Triggering fast serving cell change

Abstract

A central unit (CU) of a distributed base station transmits, to a distributed unit (DU) of the distributed base station, a CU-to-DU message related to lower layer triggered mobility (LTM) of a user equipment (UE) connected to the distributed base station, the CU-to-DU message including a cell identifier (ID) of a candidate cell. The CU receives a DU-to-CU message from the DU in response to the CU-to-DU message, the DU-to-CU message including (i) the LTM configuration of the candidate cell and (ii) the cell ID. The CU sends the LTM configuration to the UE via the DU.

Description

[0001] Cross-references to related applications

[0002] This application claims priority and benefit on the filing date of Provisional U.S. Patent Application No. 63 / 445,696, filed February 14, 2024, entitled “Triggering a Fast Serving Cell Change”. The entire contents of that provisional application are hereby expressly incorporated herein by reference. Technical Field

[0003] This disclosure relates to wireless communications, and more specifically to triggering a fast serving cell change for a user equipment (UE). Background Technology

[0004] This background description is provided for the purpose of presenting the overall context of this disclosure. The work of the inventors whose names are mentioned (to the extent described in this background section) and aspects of the specification that might not have been considered prior art at the time of filing are neither expressly nor impliedly acknowledged as prior art to this disclosure.

[0005] In telecommunications systems, the Packet Data Convergence Protocol (PDCP) sublayer of the radio protocol stack provides services such as user plane data delivery, encryption, and integrity protection. For example, the PDCP layer defined for the Evolved Universal Terrestrial Radio Access (EUTRA) radio interface (see 3GPP specification TS 36.323) and New Radio (NR) (see 3GPP specification TS 38.323) provides Protocol Data Unit (PDU) sequencing in the uplink direction (from the user equipment (UE) to the base station) and in the downlink direction (from the base station to the UE). Furthermore, the PDCP sublayer provides Signaling Radio Bearers (SRBs) and Data Radio Bearers (DRBs) to the Radio Resource Control (RRC) sublayer. Generally, the UE and base station can use SRBs to exchange RRC messages and Non-Access Stratum (NAS) messages, and can use DRBs to transmit data on the user plane.

[0006] A UE can use several types of SRBs and DRBs. When operating in dual connectivity (DC), a cell associated with a base station operating as a master node (MN) defines a master cell group (MCG), and a cell associated with a base station operating as a secondary node (SN) defines a secondary cell group (SCG). So-called SRB1 resources carry RRC messages that in some cases include NAS messages on a dedicated control channel (DCCH), while SRB2 resources support RRC messages that include logged measurement information or NAS messages also on the DCCH but with lower priority than SRB1 resources. More generally, SRB1 and SRB2 resources allow the UE and the MN to exchange RRC messages related to the MN and to embed RRC messages related to the SN, and can also be referred to as MCG SRBs. SRB3 resources allow the UE and the SN to exchange RRC messages related to the SN, and can be referred to as a SCG SRB. Split SRBs allow the UE to exchange RRC messages directly with the MN via lower layer resources of the MN and the SN. Further, DRBs using lower layer resources of the MN only can be referred to as MCG DRBs, DRBs using lower layer resources of the SN only can be referred to as SCG DRBs, and DRBs using lower layer resources of both the MCG and the SCG can be referred to as split DRBs.

[0007] In some scenarios, a UE can simultaneously utilize resources of multiple radio access network (RAN) nodes (e.g., base stations, or components of a distributed base station) interconnected by backhaul. When these network nodes support different radio access technologies (RATs), this type of connection is referred to as multi-radio dual connectivity (MR-DC). When a UE operates under MR-DC, one base station operates as a master node (MN) covering a primary cell (PCell), and another base station operates as a secondary node (SN) covering a primary secondary cell (PSCell). The UE communicates with the MN (via the PCell) and the SN (via the PSCell). In other scenarios, a UE utilizes resources of one base station at a time. One base station and / or the UE determines that the UE should establish a radio connection with another base station. For example, one base station can determine to handover the UE to a second base station and initiate a handover procedure.

[0008] When a UE moves from the coverage area of one cell in a RAN to another cell, the UE and the network must perform a serving cell change at some point in time. To perform the serving cell change, the RAN configures the UE to send layer 3 (L3) measurement results. Based on the L3 measurement results from the UE, the RAN sends an RRC reconfiguration message (e.g., the RRC reconfiguration message includes a ReconfigurationWithSync IE) for reconfiguration with synchronization for a change of serving cell (e.g., PCell or PSCell). When the UE operates in carrier aggregation (CA) with at least one secondary cell (SCell) with the PCell or PSCell, the RAN must release the at least one SCell due to the change of the PCell or PSCell. The serving cell change involves a full L2 (and LI) reset, resulting in longer latency, greater overhead, and longer interruption time.

[0009] To address these issues, 3GPP recently proposed developing mobility procedures for reducing latency and overhead for fast serving cell change described in technical document RP-221799. These procedures provide fast serving cell change and can be referred to as lower-layer triggered mobility (LTM).

[0010] The RAN can send one or more LTM configurations to the UE for fast serving cell change. However, it is currently unclear how the RAN node or the UE should trigger the fast serving cell change. SUMMARY

[0011] An example embodiment of the techniques of this disclosure is a method implemented in a central unit (CU) of a distributed base station. The method includes sending, to a distributed unit (DU) of the distributed base station, a CU-to-DU message related to lower-layer triggered mobility (LTM) for a user equipment (UE) connected to the distributed base station, the CU-to-DU message including a cell identifier (ID) of a candidate cell; receiving, from the DU in response to the CU-to-DU message, a DU-to-CU message including (i) an LTM configuration for the candidate cell and (ii) the cell ID; and sending, via the DU, the LTM configuration to the UE.

[0012] Another example embodiment of the techniques is a method implemented in a distributed unit (DU) of a distributed base station. The method includes receiving, from a central unit (CU) of the distributed base station, a CU-to-DU message related to lower tier mobility (LTM) for a user equipment (UE) connected to the distributed base station, the CU-to-DU message including a cell identifier (ID) of a candidate cell associated with the DU; in response to the CU-to-DU message, sending, to the DU, a DU-to-CU message including (i) an LTM configuration for the candidate cell and (ii) the cell ID; receiving, from the CU, the LTM configuration for the UE; and sending, to the UE, the LTM configuration.

[0013] Another example embodiment of the techniques is a radio access network (RAN) node including processing hardware and configured to implement one of the above-described methods. BRIEF DESCRIPTION OF DRAWINGS

[0014] FIG. 1A is a block diagram of an example system in which a radio access network (RAN) and a user equipment (UE) can implement techniques of the present disclosure for managing conditional procedures related to secondary nodes (SNs);

[0015] FIG. 1B is a block diagram of an example protocol stack according to which a UE of FIG. 1A may operate in the system of

[0016] FIG. 2A is a block diagram of an example protocol stack, FIG. 1A according to which a UE of

[0017] FIG. 2B is a block diagram of an example protocol stack, FIG. 1A according to which a UE of

[0018] FIG. 3 is a message passing diagram of an example scenario in which a UE performs an LTM handover from a serving cell of a DU to a candidate cell of the same DU;

[0019] FIG. 4 is a message passing diagram of an example scenario in which a UE performs an LTM handover from a serving cell of a source DU to a candidate cell of a target DU;

[0020] FIG. 5A to FIG. 5B is a message passing diagram of an example scenario in which a UE operates in dual connectivity with a master node (MN) and a secondary node (SN) and performs an LTM handover from a serving cell of a DU of the SN to a candidate cell of the same DU of the SN;

[0021] FIG. 6A to FIG. 6Bis a messaging diagram for an example scenario where a UE operates in dual connectivity with a MN and a SN and performs an LTM handover from a source DU's serving cell of the SN to a candidate cell of a target DU of the SN;

[0022] FIG. 7A to FIG. 7B is a messaging diagram for an example scenario where a UE operates in dual connectivity with a MN and a SN and performs an LTM handover from a source DU's serving cell of the SN to a candidate cell of a target DU of the SN; FIG. 5A to FIG. 5B is a messaging diagram for an example scenario where a UE operates in dual connectivity with a MN and a SN and performs an LTM handover from a source DU's serving cell of the SN to a candidate cell of a target DU of the SN;

[0023] FIG. 8A to FIG. 8B is a messaging diagram for an example scenario where a UE operates in dual connectivity with a MN and a SN and performs an LTM handover from a source DU's serving cell of the SN to a candidate cell of a target DU of the SN; FIG. 6A to FIG. 6B is a messaging diagram for an example scenario where a UE operates in dual connectivity with a MN and a SN and performs an LTM handover from a source DU's serving cell of the SN to a candidate cell of a target DU of the SN;

[0024] FIG. 9A is a flow diagram for an example method for configuring and triggering LTM for a UE using a cell ID and a cell index, which can be implemented in a DU of the present disclosure;

[0025] FIG. 9B is a flow diagram for an example method for configuring and triggering LTM for a UE using an LTM group ID, which can be implemented in a DU of the present disclosure;

[0026] FIG. 9C is a flow diagram for an example method for configuring and triggering LTM for a UE using an LTM group ID and a cell index, which can be implemented in a DU of the present disclosure;

[0027] FIG. 9D is a flow diagram for an example method for configuring and triggering LTM for a UE using a group ID, a cell ID, and a cell index, which can be implemented in a DU of the present disclosure;

[0028] FIG. 10A is a flow diagram for an example method for configuring LTM for a UE using a cell ID and a cell index, which can be implemented in a CU of the present disclosure;

[0029] FIG. 10B is a flow diagram for an example method for configuring LTM for a UE using an LTM group ID, which can be implemented in a CU of the present disclosure;

[0030] FIG. 10C is a flow diagram for an example method for configuring LTM for a UE using an LTM group ID and a cell index, which can be implemented in a CU of the present disclosure;

[0031] FIG. 10D is a flow diagram for an example method for configuring LTM for a UE using a group ID, a cell ID, and a cell index, which can be implemented in a CU of the present disclosure;

[0032] FIG. 11A to FIG. 11Dis a flowchart of a further method for configuring LTM for a UE, which can be implemented in a CU of the present disclosure;

[0033] FIG. 12 is a flowchart of an example method for triggering LTM at a UE using a cell index, which can be implemented in a DU of the present disclosure; and

[0034] FIG. 13 is a flowchart of an example method for triggering LTM at a UE using a cell index and an LTM group ID, which can be implemented in a DU of the present disclosure. DETAILED DESCRIPTION

[0035] FIG. 1A An example wireless communication system 100 in which communication devices can implement the techniques is depicted. The wireless communication system 100 includes a UE 102, a RAN 105 including base stations (BSs) 104 and 106, and a core network (CN) 110. The UE 102 initially connects to the base station 104. In some scenarios, the base station 104 can perform SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104 and the base station 106. The base stations 104 and 106 operate as an MN and an SN, respectively, for the UE 102.

[0036] In various configurations of the wireless communication system 100, the base station 104 can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station 106 can be implemented as a secondary gNB (SgNB). The UE 102 can communicate with the base station 104 and the base station 106 via the same RAT (such as EUTRA or NR) or different RATs. When the base station 104 is a MeNB and the base station 106 is a SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0037] In some cases, the MeNB or SeNB is implemented as an ng-eNB instead of an eNB. When the base station 104 is a master ng-eNB (Mng-eNB) and the base station 106 is a SgNB, the UE 102 can be in next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. When the base station 104 is a MgNB and the base station 106 is a SgNB, the UE 102 can be in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the base station 104 is a MgNB and the base station 106 is a secondary ng-eNB (Sng-eNB), the UE 102 can be in NR-EUTRA DC (NE-DC) with the MgNB and the Sng-eNB.

[0038] In the scenario where UE 102 switches from base station 104 to base station 106, base stations 104 and 106 operate as the source base station (S-BS) and the target base station (T-BS), respectively. UE 102 can, for example, communicate with base station 104 and the auxiliary base station (T-BS) under DC before the handover. FIG. 1A (Not shown in the diagram) Operation. After the handover is completed, UE 102 can continue to operate with base station 106 and the additional base station under DC or with base station 106 under single connection (SC). In this case, base stations 104 and 106 operate as the source MN (S-MN) and the target MN (T-MN), respectively.

[0039] The core network (CN) 110 can be either the Evolved Packet Core (EPC) 111 or the fifth-generation core (5GC) 160; both are... FIG. 1A The following description is provided. Base station 104 may be an eNB supporting an S1 interface for communication with EPC 111, an ng-eNB supporting an NG interface for communication with 5GC 160, or a gNB supporting an NR radio interface and an NG interface for communication with 5GC 160. Base stations 104 and 106 may support X2 or Xn interfaces to directly exchange messages with each other during the scenarios discussed below. Among other components, EPC 111 may also include a Serving Gateway (SGW) 112, a Mobility Management Entity (MME) 114, and a Packet Data Network Gateway (PGW) 116. SGW 112 is typically configured to transmit user plane packets related to audio calls, video calls, Internet traffic, etc., and MME 114 is configured to manage authentication, registration, paging, and other related functions. PGW 116 provides connectivity from the UE to one or more external packet data networks (e.g., Internet networks and / or Internet Protocol (IP) Multimedia Subsystem (IMS) networks). 5GC 160 includes User Plane Functions (UPF) 162, Access and Mobility Management (AMF) 164, and / or Session Management Functions (SMF) 166. UPF 162 is generally configured to transmit user plane packets related to audio calls, video calls, Internet services, etc., AMF 164 is configured to manage authentication, registration, paging, and other related functions, and SMF 166 is configured to manage PDU sessions.

[0040] like FIG. 1A As shown, base station 104 supports cell 124A, and base station 106 supports cell 126. Cells 124A and 126 can partially overlap, allowing UE 102 to communicate with base stations 104 and 106 under DC, where one of base stations 104 and 106 is MN and the other is SN. Base station 104 can support additional cells such as cells 124B and 124C, and base station 106 can support additional cells (…).FIG. 1A The cells 124A, 124B, and 124C can partially overlap, such that the UE 102 can communicate with the base station 104 in carrier aggregation (CA). The base station 104 can operate the cells 124A, 124B, and 124C via one or more transmission and reception points (TRPs). More specifically, when the UE 102 is in DC with the base stations 104 and 106, one of the base stations 104 and 106 operates as the MeNB, Mng-eNB, or MgNB, while the other operates as the SgNB or Sng-eNB 126.

[0041] In general, the wireless communication network 100 can include any suitable number of base stations that support NR cells and / or EUTRA cells. More specifically, the EPC 111 or the 5GC 160 can be connected to any suitable number of base stations that support NR cells and / or EUTRA cells. Although the examples below specifically refer to particular CN types (EPC, 5GC) and RAT types (5G NR and EUTRA), in general, the techniques of this disclosure can also be applied to other suitable radio access and / or core network technologies, such as sixth generation (6G) radio access and / or a 6G core network or 5G NR-6G DC.

[0042] With continued reference to FIG. 1AThe base station 104 is equipped with processing hardware 130, which can include one or more general-purpose processors (e.g., CPUs) and non-transitory computer-readable memory storing instructions for execution by the one or more general-purpose processors. Additionally or alternatively, the processing hardware 130 can include special-purpose processing units. The processing hardware 130 can include a PHY controller 132 configured to transmit data and control signals with one or more user devices (e.g., UEs 102) on physical downlink (DL) channels and DL reference signals via one or more cells (e.g., cells 124A, 124B, and / or 124C) and / or one or more TRPs. The PHY controller 132 is also configured to receive data and control signals with one or more user devices on physical uplink (UL) channels and / or UL reference signals via one or more cells (e.g., cells 124A, 124B, and / or 124C) and / or one or more TRPs. The processing hardware 130 includes, in example implementations, a MAC controller 134 configured to perform MAC functions with one or more user devices. The MAC functions include random access (RA) procedures, managing UL timing advance of one or more user devices, and / or communicating UL / DL MAC PDUs with one or more user devices. The processing hardware 130 can further include an RRC controller 136 to implement procedures and messaging at the RRC sublayer of the protocol communication stack. For example, the RRC controller 132 can be configured to support RRC messaging associated with handover procedures and / or support necessary operations when the base station 104 operates as a MN with respect to a SN or as a SN with respect to a MN. The base station 106 can include processing hardware 140 similar to the processing hardware 130. Specifically, components 142, 144, and 146 can be similar to components 132, 134, and 136, respectively.

[0043] The UE 102 is equipped with processing hardware 150, which can include one or more general-purpose processors, such as CPUs, and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special purpose processing units. The PHY controller 152 is also configured to receive data and control signals on physical DL channels and / or DL reference signals with the base station 104 or 106 via one or more cells (e.g., cells 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 base station 104 or 106 via one or more cells (e.g., cells 124A, 124B, 124C, and / or 126) and / or one or more TRPs. The processing hardware 150 includes, in example implementations, a MAC controller 154 configured to perform MAC functions with the base station 104 or 106. For example, MAC functions include random access procedures, managing UL timing advance of one or more user devices, and communicating UL / DL MAC PDUs with the base station 104 or 106. The processing hardware 150 can further include an RRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack.

[0044] In operation, the UE 102 can use radio bearers (e.g., DRBs or SRBs) that terminate at the MN 104 or the SN 106 at different times under DC. The UE 102 can apply one or more security keys when communicating on the radio bearers in the uplink (UL) (from the UE 102 to the base station) and / or downlink (from the base station to the UE 102) directions.

[0045] FIG. 1B An example distributed implementation of a base station, such as the base station 104 or 106, is depicted. In this implementation, the base station can include a central unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 is equipped with processing hardware, which can include one or more general-purpose processors, such as CPUs, and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special purpose processing units. For example, the CU 172 can include a PDCP controller, an RRC controller, and / or an RRC inactive controller. In some implementations, the CU 172 can include a radio link control (RLC) controller configured to manage or control one or more RLC operations or procedures. In further implementations, the CU 172 does not include an RLC controller.

