Methods and devices enabling early the timing synchronization with a target cell

Abstract

Methods and devices enable a user equipment (UE) to acquire early timing advance (TA) for synchronizing with a target cell of a lower-layer triggered mobility (LTM) procedure for cell switching. The UE receives, via a serving cell, an LTM configuration of an LTM procedure for switching to a target cell, and then receives an early TA acquisition configuration for acquiring a TA value enabling the UE to synchronize with the target cell.

Description

METHODS AND DEVICES ENABLING EARLY THE TIMING SYNCHRONIZATION WITH A TARGET CELLFIELD OF THE DISCLOSURE

[0001] This document describes methods and devices operating in wireless communication systems such as (but not limited to) the ones described in 3rdGeneration Partnership Project (3GPP) technical specifications (TSs). More particularly, the methods and devices enable determining early timing advance (TA) value for synchronizing a user equipment (UE) with a target cell, before the UE starts a lower-layer triggered mobility (LTM) procedure to switch from communicating via a serving cell to communicating via the target cell.BACKGROUND

[0002] This background section is provided for the purpose of generally presenting the problem solved and the operating context of later-described embodiments enabling early timing synchronization of a UE with a target cell. 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 patent application.

[0003] In telecommunication systems, the Packet Data Convergence Protocol (PDCP) sublayer of the radio protocol stack provides services such as transfer of userplane data, ciphering, integrity protection, etc. For example, the PDCP layer defined for the Evolved Universal Terrestrial Radio Access (EUTRA) radio interface (e.g., in 3GPP TS 36.323) and for the New Radio (NR) (e.g., in 3GPP TS 38.323) provides sequencing of protocol data units (PDUs) in the uplink direction (i.e. , from a UE to a base station (BS)) as well as in the downlink direction (from the BS to the UE). The PDCP sublayer provides signaling radio bearers (SRBs) and data radio bearers (DRBs) to the Radio Resource Control (RRC) sublayer. A UE and a BS may use SRBs to exchange RRC messages as well as non-access stratum (NAS) messages and DRBs to transport data on a user plane.

[0004] EUTRA and NR UEs may use several types of SRBs and DRBs. When operating in dual connectivity (DC), the cells associated with the BS operating as the master node (MN) define a master cell group (MCG), and the cells associated with the BS operating as the secondary node (SN) define the secondary cell group (SCG). So- called SRB1 resources carry RRC messages, which in some cases include NAS messages over the dedicated control channel (DCCH). SRB2 resources carry 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 (also referred to as MCG SRBs) allow the UE and the MN to exchange RRC messages related to the MN and embed RRC messages related to the SN. SRB3 (referred to as SCG SRB) allows the UE and the SN to exchange RRC messages related to the SN. Split SRBs allow the UE to exchange RRC messages directly with the MN via lower-layer resources of the MN and the SN. DRBs using the lower-layer resources of only the MN may be referred to as MCG DRBs, DRBs using the lower- layer resources of only the SN may be referred to as SCG DRBs, and DRBs using the lower-layer resources of both the MCG and the SCG may be referred to as split DRBs.

[0005] The UE may use concurrently resources of two (or more) radio access network (RAN) nodes (e.g., BSs or components of distributed BS), interconnected by a backhaul. When these RAN nodes support different radio access technologies (RATs), this type of connectivity is referred to as Multi-Radio Dual Connectivity (MR-DC). When a UE operates in MR-DC, one BS operates as an MN that covers a primary cell (PCell), and at least one other BS operates as an SN that covers a primary secondary cell (PSCell). Thus, the UE communicates with the MN (via the PCell) and with the SN (via the PSCell).

[0006] Alternatively, the UE uses resources of one BS at a time. The BS and / or the UE may determine that the UE should establish a radio connection with another BS. For example, the BS currently communicating with the UE may determine to hand the UE over to another (second) BS and initiate a handover procedure. When the UE moves from the coverage area of a current serving cell to coverage area of another cell, the RAN prompts the UE to perform a serving cell change (i.e. , switch from communicating via the current serving cell to communicating via the other cell).Conventionally, in preparation for the serving cell change, the RAN configures the UE to transmit layer 3 (L3) measurement results. Based on the L3 measurement results received from the UE, the RAN transmits an RRC reconfiguration message for reconfiguring and synchronizing the UE with the other cell (e.g., the RRC reconfiguration message may include a ReconfigurationWithSync information element, (IE) as defined in 3GPP TSs). Note that, in this document, messages and lEs defined in contemporaneous 3GPP TSs are italicized, and repeatedly invoking the source of such definitions (i.e. , 3GPP TSs made public before this document) is generally omitted.

[0007] When the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN releases the at least one SCell due to the change of the PCell or the PSCell. Therefore, the serving cell change causes complete layer 2 (L2) and layer 1 (L1) resets, leading to a long latency, a large overhead, and a long communication interruption time. New mobility techniques called low-layer triggered mobility (LTM, also referred to as L1 / L2 triggered mobility) have recently been developed and adopted. An LTM procedure (often called shorter “LTM” in this document) is a more efficient procedure for cell switching providing a reduced latency and less overhead than the conventional L3-based cell switching. In LTM, the decision to hand over the UE from one network entity (NE, e.g., a BS or a component of a distributed BS) to another NE is primarily determined by the lower layers of the network protocol stack, such as the physical and data link layers. That is, the NE initiates and controls the handover process based on a lower-layer-related (e.g., L1 ) criteria like signal strength, quality, and resource availability. When a UE connection quality deteriorates and another better connection is available (as revealed, for example, by UE’s L1 measurement report), the NE directs the UE to switch to a different cell that can provide a better connection. In contrast, the L3 layer triggered mobility means an upperlayer NE (such as a Mobility Management Entity in Long Term Evolution LTE / 4G or a Mobility Anchor Point in Mobile IP) decides to trigger a handover process based on higher-layer parameters, such as network load, service quality, or user preferences.

[0008] When a UE switches from a serving cell to a target cell in a RAN using LTM, the UE has to synchronize with the target cell. Only after a random access (RA) procedure, the UE learns the TA to apply for synchronizing with the target cell so thatthe UE can start to communicate via the target cell. The RA procedure often delays communication via the target cell.SUMMARY

[0009] In order to avoid delays caused by determining a TA value for synchronizing with a target cell after initiating an LTM procedure, the UE and a network entity (NE) perform early TA value acquisition, before the LTM procedure starts. For example, the UE and the NE may perform a random access (RA) procedure. The NE orchestrates (i.e. , configures and triggers) the RA procedure for obtaining the TA value, before transmitting the LTM command. The UE then receives the TA value, from the NE, which may be a radio access network (RAN) node, a distributed unit (DU), or a central unit (CU) of a base station.

[0010] The NE may transmit, to the UE, an early TA acquisition configuration configuring the UE for the RA procedure on the target cell. The early TA acquisition configuration may indicate an RA preamble. The NE may then prompt the UE to initiate the RA procedure (by transmitting the indicated preamble if known) thereby enabling the NE to obtain the TA value for synchronizing the UE with the target cell. The NE may refrain from early TA acquisition when (1 ) the UE does not support early TA acquisition, (2) there is no available RA preamble on the target cell, (3) the CU does not request an early TA acquisition, etc. The NE may transmit the TA value to the UE within the LTM command or via an RA response message (before transmitting the LTM command).BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated in and constitute a part of this document, illustrate one or more embodiments as well as the context of the techniques for early timing synchronization. These drawings together with the detailed description, explain these embodiments. The same or similar reference numbers may denote the same or similar functions.

[0012] Fig. 1A is a block diagram of an example system in which devices communicating via a radio access network (RAN) perform the techniques described in this section for enabling early the timing synchronization with a target cell of a configured LTM procedure for cell switching.

[0013] Fig. 1 B is a block diagram of a BS that can operate in the system of Fig. 1 A.

[0014] Fig. 2A illustrates a protocol stack usable by the UE of Fig. 1 A to communicate with BSs.

[0015] Fig. 2B illustrates a protocol stack usable the UE of Fig. 1A to communicate with a CU and a DU of a distributed BS.

[0016] Fig. 2C is a block diagram illustrating structural elements of a UE and an NE configured to perform methods enabling early the timing synchronization of a UE with a target cell of a configured LTM procedure for cell switching according to an embodiment.

[0017] Fig. 3 is a signal diagram illustrating an LTM performed by a UE in communication with a BS including a DU and a CU according to an embodiment.

[0018] Fig. 4 is a signal diagram illustrating an LTM performed by a UE in communication with a BS including a source-DU (S-DU), a target DU (T-DU), and a CU.

[0019] Figs. 5A and 5B are signal diagrams illustrating LTMs performed by UEs in communication with a master node (MN) and a secondary node (SN) including a DU and a CU operating as an SN according to other embodiments.

[0020] Figs. 6A and 6B are signal diagrams illustrating LTMs performed by UEs in communication with an MN and an SN including an S-DU, a T-DU, and a CU.

[0021] Figs. 7A and 7B are signal diagrams illustrating LTMs performed by UEs in communication with a distributed BS including a master-DU (M-DU), a secondary DU (Se-DU), and a CU.

[0022] Figs. 8A and 8B are signal diagrams illustrating LTMs performed by UEs in communication with a distributed BS including an M-Dll, an S-Dll, a T-Dll, and a CU.

[0023] Figs. 9A and 9B depict flow diagrams of an NE (e.g., a BS or a DU, called generic “RAN”) method for early TA acquisition according to various embodiments.

[0024] Fig. 10 depicts a flow diagram of a UE method for early TA acquisition according to an embodiment.

[0025] Figs. 11 A-11 C depict flow diagrams of DU methods for early TA acquisition according to various embodiments.

[0026] Figs. 12A-12C depict flow diagrams of (candidate or target) DU methods for early TA acquisition according to other embodiments.

[0027] Figs. 13A and 13B depict flow diagrams of (source) DU methods for early TA acquisition according to various embodiments.

[0028] Figs. 14A and 14B depict flow diagrams of CU methods for early TA acquisition according to various embodiments.

[0029] Figs. 15A-15C depict flow diagrams of DU methods for early TA acquisition related to intra-DU cell switch according to various embodiments.

[0030] Figs. 16A-16F depict flow diagrams illustrating CU methods for early TA acquisition according to various embodiments.DETAILED DESCRIPTION OF THE DRAWINGS

[0031] As discussed in more detail below, NEs and UEs according to various embodiments enable acquiring early (before an LTM command) a TA for synchronizing with a target cell.

[0032] Fig. 1A is a schematic representation of a wireless communication system 100 including devices that communicate via a RAN to perform various techniques related to acquiring early a TA for synchronizing with a target cell of an LTM cell switching. The wireless communication system 100 includes a UE 102, BSs 104 and 106, and a core network (CN) 110. The UE 102 initially connects to the BS 104. The BS 104 may perform a secondary node (SN) addition procedure to configure the UE 102 to operate in dual connectivity (DC) with the BS 104 and the BS 106. The BSs 104 and 106 then operate as an MN and as an SN respectively for the UE 102. In various configurations of the wireless communication system 100, the BS 104 may be a master eNB (MeNB) or a master gNB (MgNB), and the BS 106 may be a secondary gNB (SgNB). The UE 102 may employ the same RAT (such as EUTRA or NR) or different RATs to communicate with the BS 104 and the BS 106. When the BS 104 is an MeNB and the BS 106 is a SgNB, the UE 102 operates in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB. The MeNB or the SeNB may be an enhanced Long Term Evolution (LTE) eNB, which is able to communicate with a fifth-generation (5G) core and gNB, instead of an eNB. When the BS 104 is a Master ng-eNB (Mng-eNB) and the BS 106 is a SgNB, the UE 102 is in a next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. When the BS 104 is an MgNB and the BS 106 is an SgNB, the UE 102 is in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the BS 104 is an MgNB and the BS 106 is a secondary ng-eNB (Sng-eNB), the UE 102 is in NR-EUTRA DC (NE-DC) with the MgNB and the Sng-eNB.

[0033] When the UE 102 switches from a cell covered by the BS 104 to a cell covered by BS 106, the BSs 104 and 106 operate as the source BS (S-BS) and a target BS (T-BS), respectively. The UE 102 may operate in DC with the BS 104 and an additional BS (not shown in Fig. 1A) prior to the handover. The UE 102 may continue to operate in DC with the base station 106 and the additional BS or may operate in singleconnectivity (SC) with the BS 106, after completing the handover (the BSs 104 and 106 operating as a source MN (S-MN) and a target MN (T-MN), respectively).

[0034] The CN 110 may be an evolved packet core (EPC) 111 or a 5G core (5GC) 160, both of which are depicted in Fig. 1A. The BS 104 may be an eNB supporting an S1 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. The BSs 104 and 106 may support an X2 or Xn interface for directly exchanging messages with each other during the scenarios discussed below. Among other components, the EPC 111 may 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. 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 may include a User Plane Function (UPF) 162, 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. The SMF 166 is configured to manage PDU sessions.

[0035] As illustrated in Fig. 1A, the BS 104 supports cells 124A, 124B and 124C, while the BS 106 supports cell 126. The cells 124A and 126 partially overlap, so that the UE 102 may communicate in DC with the BS 104 and the BS 106 (i.e. , one of the BSs 104 and 106 being the MN and the other being the SN). The BS 104 may support additional cell(s) such as cells 124B and 124C, and the BS 106 may support additional cell(s) (not shown in Fig. 1A). The cells 124A, 124B, and 124C partially overlap, so that the UE 102 may communicate in carrier aggregation (CA) with the BS 104. The BS 104 may 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 BS 104 and the BS106, one of the BSs 104 and 106 operates as an MeNB, an Mng-eNB or an MgNB, and the other operates as an SgNB or an Sng-eNB.

[0036] The wireless communication system 100 may include any suitable number of BSs supporting NR cells and / or EUTRA cells. The EPC 111 or the 5GC 160 may be connected to any suitable number of BSs supporting NR cells and / or EUTRA cells. Although the examples described below refer to specific CN types (EPC, 5GC) and RAT types (5G NR and EUTRA), the techniques described in this section may be integrated into 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.

[0037] With continued reference to Fig. 1A, the BS 104 is equipped with processing hardware 130 that includes one or more general-purpose processors (e.g., CPUs) and a non-transitory computer-readable memory storing instructions for the one or more general-purpose processors to execute. Additionally or alternatively, the processing hardware 130 may include one or more special-purpose processing units. The processing hardware 130 may 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 may also include a MAC controller 134 configured to perform MAC functions with one or more UEs. The MAC functions include an RA (RA) procedure, managing UL timing advance for the one or more UEs, and / or communicating UL / DL MAC PDUs with the one or more UEs. The MAC functions include lower triggered mobility (LTM) related functions as described below. The processing hardware 130 may 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 BS 104 operates as an MN relative to an SN or as an SN relative to an MN. The BS 106 may include processing hardware 140 that is similarto processing hardware 130. In particular, components 142, 144, and 146 are similar to the components 132, 134, and 136, respectively.

[0038] The UE 102 is equipped with processing hardware 150 that may 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 one or more special-purpose processing units. The PHY controller 152 is configured to receive data and control signals on physical DL channels and / or DL reference signals with the BS 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126) and / or one or more TRPs. The PHY controller 152 is also configured to transmit data and control signals on physical UL channels and / or UL reference signals with the BS 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126) and / or one or more TRPs. The processing hardware 150 may also include a MAC controller 154 configured to perform MAC functions with BS 104 and / or 106. For example, the MAC functions include an RA procedure, managing UL timing advance for the one or more UEs, and communicating UL / DL MAC PDUs with the BS 104 and / or 106. The MAC functions may also include LTM related functions as described below. The processing hardware 150 may further include an RRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack.

[0039] In operation, the UE 102 in DC may use a radio bearer (e.g., a DRB or an SRB) that at different times terminates at the MN 104 or at the SN 106. The UE 102 may apply one or more security keys when communicating on the radio bearer, in the UL (from the UE 102 to a BS) and / or the DL (from a BS to the UE 102) direction.

[0040] Fig. 1 B is a block diagram of a distributed BS 170 including a centralized unit (CU) and a distributed unit (DU) usable in the system of Fig. 1A (i.e., the BS 170 may operate as the BS 104 or 106). The BS 170 includes a centralized unit (CU) 172 and a distributed unit (DU) 174 (it may include plural DUs but only one is illustrated in this figure). The CU 172 may include a module 172A specialized in managing control plane communications and a module 172B specialized in user plane communications, these modules communicating with one another via an E1 interface. The CU 172 may be equipped with processing hardware such as 130 or 140 described above.

[0041] The DU 174 which communicates with the CU (or CU modules) via F1 or W1 interfaces is also equipped with processing hardware (such as 130 or 140 described above) that includes one or more general-purpose processors (e.g., CPUs and / or special-purpose processing units) and a non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors. The processing hardware may include a medium access control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., an RA procedure) and a radio link control (RLC) controller configured to manage or control one or more RLC operations or procedures when the DU operates as an MN or an SN. The process hardware may include further a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0042] Fig. 2A is a block diagram of a protocol stack 200 that the UE 102 may use to communicate with an eNB / ng-eNB 201A or a gNB 201 B (e.g., one or more of the BSs 104, 106). In the stack 200, a physical layer (PHY) 202A of EUTRA provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logical channels to the EUTRA RLC sublayer 206A. The EUTRA RLC sublayer 206A in turn provides RLC channels to an EUTRA PDCP sublayer 208 and, in some cases, to an NR PDCP sublayer 210. Similarly, the NR PHY 202B provides transport channels to the NR MAC sublayer 204B, which in turn provides logical channels to the NR RLC sublayer 206B. The NR RLC sublayer 206B in turn provides data transfer services to the NR PDCP sublayer 210. The NR PDCP sublayer 210 in turn can provide data transfer services to Service Data Adaptation Protocol (SDAP) 212 or a radio resource control (RRC) sublayer (not shown in Fig. 2A). The UE 102, in some embodiments, supports both the EUTRA and the NR stack as shown in Fig. 2A, to support handover between EUTRA and NR BSs and / or to support DC over EUTRA and NR interfaces. Further, as illustrated in Fig. 2A, the UE 102 can support layering of NR PDCP 210 over EUTRA RLC 206A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

[0043] 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 are referred to as service data units (SDUs), and output packets (e.g., to the RLC layer 206A or 206B) that are referred to as protocol data units(PDUs). Except where the difference between SDlls and PDUs is relevant, this disclosure for simplicity refers to both SDlls and PDUs as “packets.”

[0044] On a control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide signaling radio bearers (SRBs) or RRC sublayer (not shown in Fig. 2A) to exchange RRC messages or non-access-stratum (NAS) messages, for example. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide Data Radio Bearers (DRBs) to support data exchange. Data exchanged on the NR PDCP sublayer 210 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0045] Fig. 2B illustrates, in a simplified manner, an example protocol stack 250, which the UE 102 may employ to 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 BSs 104 or 106 may 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.

[0046] Fig. 2C is a block diagram of a wireless communication system 255 illustrating structural elements of a UE 102 and an NE 280 configured to perform methods enabling early the timing synchronization of a UE with a target cell of a configured LTM procedure for cell switching according to an embodiment. The UE 102 and NE 280 may include additional functions and interfaces omitted from Fig. 2C in the interest of brevity. Signaling arrow generally represents both uplink and downlink signals transmitted between the UE 102 and the NE 280.

[0047] The UE 102 includes antennas connected to a radio frequency (RF) front end 291 , and at least one RF transceiver 292 (such as, an LTE transceiver, a 5G NR transceiver, and / or another transceiver) for communicating with the NE 280 or other NEs. The antennas and the RF front end 291 can be tuned to one or more frequency bands (e.g., subcarriers), for example, as defined by 3GPP LTE, 5G NR, and 6G communication standards and implemented by respective transceivers. The UE 102 also includes at least one processor 293 and computer-readable storage media (CRM)294. The processor(s) 293 may be a single or multiple-core processors, and CRM 294 includes any suitable memory / storage other than propagating signals. For example, memory / storage may include random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), and / or flash memory useable to store device data 295, an RA\ manager of early synchronization 296 and LTM-related executable instructions 297. The device data 295 stores instructions executable by processor(s) 293 to facilitate user-plane communication, control-plane signaling and user interaction for the UE 102. The RA manager of early synchronization 296 and the LTM-related executable instructions 297, which may be implemented not only as software but also as hardware logic and / or circuitry, causes various steps and actions associated with enabling acquisition of a TA value for synchronizing the UE 102 with a target cell early, before initiating the LTM cell switching.

[0048] The NE 280 as illustrated in Fig. 2C may provide functionality of a BS (for LTE, 5G, etc. RAT). The BS functionality may be distributed across multiple entities (e.g., a central unit, CU, a distributed unit, DU, and a radio unit, RU). The NE 280 includes antennas and an RF front end 281 and RF transceiver(s) 282 for communicating with UEs such as the UE 102 and other NEs. The NE’s antennas and RF front end 281 can be tuned to one or more frequency bands (e.g., subcarriers), for example as defined by 3GPP LTE, 5G NR, and 6G communication standards and implemented by RF transceiver(s) 282. The NE 280 includes one or more processor(s) 283 and CRM 284. The processor(s) 283 may include single or multiplecore processors, and the CRM 284 includes any suitable memory / storage except propagating signals. For example, memory / storage may include random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), and / or flash memory. The CRM 284 stores device data 285, which includes network scheduling data, radio resource management data, applications, and / or an operating system, which are executable by processor(s) 283 to enable wireless communication with the UE 102 as well as with other UEs and NEs. The CRM 284 also stores an early TA acquisition manager 286 and LTM control- related information 287. The early TA acquisition manager and the LTM control-related instructions 287 cause the NE to perform various steps and actions associated with early acquisition of the TA and the LTM cell switching. Further, the NE 280 also includes an inter-base station interface 288 and a core-network interface 289. The inter-base station interface 288 may be a standardized interface, such as an Xn and / or X2 interface, for exchanging user-plane and control-plane data with another NE. The core-network interface 289, which may be a standardized interface such as S1 , enables NE’s user-plane data and control-plane information exchange with core network functions and / or entities.

[0049] The signal diagrams in Figs. 3-8B illustrate scenarios in which an NE (e.g., a RAN node such as a BS, a DU and / or a CU) operating in the wireless communication system of Fig. 1A communicates with the UE 102. Events in Figs. 3-8B that are similar are labeled with similar reference numbers (e.g., event 316 is similar to event 416 of Figs 4A and 4B, event 516 of Fig. 5A, event 517 of Fig. 5B, event 616 of Fig. 6A, event 617 of Fig. 6B, event 716 of Fig. 7A, and event 717 of Fig. 7B), with differences discussed below where appropriate. With the exception of the differences shown in the figures and discussed below, any of the alternative embodiments 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.

[0050] Referring first to Fig. 3, in a scenario 300, the UE 102 communicates with the BS 104 that includes a CU 172 and a DU 174, the DU 174 managing communication with UEs via the cell 124A. The UE 102 initially communicates 302 with the DU 174 on the cell 124A using a serving DU configuration and communicates with the CU 172 via the DU 174 (e.g., using a serving CU configuration). In other words, the DU 174 is a serving DU that is a RAN node communicating with the UE 102. The UE 102 may communicate in CA with the DU 174 on the cell 124A and other cell(s) (also operated by DU 174) using the serving DU configuration. Alternatively, the UE 102 may communicate with the DU 174 on the cell 124A only. The UE 102 may communicate with the DU 174 on the cell 124A and / or other cell(s) via one or multiple TRPs. When the cell 124A is a PCell, the other cell(s) include SCell(s) and / or additional cell(s) associated with the PCell or an SCell. When the cell 124A is an SCell, and one of the other cell(s) is a PCell, the cells other than the PCell include SCell(s) and / or additionalcell(s) associated with the PCell or a SCell. In signal diagrams illustrated in Figs. 3 and 4, the BS 104 does not use CA, in signal diagrams illustrated in Figs. 5A-6B, the BS 104 is an SN, and in signal diagrams illustrated in Figs. 7A-8B, the BS 104 is both MN and SN.

[0051] Returning to signal diagram in Fig. 3, the UE 102 communicates 302 with the BS 104 on the cell 124A and / or other cell(s) via one or multiple TRPs. The UE 102 may communicate UL PDUs and / or DL PDUs with the BS 104 via radio bearers, which may include SRBs and / or DRB(s). The BS 104 may configure the radio bearers for the UE 102. The UL control signals may 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). The UE 102 may receive DL PDUs and / or DL control signals from the BS 104 on the cell 124A and / or other cell(s) via one or multiple TRPs. The DL control signals may include downlink control information (DCIs) and reference signals (e.g., synchronization signal block, channel state information reference signal(s) (channel state information reference signal(s) (CSI-RS(s))), and / or tracking reference signal(s)). For example, the BS 104 may transmit the DCIs on physical downlink control channel(s) (PDCCH(s)) monitored by the UE 102, on the cell 124A and / or other cell(s) via one or multiple TRPs.

[0052] The serving DU configuration may include physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. The DU 174 may transmit these configuration parameters to the CU 172. The CU 172 then generates one or more messages (e.g., RRC reconfiguration message(s)) including the configuration parameters and transmits the one or more messages to the UE 102 via the DU 174. Alternatively, the DU 174 may transmit the configuration parameters to the UE 102 directly. The serving DU configuration may be or include configuration parameters in a CellGroupConfig IE as defined in 3GPP TS 38.331 . The serving CU configuration may include PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. The serving CU configuration may be or include configuration parameters in a MeasConfig IE and / or a RadioBearerConfig IE as defined in 3GPP TS 38.331. Alternatively, the serving DU configuration may include a CSI-MeasConfig IE or configuration parameters for channelstate information (CSI) measurement and reporting. The LIE 102 may receive the serving CU configuration or the configuration parameters in the serving CU configuration from the CU 172 via the DU 174. Alternatively, the UE 102 may receive a portion of the serving CU configuration and / or a portion of the serving DU configuration from a BS other than the BS 104 and the remaining portion of these configuration parameters from the BS 104.

