with the C-MN 106B to prepare the first cell of the C-MN 106B as an LTM candidate PCell for the UE 102, similar to the procedure 598. In the procedure 898, the C-MN 106B receives a Handover Request message from the S-MN 104B, requesting to prepare a first cell of the C-MN 106B as an LTM candidate PCell for the UE 102.

[0232] After receiving the Handover Request message, the C-MN 106B transmits 805 an SN Request message to the C-SN 106A to request or indicate preparing the LTM candidate PSCell for the UE 102, similar to events 605 and / or 705. In response, the C-SN 106A transmits 807 an SN Request Acknowledge message including an LTM SCG configuration for the LTM candidate PSCell to the C-MN 106B, similar to event 607 and / or 707. After (e.g., in response to) receiving the Handover Request message, the C-MN 106B obtains (e.g., generates) an MCG LTM DU configuration as described for Fig. 7. The C-MN 106B generates a first LTM candidate configuration including the MCG LTM DU configuration and the LTM SCG configuration. In the procedure 898, the C-MN 106B then transmits a Handover Request Acknowledge message including the first LTM candidate configuration to the S-MN 104B in response to the Handover Request message. In some implementations, the S-MN 104B includes a serving DU configuration in the RRC reconfiguration message 816, similar to events 716 and / or 518. In some implementations, the C-MN 106B includes the first LTM candidate configuration in an RRC container (e.g., HandoverCommand message) and includes the RRC container in the Handover Request Acknowledge message.

[0233] In some implementations, the MN 104B includes a SCG LTM reference configuration in the Handover Request message and the C-MN 106B includes a SCG LTMreference configuration in the SN Request message. If the C-SN 106 A supports the SCG LTM reference configuration, the C-SN 106A generates the LTM SCG configuration based on the SCG LTM reference configuration as described above. Otherwise, if the C-SN 106A does not support the SCG LTM reference configuration, the C-SN 106 A generates the LTM SCG configuration as a complete configuration as described above. In other implementations, the MN 104B receives an SCG configuration from the S-SN 104A, as described for Fig. 6, and includes the SCG configuration in the Handover Request message. The C-MN 106B includes the SCG configuration in the SN Request message 805. In some implementations, the C-SN 106A generates an SCG LTM reference configuration based on the SCG configuration and includes the SCG LTM reference configuration in the SN Request Acknowledge message, as described for Fig. 6. In such cases, the C-SN 106A generates the LTM SCG configuration based on the SCG LTM reference configuration, as described above. The C-MN 106B includes the SCG LTM reference configuration in the Handover Request Acknowledge message.

[0234] In some implementations, the serving DU configuration includes a first LTM CSI report configuration. In the procedure 892, the S-MN 104B generates the first LTM CSI report configuration based on a first LTM CSI resource configuration for the LTM candidate PCell. In some implementations, the S-MN 104B obtains the first LTM CSI resource configuration as described above. In further implementations, the S-MN 104B obtains the first LTM CSI resource configuration from the C-MN 106B in an interface message. In some implementations, the interface message is the Handover Request Acknowledge message, an XnAP message, or a 6G interface message. The UE 102 transmits one or more first LI measurement reports (e.g., LTM CSI reports) to the S-MN 104B (e.g., a DU of the S-MN 104B) in accordance with the first LTM CSI report configuration, similar to events 324, 354, 382, 397, 424, 454, 482, 497, 524, 582, 554, and / or 597. The one or more first LI measurement reports include first LI measurement result(s) for LTM candidate PCell. The (S-DU of the) S-MN 104B receives the one or more first LI measurement reports from the UE 102 in accordance with the first LTM CSI report configuration. In some implementations, the (S-DU of the) S-MN 104B determines to trigger the procedure 882A and / or the procedure 897 based on the first LI measurement result(s).

[0235] In some implementations, the serving DU configuration includes a second LTM CSI report configuration. In the procedure 892, the S-MN 104B generates the second LTMCSI report configuration based on a second LTM CSI resource configuration for the LTM candidate PSCell 1. The UE 102 transmits one or more second LI measurement reports (e.g., LTM CSI reports) to (the S-DU of) the S-MN 104B in accordance with the second LTM CSI report configuration, similar to events 324, 354, 382, 397, 424, 454, 482, 497, 582, 554, and / or 597. The one or more second LI measurement reports include second LI measurement result(s) for the LTM candidate PSCell 1. The (S-DU of the) S-MN 104B receives the one or more second LI measurement reports from the UE 102 in accordance with the second LTM CSI report configuration. In some implementations, the S-MN 104B obtains the second LTM CSI resource configuration as described above. In further implementations, the S-MN 104B receives the second LTM CSI resource configuration from the C-SN 106A in an interface message. In some implementations, the interface message is the SN Request Acknowledge message, an XnAP message, or a 6G interface message. In yet further implementations, the S-MN 104B receives the second LTM CSI resource configuration from the C-MN 106B in an interface message. In some implementations, the interface message is the Handover Request Acknowledge message, an XnAP message, or a 6G interface message. In some implementations, the C-MN 106B obtains the second CSI resource configuration as described above. In further implementations, the (S-DU of the) S-MN 104B determines to trigger the procedure 882A and / or the procedure 897, based on the first LI measurement result(s) and the second LI measurement result(s). In other implementations, the S-MN 104B performs another LTM CSI report configuration procedure for the UE 102 and the LTM candidate PSCell 1 to obtain the second CSI report configuration and / or an additional serving DU configuration for the UE 102, similar to the procedure 892 and as described above. In some such cases, the S-MN 104B transmits an additional RRC reconfiguration message to the UE 102, including additional serving DU configuration or the second CSI report configuration, similar to the message 816.

[0236] In some other implementations, the UE 102 transmits one or more first L3 measurement reports (e.g., RRC measurement reports) to the S-MN 104B (e.g., the CU of the S-MN 104B via the S-DU), similar to events 304, 404, and / or 504. The one or more first L3 measurement reports include first L3 measurement result(s) for the LTM candidate PCell. In some implementations, the MN 104B (e.g., a CU of the MN 104B) determines to trigger the procedure 882A and / or the procedure 897 based on the first L3 measurement result(s). In some implementations, the UE 102 transmits one or more second L3 measurement reports(e.g., RRC measurement reports) to the S-MN 104B (e.g., the CU of the S-MN 104B via the S-DU), similar to events 304 and / or 404. The one or more second L3 measurement reports include second L3 measurement result(s) for the LTM candidate PSCell 1. In some implementations, the (CU of the) S-MN 104B determines to trigger the procedure 882A and / or the procedure 897 based on the first L3 measurement result(s) and the second L3 measurement result(s). In some implementations, in response to determining to trigger the procedure 882A and / or the procedure 897, the CU transmits a CU-to-DU message to the S-DU to cause the S-DU to trigger the procedure 882A and / or the procedure 897. In some implementations, the CU-to-DU message is a UE Context Modification Request message. In further implementations, the CU-to-DU message is an F1AP message or a 6G interface message.