[0046] Each of the DUs 174 also includes processing hardware that can include one or more general-purpose processors (e.g., CPUs) and computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. For example, the processing hardware can include a MAC controller configured to manage or control one or more MAC operations or procedures (e.g., random access procedures), and / or an RLC controller configured to manage or control one or more RLC operations or procedures. The processing hardware can also include a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0047] In some embodiments, the RAN 105 supports integrated access and backhaul (IAB) functionality. In some implementations, the DUs 174 operate as IAB nodes and the CUs 172 operate as IAB donors. In some embodiments, the RAN 105 supports non-terrestrial network (NTN) functionality.

[0048] In some implementations, the CU 172 can include a logical node CU-CP 172A that hosts the control plane portion of the PDCP protocol of the CU 172. The CU 172 can also include a logical node CU-UP 172B that hosts the user plane portion of the PDCP protocol and / or the service data adaptation protocol (SDAP) protocol of the CU 172. The CU-CP 172A can transmit control information (e.g., RRC messages, Fl application protocol messages), and the CU-UP 172B can transmit data packets (e.g., SDAP PDUs or Internet Protocol packets).

[0049] The CU-CP 172A can be connected to multiple CU-UPs 172B over an El interface. The CU-CP 172A selects an appropriate CU-UP 172B for a service requested by the UE 102. In some implementations, a single CU-UP 172B can be connected to multiple CU-CPs 172A over an El interface. The CU-CP 172A can be connected to one or more DUs 174 over an Fl-C interface. The CU-UP 172B can be connected to one or more DUs 174 over an Fl-U interface under control of the same CU-CP 172A. In some implementations, one DU 174 can be connected to multiple CU-UPs 172B under control of the same CU-CP 172A. In such implementations, the connection between the CU-UP 172B and the DU 174 is established by the CU-CP 172A using a Bearer Context Management function.

[0050] FIG. 2AAn example protocol stack 200 is shown in simplified form, by which the UE 102 can communicate with an eNB / ng-eNB 230 or gNB 232 (e.g., one or more of the base stations 104, 106).

[0051] In the example stack 200, a physical layer (PHY) 202A of EUTRA provides transport channels to a MAC sublayer 204A of EUTRA, which in turn provides logical channels to a RLC sublayer 206A of EUTRA. The RLC sublayer 206A in turn provides RLC channels to a PDCP sublayer 208 of EUTRA and, in some cases, to a NR PDCP sublayer 210. Similarly, a NR PHY 202B provides transport channels to a NR MAC sublayer 204B, which in turn provides logical channels to a 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 a service data adaptation protocol (SDAP) 212 or a radio resource control (RRC) sublayer (not shown in FIG. 2). In some implementations, the UE 102 supports both EUTRA and NR stacks, as shown in FIG. 1, to support handover between EUTRA and NR base stations and / or to support DC over EUTRA and NR interfaces. FIG. 2A FIG. 2A Further, as shown in FIG. 2, the UE 102 can support the NR PDCP 210 layered over the EUTRA RLC 206A, and the SDAP sublayer 212 layered over the NR PDCP sublayer 210. FIG. 2A

[0052] The EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 receive packets, which can be referred to as service data units (SDUs), from an Internet Protocol (IP) layer (e.g., layered directly or indirectly over the PDCP layer 208 or 210) and output packets, which can be referred to as protocol data units (PDUs), to the RLC layer 206A or 206B. Except for cases related to the difference between SDUs and PDUs, for simplicity the present disclosure refers to both SDUs and PDUs as “packets.”

[0053] On the control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide signaling radio bearers (SRBs) or RRC sublayer (not shown in FIG. 2) services to the RLC layer 206A or 206B. FIG. 2A ​​The EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can exchange, for example, RRC messages or non-access stratum (NAS) messages over the control plane (not shown). On the 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 over the NR PDCP sublayer 210 can be SDAP PDUs, Internet Protocol (IP) packets, or Ethernet packets.

[0054] FIG. 2B An example protocol stack 250 is shown in a simplified manner in which the UE 102 can communicate with a DU (e.g., the DU 174) and a CU (e.g., the CU 172). The radio protocol stack 200 is functionally split as shown in the radio protocol stack 250 in FIG. 2B The CU at either of the base stations 104 or 106 can maintain all control and upper layer functions (e.g., RRC 214, SDAP 212, NR PDCP 210), while lower layer operations (e.g., NR RLC 206B, NR MAC 204B, and NR PHY 202B) are delegated to the DU. To support connectivity to the 5GC, the NR PDCP 210 provides SRBs to the RRC 214, and the NR PDCP 210 provides DRBs to the SDAP 212 and SRBs to the RRC 214.

[0055] Next are several example scenarios in which a base station operating in a system of FIG. 1A sends a configuration to the UE 102 and later activates the configuration for use in communicating between the UE 102 and the base station. Generally, FIG. 3 to FIG. 8B similar events are labeled with similar reference numbers sharing the tens and ones place (e.g., event 306 is similar to FIG. 4 event 406 of FIG. 4, FIG. 5A and FIG. 5B event 506 of FIG. 5, FIG. 8A and FIG. 8B event 806 of FIG. 8; with the differences discussed below where appropriate. Except for the differences shown in the figures and discussed below, any of the alternative implementations discussed with respect to a particular event (e.g., for messaging and processing) can apply to events labeled with similar reference numbers in other figures. FIG. 3 event 328 of FIG. 3 is similar to FIG. 4 event 428 of FIG. 4, FIG. 5A and FIG. 5B event 528 of FIG. 5, FIG. 6A and FIG. 6B event 628 of FIG. 6, FIG. 7A and FIG. 7B event 728 of FIG. 7, FIG. 8A and FIG. 8B event 828 of FIG. 8, etc., with the differences discussed below where appropriate. Except for the differences shown in the figures and discussed below, any of the alternative implementations discussed with respect to a particular event (e.g., for messaging and processing) can apply to events labeled with similar reference numbers in other figures.

[0056] First refer to FIG. 3 In scenario 300, base station 104 includes CU 172 and DU 174, and DU 174 operates cell 124A. UE 102 initially uses the serving DU configuration to communicate with DU 174 on cell 124A 302, and, for example, uses the serving CU configuration to communicate with CU 172 via DU 174. In some implementations, UE 102 uses the serving DU configuration in cell 124A and other cells (e.g., FIG. 1A UE 102 communicates with DU 174 via carrier aggregation (CA) on cell 124D (not shown). DU 174 operates other cells. In other implementations, UE 102 communicates with DU 174 only on cell 124A. In some implementations, UE 102 communicates with DU 174 on cell 124A and / or other cells via one or more TRPs. In some implementations, cell 124A is a PCell. In such cases, other cells include SCells and / or additional cells associated with a PCell or SCell. In other implementations, cell 124A is an SCell, and one of the other cells is a PCell. In such cases, the remaining cells may include SCells and / or additional cells associated with a PCell or SCell. In the following scenarios, base station 104 can be DU 174, CU 172, or DU 174 and CU 172.

[0057] During procedure 302, UE 102 may transmit UL PDUs and / or UL control signals to base station 104 via one or more TRPs in cell 124A and / or other cells. In some implementations, UE 102 communicates UL PDUs and / or DL ​​PDUs to base station 104 via a radio bearer that may include SRBs and / or DRBs. Base station 104 may be configured to the radio bearer of UE 102. In some implementations, UL control signals include UL control information, channel state information, Hybrid Automatic Repeat Request (HARQ) acknowledgment (ACK), HARQ negative ACK, scheduling request, and / or probe reference signals. Similarly, UE 102 may receive DL PDUs and / or DL ​​control signals from base station 104 via one or more TRPs in cell 124A and / or other cells. In some implementations, DL control signals include downlink control information (DCI) and reference signals (e.g., synchronization signal blocks, channel state information reference signals (CSI-RS), and / or tracking reference signals). Base station 104 can transmit DCI via one or more TRPs on the physical downlink control channel (PDCCH) monitored by UE 102 in cell 124A and / or other cells.

[0058] In some implementations, the serving DU configuration includes physical layer configuration parameters, MAC layer configuration parameters, and / or RLC configuration parameters. In some implementations, the DU 174 can send these configuration parameters to the CU 172. The CU 172 generates one or more messages (e.g., RRC reconfiguration messages) including the configuration parameters and sends the one or more messages to the UE 102 via the DU 174. In other implementations, the DU 174 sends the configuration parameters directly to the UE 102. In some implementations, the serving DU configuration is a CellGroupConfig IE defined in 3GPP specification 38.331. In other implementations, the serving DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the serving CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the serving CU configuration includes a MeasConfig IE and / or a RadioBearerConfig IE defined in 3GPP specification 38.331, or includes configuration parameters in the MeasConfig IE and / or the RadioBearerConfig IE. In some implementations, the serving DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and reporting. In other implementations, the serving CU configuration includes the CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and reporting. In some implementations, the UE 102 receives the serving CU configuration or configuration parameters in the serving CU configuration from the CU 172 via the DU 174. In other implementations, the UE 102 receives a portion of the serving CU configuration and / or a portion of the serving DU configuration from a base station other than the base station 104, and receives the remaining portion of these configuration parameters from the base station 104.

[0059] In communicating with the base station 104, the UE 102 sends 304 at least one measurement report to the DU 174. In some implementations, the at least one measurement report includes a layer 1 (LI) measurement report and / or a layer 3 (L3) measurement report for at least one serving cell of the UE 102 and / or for at least one non-serving cell. For each of the L3 measurement reports, the DU 174 sends 306 a DU-to-CU message including the L3 measurement report to the CU 172. In some implementations, the DU-to-CU message of event 306 is a Fl application protocol (FlAP) message (e.g., UL RRC Message Transfer message). In some implementations, the DU 174 does not send or refrain from sending Ll measurement reports to the CU 172. The at least one serving cell includes the cell 124A and / or other cells, and the at least one non-serving cell includes the cell 124B and / or the cell 124C. In some implementations, the serving DU configuration or the serving CU configuration includes at least one measurement configuration. In some implementations, in event 302, the UE 102 receives one or more RRC messages (e.g., RRCReconfiguration message) including the at least one measurement configuration from the CU 172 via the DU 174. According to the at least one measurement configuration, the UE 102 performs measurements and sends 304 the at least one measurement report to the DU 174. In some implementations, the at least one measurement configuration includes a L3 measurement configuration (e.g., MeasConfig IE) and / or a LI measurement configuration. The LI measurement configuration (e.g., CSI-MeasConfig IE) can include a LI measurement resource configuration and / or a LI measurement report configuration. The LI measurement resource configuration can configure resources of reference signals (e.g., CSI-RS) for the UE 102 to measure and obtain LI measurement results. For example, the LI measurement resource configuration is a CSI-ResourceConfig IE. In another example, the LI measurement report configuration configures a manner for the UE 102 to send the LI measurement results / reports. For example, the LI measurement report configuration is a CSI-ReportConfig IE. For example, the UE 102 sends L3 measurement reports to the CU 172 via the DU 174 according to the L3 measurement configuration. The UE 102 sends LI measurement reports to the DU 174 according to the LI measurement configuration or the LI measurement report configuration. In one implementation, the DU 174 does not send the LI measurement reports to the CU 172.

[0060] In some implementations, the L1 measurement configuration is a dedicated RRC IE defined specifically for lower layer triggered mobility (LTM) and dedicated to that lower layer triggered mobility (e.g., in a related 3GPP specification such as TS 38.331). In some implementations, the L1 measurement resource configuration is a RRC IE defined specifically for lower layer triggered mobility (LTM) and dedicated to LTM (e.g., in a related 3GPP specification such as TS 38.331). In some implementations, the L1 measurement report configuration is a RRC IE defined specifically for lower layer triggered mobility (LTM) and dedicated to LTM (e.g., in a related 3GPP specification such as TS 38.331). In some implementations, each of the L1 measurement report configurations can include a trigger event configuration that configures a trigger event to trigger the UE 102 to send an L1 measurement report. If the UE 102 detects the trigger event, the UE 102 sends an L1 measurement report to the DU 174.

[0061] In some implementations, each of the L1 measurement reports can include at least one L1 measurement result. In some implementations, the at least L1 measurement result includes at least one L1 reference signal received power (L1-RSRP) value, L1 reference signal received quality (L1-RSRQ), and / or at least one L1 signal-to-interference-and-noise ratio (L1-SINR) value. In some implementations, for each of the L1 measurement reports, the UE 102 transmits, to the DU 174, a PUCCH transmission that includes the L1 measurement report. That is, the UE 102 transmits each of the L1 measurement reports on a PUCCH to the DU 174. In other implementations, for each of the L1 measurement reports, the UE 102 transmits, to the DU 174, a PUSCH transmission that includes the L1 measurement report. That is, the UE 102 transmits each of the L1 measurement reports on a PUSCH to the DU 174. In yet other implementations, the UE 102 transmits a portion of the L1 measurement reports on a PUCCH to the DU 174 and transmits a remaining portion of the L1 measurement reports on a physical UL shared channel (PUSCH). That is, for each of the portion of the L1 measurement reports, the UE 102 transmits, to the DU 174, a PUCCH transmission that includes the L1 measurement report, and for each of the remaining portion of the L1 measurement reports, the UE 102 transmits, to the DU 174, a PUSCH transmission that includes the L1 measurement report. In some implementations, each of the L1 measurement reports is a part of (i.e., a CSI component of) channel state information (CSI) or CSI. In some implementations, the UE 102 can include other CSI components in each of the above-described PUCCH transmission and / or PUSCH transmission. In one implementation, the other CSI components 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 (RI). In some implementations, the UE 102 does not transmit the L1 measurement reports to the DU 174 in the format of an RRC message. In some implementations, each of the L1 measurement reports includes an L1 event ID that identifies or indicates the L1 event that triggered the L1 measurement report. Alternatively, each of the L1 measurement reports does not include an L1 event ID that identifies or indicates the L1 event that triggered the L1 measurement report.

[0062] In some implementations, each of the L3 measurement reports can include at least one L3 measurement result. In some implementations, the at least one L3 measurement result includes at least one RSRP (value) and / or at least one SINR (value). In one implementation, the UE 102 transmits each of the L3 measurement reports to the CU 172 via the DU 174 on a PUSCH. In some implementations, each of the L3 measurement reports can be an RRC message (e.g., a MeasurementReport message). In some implementations, each of the L3 measurement configurations includes a specific measurement identity (e.g., measld) and each of the L3 measurement reports includes the specific measurement identity in the specific L3 measurement configuration. When the CU 172 receives the L3 measurement reports including the measurement identities and the L3 measurement results from the UE 102 via the DU 174, the CU 172 can determine that the L3 measurement reports are associated with the L3 measurement configurations identified by the measurement identities.

[0063] In some alternative implementations, for each of the at least one measurement report (e.g., the L1 measurement report), the UE 102 transmits, in event 304, a MAC control element (CE) including the measurement report to the DU 174. To transmit the MAC CE, the UE 102 generates, in event 304, one or more MAC PDUs to the DU 174, each of the MAC PDUs including one or more of the MAC CEs.

[0064] In some implementations, the UE 102 performs measurements on one or more reference signals according to the at least one measurement configuration. The one or more reference signals can include one or more synchronization signal (SS) / physical broadcast channel (PBCH) resource blocks (SSBs) and / or one or more CSI-RSs. The UE 102 obtains 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 cells (e.g., the cell 124B, the cell 124C, and / or a cell not shown in FIG. 1). FIG. 1A

[0065] ​After receiving one or more of the at least one measurement report from the UE 102 (e.g., in response thereto), the base station 104 (i.e., the CU 172 or the DU 174) determines to prepare a first cell (e.g., the cell 124B) for LTM for the UE 102. In some implementations, the base station 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the first cell can be used by the base station 104 to communicate with the UE 102. In some implementations, the base station 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the first cell qualifies as a candidate cell that can be used for communication with the UE 102. In some implementations, the CU 172 determines to prepare the first cell for the UE 102 if the L3 measurement report indicates that the signal strength and / or quality of the first cell is above a first predetermined threshold, is better than the strength and / or quality of the cell 124A, and / or is better than the strength and / or quality of the cell 124A by the first predetermined threshold. In other implementations, the DU 174 determines to prepare the first cell for the UE 102 if the LI measurement report indicates that the signal strength and / or quality of the first cell is above a first predetermined threshold, is better than the signal strength and / or quality of the cell 124A, and / or is better than the signal strength and / or quality of the cell 124A by the first predetermined threshold. Alternatively, the base station 104 determines to prepare the first cell for the UE 102 regardless of whether a measurement report is received from the UE 102.

[0066] When the CU 172 determines to prepare the first cell for LTM, the CU 172 sends 308 a first CU-to-DU message to the DU 174 to prepare the first cell for the UE 102. In some implementations, the CU 172 includes a cell identity (ID) (i.e., cell ID 1) of the first cell in the first CU-to-DU message to request the DU 174 to prepare the first cell for the UE 102 for LTM. For example, the cell ID is a cell global identity (CGI). In another example, the cell ID is a part 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 configuration (hereinafter referred to as LTM configuration 1) for the UE 102, which first DU configuration configures the first cell for LTM. The DU 174 then sends 310 a first DU-to-CU message including the LTM configuration 1 to the CU 172 in response to the first CU-to-DU message. In some implementations, the DU 174 can include the cell ID 1 with the LTM configuration 1 in an IE of the first DU-to-CU message to indicate that the LTM configuration 1 is associated with the first cell (i.e., cell ID 1). In the case that the DU 174 determines to prepare the first cell, the DU 174 initiates sending the first DU-to-CU message to the CU 172 instead of responding to the CU-to-DU message received from the CU 172.