[0053] While communicating with the BS 104, the UE 102 transmits 304 at least one measurement report to the DU 174. The at least one measurement report includes Layer 1 (L1 ) measurement report(s) and / or Layer 3 (L3) measurement report(s) for at least one serving cell of the UE 102 and / or at least one non-serving cell. For each of the L3 measurement report(s), the DU 174 transmits 306 a DU-to-CU message that includes the L3 measurement report to the CU 172. The DU-to-CU message(s) may be F1 application protocol (F1AP) message(s) (e.g., UL RRC Message Transfer message(s)). Alternatively, the DU 174 may refrain from transmitting the L1 measurement report(s) to the CU 172 (i.e., step 306 is optional as suggested by the dashed arrow line). The at least one serving cell includes the cell 124A and / or other cell(s), and the at least one non-serving cell may include the cell 124B and / or the cell 124C. The serving DU configuration or the serving CU configuration includes at least one measurement configuration. The UE 102 may receive one or more RRC messages (e.g., RRCReconfiguration message(s)) including the at least one measurement configuration from the CU 172 via the DU 174 at 302. In accordance with the at least one measurement configuration, the UE 102 performs measurements and transmits 304 the at least one measurement report to the DU 174. The at least one measurement configuration may include L3 measurement configuration(s) (e.g., MeasConfig IE(s)) and / or L1 measurement configuration(s). The L1 measurement configuration(s) (e.g., CSI-MeasConfig IE(s)) may include L1 measurement resource configuration(s) and / or L1 measurement reporting configuration(s). The L1 measurement resource configuration(s) specify(specifies) reference signal(s) and / or resources of the reference signal(s) for the UE 102 to measure reference signals and obtain L1 measurement results. The reference signal(s) includes CSI-RS(s) and / or SSB(s). For example, the L1 measurement resource configuration(s) is / are CSI-ResourceConfig IE(s). In anotherexample, the L1 measurement reporting configuration(s) configures the manner in which the UE 102 transmits L1 measurement results / reports. For example, the L1 measurement report configuration(s) is / are CSI-ReportConfig IE(s). For example, the UE 102 transmits the L3 measurement report(s) to the CU 172 via the DU 174 in accordance with the L3 measurement configuration(s). The UE 102 transmits the L1 measurement report(s) to the DU 174 in accordance with the L1 measurement configuration(s) or L1 measurement reporting configuration(s). In one embodiment, the DU 174 does not transmit the L1 measurement report(s) to the CU 172.

[0054] The L1 measurement configuration(s), the L1 measurement resource configuration(s), and / or the L1 measurement reporting configuration(s) may be defined RRC IE(s) (e.g., in 3GPP TS 38.331 ) related to LTM. In some embodiments, each of the L1 measurement reporting configuration(s) includes a trigger event configuration configuring a trigger event to trigger the UE 102 to transmit a L1 measurement report. If the UE 102 detects the trigger event, the UE 102 transmits a L1 measurement report to the DU 174.

[0055] In some embodiments, (each of) the L1 measurement report(s) includes at least one L1 measurement result. For example, the at least L1 measurement result may include at least one L1 -reference signal received power (L1 -RSRP) value and / or at least one L1- Signal to Interference Noise Ratio (L1 -SINR) value. For each of the L1 measurement report(s), the UE 102 may transmit a PUCCH transmission including the L1 measurement report to the DU 174. That is, the UE 102 transmits each of the L1 measurement report(s) on a PUCCH to the DU 174. Alternatively, for each of the L1 measurement report(s), the UE 102 transmits a PUSCH transmission including the L1 measurement report to the DU 174. That is, the UE 102 transmits each of the L1 measurement report(s) on a PUSCH to the DU 174. In yet other alternatives, the UE 102 transmits a portion of the L1 measurement report(s) on PUCCH(s) and the rest of the L1 measurement report(s) on physical UL shared channel(s) (PUSCH(s)) to the DU 174. That is, for each of the portion of the L1 measurement report(s), the UE 102 transmits a PUCCH transmission including the L1 measurement report to the DU 174, and for each of the rest of the L1 measurement report(s), the UE 102 transmits a PUSCH transmission including the L1 measurement report to the DU 174. In someembodiments, each of the L1 measurement report(s) is a part of channel state information (CSI) (i.e. , a CSI component) or CSI. In some embodiments, the UE 102 includes other CSI component(s) in (each of) the PUCCH transmission(s) and / or PLISCH transmission(s) described above. In one embodiment, the other CSI component(s) include a channel quality indicator (CQI), a Precoding Matrix Indicator (PMI), a CSI-RS Resource Indicator (CRI), a Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Block Indicator (SSBRI), a Layer Indicator (LI), and / or a Rank Indicator (Rl). In some embodiments, the UE 102 does not transmit the L1 measurement report(s) in format of RRC message(s) to the DU 174.

[0056] In some embodiments, each of the L3 measurement report(s) includes at least one L3 measurement result. In some embodiments, the at least one L3 measurement result includes at least one RSRP (value) and / or at least one SINR (value). In one embodiment, the UE 102 transmits each of the L3 measurement report(s) on a PUSCH to the CU 172 via the DU 174. In some embodiments, each of the L3 measurement report(s) is an RRC message (e.g., MeasurementReport message). In some embodiments, each of the L3 measurement configuration(s) includes a particular measurement identity (e.g., measld) and each of the L3 measurement report(s) includes a particular measurement identity in a particular L3 measurement configuration. When the CU 172 receives a L3 measurement report including a measurement identity and a L3 measurement result from the UE 102 via the DU 174, so that the CU 172 is able to determine that the L3 measurement report is associated to a L3 measurement configuration identified by the measurement identity.

[0057] In some alternative embodiments, for each of the at least one measurement report (e.g., L1 measurement report(s)), the UE 102 transmits a MAC control element (CE) including the measurement report to the DU 174 in the event 304. To transmit the MAC CE(s), the UE 102 generates one or more MAC PDUs each including one or more of the MAC CE(s) to the DU 174 in the event 304.

[0058] In some embodiments, the UE 102 performs measurements on one or more reference signals in accordance with the at least one measurement configuration. The one or more reference signals may include one or more Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Blocks (SSBs) and / or one or more CSI-RSs. The LIE 102 obtains the at least one L1 measurement result and / or at least one L3 measurement result from the measurements. The DU 174 transmits the one or more reference signals on the cell 124A and other cell(s) (e.g., the cell 124B, the cell 124C and / or cell(s) not shown in Fig. 1 A).

[0059] After (e.g., in response to) receiving one or some of the at least one measurement report from the UE 102, the BS 104 (i.e., the CU 172 or DU 174) determines to prepare a first cell (e.g., the cell 124B) for LTM for the UE 102. In some embodiments, the BS 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the first cell could be used by the BS 104 to communicate with the UE 102. In some embodiments, the BS 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the first cell qualifies to be a candidate cell usable for communication with the UE 102. In some other embodiments, if the L3 measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than strength and / or quality of the cell 124A, and / or is better than strength and / or quality of the cell 124A by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. In yet other embodiments, if the L1 measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than signal strength and / or quality of the cell 124A, and / or is better than signal strength and / or quality of the cell 124A by a first predetermined threshold, the DU 174 determines to prepare the first cell for the UE 102. Alternatively, the BS 104 determines to prepare the first cell for the UE 102 regardless of whether a measure report is received from the UE 102 or not.

[0060] Upon 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 embodiments, the CU 172 includes a cell identity (ID) 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 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 response to the first CU-to-DU message, the DU 174 generates a first LTM DU configuration (referred to hereinafter as LTM DU configuration 1 ) for the UE 102, whichconfigures the first cell for LTM. The DU 174 then transmits 310 a first DU-to-CU message including the LTM DU configuration 1 to the CU 172 in response to the first CU-to-DU message. In some embodiments, the DU 174 includes the cell ID 1 together with the LTM DU configuration 1 in an IE of the first DU-to-CU message to indicate that the LTM DU configuration 1 is associated with the first cell (i.e., the cell ID 1 ). Upon determining to prepare the first cell, the DU 174 initiates transmission of the first DU-to- CU message to the CU 172 in response to a CU-to-DU message received from the CU 172.

[0061] In some embodiments, the DU 174 includes, in the first DU-to-CU message, the cell ID of the first cell associated with the LTM DU configuration 1 to indicate that the LTM DU configuration 1 is configured for or associated with the first cell. The CU 172 identifies the LTM DU configuration 1 is configured for or associated with the first cell. In some scenarios and embodiments, the CU 172 includes additional cell ID(s) (e.g., cell ID(s) 2, ... , N) in the first CU-to-DU message to prepare additional cell(s) (e.g., cell(s) 2, ... , N) for LTM for the UE 102, and the DU 174 includes additional LTM DU configuration(s) (e.g., LTM DU configuration(s) 2, ... , N) each configuring a particular cell of the additional cell(s), as described below. In such cases, the DU 174 includes, in the first DU-to-CU message, the additional cell ID(s) respectively associated with the additional LTM DU configuration(s) to indicate which LTM DU configuration is associated with which cell (ID). The cell(s) 1 and / or 2, ... , N are candidate cell(s).

[0062] In some embodiments, the CU 172 does not include a (reference) LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, ... , N (i.e., non-reference LTM DU configuration(s)) based on the reference LTM DU configuration, and includes the reference LTM DU configuration in the first DU-to-CU message. In other embodiments, the CU 172 includes a reference LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates the LTM DU configuration(s) 1 , and / or 2, .... N which are delta configuration(s) to augment the reference LTM DU configuration. In yet other embodiments, the CU 172 includes a reference LTM DU configuration (e.g., a first reference LTM DU configuration) in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DUconfiguration (e.g., a second reference LTM DU configuration) replacing the first reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, N based on the second reference LTM DU configuration, and includes the second reference LTM DU configuration in the first DU-to-CU message.

[0063] In some embodiments, the reference LTM DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some embodiments, the reference LTM DU configuration is CellGroupConfig IE defined, for example, in 3GPP TS 38.331 . In other embodiments, the reference LTM DU configuration includes configuration parameters in the CellGroupConfig IE. In some embodiments, the reference LTM DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and / or reporting.

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

[0065] After receiving the first DU-to-CU message, the CU 172 generates an RRC reconfiguration message (e.g., an RRCReconfiguration message) including the LTM DU configuration 1 , and transmits 316 a second CU-to-DU message including the RRC reconfiguration message to the DU 174. In some embodiments, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316. In other embodiments, the CU 172 does not include a / the reference LTM DU configuration in the RRC reconfiguration message 316. In some embodiments, if the CU 172 transmits the reference LTM DU configuration to the UE 102 during the event 302, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message 316. In other embodiments, if the CU 172 receives the reference LTM DU configuration from the DU 174, the CU 172 includes the LTM DU configuration in the RRC reconfiguration message 316. Otherwise, if the CU 172 does not receive a referenceLTM DU configuration from the DU 174, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message 316.

[0066] In some embodiments, the CU 172 includes the LTM DU configuration 1 and / or the LTM CU configuration 1 in a first container (e.g., a field / IE) and includes the first container (e.g., LTM configuration (e.g., LTM-Config IE)) in the RRC reconfiguration message of the events 316 and 318. In such cases, the CU 172 generates the first container. The first container is to indicate the UE 102 not to apply the LTM DU configuration 1 and / or the LTM CU configuration 1 immediately. In some scenarios or embodiments, the UE 102 receives an RRC reconfiguration message (e.g., the RRC reconfiguration message of the event 318) including a configuration (e.g., the LTM DU configuration 1 ). If the configuration is included in the first container, the UE 102 refrains from immediately applying the configuration. Otherwise, if the configuration is not included in the first container, the UE 102 applies the configuration immediately. In some embodiments, the first container includes a first addition or modification list (e.g., Itm-ConfigToAddModList field, Itm-CandidateToAddModList eld, or Itm- CandidateConfigToAddModList field). The CU 172 includes the LTM DU configuration 1 and / or the LTM CU configuration 1 in a first element (referred to herein after as element 1 ) of the first addition or modification list. For example, the element 1 may be an addition or modification IE (e.g., LTM-ConfigToAddMod IE, LTM-Candidate IE, LTM- CandidateToAddMod IE or LTM-CandidateConfigToAddMod IE). When the UE 102 receives the first addition or modification list, the UE 102 may store the first addition or modification list, e.g., in a variable in its RA memory (RAM). In other alternative embodiments, the DU 174 generates the first container and includes the first container in the first DU-to-CU message. In yet other alternative embodiments, the DU 174 generates the element 1 and includes the element 1 in the first DU-to-CU message.

[0067] In some embodiments, the CU 172 includes an LTM CU configuration 1 in the RRC reconfiguration message 316, the first container or the element 1 , where the LTM CU configuration 1 is associated with the LTM DU configuration 1 . To associate the LTM CU configuration 1 with the LTM DU configuration 1 , the CU 172 may include the LTM CU configuration 1 and the LTM DU configuration in the element 1. In some embodiments, the CU 172 includes LTM CU configuration(s) 2, ... , N in the RRCreconfiguration message 316 or the second container, where the LTM CU configuration(s) 2, N associated with the LTM DU configuration(s) 2, N, respectively. To associate the LTM CU configuration(s) 2, .... N with the LTM DU configuration(s) 2, N, the CU 172 may include the LTM CU configuration(s) 2, N and the LTM DU configuration(s) in the element(s) 2, N, respectively. In other embodiments, the CU 172 includes, in the element(s) 2, ... , N, the LTM CU configuration(s) 2, ... , N associated with the LTM DU configuration(s) 2, ... , N, respectively. Alternatively, the CU 172 does not include, in the RRC reconfiguration message 316, LTM CU configuration(s) for some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ... , N.

[0068] After receiving the RRC reconfiguration message 316, the DU 174 transmits 318 the RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320 an RRC reconfiguration complete message (e.g., an RRCReconfigurationComplete message) to the DU 174, which in turn transmits 322 a second DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some embodiments, the CU 172 performs security protection (e.g., integrity protection and / or encryption) on the RRC reconfiguration message. For example, the CU 172 generates a message authentication code for integrity (MAC-I) for the RRC reconfiguration message, encrypts the RRC reconfiguration message and the MAC-I to obtain an encrypted RRC reconfiguration message and an encrypted MAC-I, and transmits a PDCP PDU including the encrypted RRC reconfiguration message and encrypted MAC-I to the UE 102 via the DU 174 in the events 316 and 318. When the UE 102 receives the PDCP PDU from the CU 172 via the DU 174 (i.e., events 316 and 318), the UE 102 decrypts the encrypted RRC reconfiguration and encrypted MAC-I to obtain the RRC reconfiguration message and MAC-I and verifies whether the MAC-I is valid. If the UE 102 verifies the MAC-I is invalid, the UE 102 discards or ignores the RRC reconfiguration message. In some embodiments, the UE 102 may perform an RRC connection reestablishment procedure in response to the invalid MAC-I.Otherwise, if the UE 102 verifies the MAC-I is valid, the UE 102 may process the RRC reconfiguration. The UE 102 refrains from applying (i.e., executing) the LTM DUconfiguration 1 until receiving an LTM command activating the LTM DU configuration 1 (e.g., events 330, 350, 398, 380, 430, 450).

[0069] The events 308 (optional) and 310 are collectively referred to in Fig. 3 as an LTM preparation procedure 390. The events 316, 318, 320, 322 are collectively referred to in Fig. 3 as an LTM configuration delivery procedure 394.

[0070] In some embodiments, the first CU-to-DU message is a UE Context Modification Request message, and the first DU-to-CU message is a UE Context Modification Response message or UE Context Modification Required message. In the case of the UE Context Modification Required message, the CU 172 may transmit a UE Context Modification Confirm message to the DU 174 in response to UE Context Modification Required message. In some embodiments, the second CU-to-DU message is a DL RRC Message Transfer message. In other embodiments, the second CU-to-DU message is a UE Context Modification Request message and the DU 174 may transmit a second DU-to-CU message (e.g., UE Context Modification Response message) to the CU 172 in response to the second CU-to-DU message.

[0071] In some embodiments, the CU 172 includes a reference LTM CU configuration in the RRC reconfiguration message 316 or the first container. In some embodiments, the CU 172 might generate the LTM CU configuration 1 (i.e., nonreference LTM CU configuration) as a delta configuration to augment the reference LTM CU configuration. Similarly, the CU 172 might generate some or all of the LTM CU configuration(s) 2, ... , N as delta configuration(s) to augment the reference LTM CU configuration. Alternatively, in the RRC reconfiguration message 316 or the first container, the CU 172 includes the reference LTM CU configuration and does not include a non-reference LTM CU configuration. In some embodiments, the CU 172 includes the reference LTM CU configuration and / or the reference LTM DU configuration in an additional container (e.g., reference LTM configuration) and include the additional container in the RRC reconfiguration message 316.

[0072] In some embodiments, the reference LTM CU configuration is different from the serving CU configuration. In some embodiments, a portion of the reference LTM CU configuration is the same as a portion of the serving CU configuration and the rest of the reference LTM CU configuration is different from the rest of the serving CUconfiguration. In yet other embodiments, the reference LTM CU configuration is the same as the serving LTM CU configuration.

[0073] In some embodiments, the CU 172 includes, in the RRC reconfiguration message, a first LTM ID (referred to herein after as ID 1 ) for identifying the LTM DU configuration 1 or the element 1. In some embodiments, the CU 172 includes the ID 1 in the first container or element 1 . In some embodiments, the CU 172 assigns the ID 1 .

[0074] In some embodiments, the CU 172 transmits the ID 1 to the DU 174, and the DU 174 associates the ID 1 with the LTM DU configuration 1. In some embodiments, in the first CU-to-DU message, the CU 172 includes the ID 1 and indicates that ID 1 is associated with the LTM DU configuration 1. In other embodiments, after receiving the first DU-to-CU message, the CU 172 transmits 312 a third CU-to-DU message including the ID 1 to the DU 174 instead of including the ID 1 in the first CU-to-DU message. In some embodiments, in the third CU-to-DU message, the CU 172 includes the LTM DU configuration 1 and the ID 1 and indicates the association between the ID 1 and LTM DU configuration 1. Thus, the DU 174 may directly associate the ID 1 with the LTM DU configuration 1 . In other embodiments, in the third CU-to-DU message, the CU 172 includes the cell ID 1 and the ID 1 (i.e. , the first LTM ID) and indicates the association between the cell ID 1 and the ID 1 . Thus, the DU 174 may associate the ID 1 with the LTM DU configuration 1 , based on the association between the cell ID 1 and the ID 1 and the association between the cell ID 1 and the LTM DU configuration 1. In yet other embodiments, in the third CU-to-DU message, the CU 172 includes the LTM DU configuration 1 , the cell ID 1 and / or the ID 1 and indicates the association between the ID 1 , LTM DU configuration 1 and / or the cell ID 1. In some embodiments, the DU 174 transmits 314 a third DU-to-CU message to the CU 172 in response to the third CU-to- DU message. In some embodiments, the third CU-to-DU message and third DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. The events 312 (optional) and 314 (optional) are collectively referred to in Fig. 3 as an LTM ID assignment procedure 392. In other embodiments, the CU 172 includes the ID 1 , the cell ID 1 , and / or the LTM DU configuration 1 in the second CU-to-DU message as described above. Thus, the third CU-to-DU message can be omitted.

[0075] When the CU 172 includes the ID 1 in the first CU-to-DU message, the DU 174 may include the ID 1 in the LTM DU configuration 1 , first container or element 1 . Alternatively, the DU 174 does not include the ID 1 in the LTM DU configuration 1 , first container and / or element 1 .

[0076] In some embodiments, the CU 172 includes the reference LTM DU configuration in the first container. For example, the CU 172 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1. In other embodiments, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316 and outside the first container. For example, the CU 172 generates a third container (e.g., a field / IE) to include the first container and the reference LTM DU configuration and includes the third container in the RRC reconfiguration message 316. In yet other embodiments, the DU 174 includes the reference LTM DU configuration in the first container. For example, the DU 174 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1 . In yet other embodiments, the DU 174 generates a fourth container (e.g., a field / IE) to include the first container and the reference LTM DU configuration and includes the fourth container in the first DU-to-CU message 310. In such cases, the CU 172 includes the fourth container in the RRC reconfiguration message 316. Alternatively, the CU 172 retrieves the reference LTM DU configuration and the LTM DU configuration 1 from the fourth container and includes the reference LTM DU configuration and the LTM DU configuration 1 as described above.

[0077] In some embodiments, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM DU configuration. In some embodiments, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM CU configuration.

[0078] In some embodiments, 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 embodiments, the plurality of configuration parameters includes physical layer configuration parameters (e.g., PhysicalCellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE), and / or RLC configuration parameters (e.g., RLC-BearerConfig IE(s)). In some further embodiments, the pluralityof configuration parameters includes a special cell configuration (e.g., SpCellConfig IE) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some embodiments, the LTM DU configuration 1 is CellGroupConfig IE defined in 3GPP TS 38.331. In other embodiments, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0079] In some embodiments, the LTM CU configuration 1 includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some embodiments, the LTM CU configuration 1 includes a MeasConfig IE and / or a RadioBearerConfig IE defined in 3GPP TS 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some embodiments, the LTM DU configuration 1 includes L1 measurement configuration 1 (e.g., a CSI-MeasConfig IE) and / or at least one configuration indicator (TCI) state configuration. In other embodiments, the LTM CU configuration 1 includes the L1 measurement configuration and / or the TCI state configuration(s) 1 . In some embodiments, the L1 measurement configuration includes at least one reference signal (RS) resource configuration 1 and / or at least one report configuration 1. In some embodiments, the RS resource configuration(s) 1 configures one or more RSs or one or more RS resources associated with the cell 1. The RS(s) includes SSB(s) and / or CSI- RS(s). In some embodiments, each of the RS resource configuration(s) 1 includes a RS resource configuration ID. In some embodiments, the RS resource configuration(s) 1 is / are (similar to) CSI-ResourceConfig IE(s). In some embodiments, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some embodiments, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configuration(s) 1. In some embodiments, each of the TCI state configuration(s) 1 configures a TCI state that associates one or two DL RSs with a corresponding quasi-colocation (QCL) type. The DL RS(s) are associated with the cell 1.

[0080] In some embodiments, the DU 174 includes the L1 measurement configuration 1 and / or the TCI state configuration(s) 1 in a serving DU configuration 1(e.g., non-LTM DU configuration). In some embodiments, the DU 174 includes the serving DU configuration in the first DU-to-CU message. In other embodiments, the DU 174 transmits an additional DU-to-CU message including the serving DU configuration to the CU 172. In some embodiments, the additional DU-to-CU message is a UE Context Modification Required message. In some embodiments, the CU 172 includes the serving DU configuration 1 in the RRC reconfiguration message 316, 318. In other embodiments, the CU 172 transmits another RRC reconfiguration message including the serving DU configuration to the UE 102 via the DU 174.

[0081] In some embodiments, the DU 174 includes an RA configuration in the LTM DU configuration 1. In other embodiments, the DU 174 does not include an RA configuration in the LTM DU configuration 1. In some embodiments, if the cell 124A and first cell are not synchronized, the DU 174 determines to include the RA configuration in the LTM DU configuration 1. Otherwise, if the cell 124A and first cell are synchronized, the DU 174 determines to not include the RA configuration in the LTM DU configuration 1 . In other embodiments, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the RA configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the RA configuration in the LTM DU configuration 1 . If the LTM DU configuration 1 includes the RA configuration, the UE 102 performs the RA procedure in the event 332 in accordance with the RA configuration, as described below. Otherwise, if the LTM DU configuration 1 does not include the RA configuration or indicates the UE 102 to skip an RA procedure in LTM, the UE 102 skips or refrains from performing the RA procedure of the event 332 in response to the LTM DU configuration 1 excluding the RA configuration.

[0082] In some embodiments, the DU 174 includes RA configuration parameters in the LTM DU configuration 1 and / or the reference LTM DU configuration regardless of whether the cell 124A and first cell are synchronized or not. The UE 102 performs the RA procedure in the event 332 in accordance with the RA configuration parameters, as described below.

[0083] In some embodiments, if the cell 124A and the first cell are synchronized, the DU 174 determines to include, in the LTM DU configuration 1 , a first indication configuring the UE 102 not to perform an RA procedure on the first cell. Otherwise, if the cell 124A and the first cell are not synchronized, the DU 174 determines to not include the first indication in the LTM DU configuration 1. In other embodiments, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to include the first indication in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to not include the first indication in the LTM DU configuration 1. If the LTM DU configuration 1 includes the first indication, the UE 102 skips or refrains from performing the RA procedure of the event 332 in accordance with or in response to the first indication. Otherwise, if the LTM DU configuration 1 does not include the first indication, the UE 102 performs the RA procedure in accordance with the RA configuration in the event 332, in response to the LTM DU configuration 1 excluding the first indication, as described below.

[0084] In some embodiments, the DU 174 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In other embodiments, the DU 174 does not include a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In some embodiments, if the cell 124A and the first cell are not synchronized, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1 . Otherwise, if the cell 124A and the first cell are synchronized, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1 . In other embodiments, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1 . In some embodiments, if the LTM DU configuration 1 includes the reconfiguration with sync configuration, the UE 102 performs the RA procedure in the event 332 asdescribed below, in response to or in accordance with the reconfiguration with sync configuration. Otherwise, if the LTM DU configuration 1 does not include the reconfiguration with sync configuration, the UE 102 skips or refrains from performing the RA procedure of the event 332. In some embodiments, the DU 174 includes a cell ID (i.e. , cell ID 1 ) of cell 1 (i.e. , the first cell) in the LTM DU configuration 1 . In one embodiment, the cell ID 1 may be a PCI. In another embodiment, the cell ID 1 is a CGI. In some embodiments, the cell ID 1 included in the LTM DU configuration 1 is a PCI, while the cell ID 1 included in the first CU-to-DU message is a CGI. In some further embodiments, the LTM DU configuration 1 includes a cell index 1 indexing the cell ID 1 or the first cell. The cell index 1 is not a cell ID. The cell index takes fewer bits than the cell ID. In some embodiments, the CU 172 sets the cell index 1 to a value and includes the cell index 1 in the first CU-to-DU message of the event 308.