[0237] In some implementations, the S-MN 104B includes, in the Handover Request message, the at least one second measurement result for the first cell of the C-SN 106A and / or the measurement result(s) for the other cell(s) (e.g., as described for Fig. 7). In some implementations, based on the at least one second measurement result for the first cell of the C-SN 106A and / or the measurement result(s) for the other cell(s), the C-MN 106B transmits or determines to transmit 805 the SN Request message.

[0238] In some implementations, the C-SN 106A and the S-SN 104A are same SN. In other implementations, the C-SN 106A and the S-SN 104A are different SNs. In some implementations, after (e.g., in response to) receiving 820 the RRC reconfiguration complete message, the S-MN 104B transmits 819 an MN Complete message to the C-MN 106B, indicating that the first LTM candidate configuration has been sent to the UE 102. In some implementations, after or in response to receiving the MN Complete message, the C-MN 106B then transmits 821 an SN Complete message to the C-SN 106A, indicating that the LTM SCG configuration has been sent to the UE 102.

[0239] Descriptions for Figs. 3-7 can apply to Fig. 8.

[0240] Next, several example methods, which may be implemented in a RAN node (e.g., an MN 104B, an SN 104A and / or 106A, a CU 172, or a DU 174 described above) or a UE (e.g., a UE 102 described above) for an LTM cell switch to an LTM candidate cell of a C-SN, are discussed next with reference to Figs. 9-17. Descriptions and example implementations described for Figs. 3-8 can apply to Figs. 9-17. Each of the example methods describedwithin this document with respect to Figs. 9-17 may include additional or alternate steps, in embodiments.

[0241] Fig. 9 illustrates an example method 900, which can be implemented by a UE. The method 900 begins at block 902, where the UE communicates with a first MN using a serving MCG configuration. At block 916, the UE receives a first LTM candidate configuration from the first MN, including a first MCG LTM candidate configuration and a first SCG LTM candidate configuration, where the first MCG LTM candidate configuration configures a first LTM candidate PCell and the first SCG LTM candidate configuration configures a first LTM candidate PSCell of a RAN node. At block 954, the UE transmits at least one measurement report to the first MN. At block 926, the UE receives from the first MN, a first LTM Cell Switch Command commanding the UE to apply the first LTM candidate configuration. At block 972, the UE initiates an LTM cell switch in response to the first LTM Cell Switch Command. At block 946, the UE manages (e.g., administrates or controls) radio configurations for a MCG in response to initiating the LTM cell switch. At block 932-1, the UE accesses the first LTM candidate PCell in accordance with the first MCG LTM candidate configuration in response to initiating the LTM cell switch. At block 932-2, the UE accesses the first LTM candidate PSCell in accordance with the first SCG LTM candidate configuration in response to initiating the LTM cell switch. At block 936, the UE transmits a RRC reconfiguration complete message to a second MN in response to initiating the LTM cell switch. At block 940-1, the UE communicates with the second MN via the first LTM candidate PCell in accordance with the first MCG LTM candidate configuration. At block 940-2, the UE communicates with the RAN node via the first LTM candidate PSCell in accordance with the first SCG LTM candidate configuration.

[0242] In some implementations, the first LTM candidate configuration is configured for a MCG LTM with SCG configuration. In some implementations, the first MCG LTM candidate configuration and the first SCG LTM candidate configuration is a MCG LTM DU configuration and an LTM SCG configuration respectively, as described for Figs. 7 and 8.

[0243] In some implementations, the first MN and the second MN are different MNs. In other implementations, the first MN and the second MN are the same MN. In some implementations, the UE receives a first LTM ID (e.g., a configuration ID) identifying the first LTM candidate configuration from the first MN. In some implementations, the firstLTM Cell Switch Command includes the first LTM ID. For example, the first LTM Cell Switch Command includes a field with a value indicating the first LTM ID.

[0244] In some implementations, the UE operates in DC with the first MN and an S-SN while communicating with the first MN at block 902. In these cases, the UE communicates with an S-SN via a serving PSCell using a serving SCG configuration. In some implementations, the first LTM candidate PSCell is the serving PSCell. In other implementations, the first LTM candidate PSCell is a non-serving PSCell. In some implementations, the UE manages (e.g., administrates, controls, etc.) radio configurations for a SCG in response to initiating the LTM cell switch.

[0245] In some implementations, managing the radio configurations for the MCG includes releasing and / or clearing some or all dedicated and common radio configurations in the serving MCG configuration. In some further implementations, managing the radio configurations for the MCG includes keeping (e.g., maintaining) at least one of the following configurations:1) One or more radio bearer configurations (e.g., RadioBearerConfig IE(s)), e.g., for configuring one or more SRBs and / or one or more DRBs. For example, the UE receives one or more messages (e.g., RRC reconfiguration message(s) and / or RRC resume message(s)) including the one or more radio bearer configurations from the first MN before initiating the LTM cell switch.2) One or more logical channel identities (e.g., logicalChannelldentity and / or logicalChannelldentityExt fields), state variable(s), buffer(s), and / or timer(s) for one or more RLC bearers and / or RLC entities for MCG, except for triggering the RLC entity / entities to set or reset variable RETX_COUNT to an initial value. In some implementations, the one or more messages include one or more RLC configurations (e.g., RLC-BearerConfig IES) for configuring the one or more RLC bearers and the UE establishes the one or more RLC entities in accordance with the one or more RLC configurations.3) One or more logical channel identities (e.g., bh-LogicalChannelldentity fields), state variable(s), buffers, and / or timers for one or more BH RLC channels and / or RLC entities for MCG, except for triggering the RLC entity / entities to set or reset variable RETX_COUNT to an initial value. In some implementations, the one or moremessages include one or more RLC configurations (e.g., RLC-BearerConfig IES) for configuring the one or more RLC bearers and the UE establishes the one or more RLC entities in accordance with the one or more RLC configurations.4) Variables (e.g., IEs) VarLTM-ServingCellNoResetID and / or VarLTM- ServingCellUE-MeasuredTA-ID. The VarLTM-ServingCellNoResetID may be used to store a serving cell ID based on which the UE determines whether a L2 reset is needed or not upon an LTM cell switch procedure. The VarLTM-ServingCellUE- MeasuredTA-ID may be used to store a serving cell ID based on which the UE determines whether UE-based TA measurements are needed or not.5) One or more LTM candidate configurations (including the first LTM candidate configuration) for one or more LTM candidate PCells, intra- MN LTM with or without SCG configuration, and / or inter- MN LTM with or without SCG configuration.6) A MCG C-RNTI used by the UE to communicate with the first MN before initiating the LTM cell switch.7) One or more AS security configurations and / or a master key used by the UE to communicate with the first MN before initiating the LTM cell switch.8) A logged measurement configuration.