[0067] In some implementations, the DU 174 includes a cell ID of the first cell associated with the LTM configuration 1 in the first DU-to-CU message to indicate that the LTM configuration 1 is configured for or associated with the first cell. The CU 172 identifies that the LTM configuration 1 is configured for or associated with the first cell. In some scenarios and implementations, the CU 172 can include additional cell IDs (e.g., cell IDs 2, …, N) in the first CU-to-DU message to prepare additional cells (e.g., cells 2, …, N) for the UE 102 for LTM, and the DU 174 includes additional LTM configurations (e.g., LTM configurations 2, …, N), each of which configures a particular one of the additional cells, as described below. In such cases, the DU 174 includes the additional cell IDs respectively associated with the additional LTM configurations in the first DU-to-CU message to indicate which LTM configuration is associated with which cell (ID). The cells 1 and / or 2, …, N are candidate cells.

[0068] In some implementations, the CU 172 does not include the (reference) LTM configuration in the first CU-to-DU message. In such cases, the DU 174 generates the reference LTM configuration, generates the LTM configurations 1 and / or 2, …, N based on the reference LTM configuration (i.e., non-reference LTM configurations), and includes the reference LTM configuration in the first DU-to-CU message. In other implementations, the CU 172 includes the reference LTM configuration in the first CU-to-DU message. In such cases, the DU 174 generates the LTM configurations 1 and / or 2, …, N, which are delta configurations to enhance the reference LTM configuration. In yet other implementations, the CU 172 includes a reference LTM configuration (e.g., a first reference LTM configuration) in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM configuration that replaces the first reference LTM configuration (e.g., a second reference LTM configuration), generates the LTM configurations 1 and / or 2, …, N based on the second reference LTM configuration, and includes the second reference LTM configuration in the first DU-to-CU message.

[0069] In some implementations, the reference LTM configuration includes physical layer configuration parameters, MAC layer configuration parameters, and / or RLC configuration parameters. In some implementations, the reference LTM configuration is a CellGroupConfig IE defined in 3GPP specification 38.331. In other implementations, the reference LTM configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the reference LTM configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and / or reporting.

[0070] In some implementations, the reference LTM configuration is different from the serving DU configuration. In some implementations, a portion of the reference LTM configuration is the same as a portion of the serving DU configuration, and a remaining portion of the reference LTM configuration is different from a remaining portion of the serving DU configuration. In other implementations, the reference LTM configuration is the same as the serving DU configuration.

[0071] After receiving the first DU-to-CU message, the CU 172 generates an RRC reconfiguration message (e.g., an RRCReconfiguration message) that includes the LTM configuration 1 and sends 316 a second CU-to-DU message that includes the RRC reconfiguration message to the DU 174. In some implementations, the CU 172 includes the reference LTM configuration in the RRC reconfiguration message 316. In other implementations, the CU 172 does not include the reference LTM configuration in the RRC reconfiguration message 316. In some implementations, the CU 172 does not include the reference LTM configuration in the RRC reconfiguration message 316 if the CU 172 sent the reference LTM configuration to the UE 102 during event 302. In other implementations, the CU 172 includes the LTM configuration in the RRC reconfiguration message 316 if the CU 172 received the reference LTM configuration from the DU 174. Otherwise, the CU 172 does not include the reference LTM configuration in the RRC reconfiguration message 316 if the CU 172 did not receive the reference LTM configuration from the DU 174.

[0072] After receiving the RRC reconfiguration message 316, the DU 174 sends 318 an RRC reconfiguration message to the UE 102. In response, the UE 102 sends 320 an RRC reconfiguration complete message (e.g., RRCReconfigurationComplete message) to the DU 174, which in turn sends 322 a second DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some implementations, the CU 172 performs security protection (e.g., integrity protection and / or encryption) on the RRC reconfiguration message. For example, the CU 172 generates an integrity message authentication code (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 sends, via the DU 174, a PDCP PDU including the encrypted RRC reconfiguration message and the encrypted MAC-I to the UE 102 in 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 the encrypted MAC-I to obtain the RRC reconfiguration message and the MAC-I and verifies whether the MAC-I is valid. If the UE 102 verifies that the MAC-I is invalid, the UE 102 discards or ignores the RRC reconfiguration message. In some implementations, the UE 102 can perform an RRC connection reestablishment procedure in response to the invalid MAC-I. Otherwise, if the UE 102 verifies that the MAC-I is valid, the UE 102 can process the RRC reconfiguration. The UE 102 refrains from applying (i.e., performing) the LTM configuration 1 until receiving a configuration activation command that activates the LTM configuration 1 (e.g., event 330).

[0073] Events 308 (optional) and 310 are collectively referred to as the LTM preparation procedure 390 in FIG. 3 Events 316, 318, 320, 322 are collectively referred to as the LTM configuration delivery procedure 394 in FIG. 3 Events 316, 318, 320, 322 are collectively referred to as the LTM configuration delivery procedure 394 in

[0074] In some implementations, the DU 174 sends a reference LTM configuration to the UE 102 in a procedure similar to procedures 390 and 392 prior to receiving the first CU-to-DU message. In such cases, the DU 174 does not include the reference LTM configuration in the first DU-to-CU message.

[0075] In some implementations, where the CU 172 performs multiple LTM preparation procedures 390, the DU 174 includes the reference LTM configuration in a first DU-to-CU message in a first LTM preparation procedure of the LTM preparation procedures 390. In such cases, the DU 174 can not include the reference LTM configuration in DU-to-CU messages in the remainder of the LTM preparation procedures 390.

[0076] In some implementations, the first CU-to-DU message is a UE Context Modification Request message and the first DU-to-CU message is a UE Context Modification Response message or a UE Context Modification Required message. In the case of a UE Context Modification Required message, the CU 172 can send a UE Context Modification Acknowledge message to the DU 174 in response to the UE Context Modification Required message. In some implementations, the second CU-to-DU message is a DL RRC Message Transfer message. In other implementations, the second CU-to-DU message is a UE Context Modification Request message and the DU 174 can send a second DU-to-CU message (e.g., a UE Context Modification Response message) to the CU 172 in response to the second CU-to-DU message.

[0077] In some implementations, the CU 172 includes the LTM configuration 1 in a first container (e.g., a field / IE) and includes the first container in the RRC reconfiguration messages of events 316 and 318. In such cases, the CU 172 generates the first container. The first container is used to indicate to the UE 102 not to apply the LTM configuration 1 immediately. In some scenarios and implementations, the UE 102 receives an RRC reconfiguration message (e.g., the RRC reconfiguration message of event 318) that includes a configuration (e.g., the LTM configuration 1). If the configuration is included in the first container, the UE 102 refrains from applying the configuration immediately. Otherwise, if the configuration is not included in the first container, the UE 102 can apply the configuration immediately. In some implementations, the first container can be a first add or modify list (e.g., a ltm-ConfigToAddModList field, a LTM-ConfigToAddModList IE, a ltm-CandidateConfigToAddModList field, or a LTM-CandidateConfigToAddModList IE). The CU 172 includes the LTM configuration 1 in a first element (hereinafter referred to as element 1) of the first add or modify list. For example, the element 1 can be an add or modify IE (a ltm-ConfigToAddMod field, a LTM-ConfigToAddMod IE, a ltm-CandidateConfigToAddMod field, or a LTM-CandidateConfigToAddMod IE). When the UE 102 receives the first add or modify list, the UE 102 can store the first add or modify list (e.g., in a variable in a random access memory (RAM)). In other alternative implementations, the DU 174 generates the first container and includes the first container in the first DU to CU message. In yet other alternative implementations, the DU 174 generates the element 1 and includes the element 1 in the first DU to CU message.

[0078] In some implementations, the CU 172 includes a first LTM ID (referred to herein as ID 1) for identifying the LTM configuration 1 or the element 1 in the RRC reconfiguration messages. In some implementations, the CU 172 includes the ID 1 in the first container or the element 1. In some implementations, the CU 172 assigns the ID 1. In other implementations, the CU 172 receives the ID 1 in the first DU to CU message from the DU 174, as described below.

[0079] In the case that CU 172 assigns or generates ID 1, CU 172 can send ID 1 to DU 174, and DU 174 associates ID 1 with LTM configuration 1. In some implementations, in the first CU-to-DU message, CU 172 includes ID 1 and indicates that ID 1 is associated with LTM configuration 1. In other implementations, after receiving the first DU-to-CU message, CU 172 sends 312 a third CU-to-DU message including ID 1 to DU 174, instead of including ID 1 in the first CU-to-DU message. In some implementations, in the third CU-to-DU message, CU 172 can include LTM configuration 1 and ID 1 and indicate the association between ID 1 and LTM configuration 1. Accordingly, DU 174 can directly associate ID 1 with LTM configuration 1. In other implementations, in the third CU-to-DU message, CU 172 can include cell ID 1 and ID 1 (i.e., the first LTM ID) and indicate the association between cell ID 1 and ID 1. Accordingly, DU 174 associates ID 1 with LTM configuration 1 based on the association between cell ID 1 and ID 1 and the association between cell ID 1 and LTM configuration 1. In yet other implementations, in the third CU-to-DU message, CU 172 can include LTM configuration 1, cell ID 1, and ID 1 and indicate the association between ID 1, LTM configuration 1, and cell ID 1. In some implementations, DU 174 can send 314 a third DU-to-CU message to CU 172 in response to the third CU-to-DU message. In some implementations, the third CU-to-DU message and the third DU-to-CU message are a UE context modification request message and a UE context modification response message. Events 312 (optional) and 314 (optional) are collectively referred to as the LTM ID assignment procedure 392 in FIG. 3 In other implementations, CU 172 can include ID 1, cell ID 1, and / or LTM configuration 1 in the second CU-to-DU message, as described above. Accordingly, the third CU-to-DU message can be omitted.

[0080] In the case that CU 172 includes ID 1 in the first CU-to-DU message, DU 174 can include ID 1 in LTM configuration 1, first container, or element 1. Alternatively, DU 174 does not include ID 1 in LTM configuration 1, first container, and / or element 1.

[0081] In some alternative implementations, the DU 174 assigns an ID 1 that identifies the LTM configuration 1. In some implementations, the DU 174 includes the ID 1 in the first DU-to-CU message. The CU 172 can include the ID 1 in the RRC reconfiguration message, as described above. In other implementations, the DU 174 includes the ID 1 in the LTM configuration 1, the first container, or element 1. Thus, the CU 172 does not include an ID that identifies the LTM configuration 1 in the RRC reconfiguration message, the first container, and / or element 1.

[0082] In some implementations, the CU 172 includes the reference LTM configuration in the first container. For example, the CU 172 includes the reference LTM configuration in a different field of the first container than the field of the first container that includes the LTM configuration 1. In other implementations, the CU 172 includes the reference LTM configuration in the RRC reconfiguration message 316 and outside of the first container. For example, the CU 172 generates a third container (e.g., field / IE) to include the first container and the reference LTM configuration, and includes the third container in the RRC reconfiguration message 316. In yet other implementations, the DU 174 includes the reference LTM configuration in the first container. For example, the DU 174 includes the reference LTM configuration in a different field of the first container than the field of the first container that includes the LTM configuration 1. In yet other implementations, the DU 174 generates a fourth container (e.g., field / IE) to include the first container and the reference LTM 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 configuration and the LTM configuration 1 from the fourth container, and includes the reference LTM DU configuration and the LTM DU configuration 1, as described above.

[0083] In some implementations, neither the CU 172 nor the DU 174 assigns an ID for identifying the reference LTM configuration. In such cases, there is no ID for the reference LTM configuration.

[0084] In some implementations, the LTM configuration 1 includes a plurality of configuration parameters for the UE 102 to communicate with the DU 174 on the first cell. In some implementations, the plurality of configuration parameters includes physical layer configuration parameters (e.g., PhysicalCellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE), and / or RLC configuration parameters (e.g., RLC-BearerConfig IE). In some further implementations, the plurality of configuration parameters includes special cell configuration (e.g., SpCellConfig IE) and / or one or more SCell configurations (e.g., SCellConfig IE). In some implementations, the LTM configuration 1 is a CellGroupConfig IE defined in 3GPP specification 38.331. In other implementations, the LTM configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0085] In some implementations, the DU 174 includes the random access configuration in the LTM configuration 1. In other implementations, the DU 174 does not include the random access configuration in the LTM configuration 1. In some implementations, the DU 174 determines to include the random access configuration in the LTM configuration 1 if the cell 124A and the first cell are not synchronized. Otherwise, the DU 174 determines not to include the random access configuration in the LTM configuration 1 if the cell 124A and the first cell are synchronized. In other implementations, the DU 174 determines to include the random access configuration in the LTM configuration 1 if the DU 174 determines that the UE 102 has not synchronized with the first cell in the UL. Otherwise, the DU 174 determines not to include the random access configuration in the LTM configuration 1 if the DU 174 determines that the UE 102 has synchronized with the first cell in the UL. If the LTM configuration 1 includes the random access configuration, the UE 102 performs the random access procedure in event 332 according to the random access configuration, as described below. Otherwise, if the LTM configuration 1 does not include the random access configuration, the UE 102 skips or refrains from performing the random access procedure of event 332 in response to the LTM configuration 1 excluding the random access configuration.

[0086] In some implementations, the DU 174 includes the random access configuration parameters in the LTM configuration 1 and / or the reference LTM configuration regardless of whether the cell 124A and the first cell are synchronized. The UE 102 performs the random access procedure in event 332 according to the random access configuration parameters, as described below.

[0087] In some implementations, if the cell 124A and the first cell are synchronized, the DU 174 determines to include a first indication in the LTM configuration 1 that configures the UE 102 to not perform a random access procedure on the first cell. Otherwise, if the cell 124A and the first cell are not synchronized, the DU 174 determines not to include the first indication in the LTM configuration 1. In other implementations, if the DU 174 determines that the UE 102 has synchronized with the first cell in the UL, the DU 174 determines to include the first indication in the LTM configuration 1. Otherwise, if the DU 174 determines that the UE 102 has not synchronized with the first cell in the UL, the DU 174 determines not to include the first indication in the LTM configuration 1. If the LTM configuration 1 includes the first indication, the UE 102 skips or avoids performing the random access procedure of event 332 according to or in response to the first indication. Otherwise, if the LTM configuration 1 does not include the first indication, the UE 102 performs the random access procedure in event 332 according to the random access configuration in response to the LTM configuration 1 excluding the first indication, as described below.

[0088] In some implementations, the DU 174 includes the reconfiguration with synchronization configuration (e.g., ReconfigurationWithSync IE) in the LTM configuration 1 or the special cell configuration. In other implementations, the DU 174 does not include the reconfiguration with synchronization configuration (e.g., ReconfigurationWithSync IE) in the LTM configuration 1 or the special cell configuration. In some implementations, the DU 174 determines to include the reconfiguration with synchronization configuration in the LTM configuration 1 if the cell 124A and the first cell are not synchronized. Otherwise, the DU 174 determines not to include the reconfiguration with synchronization configuration in the LTM configuration 1 if the cell 124A and the first cell are synchronized. In other implementations, the DU 174 determines to include the reconfiguration with synchronization configuration in the LTM configuration 1 if the DU 174 determines that the UE 102 has not synchronized with the first cell in the UL. Otherwise, the DU 174 determines not to include the reconfiguration with synchronization configuration in the LTM configuration 1 if the DU 174 determines that the UE 102 has synchronized with the first cell in the UL. In some implementations, the UE 102 performs the random access procedure in the event 332 in response to or in accordance with the reconfiguration with synchronization configuration if the LTM configuration 1 includes the reconfiguration with synchronization configuration, as described below. Otherwise, the UE 102 skips or refrains from performing the random access procedure of the event 332 if the LTM configuration 1 does not include the reconfiguration with synchronization configuration. In some implementations, the DU 174 includes the cell ID (i.e., cell ID 1) of the cell 1 (i.e., the first cell) in the LTM configuration 1. In one implementation, the cell ID 1 can be a PCI. In another implementation, the cell ID 1 is a CGI. In some implementations, the cell ID 1 included in the LTM configuration 1 is a PCI, while the cell ID 1 included in the first CU-to-DU message is a CGI. In some further implementations, the LTM 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 occupies less number of bits than the cell ID. In some implementations, the CU 172 sets the cell index 1 to a value and includes the cell index 1 in the first CU-to-DU message of the event 308.

[0089] In some implementations, the base station 104 (i.e., the CU 172 or the DU 174) determines to prepare an additional cell (i.e., cell 2,..., N) of the base station 104 for LTM for the UE 102 after (e.g., in response to) receiving one or some of the at least one measurement report of the event 304. In one implementation, the base station 104 determines to prepare an additional cell for LTM for the UE 102 because the at least one measurement report indicates that the additional cell can be used by the base station 104 to communicate with the UE 102. The additional cell can include the cell 124C and / or a cell other than the cells 124A, 124B, and 124C. In some implementations, the CU 172 determines to prepare a particular cell of the additional cells for LTM for the UE 102 if the L3 measurement report indicates that the signal strength and / or quality of the particular cell is above a respective predetermined threshold and / or better than the cell 124A. In other implementations, the DU 174 determines to prepare a particular cell of the additional cells for LTM for the UE 102 if the LI measurement report indicates that the signal strength and / or quality of the particular cell is above the first predetermined threshold and / or better than the cell 124A. In one implementation, the respective predetermined threshold of the additional cell can be different from the first predetermined threshold. In another implementation, the respective predetermined threshold of the additional cell can be the same as the first predetermined threshold. In some implementations, the respective predetermined thresholds of the additional cells can be the same or different. Alternatively, the base station 104 determines to prepare the additional cell regardless of whether a measurement report is received from the UE 102.