[0085] In some embodiments, after (e.g., in response to) receiving one or some of the at least one measurement report of the event 304, the BS 104 (i.e., the CU 172 or DU 174) determines to prepare additional cell(s) (i.e., cell(s) 2, ... , N) of the BS 104 for LTM for the UE 102. In one embodiment, the BS 104 determines to prepare the additional cell(s) for LTM for the UE 102 because the at least one measurement report indicates that the additional cell(s) could be used by the BS 104 to communicate with the UE 102. The additional cell(s) may include the cell 124C and / or cell(s) other than the cells 124A, 124B, and 124C. In some embodiments, if the L3 measurement report(s) indicates that signal strength and / or quality of a particular cell of the additional cell(s) is above a respective predetermined threshold and / or is better than the cell 124A, the CU 172 determines to prepare the particular cell for LTM for the UE 102. In other embodiments, if the L1 measurement report(s) indicates that signal strength and / or quality of a particular cell of the additional cell(s) is above a first predetermined threshold and / or is better than the cell 124A, the DU 174 determines to prepare the particular cell for LTM for the UE 102. In one embodiment, the respective predetermined threshold(s) for the additional cells may be different from the first predetermined threshold. In another embodiment, the respective predetermined threshold(s) for the additional cell(s) may be the same as the first predetermined threshold. In some embodiments, the respective predetermined thresholds for the additional cells may bethe same or different. Alternatively, the BS 104 determines to prepare the additional cell(s) for the UE 102 regardless of whether a measurement report is received from the UE 102 or not.

[0086] In the case that the ClI 172 determines to prepare the additional cell(s), the CU 172 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the DU 174 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390. In the case that the DU 174 determines to prepare the additional cell(s), the DU 174 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the CU 172 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390.

[0087] In some embodiments, the CU 172 and DU 174 perform LTM preparation procedure(s) 2, ... , N to prepare the cell(s) 2, ... , N, respectively, similar to the procedure 390. The CU 172 may include the cell ID(s) 2, ... , N in CU-to-DU message(s) 2, ... , N in the LTM preparation procedure(s) 2, ... , N, respectively, similar to the first CU-to-DU message. In the LTM preparation procedure(s) 2, ... , N, the DU 174 generates LTM DU configuration(s) 2, ... , N configuring the cell(s) 2, ... , N and includes the LTM DU configuration(s) 2, ... , N in DU-to-CU message(s) 2, ... , N, respectively, as described for the LTM DU configuration 1 . In the case that the DU 174 receives the CU-to-DU message(s) 2, ... , N, the DU-to-CU message(s) 2, ... , N responds to the CU-to-DU message(s) 2, ... , N, respectively. Here “N” is an integer larger than one. For example, “N” is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13 14, 15 or 16. In another example, the maximum number of “N” is 4, 8, 16, or 32. Examples and embodiments of the LTM DU configuration 1 may apply to the LTM DU configuration(s) 2, ... , N.

[0088] In other embodiments, the CU 172 and DU 174 perform a single LTM preparation procedure (i.e. , the LTM preparation procedure 390) to prepare the cell(s) 1 , 2, ... , N. In such cases, the DU 174 includes the LTM DU configuration(s) 1 , 2, ... , N for the cell(s) 1 , 2, ... , N, respectively in the first DU-to-CU message. In the first DU-to-CU message, the DU 174 may include the cell ID(s) 1 , 2, ... , N respectively associated with the LTM DU configuration(s) 1 , 2, ... , N to indicate that the LTM DU configuration(s) 1 ,2, , N are configured for the cell ID(s) 1 , 2, ... , N, respectively. In the case that the CU 172 determines to perform the LTM preparation procedure 390, the CU 172 includes the cell ID(s) 1 , 2, ... , N in the first CU-to-DU message to request the DU 174 to prepare the cell(s) 1 , 2, ..., N, respectively, for LTM.

[0089] After receiving the LTM DU configuration(s) 2, ... , N from the DU 174, the CU 172 may include the LTM DU configuration(s) 2, ... , N in the first container. In some embodiments, the CU 172 includes the LTM DU configuration(s) 2, ... , N in element(s) 2, ... , N, respectively, and includes the element(s) 2, ... , N in the first container. In some embodiments, the CU 172 includes, in the RRC reconfiguration message, LTM ID(s) (i.e., ID(s) 2, ... , N) for identifying the LTM DU configuration(s) 2, ... , N, respectively. In some embodiments, the CU 172 includes the ID(s) 2, ... , N in the first container. For example, the CU 172 includes the ID(s) 2, ... , N and LTM DU configuration(s) 2, ... , N in the element(s) 2, ... , N in the first addition or modification list.

[0090] In some embodiments, the CU 172 assigns the ID(s) 2, .... N for the LTM DU configuration(s) 2, ... , N, respectively. In other embodiments, the CU 172 receives the ID(s) 2, ... , N from the DU 174 in the first DU-to-CU message of the procedure 390. In yet other embodiments, the CU 172 receives from the DU 174 the ID(s) 2, ... , N in the DU-to-CU message(s) 2, ... , N of the LTM preparation procedure(s) 2, ... , N, respectively.

[0091] In some embodiments, the CU 172 performs an LTM ID assignment procedure with the DU 174 for each of the LTM DU configuration(s) 2, ... , N, similar to the procedure 392. In other embodiments, the CU 172 includes the ID(s) 2, ... , N and the LTM DU configuration(s) 2, ... , N in the third CU-to-DU message and indicate the association between the ID(s) 2, ... , N and the LTM DU configuration(s) 2, ... , N, respectively. Thus, the DU 174 may associate the LTM DU configuration(s) 2, ... , N with the ID(s) 2, ... , N, respectively. In yet other embodiments, the CU 172 includes the cell ID(s) 2, ... , N and the ID(s) 2, ... , N in the third CU-to-DU message and indicate the association between the cell ID(s) 2, ... , N, and the ID(s) 2, ... , N, respectively. Thus, the DU 174 may associate the LTM DU configuration(s) 2, ... , N with the ID(s) 2, ... , N, respectively, based on the association between the cell ID(s) 2, ... , N and the ID(s) 2, ... , N and the association between the cell ID(s) 2, ... , N and the LTM DUconfiguration(s) 2, N, respectively. In other embodiments, the CU 172 includes the ID(s) 2, N, the cell ID(s) 2, , N and / or the LTM DU configuration(s) 2, ... , N in the second CU-to-DU message as described above. Thus, the third CU-to-DU message can be omitted. In yet other embodiments, the CU 172 includes the ID(s) 2, ... , N in the first CU-to-DU message and indicate the ID(s) 2, ... , N is / are respectively associated with the cell ID(s) 2, ... , N. In one embodiment, the DU 174 includes the ID(s) 2, ... , N in the LTM DU configuration(s) 2, ... , N. Thus, the CU 172 does not include the ID(s) 2, ... , N in the RRC reconfiguration message, first container and / or element(s) 2, ... , N.

[0092] In some alternative embodiments, the DU 174 assigns the ID(s) 2, ... , N. In some embodiments, the DU 174 includes the ID(s) 2, ... , N in the first DU-to-CU message of the procedure 390. In yet other embodiments, the DU 174 includes the ID(s) 2, ... , N in the DU-to-CU message(s) 2, ... , N of the LTM preparation procedure(s) 2, ... , N. The CU 172 may include the ID(s) 2, ... , N in the RRC reconfiguration message. In other embodiments, the DU 174 includes the ID(s) 2, ... , N in the LTM DU configuration(s) 2, ... , N. Thus, the CU 172 does not include an ID (e.g., LTM ID) identifying each of the LTM DU configuration(s) 2, ... , N in the RRC reconfiguration message, first container and / or element 1 .

[0093] In some alternative embodiments, the CU 172 may generate a second container including the LTM DU configuration(s) 2, ... , N or element(s) 2, ... , N instead of using the first container. The CU 172 then transmits an additional RRC reconfiguration message including the second container to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits an additional RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. In some embodiments, the second container may be a second addition or modification list (e.g., Itm-ConfigToAddModList field, LTM-ConfigToAddModList IE, Itm- CandidateConfigToAddModList \e\d, or LTM-CandidateConfigToAddModList IE), and each of the element(s) 2, ... , N may be an addition or modification IE (e.g., Itm- ConfigToAddMod field, LTM-ConfigToAddMod IE, Itm-CandidateConfigToAddMod field, or LTM-CandidateConfigToAddMod IE). When the UE 102 receives the second addition or modification list, the UE 102 may store the second addition or modification listtogether with the first addition or modification list, e.g., in a variable in its random access memory (RAM).

[0094] In some embodiments, the DU 174 includes cell ID(s) 2, ... , N in the LTM DU configuration(s) 2, ... , N to identify the cell(s) 2, ... , N, respectively. In one embodiment, each of the cell ID(s) 2, ... , N is a PCI. In some further embodiments, the LTM DU configuration(s) 2, ... , N includes cell index(es) 2, ... , N indexing the cell ID(s) 2, ... , N or the cell(s) 2, ... , N, respectively. In the case that the CU 172 prepares the cell(s) 2, ... , N for LTM in the procedure 390, the CU 172 may set the cell index(es) 2, ... , N to different value(s) and include the cell index(es) 2, ... , N in the first CU-to CU-to-DU message of the event 308. In the case that the CU 172 prepares the cell(s) 2, ... , N in the additional LTM preparation procedure(s), the CU 172 may set the cell index(es) 2, ... , N to different values and include the cell index(es) 2, ... , N in CU-to-DU message(s) of the additional LTM preparation procedure(s). The CU 172 sets the cell index(es) 1 , ... , N to different values. In some embodiments, the cell ID(s) 1 , ... , N in the LTM DU configuration(s) 1 , ... , N are different from the cell ID(s) 1 , ... , N in the CU-to-DU message(s) described above.

[0095] In some embodiments, each of the LTM DU configuration(s) 1 , ... , N includes physical configuration parameters, MAC configuration parameters, RLC configuration parameters, and / or L1 measurement configuration(s). In some embodiments, each of the LTM DU configuration(s) 1 , ... , N may be a CellGroupConfig IE as defined in 3GPP TS 38.331. In other embodiments, each of the LTM DU configuration(s) 1 , ... , N include configuration parameters included in a CellGroupConfig IE as defined in 3GPP TS 38.331 . In some further embodiments, the plurality of configuration parameters in each of the LTM DU configuration(s) includes a particular special cell configuration (e.g., SpCellConfig IE) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some embodiments, the LTM DU configuration(s) 1 , ... , N are CellGroupConfig IE(s) defined in 3GPP TS 38.331. In other embodiments, the LTM DU configuration(s) 1 , ... , N include configuration parameters in the CellGroupConfig IE.

[0096] In some embodiments, the CU 172 includes one or more additional LTM CU configurations in at least one of the elements 2, ... , N, the first container or the second container. Each of the additional LTM CU configurations are associated with a particularLTM DU configuration of the LTM DU configuration(s) 2, N. Examples and embodiments of the additional LTM CU configurations are similar to the LTM CU configuration 1 .

[0097] In some embodiments, the CU 172 determines to release the LTM DU configuration M of the LTM DU configuration(s) 1 , N (or the element M of the element(s) 1 , , M). 1 < M < N. In response to the determination, the CU 172 transmits an RRC reconfiguration message to the UE 102 via the DU 174 to indicate the UE 102 to release the LTM DU configuration M or element M. In one embodiment, the CU 172 generates a release list including the ID (i.e. , LTM ID) M for releasing the LTM DU configuration M or element M and includes the release list in the RRC reconfiguration message. In response to the RRC reconfiguration message, the UE 102 releases the LTM DU configuration M or element M and transmits an RRC reconfiguration complete message to the CU 172 via the DU 174. In response to the determination, the CU 172 transmits a CU-to-DU message to the DU 174 to indicate the DU 174 to release the LTM DU configuration M. To indicate the DU 174 to release the LTM DU configuration M, the CU 172 may include the cell ID M or the ID (i.e., LTM ID) M in a release indication (e.g., a field or IE) in the CU-to-DU message. In response, the DU 174 releases the LTM DU configuration M and transmits a DU-to-CU message to the CU 172. In some embodiments, the CU-to-DU message and DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0098] In other embodiments, the DU 174 determines to release the LTM DU configuration K. In response to the determination, the DU 174 transmits a DU-to-CU message to the CU 172 to release the LTM DU configuration K. To indicate the LTM DU configuration K is released, the DU 174 may include the cell ID K or the ID (i.e., LTM ID) K in a release indication (e.g., a field or IE) in the DU-to-CU message. 1 < K < N. After (e.g., in response to) receiving the DU-to-CU message, the CU 172 generates a release list including the ID (i.e., LTM ID) K to release the LTM DU configuration K or element K and transmits an RRC reconfiguration message including the release list to the UE 102 via the DU 174. In response, the UE 102 releases the LTM DU configuration K or element K and transmits an RRC reconfiguration complete message to the UE 102 viathe DU 174. The CU 172 may transmit a CU-to-DU message to the DU 174 in response to the DU-to-CU message. In some embodiments, the DU-to-CU message and CU-to-DU message are a UE Context Modification Required message and a UE Context Modification Confirm message, respectively.

[0099] After receiving the RRC reconfiguration in the event 318 or transmitting the RRC reconfiguration complete message in the event 320, the UE 102 transmits 324 at least one measurement report to the DU 174, similar to the event 304. In some embodiments, the DU 174 may transmit 326 a DU-to-CU message including the at least one measurement report to the CU 172, similar to the event 306. In other embodiments, the DU 174 does not transmit the at least one measurement report to the CU 172. In some embodiments, the at least one measurement report of the event 324 include L1 measurement report(s) or L3 measurement repot(s), as described for the event 304. In some embodiments, the UE 102 transmits 324 the at least one measurement report on PUCCH(s) and / or PUSCH(s) to the DU 174, similar to the event 304. In other embodiments, the UE 102 transmits 324 at least one MAC CE including the at least one measurement report to the DU 174, similar to the event 304. In some embodiments, the UE 102 does not transmit the L1 measurement report(s) in format of RRC message(s) to the DU 174.

[0100] In some embodiments, the UE 102 transmits 324 the at least one measurement report to the DU 174 in accordance with at least one measurement configuration. The at least one measurement configuration configures the UE 102 to perform measurements and report measurement results. The CU 172 transmits the at least one measurement configuration to the UE 102 via the DU 174. For example, the CU 172 may transmit one or more RRC messages (e.g., RRCReconfiguration message(s)) including the at least one measurement configuration to the UE 102 via the DU 174 in the event 302 and / or 316 and / or after the event 306 or 316. The one or more RRC messages may or may not include the RRC reconfiguration message of the event 316. In accordance with the at least one measurement configuration, the UE 102 performs measurements on one or more reference signals. The one or more reference signals include one or more SSBs and / or one or more CSI-RSs. The UE 102 obtains the at least one L1 measurement result and / or at least one L3 measurement result fromthe measurements and includes the at least one L1 measurement result and / or at least one L3 measurement result in the at least measurement report of the event 324. The DU 174 transmits the one or more reference signals on the cell 124A, the cell 1 and / or the cell(s) 2, N. The one or more reference signals may be CSI-RS(s) or SSB(s).

[0101] In some embodiments, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)), as described for the event 304. In other embodiments, the at least one measurement configuration includes or is L1 measurement configuration(s), as described above. In yet other embodiments, the L1 measurement configuration(s) may be CSI-MeasConfig IE(s) defined in 3GPP TS 38.331. The L1 measurement configuration(s) may include RS resource configuration(s) and / or report configuration(s). The UE 102 transmits 324 the L1 measurement report(s) on UL resources (e.g., PUCCH resources or PUSCH resources) to the DU 174 in accordance with the report configuration(s). The DU 174 receives the L1 measurement report(s) on the UL resources in accordance with the report configuration(s). In some embodiments, the report configuration(s) are or are similar to CSI-ReportConfig IE(s). In other embodiments, each of the report configuration(s) is a new RRC IE. In some embodiments, (each of) the report configuration(s) configures periodically reporting and / or event-triggered reporting of the L1 measurement result(s).

[0102] In some embodiments, the L1 measurement report(s) is / are CSI report(s). In other embodiments, the L1 measurement report(s) is / are MAC CE(s). In some embodiments, each of the measurement report(s) includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) and / or the report configuration(s) and obtains the quantized measurement values from the measurements. In some embodiments, the RS resource indicator(s) indicates the RS(s) or an RS resource(s) where the UE 102 performs measurements or obtains the quantized measurement values. In some embodiments, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values might include one or more L1 -RSRP values and / or one or more L1 -SINR values.

[0103] In yet other embodiments, the at least one measurement configuration includes new-type measurement configuration(s) (e.g., LTM measurement configuration(s)). The new-type measurement configuration may already be defined in a 3GPP TS. In some embodiments, the new-type measurement configuration(s) includes reference signal resource configuration(s) configuring resources where the DU 174 transmits reference signal(s). For example, the reference signal resource configuration(s) include CSI-RS(s) and / or SSB(s). In one embodiment, the reference signal resource configuration(s) is / are CSI-ResourceConfig IE(s). In another embodiment, the new-type measurement configuration(s) include measurement report configuration(s), as described above. The UE 102 transmits the measurement report(s) on PUCCH(s) or MAC CE(s) to the DU 174 in accordance with the measurement report configuration(s). The DU 174 receives the measurement report(s) on PUCCH(s) or MAC CE(s) in accordance with the measurement report configuration(s). In such cases, the measurement report(s) may be L1 measurement report(s) or new-type measurement report(s) (e.g., LTM measurement report(s)). In some embodiments, the new-type measurement configuration includes configuration parameters already defined in a 3GPP TS.

[0104] After (e.g., in response to) receiving the at least one measurement report in the event 324, the DU 174 generates a first LTM command to activate the LTM DU configuration 1 (i.e. , the first LTM command commands the UE 102 to apply the LTM DU configuration 1 or to perform a serving cell change to the cell 1 ). The DU 174 then transmits 330 the first LTM command to the UE 102. In some embodiments, the DU 174 transmits the first LTM command on the cell 124A to the UE 102. In other embodiments, the DU 174 transmits the first LTM command on the cell 124D to the UE 102. In some embodiments, the DU 174 includes the ID 1 in the first LTM command to indicate the LTM DU configuration 1 or element 1 , and the UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 in accordance with the ID 1 .

[0105] In other embodiments, the DU 174 includes the cell index 1 indexing the cell ID 1 in the first LTM command. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 , based on the cell index 1 . Before receiving the first LTM command, the UE 102 retrieves the cell index 1 from the LTM DU configuration 1 orelement 1 , and establishes an association 1 between the cell index 1 and the LTM DU configuration 1 or element 1 . In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell index 1 , before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell index 1 and the association 1 . Before receiving the first LTM command, the UE 102 retrieves the cell index(es) 2, ... , N from the LTM DU configuration(s) or element(s) 2, ... , N and establishes association(s) 2, ... , N between the cell index(es) 2, ... , N and the LTM DU configuration(s) or element(s) 2, ... , N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, ... , N to obtain the cell index(es) 2, ... , N, before receiving the first LTM command.

[0106] In yet other embodiments, the DU 174 includes the cell ID 1 in the first LTM command. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 , based on the cell ID 1 . Before receiving the first LTM command, the UE 102 retrieves the cell ID 1 from the LTM DU configuration 1 or element 1 and establishes an association 1 between the cell ID 1 and the LTM DU configuration 1 or element 1 . In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell ID 1 , before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell ID 1 (received in the first LTM command) and the association 1 . Before receiving the first LTM command, the UE 102 retrieves the cell ID(es) 2, ... , N from the LTM DU configuration(s) or element(s) 2, ... , N and establishes association(s) 2, ... , N between the cell ID(es) 2, ... , N and the LTM DU configuration(s) or element(s) 2, ... , N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, ... , N to obtain the cell ID(es) 2, ... , N, before receiving the first LTM command.

[0107] In yet other embodiments, the DU 174 includes a bit map in the first LTM command to activate the LTM DU configuration 1 , instead of the ID 1 or cell index 1 . The number of bits in the bit map is larger than or equal to “N”. In one embodiment, bit 1 , ... , N corresponds to the cell index(es) 1 , ... , N, the ID(s) 1 , ... , N, the LTM DU configuration(s) 1 , ... , N or the element(s) 1 , ... , N, respectively, and the DU 174 sets a corresponding bit (e g., bit 1 ) in the bit map to a first value to indicate the cell index 1 ,the ID 1 , the LTM DU configuration 1 or the element 1. Thus, the UE 102 may determine the cell index 1 , the ID 1 , LTM DU configuration 1 , or element 1 in accordance with the bit 1 set to the first value in the bit map. In another embodiment, bit 0, ... , N-1 corresponds to the cell index(es) 1 , ... , N, the ID(s) 1 , ... , N, the LTM DU configuration(s) 1 , ... , N or the element (s) 1 , ... , N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 0) in the bit map to a first value to indicate the cell index 1 , the ID 1 the LTM DU configuration 1 or the element 1. Thus, the UE 102 may determine the cell index 1 , the ID 1 LTM DU configuration 1 or element 1 in accordance with the bit 0 set to the first value in the bit map. In such embodiments, the DU 174 sets the remaining bits in the bit map to a second value to indicate that the rest of the LTM DU configuration(s) 1 , ... , N is / are not activated. In some embodiments, the first value is one and the second value is zero. In other embodiments, the first value is zero and the second value is one. Generally, if the DU 174 determines to activate the LTM DU configuration L or change a serving cell to the cell L for the UE 102, the DU 174 may set the corresponding bit (e.g., bit L or bit L-1) in the bit map to the first value and set the remaining bits to the second value, where 1 < L < N. In some embodiments, the DU 174 sets at most one bit in the bit map to the first value.

[0108] After determining or identifying the LTM DU configuration 1 or element 1 , the UE 102 then applies the LTM DU configuration 1 and / or LTM CU configuration, after (e.g., in response to) receiving the first LTM command.

[0109] In some embodiments, the at least one measurement report (e.g., L1 measurement report(s) or new-type measurement report(s)) of the event 324 includes at least one measurement result for the first cell, TRP(s) of the first cell or reference signal(s) transmitted on the first cell. The reference signal(s) may be CSI-RS(s) or SSB(s). The DU 174 determines to activate the LTM DU configuration 1 or transmit the first LTM command, based on the at least one measurement result. In some embodiments, the DU 174 determines to activate the LTM DU configuration 1 because, when or if the at least one measurement result is above a second predetermined threshold. In some embodiments, the at least one measurement result includes L1- RSRP value(s), L1-RSRQ value(s) and / or L1-SINR value(s). In other embodiments, the at least one measurement result includes RSRP value(s), RSRQ value(s) and / or SINRvalue(s) for the new-type measurement report(s). In some embodiments, the second predetermined threshold is different from the first predetermined threshold. In one embodiment, the second predetermined threshold is larger than the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell is suitable for communication with the UE 102. In another embodiment, the second predetermined threshold is equal to the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This indicates that the first cell is suitable for communication with the UE 102. Thus, the DU 174 determines to activate the LTM DU configuration 1 in response to that signal strength or quality of the first cell is above the second predetermined threshold for the UE 102.

[0110] In some embodiments, the at least one measurement report (e.g., L3 measurement report(s)) of the events 324 and 326 includes at least one measurement result for the first cell. The CU 172 determines to activate the LTM DU configuration 1 or transmit the first LTM command, because the at least one measurement result indicates that signal strength or quality of the first cell is above a second predetermined threshold. The second predetermined threshold is different from the first predetermined threshold. In one embodiment, the second predetermined threshold is larger than the first predetermined threshold. In such an embodiment, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell is suitable for communication with the UE 102. In another embodiment, the second predetermined threshold is equal to the first predetermined threshold. In such an embodiment, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This also indicates that the first cell is suitable for communication with the UE 102. Thus, the CU 172 determines to activate the LTM DU configuration 1 in response to that signal strength or quality of the first cell is above the second predetermined threshold. In response to the determination, the CU 172 transmits 328 a fourth CU-to-DU message to the DU 174 to activate the LTM DU configuration 1 or trigger a serving cell change to the cell 1 for the UE 102. In someembodiments, the CU 172 includes the ID 1 in the fourth CU-to-DU message. In other embodiments, the CU 172 includes the cell index 1 in the fourth CU-to-DU message. In response to the fourth CU-to-DU message, the DU 174 transmits 330 the first LTM command to the UE 102 and optionally transmits a fourth DU-to-CU message to the CU 172. In some embodiments, the CU 172 includes the cell index 1 in the fourth CU-to- DU message. Thus, the DU 174 may determine to activate the LTM DU configuration 1 in accordance with the cell index 1 . In other embodiments, the CU 172 may include the cell ID 1 in the fourth CU-to-DU message. Thus, the DU 174 determines to activate the LTM DU configuration 1 in accordance with the cell ID 1 . In yet other embodiments, the CU 172 includes the ID 1 in the fourth CU-to-DU message. Thus, the DU 174 may determine to activate the LTM DU configuration 1 in accordance with the ID 1 . In some embodiments, the fourth CU-to-DU message and fourth DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In other embodiments, the fourth CU-to-DU message and / or fourth DU-to-CU message are new interface messages, e.g., F1 application protocol (F1AP) messages defined in 3GPP TS 38.473.