[0246] In some implementations, managing the radio configurations for the SCG includes releasing and / or clearing some or all dedicated and common radio configurations in the serving SCG configuration.

[0247] In some further implementations, managing the radio configurations for the SCG includes keeping (e.g., maintaining) at least one of the following configurations:1) One or more radio bearer configurations (e.g., RadioBearerConfig IE(s)), e.g., for configuring one or more SRBs and / or one or more DRBs. For example, the UE receives one or more messages (e.g., RRC reconfiguration message(s) and / or RRC resume message(s)) including the radio bearer configuration from the MN or the S-SN before initiating the LTM cell switch.2) One or more logical channel identities (e.g., logicalChannelldentity and / or logicalChannelldentityExt fields), state variable(s), buffer(s), and / or timer(s) for one or more RLC bearers and / or RLC entities for SCG, except for triggering the RLCentity / entities to set or reset variable RETX_COUNT to an initial value. In some implementations, the one or more RRC messages include one or more RLC configurations (e.g., RLC-BearerConfig IES) configuring the one or more RLC bearers and the UE establishes the one or more RLC entities in accordance with the one or more RLC configurations.3) One or more logical channel identities (e.g., bh-LogicalChannelldentity fields), state variable(s), buffers, and / or timers for one or more BH RLC channels and / or RLC entities for SCG, except for triggering the RLC entity / entities to set or reset variable RETX_COUNT to an initial value. In some implementations, the one or more RRC messages include one or more RLC configurations (e.g., RLC-BearerConfig IEs) configuring the one or more RLC bearers and the UE establishes the one or more RLC entities in accordance with the one or more RLC configurations.4) Variables (e.g., IEs) VarLTM-ServingCellNoResetID and / or VarLTM- ServingCellUE-MeasuredTA-ID for SCG. The VarLTM-ServingCellNoResetID may be used to store a serving cell ID based on which the UE determines whether a L2 reset is needed or not upon an LTM cell switch procedure. The VarLTM- ServingCellUE-MeasuredTA-ID may be used to store a serving cell ID based on which the UE determines whether UE-based TA measurements are needed or not. 5) One or more LTM candidate configurations for one or more LTM candidate PSCells, intra-SN LTM, and / or inter-SN LTM.6) One or more AS security configurations and / or a secondary keyused by the UE to communicate with the S-SN before initiating the LTM cell switch.7) A logged measurement configuration.

[0248] The descriptions and example implantations described in the Fig. 9 can be applied to the Figs. 10-17 if applicable.

[0249] Fig. 10 illustrates an example method 1000, which can be implemented by a UE. The method 1000 begins at block 1002, where the UE communicates with a first MN and an S-SN using a serving MCG configuration and a serving SCG configuration, respectively. At block 1016, the UE receives a first LTM candidate configuration from the first MN. The flow proceeds to blocks 926 and 972 and then to block 1017. At block 1017, the UE retrieves afirst MCG LTM candidate configuration from the first LTM candidate configuration. The flow proceeds to blocks 946, 932-1, and 940-1 and then to block 1035. At block 1035, the UE determines whether the first LTM candidate configuration includes a SCG LTM candidate configuration. If the first LTM candidate configuration includes a SCG LTM candidate configuration (e.g., the “Yes” branch), the flow may proceed from block 1035 to block 1046, where the UE manages (e.g., administrates, controls, etc.) radio configurations associated with a SCG in response to initiating the LTM cell switch. The flow proceeds to blocks 932-2 and 940-2. Alternatively, the flow may proceed from block 1035 to blocks 932-2 and 940-2 directly. If the first LTM candidate configuration does not include a SCG LTM candidate configuration (e.g., the “No” branch), the flow proceeds from block 1035 to block 1048, where the UE continues to communicate with the S-SN using the serving SCG configuration.

[0250] Fig. 11 illustrates an example method 1100 similar to method 900 or 1000, which can be implemented by a UE. The method 1100 begins at blocks 902, 916 and (optionally) 954 and proceeds to block 1170. At block 1170, the UE detects a failure (e.g., a radio link failure (RLF)). At block 1172, the UE initiates an LTM cell switch in response to detecting the failure. The flow proceeds to block 946, where the UE manages (e.g., administrates, controls, etc.) radio configurations for a MCG in response to initiating the LTM cell switch. The flow proceeds to blocks 932-1, 932-2, 936, 940-1, and 940-2.

[0251] Fig. 12 illustrates an example method 1200 similar to method 900, 1000, or 1100, which can be implemented by a UE. The method 1200 begins at blocks 1002, 1016, 1170 and 1172 and proceeds to block 1017. At block 1017, the UE retrieves a first MCG LTM candidate configuration from the first LTM candidate configuration. The flow proceeds to blocks 946, 932-1, 940-1 and to block 1035. At block 1035, the UE determines whether the first LTM candidate configuration includes a SCG LTM candidate configuration. If the first LTM candidate configuration includes a SCG LTM candidate configuration (e.g., the “Yes” branch), the flow may proceed from block 1035 to block 1046 where the UE manages (e.g., administrates, controls, etc.) radio configurations associated with a SCG in response to initiating the LTM cell switch and to blocks 932-2 and 940-2. Alternatively, the flow may proceed from block 1035 to blocks 932-2 and 940-2 directly. If the first LTM candidate configuration does not include a SCG LTM candidate configuration (e.g., the “No” branch), the flow proceeds from block 1035 to block 1249 where the UE releases the serving SCG configuration.

[0252] Fig. 13 illustrates an example method 1300 similar to method 900, 1000, 1100, or 1200, which can be implemented by a UE. The method 1300 begins at block 1302, where the UE communicates with a first MN and an S-SN via a serving PCell and a serving PSCell, using a serving MCG configuration and a serving SCG configuration. At block 1316, the UE receives a first LTM candidate configuration from the first MN, including a first LTM MCG configuration and a first SCG LTM candidate configuration, where the first LTM MCG candidate configuration include MCG configuration parameters and the first SCG LTM candidate configuration configures a first LTM candidate PSCell of a RAN node. At block 1354, the UE may transmit at least one measurement report to the S-SN. At block 1326, the UE receives, from the S-SN, a first LTM Cell Switch Command commanding the UE to apply the first LTM candidate configuration. The flow proceeds to blocks 972 and 946 and to block 1346. At block 1346, the UE manages (e.g., administrates, controls, etc.) radio configurations for a SCG in response to initiating the LTM cell switch. At block 932-2, the UE accesses the first LTM candidate PSCell in accordance with the first SCG LTM candidate configuration in response to initiating the LTM cell switch. At block 1336, the UE transmits a RRC reconfiguration complete message to the first MN in response to initiating the LTM cell switch. At block 1340-1, the UE communicates with the first MN via the serving PCell in accordance with the first MCG LTM candidate configuration. At block 940-2, the UE communicates with the RAN node via the first LTM candidate PSCell in accordance with the first SCG LTM candidate configuration.