[0090] In the case that the CU 172 determines to prepare the additional cell, the CU 172 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure) with the DU 174 to prepare the additional cell for LTM, where each of the LTM preparation procedures is similar to the procedure 390. In the case that the DU 174 determines to prepare the additional cell, the DU 174 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure) with the CU 172 to prepare the additional cell for LTM, where each of the LTM preparation procedures is similar to the procedure 390.

[0091] In some implementations, the CU 172 and the DU 174 perform LTM preparation procedures 2,..., N similar to the procedure 390 to prepare cells 2,..., N, respectively. The CU 172 can include the cell IDs 2,..., N in the CU-to-DU messages 2,..., N in the LTM preparation procedures 2,..., N, similar to the first CU-to-DU message. In the LTM preparation procedures 2,..., N, the DU 174 generates the LTM configurations 2,..., N configuring the cells 2,..., N, respectively, and includes the LTM configurations 2,..., N in the DU-to-CU messages 2,..., N, respectively, as described for the LTM configuration 1. The DU-to-CU messages 2,..., N are received by the DU 174 in response to the CU-to-DU messages 2,..., N, respectively. “N” is an integer and greater 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. The examples and implementations of the LTM configuration 1 can be applicable to the LTM configurations 2,..., N.

[0092] In other implementations, the CU 172 and the DU 174 perform a single LTM preparation procedure (i.e., the LTM preparation procedure 390) to prepare the cells 1, 2,..., N. In such cases, the DU 174 includes the LTM configurations 1, 2,..., N of the cells 1, 2,..., N in a first DU-to-CU message, respectively. In the first DU-to-CU message, the DU 174 can include the cell IDs 1, 2,..., N associated with the LTM configurations 1, 2,..., N, respectively, to indicate that the LTM configurations 1, 2,..., N are configured for the cell IDs 1, 2,..., N, respectively. In a case where the CU 172 determines to perform the LTM preparation procedure 390, the CU 172 includes the cell IDs 1, 2,..., N in the first CU-to-DU message to request the DU 174 to prepare the cells 1, 2,..., N for the LTM, respectively.

[0093] After receiving the LTM configurations 2,..., N from the DUs 174, the CU 172 can include the LTM configurations 2,..., N in the first container. In some implementations, the CU 172 can include the LTM configurations 2,..., N in elements 2,..., N, respectively, and include the elements 2,..., N in the first container. In some implementations, the CU 172 includes LTM IDs (i.e., IDs 2,..., N) for identifying the LTM configurations 2,..., N, respectively, in the RRC reconfiguration message. In some implementations, the CU 172 includes the IDs 2,..., N in the first container. For example, the CU 172 can include the IDs 2,..., N and the LTM configurations 2,..., N in elements 2,..., N, respectively, in the first add or modify list.

[0094] In some implementations, the CU 172 assigns the IDs 2,..., N for the LTM configurations 2,..., N, respectively. In other implementations, the CU 172 receives the IDs 2,..., N from the DUs 174 in the first DU-to-CU message of the procedure 390. In yet other implementations, the CU 172 receives the IDs 2,..., N from the DUs 174 in the DU-to-CU messages 2,..., N, respectively, of the LTM preparation procedures 2,..., N.

[0095] In some implementations, the CU 172 can perform an LTM ID assignment procedure similar to procedure 392 with the DU 174 for each of the LTM configurations 2,..., N. In other implementations, the CU 172 can include the IDs 2,..., N and the LTM configurations 2,..., N in the third CU-to-DU message and indicate an association between the IDs 2,..., N and the LTM configurations 2,..., N, respectively. Accordingly, the DU 174 can associate the LTM configurations 2,..., N with the IDs 2,..., N, respectively. In yet other implementations, the CU 172 can include the cell IDs 2,..., N and the IDs 2,..., N in the third CU-to-DU message and indicate an association between the cell IDs 2,..., N and the IDs 2,..., N, respectively. Accordingly, the DU 174 can associate the LTM configurations 2,..., N with the IDs 2,..., N, respectively, based on the association between the cell IDs 2,..., N and the IDs 2,..., N, respectively, and the association between the cell IDs 2,..., N and the LTM configurations 2,..., N, respectively. In other implementations, the CU 172 can include the IDs 2,..., N, the cell IDs 2,..., N, and / or the LTM configurations 2,..., N in the second CU-to-DU message, as described above. Accordingly, the third CU-to-DU message can be omitted. In yet other implementations, the CU 172 can include the IDs 2,..., N in the first CU-to-DU message and indicate that the IDs 2,..., N are associated with the cell IDs 2,..., N, respectively. In one implementation, the DU 174 includes the IDs 2,..., N in the LTM configurations 2,..., N. Accordingly, the CU 172 does not include the IDs 2,..., N in the RRC reconfiguration message, the first container, and / or the elements 2,..., N.

[0096] In some alternative implementations, the DU 174 assigns the IDs 2,..., N. In some implementations, the DU 174 includes the IDs 2,..., N in the first DU-to-CU message of procedure 390. In yet other implementations, the DU 174 includes the IDs 2,..., N in the DU-to-CU messages 2,..., N of the LTM preparation procedures 2,..., N. The CU 172 can include the IDs 2,..., N in the RRC reconfiguration message. In other implementations, the DU 174 includes the IDs 2,..., N in the LTM configurations 2,..., N. Accordingly, the CU 172 does not include an ID (e.g., an LTM ID) identifying each of the LTM configurations 2,..., N in the RRC reconfiguration message, the first container, and / or the element 1.

[0097] In some alternative implementations, CU 172 can generate a second container including LTM configurations 2,..., N or elements 2,..., N instead of using the first container. Then, similar to events 316 and 318, CU 172 sends an additional RRC reconfiguration message including the second container to UE 102 via DU 174. In response, similar to events 320 and 322, UE 102 sends an additional RRC reconfiguration complete message to CU 172 via DU 174. In some implementations, the second container can be a second add or modify list (e.g., a ltmtm-ConfigToAddModList field, a LTM-ConfigToAddModList IE, a ltmtm-CandidateConfigToAddModList field, or a LTM-CandidateConfigToAddModList IE), and each of elements 2,..., N can be an add or modify IE (e.g., a ltmtm-ConfigToAddMod field, a LTM-ConfigToAddMod IE, a ltmtm-CandidateConfigToAddMod field, or a LTM-CandidateConfigToAddMod IE). When UE 102 receives the second add or modify list, UE 102 can store the second add or modify list together with the first add or modify list (e.g., in a variable in its random access memory (RAM)).

[0098] In some implementations, DU 174 includes cell IDs 2,..., N in LTM configurations 2,..., N, respectively, to identify cells 2,..., N. In one implementation, each of cell IDs 2,..., N is a PCI. In some further implementations, LTM configurations 2,..., N include cell indices 2,..., N that index cell IDs 2,..., N or cells 2,..., N, respectively. When CU 172 prepares cells 2,..., N for LTM in process 390, CU 172 can set cell indices 2,..., N to different values and include cell indices 2,..., N in the first CU-to-CU-to-DU message of event 308. In case CU 172 prepares cells 2,..., N in an additional LTM preparation process, CU 172 can set cell indices 2,..., N to different values and include cell indices 2,..., N in the CU-to-DU message of the additional LTM preparation process. CU 172 sets cell indices 1,..., N to different values. In some implementations, cell IDs 1,..., N in LTM configurations 1,..., N can be different from cell IDs 1,..., N in the CU-to-DU message described above.

[0099] In some implementations, each of the LTM configurations 1,..., N includes physical configuration parameters, MAC configuration parameters, RLC configuration parameters, and / or L1 measurement configuration. In some implementations, each of the LTM configurations 1,..., N can be a CellGroupConfig IE as defined in 3GPP specification 38.331. In other implementations, each of the LTM configurations 1,..., N includes configuration parameters included in a CellGroupConfig IE as defined in 3GPP specification 38.331. In some further implementations, the multiple configuration parameters in each of the LTM configurations include a particular special cell configuration (e.g., SpCellConfig IE) and / or one or more SCell configurations (e.g., SCellConfig IE). In some implementations, the LTM configurations 1,..., N are CellGroupConfig IEs defined in 3GPP specification 38.331. In other implementations, the LTM configurations 1,..., N include configuration parameters in a CellGroupConfig IE.

[0100] In some implementations, the CU 172 determines to release an LTM configuration M (or element M in elements 1,..., M) in the LTM configurations 1,..., N. 1 ≤ M ≤ N. In response to the determination, the CU 172 sends, to the UE 102 via the DU 174, an RRC reconfiguration message to instruct the UE 102 to release the LTM configuration M or element M. In one implementation, the CU 172 generates a release list including an ID (i.e., LTM ID) M for releasing the LTM 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 configuration M or element M, and sends, to the CU 172 via the DU 174, an RRC reconfiguration complete message. In response to the determination, the CU 172 sends, to the DU 174, a CU-to-DU message to instruct the DU 174 to release the LTM configuration M. To instruct the DU 174 to release the LTM configuration M, the CU 172 can include the cell ID M or the ID (i.e., LTM ID) M in a release indication (e.g., a field or an IE) in the CU-to-DU message. In response, the DU 174 releases the LTM configuration M, and sends, to the CU 172, a DU-to-CU message. In some implementations, the CU-to-DU message and the DU-to-CU message are a UE context modification request message and a UE context modification response message, respectively.

[0101] In other implementations, the DU 174 determines to release the LTM configuration K. In response to the determination, the DU 174 sends a DU-to-CU message to the CU 172 to release the LTM configuration K. To indicate that the LTM configuration K is released, the DU 174 can include the cell ID K or ID (i.e., LTM ID) K in a release indication (e.g., a field or an IE) in the DU-to-CU message. 1 < K < N. Upon receiving the DU-to-CU message (e.g., in response thereto), the CU 172 generates a release list including the ID (i.e., LTM ID) K for releasing the LTM configuration K or element K and sends an RRC reconfiguration message including the release list to the UE 102 via the DU 174. In response, the UE 102 releases the LTM configuration K or element K and sends an RRC reconfiguration complete message to the UE 102 via the DU 174. The CU 172 can send a CU-to-DU message to the DU 174 in response to the DU-to-CU message. In some implementations, the DU-to-CU message and the CU-to-DU message are a UE context modification required message and a UE context modification confirm message, respectively.

[0102] After receiving the RRC reconfiguration in event 318 or sending the RRC reconfiguration complete message in event 320, the UE 102 sends 324 at least one measurement report to the DU 174, similar to event 304. In some implementations, the DU 174 can send 326 a DU-to-CU message including the at least one measurement report to the CU 172, similar to event 306. In other implementations, the DU 174 does not send the at least one measurement report to the CU 172. In some implementations, the at least one measurement report of event 324 includes an L1 measurement report or an L3 measurement report, as described for event 304. In some implementations, the UE 102 sends 324 the at least one measurement report to the DU 174 on a PUCCH and / or a PUSCH, similar to event 304. In other implementations, the UE 102 sends 324 at least one MAC CE including the at least one measurement report to the DU 174, similar to event 304. In some implementations, the UE 102 does not send an L1 measurement report to the DU 174 in a format of an RRC message.

[0103] In some implementations, the UE 102 sends 324 at least one measurement report to the DU 174 according to 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 sends the at least one measurement configuration to the UE 102 via the DU 174. For example, the CU 172 can send one or more RRC messages (e.g., RRCReconfiguration messages) including the at least one measurement configuration to the UE 102 via the DU 174 in event 302 and / or 316 and / or after event 306 or 316. The one or more RRC messages can or can not include the RRC reconfiguration message of event 316. According to the at least one measurement configuration, the UE 102 performs measurements on one or more reference signals. The one or more reference signals can include one or more SSBs and / or one or more CSI-RSs. The UE 102 obtains at least one L1 measurement result and / or at least one L3 measurement result from the measurements and includes the at least one L1 measurement result and / or the at least one L3 measurement result in the at least measurement report of event 324. The DU 174 transmits the one or more reference signals on the cell 124A, cell 1, and / or cell 2, …, N. The one or more reference signals can be CSI-RSs or SSBs.

[0104] In some implementations, the at least one measurement configuration includes an L3 measurement configuration (e.g., MeasConfig IE), as described for event 304. In other implementations, the at least one measurement configuration includes an L1 measurement configuration, as described for event 304. For example, the L1 measurement configuration can be a CSI-MeasConfig IE defined in 3GPP specification 38.331 v18.0.0 and / or later versions. The L1 measurement configuration can include a measurement reporting configuration. The UE 102 sends an L1 measurement report on a PUCCH or a MAC CE to the DU 174 according to the measurement reporting configuration. The DU 174 receives the L1 measurement report on the PUCCH or the MAC CE according to the measurement reporting configuration. In some implementations, the measurement reporting configuration is a CSI-ReportConfig IE. In other implementations, each of the measurement reporting configurations is a RRC IE that is specific to and specially defined for LTM. In some implementations, the measurement reporting configuration(s) configures periodic reporting and / or event-triggered reporting of L1 measurement results.

[0105] In yet other implementations, the at least one measurement configuration includes an “LTM-specific type” measurement configuration (e.g., LTM measurement configuration) defined specifically for LTMs and specific to LTMs. The LTM-specific type measurement configuration can be defined in the relevant 3GPP specification. In some implementations, the LTM-specific type measurement configuration includes a reference signal resource configuration configuring resources in which the DU 174 transmits reference signals. For example, the reference signal resource configuration includes CSI-RS and / or SSB. In one implementation, the reference signal resource configuration is a CSI-ResourceConfig IE. In another implementation, as described above, the LTM-specific type measurement configuration includes a measurement reporting configuration. The UE 102 transmits a measurement report to the DU 174 on a PUCCH or MAC CE according to the measurement reporting configuration. The DU 174 receives the measurement report on the PUCCH or MAC CE according to the measurement reporting configuration. In such cases, the measurement report can be an L1 measurement report or an LTM-specific type measurement report (e.g., LTM measurement report). In some implementations, the LTM-specific type measurement configuration includes configuration parameters specifically defined in the relevant 3GPP specification in connection with LTM procedures.

[0106] After receiving the at least one measurement report in event 324 (e.g., in response thereto), the DU 174 generates a first LTM command to activate LTM configuration 1 (i.e., the first LTM command instructs the UE 102 to apply LTM configuration 1 or perform a serving cell change to cell 1). The DU 174 then transmits 330 the first LTM command to the UE 102. In some implementations, the DU 174 transmits the first LTM command to the UE 102 on cell 124A. In other implementations, the DU 174 transmits the first LTM command to the UE 102 on cell 124D. In some implementations, the DU 174 can include ID 1 in the first LTM command to indicate LTM configuration 1, and the UE 102 determines (e.g., identifies) LTM configuration 1 or element 1 according to ID 1. In other implementations, the DU 174 can include a cell index 1 indexing cell ID 1 in the first LTM command. The UE 102 determines (e.g., identifies) LTM configuration 1 or element 1 based on cell index 1. After determining LTM configuration 1 or element 1, the UE 102 then applies LTM configuration 1 in response to receiving the first LTM command.

[0107] In yet other implementations, the DU 174 can include a bitmap in the first LTM command to activate LTM configuration 1 instead of ID 1 or cell index 1. The number of bits in the bitmap is greater than or equal to “N”. In one implementation, bits 1, …, N correspond to cell indexes 1, …, N, IDs 1, …, N, LTM configurations 1, …, N, or elements 1, …, N, respectively, and the DU 174 sets the corresponding bit (e.g., bit 1) in the bitmap to a first value to indicate cell index 1, ID 1, LTM configuration 1, or element 1. Thus, the UE 102 can determine cell index 1, ID 1, LTM configuration 1, or element 1 from bit 1 in the bitmap that is set to the first value. In another implementation, bits 0, …, N-1 correspond to indexes 1, …, N, IDs 1, …, N, LTM configurations 1, …, N, or elements 1, …, N, respectively, and the DU 174 sets the corresponding bit (e.g., bit 0) in the bitmap to a first value to indicate cell index 1, ID 1, LTM configuration 1, or element 1. Thus, the UE 102 can determine cell index 1, ID 1, LTM configuration 1, or element 1 from bit 0 in the bitmap that is set to the first value. In such implementations, the DU 174 sets the remaining bits in the bitmap to a second value to indicate that the remaining ones of LTM configurations 1, …, N are not activated. In some implementations, the first value is one and the second value is zero. In other implementations, the first value is zero and the second value is one. In general, if the DU 174 determines to activate LTM configuration L or change the serving cell to cell L, the DU 174 can set the corresponding bit (e.g., bit L or bit L-1) in the bitmap to the first value and the remaining bits to the second value, where 1 ≤ L ≤ N. In some implementations, the DU 174 sets at most one bit in the bitmap to the first value.

[0108] In some implementations, the at least one measurement report (e.g., an L1 measurement report or a dedicated type measurement report) of the event 324 includes at least one measurement result of the first cell, a TRP of the first cell, or a reference signal transmitted on the first cell. The reference signal can be a CSI-RS or an SSB. The DU 174 determines to activate the LTM configuration 1 or transmit the first LTM command based on the at least one measurement result. In some implementations, the DU 174 determines to activate the LTM configuration 1 because, when, or if the at least one measurement result is above a second predetermined threshold. In some implementations, the at least one measurement result includes an L1-RSRP value, an L1-RSRQ value, and / or an L1-SINR value. In other implementations, the at least one measurement result includes an RSRP value, an RSRQ value, and / or an SINR value of a dedicated type measurement report. In some implementations, the second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is greater than the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell is suitable for communicating with the UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell has been consistently above the second predetermined threshold or the first predetermined threshold. This indicates that the first cell is suitable for communicating with the UE 102. Thus, in response to the signal strength or quality of the first cell being above the second predetermined threshold of the UE 102, the DU 174 determines to activate the LTM configuration 1.