[0111] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 330, the DU 174 might transmit 329 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some embodiments, the DU 174 includes the cell ID 1 or the ID 1 (i.e., LTM ID) in the DU-to-CU message 329 to indicate that the DU 174 is to activate the LTM DU configuration 1 or trigger a fast serving cell change (i.e., an LTM serving cell change). The DU may transmit the DU-to- CU message 329 to the CU 172 before or after transmitting the LTM command 330.

[0112] In some embodiments, the first LTM command is a MAC CE included in a MAC PDU that the UE 102 receives from the DU 174 in the event 330. The MAC CE may be a new MAC CE defined in 3GPP TS 38.321. In one embodiment, the DU 174 includes a subheader identifying the new MAC CE in the MAC PDU and the UE 102 identifies the new MAC CE in the MAC PDU in accordance with the subheader. The subheader may include a logical channel ID or extended logical channel ID defined in a 3GPP specification to identify the new MAC CE. For example, the logical channel ID or extended logical channel ID are newly defined in 3GPP TS 38.321. In otherembodiments, the first LTM command is a DCI that the UE 102 receives on a PDCCH from the DU 174 in the event 330. The DU 174 generates a CRC for the DCI, scrambles the CRC with a first C-RNTI of the UE 102, and transmits the DCI and scrambled CRC on the PDCCH in the event 330. In one embodiment, a format of the DCI may be an existing DCI format defined in a 3GPP specification (e.g., 38.212). In another embodiment, the format of the DCI may be a new DCI format defined in a 3GPP specification (e.g., 3GPP TS 38.212).

[0113] In some embodiments, the DU 174 does not perform security protection (e.g., integrity protection and / or encryption) on the first LTM command. This speeds up processing the first LTM command in the UE 102 because the UE 102 does not perform security check (e.g., decryption and / or integrity check) on the first LTM command.

[0114] In some embodiments, after receiving the first LTM command, the UE 102 may transmit 331 an acknowledgement to the DU 174 on the cell 124A or cell 124D to indicate that the UE 102 receives the first LTM command. In some embodiments, the acknowledgement is a HARQ ACK. In other embodiments, the acknowledgement is a MAC CE. For example, the MAC CE is an existing MAC CE defined in 3GPP TS 38.321 . In another example, the MAC CE is a new MAC CE defined in latest versions of 3GPP TS 38.321 . In yet other embodiments, the acknowledgement is a PUCCH transmission.

[0115] In some embodiments, the CU 172 transmits 316 the RRC reconfiguration message in response to the L3 measurement report 306 for the first cell. To configure the UE 102 to transmit the L3 measurement report 306, the CU 172 may transmit a first RRC reconfiguration message including the L3 measurement configuration (e.g., a MeasConfig IE) to the UE 102 before the event 306. In some embodiments, the DU 174 transmits 330 the first LTM command in response to the L1 measurement report(s) 324 for the first cell. To configure the UE 102 to transmit the L1 or new-type measurement report(s) 324, the CU 172 may transmit a second RRC reconfiguration message including the L1 or new-type measurement configuration(s) to the UE 102. In some embodiments, the first and second RRC reconfiguration messages are the same message (i.e., the same instance). In other embodiments, the first and second RRC reconfiguration messages are different messages. In some embodiments, the secondRRC reconfiguration message is the RRC reconfiguration message of the event 316. In other embodiments, the second RRC reconfiguration message is different from the RRC reconfiguration message of the event 316.

[0116] After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 the first cell. The UE 102 identifies the LTM DU configuration 1 in accordance with the ID 1 , the cell ID 1 or the cell index 1 received in the first LTM command and applies the LTM DU configuration 1 to communicate with the DU 174 on the first cell. In some embodiments, the UE 102 disconnects from the cell 124A, after (e.g., in response to) receiving the first LTM command or after transmitting 331 the acknowledgement. In some embodiments, the UE 102 stops communicating on the cell 124A after (e.g., in response to) receiving 330 the first LTM command, or transmitting 331 the acknowledgement. In some embodiments, the UE 102 accesses the first cell by performing an RA procedure on the first cell with the DU 174, in response to receiving the first LTM command. In other embodiments, the UE 102 skips an RA procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174, after (e.g., in response to) receiving the first LTM command.

[0117] In some embodiments, the DU 174 configures the access of the UE 102 to the first cell, including whether or not the UE 102 performs an RA procedure, in the LTM DU configuration 1 . When receiving the first LTM command (e.g., the first LTM command), the UE 102 determines whether to perform an RA procedure on the first cell in accordance with the LTM DU configuration 1. If the LTM DU configuration 1 configures the UE 102 to perform an RA procedure, the UE 102 performs an RA procedure on the first cell in the event 332, in order to connect to the first cell. For example, the LTM DU configuration 1 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) to configure that the UE 102 performs an RA procedure when the UE 102 receives an LTM command for the first cell. In other embodiments, in the LTM DU configuration 1 , the DU 174 configures the UE 102 to skip the RA procedure for an LTM serving cell change to the first cell. In such cases, after receiving the first LTM command, the UE 102 skips the RA procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell tothe DU 174 in the event 332. In some embodiments, the DU 174 excludes a reconfiguration with sync configuration in the LTM DU configuration 1 to configure the UE 102 skipping an RA procedure for an LTM serving cell change to the first cell.

[0118] In other embodiments, the LTM DU configuration 1 includes the reconfiguration with sync configuration or the RA configuration. In such cases, the DU 174 configures whether the UE 102 performs an RA procedure on the first cell in an LTM command. Thus, the UE 102 determines whether to perform the RA procedure on the first cell in the event 332 in accordance with the first LTM command. In some embodiments, the DU 174 includes, in the first LTM command, an indication (e.g., a field) indicating skipping an RA procedure. In response to the indication or the first LTM command including the indication, the UE 102 skips an RA procedure and directly transmits the first transmission (e g., a PUSCH transmission or a PUCCH transmission) on the first cell to access the first cell. In other embodiments, the DU 174 excludes the indication in the first LTM command to configure the UE 102 to perform an RA procedure. In response to the first LTM command excluding the indication, the UE 102 performs an RA procedure on the first cell to access the first cell. In some other embodiments, the DU 174 includes a timing advance value in the first LTM command to indicate skipping an RA procedure. In response to receiving the timing advance value or the first LTM command including the timing advance value, the UE 102 skips the RA procedure and transmits the first transmission on the first cell to access the first cell, using the timing advance value. In yet other embodiments, the DU 174 excludes, in the first LTM command, a timing advance value to configure the UE 102 to perform an RA procedure. In response to the first LTM command excluding a timing advance command, the UE 102 performs an RA procedure on the first cell to access the first cell.

[0119] In some embodiments, the RA procedure is a four-step RA procedure. In other embodiments, the RA procedure is a two-step RA procedure. In some embodiments, the RA procedure is a contention-free RA procedure. In other embodiments, the RA procedure is a contention-based RA procedure. In cases where the RA procedure is a four-step RA procedure, the UE 102 transmits a Message 3 including a UE identity to the DU 174 via the first cell in the RA procedure. The DU 174 transmits a contention resolution message (e.g., a Message 4) to the UE 102 in response to the Message 3.In cases where the RA procedure is a two-step RA procedure, the UE 102 transmits a Message A including the UE identity to the DU 174 via the first cell in the RA procedure. The DU 174 transmits a contention resolution message (e.g., Message B) to the UE 102 in response to the Message A. In some embodiments, when the UE 102 receives the contention resolution message from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the RA procedure (i.e., the UE 102 successfully accesses the first cell). In some embodiments, the LTM DU configuration 1 includes a second C-RNTI and the UE identity is the second C-RNTI of the UE 102. In such embodiments, the contention resolution message is a PDCCH transmission addressed to the second C-RNTI. In other embodiments, the LTM DU configuration 1 does not include a C-RNTI, the UE identity is the first C-RNTI. In such embodiments, the contention resolution message is a PDCCH transmission addressed to the first C-RNTI.

[0120] In cases where the LTM DU configuration 1 includes a dedicated RA preamble, the RA procedure is a contention free RA procedure. In such cases, the UE 102 transmits the dedicated RA preamble to the DU 174 via the first cell. When the UE 102 receives an RA response including an ID of the dedicated RA preamble from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the RA procedure (i.e., the UE 102 successfully accesses the first cell).

[0121] If the DU 174 configures the UE 102 to perform an RA procedure on the first cell as described above, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives Message 3, Message A, or the dedicated preamble in the RA procedure. If the DU 174 configures the UE 102 to skip an RA procedure, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives the first transmission.

[0122] In some embodiments, the UE 102 transmits the first transmission (e.g., the PUSCH transmission) on the first cell using a UL grant. In some embodiments, the first LTM command includes the UL grant. In other embodiments, when the UE 102 performs an LTM serving cell change to the first cell in response to the first LTM command, the UE 102 receives a first DCI including the UL grant on a PDCCH on the first cell. In some embodiments, the UE 102 attempts to receive the first DCI or the UL grant by monitoring one or more PDCCHs on the first cell in accordance with the LTMDU configuration 1 , when the UE 102 switches to the first cell in response to the first LTM command. While monitoring one or more PDCCHs on the first cell, the UE 102 receives the first DCI and a CRC of the first DCI on the PDCCH. In the case that the LTM DU configuration 1 includes the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the second C-RNTI. In the case that the LTM DU configuration 1 does not include the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the first C- RNTI.

[0123] In some embodiments, the CU 172 transmits at least one first TCI state configuration to the UE 102 via the DU 174. In some embodiments, each of the first TCI state configuration(s) configures a TCI state for the UE 102 to transmit and / or receive data and / or control signal on the first cell. Each TCI state associates one or two DL RSs with a corresponding QCL type, and the DL RS(s) might be associated with a particular cell of the cell(s) 1 , ... , N. In some embodiments, the CU 172 receives a DU- to-CU message including the first TCI state configuration(s) from the DU 174 and transmits an RRC message including the first TCI state configuration(s) to the UE 102 via the DU 174. In further embodiments, the DU 174 includes the first TCI state configuration(s) in a serving DU configuration (e.g., CellGroupConfig IE) and includes the serving DU configuration in the DU-to-CU message. In some embodiments, the DU 174 includes the LTM DU configuration 1 in a first interface protocol lE / field in the message 312 and includes the serving DU configuration in a second interface protocol lE / field in the DU-to-CU message.

[0124] In some embodiments, the first interface protocol lE / field is defined as part of a format of the DU-to-CU message. The CU 172 includes the serving DU configuration in the RRC message. In some embodiments, the CU 172 refrains from including the serving DU configuration in a container for LTM (e.g., the first container). In other embodiments, the CU 172 includes the first TCI state configuration(s) in an element for LTM, an addition or modification list for LTM, or a container, similar to the element 1 , the first addition or modification list, or the first container respectively. In some embodiments, the RRC message is the RRC reconfiguration message 316, 318 or another RRC reconfiguration message (not shown in Fig. 3). In some embodiments,the DU-to-CU message is the message 312, the message 314, a UE Context Modification Response message, or a UE Context Modification Required message. In some embodiments, the DU 174 also includes the first TCI state configuration(s) in the LTM DU configuration 1. In other embodiments, the DU 174 refrains from including the first TCI state configuration(s) in the LTM DU configuration 1 .

[0125] In some embodiments, the first interface protocol lE / field is a first F1 AP lE / field and the second interface protocol lE / field is a second F1AP lE / field. In some embodiments, one of the first F1AP lE / field and the second F1AP lE / field is a F1AP CellGroupConfig lE / field and the other is not the F1AP CellGroupConfig lE / field. In some embodiments, the DU 174 includes the first F1AP lE / field in a DU to CU RRC Information IE in the message 312 and includes the second F1AP lE / field in the DU to CU RRC Information IE in the DU-to-CU message. In other embodiments, neither the first F1AP lE / field nor the second F1AP IE is a F1AP CellGroupConfig lE / field. In other embodiments, the second F1 AP lE / field is the DU to CU RRC Information IE and the first F1AP lE / field is a new IE specific for including an LTM DU configuration.

[0126] In some embodiments, after (e.g., in response to) receiving the first LTM command or while accessing 332 the first cell, the UE 102 monitors one or more PDCCHs on the first cell using some or all of the first TCI state configuration(s). In some embodiments, each of the first TCI state configuration(s) includes a TCI state ID identifying the corresponding TCI state configuration. For example, the first TCI state configuration(s) includes TCI state configuration(s) 1 , ..., L, where L is a positive integer larger than zero. The TCI state configuration(s) 1 , ... , L include TCI state ID(s) 1 , ... , L identifying the TCI state configuration(s) 1 , ... , L, respectively. The DU 174 includes the TCI state ID 1 in the first LTM command to indicate to the UE 102 to apply the TCI state configuration 1 to communicate on the first cell. After (e.g., in response to) receiving the first LTM command, the UE 102 accesses and / or communicates on the first cell using the TCI state configuration 1 in accordance with the TCI state ID 1 . For example, the UE 102 monitors one or more PDCCHs and / or transmits the first transmission, using the TCI state configuration 1. In some embodiments, the DU 174 detects that the UE 102 accesses the first cell and communicates with the UE 102 on the first cell, based on theTCI state configuration 1 . For example, the DU 174 receives the first transmission from the UE 102 on the first cell, based on the TCI state configuration 1 .

[0127] In some embodiments, the DU 174 includes the TCI state ID 2 in the first LTM command to indicate to the UE 102 to apply the TCI state configuration 2 to communicate on the first cell, in addition to the TCI state ID 1 . After (e.g., in response to) receiving the first LTM command, the UE 102 accesses and / or communicates on the first cell using the TCI state configurations 1 and 2 in accordance with the TCI state ID 1 and the TCI state ID 2. For example, the UE 102 monitors one or more PDCCHs on the first cell using the TCI state configuration 1 and transmits the first transmission on the first cell using the TCI state configuration 2. In another example, the UE 102 monitors one or more PDCCHs on the first cell using the TCI state configuration 1 and the TCI state configuration 2 and transmits the first transmission on the first cell using one of the TCI state configuration 1 and the TCI state configuration 2. In some embodiments, the DU 174 detects that the UE 102 accesses the first cell and communicates with the UE 102 on the first cell, based on the TCI state configuration 1 and / or the TCI state configuration 2. For example, the DU 174 receives the first transmission from the UE 102 on the first cell, based on one of the TCI state configuration 1 and the TCI state configuration 2.

[0128] In some alternative embodiments, the DU 174 might not include a TCI state ID in the first LTM command. In such cases, the UE lOcommunicates on the first cell with the first DU using the at least one first TCI state, after (e.g., in response to) receiving the first LTM command. In some embodiments, the DU 174 detects that the UE 102 accesses the first cell and communicates with the UE 102 on the first cell, based on the first TCI state configuration(s).

[0129] In some embodiments, before transmitting the first LTM command, the DU 174 might transmit one or more activation commands to activate some or all of the first TCI state configuration(s). In some embodiments, each of the activation command(s) is a MAC CE. In other embodiments, each of the activation command(s) is a DCI. In some embodiments, the DU 174 includes the TCI state ID 1 and / or TCI state ID 2 in the activation command(s) to activate the TCI state configuration 1 and / or the TCI state configuration 2, respectively. Accordingly, the UE 102 determines or identifies that theTCI state configuration 1 and / or the TCI state configuration 2 is / are activated upon receiving the activation command(s). In other embodiments, the DU 174 includes all the TCI state ID(s) for the first TCI state configuration(s) in the activation command(s). Accordingly, the UE 102 determines or identifies that the first TCI state configuration(s) is / are activated upon receiving the activation command(s). In some embodiments, the DU 174 refrains from including, in the first LTM command, a TCI state ID for a TCI state configuration that the DU 174 has not activated for the UE 102. In some embodiments, the DU 174 includes the cell ID 1 or the cell index 1 in the activation command(s). Based on the cell ID 1 or cell index 1 , and the one or more TCI state IDs in the activation command(s), the UE 102 determines that the activation command(s) activates the one or more TCI state configurations in the first TCI state configuration(s), where each of the TCI state ID(s) identifies a particular TCI state configuration of the TCI state configuration(s).

[0130] In some embodiments, the UE 102 communicates with the DU 174 on the cell 124A (e.g., events 302, 304, 318, 320, 324, 330), using one or more TCI state configurations. In some embodiments, each of the TCI state configuration(s) configures a TCI state for the UE 102 to transmit and / or receive data and / or control signal on the cell 124A. In some embodiments, the UE 102 stops using the TCI configuration(s) upon receiving the first LTM command.

[0131] After successfully accessing the first cell, the UE 102 communicates 336 with the DU 174 on the first cell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the DU 174. In such cases, the DU 174 communicates 336 with the UE 102 on the first cell using the LTM DU configuration 1 . In some scenarios or embodiments, the UE 102 communicates 336 PUSCH transmissions, PDSCH transmissions, PUCCH transmissions, PDCCH transmissions, and / or sounding reference signal (SRS) transmissions with the DU 174 on the first cell. In some embodiments, the UE 102 uses some or all of the first TCI state configuration(s) to perform 336 the communication with the DU 174. Similarly, the DU 174 uses some or all of the first TCI state configuration(s) to perform 336 the communication with the UE 102. In some embodiments, the DU 174 includes one or more additional TCI state configurations in the LTM DU configuration 1 . In such cases,the DU 174 might transmit one or more activation commands to the UE 102 via the first cell in the event 336 to activate the additional TCI state configuration(s). The UE 102 determines that the additional TCI state configuration(s) is / are activated upon receiving the activation command(s). In some embodiments, each of the activation command(s) is a MAC CE. In other embodiments, each of the activation command(s) is a DCI. After receiving the activation command(s), the UE 102 uses the additional TCI state configuration(s) to communicate with the DU 174 on the first cell. Similarly, after transmitting the activation command(s), the DU 174 uses the additional TCI state configuration(s) to communicate with the UE 102 on the first cell.

[0132] In the case that the UE 102 receives the reference LTM DU configuration as described above, the UE 102 communicates 336 with and the DU 174 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the UE 102 communicates 336 with the DU 174 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration. Similarly, the DU 174 communicates 336 with the UE 102 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the DU 174 communicates 336 with the UE 102 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration.

[0133] In the case that the UE 102 receives neither the LTM CU configuration 1 nor a / the reference LTM CU configuration, the UE 102 communicates 336 with the CU 172 via the DU 174 using the serving CU configuration. Correspondingly, if the CU 172 neither transmits the LTM CU configuration 1 nor a / the reference CU configuration to the UE 102, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving CU configuration. In the case that the UE 102 receives the LTM CU configuration 1 and the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CU configuration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1 .

[0134] In the case that the UE 102 receives the LTM CU configuration 1 and does not receive the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CU configuration 1. If the LTM CU configuration 1 is a full configuration, the UE 102 and CU 172 communicate 336 with each other via the DU 174 using the LTM CU configuration 1 instead of the serving CU configuration. In some embodiments, if the UE 102 does not receive a / the reference LTM CU configuration from the BS 104, the UE 102 determines that the LTM CU configuration 1 is a full configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a full configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In other embodiments, the CU 172 includes a first indication (e.g., a field or IE) in the LTM CU configuration 1 , the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration 1 is a full configuration. If the LTM CU configuration 1 is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the LTM CU configuration 1 and at least a portion of the serving CU configuration not augmented by the LTM CU configuration 1. In some embodiments, if the UE 102 does not receive a / the reference LTM CU configuration from the BS 104, the UE 102 determines that the LTM CU configuration 1 is a delta configuration to augment the serving CU configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a delta configuration to augment the serving CU configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In some embodiments, the CU 172 indicates that the LTM CU configuration 1 is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the LTM CU configuration 1 , the first container, the element 1 and / or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the LTM CU configuration 1 , the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration 1 is a delta configuration to augment the serving CU configuration. In some embodiments, the CU 172 indicates that the LTM CUconfiguration 1 is a full configuration, by excluding the second indication in the LTM CU configuration 1 , the first container, the element 1 and / or the RRC reconfiguration message 316.

[0135] In the case that the UE 102 receives the reference LTM CU configuration and does not receive the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the reference LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the reference LTM CU configuration. If the reference LTM CU configuration is a full configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration instead of the serving CU configuration. In some embodiments, the UE 102 and CU 172 determine that the reference LTM CU configuration 1 is a full configuration as specified in a 3GPP TS (e.g., 3GPP TS 38.331 ). In other embodiments, the CU 172 includes a first indication (e.g., a field or IE) in the reference LTM CU configuration, the first container or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a full configuration. If the reference LTM CU configuration is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration and at least a portion of the serving CU configuration not augmented by the reference LTM CU configuration. In some embodiments, the CU 172 indicates that the reference LTM CU configuration is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the reference LTM CU configuration, the first container, the element 1 and / or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the reference LTM CU configuration, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a delta configuration to augment the serving CU configuration. In some embodiments, the CU 172 indicates that the reference LTM CU configuration is a full configuration, by excluding the second indication in the reference LTM CU configuration, the first container, the element 1 and / or the RRC reconfiguration message 316.

[0136] In the case that the UE 102 neither receives the reference LTM CU configuration and nor the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the serving LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving LTM CU configuration.

[0137] In some embodiments, the UE 102 transmits an RRC message (e.g., RRC reconfiguration complete message) to the CU 172 via the DU 174 and the first cell to indicate that the UE 102 applies the LTM DU configuration 1 . In the case that the UE 102 performs the RA procedure 332, the UE 102 may include the RRC message in the Message 3 or Message A. Alternatively, the UE 102 transmits the RRC message after completing the RA procedure. In the case that the UE 102 skip the RA procedure 332, the UE 102 includes the RRC message in a PUSCH transmission of the at least one PUSCH transmission. In some embodiments, if the UE 102 maintains communication on the cell 124A with the BS 104 (i.e., the UE 102 does not disconnect from the cell 124A), the UE 102 may transmit the RRC message to the BS 104 via the cell 124A. When the DU 174 receives the RRC message, the DU 174 transmits the RRC message to the CU 172.

[0138] In other embodiments, the UE 102 refrains from transmitting the RRC message to the BS 104 in response to applying the LTM DU configuration 1 or receiving the first LTM command. In such cases, the UE 102 may include or transmit data in the Message 3, Message A or PUSCH transmission as described above. The UE 102 may generate a MAC PDU and / or a RLC PDU including the data and transmits or includes the MAC PDU and / or RLC PDU in the PUSCH transmission. For example, the data may be a PDCP PDU, a SDAP PDU, an LTE Positioning Protocol (LPP) PDU, an RRC PDU and / or a NAS PDU. The RRC PDU includes a UL-DCCH-Message excluding an RRC reconfiguration complete message. The NAS PDU includes a Mobility Management (MM) message or a Session Management (SM) message. The MM message may be a 5G MM message or a 6G MM message, and the SM message may be a 5G SM message or a 6G SM message. When the DU 174 receives the data, the DU 174 transmits the data to the CU 172.

[0139] When the DU 174 determines that the UE 102 successfully connects to the first cell in the event 332 or 336, the DU 174 may transmit 334 a DU-to-CU message (e.g., Access Success message) to the CU 172 (e.g., a CP of the CU 172). In some embodiments, the DU 174 includes the cell ID 1 of the first cell in the DU-to-CU message of the event 334. The cell ID may be a PCI or a CGI. Thus, the CU 172 determines that the UE 102 connects to the first cell upon receiving the DU-to-CU message of the event 334. When the DU 174 determines that the UE 102 successfully connect to the first cell in the event 332 or 336, the DU 174 may transmit a DL Data Delivery Status message or frame to the CU 172 (e.g., a UP of the CU 172). In some embodiments, when or after the CU 172 receives the DU-to-CU message 329, the CU 172 might stop or suspend transmitting DL data for the UE 102 to the DU 174 until receiving the DU-to-CU message 334. The CU 172 might do so because the DU 174 cannot buffer DL data for the UE 102 during the LTM execution in the events 330 and / or 332. After receiving the DU-to-CU message 334, the CU 172 continues or resumes transmitting DL data for the UE 102 to the DU 174. In other embodiments, when the CU 172 receives the DU-to-CU message 329, the CU 172 might continue transmitting DL data for the UE 102 to the DU 174. The CU 172 might do so because the DU 174 can buffer DL data for the UE 102 during the LTM execution in the events 330 and / or 332. When or after the DU 174 detects that UE 102 accesses the cell 1 , the DU 174 transmits the DL data to the UE 102 via the cell 1.

[0140] In some embodiments, upon (A) determining that the UE 102 connects to the first cell, (B) transmitting 330 the first LTM command, or (C) receiving 331 the acknowledgement, the DU 174 stops communicating with the UE 102 on the cell 124A and / or release resources of the cell 124A configured for the UE 102.

[0141] In some embodiments, the DU 174 generates some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ..., N as full configuration(s) to replace the serving DU configuration. If the LTM DU configuration 1 is a full configuration, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM DU configuration 1 instead of the serving DU configuration. In some embodiments, the DU 174 includes an indication indicating that the LTM DU configuration 1 is a full configuration in the LTM DU configuration 1. In each of the LTMDU configuration(s) 2, ... , N, the DU 174 may include an indication to indicate that the corresponding DU configuration is a full configuration. Each of the indication(s) in the LTM DU configuration(s) 1 , N may be a field or IE (i.e., the same field or IE). In other embodiments, the CU 172 includes, in the RRC reconfiguration message of the events 316, 318, a single indication indicating that the LTM DU configuration(s) 1 and / or 2, ... , N is / are full configuration(s). In the case of the second container, the CU 172 may include, in the additional RRC reconfiguration message, a single indication indicating that the LTM DU configuration(s) 2, ... , N is / are full configuration(s). In yet other embodiments, the CU 172 includes, in the first container, a single indication indicating that the LTM DU configuration(s) 1 and / or 2, ... , N is / are full configuration(s). In yet other embodiments, for each of the LTM DU configuration(s) 2, ... , N, the CU 172 includes, in the first container, a particular indication indicating the corresponding LTM DU configuration is a full configuration. In the case of the second container, the CU 172 may include, in the second container, a single indication indicating that the LTM DU configuration(s) 2, ... , N is / are full configuration(s). In yet other embodiments, the CU 172 includes, in the element 1 , an indication indicating that the LTM DU configuration 1 is a full configuration. In each of the element(s) 2, ... , N, the CU 172 may include an indication indicating that the corresponding LTM DU configuration is a full configuration. The UE 102 may determine that the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ... , N is / are full configuration(s) based on the indication(s) above. In some embodiments, each of the indication(s) above is different from a fullConfig field defined in the current 3GPP specification. In some embodiments, each of the indication(s) above is a fullConfig field defined in the current 3GPP specification. In the case that the LTM DU configuration 1 is a full configuration, the UE 102 in the event 336 does not apply the reference LTM DU configuration if received from the BS 104, e.g., in the RRC reconfiguration message 318. In such cases, the DU 174 might not include a / the reference LTM DU configuration in the first DU-to-CU message 310.