[0253] Fig. 14 illustrates an example method 1400 similar to method 900, 1000, 1100, 1200, or 1300, which can be implemented by a UE. The method 1400 begins at blocks 1302 and 1016 and proceeds to block 1472. At block 1472, the UE initiates an LTM cell switch for a SCG based on the first LTM candidate configuration. The flow proceeds to blocks 1346, 932-2, and 940-2 and to block 1437. At block 1437, the UE determines whether the first LTM candidate configuration includes an LTM MCG configuration. If the first LTM candidate configuration includes an LTM MCG configuration (e.g., the “Yes” branch), the flow may proceed from block 1437 to block 946 and then to block 940-1. Alternatively, the flow may proceed from block 1437 to block 940-1 directly. If the first LTM candidate configuration does not include an LTM MCG configuration (e.g., the “No” branch), the flow proceed from block 1437 to block 1449, where the UE continues to communicate with the first MN using the serving MCG configuration.

[0254] Fig. 15 illustrates an example method 1500 similar to method 900, 1000, 1100, 1200, 1300, or 1400, which can be implemented by a UE. The method 1500 begins at blocks 1002 and 1016 and proceed to block 1572. At block 1572, the UE initiates an LTM cell switch for a MCG based on the first LTM candidate configuration. The flow proceeds to blocks 946, 932-1 and 940-1 and to block 1539. At block 1539, the UE determines whether the first LTM candidate configuration is configured for MCG LTM with a SCG configuration. If the first LTM candidate configuration is configured for MCG LTM with a SCG configuration (e.g., the “Yes” branch), the flow may proceed from block 1539 to block 1046, where the UE manages (e.g., administrates, controls, etc.) radio configurations associated with a SCG in response to initiating the LTM cell switch, and then to blocks 932-2 and 940-2. Alternatively, the flow may proceed from block 1539 to blocks 932-2 and 940-2 directly. If the first LTM candidate configuration is not configured for MCG LTM with a SCG configuration (e.g., the “No” branch), the flow proceeds from block 1539 to block 1048, where the UE continues to communicate with the S-SN using the serving SCG configuration.

[0255] Fig. 16 illustrates an example method 1600, which can be implemented by a RAN. The method 1600 begins at block 1602, where the RAN communicates with a UE by a first MN, using a serving MCG configuration. At block 1616, the RAN transmits a first LTM candidate configuration for MCG LTM to the UE by the first MN, including a first MCG LTM candidate configuration and a first SCG LTM candidate configuration, where the first MCG LTM candidate configuration configures a first LTM candidate PCell and the first SCG LTM candidate configuration configures a first LTM candidate PSCell of a RAN node. At block 1654, the RAN may receive at least one measurement report from the UE by the first MN. At block 1626, the RAN transmits, by the first MN and to the UE, a first LTM Cell Switch Command to trigger the UE to perform an LTM cell switch, where the first LTM Cell Switch Command commands the UE to apply the first LTM candidate configuration. At block 1646, the RAN manages (e.g., administrates, controls, etc.) radio configurations for a MCG in response to triggering the LTM cell switch. At block 1632-1, the RAN detects that the UE accesses the first LTM candidate PCell by a second MN in accordance with the first MCG LTM candidate configuration after (e.g., in response to or subsequently to) triggering the LTM cell switch. At block 1632-2, the RAN detects that the UE accesses the first LTM candidate PSCell by a RAN node in accordance with the first SCG LTM candidate configuration after (e.g., in response to or subsequently to) triggering the LTM cell switch. Atblock 1636, the RAN receives a RRC reconfiguration complete message from the UE and by the second MN after (e.g., in response to or subsequently to) triggering the LTM cell switch. At block 1640-1, the RAN communicates with the UE via the first LTM candidate PCell, by the second MN, in accordance with the first MCG LTM candidate configuration. At block 1640-2, the RAN communicates with the UE via the first LTM candidate PSCell, by the RAN node, in accordance with the first SCG LTM candidate configuration.