[0109] In some implementations, the at least one measurement report (e.g., L3 measurement report) of event 324 and 326 includes at least one measurement result of the first cell. CU 172 determines to activate LTM configuration 1 or send the first LTM command because the at least one measurement result indicates that the signal strength or quality of the first cell is above a second predetermined threshold. The second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is greater than the first predetermined threshold. In such an implementation, the at least one measurement report of event 326 indicates that the signal strength or quality of the first cell is suitable for communicating with UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In such an implementation, the at least one measurement report of event 326 indicates that the signal strength or quality of the first cell has been consistently above the second predetermined threshold or the first predetermined threshold. This also indicates that the first cell is suitable for communicating with UE 102. Accordingly, in response to the signal strength or quality of the first cell being above the second predetermined threshold, CU 172 determines to activate LTM configuration 1. In response to the determination, CU 172 sends 328 a fourth CU-to-DU message to DU 174 to activate LTM configuration 1 or trigger a service change to cell 1 for UE 102. In some implementations, CU 172 includes ID 1 in the fourth CU-to-DU message. In other implementations, CU 172 includes cell index 1 in the fourth CU-to-DU message. In response to the fourth CU-to-DU message, DU 174 sends 330 the first LTM command to UE 102 and, optionally, a fourth DU-to-CU message to CU 172. In some implementations, CU 172 includes cell index 1 in the fourth CU-to-DU message. Accordingly, DU 174 can determine to activate LTM configuration 1 according to cell index 1. In other implementations, CU 172 can include cell ID 1 in the fourth CU-to-DU message. Accordingly, DU 174 determines to activate LTM configuration 1 according to cell ID 1. In yet other implementations, CU 172 can include ID 1 in the fourth CU-to-DU message. Accordingly, DU 174 can determine to activate LTM configuration 1 according to ID 1. In some implementations, the fourth CU-to-DU message and the fourth DU-to-CU message are a UE context modification request message and a UE context modification response message, respectively. In other implementations, the fourth CU-to-DU message and / or the fourth DU-to-CU message are dedicated interface messages, e.g., Fl application protocol (FlAP) messages, that are specifically defined in a relevant 3GPP specification, such as TS 38.473, in connection with the LTM procedure.

[0110] When or in response to determining to activate LTM configuration 1 or sending the first LTM command, DU 174 can send 329 a DU-to-CU message to CU 172 indicating that LTM is being performed. In some implementations, DU 174 includes cell ID 1 or ID 1 (i.e., the LTM ID) in the DU-to-CU message 329 to indicate that DU 174 is to activate LTM configuration 1. DU can send the DU-to-CU message 329 to CU 172 before or after sending the LTM command 330.

[0111] In some implementations, the first LTM command is a MAC CE included in a MAC PDU that UE 102 receives from DU 174 in event 330. The MAC CE can be a dedicated MAC CE that is defined specifically for LTM and dedicated for LTM (e.g., in a relevant 3GPP specification such as TS 38.321). In one implementation, DU 174 includes a subheader that identifies the dedicated MAC CE in the MAC PDU, and UE 102 identifies the new MAC CE in the MAC PDU according to the subheader. The subheader includes a logical channel ID or an extended logical channel ID to identify the dedicated MAC CE defined in the 3GPP specification. For example, the logical channel ID or the extended logical channel ID can be defined specifically for these procedures in a relevant 3GPP specification such as TS 38.321. In other implementations, the first LTM command is a DCI that UE 102 receives from DU 174 on PDCCH in event 330. DU 174 generates a CRC for the DCI, scrambles the CRC with the first C-RNTI of UE 102, and sends the DCI and the scrambled CRC on PDCCH in event 330. In one implementation, the format of the DCI can be a DCI format defined in a 3GPP specification (e.g., 38.212) before the LTM feature is introduced. In another implementation, the format of the DCI is a dedicated DCI format defined specifically for LTM in a relevant 3GPP specification such as TS 38.212.

[0112] In some implementations, DU 174 does not perform security protection (e.g., integrity protection and / or ciphering) on the first LTM command. This speeds up the processing of the first LTM command in UE 102 because UE 102 does not perform security checks (e.g., deciphering and / or integrity check) on the first LTM command.

[0113] In some implementations, after receiving the first LTM command, the UE 102 can send 331 an acknowledgement to the DU 174 on the cell 124A or the cell 124D to indicate that the UE 102 received the first LTM command. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. For example, the MAC CE is an existing MAC CE defined in 3GPP specification 38.321 vl7.2.0 and / or later versions. In another example, the MAC CE is an LTM-dedicated MAC CE defined in a related 3GPP specification, such as TS 38.321, specifically for LTM purposes. In yet other implementations, the acknowledgement is a PUCCH transmission.

[0114] In some implementations, the CU 172 sends 316 an RRC reconfiguration message in response to the L3 measurement report 306 for the first cell. To configure the UE 102 to send the L3 measurement report 306, the CU 172 can send a first RRC reconfiguration message including an L3 measurement configuration (e.g., a MeasConfig IE) to the UE 102 prior to the event 306. In some implementations, the DU 174 sends 330 the first LTM command in response to the L1 measurement report 324 for the first cell. To configure the UE 102 to send the L1 or LTM-dedicated type measurement report 324, the CU 172 can send a second RRC reconfiguration message including an L1 or LTM-dedicated type measurement configuration to the UE 102. In some implementations, the first RRC reconfiguration message and the second RRC reconfiguration message can be the same message (i.e., the same instance). In other implementations, the first RRC reconfiguration message and the second RRC reconfiguration message are different messages. In some implementations, the second RRC reconfiguration message is the RRC reconfiguration message of the event 316. In other implementations, the second RRC reconfiguration message is different from the RRC reconfiguration message of the event 316.

[0115] After receiving the first LTM command (e.g., in response thereto), the UE 102 identifies the LTM configuration 1 according to the ID 1 and applies the LTM configuration 1. In some implementations, the UE 102 can perform 332 a random access procedure with the DU 174 on the first cell in response to applying the LTM configuration 1 or receiving the first LTM command. In some implementations, the UE 102 disconnects from the cell 124A after receiving the first LTM command or after sending the acknowledgement (e.g., in response thereto). In other words, the UE 102 stops communicating on the cell 124A after receiving 330 the first LTM command or sending 331 the acknowledgement (e.g., in response thereto). In such cases, the UE 102 performs 332 the random access procedure after disconnecting from the cell 124A. The UE 102 can determine whether to perform the random access procedure according to the LTM configuration 1. In one implementation, the UE 102 performs the random access procedure in event 332 if the LTM configuration 1 configures the UE 102 to perform the random access procedure. For example, the LTM configuration 1 includes a reconfiguration with synchronization configuration (e.g., ReconfigurationWithSync IE) to configure the UE 102 to perform the random access procedure. Otherwise, if the LTM configuration 1 does not configure the UE 102 to perform the random access procedure or does not configure the UE 102 to skip the random access procedure, the UE 102 refrains from performing the random access procedure with the DU 174 upon receiving the first LTM command. In such cases, the UE 102 skips event 316. For example, the LTM configuration 1 configures the UE 102 to not perform the random access procedure if the LTM configuration 1 excludes a reconfiguration with synchronization configuration. In some implementations, the random access procedure is a four-step random access procedure. In other implementations, the random access procedure is a two-step random access procedure. In some implementations, the random access procedure is a contention-free random access procedure. In other implementations, the random access procedure is a contention-based random access procedure.

[0116] In cases where the UE 102 performs 332 the random access procedure, the UE 102 communicates 336 with the DU 174 on the first cell using the LTM configuration 1 and / or the reference LTM configuration, and communicates with the CU 172 via the DU 174 after successfully completing the random access procedure. In such cases, the DU 174 communicates with the UE 102 on the first cell using the LTM configuration 1 in event 332 and / or event 336. In some scenarios or implementations, the UE 102 communicates UL PDUs, DL PDUs, and / or physical layer signals (e.g., PUCCH transmissions and PDCCH transmissions) with the base station 104 in event 336. In some implementations, the UE 102 determines that the UE 102 successfully completes the random access procedure when the UE 102 receives a contention resolution from the DU 174. In cases where the random access procedure is a four-step random access procedure, the UE 102 transmits a message 3 including a UE identity to the DU 174 via the first cell in the random access procedure. In cases where the random access procedure is a two-step random access procedure, the UE 102 transmits a message A including a UE identity to the DU 174 via the first cell in the random access procedure. In some implementations, the UE identity is a second C-RNTI of the UE 102 if the LTM configuration 1 includes the second C-RNTI. Otherwise, the UE identity is a first C-RNTI if the LTM configuration 1 does not include the C-RNTI. In cases where the random access procedure is a contention-free random access procedure, the UE 102 transmits a dedicated random access preamble to the DU 174 via the first cell. In such cases, the LTM configuration 1 includes the dedicated random access preamble.

[0117] The DU 174 identifies or determines that the UE 102 is connected to the first cell when the DU 174 receives the UE identity or the dedicated preamble from the UE 102 in the random access procedure 332.

[0118] In the case that the UE 102 skips the random access procedure, the UE 102, after (e.g., in response to) receiving the first LTM command, communicates 336 directly with the DU 174 on the first cell according to the LTM configuration 1 and communicates with the CU 172 via the DU 174. For example, the UE 102 communicates UL PDUs, DL PDUs, and / or physical layer signals (e.g., PUCCH transmissions and PDCCH transmissions) directly with the base station 104 in event 336. In some implementations, the DU 174 can include a configuration parameter in the LTM configuration 1 that configures a resource for the UE 102 to transmit at least one PUCCH or PUSCH transmission, and the UE 102 transmits the at least one PUCCH or PUSCH transmission on the resource using the configuration parameter to indicate that the UE 102 is connected to the first cell. In other implementations, the DU 174 can transmit at least one DCI to the UE 102 on a PDCCH on the first cell to command the UE 102 to transmit at least one PUCCH or PUSCH transmission after transmitting the first LTM command. The at least one DCI configures a resource for the UE 102 to transmit the at least one PUCCH or PUSCH transmission, and the UE 102 transmits the at least one PUCCH or PUSCH transmission on the resource. The DU 174 identifies or determines that the UE 102 is connected to the first cell upon receiving the PUCCH or PUSCH transmission. The DU 174 identifies or determines that the UE 102 is connected to the first cell when the PUCCH or PUSCH transmission is received on the resource configured in the LTM configuration 1 or the at least one DCI.

[0119] In the case that the UE 102 receives the reference LTM configuration as described above, the UE 102 communicates 336 with the DU 174 on the first cell according to at least a portion of the LTM configuration 1 and the reference LTM configuration. In other words, the UE 102 communicates 336 with the DU 174 according to configuration parameters in the LTM configuration 1 and the reference LTM configuration. Similarly, the DU 174 communicates 336 with the UE 102 on the first cell according to at least a portion of the LTM configuration 1 and the reference LTM configuration. In other words, the DU 174 communicates 336 with the UE 102 according to configuration parameters in the LTM configuration 1 and the reference LTM configuration.

[0120] In some implementations, the UE 102 sends, via the DU 174 and the first cell, an RRC message (e.g., an RRC reconfiguration complete message) to the CU 172 to indicate that the UE 102 applies the LTM configuration 1. In case the UE 102 performs the random access procedure 332, the UE 102 can include the RRC message in the message 3 or the message A. Alternatively, the UE 102 sends the RRC message after completing the random access procedure. In case the UE 102 skips the random access procedure 332, the UE 102 includes the RRC message in the PUSCH transmission in the at least one PUSCH transmission. In some implementations, if the UE 102 maintains the communication with the base station 104 on the cell 124A (i.e., the UE 102 does not disconnect from the cell 124A), the UE 102 can send the RRC message to the base station 104 via the cell 124A. When the DU 174 receives the RRC message, the DU 174 sends the RRC message to the CU 172.

[0121] In other implementations, the UE 102 refrains from sending the RRC message to the base station 104 in response to applying the LTM configuration 1 or receiving the first LTM command. In such cases, the UE 102 can include or send data in the message 3, the message A, or the PUSCH transmission as described above. The UE 102 can generate a MAC PDU and / or a RLC PDU including the data and send or include the MAC PDU and / or the RLC PDU in the PUSCH transmission. For example, the data can be a PDCP PDU, a SDAP PDU, a LTE Positioning Protocol (LPP) PDU, an RRC PDU, and / or a NAS PDU. The RRC PDU includes an UL-DCCH-Message excluding the RRC reconfiguration complete message. The NAS PDU includes a mobility management (MM) message or a session management (SM) message. The MM message can be a 5G MM message or a 6G MM message, and the SM message can be a 5G SM message or a 6G SM message. When the DU 174 receives the data, the DU 174 sends the data to the CU 172.

[0122] When the DU 174 determines in event 332 or 336 that the UE 102 successfully connected to the first cell, the DU 174 can send 334 a DU-to-CU message (e.g., an access success message) to the CU 172 (e.g., a CP of the CU 172). In some implementations, the DU 174 can include the cell ID 1 of the first cell in the DU-to-CU message of event 334. The cell ID can be a PCI or a CGI. Thus, the CU 172 determines that the UE 102 connected to the first cell upon receiving the DU-to-CU message of event 334. When the DU 174 determines in event 332 or 336 that the UE 102 successfully connected to the first cell, the DU 174 can send a DL data delivery status message or frame to the CU 172 (e.g., a UP of the CU 172).

[0123] In some implementations, when the UE 102 is determined to be connected to the first cell, the first LTM command is sent 330, or the acknowledgement is received 331, the DU 174 can stop communicating with the UE 102 on the cell 124A and / or release resources of the cell 124A configured for the UE 102.

[0124] In some implementations, the DU 174 can generate some or all of the LTM configuration 1 and / or LTM configuration 2,..., N as a complete configuration for replacing the serving DU configuration. If the LTM configuration 1 is a complete configuration, the UE 102 and the DU 174 communicate with each other 336 according to the LTM configuration 1 instead of the serving DU configuration. In some implementations, the DU 174 includes an indication in the LTM configuration 1 that the LTM configuration 1 is a complete configuration. In each of the LTM configuration 2,..., N, the DU 174 can include an indication for indicating that the corresponding DU configuration is a complete configuration. Each of the indications in the LTM configuration 1,..., N can be a field or an IE (i.e., the same field or IE). In other implementations, the CU 172 can include a single indication in the RRC reconfiguration message of the events 316, 318 that the LTM configuration 1 and / or 2,..., N is a complete configuration. In the case of the second container, the CU 172 can include a single indication in the additional RRC reconfiguration message that the LTM configuration 2,..., N is a complete configuration. In yet other implementations, the CU 172 can include a single indication in the first container that the LTM configuration 1 and / or 2,..., N is a complete configuration. In yet other implementations, the CU 172 can include a specific indication in the first container for each of the LTM configuration 2,..., N that the corresponding LTM configuration is a complete configuration. In the case of the second container, the CU 172 can include a single indication in the second container that the LTM configuration 2,..., N is a complete configuration. In yet other implementations, the CU 172 can include an indication in element 1 that the LTM configuration 1 is a complete configuration. In each of the element 2,..., N, the CU 172 can include an indication that the corresponding LTM configuration is a complete configuration. Based on the above indications, the UE 102 can determine that the LTM configuration 1 and / or the LTM configuration 2,..., N is a complete configuration. In some implementations, each of the above indications is different from the fullConfig field defined in the current 3GPP specification. In some implementations, each of the above indications is the fullConfig field defined in the current 3GPP specification. In the case that the LTM configuration 1 is a complete configuration, the UE 102 in the event 336 does not apply the reference LTM configuration if received from the base station 104, for example, in the RRC reconfiguration message 318. In such a case, the DU 174 can not include the reference LTM configuration in the first DU to CU message 310.

[0125] In other implementations, the DU 174 can generate the LTM configuration 1 and / or the LTM configuration 2,..., N as a delta configuration that enhances (part of) a reference LTM configuration. In other words, the DU 174 generates the LTM configuration 1,..., N based on a reference LTM configuration. For example, if the LTM configuration 1 is a delta configuration, the UE 102 and the DU 174 utilize the LTM configuration 1 to enhance (part of) a reference LTM configuration. Accordingly, the UE 102 and the DU 174 communicate 336 with each other according to the LTM configuration 1 and an unenhanced portion of the reference LTM configuration. In some implementations, the LTM configuration 1 and / or 2,..., N, the first container, the second container, or the element 1,..., N excludes an indication that the LTM configuration 1 and / or 2,..., N is a complete configuration to indicate that the LTM configuration 1 and / or 2,..., N is a delta configuration. The UE 102 can determine that each of the LTM configuration 1 and / or 2,..., N is a delta configuration based on the indication being excluded in the LTM configuration 1 and / or 2,..., N, the first container, the second container, or the element 1 and / or 2,..., N.

[0126] In some implementations, if the UE 102 does not receive a reference LTM configuration for the LTM configuration 1 and / or the LTM configuration 2,..., N, the UE 102 determines that the LTM configuration 1 and / or the LTM configuration 2,..., N is a complete configuration. Correspondingly, if the DU 174 does not obtain a reference LTM configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM configuration for the UE 102 and / or receive a reference LTM configuration for the UE 102 from the CU 172), the DU 174 generates the LTM configuration 1 and / or the LTM configuration 2,..., N as a complete configuration.

[0127] In other implementations, if the UE 102 does not receive a reference LTM configuration for the LTM configuration 1 and / or the LTM configuration 2,..., N, the UE 102 determines that the LTM configuration 1 and / or the LTM configuration 2,..., N is a delta configuration to enhance a serving DU configuration. In such cases, the UE 102 communicates 336 with the DU 174 according to the LTM configuration 1 and at least a portion of the serving DU configuration that is not enhanced by the LTM configuration 1. Correspondingly, if the DU 174 does not obtain a reference LTM configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM configuration for the UE 102 and / or receive a reference LTM configuration for the UE 102 from the CU 172), the DU 174 generates the LTM configuration 1 and / or the LTM configuration 2,..., N as a delta configuration to enhance a serving DU configuration. In such cases, the DU 174 communicates 336 with the UE 102 according to the LTM configuration 1 and at least a portion of the serving DU configuration.