[0142] In other embodiments, the DU 174 generates the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ... , N as delta configuration(s) that augment (a portion of) the reference LTM DU configuration. In other words, the DU 174 generates the LTM DU configuration(s) 1 , ... N based on the reference LTM DU configuration. Forexample, if the LTM DU configuration 1 is a delta configuration, the UE 102 and DU 174 augment (the portion of) the reference LTM DU configuration with the LTM DU configuration 1. Thus, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM DU configuration 1 and un-augmented portion of the reference LTM DU configuration. In some embodiments, the LTM DU configuration(s) 1 , and / or 2... , N, first container, second container or element(s) 1 , ... , N exclude indication(s) indicating that the LTM DU configuration(s) 1 , and / or 2... , N is / are full configuration(s) to indicate that the LTM DU configuration(s) 1 and / or 2, .... N is / are delta configuration(s). The UE 102 may determine that each of the LTM DU configuration(s) 1 and / or 2, ... , N is a delta configuration based on that the indication is excluded in the LTM DU configuration(s) 1 and / or 2, ... , N, first container, second container or element(s) 1 and / or 2, ... , N.

[0143] In some embodiments, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and / or the LTM DU configuration(s) 2, ... , N, the UE 102 determines that the LTM DU configuration 1 , and / or the LTM DU configuration(s) 2, ... , N are full configuration(s). Correspondingly, if the DU 174 does not obtain a reference LTM DU configuration for the UE 102 (i.e. , the DU 174 does not generate a reference LTM DU configuration for the UE 102 and / or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1 , and / or the LTM DU configuration(s) 2, ... , N as full configuration(s).

[0144] In other embodiments, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and / or the LTM DU configuration(s) 2, ... , N, the UE 102 determines that the LTM DU configuration 1 , and / or the LTM DU configuration(s) 2, ... , N are delta configuration(s) to augment the serving DU configuration. In such cases, the UE 102 communicates 336 with the DU 174 in accordance with the LTM DU configuration 1 and at least a portion of the serving DU configuration not augmented by LTM DU configuration 1. Correspondingly, if the DU 174 does not obtain a reference LTM DU configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM DU configuration for the UE 102 and / or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1 , and / or the LTM DU configuration(s) 2, ... , N asdelta configuration(s) to augment the serving DU configuration. In such cases, the DU 174 communicates 336 with the UE 102 in accordance with the LTM DU configuration 1 and the at least a portion of the serving DU configuration.

[0145] In some embodiments, the UE 102 uses a UE MAC entity (e.g., MAC 204B) to communicate with a DU MAC entity (e.g., MAC 204B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330 and / or 331 ). In some embodiments, the UE 102 resets the UE MAC entity, after or in response to receiving the first LTM command and before performing 332 the RA procedure or communicating 336 with the DU 174 via the first cell. In some embodiments, the DU 174 resets the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell.

[0146] In some embodiments, when the UE 102 resets the UE MAC entity, the UE 102 performs at least one of the following actions for the UE MAC entity (i.e. , UE MAC reset or full UE MAC reset):• initialize Bj for configured logical channel(s) to zero;• stop one or more timers;• consider timeAlignmentTimer(s) as expired, if the UE 102 is configured to perform the RA procedure (e.g., the event 332) in the configuration (e.g., the configuration 1 );• set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0;• set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1 ;• flush Msg3 buffer;• flush MSGA buffer;• cancel, if any, triggered Scheduling Request procedure;• cancel, if any, triggered Buffer Status Reporting procedure;• cancel, if any, triggered Power Headroom Reporting procedure;• cancel, if any, triggered consistent LBT failure;• cancel, if any, triggered BFR;• cancel, if any, triggered Sidelink Buffer Status Reporting procedure;• cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure;• cancel, if any, triggered Timing Advance Reporting procedure;• cancel, if any, triggered Recommended bit rate query procedure;• cancel, if any, triggered configured uplink grant confirmation;• cancel, if any, triggered configured sidelink grant confirmation;• cancel, if any, triggered Desired Guard Symbol query;• cancel, if any, triggered Positioning Measurement Gap Activation / Deactivation Request procedure;• flush soft buffers for DL HARQ process(es);• for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission;• release, if any, Temporary C-RNTI;• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0147] In some embodiments, when the DU 174 resets the DU MAC entity, the DU 174 performs at least one of the following actions for the DU MAC entity (i.e., DU MAC reset or full DU MAC reset):• stop one or more timers;• consider timeAlignmentTimer(s), that the DU 174 starts and / or maintains for the UE 102, as expired, if the UE 102 is configured to perform the RA procedure (e.g., the event 332) in the configuration (e.g., the configuration 1 );• set NDI(s) for DL HARQ process(es) to value 0;• flush soft buffers for UL HARQ process(es);• for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission;• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0148] Depending on embodiment, the UE 102 may determine to reset the UE MAC entity partially or fully. In some embodiments, when the UE 102 resets the UE MAC entity as described above, the UE 102 fully resets the UE MAC entity (i.e., a full UE MAC reset). In the full UE MAC reset, the UE 102 performs some or all of the actions described above. In other embodiments, when the UE 102 resets the UE MAC entity as described above, the UE 102 partially resets the UE MAC entity (i.e., a partial UE MACreset). In the partial LIE MAC reset, the UE 102 performs a subset or portion of the some or all of the actions in the full UE MAC reset.

[0149] In some embodiments, the partial UE MAC reset includes at least one of the following actions:• consider timeAlignmentTimer(s) of the UE 102 as expired, if the UE 102 is configured to perform the RA procedure (e.g., the event 332) in the configuration (e.g., the configuration 1 );• flush Msg3 buffer;• flush MSGA buffer;• release, if any, Temporary C-RNTI;• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0150] In some embodiments, the partial UE MAC reset further includes at least one of the following actions:• cancel, if any, triggered Scheduling Request procedure;• cancel, if any, triggered Buffer Status Reporting procedure;• cancel, if any, triggered Power Headroom Reporting procedure;• cancel, if any, triggered consistent LBT failure;• cancel, if any, triggered BFR;• cancel, if any, triggered Sidelink Buffer Status Reporting procedure;• cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure;• cancel, if any, triggered Timing Advance Reporting procedure;• cancel, if any, triggered Recommended bit rate query procedure;• cancel, if any, triggered configured uplink grant confirmation;• cancel, if any, triggered configured sidelink grant confirmation;• cancel, if any, triggered Desired Guard Symbol query;• cancel, if any, triggered Positioning Measurement Gap Activation / Deactivation Request procedure.

[0151] In some embodiments, the partial UE MAC reset further includes at least one of the following actions:• stop a first portion of the one or more timers and retain the rest of the one or more timers;• set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0;• set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1 ;• flush soft buffers for DL HARQ process(es);• for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission.

[0152] Depending on embodiments, the DU 174 may determine to reset the DU MAC entity partially or fully. In some embodiments, when the DU 174 resets the DU MAC entity as described above, the DU 174 fully resets the DU MAC entity (i.e., a full DU MAC reset). In the full DU MAC reset, the DU 174 performs some or all of the actions described above. In other embodiments, when the DU 174 resets the DU MAC entity as described above, the DU 174 partially resets the DU MAC entity (i.e., a partial DU MAC reset). In the partial DU MAC reset, the DU 174 performs a subset or portion of the some or all of the actions in the full DU MAC reset.

[0153] In some embodiments, the partial DU MAC reset includes at least one of the following actions in the partial MAC reset:• consider timeAlignmentTimer(s), that the DU 174 starts and / or maintains for the UE 102, as expired, if the UE 102 is configured to perform the RA procedure (e.g., the event 332) in the configuration (e.g., the configuration 1 );• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs)

[0154] In some embodiments, when the partial DU MAC reset includes at least one of the following actions for the MAC entity (i.e., DU MAC reset):• stop a first portion of the one or more timers and retain the rest of the one or more timers;• set NDI(s) for DL HARQ process(es) to value 0;• flush soft buffers for UL HARQ process(es);• for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission;• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs)

[0155] In other embodiments, the UE 102 refrains from resetting the UE MAC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from resetting the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the UE MAC entity (not reset). Similarly, the DU 174 communicates with the UE 102 using the DU MAC entity (not reset) on the first cell during or after the RA procedure 332 or after determining that the UE 102 connects to the first cell.

[0156] In some embodiments, the UE 102 uses at least one UE RLC entity (e.g., RLC 206B) to communicate RLC PDUs with at least one DU RLC entity (e.g., RLC 206B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330 and / or 331 ). In some embodiments, the UE 102 reestablishes some or all of the at least one UE RLC entity, after or in response to receiving the first LTM command and before performing 332 the RA procedure or communicating 336 with the DU 174 via the first cell. In some embodiments, the DU 174 reestablishes some or all of the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell.

[0157] In some embodiments, the LTM DU configuration 1 may or may not include one or more RLC reestablishment indications (e.g., reestablishRLC field(s)) configuring the UE 102 to reestablish some or all of the at least one UE RLC entity. If the LTM DU configuration 1 includes an RLC reestablishment indication configuring the UE 102 to reestablish a first UE RLC entity of the at least one UE RLC entity, that the UE 102 uses to communicate RLC PDU(s) with the DU 174, the UE 102 reestablishes the first UE RLC entity in response to the RLC reestablishment indication and the first LTM command. In some embodiments, the UE 102 reestablishes the first UE RLC entity before performing 332 the RA procedure or communicating 336 with the DU 174 via the first cell. In other embodiments, the UE 102 reestablishes the first UE RLC entity while or after performing 332 the RA procedure. Otherwise, if the LTM DU configuration 1 does not include the RLC reestablishment indication, the UE 102 refrains from reestablishing the first UE RLC entity in response to the first LTM command.

[0158] In some embodiments, when the UE 102 reestablishes the first UE RLC entity, the UE 102 performs at least one of the following actions for the first UE RLC entity:• discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any;• stop and reset timer(s), if running;• reset state variables to initial values.In some embodiments, the state variables and timer(s) are defined in 3GPP TS 38.322.

[0159] Otherwise, if the LTM DU configuration 1 does not include the RLC reestablishment indication for the first UE RLC entity, the UE 102 refrains from reestablishing the first UE RLC entity upon or when receiving the first LTM command. In other words, the UE 102 refrains from performing the actions for reestablishing the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. In some embodiments, if the LTM DU configuration 1 or element 1 does not include the RLC reestablishment indication and includes an indication indicating that the configuration 1 is a full configuration, the UE 102 reestablishes the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. Otherwise, if the LTM DU configuration 1 or element 1 does not include the RLC reestablishment indication and the indication indicating that the configuration 1 is a full configuration, the UE 102 refrains from reestablishing the first UE RLC entity upon or when receiving the first LTM command.

[0160] Similarly, the DU 174 reestablishes some or all of at least one DU RLC entity (e.g., NR RLC 206B) that the DU 174 uses to communicate with the at least one UE RLC entity of the UE 102 (e.g., the events 302, 304, 318, 320, 324, 330 and / or 331 ) in response to the RLC reestablishment indication. In some embodiments, the DU 174 reestablishes a first DU RLC entity of the at least one DU RLC entity after transmitting the first LTM command, receiving an acknowledgement for the first LTM command from the UE 102, or determining that the UE 102 connects to the first cell. In some embodiments, the acknowledgement is a HARQ ACK. In other embodiments, the acknowledgement is a MAC CE. In yet other embodiments, the acknowledgement is a PUCCH transmission. In some embodiments, when the BS 104 reestablishes the first DU RLC entity, the DU 174 performs at least one of the following actions for the first DU RLC entity:discard RLC SDll(s), RLC SDU segment(s), and RLC PDU(s), if any; stop and reset timer(s), if running; reset state variables to initial values.

[0161] In some embodiments, the state variables and timer(s) are defined in 3GPP TS 38.322.

[0162] In other embodiments, the UE 102 refrains from reestablishing some or all of the at least one UE RLC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from reestablishing some or more of the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 , or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the some or all of the at least one UE RLC entity (not reestablished). For example, the some or all of the at least one UE RLC entity includes the first UE RLC entity and / or a second UE RLC entity. Similarly, the DU 174 communicates with the UE 102 using the some or all of the at least one DU RLC entity (not reestablished) on the first cell during or after the RA procedure 332 or after determining that the UE 102 connects to the first cell. For example, the some or all of the at least one DU RLC entity includes the first DU RLC entity and / or a second DU RLC entity.

[0163] In some embodiments, the UE 102 uses at least one UE PDCP entity (e.g., PDCP 210) to communicate UL PDCP PDUs and / or DL PDCP PDUs with at least one CU PDCP entity (e.g., PDCP 210) of the CU 172 in the event 302. In some embodiments, the UE 102 performs a PDCP recovery procedure for some or all of the at least one UE PDCP entity, after or in response to receiving the first LTM command. For example, the UE 102 performs a PDCP recovery procedure for a first UE PDCP entity of the at least one UE PDCP entity, after or in response to receiving the first LTM command. In the PDCP recovery procedure, the UE 102 may or may not reestablish the first UE PDCP entity. After or in response to performing the PDCP recovery procedure, the UE 102 may retransmit at least a portion of the UL PDCP PDUs to the CU 172 via the DU 174 and the first cell in the event 336. Similarly, the CU 172 performs a PDCP recovery procedure for some or all of the at least one CU PDCP entity after or in response to transmitting the first LTM command. For example, the CU172 performs a PDCP recovery procedure for a first CU PDCP entity of the at least one CU PDCP entity, after or in response to transmitting the first LTM command. In some embodiments, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DU-to-CU message 329 or 334. In other embodiments, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DL Data Delivery Status message. In the PDCP recovery procedure, the CU 172 may or may not reestablish the first CU PDCP entity. After or in response to performing the PDCP recovery procedure, the CU 172 may retransmit at least a portion of the DL PDCP PDUs to the UE 102 via the DU 174 and the first cell in the event 336.

[0164] In other embodiments, the UE 102 refrains from reestablishing some or all of the at least one UE PDCP entity in response to receiving the first LTM command. For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and / or a second UE PDCP entity. Similarly, the CU 172 refrains from reestablishing some or more of the at least one CU PDCP entity, after (e.g., in response to) receiving the DU-to-CU message 329 or 340 or after (e.g., in response to) receiving the DL Data Delivery Status message. In other words, the UE 102 communicates with the CU 172 via the DU 174 and the first cell using the some or all of the at least one UE PDCP entity (not reestablished). For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and / or a second UE PDCP entity. Similarly, the CU 172 communicates with the UE 102 using the some or all of the at least one CU PDCP entity (not reestablished) via the DU 174 and the first cell. For example, the some or all of the at least one CU PDCP entity includes the first CU PDCP entity and / or a second CU PDCP entity.

[0165] In some embodiments, after determining that the UE 102 connects to the first cell, the CU 172 transmits 338 a CU-to-DU message (e.g., a UE Context Modification Request message) to the DU 174 to indicate the DU 174 to stop communicating with the UE 102 and / or to release or suspend resources, of the cell 124A, configured for the UE 102. In response, the DU 174 may stop communicating on the cell 124A with the UE 102 and / or release or suspend resources, of the cell 124A, configured for the UE 102, and transmit 340 a DU-to-CU message (e.g., a UE Context Modification Responsemessage) to the CU-172. The events 338 (optional) and 340 (optional) are collectively referred to in Fig. 3 as a resource release procedure 396.

[0166] After or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351 , 352, 354 and / or 356 might occur, similar to the events 324, 326, 328, 330, 331 , 332, 334 and / or 336, respectively. The UE 102 transmits 344 at least one measurement report to the DU 174. The at least one measurement report includes at least one measurement result for a second cell (i.e. , the cell 2). The at least one measurement result indicates that the second cell is suitable for communication with UE 102 and / or the first cell is not suitable for communication with the UE 102. After (e.g., in response to) receiving the at least one measurement report, the DU 174 determines to activate the LTM DU configuration 2 and generates a second LTM command to activate the LTM DU configuration 2 (i.e., the second LTM command commands the UE 102 to apply the LTM DU configuration 2). The DU 174 then transmits 350 the second LTM command to the UE on the first cell to the UE 102.

[0167] When or in response to determining to activate the LTM DU configuration 2 or transmit the second LTM command, the DU 174 might transmit 349 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some embodiments, the DU 174 includes the cell ID 2 or the ID 2 (i.e., LTM ID) in the DU-to-CU message 349 to indicate that the DU 174 is to activate the LTM DU configuration 2. The DU may transmit the DU-to-CU message 349 to the CU 172 before or after transmitting the LTM command 350.

[0168] The descriptions for the events 324, 326, 328, 330, 331 , 332, 334 and / or 336 can be applied to the events 344, 346, 348, 350, 351 , 352, 354 and / or 356 with simple changes. For example, “cell 124A”, “first LTM command”, “first cell”, “ID 1”, “LTM DU configuration 1” and / or “LTM CU configuration 1” are replaced with “first cell”, “second LTM command” and “second cell”, “ID 2”, “LTM DU configuration 2” and / or “LTM CU configuration 2”, respectively.

[0169] The events 344, 346, 348, 350, 351 , 352, 354 are collectively referred to in Fig. 3 as an LTM execution procedure 398. The events 304, 306, 390, 392, 394, 324, 326, 328, 329, 330, 331 , 332, 334, 336, 396, 398, 356 are collectively referred to in Fig. 3 as an LTM DU configuration and / or activation procedure 380.

[0170] Referring next to Fig. 4, in a scenario 400, the BS 104 includes a CU 172, a source DU (S-DU) 174A and a target DU (T-DU) 174B. The S-DU 174A operates the cell 124A and optionally additional cell(s), while the T-DU 174B operates a first cell (e.g., cell 124C). The scenario 400 is similar to the scenario 300. Thus, the descriptions for the scenario 300 generally apply to the scenario 400. The differences between the scenarios 300 and 400 are described below.

[0171] Initially, the UE 102 communicates 402 with the S-DU 174A on cell 124A using a serving DU configuration and communicates with the CU 172 via the S-DU 174A. The S-DU 174A is a serving DU similar to the DU 174 in Fig. 3A. During the communication 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 at least one measurement report, the CU 172 determines to prepare cell(s) 1 , ... , N (operated by the T-DU 174B) for LTM for the UE 102, where N is a positive integer larger than 0 or 1. The cell(s) 1 , ... , N are identified by cell ID(s) 1 , ... , N, respectively. In response to the determination, the CU 172 performs 490 an LTM preparation procedure with the T-DU 174B to (request the T-DU 174B to) prepare cell(s) 1 , ... , N for LTM for the UE 102. N can be a positive integer larger than zero or 1 . In the LTM preparation procedure 490, the CU 172 transmits a CU-to-DU message including the cell ID(s) 1 , ... , N to the T-DU 174B to request the T-DU 174B to prepare the cell(s) 1 , ... , N for LTM for the UE 102, similar to the event 308. In response, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) 1 , ... , N to the CU 172, similar to the event 310. The LTM DU configuration(s) 1 , ... , N configures the cell(s) 1 , ... , N for LTM, respectively. In detail, the LTM DU configuration(s) 1 , ... , N include configuration parameters for communication on the cell(s) 1 , ... , N, respectively. In some embodiments, the CU-to-DU message and DU-to-CU message in the procedure 490 are UE Context Setup Request message and UE Context Setup Response message, respectively. The CU 172 then transmits the LTM DU configuration(s) 1 , ... , N in an RRC reconfiguration message in an LTM configuration delivery procedure 494, similar to the LTM configuration delivery procedure 394. In some embodiments, the T-DU 174B may include cell index(es) 1 , ... , N in the LTM DU configuration(s) 1 , ... , N, respectively. In some embodiments, the CU 172 may set thecell index(es) 1 , N to different values and include the cell index(es) 1 , N in the CU-to-DU message of the procedure 490.

[0172] After performing the LTM preparation procedure 490, the CU 172 might perform an additional LTM preparation procedure(s) with the T-DU 174B to prepare cell(s) N+1 , , N+M for LTM for the UE 102, similar to the procedure 490. M is a positive integer larger than zero. The CU 172 might determine to do so based on one or more measurement reports received from the UE 102 via the S-DU 174A, similar to the events 404, 406. In the additional LTM preparation procedure, the CU 172 transmits a CU-to-DU message including cell ID(s) N+1 , ... , N+M to the T-DU 174B to request the T-DU 174B to prepare the cell(s) N+1 , ... , N+M for LTM for the UE 102. The cell ID(s) N+1 , ... , N+M identifies the cell ID(s) N+1 , ... , N+M, respectively. In response to the CU-to-DU message, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) N+1 , ... , N+M to the CU 172. The LTM DU configuration(s) N+1 , ... , N+M configures the cell(s) N+1 , .... N+M for LTM, respectively. In details, the LTM DU configuration(s) N+1 , ... , N+M include configuration parameters for communication on the cell(s) N+1 , ... , N+M, respectively. The CU 172 then transmits the LTM DU configuration(s) N+1 , ... , N+M in an RRC reconfiguration message in an additional LTM configuration delivery procedure, similar to the LTM configuration delivery procedure 394 or 494.

[0173] In some embodiments, the LTM preparation procedure 490 is a UE Context Setup procedure, and the additional LTM preparation procedure is a UE Context Modification procedure.

[0174] In some embodiments, the CU 172 and S-DU 174A might perform the procedure 380 with the UE 102, as described relative to Fig. 3. In the procedure 380, the CU 172 and S-DU 174A perform the procedure(s) 390 and / or 392 to prepare cell(s) of the S-DU 174A for LTM for the UE 102. Note, the value N in the procedure 380 or described relative to Fig. 3 may be the same as or different from the value N described relative to Fig. 4. In the procedure 390, the CU 172 might receive the first DU-to-CU message including the reference LTM DU configuration from the S-DU 174A in the event 310. In other embodiments, the CU 172 and S-DU 174A does not perform the procedure 380 with the UE 102. In such cases, the CU 172 may perform 488 areference LTM DU configuration query procedure with the S-DU 174A to obtain a reference LTM DU configuration. In the procedure 488, the CU 172 transmits 460 a CU- to-DU message to the S-DU 174A to request or query a reference LTM DU configuration. In some embodiments, the CU 172 may include an indication in the CU- to-DU message to request or query a reference LTM DU configuration. In response to the indication or CU-to-DU message 460, the S-DU 174A transmits 462 a DU-to-CU message including a reference LTM DU configuration to the CU 172. In some embodiments, the indication is a reference LTM DU configuration query indication. In other embodiments, the indication is an LTM indication, and the CU 172 might include a query indication (e.g., GNB-DU Configuration Query IE) in the CU-to-DU message. After receiving the reference LTM DU configuration (i.e., either in the procedure 390 or in the procedure 488), the CU 172 includes the reference LTM DU configuration (received from the S-DU 174A) in the CU-to-DU message in the LTM preparation procedure 490. The T-DU 174B generates the LTM DU configuration(s) 1 , , N based on the reference LTM DU configuration received from the CU 172. In such cases, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. The CU 172 might not include the reference LTM DU configuration in CU-to-DU message in the additional LTM preparation procedure with the T-DU 174B. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+1 , ... , N+M based on the reference LTM DU configuration received from the CU 172.

[0175] In some embodiments, the CU 172 does not provide a reference LTM DU configuration to the T-DU 174B in the LTM preparation procedure 490. In such cases, the T-DU 174B generates a reference LTM DU configuration and generates the LTM DU configuration(s) 1 , ... , N based on the reference LTM DU configuration. In such cases, the T-DU 174B includes the reference LTM DU configuration in the DU-to-CU message in the procedure 490. The CU 172 transmits the reference LTM DU configuration in the RRC reconfiguration message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DUconfiguration(s) N+1 , ... , N+M based on the reference LTM DU configuration. In this case, the T-DU 174B might not include the reference LTM DU configuration in the DU- to-CU message in the additional LTM preparation procedure. In some embodiments, the reference LTM DU configuration generated by the T-DU 174B is different from the reference LTM DU configuration generated by the S-DU 174A. In other embodiments, the reference LTM DU configuration generated by the T-DU 174B is the same as the reference LTM DU configuration generated by the S-DU 174A.

[0176] In some embodiments, the CU 172 includes the LTM DU configuration(s)1 , ... , N of the procedure 380 in the CU-to-DU message of the procedure 490, and the T-DU 174B generates the LTM DU configuration(s) 1 , ... , N and / or N+1 , ... , N+M, considering or based on configuration(s) in the LTM DU configuration(s) of the procedure 380.