[0256] Fig. 17 illustrates an example method 1700 similar to method 1600, which can be implemented by a RAN. The method 1700 begins at blocks 1602, 1616, and may proceed to block 1654, and to block 1732-1. At block 1732-1, the RAN detects that the UE accesses the first LTM candidate PCell by a second MN in accordance with the first MCG LTM candidate configuration. At block 1746, the RAN may manage (e.g., administer, control, etc.) radio configurations for a MCG in response to detecting the UE accessing the first LTM candidate PCell. At block 1732-2, the RAN detects that the UE accesses the first LTM candidate PSCell by a RAN node in accordance with the first SCG LTM candidate configuration. The flow proceeds to blocks 1636, 1640-1 and 1640-2. The following describes changes to 3GPP specification 38.331 to incorporate the methods above into the 3GPP specification.5.3.5.18.6 LTM cell switch executionUpon the indication by lower layers that an LTM cell switch procedure is triggered, or upon performing LTM cell switch following cell selection performed while timer T311 was running, as specified in 5.3.7.3, the UE shall:1 > if the LTM cell switch is triggered on the MCG:2> release / clear all current dedicated and common radio configurations which have neither been received via SRB1 within mrdc-SecondaryCellGroup, nor via SRB3 except for the following: - the radio bearer configuration (configured via RadioBearerConfig)- the logicalChannelldentity and logicalChannelldentityExt of RLC bearers configured in RLC- BearerConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX_COUNT its initial value, as specified in TS 38.322 [4];- the bh-LogicalChannelldentity of BH RLC channels configured in BH-RLC-ChannelConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX_COUNT its initial value, as specified in TS 38.322 [4];- the UE variables VarLTM-ServingCellNoResetID and VarLTM-ServingCellUE-MeasuredTA- ID;- the Itm-Config (if configured) and / or Itm-ConfigSCG (if configured);- the MCG C-RNTI;- the AS security configurations associated with the master key;- the logged measurement configuration;2> if a RRCReconfiguration is included within mrdc-SecondarvCellGroup in the LTM candidate configuration triggered by the LTM cell switch:3> release / clear some or all current dedicated and common radio configurations which have been received either via SRB1 within mrdc-SecondaryCellGrouv or via SRB3 except for none or at least one of the following:- the radio bearer configuration (configured via RadioBearerConfig IE)- the logicalChannelldentity and logicalChannelldentityExt of RLC bearers configured in RLC- BearerConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX COUNT its initial value, as specified in TS 38.322 141;- the bh-LogicalChannelldentity of BH RLC channels configured in BH-RLC-ChannelConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX COUNT its initial value, as specified in TS 38.322 141;- the UE variables VarLTM-ServingCellNoResetID and VarLTM-ServingCellUE-MeasuredTA- ID;- the Itm-Config (if configured) and / or Itm-ConfigSCG (if configured);- the AS security configurations associated with the secondary key;1 > else, if the LTM cell switch is triggered on the SCG:2> release / clear all current dedicated and common radio configurations which have been received either via SRB1 within mrdc-SecondaryCellGroup, or via SRB3 except for the following:- the radio bearer configuration (configured via RadioBearerConfig IE)- the logicalChannelldentity and logicalChannelldentityExt of RLC bearers configured in RLC- BearerConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX_COUNT its initial value, as specified in TS 38.322 [4];- the bh-LogicalChannelldentity of BH RLC channels configured in BH-RLC-ChannelConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX_COUNT its initial value, as specified in TS 38.322 [4];- the UE variables VarLTM-ServingCellNoResetID and VarLTM-ServingCellUE-MeasuredTA- ID;- the Itm-Config (if configured) and / or Itm-ConfigSCG (if configured);- the AS security configurations associated with the secondary key;2> if the LTM candidate configuration triggered by the LTM cell switch includes configurations for MCG (i.e., LTM MCG configuration):3> release / clear some or all current dedicated and common radio configurations which have been received either via SRB1 within mrdc-SecondaryCellGrouv or via SRB3 except for none or at least one of the following:- the radio bearer configuration (configured via RadioBearerConfig IE)- the logicalChannelldentity and logicalChannelldentityExt of RLC bearers configured in RLC- BearerConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX COUNT its initial value, as specified in TS 38.322 141;- the bh-LogicalChannelldentity of BH RLC channels configured in BH-RLC-ChannelConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX COUNT its initial value, as specified in TS 38.322 141;- the UE variables VarLTM-ServingCellNoResetID and VarLTM-ServingCellUE-MeasuredTA- ID;- the Itm-Config (if configured) and / or Itm-ConfigSCG (if configured);- the AS security configurations associated with the master key;> for each SRB / DRB in the current UE configuration:2> if the LTM cell switch is triggered on the MCG and the SRB / DRB using the master key; or 2> if the LTM cell switch is triggered on the SCG and the SRB / DRB using the secondary key:3> keep the associated PDCP and SDAP entities, their state variables, buffers and timers;3> release all fields related to the SRB / DRB configuration except for srb-Identity and drb-Identity, > apply the default LI parameter values as specified in corresponding physical layer specifications except for the parameters for which values are provided in SIB 1 ;> use the default values specified in 9.2.3 for timers T310, T311 and constants N310, N311 associated with the cell group for which the LTM cell switch procedure is triggered, where T310, N310, and N311 are for both MCG and SCG, and T311 is only for the MCG;> apply the default MAC Cell Group configuration as specified in 9.2.2 for the cell group for which the LTM cell switch procedure is triggered;> for each srb-Identity in the current UE configuration:2> apply the default SRB configuration defined in 9.2.1 for the corresponding SRB;> if the LTM-Candidate IE in Itm-Config indicated by lower layers or for the selected cell in accordance with 5.3.7.3 does not contain the field Itm-NoResetID and if the UE does not have any value stored of Itm-ServingCellNoResetlD within VarLTM-ServingCellNoResetID', or> if the value of field Itm-NoResetID contained within the LTM-Candidate IE in Itm-Config indicated by lower layers or for the selected cell in accordance with 5.3.7.3 is not equal to the value of Itm- ServingCellNoResetlD within VarLTM-ServingCellNoResetID'.2> for each logicalChannelldentity and logicalChannelldentityExt that is part of the current UE configuration for the cell group for which the LTM cell switch procedure is triggered:3> if servedRadioBearer is set to drb-Identity:4> after the end of this procedure, re-establish the corresponding RLC entity as specified in TS 38.322 [4], after applying the LTM configuration in Itm-CandidateConfig within the LTM- Candidate IE in Itm-Config',2> for each bh-LogicalChannelldentity that is part of the current UE configuration for the cell group for which the LTM cell switch procedure is triggered:3> after the end of this procedure, re-establish the corresponding RLC entity as specified in TS 38.322 [4], after applying the LTM configuration in Itm-CandidateConfig within the LTM- Candidate IE in Itm-Config',2> for each drb-Identity value that is part of the current UE configuration:3> if this DRB is an AM DRB:4> after the end of this procedure, trigger the PDCP entity of this DRB to perform data recovery as specified in TS 38.323 [5], after applying the LTM configuration in Itm- CandidateConfig within LTM-Candidate IE in Itm-Config',2> if the value of field Itm-NoResetID contained within the LTM-Candidate IE in Itm-Config indicated by lower layers or for the selected cell in accordance with 5.3.7.3 is not equal to the value of Itm- ServingCellNoResetlD within VarLTM-ServingCellNoResetID'.3> replace the value of Itm-ServingCellNoResetlD in VarLTM-ServingCellNoResetID with the value of Itm-NoResetID in the LTM-Candidate in Itm-Config indicated by lower layers or for the selected cell in accordance with 5.3.7.3;> if the LTM-Candidate IE in Itm-Config indicated by lower layers or for the selected cell in accordance with 5.3.7.3 contains the field Itm-UE-MeasuredTA-ID'.2> if the value of Itm-UE-MeasuredTA-ID is not equal to the value of Itm-ServingCellUE- MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID'.3> replace the value of Itm-ServingCellUE-MeasuredTA-ID in VarLTM-ServingCellUE- MeasuredTA-ID with the value received within Itm-UE-MeasuredTA-ID',3> for each LTM-Candidate IE in Itm-Config'.4> if the value of Itm-UE-MeasuredTA-ID within LTM-Candidate IE is equal to the value of Itm-ServingCellUE-MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID: 5> inform lower layers that the UE is configured with UE -based TA measurements for the LTM-Candidate',4> else:5> inform lower layers that the UE is not configured with UE-based TA measurements for the LTM-Candidate',NOTE 0: The UE is not expected to perform UE-based TA measurements for an SpCell.1> else if the LTM-Candidate IE in Itm-Config indicated by lower layers or for the selected cell in accordance with 5.3.7.3 does not contain the field Itm-UE-MeasuredTA-ID:2> inform lower layers that the UE is not configured with UE-based TA measurements for the LTM- Candidate.1> if Itm-ConfigComplete is not included within the LTM-Candidate IE in Itm-Config indicated by lower layers or for the selected cell in accordance with 5.3.7.3:2> consider Itm-ReferenceConfiguration in Itm-Config, associated with the cell group for which the LTM cell switch procedure is triggered, to be the current UE configuration for the fields and configurations to be released by the actions above in this procedure;2> if measConfig is included within Itm-ReferenceConfiguration in Itm-Config',3> perform the measurement configuration procedure as specified in clause 5.5.2 by considering the measConfig within Itm-ReferenceConfiguration in Itm-Config as the received measConfig: NOTE 1 : When the UE considers the reference configuration to be the current UE configuration, the UE should store fields and configurations that are part of the reference configuration but should not execute any actions or procedures triggered by the reception of an RRCRe configuration message which are described in clause 5.3.5.3, unless specified otherwise in this clause.1> if the LTM cell switch is triggered by an indication from lower layers:2> apply the RRCReconfiiguration message in Itm- Candidate Config within LTM-Candidate IE in Itm- Config identified by the LTM candidate configuration identity received from lower layers according to clause 5.3.5.3;1> else (LTM cell switch triggered upon cell selection performed while timer T311 was running):2> apply the RRCReconfiiguration message in Itm- Candidate Config within LTM-Candidate IE in Itm- Config related to the LTM candidate configuration identity for the selected cell (i.e., in accordance with 5.3.7.3) according to clause 5.3.5.3;1 > release the radio bearer(s) and the logical channel(s) that were part of the UE configuration before of this LTM cell switch procedure but not part of the LTM candidate configuration either indicated by lower layers or for the selected cell in accordance with 5.3.7.3, or the LTM reference configuration (in case the LTM candidate configuration does not include Itm-ConfigComplete).NOTE 2: When Itm-ConfigComplete is not included for an LTM candidate configuration, before an LTM cell switch is triggered a UE implementation may generate and store an RRCRe configuration message by applying the received LTM candidate configuration on top of the LTM reference configuration, and the stored RRCRe configuration message is applied when the LTM cell switch is triggered. It is up to the UE to ensure that the RRC reconfiguration applied at the time of LTM cell switch is in accordance with the latest LTM reference configuration and LTM candidate configuration.