[0128] In some implementations, the UE 102 uses a UE MAC entity (e.g., MAC 204B) to communicate with a DU MAC entity (e.g., MAC 204B) of the DU 174 (e.g., events 302, 304, 318, 320, 324, 330, and / or 331). In some implementations, the UE 102 resets the UE MAC entity after or in response to receiving the first LTM command and before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In some implementations, the DU 174 resets the DU MAC entity after (e.g., in response to) sending the first LTM command, receiving the acknowledgement 331, or determining that the UE 102 is connected to the first cell.

[0129] In some implementations, when the UE 102 resets the UE MAC entity, the UE 102 performs at least one of the following actions on the UE MAC entity (i.e., UE MAC reset or full UE MAC reset):

[0130] • initializes Bj for configured logical channels to zero;

[0131] • stops one or more timers;

[0132] • considers the timeAlignmentTimer to be expired if the UE 102 is configured to perform a random access procedure (e.g., event 332) in a configuration (e.g., configuration 1);

[0133] • sets a new data indicator (NDI) for UL HARQ processes to a value of 0;

[0134] • sets the NDI for HARQ process IDs to a value of 0 to monitor PDCCH in Sidelink Resource Allocation Mode 1;

[0135] • flushes a Msg3 buffer;

[0136] • flushes a MSGA buffer;

[0137] • cancels (if any) triggered scheduling request procedures;

[0138] • cancels (if any) triggered buffer status reporting procedures;

[0139] • cancels (if any) triggered power headroom reporting procedures;

[0140] • cancels (if any) triggered consistent LBT failures;

[0141] • cancel (if any) triggered BFR;

[0142] • cancel (if any) triggered sidelink buffer status reporting procedure;

[0143] • cancel (if any) triggered pre-emptive buffer status reporting procedure;

[0144] • cancel (if any) triggered timing advance reporting procedure;

[0145] • cancel (if any) triggered recommended bit rate query procedure;

[0146] • cancel (if any) triggered configured uplink grant confirmation;

[0147] • cancel (if any) triggered configured sidelink grant confirmation;

[0148] • cancel (if any) triggered expected guard symbol query;

[0149] • cancel (if any) triggered positioning measurement gap activation / deactivation request procedure;

[0150] • flush the soft buffer for DL HARQ processes;

[0151] • for each of the DL HARQ processes, consider the next received transmission for a TB as the first transmission;

[0152] • release (if any) temporary C-RNTI;

[0153] • reset one or more counters (e.g., BFI_COUNTER and / or LBT_COUNTER).

[0154] In some implementations, when the DU 174 resets the DU MAC entity, the DU 174 performs at least one of the following actions on the DU MAC entity (i.e., DU MAC reset or full DU MAC reset):

[0155] • stop one or more timers;

[0156] • consider the timeAlignmentTimer that the DU 174 started and / or maintained for the UE 102 as expired if the UE 102 is configured to perform a random access procedure (e.g., event 332) in a configuration (e.g., configuration 1);

[0157] • set the NDI for DL HARQ processes to value 0;

[0158] • flush the soft buffer for the UL HARQ process;

[0159] • for each of the UL HARQ processes, consider the next received transmission for the TB as the first transmission;

[0160] • reset one or more counters (e.g., BFI_COUNTER and / or LBT_COUNTER)

[0161] Depending on the implementation, the UE 102 can determine to partially or fully reset the UE MAC entity. In some implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 fully resets the UE MAC entity (i.e., full UE MAC reset). In the full UE MAC reset, the UE 102 performs some or all of the above-described actions. In other implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 partially resets the UE MAC entity (i.e., partial UE MAC reset). In the partial UE MAC reset, the UE 102 performs a subset or portion of some or all of the actions in the full UE MAC reset.

[0162] In some implementations, the partial UE MAC reset includes at least one of the following actions:

[0163] • consider the UE 102's timeAlignmentTimer as expired if the UE 102 is configured to perform a random access procedure (e.g., event 332) in a configuration (e.g., configuration 1);

[0164] • flush the Msg3 buffer;

[0165] • flush the MSGA buffer;

[0166] • release (if any) the temporary C-RNTI;

[0167] • reset one or more counters (e.g., BFI_COUNTER and / or LBT_COUNTER).

[0168] In some implementations, the partial UE MAC reset further includes at least one of the following actions:

[0169] • cancel (if any) the triggered scheduling request procedure;

[0170] • cancel (if any) the triggered buffer status reporting procedure;

[0171] • cancel, if any, triggered power headroom reporting procedure;

[0172] • cancel, if any, triggered consistent LBT failure;

[0173] • cancel, if any, triggered BFR;

[0174] • cancel, if any, triggered sidelink buffer status reporting procedure;

[0175] • cancel, if any, triggered pre-empted buffer status reporting procedure;

[0176] • cancel, if any, triggered timing advance reporting procedure;

[0177] • cancel, if any, triggered recommended bit rate query procedure;

[0178] • cancel, if any, triggered configured uplink grant confirmation;

[0179] • cancel, if any, triggered configured sidelink grant confirmation;

[0180] • cancel, if any, triggered expected guard symbol query;

[0181] • cancel, if any, triggered positioning measurement gap activation / deactivation request procedure;

[0182] In some implementations, the partial UE MAC reset further comprises at least one of the following actions:

[0183] • stop a first part of one or more timers and preserve a remaining part of the one or more timers;

[0184] • set a new data indicator (NDI) for a UL HARQ process to a value 0;

[0185] • set a NDI for a HARQ process ID to a value 0 to monitor PDCCH in a sidelink resource allocation mode 1;

[0186] • flush a soft buffer for a DL HARQ process;

[0187] • for each of the DL HARQ processes, consider a next received transmission for a TB as a first transmission;

[0188] Depending on the implementation, the DU 174 can determine to partially or fully reset the DU MAC entity. In some implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 fully resets the DU MAC entity (i.e., full DU MAC reset). In the full DU MAC reset, the DU 174 performs some or all of the actions described above. In other implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 partially resets the DU MAC entity (i.e., partial DU MAC reset). In the partial DU MAC reset, the DU 174 performs a subset or portion of some or all of the actions in the full DU MAC reset.

[0189] In some implementations, the partial DU MAC reset includes at least one of the following actions in the partial MAC reset:

[0190] • considers the timeAlignmentTimer that the DU 174 started and / or maintained for the UE 102 as expired if the UE 102 is configured to perform a random access procedure (e.g., event 332) in the configuration (e.g., configuration 1);

[0191] • resets one or more counters (e.g., BFI_COUNTER and / or LBT_COUNTER)

[0192] In some implementations, when the partial DU MAC reset includes at least one of the following actions for the MAC entity (i.e., DU MAC reset):

[0193] • stops a first portion of one or more timers and preserves a remaining portion of the one or more timers;

[0194] • sets the NDI for a DL HARQ process to a value of 0;

[0195] • flushes a soft buffer for an UL HARQ process;

[0196] • for each of the UL HARQ processes, considers a next received transmission for a TB as a first transmission;

[0197] • resets one or more counters (e.g., BFI_COUNTER and / or LBT_COUNTER)

[0198] In other implementations, the UE 102 refrains from resetting the UE MAC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from resetting the DU MAC entity after (e.g., in response to) sending the first LTM command, receiving the acknowledgement 331, or determining that the UE 102 is connected to the first cell. In other words, the UE 102 uses the UE MAC entity (unreset) to communicate with the DU 174 on the first cell. Similarly, the DU 174 uses the DU MAC entity (unreset) to communicate with the UE 102 on the first cell during or after the random access procedure 332 or after determining that the UE 102 is connected to the first cell.

[0199] In some implementations, the UE 102 uses at least one UE RLC entity (e.g., RLC 206B) to communicate RLC PDUs to at least one DU RLC entity (e.g., RLC 206B) of the DU 174 (e.g., events 302, 304, 318, 320, 324, 330, and / or 331). In some implementations, the UE 102 reestablishes some or all of the at least one UE RLC entity after or in response to receiving the first LTM command and before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In some implementations, the DU 174 reestablishes some or all of the at least one DU RLC entity after (e.g., in response to) sending the first LTM command, receiving the acknowledgement 331, or determining that the UE 102 is connected to the first cell.

[0200] In some implementations, the LTM configuration 1 can or can not include one or more RLC reestablishment indications (e.g., reestablishRLC field) that configure the UE 102 to reestablish some or all of the at least one UE RLC entity. If the LTM configuration 1 includes an RLC reestablishment indication that configures 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 PDUs 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 implementations, the UE 102 can reestablish the first UE RLC entity before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In other implementations, the UE 102 can reestablish the first UE RLC entity while or after performing 332 the random access procedure. Otherwise, if the LTM configuration 1 does not include an RLC reestablishment indication, the UE 102 refrains from reestablishing the first UE RLC entity in response to the first LTM command.

[0201] In some implementations, when the UE 102 reestablishes the first UE RLC entity, the UE 102 performs at least one of the following actions for the first UE RLC entity:

[0202] • discards the RLC SDU, RLC SDU segments, and RLC PDUs, if any;

[0203] • stops and resets timers, if running;

[0204] • resets state variables to initial values.

[0205] In some implementations, the state variables and timers are defined in 3GPP specification 38.322.

[0206] Otherwise, if the LTM 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 to reestablish the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. In some implementations, if the LTM configuration 1 or element 1 does not include the RLC reestablishment indication and includes an indication that the configuration 1 is a full configuration, the UE 102 can reestablish the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. Otherwise, if the LTM configuration 1 or element 1 does not include the RLC reestablishment indication and the indication 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.

[0207] Similarly, the DU 174 reestablishes some or all of the 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., events 302, 304, 318, 320, 324, 330, and / or 331) in response to the RLC reestablishment indication. In some implementations, the DU 174 reestablishes a first DU RLC entity of the at least one DU RLC entity after sending the first LTM command, receiving an acknowledgement of the first LTM command from the UE 102, or determining that the UE 102 is connected to the first cell. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. In yet other implementations, the acknowledgement is a PUCCH transmission. In some implementations, when the base station 104 reestablishes the first DU RLC entity, the DU 174 performs at least one of the following actions for the first DU RLC entity:

[0208] • discard the RLC SDU, RLC SDU segments, and RLC PDU, if any;

[0209] • stop and reset the timer, if running;

[0210] • reset the status variables to the initial values.

[0211] In some implementations, the status variables and timers are defined in 3GPP specification 38.322.

[0212] In other implementations, the UE 102 refrains from reestablishing some or all of the at least one UE RLC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from reestablishing some or more of the at least one DU RLC entity after (e.g., in response to) sending the first LTM command, receiving the acknowledgement 331, or determining that the UE 102 is connected to the first cell. In other words, the UE 102 uses some or all of the at least one UE RLC entity (not reestablished) to communicate with the DU 174 on the first cell. For example, the some or all of the at least one UE RLC entity includes the first UE RLC entity and / or the second UE RLC entity. Similarly, the DU 174 uses some or all of the at least one DU RLC entity (not reestablished) to communicate with the UE 102 on the first cell during or after the random access procedure 332 or after determining that the UE 102 is connected 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 the second DU RLC entity.

[0213] In some implementations, the UE 102 uses the at least one UE PDCP entity (e.g., PDCP 210) to communicate UL PDCP PDUs and / or DL PDCP PDUs to at least one CU PDCP entity (e.g., PDCP 210) of the CU 172 in event 302. In some implementations, the UE 102 performs a PDCP recovery procedure for some or all of the at least one UE PDCP entity after or in response to receiving the first LTM command. For example, the UE 102 performs a PDCP recovery procedure for a first UE PDCP entity of the at least one UE PDCP entity after or in response to receiving the first LTM command. In the PDCP recovery procedure, the UE 102 can or can not reestablish the first UE PDCP entity. After or in response to performing the PDCP recovery procedure, the UE 102 can resend at least a portion of the UL PDCP PDUs to the CU 172 via the DU 174 and the first cell in 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 sending the first LTM command. For example, the CU 172 performs a PDCP recovery procedure for a first CU PDCP entity of the at least one CU PDCP entity after or in response to sending the first LTM command. In some implementations, 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 implementations, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DL data delivery status message. In the PDCP recovery procedure, the CU 172 can or can not reestablish the first CU PDCP entity. After or in response to performing the PDCP recovery procedure, the CU 172 can resend at least a portion of the DL PDCP PDUs to the UE 102 via the DU 174 and the first cell in event 336.

[0214] In other implementations, the UE 102 refrains from reestablishing some or all of the at least one UE PDCP entity in response to receiving the first LTM command. For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and / or the 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 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 the second UE PDCP entity. Similarly, the CU 172 communicates with the UE 102 via the DU 174 and the first cell using some or all of the at least one CU PDCP entity (not reestablished). For example, the some or all of the at least one CU PDCP entity includes the first CU PDCP entity and / or the second CU PDCP entity.

[0215] In some implementations, after determining that the UE 102 is connected to the first cell, the CU 172 can send 338 a CU-to-DU message (e.g., a UE context modification request message) to the DU 174 to instruct 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 can stop communicating with the UE 102 on the cell 124A and / or release or suspend resources of the cell 124A configured for the UE 102 and send 340 a DU-to-CU message (e.g., a UE context modification response message) to the CU 172. The events 338 (optional) and 340 (optional) are collectively referred to as a resource release procedure 396 in FIG. 3 .

[0216] After or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351, 352, 354, and / or 356 can occur that are similar to events 324, 326, 328, 330, 331, 332, 334, and / or 336, respectively. The UE 102 sends 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., Cell 2). The at least one measurement result indicates that the second cell is suitable for communication with the UE 102 and / or that 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 LTM configuration 2 and generates a second LTM command to activate LTM configuration 2 (i.e., the second LTM command instructs the UE 102 to apply LTM configuration 2). The DU 174 then sends 350 the second LTM command for the UE to the UE 102 on the first cell.

[0217] When or in response to determining to activate LTM configuration 2 or sending the second LTM command, the DU 174 can send 349 a DU-to-CU message to the CU 172 indicating that LTM is being performed. In some implementations, the DU 174 includes cell ID 2 or ID 2 (i.e., LTM ID) in the DU-to-CU message 349 to indicate that the DU 174 will activate LTM configuration 2. The DU can send the DU-to-CU message 349 to the CU 172 before or after sending the LTM command 350.

[0218] The description for events 324, 326, 328, 330, 331, 332, 334, and / or 336 can be applied to 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,” and / or “LTM configuration 1” are replaced with “first cell,” “second LTM command,” “second cell,” “ID 2,” and / or “LTM configuration 2,” respectively.

[0219] Events 344, 346, 348, 350, 351, 352, 354 are collectively referred to as an LTM execution procedure 398 in FIG. 3 Events 304, 306, 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, 356 are collectively referred to as an LTM configuration and / or activation procedure 380 in FIG. 3 Events 304, 306, 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, 356 are collectively referred to as an LTM configuration and / or activation procedure 380 in

[0220] Next reference is made to FIG. 4In the scenario 400, the base station 104 includes the 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 cells, while the T-DU 174B operates a first cell (e.g., the cell 124C). The scenario 400 is similar to the scenario 300. Thus, the description for the scenario 300 can generally apply to the scenario 400. Differences between the scenarios 300 and 400 are described below.

[0221] Initially, the UE 102 communicates 402 with the S-DU 174A on the cell 124A using the serving DU configuration and communicates with the CU 172 via the S-DU 174A. During the communication 402, the UE 102 sends 404, 406 at least one measurement report (e.g., L3 measurement report) to the CU 172 via the S-DU 174A. Based on the at least one measurement report, the CU 172 determines to prepare cells 1,..., N (operated by the T-DU 174B) for LTM for the UE 102, where N is a positive integer greater than 0 or 1. The cells 1,..., N are respectively identified by cell IDs 1,..., N. 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 the cells 1,..., N for LTM for the UE 102. N can be a positive integer greater than zero or 1. In the LTM preparation procedure 490, similar to the event 308, the CU 172 sends a CU-to-DU message including the cell IDs 1,..., N to the T-DU 174B to request the T-DU 174B to prepare the cells 1,..., N for LTM for the UE 102. In response, similar to the event 310, the T-DU 174B sends a DU-to-CU message including LTM configurations 1,..., N to the CU 172. The LTM configurations 1,..., N respectively configure the cells 1,..., N for LTM. In detail, the LTM configurations 1,..., N respectively include configuration parameters for communication on the cells 1,..., N. In some implementations, the CU-to-DU message and the DU-to-CU message in the procedure 490 are respectively a UE Context Setup Request message and a UE Context Setup Response message. Similar to the LTM configuration delivery procedure 394, the CU 172 then sends the LTM configurations 1,..., N in an RRC reconfiguration message in an LTM configuration delivery procedure 494. In some implementations, the T-DU 174B can include cell indices 1,..., N respectively in the LTM configurations 1,..., N. In some implementations, the CU 172 can set the cell indices 1,..., N to different values and include the cell indices 1,..., N in the CU-to-DU message of the procedure 490.