[0177] In some embodiments, the LTM DU configuration X of the procedure 380 includes at least one reference signal (RS) resource configuration X, where 1 < X < N. Each of the RS resource configuration(s) X configures one or more RSs or one or more RS resources associated with the cell X of the S-DU 174A. The RS(s) includes SSB(s) and / or CSI-RS(s). The RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some embodiments, each of the RS resource configuration(s) X includes a RS resource configuration ID. In some embodiments, the RS resource configuration(s) X is / are (similar to) CSI-ResourceConfig IE(s). In some embodiments, the LTM DU configuration X includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI-ResourceConfig IE(s). The T-DU 174B generates at least one report configuration 1 for reporting, on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s) and includes the report configuration(s) 1 in the LTM DU configuration 1 . In some embodiments, the report configuration(s) 1 is / are (similar to) CSI-ReportConfig IE(s). In some embodiments, the T-DU 174B generates at least one RS resource configuration 1 , considering or based on the RS resource configuration(s) X and includes the RS resource configuration(s) 1 in the LTM DU configuration 1. In some embodiments, the T-DU 174B includes the RS resource configuration(s) X in the RS resource configuration(s) 1. In other embodiments, the T-DU 174B includes each of the RS resource configuration(s) X in the RS resource configuration(s) 1 , except the RSresource configuration ID(s) in the RS resource configuration(s) X. The T-Dll 174B assigns an RS resource configuration ID to a value for each of the RS resource configuration(s) 1 (including the RS resource configuration(s) X) and includes the RS resource configuration ID in the corresponding RS resource configuration.

[0178] In some embodiments, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some embodiments, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configuration(s) 1. After the UE 102 performs an LTM serving cell change to the cell 1 from the cell 124A, the UE 102 communicates with the S-DU 174B (i.e. , the T-DU 17B becomes a S-DU for the UE 102) and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the report configuration(s) 1. Correspondingly, the S- DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the report configuration(s) 1. In some embodiments, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) 1 and / or the report configuration(s) 1 and obtains the quantized measurement values from the measurements. In some embodiments, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some embodiments, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values might include one or more L1-RSRP values and / or one or more L1 -SINR values.

[0179] In some embodiments, the T-DU 174B also includes additional RS resource configuration(s) in the LTM DU configuration 1. Each of the additional RS resource configuration(s) configures one or more additional RSs or one or more additional RS resources associated with the cell 1 . The additional RS(s) includes SSB(s) and / or CSI- RS(s). The additional RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some embodiments, each of the additional RS resource configuration(s)includes a RS resource configuration ID. In some embodiments, the additional RS resource configuration(s) is / are (similar to) CSI-ResourceConfig IE(s). In some embodiments, the T-DU 174B includes the CSI-ResourceConfig IE(s) in the CSI- MeasConfig IE. The T-DU 174B generates at least one additional report configuration for reporting, on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s) and includes the additional report configuration(s) in the LTM DU configuration 1 . In some embodiments, the additional report configuration(s) is / are (similar to) CSI-ReportConfig IE(s).

[0180] In some embodiments, the additional report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some embodiments, each of the additional report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the additional RS resource configuration(s). After the UE 102 performs an LTM serving cell change to the cell 1 from the cell 124A, the UE 102 communicates 436 with the S-DU 174B and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the additional report configuration(s). Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the additional report configuration(s). In some embodiments, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the additional RS(s) or the additional RS resource(s) in accordance with the additional RS resource configuration(s) and / or the additional report configuration(s) and obtains the quantized measurement values from the measurements. In some embodiments, the RS resource indicator(s) indicates the additional RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some embodiments, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values might include one or more L1-RSRP values and / or one or more L1-SINR values.

[0181] Similarly, the T-DU 174B may generate RS resource configuration(s) 2, N, and / or N+1 , N+M and / or report configuration(s) 2, N, and / or N+1 , N+M, considering or based on the RS resource configuration(s) X, and include the RS resource configuration(s) 2, N, and / or N+1 , N+M and / or the report configuration(s) 2, N, and / or N+1 , N+M in the LTM DU configuration(s) 2, N, and / or N+1 , .... N+M, respectively, as described above.

[0182] In other embodiments, the LTM DU configuration X of the procedure 380 includes at least one TCI state configuration X, where 1 < X < N. Each of the TCI state configuration(s) X configures a TCI state that associates one or two DL RSs with a corresponding QCL type. In some embodiments, the DL RS(s) may be associated with the cell X operated by the S-DU 174A. In some embodiments, each of the TCI state configuration(s) X includes a TCI state ID. In some embodiments, each of the TCI state configuration(s) X is a TCI-State IE. In some embodiments, the TCI state configuration(s) X includes / is / are an ul-TCI-ToAddModList-r17 field, one or more TCI- UL-State-r17 lEs, a dl-OrJointTCI-StateToAddModList-r17 field, one or more TCI-State lEs, TCI-ActivatedConfig IE and / or a tci-StatesToAddModList field. In some embodiments, the LTM DU configuration X includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) X. In some embodiments, the T-DU 174B generates at least one TCI state configuration 1 , considering or based on the TCI state configuration(s) X and includes the TCI state configuration(s) 1 in the LTM DU configuration 1. In some embodiments, the TCI state configuration(s) 1 includes the TCI state configuration(s) X. In other embodiments, the T-DU 174B includes each of the TCI state configuration(s) X in the TCI state configuration(s) 1 , except the TCI state ID(s) in the TCI state configuration(s) X. The T-DU 174B assigns a TCI state ID to a value for each of the TCI state configuration(s) 1 (including the TCI state configuration(s) X) and includes the TCI state ID in the corresponding TCI state configuration. While the UE 102 and the S-DU 174B communicate 436 with one another, the S-DU 174B might transmit an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell X. The S-DU 174B includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell X, where the TCIstate configuration is one of the TCI state configurations X or includes configurations of one of the TCI state configuration(s) X.

[0183] Similarly, the T-DU 174B may generate TCI state configuration(s) 2, N, considering or based on the RS resource configuration(s) X, and include the TCI state configuration(s) 2, N, and / or N+1 , N+M in the LTM DU configuration(s) 2, N, and / or N+1 , .... N+M, respectively, as described above.

[0184] In some embodiments, in cases where the CU 172 performs the procedure 380 after performing the procedure 490, the CU 172 includes the LTM DU configuration(s) 1 , ... , N of the procedure 490 in the CU-to-DU message of the procedure 380, and the S-DU 174A generates the LTM DU configuration(s) 1 , , N of the procedure 380, considering or based on configurations in the LTM DU configuration(s) of the procedure 490, in a similar way as described above.

[0185] In some embodiments, the CU 172 assigns ID(s) 1 , ... , N identifying the LTM DU configuration(s) 1 , ... , N (received from the T-DU 174B), respectively, and performs the procedure 492 with the T-DU 174B to provide the ID(s) 1 , ... , N and / or cell ID(s) 1 , ... , N to the T-DU 174B, similar to the procedure 392. Thus, the T-DU 174B associates the ID(s) 1 , ... , N with the LTM DU configuration(s) 1 , ... , N and / or the cell ID(s) 1 , ... , N, respectively. In other embodiments, the T-DU 174B assigns ID(s) 1 , ... , N identifying the LTM DU configuration(s) 1 , ... , N (generated by the T-DU 174B), respectively and includes the ID(s) 1 , ... , N in the DU-to-CU message of the procedure 490, similar to the event 310. In some embodiments, the CU 172 assigns ID(s) N+1 , ... , N+M identifying the LTM DU configuration(s) N+1 , ... , N+M, respectively, and performs a procedure (similar to the procedure 492) with the T-DU 174B to provide the ID(s) N+1 , ... , N+M and / or cell ID(s) N+1 , ... , N+M to the T-DU 174B, similar to the procedure 392. Thus, the T-DU 174B associates the ID(s) N+1 , ... , N+M with the LTM DU configuration(s) N+1 , ... , N+M and / or the cell ID(s) N+1 , ... , N+M, respectively. In other embodiments, the T-DU 174B assigns ID(s) N+1 , ... , N+M identifying the LTM DU configuration(s) N+1 , ... , N+M, respectively and includes the ID(s) 1 , ... , N in the DU-to- CU message of the additional LTM preparation procedure, similar to the event 310.

[0186] In some embodiments, the CU 172 transmits 412 a CU-to-DU message including the ID(s) 1 , ... , N to the S-DU 174A and receives 414 a DU-to-CU messagefrom the S-Dll 174A in response. The CU-to-DU message 412 and DU-to-CU message 414 are collectively referred to in Fig. 4 as an LTM ID transfer procedure 493 or an LTM cell index transfer procedure 493. In some embodiments, the message 412 and message 414 may be LIE Context Modification Request message and UE Context Modification Response message, respectively. In some embodiments, the CU 172 includes the LTM DU configuration(s) 1 , ... , N and / or cell ID(s) 1 , .... N in the CU-to-DU message 412. In one embodiment, the CU 172 includes the ID(s) 1 , ... , N in the CU-to- DU message 412. In another embodiment, the CU 172 includes the cell index(es) 1 , ... , N in the CU-to-DU message 412. In some alternative embodiments, the CU 172 may perform multiple LTM ID transfer procedures to transmit the ID(s) 1 , ... , N, cell ID(s) 1 , ... , N and / or LTM DU configuration(s) 1 , ... , N to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the ID(s) 1 , ... , N, cell ID(s) 1 , ... , N and / or LTM DU configuration(s) 1 , ... , N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associates the ID(s) 1 , ... , N with the LTM DU configuration(s) 1 , ... , N and / or the cell ID(s) 1 , ... , N, respectively. In other alternative embodiments, the CU 172 may perform multiple LTM cell index transfer procedures to transmit the cell index(es) 1 , ... , N, cell ID(s) 1 , ... , N and / or LTM DU configuration(s) 1 , ... , N to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the cell index(es) 1 , ... , N, cell ID(s) 1 , ... , N and / or LTM DU configuration(s) 1 , ... , N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associates the cell index(es) 1 , ... , N with the LTM DU configuration(s) 1 , ... , N and / or the cell ID(s) 1 , ... , N, respectively.

[0187] In some embodiments, the S-DU 174A generates a first serving DU configuration, based on the LTM DU configuration(s) 1 , 2, ... , and / or N, and includes the first serving DU configuration in the DU-to-CU message 414. In some embodiments, the first serving DU configuration includes configurations for updating (e.g., augmenting, modifying or replacing) the serving DU configuration 402. In other embodiments, the first serving DU configuration includes configurations that are not included in the serving DU configuration 402. The CU 172 transmits an RRC reconfiguration message including the first serving DU configuration to the UE 102. The UE 102 applies the first serving DU configuration to communicate with the serving DU upon receiving the RRCreconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on embodiments, the UE 102 communicates with the S-DU 174A using configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. The following are example embodiments of generating the first serving DU configuration based on the LTM DU configuration 1 , ... , N.

[0188] In some embodiments, the LTM DU configuration Y of the procedure 490 includes at least one RS resource configuration Y, where 1 < Y < N. Each of the RS resource configuration(s) Y configures one or more RSs or one or more RS resources associated with the cell Y of the T-DU 174B. The RS(s) includes SSB(s) and / or CSI- RS(s). The RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some embodiments, each of the RS resource configuration(s) Y includes an RS resource configuration ID. In some embodiments, the RS resource configuration(s) Y is / are (similar to) CSI-ResourceConfig IE(s). In some embodiments, the LTM DU configuration Y includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI-ResourceConfig IE(s). The S-DU 174A generates at least one serving report configuration for reporting, on the cell 124A, measurement results of the RS(s) or RS resource(s) and includes the serving report configuration(s) in the first serving DU configuration. In some embodiments, the serving report configuration(s) is / are (similar to) CSI-RepoiiConfig IE(s). In some embodiments, the S-DU 174A generates at least one serving RS resource configuration, considering or based on the RS resource configuration(s) Y and includes the serving RS resource configuration(s) in the first serving DU configuration. In some embodiments, the S-DU 174A includes the RS resource configuration(s) Y in the serving RS resource configuration(s). In other embodiments, the S-DU 174A includes each of the RS resource configuration(s) Y in the serving RS resource configuration(s), except the RS resource configuration ID(s) in the RS resource configuration(s) Y. The S-DU 174A assigns a RS resource configuration ID to a value for each of the serving RS resource configuration(s) (including the RS resource configuration(s) Y) and includes the RS resource configuration ID in the corresponding serving RS resource configuration.

[0189] In some embodiments, the serving report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 124A for the UE 102 to transmit measurement results. In some embodiments, each of the serving report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the serving RS resource configuration(s). While the UE 102 communicates with the S-DU 174A, the UE 102 transmits measurement results on the UL resource(s) via the cell 124A to the S-DU 174A, in accordance with the serving report configuration(s) (e.g., event 424). Correspondingly, the S-DU 174A receives the measurement results on the UL resource (s) via the cell 124A from the UE 102, in accordance with the serving report configuration(s). In some embodiments, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values.The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the serving RS resource configuration(s) and / or the serving report configuration(s) and obtains the quantized measurement values from the measurements. In some embodiments, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some embodiments, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values might include one or more L1-RSRP values and / or one or more L1-SINR values.

[0190] In other embodiments, the LTM DU configuration Y of the procedure 490 includes at least one TCI state configuration Y, where 1 < Y < N. Each of the TCI state configuration(s) Y configures a TCI state that associates one or two DL RSs with a corresponding QCL type. In some embodiments, the DL RS(s) may be associated with the cell Y operated by the T-DU 174B. In some embodiments, each of the TCI state configuration(s) Y includes a TCI state ID. In some embodiments, each of the TCI state configuration(s) Y is a TCI-State IE. In some embodiments, the TCI state configuration(s) Y includes / is / are an ul-TCI-ToAddModList-r17 field, one or more TCI- UL-State-r17 lEs, a dl-OrJointTCI-StateToAddModList-r17 field, one or more TCI-State lEs, TCI-ActivatedConfig IE and / or a tci-StatesToAddModList field. In someembodiments, the LTM DU configuration Y includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) Y. In some embodiments, the S-DU 174A generates at least one serving TCI state configuration, considering or based on the TCI state configuration(s) Y and includes the serving TCI state configuration(s) in the first serving DU configuration. In some embodiments, the serving TCI state configuration(s) 1 includes the TCI state configuration(s) Y. In other embodiments, the S-DU 174A includes each of the TCI state configuration(s) Y in the serving TCI state configuration(s), except the TCI state ID(s) in the TCI state configuration(s) Y. The S- DU 174A assigns a TCI state ID to a value for each of the serving TCI state configuration(s) (including the TCI state configuration(s) Y) and includes the TCI state ID in the corresponding serving TCI state configuration. While the S-DU 174A communicates 436 with the UE 102, the S-DU 174A might transmit an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell Y. The S-DU 174A includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell Y, where the TCI state configuration is one of the TCI state configuration(s) Y or includes configurations of one of the TCI state configuration(s) Y.

[0191] In some embodiments, the CU 172 transmits a CU-to-DU message including the ID(s) N+1 , ... , N+M to the S-DU 174A and receives a DU-to-CU message from the S-DU 174A in response, similar to the CU-to-DU message 412 and the DU-to-CU message 414, respectively. In some embodiments, the CU 172 includes the LTM DU configuration(s) N+1 , ... , N+M and / or cell ID(s) N+1 , ... , N+M in the CU-to-DU message. In some alternative embodiments, the CU 172 may perform multiple LTM ID transfer procedures to transmit the ID(s) N+1 , ... , N+M, cell ID(s) N+1 , ... , N+M and / or LTM DU configuration(s) N+1 , .... N+M to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the ID(s) N+1 , ... , N+M, cell ID(s) N+1 , ... , N+M and / or LTM DU configuration(s) 1 , ... , N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associates the ID(s) N+1 , ... , N+M with the LTM DU configuration(s) N+1 , ... , N+M and / or the cell ID(s) N+1 , ... , N+M, respectively. In some embodiments, the S-DU 174A generates a second serving DU configuration, based on the LTM DU configuration(s) N+1 , N+2, ... , and / or N+M, and includes thesecond serving DU configuration in the DU-to-CU message. In some embodiments, the second serving DU configuration including configurations updating (e.g., augmenting, modifying or replacing) the first serving DU configuration and / or updating configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. In other embodiments, the second serving DU configuration includes configurations that are not included in the first serving DU configuration. The CU 172 transmits an RRC reconfiguration message including the second serving DU configuration to the UE 102 via the S-DU 174A. The UE 102 applies the second serving DU configuration to communicate with the serving DU upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on embodiments, the UE 102 communicates with the S-DU 174A using configurations included in the serving DU configuration 402 and / or the first serving DU configuration and not updated by the second serving DU configuration. In some embodiments, the S- DU 174A generates one or more new L1 measurement configurations, based on L1 measurement configuration(s) in the LTM DU configuration(s) N+1 , N+2, ... , and / or N+M, and includes the new L1 measurement configuration(s) in the second serving DU configuration. In some embodiments, the S-DU 174A generates one or more new TCI state configuration, based on TCI state configuration(s) in the LTM DU configuration(s) N+1 , N+2, ... , and / or N+M, and includes the new TCI state configuration(s) in the second serving DU configuration.

[0192] In some embodiments, in the case that the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the ID(s) 1 , ... , N of the procedure 380 are different from value(s) of the ID(s) 1 , ...., N, and the ID(s) N+1 , ...., N+M described for the scenario 400. In some embodiments, in the case that the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the cell ID(s) 1 , ... , N of the procedure 380 are different from value(s) of the cell ID(s) 1 , ... ., N, and the cell ID(s) N+1 , ... , N+M described for the scenario 400. In some embodiments, in the case that the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the cell index(es) 1 , ... , N of the procedure 380 are different from value(s) of the cell index(es) 1 , ... , N, and the cell index(es) N+1 , ... , N+M described for the scenario 400.

[0193] Later in time, the UE 102 might transmit 424 at least one measurement report to the S-DU 174A, similar to the event 324. The at least one measurement report (e.g., L1 measurement report(s)) includes an event ID, first measurement result(s) for the cell 1 of the T-DU 174B, and / or includes second measurement result(s) for the cell 124A. In some embodiments, the first measurement result(s) may be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 1 . Likewise, the second measurement result(s) may be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 124A. In some embodiments, the event ID, RSRP, RSRQ and / or SINR are L1 -event ID, L1- RSRP, L1-RSRQ and / or L1 -SINR, respectively. Based on the first measurement result(s) and / or second measurement result(s), the S-DU 174A might transmit 430 a first LTM command (i.e. , LTM command 1 ) including the ID 1 to the UE 102 to order the UE 102 to perform a serving cell change to the cell 1 of the T-DU 174B. In some embodiments, the first LTM command includes the ID 1. In other embodiments, the first LTM command includes the cell index 1 . When the UE 102 receives the first LTM command, the UE 102 performs a serving cell change to the cell 1 from a serving cell in accordance with the LTM DU configuration 1 . After (e.g., in response to) receiving the first LTM command, the UE 102 might or might not perform 432 an RA procedure with the T-DU 174B, similar to the event 332. After (e.g., in response to) receiving the first LTM command or completing the RA procedure 432, the UE 102 might communicate 436 with the T-DU 174B on the first cell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the T-DU 174B, similar to the event 336. If a serving cell change occurs in the procedure 380, the serving cell may be the cell 1 or cell 2 of the S-DU 174A. Otherwise, if no serving cell change occurs in the procedure 380 or the procedure 380 is not performed, the serving cell is the cell 124A. If the first LTM command includes the ID 1 , the UE 102 identifies the LTM DU configuration 1 and / or cell ID 1 (i.e., the cell 1 ), based the ID 1 , as described relative to Fig. 3. If the first LTM command includes the cell index 1 , the UE 102 identifies the LTM DU configuration 1 , cell ID 1 (i.e., the cell 1 ) and / or LTM ID 1 , based the cell index 1 , as described relative to Fig. 3. The UE 102 applies the LTM DUconfiguration 1 to communicate with the T-Dll 174B, after (e.g., in response to) receiving the first LTM command or successfully accessing the cell 1 .

[0194] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 430, the S-DU 174A might transmit 429 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some embodiments, the S- DU 174A includes the cell ID 1 or the ID 1 (i.e., LTM ID) in the DU-to-CU message 429 to indicate that the S-DU 174A is to activate the LTM DU configuration 1 or trigger an LTM serving cell change. The S-DU 174A may transmit the DU-to-CU message 429 to the CU 172 before or after transmitting the LTM command 430. In some embodiments, when or after the CU 172 receives the DU-to-CU message 429, the CU 172 might stop or suspend transmitting DL data for the UE 102 to the S-DU 174A until receiving the DU-to-CU message 434. After receiving the DU-to-CU message 434, the CU 172 starts, continues or resumes transmitting DL data for the UE 102 to the T-DU 174B. When or after the T-DU 174B detects that UE 102 accesses the cell 1 , the T-DU 174B transmits the DL data to the UE 102 via the cell 1 .

[0195] The resource release procedure 496 may be similar to the procedure 396. Alternatively, in the resource release procedure 496, the CU 172 may transmit a CU-to- DU message (e.g., a UE Context Release Command message) to the S-DU 174A to release a UE context of the UE 102. In response, the S-DU 174A releases a UE context of the UE 102 and transmits 440 a DU-to-CU message (e.g., a UE Context Release Complete message) to the CU-172.

[0196] The events 380, 404, 406, 490, 492, 494, 494, 424, 426, 428, 429, 430, 431 , 432, 434, 436, 496, 498, 456 are collectively referred to in Fig. 4 as an LTM configuration and / or activation procedure 480.

[0197] Referring next to Fig. 5A, in a scenario 500A, the BS 106 operates as an MN, and the BS 104 operates as an SN. The SN 104 includes a CU 172 and a DU 174. The scenario 500A is similar to the scenario 300, except that the scenario 500A is a DC scenario and the scenario 300 is a single connectivity (SC) scenario. The MN 106 may include a CU and a DU similar to the BS 104 of Fig. 3.

[0198] Initially, the UE 102 in DC communicates with the MN 106 and with SN 104. In the event 502, the UE 102 communicates with the DU 174 on cell 124A using a servingDU configuration and communicates with the CU 172 via the DU 174 using a serving CU configuration, similar to the event 302. In some alternative embodiments, the UE 102 does not communicate with the CU 172 via the DU 174 in the event 302. In some embodiments, the UE 102 in DC may communicate 502 UL PDUs and / or DL PDUs with the MN 106 and / or SN 104 via radio bearers which may include SRBs and / or DRB(s). The MN 106 and / or the SN 104 may configure the radio bearers to the UE 102. The UE 102 in DC communicates 502 UL PDUs and / or DL PDUs with the SN 104 on an SCG (i.e., SCG radio resources) that the SN 104 configures for communication with the UE 102. The UE 102 in DC communicates UL PDUs and / or DL PDUs with the MN 106 on an MCG (i.e., MCG radio resources) in accordance with a MN configuration (i.e., MCG configuration). In some embodiments, the serving DU configuration is an SN configuration (i.e., SCG configuration). In the MN configuration, the MN 106 configures the MCG which includes at least one serving cell (e.g., the cell 126 and / or other cell(s)) operated by the MN 106. In the serving DU configuration, the SN 106A configures the SCG which includes at least one serving cell (e.g., the cell 124A and / or other cell(s)) operated by the SN 104. In some embodiments, the MN configuration includes multiple configuration parameters, and the UE 102 receives the configuration parameters in one or more RRC messages from the MN 106. As described relative to relative to Fig. 3, the serving DU configuration includes multiple configuration parameters. In some embodiments, the UE 102 receives these configuration parameters in one or more RRC messages from the SN 104, e.g., via the MN 106 and / or on an SRB (e.g., SRB3) that the MN 106 or SN 104 configures to exchange RRC messages between the UE 102 and the SN 104.

[0199] While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 may perform 580 an LTM DU configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. In some embodiments, while communicating in DC with the MN 106 and SN 104, the UE 102 may transmit the at least one measurement report to the CU 172 via the DU 174 and cell 124A in the events 504 and 506, similar to the events 304 and 306, respectively. In other embodiments, while communicating in DC with the MN 106 and SN 104, the UE 102 may transmit 505 at least one measurement report to the MN 106 via the cell 126. The MN 106 in turntransmits 507 the at least one measurement report to the CU 172. In some embodiments, the MN 106 generates at least one SN message including the at least one measurement report and transmits the at least one SN message to the CU 172 in the event 507. In one embodiment, the at least one SN message include RRC Transfer message(s) and / or SN Modification Request message(s).

[0200] After (e.g., in response to) receiving the at least one measurement report or while the SN 104 communicates with the UE 102, the SN 104 determines to prepare the first cell for the UE 102, as described relative to relative to Fig. 3. The events 590, 592, 594, 524, 526, 528, 529, 530, 531 , 532, 534, 536, 596, 598, and 556 are similar to the events 390, 392, 394, 324, 326, 328, 329, 330, 331 , 332, 334, 336, 396, 398, and 356, respectively. After receiving the first LTM command 530, transmitting the acknowledgement 531 , or determining that the UE 102 successfully connects to the first cell 532 or 536, the UE 102 operating in DC with the MN 106 and SN 104 communicates 536 with the DU 174 on the first cell in accordance with the LTM DU configuration 1 and communicates 536 with the CU 172 via the DU 174, similar to the event 336. Later in time, the DU 174 and / or CU 172 may perform the LTM execution procedure 598 with the UE 102 to command the UE 102 to perform a cell change from the first cell to the second cell, similar to the procedure 398 or 498. As a result of the procedure 598, the UE 102 operating in DC with the MN 106 and SN 104 communicates 556 with the DU 174 on the second cell in accordance with the LTM DU configuration 2 and communicates 556 with the CU 172 via the DU 174, similar to the event 356.

[0201] The events 504, 506, 505, 507, 590, 592, 594, 524, 526, 528, 529, 530, 531 , 532, 534, 536, 596, 598, 556 are collectively referred to in Fig. 5A as an LTM DU configuration and / or activation procedure 581 .