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

[0258] Example 1. A method implemented in a user equipment (UE), the method comprising: first communicating, by the UE, with a radio access network (RAN) in connectivity with a master node (MN) using a master cell group (MCG); receiving, from the MN, a lower-layer triggered mobility (LTM) candidate configuration, the LTM candidate configuration including an MCG-LTM candidate configuration and an SCG-LTM candidate configuration; initiating an LTM cell switch; and subsequent to the initiating of the LTM cell switch, second communicating with the RAN in accordance with at least one of the MCG-LTM candidate configuration or the SCG-LTM candidate configuration.

[0259] Example 2. The method of example 1, wherein the UE is in single connectivity with the MN using the MCG.

[0260] Example 3. The method of example 1, wherein the UE is in dual connectivity (DC) with the MN using the MCG and a secondary node (SN) using a secondary cell group (SCG).

[0261] Example 4. The method of any one of examples 2-3, wherein the second communicating includes: communicating with the MN in accordance with the MCG-LTM candidate configuration.

[0262] Example 5. The method of any one of examples 2-3, wherein the MN is a source MN, and the second communicating includes: communicating with a second MN in accordance with the MCG-LTM candidate configuration.

[0263] Example 6. The method of any one of examples 1-5, wherein the MCG-LTM candidate configuration includes an LTM candidate primary cell (PCell) configuration, and the second communicating with the RAN is via a PCell in accordance with the MCG-LTM candidate configuration.

[0264] Example 7. The method of example 3, wherein the SN is a source SN, and the second communicating includes: communicating with a second SN in accordance with the SCG-LTM candidate configuration.

[0265] Example 8. The method of example 3, wherein the second communicating includes: communicating with the SN in accordance with the SCG-LTM candidate configuration.

[0266] Example 9. The method of any one of examples 7-8, wherein the SCG-LTM candidate configuration includes an LTM candidate primary secondary cell (PSCell) configuration, and the second communicating by the UE with the RAN is via a PSCell in accordance with the LTM candidate PSCell configuration.

[0267] Example 10. The method of any one of examples 2-6 in combination with the method of any one of examples 7-9.

[0268] Example 11. The method of example 10, further comprising: determining that the LTM candidate configuration includes the SCG-LTM candidate configuration, and the method of any one of examples 7-9 is performed responsive to the determination.

[0269] Example 12. The method of any one of examples 1-11, wherein: the method further comprises receiving, from the MN, an LTM cell switch command; and the initiating of the LTM cell switch is responsive to the received command.

[0270] Example 13. The method of any one of examples 2-6, wherein: the method further comprises detecting a radio link failure (RLF); and the initiating of the LTM cell switch includes initiating the LTM cell switch responsive to the detection.

[0271] Example 14. The method of example 13, wherein: the method further includes the method of any one of examples 7-9; and the communicating with a source SN or with a secondary SN using a secondary cell group (SCG) in accordance with the SCG-LTM candidate configuration is subsequent to the communicating with the RAN in accordance with the MCG-LTM candidate configuration.

[0272] Example 15. The method of example 14, further comprising determining that the LTM candidate configuration includes the SCG-LTM candidate configuration; and based on the determining, performing the method of any one of examples 7-8.

[0273] Example 16. The method of example 4, wherein: the first communicating of the UE with the RAN in DC is (i) with the MN using the MCG and via a serving PCell, and (ii) with a secondary node (SN) using a secondary cell group (SCG) and via a serving PSCell; the method further comprises receiving, from the SN, an LTM cell switch command, and the initiating of the LTM cell switch is responsive to the received command; and the second communicating includes communicating with the RAN via a second PSCell in accordancewith an LTM candidate PSCell configuration included in the SCG-LTM candidate configuration.

[0274] Example 17. The method of example 16, wherein the second PSCell is supported by the SN.

[0275] Example 18. The method of example 16, wherein the SN is a source SN, and the second PSCell is supported by a second SN.

[0276] Example 19. The method of any one of examples 16-18, wherein: the MCG-LTM candidate configuration includes MCG configuration parameters; and the communicating with the MN in accordance with the MCG-LTM candidate configuration includes communicating with the MN via the serving PCell in accordance with the MCG configuration parameters.

[0277] Example 20. The method of example 19, wherein the MCG-LTM candidate configuration excludes any LTM candidate PCell configuration.