[0222] After performing the LTM preparation procedure 490, the CU 172 can perform an additional LTM preparation procedure with the T-DU 174B to prepare cells N+1,..., N+M for LTM for the UE 102. M is a positive integer greater than zero. Similar to events 404, 406, the CU 172 can determine to do so based on one or more measurement reports received from the UE 102 via the S-DU 174A. In the additional LTM preparation procedure, the CU 172 sends a CU-to-DU message including cell IDs N+1,..., N+M to the T-DU 174B to request the T-DU 174B to prepare cells N+1,..., N+M for LTM for the UE 102. The cell IDs N+1,..., N+M identify the cell IDs N+1,..., N+M, respectively. In response to the CU-to-DU message, the T-DU 174B sends a DU-to-DU message including LTM configurations N+1,..., N+M to the CU 172. The LTM configurations N+1,..., N+M configure the cells N+1,..., N+M, respectively, for LTM. In detail, the LTM configurations N+1,..., N+M include configuration parameters for communications on the cells N+1,..., N+M, respectively. Similar to the LTM configuration delivery procedure 394 or 494, the CU 172 then sends the LTM configurations N+1,..., N+M in RRC reconfiguration messages in an additional LTM configuration delivery procedure.

[0223] In some implementations, the LTM preparation procedure 490 is a UE context setup procedure, and the additional LTM preparation procedure is a UE context modification procedure.

[0224] In some implementations, the CU 172 and the S-DU 174A can perform the procedure 380 with the UE 102, as described for FIG. 3 the procedure 380. In the procedure 380, the CU 172 and the S-DU 174A perform the procedures 390 and / or 392 to prepare a cell of the S-DU 174A for LTM for the UE 102. Note that the value N in the procedure 380 or described for FIG. 3 may be the same as the value N described for FIG. 4The described value N is the same or different. In procedure 390, CU 172 can receive a first DU-to-CU message including the reference LTM configuration from S-DU 174A in event 310. In other implementations, CU 172 and S-DU 174A do not perform procedure 380 with UE 102. In such cases, CU 172 can perform 488 a reference LTM configuration query procedure with S-DU 174A to obtain the reference LTM configuration. In procedure 488, CU 172 sends 460 a CU-to-DU message to S-DU 174A to request or query the reference LTM configuration. In some implementations, CU 172 can include an indication in the CU-to-DU message to request or query the reference LTM configuration. In response to the indication or CU-to-DU message 460, S-DU 174A sends 462 a DU-to-CU message including the reference LTM configuration to CU 172. In some implementations, the indication is a reference LTM configuration query indication. In other implementations, the indication is an LTM indication, and CU 172 can include a query indication (e.g., a GNB-DU configuration query IE) in the CU-to-DU message. After receiving the reference LTM configuration (i.e., in procedure 390 or in procedure 488), CU 172 includes the reference LTM configuration (received from S-DU 174A) in a CU-to-DU message in LTM preparation procedure 490. T-DU 174B generates LTM configurations 1,..., N based on the reference LTM configuration received from CU 172. In such cases, T-DU 174B does not include the reference LTM configuration in a DU-to-CU message in procedure 490. In the case of additional LTM preparation procedures, T-DU 174B does not include the reference LTM configuration in a DU-to-CU message in the additional LTM preparation procedures. CU 172 can not include the reference LTM configuration in a CU-to-DU message in the additional LTM preparation procedures with T-DU 174B. In the case of additional LTM preparation procedures, T-DU 174B generates LTM configurations N+1,..., N+M based on the reference LTM configuration received from CU 172.

[0225] In some implementations, the CU 172 does not provide the reference LTM configuration to the T-DU 174B in the LTM preparation procedure 490. In such cases, the T-DU 174B generates the reference LTM configuration and generates the LTM configurations 1,..., N based on the reference LTM configuration. In such cases, the T-DU 174B includes the reference LTM configuration in the DU to CU message in the procedure 490. The CU 172 sends the reference LTM configuration in the RRC reconfiguration message in the procedure 490. In the case of additional LTM preparation procedures, the T-DU 174B generates the LTM configurations N+1,..., N+M based on the reference LTM configuration. In this case, the T-DU 174B can not include the reference LTM configuration in the DU to CU message in the additional LTM preparation procedures. In some implementations, the reference LTM configuration generated by the T-DU 174B is different from the reference LTM configuration generated by the S-DU 174A. In other implementations, the reference LTM configuration generated by the T-DU 174B is the same as the reference LTM configuration generated by the S-DU 174A.

[0226] In some implementations, the CU 172 assigns IDs 1,..., N that respectively identify the LTM configurations 1,..., N (received from the T-DU 174B) and performs a procedure 492 with the T-DU 174B similar to the procedure 392 to provide the IDs 1,..., N and / or the cell IDs 1,..., N to the T-DU 174B. Accordingly, the T-DU 174B associates the IDs 1,..., N with the LTM configurations 1,..., N and / or the cell IDs 1,..., N, respectively. In other implementations, the T-DU 174B assigns IDs 1,..., N that respectively identify the LTM configurations 1,..., N (generated by the T-DU 174B) and includes the IDs 1,..., N in the DU to CU message of the procedure 490 similar to the event 310. In some implementations, the CU 172 assigns IDs N+1,..., N+M that respectively identify the LTM configurations N+1,..., N+M and performs a procedure (similar to the procedure 492) with the T-DU 174B to provide the IDs N+1,..., N+M and / or the cell IDs N+1,..., N+M to the T-DU 174B similar to the procedure 392. Accordingly, the T-DU 174B associates the IDs N+1,..., N+M with the LTM configurations N+1,..., N+M and / or the cell IDs N+1,..., N+M, respectively. In other implementations, the T-DU 174B assigns IDs N+1,..., N+M that respectively identify the LTM configurations N+1,..., N+M and includes the IDs 1,..., N in the DU to CU message of the additional LTM preparation procedures similar to the event 310.

[0227] In some implementations, the CU 172 sends 412 a CU-to-DU message including IDs 1,..., N to the S-DU 174A and receives 414 a DU-to-CU message from the S-DU 174A in response. The CU-to-DU message 412 and the DU-to-CU message 414 are collectively referred to as an LTM ID transfer procedure 493 or an LTM cell index transfer procedure 493 in FIG. 4 some implementations. In some implementations, the message 412 and the message 414 can be a UE Context Modification Request message and a UE Context Modification Response message, respectively. In some implementations, the CU 172 includes the LTM configurations 1,..., N and / or the cell IDs 1,..., N in the CU-DU message 412. In one implementation, the CU 172 includes the IDs 1,..., N in the CU-DU message 412. In another implementation, the CU 172 includes the cell indices 1,..., N in the CU-DU message 412. In some alternative implementations, the CU 172 can perform multiple LTM ID transfer procedures to send the IDs 1,..., N, the cell IDs 1,..., N, and / or the LTM configurations 1,..., N to the S-DU 174A. In each of the procedures, the CU 172 includes a particular portion of the IDs 1,..., N, the cell IDs 1,..., N, and / or the LTM configurations 1,..., N in a CU-to-DU message similar to the message 412. As a result, the S-DU 174A associates the IDs 1,..., N with the LTM configurations 1,..., N and / or the cell IDs 1,..., N, respectively. In other alternative implementations, the CU 172 can perform multiple LTM cell index transfer procedures to send the cell indices 1,..., N; the cell IDs 1,..., N, and / or the LTM configurations 1,..., N to the S-DU 174A. In each of the procedures, the CU 172 includes a particular portion of the cell indices 1,..., N; the cell IDs 1,..., N, and / or the LTM configurations 1,..., N in a CU-to-DU message similar to the message 412. As a result, the S-DU 174A associates the cell indices 1,..., N with the LTM configurations 1,..., N and / or the cell IDs 1,..., N, respectively.

[0228] In some implementations, the CU 172 sends CU-to-DU messages including IDs N+l,..., N+M to the S-DU 174A and receives DU-to-CU messages 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 implementations, the CU 172 includes the LTM configurations N+l,..., N+M and / or the cell IDs N+l,..., N+M in the CU-to-DU messages. In some alternative implementations, the CU 172 can perform multiple LTM ID transfer procedures to send the IDs N+l,..., N+M, the cell IDs N+l,..., N+M, and / or the LTM configurations N+l,..., N+M to the S-DU 174A. In each of the procedures, the CU 172 includes a particular portion of the IDs N+l,..., N+M, the cell IDs N+l,..., N+M, and / or the LTM configurations 1,..., N in a CU-DU message similar to the message 412. Accordingly, the S-DU 174A associates the IDs N+l,..., N+M with the LTM configurations N+l,..., N+M and / or the cell IDs N+l,..., N+M, respectively.

[0229] In some implementations, the values of the IDs 1,..., N of the procedure 380 are different from the values of the IDs 1,..., N and the IDs N+l,..., N+M described for the scenario 400 in the case that the CU 172 and the S-DU 174A perform the procedure 380 with the UE 102. In some implementations, the values of the cell IDs 1,..., N of the procedure 380 are different from the values of the cell IDs 1,..., N and the cell IDs N+l,..., N+M described for the scenario 400 in the case that the CU 172 and the S-DU 174A perform the procedure 380 with the UE 102. In some implementations, the values of the cell indexes 1,..., N of the procedure 380 are different from the values of the cell indexes 1,..., N and the cell indexes N+l,..., N+M described for the scenario 400 in the case that the CU 172 and the S-DU 174A perform the procedure 380 with the UE 102.

[0230] Later, similar to event 324, UE 102 can send 424 at least one measurement report to S-DU 174A. The at least one measurement report (e.g., an L1 measurement report) includes an event ID, a first measurement result for cell 1 of T-DU 174B, and / or includes a second measurement result for cell 124A. In some implementations, the first measurement result can be or include a RSRP, a RSRQ, and / or a SINR obtained by UE 102 from a reference signal transmitted on cell 1. Likewise, the second measurement result can be or include a RSRP, a RSRQ, and / or a SINR obtained by UE 102 from a reference signal transmitted on cell 124A. In some implementations, the event ID, the RSRP, the RSRQ, and / or the SINR are an L1 event ID, an L1-RSRP, an L1-RSRQ, and / or an L1-SINR, respectively. Based on the first measurement result and / or the second measurement result, S-DU 174A can send 430 a first LTM command (i.e., LTM command 1) to UE 102 to instruct UE 102 to perform a serving cell change to cell 1 of T-DU 174B. In some implementations, the first LTM command includes ID 1. In other implementations, the first LTM command includes a cell index 1. When UE 102 receives the first LTM command, UE 102 performs a serving cell change from a serving cell to cell 1 according to LTM configuration 1. If the serving cell change occurred in procedure 380, the serving cell can be cell 1 or cell 2 of S-DU 174A. Otherwise, if the serving cell change did not occur in procedure 380 or procedure 380 was not performed, the serving cell is cell 124A. If the first LTM command includes ID 1, UE 102 identifies LTM configuration 1 and / or cell ID 1 (i.e., cell 1) based on ID 1, as described above for event 324. If the first LTM command includes the cell index 1, UE 102 identifies LTM configuration 1, cell ID 1 (i.e., cell 1), and / or LTM ID 1 based on the cell index 1, as described above for event 324. After receiving the first LTM command or successfully accessing cell 1 (e.g., in response thereto), UE 102 applies LTM configuration 1 to communicate with T-DU 174B. FIG. 3 If the first LTM command includes ID 1, UE 102 identifies LTM configuration 1 and / or cell ID 1 (i.e., cell 1) based on ID 1, as described above for event 324. If the first LTM command includes the cell index 1, UE 102 identifies LTM configuration 1, cell ID 1 (i.e., cell 1), and / or LTM ID 1 based on the cell index 1, as described above for event 324. After receiving the first LTM command or successfully accessing cell 1 (e.g., in response thereto), UE 102 applies LTM configuration 1 to communicate with T-DU 174B. FIG. 3 If the first LTM command includes ID 1, UE 102 identifies LTM configuration 1 and / or cell ID 1 (i.e., cell 1) based on ID 1, as described above for event 324. If the first LTM command includes the cell index 1, UE 102 identifies LTM configuration 1, cell ID 1 (i.e., cell 1), and / or LTM ID 1 based on the cell index 1, as described above for event 324. After receiving the first LTM command or successfully accessing cell 1 (e.g., in response thereto), UE 102 applies LTM configuration 1 to communicate with T-DU 174B.

[0231] Similar to event 332, after receiving the first LTM command (e.g., in response thereto), the UE 102 can perform 432 a random access procedure with the T-DU 174B. After receiving the first LTM command or completing the random access procedure 432 (e.g., in response thereto), the UE 102 communicates 436 with the T-DU 174B on the first cell using the LTM configuration 1 and / or the reference LTM configuration, and communicates with the CU 172 via the T-DU 174B, similar to event 336.

[0232] The resource release procedure 496 can be similar to procedure 396. Alternatively, in the resource release procedure 496, the CU 172 can send a CU-to-DU message (e.g., a UE Context Release Command message) to the S-DU 174A to release the UE context of the UE 102. In response, the S-DU 174A releases the UE context of the UE 102 and sends 440 a DU-to-CU message (e.g., a UE Context Release Complete message) to the CU 172.

[0233] Events 380, 404, 406, 490, 492, 494, 494, 424, 426, 428, 429, 430, 431, 432, 434, 436, 496, 498, 456 are collectively referred to as LTM configuration and / or activation procedures 480 in FIG. 4

[0234] Next, reference is made to FIG. 5A In scenario 500A, the base station 106 operates as the MN and the base station 104 operates as the 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 can include a CU and a DU similar to the CU and the DU of the base station 104 in FIG. 3

[0235] ​​Initially, the UE 102 communicates with the MN 106 and the SN 104 in DC. In event 502, the UE 102 communicates with the DU 174 on the cell 124A using a serving DU configuration and with the CU 172 via the DU 174 using a serving CU configuration, similar to event 302. In some alternative implementations, the UE 102 does not communicate with the CU 172 via the DU 174 in event 302. In some implementations, the UE 102 can communicate 502 UL PDUs and / or DL PDUs with the MN 106 and / or the SN 104 in DC via radio bearers, which can include SRBs and / or DRBs. The MN 106 and / or the SN 104 can configure the radio bearers to the UE 102. The UE 102 communicates 502 UL PDUs and / or DL PDUs with the SN 104 on the SCG (i.e., SCG radio resources) configured for communication with the UE 102 by the SN 104 in DC. The UE 102 communicates UL PDUs and / or DL PDUs with the MN 106 on the MCG (i.e., MCG radio resources) according to the MN configuration (i.e., MCG configuration) in DC. In some implementations, the serving DU configuration is the 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 cells) 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 cells) operated by the SN 104. In some implementations, the MN configuration includes a plurality of configuration parameters and the UE 102 receives the configuration parameters in one or more RRC messages from the MN 106. As described for FIG. 3 the serving DU configuration, the serving DU configuration includes a plurality of configuration parameters. In some implementations, the UE 102 receives the configuration parameters in the one or more RRC messages from the SN 104, e.g., via the MN 106 and / or on a SRB (e.g., SRB3) that the MN 106 or the SN 104 configures for the UE 102 to exchange RRC messages between the UE 102 and the SN 104.

[0236] When UE 102 communicates with MN 106 and SN 104 under DC, MN 106 may perform an LTM configuration and / or activation procedure similar to procedures 380 and / or 480 with UE 102. In some implementations, when communicating with MN 106 and SN 104 under DC, UE 102 may send at least one measurement report to CU 172 via DU 174 and cell 124A in events 504 and 506, respectively, similar to events 304 and 306. In other implementations, when communicating with MN 106 and SN 104 under DC, UE 102 may send at least one measurement report to MN 106 via cell 126. MN 106 then sends at least one measurement report to CU 172. In some implementations, MN 106 generates at least one SN message including at least one measurement report and sends at least one SN message to CU 172 in event 507. In one implementation, at least one SN message includes an RRC Transfer message and / or an SN Modification Request message.

[0237] Upon receiving at least one measurement report (e.g., in response to this) or during communication between SN 104 and UE 102, SN 104 determines to prepare a first cell for UE 102, as for... FIG. 3 As described. Events 590, 592, 594, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, and 556 are similar to events 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, and 356. After receiving the first LTM command 530, sending an acknowledgment 531, or confirming that UE 102 has successfully connected to the first cell 532 or 536, similar to event 336, UE 102, operating under DC with MN 106 and SN 104, communicates 536 with DU 174 on the first cell according to LTM configuration 1, and communicates 536 with CU 172 via DU 174. Later, DU 174 and / or CU 172 may perform an LTM execution procedure 598 with UE 102, similar to procedure 398 or 498, to command UE 102 to perform a cell change from the first cell to the second cell. As a result of procedure 598, similar to event 356, UE 102, operating under DC with MN 106 and SN 104, communicates with DU 174 on the second cell according to LTM configuration 2, and communicates with CU 172 via DU 174, 556.

[0238] Events 504, 506, 505, 507, 590, 592, 594, 594, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, 556 are collectively referred to as LTM configuration and / or activation procedure 581 in FIG. 5A

[0239] Referring next to FIG. 5B , scenario 500B is generally similar to scenario 500A, except that SN 104 sends 517, 519 RRC reconfiguration messages to UE 102 via MN 106, and receives 521, 523 RRC reconfiguration complete messages from UE 102 via MN 106. RRC reconfiguration messages 517, 519 are similar to RRC reconfiguration messages 316, 318. RRC reconfiguration complete messages 521, 523 are similar to RRC reconfiguration messages 320, 322. In some implementations, SN 104 generates a first SN message (e.g., a SN Modification Required message, a SN Modification Required message, or an RRC Transfer message) that includes the RRC reconfiguration messages, and sends the first SN message to MN 106 in event 517. MN 106 generates an MN RRC message that includes the RRC reconfiguration messages, and sends the MN RRC message to UE 102 519. In response, UE 102 generates an MN RRC response message that includes the RRC reconfiguration complete messages, and sends the MN RRC response message to MN 106 521. In some implementations, MN 106 generates a second SN message (e.g., a SN Reconfiguration Complete message or an RRC Transfer message) that includes the RRC reconfiguration complete messages, and sends the second SN message to SN 104 in event 523. In some implementations, the MN RRC message and the MN RRC response message can be the RRC reconfiguration messages and the RRC reconfiguration complete messages, respectively.