[0202] Referring next to Fig. 5B, a scenario 500B is generally similar to the scenario 500A, except that the SN 104 transmits 517, 519 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 521 , 523 the RRC reconfiguration complete message from the UE 102 via the MN 106. The RRC reconfiguration message 517, 519 is similar to the RRC reconfiguration message 316, 318. The RRC reconfiguration complete message 521 , 523 is similar to the RRC reconfiguration message 320, 322. Insome embodiments, the SN 104 generates a first SN message (e.g., SN Modification Required message, SN Modification Required message, or RRC Transfer message) including the RRC reconfiguration message and transmits the first SN message to the MN 106 in the event 517. The MN 106 generates a MN RRC message including the RRC reconfiguration message and transmits 519 the MN RRC message to the UE 102. In response, the UE 102 generates a MN RRC response message including the RRC reconfiguration complete message and transmits 521 the MN RRC response message to the MN 106. In some embodiments, the MN 106 generates a second SN message (e.g., SN Reconfiguration Complete message or RRC Transfer message) including the RRC reconfiguration complete message and transmits the second SN message to the SN 104 in the event 523. In some embodiments, the MN RRC message and MN RRC response message can be an RRC reconfiguration message and an RRC reconfiguration complete message, respectively.

[0203] The events 504, 506, 505, 507, 590, 592, 594, 517, 519, 521 , 523, 524, 526, 528, 529, 530, 531 , 532, 534, 536, 596, 598, 556 are collectively referred to in Fig. 5B as an LTM DU configuration and / or activation procedure 582.

[0204] Referring next to Fig. 6A, in a scenario 600A, the BS 106 operates as an MN, and the BS 104 operates as an SN, similar to the scenarios 300-500B. The SN 104 includes a CU 172, an S-DU 174A and a T-DU 174B, similar to the BS 104 in the scenario 400. While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 can perform 680 an LTM DU configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 681 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A or S-DU 174B, similar to the procedure 581 or 582.

[0205] Referring next to Fig. 6B, a scenario 600B similar to the scenarios 300-500B and 600A, except that that the SN 104 transmits 617, 619 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 621 , 623 the RRC reconfiguration complete message from the UE 102 via the MN 106.

[0206] Referring next to Fig. 7A, in a scenario 700A, the BS 104 operates as an MN and an SN, similar to the scenarios 300-600B. The BS 104 includes a CU 172, a masterDU (M-DU) 174A and a secondary DU (S-DU) 174B. The CU 172 operates with the M- DU 174A as a MN, similar to the BS 104 in Fig. 3 or the MN 106 in Figs. 5A-6B, and the CU 172 operates with the S-DU 174B as a SN, similar to the SN 104 in Figs. 5A-6B.

[0207] In the scenario 700A, the UE 102 initially communicates 702 in DC with the M- DU 174A and S-DU 174B and communicates 702 with the CU 172 via the M-DU 174A and S-DU 174B. In the event 702, the UE 102 communicates with the S-DU 174B on cell 124A using a serving DU configuration and communicates with the CU 172 via the S-DU 174B using a serving CU configuration, similar to the event 302. Events 704 and 706 are similar to the events 304 and 306. In some embodiments, the UE 102 can transmit 705 at least one measurement report to the M-DU 174A, similar to the event 304. The M-DU 174A in turn transmits 707 at least one DU-to-CU message including the at les tone measurement report to the CU 172, similar to the event 306. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 780 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380.

[0208] The events 704, 706, 705, 707, 790, 792, 794, 724, 726, 728, 729, 730, 731 , 732, 734, 736, 796, 798, 756 are collectively referred to in Fig. 7A as an LTM configuration and / or activation procedure.

[0209] Referring next to Fig. 7B, a scenario 700B similar to the scenarios 300-600B and 700A, except that that the CU 172 transmits 717, 719 the RRC reconfiguration message to the UE 102 via the M-DU 174A and receives 721 , 723 the RRC reconfiguration complete message from the UE 102 via the M-DU 174A.

[0210] The events 704, 706, 705, 707, 790, 792, 794, 717, 719, 721 , 723, 724, 726, 728, 729, 730, 731 , 732, 734, 736, 796, 798, 756 are collectively referred to in Fig. 7B as an LTM DU configuration and / or activation procedure.

[0211] Referring next to Fig. 8A, in a scenario 800A, the BS 104 operates as an MN and an SN, similar to the scenarios 300-700B. The BS 104 includes a CU 172, a master DU (M-DU) 174A, a secondary DU (S-DU) 174B and a target secondary DU (T- DU) 174C. The CU 172 operates with the M-DU 174A as a MN and operates with the S-DU 174B as a SN. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 880 an LTM DU configuration and / or activationprocedure with the UE 102 via the M-Dll 174A, similar to the procedure 380. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 881 an LTM DU configuration and / or activation procedure with the UE 102 via the S-DU 174A, similar to the procedure 581 or 582.

[0212] Referring next to Fig. 8B, a scenario 800B similar to the scenarios 300-700B and 800A, except that that the CU 172 transmits 817, 819 the RRC reconfiguration message to the UE 102 via the M-DU 174A and receives 821 , 823 the RRC reconfiguration complete message from the UE 102 via the M-DU 174A.

[0213] Next, several example methods that may be performed by an NE (i.e. , a RAN node such as a BS, a DU or a CU) or a UE, to enable early acquisition of a TA value in view of a configured LTM to a target cell (i.e., enabling early timing synchronization with the target cell) are discussed next with reference to Figs. 9A-16F. Details provided relative to Figs. 3-8B apply to Figs. 9A-16F.

[0214] Fig. 9A depicts a flow diagram of a method 900A performed by an NE (i.e., a RAN node that may be the BS 104 or 106, the CU 172, DU 174, 174A, 174B or 174C of the BS 104 or 106 in Figs. 3-8B, RAN 105), for configuring early TA acquisition enabling synchronization with a first cell (i.e., the target cell) of a configured LTM.

[0215] The method 900A starts with the NE communicating 902 with a UE via a serving cell (the step 902 corresponding, e.g., to events 302, 402, 502, 602, 702, 802, 380, 480, 580, 680, 780, 880, 581 , 582, 681 , 780, 880, and 881 ). The method 900A then includes transmitting 904 a first LTM configuration to the UE, the first LTM configuration configuring a serving cell change from the serving cell to the first cell (the step 904 corresponding, e.g., to events 316, 318, 394, 380, 494, 480, 580, 594, 581 , 582, 680, 694, 617, 619, 780, 794, 880, 881 , 894, 817, 819). The first LTM configuration may include a first LTM DU configuration configuring the first cell for LTM as already described. The first LTM DU configuration may be included in a first RRC message (e.g., an RRC reconfiguration message), the first RRC message being included in the first LTM configuration. A first LTM CU configuration may be included in the first RRC message. The first LTM CU configuration and first LTM DU configuration are any one of the configurations described above. The first LTM configuration may bean LTM -Candi date IE or an LTM-CandidateToAddMod IE. Alternatively, the first LTM configuration may be an LTM-Config IE.

[0216] Method 900A further includes transmitting 906, to the UE, a first early TA acquisition configuration to enable an early TA acquisition (the step 906 corresponding, e.g., to events 316, 318, 394, 380, 494, 480, 580, 594, 581 , 582, 680, 694, 617, 619, 780, 794, 880, 881 , 894, 817, 819). The NE may transmit a second RRC message (e.g., an RRC reconfiguration message) including the first LTM configuration and the first early TA acquisition configuration to the UE. Alternatively, the first LTM configuration may include the first early TA acquisition configuration, the first LTM configuration being transmitted to the UE in a second RRC message. When the first LTM configuration includes the first early TA acquisition configuration, the NE refrains from including the first early TA acquisition configuration in the first LTM DU configuration, the first LTM CU configuration, and / or the first RRC message. Therefore, in this case, the UE retrieves the first early TA acquisition configuration from the first LTM configuration without decoding the first LTM DU configuration, the first LTM CU configuration, and / or the first RRC message. Therefore, the UE saves power otherwise used to decode the first LTM DU configuration, the first LTM CU configuration, and / or the first RRC message.

[0217] The method 900A further includes transmitting 908 a first command (e.g., an RA triggering command) to the UE. Note that step 908 is illustrated using a dash-line box; the use of dash line boxes in Figs. 9A-16F indicates that presence and execution of such steps is optional. The first command directs the UE to transmit a first RA preamble on the first cell thereby initiating the early TA acquisition. The first command may include a first index (i.e. , an RA preamble index) identifying the first RA preamble, thereby enabling the UE to determine or generate the first RA preamble in accordance with the first index. The NE may transmit the first command on a PDCCH on the serving cell. The first command may be a DCI or a PDCCH order. Alternatively, the first command may be a MAC CE. The NE may transmit the first early TA acquisition configuration to the UE in order to configure or enable the UE to receive the first command. Without receiving the first early TA acquisition configuration, the UE does not monitor for receiving the first command.

[0218] The method 900A further includes receiving 910 the first RA preamble on the first cell from the UE. The first command may include a first cell ID identifying the first cell thereby enabling the UE to transmit the first RA preamble on the first cell in accordance with the first cell ID. Alternatively, the first command may include a first cell index indicating the first cell enabling the UE to transmit the first RA preamble on the first cell in accordance with the first cell index. The method 900A then includes obtaining 912 a TA value for the UE according to the time of receiving the first RA preamble from the UE.

[0219] In one (first) embodiment, the method 900A continues with steps 913 and 915 after step 912. In another (second) embodiment, the method 900A continues with step 914 after step 912. According to the first embodiment, after obtaining 912 the TA value, the method includes transmitting 913 an RA response including the TA value to the UE. The RA response may be transmitted to the UE via the serving cell. Alternatively, the RA response is transmitted to the UE via the first cell. The NE communicates with the UE via the serving cell, after receiving the RA preamble, transmitting the RA response message, or before transmitting, to the UE, an LTM command directing the UE to connect to the first cell. According to the first embodiment, the method further includes transmitting 915 an LTM command to the UE via the serving cell, the LTM command directing the UE to connect to the first cell (step 915 corresponding, e.g., to events 330, 350, 398, 380, 430, 450, 498, 480, 580, 530, 598, 581 , 582, 680, 681 , 630, 698, 780, 730, 798, 880, 881 , 830, 898). According to the second embodiment, the method further includes transmitting 914 an LTM command to the UE via the serving cell, the LTM command directing the UE to connect to the first cell and including the TA value (the step 914 corresponding, e.g., to events 330, 350, 398, 380, 430, 450, 498, 480, 580, 530, 598, 581 , 582, 680, 681 , 630, 698, 780, 730, 798, 880, 881 , 830, 898). Regardless of whether the TA value is transmitted as in the first embodiment or as in the second embodiment, the NE completes early the uplink synchronization with the UE on the first cell, before the UE accesses the first cell and / or communicates on the first cell. Thus, this approach (early acquisition of the TA value) prevents the data communication interruption due to uplink synchronization during the serving cell change from the serving cell to the first cell. The method 900A then includes detecting 916 thatthe UE accesses the first cell (step 916 corresponding, e.g., to events 332, 352, 398, 380, 432, 452, 498, 480, 580, 532, 598, 581 , 582, 680, 632, 698, 681 , 780, 732, 798, 880, 881 , 832, 898). The method 900A then includes communicating 918 with the UE on the first cell, using the first LTM configuration (step 918 corresponding, e.g., to events 336, 356, 380, 436, 456, 480, 536, 556, 580, 581 , 582, 636, 656, 680, 681 , 736, 756, 780, 836, 856, 880, 881 ). The NE may communicate with the UE on the first cell, using the first LTM DU configuration. If the first LTM CU configuration is included in the first LTM configuration, the NE communicates with the UE on the first cell, using the first LTM DU configuration and the first LTM CU configuration.

[0220] Further to the steps illustrated in Fig. 9A, an embodiment may include transmitting a second LTM configuration to the UE, the second LTM configuration configuring the UE for another serving cell change to a second cell. The second LTM configuration may include a second LTM DU configuration for configuring the second cell for LTM as described above. The second LTM DU configuration may be included in a third RRC message (e.g., an RRC reconfiguration message) and the third RRC message may be included in the second LTM configuration. The third RRC message may include a second LTM CU configuration. The second LTM CU configuration and second LTM DU configuration are any of the respective configurations already described. The second LTM configuration may be an LTM-Cand / date IE or an LTM- CandidateToAddMod IE. Alternatively, the second LTM configuration may be an LTM- Config IE. The method may also include transmitting a fourth RRC message (e.g., an RRC reconfiguration message) including the second LTM configuration to the UE. The first early TA acquisition configuration may be specifically for the first cell. Alternatively, the first early TA acquisition configuration may be configured for both the first cell and the second cell. In some embodiments, the RAN configures a second early TA acquisition configuration specifically for the second cell. Alternatively, the fourth RRC message includes the second early TA acquisition configuration (in addition to the second LTM configuration). In some embodiments, the second LTM configuration includes the second early TA acquisition configuration.

[0221] Fig. 9B depicts another flow diagram of a method 900B performed by an NE for configuring early TA acquisition enabling synchronization with a first cell (i. e. , thetarget cell) of a configured LTM. The method 900B is similar to the method 900A, except that method 900B includes additional steps 905, 920, 922, and 924. After steps 902 and 904 described relative to Fig. 9A, the NE determines 905 whether the UE supports early TA acquisition. When the UE supports early TA acquisition (the “Yes” branch of 905), the method continues by performing steps 906-912, (913, 915) or 914, 916 and 918 (similar to Fig. 9A). Otherwise, if the NE determines that the UE does not support early TA acquisition (the “No” branch of 905), the method continues with refraining 920 from transmitting an early TA acquisition configuration to the UE. The method may further include transmitting 922 an LTM command to the UE via the serving cell, the LTM command directing the UE to connect to the first cell (step 922 corresponding, e.g., to events 330, 350, 398, 380, 430, 450, 498, 480, 580, 530, 598, 581 , 582, 680, 681 , 630, 698, 780, 730, 798, 880, 881 , 830, 898). Unlike in step 914, the LTM command does not include a TA value to configure the UE to perform an RA procedure on the first cell upon receipt of the LTM command. The method may further include performing 924 an RA procedure with the UE on the first cell after transmitting the LTM command (step 924 corresponding, e.g., to events 332, 352, 398, 380, 432, 452, 498, 480, 580, 532, 598, 581 , 582, 680, 632, 698, 681 , 780, 732, 798, 880, 881 , 832, 898). Upon receiving the LTM command, the UE initiates the RA procedure on the first cell. The step 924 may follow step 913.

[0222] In some embodiments, the NE receives from the UE or a CN (e.g., the AMF 164), a UE capability IE specifying a plurality of UE capabilities of the UE. The NE may then determine whether the UE supports early TA acquisition based on the UE capability IE. For example, the UE capability IE is a UE-NR-Capability IE. In another example, the UE capability IE is a UE-6G-Capability IE. When the UE capability IE includes a capability indicating support of early TA acquisition, the UE supports early TA acquisition, otherwise (i.e. , the UE capability IE does not include the capability indicating support of early TA acquisition) the UE does not support early TA acquisition.

[0223] Fig. 10 depicts a flow diagram of a method 1000 performed by a UE, for early TA acquisition according to an embodiment. The method 1000 starts with the UE communicating 1002 with an NE via a serving cell (step 1002 corresponding, e.g., to events 302, 402, 502, 602, 702, 802, 380, 480, 580, 680, 780, 880, 581 , 582, 681 , 780,880, 881 ). The method 1000 then includes receiving 1004 from the NE, a first LTM configuration that configures the UE for a serving cell change to a first cell (step 1004 corresponding, e.g., to events 316, 318, 394, 380, 494, 480, 580, 594, 581 , 582, 680, 694, 617, 619, 780, 794, 880, 881 , 894, 817, 819). The method 1000 further includes receiving 1006 from the NE, a first early TA acquisition configuration that configures the UE for an early TA acquisition (step 1006 corresponding, e.g., to events 316, 318, 394, 380, 494, 480, 580, 594, 581 , 582, 680, 694, 617, 619, 780, 794, 880, 881 , 894, 817, 819). The method 1000 may further include the UE (optionally) receiving 1008 a first command from the RAN via the serving cell, the first command directing the UE to transmit a first RA preamble on the first cell for early TA acquisition. The first command may be received via the serving cell after receiving the first early timing advance acquisition configuration. The method 1000 then may include transmitting the first RA preamble on the first cell in response to the first command. The first command may indicate a first index (i.e. , an RA preamble index) identifying the first RA preamble. The UE then generates or transmits the first RA preamble in accordance with the first index. The UE may receive the first command on a PDCCH on the serving cell. The first command may include a first cell ID or a first cell index identifying the first cell, as described relative to Fig. 9A, the UE then transmitting the first RA preamble on the first cell in accordance with the first cell ID or the first cell index.

[0224] A first embodiment of the method 1000 then includes steps 1013 and 1015. A second embodiment of the method 1000 then includes step 1014. According to the first embodiment, the method continues with receiving 1013 an RA response including the TA value from the NE, followed by receiving 1015 an LTM command from the NE via the serving cell, the LTM command directing the UE to connect the first cell (step 1015 corresponding, e.g., to events 330, 350, 398, 380, 430, 450, 498, 480, 580, 530, 598, 581 , 582, 680, 681 , 630, 698, 780, 730, 798, 880, 881 , 830, 898). The LTM command received after receiving the RA response does not include the TA value. According to the second embodiment, the method further includes receiving 1014 an LTM command from the RAN via the serving cell, the LTM command directing the UE to connect the first cell and including the TA value (step 1014 corresponding, e.g., to events 330, 350, 398, 380, 430, 450, 498, 480, 580, 530, 598, 581 , 582, 680, 681 , 630, 698, 780, 730,798, 880, 881 , 830, 898). According to both the first and the second embodiment, the method 1000 then includes accessing 1016 the first cell in response to receiving the LTM command (step 1016 corresponding, e.g., to events 332, 352, 398, 380, 432, 452, 498, 480, 580, 532, 598, 581 , 582, 680, 632, 698, 681 , 780, 732, 798, 880, 881 , 832, 898). The method then includes communicating 1018 with the NE via the first cell (step 1018 corresponding, e.g., to events 336, 356, 380, 436, 456, 480, 536, 556, 580, 581 , 582, 636, 656, 680, 681 , 736, 756, 780, 836, 856, 880, 881 ).

[0225] The UE performing the method depicted in Fig. 10 and the NE it communicates with may be the same as the NEs performing the methods depicted in Figs. 9A and 9B and the respective UE. Descriptions relative to Figs. 9A and 9B may apply to Fig. 10.

[0226] Figs. 11 A-11 C depict flow diagrams of DU methods for early TA acquisition according to various embodiments. Fig. 11A illustrates a method 1100A performed by a DU (e.g., the DU 174, 174A, 174B, or 174C of the BS 104 or 106 in Figs. 3-8B), for enabling early TA acquisition for LTM. The method 1100A starts with the DU receiving 1102 a first CU-to-DU message from a CU, the first CU-to-DU message directing the DU to prepare a first cell for an LTM for a UE (step 1102 corresponding, e.g., to events 308, 390, 380, 490, 480, 580, 590, 581 , 582, 680, 690, 681 , 780, 790, 880, 890, 881 ).. The method 1100A then continues with reserving 1104 a first RA preamble for the UE to transmit on the first cell . The DU may reserve the first RA preamble, after (e.g., in response to) receiving the first CU-to-DU message. The DU may reserve the first RA preamble from a first plurality of available RA preambles. The method 1100A then includes transmitting 1106 a first DU-to-CU message including a first LTM DU configuration for the UE to the CU (step 1106 corresponding, e.g., to events 310, 390, 380, 490, 480, 580, 590, 581 , 582, 680, 690, 681 , 780, 790, 880, 890, 881 ). The DU may transmit the first DU-to-CU message to the CU after (e.g., in response to) receiving the first CU-to-DU message. The DU may include information (e.g., an early TA acquisition configuration) in the first DU-to-CU message, the information indicating that the DU enables or configures early TA acquisition for the UE. The CU may transmit the information to the UE (as, e.g., in events 316, 318, 394, 380, 494, 480, 580, 594, 581 , 582, 680, 694, 617, 619, 780, 794, 880, 881 , 894, 817, 819). Alternatively, the CUgenerates a first early TA acquisition configuration in response to receiving the information and transmits the first early TA acquisition configuration to the UE (similar to step 906).

[0227] The method 1100A further includes transmitting 1108 a second DU-to-CU message including a first index (i.e. , an RA preamble index) to the CU, the first index identifying the first RA preamble. The DU may include a first cell ID in the second DU- to-CU message, the first cell ID identifies the first cell and being associated with the first RA preamble index. Alternatively, the DU includes a first cell index in the second DU- to-CU message, the first cell index indicating the first cell and is associated with the first RA preamble index.

[0228] The method 1100A may continue (i.e., next steps are optional as indicated by the use of dashed-line boxes) with receiving 1110 the first RA preamble on the first cell, from the UE, after transmitting the second DU-to-CU message or the first index to the CU. The method 1100A then includes obtaining 1112 a TA value for the UE according to the time of receiving the first RA preamble.

[0229] In one (first) embodiment, the method 1100A continues with step 1113 after step 1112. In another (second) embodiment, the method 1100A continues with step 1114 after step 1112. According to the first embodiment, the method includes transmitting 1113 an RA response including the TA value to the UE. According to the second embodiment, the method includes transmitting 1114 a third DU-to-CU message including the TA value to the CU. Regardless of whether the method includes step 1113 or step 1114, the method further includes detecting 1116 that the UE accesses the first cell (step 1116 corresponding, e g., to events 332, 352, 398, 380, 432, 452, 498, 480, 580, 532, 598, 581 , 582, 680, 632, 698, 681 , 780, 732, 798, 880, 881 , 832, 898). Last, the method 1100A includes communicating 1118 with the UE via the first cell (step 1118 corresponding, e.g., to events 336, 356, 380, 436, 456, 480, 536, 556, 580, 581 , 582, 636, 656, 680, 681 , 736, 756, 780, 836, 856, 880, 881 ).

[0230] The DU may include the first LTM DU configuration in a first interface protocol field / IE and the first interface protocol field / IE in the first DU-to-CU message. Based on the first interface protocol field / IE, the CU can determine that the first LTM DU configuration is included in the first DU-to-CU message. The DU may include the firstRA preamble index in a second interface protocol field / IE and includes the second interface protocol field / IE in the second DU-to-CU message. Based on the second interface protocol field / IE, the CU can determine that the first RA preamble index is included in the second DU-to-CU message. The DU may include the first cell ID or the first cell index in the second interface protocol field / IE or in a third interface protocol field / IE which is included in the second DU-to-CU message. The third interface protocol field / IE may be associated with the second interface protocol field / IE; to indicate the association, the DU may include the second interface protocol field / IE and the third interface protocol field / IE in a first parent field / IE and includes the first parent field / IE in the second DU-to-CU message. The first interface protocol field / IE, the second interface protocol field / IE, the third interface protocol field / IE and / or the first parent field / IE are F1AP fields / IEs.

[0231] The DU performing method 1100A may be a T-DU (e.g., T-DU 174B in Figs. 4, 6A and 6B, T-DU 174C in Figs. 8A and 8B). The first DU-to-CU message and the second DU-to-CU message may be combined and transmitted as a single message. Alternatively, the first DU-to-CU message and the second DU-to-CU message are separate messages. The DU may refrain from including the first index in the first LTM DU configuration.

[0232] The CU may transmit a CU-to-DU message including the first RA preamble index to a source DU (e.g., S-DU 174A in Figs. 4, 6A and 6B, S-DU 174B in Figs. 8A and 8B) as described later relative to Figs. 13A and 13B. The source DU then transmits the first command to the UE on a serving cell, the first command directing the UE to transmit the first RA preamble on the first cell. The CU may include the first cell ID or the first cell index in the CU-to-DU message and the source DU then includes the first cell ID or the first cell index in the first command.

[0233] The DU may receive a second CU-to-DU message from a CU, the second CU-to-DU message directing the DU to prepare a second cell for LTM for the UE. The DU may then reserve a second RA preamble for the UE to transmit on the second cell, after (e.g., in response to) receiving the second CU-to-DU message. The DU may reserve the second RA preamble from a second plurality of available RA preambles. The DU may then transmit a third DU-to-CU message including the second LTM DUconfiguration to the CU after (e.g., in response to) receiving the second CU-to-DU message. The DU may then transmit a fourth DU-to-CU message including a second index (e.g., an RA preamble index) to the CU, the second index indicating the second RA preamble. The DU may include a second cell ID in the fourth DU-to-CU message, the second cell ID identifying the second cell and being associated with the second RA preamble index. Alternatively, the DU may include a second cell index in the fourth DU- to-CU message, the second cell index indicating the second cell and being associated with the second RA preamble index.

[0234] The DU may include the second LTM DU configuration in a fourth interface protocol field / IE and includes the fourth interface protocol field / IE in the third DU-to-CU message. Based on the fourth interface protocol field / IE, the CU can determine that the second LTM DU configuration is included in the third DU-to-CU message. The DU may include the second RA preamble index in a fifth interface protocol field / IE and includes the fifth interface protocol field / IE in the fourth DU-to-CU message. Based on the fifth interface protocol field / IE, the CU can determine that the second RA preamble index is included in the fourth DU-to-CU message. The DU may include the second cell ID or the second cell index in the fifth interface protocol field / IE. Alternatively, the DU may include the second cell ID or the second cell index in a sixth interface protocol field / IE and includes the sixth interface protocol field / IE in the fourth DU-to-CU message. The sixth interface protocol field / IE may be associated with the fifth interface protocol field / IE; to indicate the association, the DU may include the fifth interface protocol field / IE and the sixth interface protocol field / IE in a second parent field / IE and includes the second parent field / IE in the fourth DU-to-CU message. The fourth interface protocol field / IE may be the same as the first interface protocol field / IE. Alternatively, the fourth interface protocol field / IE is different from the first interface protocol field / IE. The fifth interface protocol field / IE may be the same as the second interface protocol field / IE. Alternatively, the fifth interface protocol field / IE is different from the fourth interface protocol field / IE. The sixth interface protocol field / IE may be the same as the third interface protocol field / IE. Alternatively, the sixth interface protocol field / IE is different from the third interface protocol field / IE. The second parent field / IE may be the same as the first parent field / IE. Alternatively, the second parent field / IE is differentfrom the first parent field / IE. The fourth interface protocol field / IE, the fifth interface protocol field / IE, the sixth interface protocol field / IE and / or the second parent field / IE are F1AP fields / IEs.