[0278] Example 21. The method of example 3, wherein: the first communicating with the RAN in DC is (i) with the MN using the MCG and via a serving PCell, and (ii) with the SN using an SCG and via a serving PSCell; the initiating of the LTM cell switch includes initiating an LTM cell switch for the SCG; and the second communicating includes communicating with the RAN via a second PSCell in accordance with an LTM candidate PSCell configuration included in the SCG-LTM candidate configuration.

[0279] Example 22. The method of example 21, wherein the second PSCell is supported by the SN.

[0280] Example 23. The method of example 21, wherein the SN is a source SN and the second PSCell is supported by a second SN.

[0281] Example 24. The method of any one of examples 21-23, further comprising determining that the LTM candidate configuration includes the MCG-LTM configuration; and wherein the second communicating includes communicating, based on the determining, with the RAN via a second PCell in accordance with an LTM candidate PCell configuration included in the MCG-LTM candidate configuration.

[0282] Example 25. The method of example 24, wherein the second PCell is supported by the MN.

[0283] Example 26. The method of example 24, wherein the second PCell is supported by a second MN.

[0284] Example 27. The method of any one of examples 1-3, wherein: the initiating of the LTM cell switch includes initiating an LTM cell switch for the MCG; and the second communicating with the RAN is in accordance with the MCG-LTM candidate configuration.

[0285] Example 28. The method of example 27, wherein the second communicating with the RAN is via a PCell in accordance with the MCG-LTM candidate configuration.

[0286] Example 29. The method of example 28, wherein the MCG-LTM candidate configuration includes an LTM candidate PCell configuration.

[0287] Example 30. The method of any one of examples 27-29, further comprising determining that the LTM candidate configuration includes the SCG-LTM candidate configuration; and the second communicating includes communicating, based on the determining, with the RAN in accordance with the SCG-LTM candidate configuration.

[0288] Example 31. The method of example 30, wherein the communicating with the RAN in accordance with the SCG-LTM candidate configuration is via a PSCell in accordance with the SCG-LTM candidate configuration.

[0289] Example 32. The method of example 31, wherein the SCG-LTM candidate configuration includes an LTM candidate PSCell configuration.

[0290] Example 33. The method of example 32, wherein the PSCell is supported by a source SN.

[0291] Example 34. The method of example 32, wherein the PSCell is supported by a second SN.

[0292] Example 35. A user equipment (UE) comprising processing hardware configured to perform the method of any one of examples 1-34.

[0293] Example 36. A method implemented in a radio access network (RAN), the method comprising: communicating, by the RAN, with a user equipment (UE) in connectivity with the RAN via a master node (MN) using a master cell group (MCG); and transmitting, to the UE, a lower-layer triggered mobility (LTM) candidate configuration for the UE to utilize for an LTM cell switch, the LTM candidate configuration including an MCG-LTM candidate configuration and an SCG-LTM candidate configuration.

[0294] Example 37. The method of example 36, wherein the UE is in single connectivity with the MN using the MCG.

[0295] Example 38. The method of example 36, wherein the UE is in dual connectivity (DC) with the MN using the MCG and a secondary node (SN) using a secondary cell group (SCG).

[0296] Example 39. The method of any one of examples 36-38, wherein the communicating includes communicating with the UE in DC via the MN using the MCG and via a serving primary cell (PCell).

[0297] Example 40. The method of example 39, wherein: the MCG-LTM candidate configuration includes MCG configuration parameters; and the method further comprises communicating, subsequent to the LTM cell switch, with the UE via the serving PCell in accordance with the MCG configuration parameters.

[0298] Example 41. The method of example 40, wherein the MCG-LTM candidate configuration excludes any LTM candidate PCell configuration.

[0299] Example 42. The method of example 40, wherein the MCG-LTM candidate configuration includes an LTM candidate PCell configuration.

[0300] Example 43. The method of any one of examples 36-42, wherein the SCG-LTM candidate configuration includes an LTM candidate primary secondary cell (PSCell) configuration.

[0301] Example 44. The method of any one of examples 36-43, wherein the communicating is first communicating, and the method further comprises: subsequent to the LTM cell switch, second communicating with the UE in accordance with at least one of the MCG-LTM candidate configuration or the SCG-LTM candidate configuration.

[0302] Example 45. The method example 44, wherein the second communicating includes: communicating with the UE via a source SN in accordance with the SCG-LTM candidate configuration.

[0303] Example 46. The method of example 44, wherein the second communicating includes: communicating with the UE via a second SN in accordance with the SCG-LTM candidate configuration.

[0304] Example 47. The method of any one of examples 45-46, wherein the SCG-LTM candidate configuration includes an LTM candidate PSCell configuration, and the second communicating with the UE is via a PSCell in accordance with the LTM candidate PSCell configuration.

[0305] Example 48. The method of example 47, wherein: the first communicating with the UE is via a serving PSCell of a secondary cell group (SCG), and the PSCell in accordance with the LTM candidate PSCell configuration is a second PSCell of the SCG.

[0306] Example 49. The method of example 44, wherein the first communicating is via a serving PCell of the MCG, and the second communicating includes communicating with the UE via a second PCell in accordance with a LTM candidate PCell configuration included in the MCG-LTM candidate configuration.

[0307] Example 50. The method of example 49, wherein the second PCell is supported by the MN.

[0308] Example 51. The method of example 49, wherein the MN is a source MN, and the second PCell is supported by a second MN.

[0309] Example 52. The method of example 44, wherein the MN is a source MN, and the second communicating includes: communicating with the UE in accordance with the MCG-LTM candidate configuration via a second MN.

[0310] Example 53. The method of example 52, wherein the communicating with the UE in accordance with the MCG-LTM candidate configuration via the second MN is via a PCell supported by the second MN.

[0311] Example 54. The method of example 53, wherein the MCG-LTM candidate configuration includes an LTM candidate PCell configuration, and the second communicating with the UE via the PCell is in accordance with the LTM candidate PCell configuration.

[0312] Example 55. The method of any one of examples 36-54, further comprising transmitting, to the UE, a command to initiate the LTM cell switch, and the LTM cell switch of the UE is responsive to the command.

[0313] Example 56. The method of example 55, wherein the transmitting of the command to initiate the LTM cell switch is via the MN.

[0314] Example 57. The method of example 55, wherein the transmitting of the command to initiate the LTM cell switch is via a source secondary node (SN).

[0315] Example 58. The method of any one of examples 36-54, further comprising detecting that the UE has initiated the LTM cell switch.

[0316] Example 59. A radio access network (RAN) node comprising processing hardware configured to perform the method of any one of examples 36-58.

[0317] The following description may be applied to the description above.

[0318] 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.