[0235] The third DU-to-CU message and the fourth DU-to-CU message may be combined and transmitted as a single message. Alternatively, the third DU-to-CU message and the fourth DU-to-CU message are separate messages. The DU may refrain from including the second index in the second LTM DU configuration.

[0236] The DU may refrain from reserving an RA preamble for the UE to transmit on the second cell, after (e.g., in response to) receiving the second CU-to-DU message because the DU does not have an available RA preamble to reserve for the UE to transmit on the second cell.

[0237] Fig. 11 B is a flow diagram of a method 1100B similar to the method 1100A, except that the method 1100B includes steps 1103, 1120, and 1122. The method 1100B includes determining 1103 whether the UE supports early TA acquisition. When the UE does indeed support the early TA acquisition (i.e., “Yes” branch of 1103), the method continues with steps 1104, 1108, 1110, 1112, (1113 or 1114), 1116 and 1118. Otherwise, when the UE does not support early TA acquisition (i.e., “No” branch of 1103), the method 1100B continues with refraining 1120 from reserving an RA preamble for the early TA acquisition for the UE. After 1120, the method 1100B may include performing 1122 an RA procedure with the UE on the first cell (step 1122 corresponding, e.g., to events 332, 352, 398, 380, 432, 452, 498, 480, 580, 532, 598, 581 , 582, 680, 632, 698, 681 , 780, 732, 798, 880, 881 , 832, 898) followed by communicating 1118 with the UE via the first cell.

[0238] The DU may receive a UE capability IE specifying a plurality of UE capabilities of the UE from the CU. For example, the first CU-to-DU message may include the UE capability IE. Alternatively, the UE capability UE is included in another CU-to-DU message from the CU. The DU determines whether the UE supports early TA acquisition based on the UE capability IE. For example, the UE capability IE is a UE- NR-Capability IE. In another example, the UE capability IE is a UE-6G-Capability IE. When the UE capability IE includes a capability indicating support of early TA acquisition, the DU determines that the UE supports early TA acquisition. Otherwise,when the UE capability IE does not include the capability indicating support of early timing synchronization, the DU determines that the UE does not support early TA acquisition.

[0239] Fig. 11 C is a flow diagram of an example method 1100C that is similar to the method 1100B, except that method 1100C includes step 1105 instead of 1103. After steps 1102 and 1106, the method 1100C includes determining 1105 whether the first CU-to-DU message requests an early TA acquisition. Upon determining that the first CU-to-DU message requests indeed the early TA acquisition (i.e., “Yes” branch of 1105), the method 1100C continues with steps 1104, 1106, 1108, 1110, 1112, (1113 or 1114), 1116, and 1118. Otherwise, upon determining that the first CU-to-DU message does not request early TA acquisition (i.e., “No” branch of 1105), the method 1100C proceeds with steps 1120, 1122, and 1118 (previously described).

[0240] The first CU-to-DU message may include an indication for requesting an early TA acquisition. When the CU determines that the UE supports the early TA acquisition, the CU includes the indication in the first CU-to-DU message. Otherwise, when the CU determines that the UE does not support early TA acquisition, the CU does not include such an indication in the first CU-to-DU message.

[0241] Figs. 12A-12C depict flow diagrams of (candidate or target) DU methods for early TA acquisition according to other embodiments. Descriptions relative to Figs. 9A, 9B, and 10 can apply to Figs. 11A-11 C and 12A-12C. The methods in Figs. 12A, 12B, and 12C may be performed by a DU such as the DU 174, 174A, 174B or 174C of the BS 104 or 106 in Figs. 3-8B, for enabling an early TA acquisition for LTM.

[0242] The method 1200A starts with receiving 1202 a CU-to-DU message from a CU, the first CU-to-DU message directing the DU to prepare a cell for LTM for a UE (step 1202 corresponding, e.g., to events 308, 390, 380, 490, 480, 580, 590, 581 , 582,680, 690, 681 , 780, 790, 880, 890, 881 ). The method 1200A then includes generating 1204 a DU-to-CU message including an LTM DU configuration for the UE (step 1204 corresponding, e.g., to events 310, 390, 380, 490, 480, 580, 590, 581 , 582, 680, 690,681 , 780, 790, 880, 890, 881 ), the LTM DU configuration configuring the cell for LTM. The method 1200A further includes determining 1206 whether the UE supports early TA acquisition. When determined that the UE supports early TA acquisition (i.e., “Yes”branch of 1206), the method 1200A continues with including 1208 an index (i.e. , an RA preamble index) in the DU-to-CU message, the index indicating an RA preamble, and then transmitting 1210 the DU-to-CU message to the CU. Otherwise, when determined that the UE does not support early TA acquisition (i.e., “No” branch of 1206), the method 1200A proceeds to step 1210. Step 1210 corresponds, e.g., to events 310, 390, 380, 490, 480, 580, 590, 581 , 582, 680, 690, 681 , 780, 790, 880, 890, 881 . In other words, if the DU determines that the UE does not support early TA acquisition in step 1206, the DU refrains from including the index in the DU-to-CU message.

[0243] The CU-to-DU message may be a UE Context Setup Request message or a UE Context Modification Request message. The DU-to-CU message may be a UE Context Setup Response message, a UE Context Modification Response message or a UE Context Modification Required message.

[0244] Fig. 12B is a flow diagram of a method 1200B similar to the method 1200A, except that the method 1200B includes step 1207 instead of step 1206. The DU determines 1207 whether the CU-to-DU message requests an early TA acquisition. When the DU determines that the CU-to-DU message requests the early TA acquisition (i.e., “Yes” branch of 1207), the message continues with steps 1208 and 1210.Otherwise (i.e., “No” branch of 1207), when the DU determines that the CU-to-DU message does not request an early TA acquisition, the method continues with step 1210.

[0245] Fig. 12C is a flow diagram of a method 1200C similar to the method 1200A, except that the method 1200C includes step 1205 instead of step 1206. The DU determines 1205 whether the CU-to-DU message has an available RA preamble for the early TA acquisition on the cell. When the DU determines that the DU has an available RA preamble for the early TA acquisition on the cell (i.e., “Yes” branch of 1205), the method continues with steps 1208 and 1210. Otherwise (i.e., “No” branch of 1205), when the DU determines that the DU has no available RA preamble for the early TA acquisition on the cell, the method continues with step 1210.

[0246] Figs. 13A and 13B depict flow diagrams of (source) DU methods for early TA acquisition according to various embodiments. Descriptions relative to Fig. 9A-12B can apply to Figs. 13A and 13B. The methods in Figs. 13A and 13B may be performed byby a DU such as the DU 174, 174A, 174B or 174C of the BS 104 or 106 in Figs. 3-8B, for enabling an early TA acquisition for LTM.

[0247] The method 1300A starts with communicating 1302 with a UE via a serving cell (step 1302 corresponding, e.g., to events 302, 402, 502, 602, 702, 802, 380, 480, 580, 680, 780, 880, 581 , 582, 681 , 780, 880, 881 ). The method 1300A continues with receiving 1312 a first CU-to-DU message including a first index (i.e., an RA preamble index) for a UE from a CU, the first index indicating an RA preamble (step 1312 corresponding, e.g., to events 412, 493, 693, 893). The method 1300A then includes generating 1306 a first command (e.g., an RA triggering command) for the UE, the first command including the index and directing the UE to transmit the first RA preamble on a first cell. Step 1306 corresponds to step 908. The method 1300A then includes transmitting 1310 the first command to the UE via the serving cell. Step 1310 corresponds to step 908. When the UE receives the first command, the UE transmits the first RA preamble on the first cell in response to the first command. The first CU-to- DU message may include a first cell ID that identifies the first cell. Alternatively, the DU assigns the first cell ID. The first cell ID may be included in the first command to indicate the first cell. The first CU-to-DU message may include a first cell index that indicates the first cell. Alternatively, the DU assigns the first cell index. The first command may include the first cell index to indicate the first cell. When the UE receives the first command, the UE determines or generates an RA preamble (i.e., the first RA preamble) in accordance with the first index. When the UE receives the first command, the UE determines a cell (i.e., the first cell) to transmit the first RA preamble in accordance with first cell ID or the first cell index.

[0248] The method 1300A continues with receiving 1321 a second CU-to-DU message, including a TA value for the UE, from the CU. According to a first embodiment, the method continues with transmitting 1323 an RA response including the TA value to the UE, and then transmitting 1325 an LTM command to the UE, the LTM command directing the UE to connect to the first cell (step 1325 corresponding, e.g., to events 330, 350, 398, 380, 430, 450, 498, 480, 580, 530, 598, 581 , 582, 680, 681 , 630, 698, 780, 730, 798, 880, 881 , 830, 898). This LTM command does not include a TA value. According to a second embodiment, the method continues with transmitting1324 an LTM command including the TA value to the UE and directing the UE to connect to the first cell (e.g., events 330, 350, 398, 380, 430, 450, 498, 480, 580, 530, 598, 581 , 582, 680, 681 , 630, 698, 780, 730, 798, 880, 881 , 830, 898).

[0249] The first CU-to-DU message may include a first cell ID that identifies the first cell and is associated with the first RA preamble index. The first cell ID may be included in the first command. The first CU-to-DU message may include a first cell index that indicates the first cell and is associated with the first RA preamble index. The first cell index may be included in the first command.

[0250] The DU may be a source DU such as S-DU 174A in Figs. 4, 6A and 6B, S-DU 174B in Figs. 8A and 8B. The first CU-to-DU message and the second CU-to-DU message may be UE Context Modification Request messages. The CU may receive a DU-to-CU message including the TA value from a target DU (e.g., T-DU 174B in Figs. 4, 6A and 6B, T-DU 174C in Figs. 8A and 8B) and includes the TA value in the second CU-to-DU message. The target DU operates the first cell and obtains the TA value based on receiving the first RA preamble from the UE on the first cell, as described above.

[0251] Fig. 13B is a flow diagram of a method 1300B similar to the method 1300A, except that the method 1300B includes step 1305. After steps 1302 and 1312, the method 1300B includes determining 1305 whether the UE qualifies for early TA acquisition on the first cell. When the UE qualifies for early TA acquisition on the first cell (i.e., “Yes” branch of 1305), the method continues as method 1300A with steps 1310, 1321 , (1323 and 1325) or 1324. Otherwise (i.e., “No” branch of 1305), when the DU determines that the UE does not qualify for early TA acquisition on the first cell, the method continues with transmitting 1326 an LTM command to the UE, the LTM command directing the UE to connect to the first cell.

[0252] The DU may receive at least one measurement result for the first cell from the UE (e.g., events 324, 344, 398, 380, 424, 444, 498, 480, 580, 524, 598, 581 , 582, 680, 681 , 624, 698, 780, 724, 798, 880, 881 , 824, 898) and determines whether the UE qualifies for early TA acquisition on the first cell, based on the at least one measurement result. When the at least one measurement result is above a first threshold, the DU determines that the UE qualifies for early TA acquisition on the firstcell. Otherwise, when the at least one measurement result is below or equal to the first threshold or a second threshold, the DU determines that the UE does not qualify for early TA acquisition on the first cell. The second threshold may be smaller than the first threshold. The DU may process the at least one measurement result with a function to obtain a first result When the first result is above a first threshold, the DU determines that the UE qualifies for early TA acquisition on the first cell. Otherwise, when the first result is below or equal to the first threshold or a second threshold, the DU determines that the UE does not qualify for early TA acquisition on the first cell.

[0253] Figs. 14A and 14B depict flow diagrams of CU methods for early TA acquisition according to various embodiments. The CU and the target DU may be the CU and the DU performing the methods in Figs. 11A-11 C and Figs. 13A and 13B, respectively. Descriptions relative to Figs. 11A-11 C, 13A and 13B may apply to Figs. 14A and 14B.

[0254] Fig. 14A illustrates a method 1400A performed by a CU (e.g., the CU 172 in Figs. 3-8B), for configuring early TA acquisition for LTM. The method 1400A starts with communicating 1402 with a UE via a source DU (step 1402 corresponding, e.g., to events 302, 402, 502, 602, 702, 802, 380, 480, 580, 680, 780, 880, 581 , 582, 681 , 780, 880, 881 ). The method 1400A further includes transmitting 1408 a first CU-to-DU message to a target DU to request preparing a first cell for LTM for a UE (step 1408 corresponding, e.g., to events 308, 390, 380, 490, 480, 580, 590, 581 , 582, 680, 690, 681 , 780, 790, 880, 890, 881 ). The method 1400A continues with receiving 1410 a first DU-to-CU message including a first LTM DU configuration configuring the first cell for LTM from the target DU (step 1410 corresponding, e.g., to events 310, 390, 380, 490, 480, 580, 590, 581 , 582, 680, 690, 681 , 780, 790, 880, 890, 881 ). The method 1400A further includes receiving 1411 a second DU-to-CU message including an index (i.e. , an RA preamble index) from the target DU, the index identifying an RA preamble (step 1411 also corresponding, e.g., to events 310, 390, 380, 490, 480, 580, 590, 581 , 582, 680, 690, 681 , 780, 790, 880, 890, 881 ). The method 1400A then continues with transmitting 1421 a second CU-to-DU message including the index to the source DU (step 1421 corresponding to step 1312 and, e.g., to events 412, 493, 693, 893). The method 1400A may then include receiving 1428 a third DU-to-CU message including aTA value from the target DU, and transmitting 1429 a third CU-to-DU message including the TA value to the source DU.

[0255] The first CU-to-DU message and the first DU-to-CU message may be a UE Context Setup Request message and a UE Context Setup Response message, respectively. Alternatively, the first CU-to-DU message and the first DU-to-CU message may be a UE Context Modification Request message and a UE Context Modification Response message, respectively. In some other alternatives, the first DU-to-CU message is a UE Context Modification Required message. In response to the UE Context Modification Required message, the CU transmits a UE Context Modification Confirm message to the target DU. The second DU-to-CU message may be a UE Context Modification Required message. In response to the UE Context Modification Required message, the CU transmits a UE Context Modification Confirm message to the target DU. The third DU-to-CU message may be a UE Context Modification Required message. In response to the UE Context Modification Required message, the CU transmits a UE Context Modification Confirm message to the target DU. Alternatively, the third CU-to-DU message may be a UE Context Modification Request message. In response to the UE Context Modification Request message, the CU receives a UE Context Modification Response message from the source DU.

[0256] Fig. 1 B is a flow diagram of a method 1400B similar to the method 1400A, except that the method 1400B includes step 1409 instead of steps 1410 and 1411. Thus, after steps 1402 and 1408, the method 1400B includes receiving 1409 a first DU- to-CU message including the first LTM DU configuration and an index (i.e. , an RA preamble) from the target DU, the first LTM DU configuration configuring the first cell for LTM and the index identifying an RA preamble. Unlike in the method 1400A, in the method 1400B the first LTM DU configuration and the index are transmitted in a single DU-to-CU message (i.e., the first DU-to-CU message).

[0257] Figs. 15A-15C depict flow diagrams of DU methods for early TA acquisition related to intra-DU cell switch according to various embodiments. Figs. 15A, 15B, and 15C illustrate methods for configuring early TA acquisition for LTM performed by a DU such as the DU 174 in Figs. 3 and 5A-5B, the S-DU 174A in Figs. 4, 6A-6B, and 7A-7B, and the M-DU 174A and S-DU 174B in Figs. 8A-8B. Steps 1502, 1504, 1506, 1510,1512, 1516, and 1518 are similar to steps 1102, 1104, 1106, 1110, 1112, 1116, and 1118, respectively. Steps 1513, 1514, and 1515 are similar to steps 1323, 1324, and 1325, respectively. Step 1508 is similar to step 908 or step 1310. Descriptions relative to Figs 9A, 11A, and 13A apply to Fig. 15A.

[0258] Fig. 15B is a flow diagram of a method 1500B similar to the method 1500A, except that the method 1500B includes steps 1503, 1520, and 1522. Steps 1503, 1520, and 1522 are similar to steps 1103, 1120, and 1122, respectively. Descriptions relative to Fig. 11 B apply to Fig. 15B.

[0259] Fig. 15C is a flow diagram of a method 1500C similar to the method 1500B, except that the method 1500C includes step 1505 instead of step 1503. Step 1505 is similar to step 1105. Descriptions relative to Fig. 11 C apply to Fig. 15C.

[0260] Figs. 16A-16F depict flow diagrams illustrating CU methods for early TA acquisition according to various embodiments. Descriptions relative to Figs. 9A-15C apply to Figs. 16A-16F. The methods in Figs. 16A-16F are performed by a CU (e.g., the CU 172 in Figs. 3-8B), for configuring early TA acquisition for LTM.

[0261] The method 1600A starts with transmitting 1608 a CU-to-DU message to a DU to request preparing a cell for LTM for a UE (step 1608 corresponding, e.g., to events 308, 390, 380, 490, 480, 580, 590, 581 , 582, 680, 690, 681 , 780, 790, 880, 890, 881 ). The method 1600A continues with receiving 1610, from the target DU, a DU-to- CU message including an LTM DU configuration configuring the cell for LTM (step 1610 corresponding, e.g., to events 310, 390, 380, 490, 480, 580, 590, 581 , 582, 680, 690, 681 , 780, 790, 880, 890, 881 ). The method 1600A further includes transmitting 1616 a first RRC message including the LTM DU configuration to the UE (step 1616 corresponding, e.g., to events 316, 318, 394, 380, 494, 480, 580, 594, 581 , 582, 680, 694, 617, 619, 780, 794, 880, 881 , 894, 817, 819). The method 1600A then includes receiving 1630 an early TA acquisition configuration for the UE from the DU, the early TA acquisition configuration configuring an early TA acquisition on the first cell for the UE. The DU-to-CU message may include the early TA acquisition configuration. Alternatively, the CU receives another DU-to-CU message including the early TA acquisition configuration from the DU. The method 1600A then includes transmitting 1632 a second RRC message including the early TA acquisition configuration to the UE.

[0262] Fig. 16B is a flow diagram of an example method 1600B similar to the method 1600A, except that the method 1600B includes steps 1633 instead of steps 1616 and 1632. Thus, the method 1600B includes transmitting 1633 an RRC message including the LTM configuration and the early TA acquisition configuration to the UE (step 1633 corresponding, e.g., to events 316, 318, 394, 380, 494, 480, 580, 594, 581 , 582, 680, 694, 617, 619, 780, 794, 880, 881 , 894, 817, 819).

[0263] Fig. 16C is a flow diagram of an example method 1600C similar to the method 1600A, except that the method 1600C includes steps 1617 and 1619 instead of step 1630. Thus the method 1600C includes receiving 1617 information related to early TA acquisition for the UE from the DU. The information may indicate that the DU enables or configures an early TA acquisition on the cell for the UE. The method 1600C further includes generating 1619 an early TA acquisition configuration (such as an RRC field / IE), e.g., in response to receiving the information. The information may include an index indicating an RA preamble for the UE. The information includes an indication that the DU enables early TA acquisition for the UE. The information may also include an early TA acquisition configuration (e.g., an interface protocol field / IE) for the UE.

[0264] Fig. 16D is a flow diagram of a method 1600D including steps 1608, 1610, 1617, 1619, and 1633 described relating to the methods 1600A, 1600B, and 1600C.

[0265] Fig. 16E is a flow diagram of a method 1600E similar to the methods 1600A and 1600B, except that the method 1600E includes step 1603. Thus, the method 1600E includes determining 1603 whether the DU-to-CU message includes an early TA acquisition configuration for the UE. When the DU-to-CU message does not include an early TA acquisition configuration for the UE (i.e. , the “No” branch of 1603), the method continues with step 1616. In this case, the CU does not include an early TA acquisition configuration for the UE in the first RRC message. Otherwise (i.e., the “Yes” branch of 1603), when the DU-to-CU message includes an early TA acquisition configuration for the UE, the method continues with step 1633.

[0266] Fig. 16F is a flow diagram of a method 1600F including steps described for the methods 1600A, 1600B, and 1600E, except that the method WOOF includes step 1605. Thus, the method WOOF includes determining 1605 whether the DU-to-CU message includes information for early TA acquisition for the UE. When the DU-to-CUmessage does not include information for early TA acquisition (i.e. , “No” branch of 1605), the method continues with step 1616. Otherwise (i.e., “Yes” branch of 1605), when the CU determines that that the DU-to-CU message includes information for the early TA acquisition, the method continues with steps 1619 and 1633.

[0267] The embodiment descriptions in this section refer to the accompanying drawings. The detailed descriptions do not preclude other embodiments within the scope of the appended claims.

[0268] Reference throughout this section to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0269] Numerical adjectives “first”, “second”, and “third” do not imply any order (are not ordinals) but are markers to distinguish separate instances of similar elements. References to the singular (e.g., “a” or “an”, “the”) should include the plural unless clearly indicated otherwise.

[0270] As used herein, a phrase referring to “at least one of” or “one or more of” a list of items refers to any combination of those items, including single members. For example, “at least one of: a, b, or c” is intended to cover the possibilities of: a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c.

[0271] Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. The methods or flowcharts may be implemented in a computer program, software or firmware tangibly embodied in a computer-readable storage medium for execution by a specifically programmed computer or processor.

Claims

What is claimed is:1 . A wireless communication method (900A, 900B) performed by a network entity, NE, (170, 172, 174, 104), the method comprising: transmitting (904), to a user equipment, UE, via a serving cell, a lower-layer triggered mobility, LTM, configuration of an LTM procedure for switching to a target cell; and transmitting (906), to the UE via the serving cell, an early timing advance, TA, acquisition configuration for acquiring, before performing the LTM procedure, a TA value enabling the UE to synchronize with the target cell.

2. The wireless communication method of claim 1 , further comprising: obtaining (912) the TA value during a random-access, RA, procedure based on the early TA acquisition configuration; and transmitting (913, 914), to the UE, the TA value.

3. The wireless communication method of claim 2, wherein the transmitting of the TA value occurs before transmitting (915), to the UE, an LTM command directing the UE to switch from communicating via the serving cell to communicating via the target cell.

4. The wireless communication method of claim 2, wherein the transmitting of the TA value comprises transmitting (915), to the UE, the TA value included in an LTM command directing the UE to switch from communicating via the serving cell to communicating via the target cell.

5. The wireless communication method of any of claims 2 to 4, wherein the obtaining of the TA value comprises: transmitting (908), to the UE communicating via the serving cell, a command directing the UE to initiate an RA procedure by transmitting an RA preamble on the target cell; andobtaining (912) a TA value for synchronizing the UE with the target cell based on a timing of reception of a RA preamble from the UE.

6. The wireless communication method of any of claims 1 to 5, further comprising: determining (905) whether the UE supports an early TA acquisition; and when determined that the UE does not support the early TA acquisition, refraining (920) from performing the transmitting of the early TA acquisition configuration.

7. The wireless communication method of any of claims 1 to 6, wherein the NE is a distributed unit, DU, (174) of a base station, BS, (170) and the method further comprises: receiving (1102), from a central unit, CU, (172) of the BS, a CU-to-DU message requesting the DU to prepare the LTM procedure for the UE.

8. The wireless communication method of claim 7, further comprising: reserving (1104) an RA preamble for a RA procedure; and transmitting (1106, 1108), to the CU, an indication of the reserved RA preamble.

9. The wireless communication method of claim 7, further comprising: determining (1105) whether the CU-to-DU message requests an early TA acquisition; and when determined that the CU-to-DU message does not request the early TA acquisition, refraining (1120) from performing the transmitting of the early TA acquisition configuration.

10. The wireless communication method of any of claims 1 to 4, wherein the NE is a central unit, CU, (172) of a base station, BS, (170) and the method further comprises:transmitting (1404), to a target distributed unit, T-Dll, associated with the target cell, a request to prepare the LTM procedure for the UE; receiving (1406,1408), from the T-DU, an index of an RA preamble; and transmitting (1410), to a source DU, S-DU, associated with the serving cell, the index of the RA preamble.11 . The wireless communication method of claim 10, further comprising: receiving (1412), from the T-DU, the TA value; and transmitting (1414), to the S-DU, the TA value.

12. A wireless communication method (1000) performed by a user equipment, UE, (102) in a radio access network, RAN, the method comprising: receiving (1004), via a serving cell, a lower-layer triggered mobility, LTM, configuration of an LTM procedure for switching to a target cell; and receiving (1006), via the serving cell, an early timing advance, TA, acquisition configuration for acquiring a TA value enabling the UE to synchronize with the target cell.

13. The wireless communication method of claim 12, further comprising: initiating (1010) a random access, RA, procedure based on the early TA acquisition configuration; and receiving (1013, 1014), via the serving cell, the TA value before receiving (1014, 1015) an LTM command directing the UE to switch from communicating via the serving cell to communicating via the target cell based on the LTM configuration, or receiving the TA valued included in the LTM command.

14. The wireless communication method of claim 12 or 13, wherein the early TA acquisition configuration includes an RA preamble, and the method further comprises: receiving (1008), from the RAN via the serving cell, an RA command directing the UE to initiate the RA procedure by transmitting the RA preamble on the target cell.

15. A wireless communication device (104, 170, 172, 174, 102) comprising a transceiver (282, 292), a processor (283, 293) and computer-readable storage media (284, 294) storing executable instructions for the processor to perform any of the methods recited in claims 1 -14, using the transceiver.

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