[0319] In some implementations, “message” is used and can be replaced by “information element (IE)”, and vice versa. In some implementations, “IE” is used and can be replaced by “field”, and vice versa. In some implementations, “configuration” can be replaced by “configurations” or “configuration parameters”, and vice versa. In some implementations, the “LTM command” can be replaced by “serving cell change command”, “Layer 1 / Layer 2 LTM cell switch command”, “lower layer switching command” or “lower layer serving cell change command”. In some implementations, “some” means “one or more”. In some implementations, “at least one” means “one or more”. In some implementations, the “DU configuration” can be replaced by “cell group configuration”. In some implementations, the “cell index” can be replaced with “serving cell index”, “LTM cell index”, “special cell (SpCell) index”, “PCell index” or “PSCell index”. In some implementations, the “serving” can be replaced by “source”. In some implementations, the “measurement report” can be replaced by “measurement result(s)” or “CSI report”. In some implementations, the “early TA acquisition” can be replaced by “early UL timing synchronization” or “early ULsynchronization”. In some implementations, the “early TA acquisition on a / the candidate cell” can be replaced by “early UL timing synchronization with a / the candidate cell” or “early UL synchronization with a / the candidate cell”. In some implementations, “include” can be replaced by “comprise”. In some implementations, “exclude” can be replaced by “refrain from including”. In some implementations, “Handover Request” and “Handover Request Acknowledge” described above are for illustration of the 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, “SN Request”, “SN Confirm”, “SN Request” and “SN Request Acknowledge” described above are for illustration of the invention and can be replaced by messages with general names. For example, the “SN Required message” can be replaced by a SN-to-MN message. In another example, the “SN Confirm message” can be replaced by a MN-to-SN message. In some implementations, the “LTM MCG” and “MCG LTM” are interchangeable. In some implementations, “SCG LTM” and “LTM SCG” are interchangeable. In some implementations, the “SCG LTM reference configuration” represents SCG configuration parameters of an LTM reference configuration, and the “MCG LTM reference configuration” represents MCG configuration parameters of the LTM reference configuration. In some implementations, the “SN” can be replaced by “S-Node”.

[0320] 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 includeone or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0321] Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules may 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.

[0322] 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.

[0323] Upon reading this disclosure, those of skill in the art will appreciate still additional and alternative structural and functional designs for handling mobility between base stations through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

Claims

1. What is claimed is:

1. A method implemented in a user equipment (UE), the method comprising: first communicating with a radio access network (RAN) in single connectivity with a master node (MN) using a master cell group (MCG);receiving, from the MN, a lower-layer triggered mobility (LTM) candidate configuration, the LTM candidate configuration including an MCG-LTM candidate configuration and an SCG-LTM candidate configuration;initiating an LTM cell switch; andsubsequent to the initiating of the LTM cell switch, second communicating with the RAN in accordance with at least one of the MCG-LTM candidate configuration or the SCG-LTM candidate configuration.

2. The method of claim 1, wherein:the second communicating includes communicating with the MN in accordance with the MCG-LTM candidate configuration.

3. The method of claim 2, wherein at least one of:the MN is a source MN, and the second communicating includes communicating with a second MN in accordance with the MCG-LTM candidate configuration; orthe MCG-LTM candidate configuration includes an LTM candidate primary cell (PCell) configuration, and the second communicating with the RAN is via a PCell in accordance with the MCG-LTM candidate configuration.

4. The method of any one of claims 1-3, wherein:the second communicating includes communicating with a secondary node (SN) in accordance with the SCG-LTM candidate configuration.

5. The method of claim 4, wherein:the SCG-LTM candidate configuration includes an LTM candidate primary secondary cell (PSCell) configuration, and the second communicating with the RAN is via a PSCell in accordance with the SCG-LTM candidate configuration.Ill6. The method of any one of claims 4-5,further comprising determining that the LTM candidate configuration includes the SCG-LTM candidate configuration; andwherein the method of any one of claims 3-4 is performed responsive to the determining.

7. The method of any one of claims 1-6, wherein the second communicating includes communicating with the RAN in accordance with the SCG-LTM candidate configuration subsequent to communicating with the RAN in accordance with the MCG-LTM candidate configuration.

8. The method of any one of claims 1-7, wherein one of:the method further comprises receiving, from the MN, an LTM cell switch command and the initiating of the LTM cell switch is responsive to the received command;the method further comprises detecting a radio link failure (RLF) and the initiating of the LTM cell switch includes initiating the LTM cell switch responsive to the detection; or the initiating of the LTM cell switch includes initiating an LTM cell switch for the MCG.

9. A user equipment (UE) comprising processing hardware configured to perform the method of any one of claims 1-8.

10. A method implemented in a radio access network (RAN), the method comprising:first communicating with a user equipment (UE) in single connectivity with the RAN via a master node (MN) using a master cell group (MCG); andtransmitting, to the UE, a lower-layer triggered mobility (LTM) candidate configuration for the UE to utilize for an LTM cell switch, the LTM candidate configuration including an MCG-LTM candidate configuration and an SCG-LTM candidate configuration.

11. The method of claim 10, further comprising:subsequent to the LTM cell switch, second communicating with the UE in accordance with at least one of the MCG-LTM candidate configuration or the SCG-LTM candidate configuration.

12. The method of claim 11, wherein the second communicating, subsequent to the LTM switch, includes communicating with the UE in accordance with the SCG-LTM candidate configuration.

13. The method of claim 11, wherein the second communicating, subsequent to the LTM switch, includes communicating with the UE via a primary secondary cell (PSCell) in accordance with an LTM candidate PSCell configuration included in the SCG-LTM candidate configuration.

14. The method of any one of claims 11-13, wherein the second communicating, subsequent to the LTM switch, includes communicating with the UE in accordance with the MCG-LTM candidate configuration.

15. The method of claim 14, wherein the second communicating, subsequent to the LTM switch, includes communicating with the UE via a primary cell (PCell) in accordance with an LTM candidate PCell configuration included in the MCG-LTM candidate configuration.

16. The method of any one of claims 11-15, wherein the first communicating is via a serving PCell of the MCG, and the second communicating includes communicating with the UE via a second PCell in accordance with the MCG-LTM candidate configuration.

17. The method of claim 16, wherein one of:the second PCell is supported by the MN; orthe MN is a source MN and the second PCell is supported by a second MN.

18. The method of any one of claims 10-17, wherein:the method further comprises transmitting, to the UE, a command to initiate the LTM cell switch, and the LTM cell switch of the UE is responsive to the command; orthe method further comprises detecting that the UE has initiated the LTM cell switch.

19. A radio access network (RAN) node comprising processing hardware configured to perform the method of any one of claims 10-18.

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