[0240] 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 as LTM configuration and / or activation procedure 582 in FIG. 5B

[0241] Referring next to FIG. 6A ​​In scenario 600A, similar to scenarios 300-500B, base station 106 operates as a MN and base station 104 operates as a SN. Similar to base station 104 in scenario 400, SN 104 includes CU 172, S-DU 174A, and T-DU 174B. When UE 102 communicates with MN 106 and SN 104 under DC, MN 106 can perform 680 an LTM configuration and / or activation procedure similar to procedures 380 and / or 480 with UE 102. When UE 102 communicates with M-DU 174A and S-DU 174B under DC, CU 172 can perform 681 an LTM configuration and / or activation procedure similar to procedures 581 and / or 582 with UE 102 via M-DU 174A or S-DU 174B.

[0242] Next, reference is made to FIG. 6B Scenario 600B is similar to scenarios 300-500B and 600A, except that SN 104 sends 617, 619 RRC reconfiguration messages to UE 102 via MN 106 and receives 621, 623 RRC reconfiguration complete messages from UE 102 via MN 106.

[0243] Next, reference is made to FIG. 7A In scenario 700A, base station 104 operates as a MN and a SN, similar to scenarios 300-600B. Base station 104 includes CU 172, master DU (M-DU) 174A, and secondary DU (S-DU) 174B. Similar to FIG. 3 CU 172 operates with M-DU 174A as a MN and similar to FIG. 5A to FIG. 6B MN 106 in scenario 400, CU 172 operates with S-DU 174B as a SN. FIG. 5A to FIG. 6B

[0244] ​In scenario 700A, UE 102 initially communicates 702 with M-DU 174A and S-DU 174B in DC and communicates 702 with CU 172 via M-DU 174A and S-DU 174B. In event 702, similar to event 302, UE 102 communicates with S-DU 174B on cell 124A using a serving DU configuration and communicates with CU 172 via S-DU 174B using a serving CU configuration. Events 704 and 706 are similar to events 304 and 306. In some implementations, similar to event 304, UE 102 can send 705 at least one measurement report to M-DU 174A. Similar to event 306, M-DU 174A in turn sends 707 at least one DU-to-CU message including the at least one measurement report to CU 172. While UE 102 is communicating with M-DU 174A and S-DU 174B in DC, CU 172 can perform 780 an LTM configuration and / or activation procedure similar to procedure 380 with UE 102 via M-DU 174A.

[0245] Events 704, 706, 705, 707, 790, 792, 794, 724, 726, 728, 729, 730, 731, 732, 734, 736, 796, 798, 756 are collectively referred to as LTM configuration and / or activation procedure 781 in FIG. 7A

[0246] Next, with reference to FIG. 7B Scenario 700B is similar to scenarios 300-600B and 700A, except that CU 172 sends 717, 719 RRC reconfiguration messages to UE 102 via M-DU 174A and receives 721, 723 RRC reconfiguration complete messages from UE 102 via M-DU 174A.

[0247] 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 as LTM DU configuration and / or activation procedure 782 in FIG. 7B

[0248] Next, with reference to FIG. 8A ​​In scenario 800A, similar to scenarios 300-700B, the base station 104 operates as a MN and a SN. The base station 104 includes a CU 172, a master DU (M-DU) 174A, a secondary DU (S-DU) 174B, and a target secondary DU (T-DU) 174C. The CU 172 operates with the M-DU 174A as a MN and with the S-DU 174B as a SN. The CU 172 can perform 880 an LTM configuration and / or activation procedure similar to procedure 380 with the UE 102 via the M-DU 174A when the UE 102 communicates with the M-DU 174A and the S-DU 174B in DC. The CU 172 can perform 881 an LTM configuration and / or activation procedure similar to procedure 581 or 582 with the UE 102 via the S-DU 174A when the UE 102 communicates with the M-DU 174A and the S-DU 174B in DC.

[0249] Next, reference is made to FIG. 8B Scenario 800B is similar to scenarios 300-700B and scenario 800A, except that the CU 172 sends 817, 819 RRC reconfiguration messages to the UE 102 via the M-DU 174A and receives 821, 823 RRC reconfiguration complete messages from the UE 102 via the M-DU 174A.

[0250] Next, reference is made to FIG. 9A to FIG. 11B A number of example methods for supporting configuring configurations for LTM that can be implemented in a RAN node such as a DU or CU are discussed. For FIG. 3 to FIG. 8B The examples and implementations described can be applied to FIG. 9A to FIG. 11B .

[0251] FIG. 9A An example method 900A for configuring or triggering LTM for a UE (e.g., UE 102) that can be implemented by a DU (e.g., a DU 174 of a base station 104 or 106) is shown.

[0252] The method 900A starts at block 902A, where the DU receives a first CU-to-DU message from the CU, the first CU-to-DU message including cell IDs 1,..., N and cell indexes 1,..., N to request cell 1,..., N for the UE to prepare for LTM, where N is a positive integer, the cell IDs 1,..., N identify the cells 1,..., N, respectively, and the cell indexes 1,..., N index the cells 1,..., N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 904, the DU generates LTM configurations 1,..., N including the cell indexes 1,..., N to configure the cells 1,..., N for LTM, respectively (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 906, the DU sends a first DU-to-CU message including the LTM configurations 1,..., N to the CU (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 908, the DU sends a message including LTM IDs 1,..., N and the LTM configurations 1,..., N to the UE, where N is a positive integer and the LTM IDs 1,..., N identify the LTM configurations 1,..., N, respectively (e.g., events 318, 394, 380, 480, 494, 580, 594, 581, 517, 519, 582, 680, 694, 681, 617, 619, 682, 780, 794, 781, 717, 719, 782, 880, 894, 881, 817, 819, 882). At block 910, the DU associates the LTM configurations 1,..., N with the cells 1,..., N, respectively. The DU can perform the association when the LTM configurations are generated. In some implementations, the DU associates the LTM configurations 1,..., N with the cell indexes 1,..., N and / or the cell IDs 1,..., N, respectively.

[0253] At block 912, the DU receives, from the first UE, at least one measurement (e.g., events 324, 380, 424, 480, 580, 524, 581, 582, 680, 624, 681, 682, 780, 724, 781, 782, 880, 824, 881, 882) for cell 1 (identified by cell ID 1). At block 914, the DU determines to trigger a serving cell change for the UE to cell 1. In some implementations, the DU makes the determination based on the at least one first measurement. At block 916, the DU transmits, to the first UE, an LTM command including cell index 1 (e.g., events 330, 380, 480, 430, 580, 530, 581, 582, 680, 630, 681, 682, 780, 730, 781, 782, 880, 830, 881, 882). In some implementations, the DU transmits the LTM command to the UE on the serving cell in response to the determination of block 914. At block 918, the DU communicates with the UE via cell 1 using LTM configuration 1 (e.g., events 336, 380, 480, 436, 580, 536, 581, 582, 680, 636, 681, 682, 780, 736, 781, 782, 880, 836, 881, 882).

[0254] When the UE receives the LTM command, the UE determines or identifies LTM configuration 1 and cell ID 1 based on cell index 1. In some implementations, the UE determines or identifies LTM configuration 1 based on cell index 1 and identifies cell ID 1 in LTM configuration 1. The UE accesses cell 1 (identified by cell ID 1) (e.g., events 332, 380, 432, 480, 580, 532, 581, 582, 680, 632, 681, 682, 780, 732, 781, 782, 880, 832, 881, 882). The UE communicates with the DU via cell 1 using LTM configuration 1 (e.g., events 336, 380, 480, 436, 580, 536, 581, 582, 680, 636, 681, 682, 780, 736, 781, 782, 880, 836, 881, 882), as described for block 918.

[0255] In some implementations, the CU or RAN operating the CU can configure the UE with a maximum number of LTM cells of 7, 8, 15, 16, 31, 32, 63, or 64. For example, the number N can be less than 8, 9, 16, 17, 32, 33, 64, or 65 cells.

[0256] In some implementations, the DU is a serving DU for the UE. For example, the DU is FIG. 3 、 FIG. 5A andFIG. 5B DU 174 in FIG. 1, FIG. 4 , FIG. 6A and FIG. 6B S-DU 174A in FIG. 1, or FIG. 7A , FIG. 7B , FIG. 8A and FIG. 8B S-DU 174B in FIG. 1. The serving DU can perform blocks 902A-918. In other implementations, the DU is a non-serving DU. For example, the DU is T-DU 174B in FIG. 4 , FIG. 6A and FIG. 6B FIG. 1 and T-DU 174C in FIG. 8A and FIG. 8B FIG. 1. The non-serving DU can perform blocks 902A-906, 910, and / or 918. In such cases, the serving DU for the UE performs blocks 908, 912, 914, and 916. The serving DU can receive cell indices 1,..., N and / or LTM configurations 1,..., N from the CU, so that the serving DU can send LTM commands to the UE.

[0257] In some implementations, cells 1,..., N are candidate PCells. In other implementations, cells 1,..., N are candidate PSells. In some implementations, the DU can include cell IDs 1,..., N associated with LTM configurations 1,..., N, respectively, in the first DU-to-CU message. In some implementations, the DU communicates with the UE via a serving cell, and the DU receives at least one first measurement result from the UE via the serving cell. In some implementations, the DU can include LTM configurations 1,..., P without including LTM configurations P+1,..., N in the DU-to-CU message, where 0 < P < N. The DU can include cell IDs 1,..., P associated with LTM configurations 1,..., P, respectively, in the DU-to-CU message. In such cases, the DU declines to prepare cells P+1,..., N for LTM.

[0258] In some implementations, the DU sends, to the UE via the CU, a first measurement configuration to configure at least one first reference signal for measurement. For example, the DU sends, to the CU, a CU-to-DU message including the first measurement configuration, which the CU in turn sends, to the UE, a message (e.g., an RRC reconfiguration message) including the first measurement configuration. In one implementation, the first measurement configuration or the at least one first reference signal is specific to the LTM. In another implementation, the first measurement configuration is a CSI measurement configuration (e.g., CSI-MeasConfig) for CSI measurement. The first measurement configuration can include or configure a first resource configuration configuring the at least one first reference signal for measurement. The first measurement configuration can include or configure a first reporting configuration configuring a reporting periodicity, an offset, and / or a reporting resource (e.g., a PUCCH resource) for sending measurement results obtained by the UE from measurements on the at least one first reference signal. The UE sends at least one first measurement result based on the first reporting configuration. For example, the UE sends each of the at least one first measurement result on the reporting resource with different periodicity based on the periodicity and / or the offset.

[0259] In some implementations, the DU sends, to the UE, a first measurement activation command to instruct the UE to start performing measurements on the at least one first reference signal. The UE starts performing at least one measurement on the at least one first reference signal upon receiving the first measurement activation command and according to the first measurement configuration. The DU can start transmitting the at least one first reference signal on the cell 1 before or after sending the first measurement activation command. Based on the measurements, the UE can obtain at least one first measurement result. In one implementation, the UE sends the at least one first measurement result according to the first reporting configuration. In other implementations, the UE starts performing at least one measurement on the at least one first reference signal upon receiving the first measurement configuration. In such cases, the DU can not send a measurement activation command to instruct the UE to perform measurements on the at least one first reference signal. Based on the measurements, the UE can obtain at least one first measurement result.

[0260] In some implementations, the at least one first measurement result does not include the cell ID 1. In such cases, the DU determines or identifies the at least one first measurement result for the cell 1 or the cell ID 1 based on the first resource configuration and / or the first reporting configuration. Based on the determination or identification, the DU can determine the cell ID 1. In other implementations, the at least one first measurement result includes the cell ID 1 or a cell index 1.

[0261] In some implementations, the at least one first measurement includes at least one of a CSI, an RSRP value, an RSRQ value, an SINR value, and / or an event ID. The RSRP, RSRQ, and / or SINR value can be an Ll-RSRP, Ll-RSRQ, and / or Ll-SINR value, respectively. In one implementation, the event ID indicates an event in which the UE detects that the signal strength and / or quality of cell 1 is above a threshold value. The threshold value can be predetermined by the first DU. In another implementation, the event ID indicates an event in which the UE detects that the signal strength and / or quality of cell 1 is above a first threshold value and the signal strength and / or quality of the serving cell is below a second threshold value. The first and second threshold values are predetermined by the DU. In yet another implementation, the event ID indicates an event in which the UE detects that the signal strength and / or quality of cell 1 is above (the signal strength and / or quality of the serving cell plus a threshold value). The threshold value can be predetermined by the DU.

[0262] In some implementations, the DU receives, from the first UE, at least one second measurement for the serving cell (identified by the cell ID of the serving cell). In some implementations, the DU sends, to the UE via the CU, a second measurement configuration to configure at least one second reference signal for measurement. For example, the DU sends a CU-to-DU message including the second measurement configuration to the CU, which in turn sends a message (e.g., an RRC reconfiguration message) including the second measurement configuration to the UE. In one implementation, the second measurement configuration or the at least one second reference signal is specific to the LTM. In another implementation, the second measurement configuration is a CSI measurement configuration (e.g., CSI-MeasConfig) for CSI measurement. The second measurement configuration can include or configure a second resource configuration that configures the at least one second reference signal for measurement. The second measurement configuration can include or configure a second reporting configuration that configures a reporting periodicity, an offset, and / or a reporting resource (e.g., a PUCCH resource) for sending measurement results obtained by the UE from measurements on the at least one second reference signal. The UE sends the at least one second measurement result based on the second reporting configuration. For example, the UE sends each of the at least one second measurement result on the reporting resource with different periodicity based on the periodicity and / or offset.

[0263] In some implementations, the DU sends a second measurement activation command to the UE to instruct the UE to start performing measurements on the at least one second reference signal. Alternatively, the DU instructs the UE to start performing measurements on the at least one second reference signal in the first measurement activation command. The UE starts performing at least one measurement on the at least one second reference signal according to the first measurement configuration upon receiving the first measurement activation command or the second measurement activation command. The DU can start transmitting the at least one second reference signal on the cell 1 before or after sending the first measurement activation command or the second measurement activation command. Based on the measurements, the UE can obtain at least one second measurement result. In one implementation, the UE transmits the at least one second measurement result according to a second reporting configuration. In other implementations, the UE starts performing at least one measurement on the at least one second reference signal upon receiving the second measurement configuration. In such cases, the DU can not send a measurement activation command to instruct the UE to perform measurements on the second reference signal. Based on the measurements, the UE can obtain at least one second measurement result.

[0264] In some implementations, the at least one second measurement result does not include the cell ID of the serving cell. In such cases, the DU determines or identifies the at least one second measurement result or the cell ID of the serving cell for the serving cell based on the second resource configuration and / or the second reporting configuration. In other implementations, the at least one second measurement result includes the cell ID of the serving cell or a cell index of the serving cell.

[0265] In some implementations, the at least one second measurement result includes at least one of a CSI, an RSRP value, an RSRQ value, and / or a SINR value for the serving cell. In some implementations, the DU determines to trigger a serving cell change to the cell 1 or to send an LTM command based on the at least one first measurement result and / or the at least one second measurement result. For example, if the DU determines that the at least one first measurement result (i.e., value) is above a first threshold and the at least one second measurement result (i.e., value) is below a second threshold, the DU sends or determines to send an LTM command. The first threshold and the second threshold can be predetermined by the DU. Otherwise, if the at least one first measurement result is below the first threshold or the at least one second measurement result is above the second threshold, the UE does not send or determines not to send an LTM command. In another example, if the DU determines that the at least one first measurement result is above (the at least one second measurement result plus a threshold), the DU sends or determines to send an LTM command. The threshold can be predetermined by the DU. Otherwise, if the at least one first measurement result is not above (the at least one second measurement result plus the threshold), the UE does not send or determines not to send an LTM command.

[0266] In some implementations, after block 918, the DU receives, from the first UE, at least one third measurement result for cell 2 (identified by cell ID 2). For example, the DU receives the at least one third measurement result from the UE via cell 1. The DU determines to trigger a serving cell change to cell 2 for the UE based on the at least one third measurement result. Similar to block 916, in response to the determination, the DU sends an LTM command (e.g., events 350, 398, 380, 450, 498, 480, 580, 598, 581, 582, 680, 698, 681, 682, 780, 798, 781, 782, 880, 898, 881, 882) to the UE on cell 1 or another serving cell including cell index 2. When the UE receives the LTM command, the UE determines or identifies LTM configuration 2 and cell ID 2 based on cell index 2. In some implementations, the UE determines or identifies LTM configuration 2 based on cell index 2 and identifies cell ID 2 in LTM configuration 2. The UE accesses cell 2 (e.g., events 352, 398, 380, 452, 498, 480, 580, 598, 581, 582, 680, 698, 681, 682, 780, 798, 781, 782, 880, 898, 881, 882) identified by cell ID 2. The UE communicates with the DU via cell 2 using LTM configuration 2 (e.g., events 356, 380, 480, 456, 580, 556, 581, 582, 680, 656, 681, 682, 780, 756, 781, 782, 880, 856, 881, 882).

[0267] In some implementations, the DU sends, to the UE via the CU, a third measurement configuration to configure at least one third reference signal for measurement. For example, the DU sends a CU-to-DU message including the third measurement configuration to the CU, which in turn sends a message (e.g., RRC reconfiguration message) including the third measurement configuration to the UE. In one implementation, the third measurement configuration or the at least one third reference signal is specific to the LTM. In another implementation, the third measurement configuration is a CSI measurement configuration (e.g., CSI-MeasConfig) for CSI measurement. The third measurement configuration can include or configure a third resource configuration that configures the at least one third reference signal for measurement. The third measurement configuration can include or configure a third reporting configuration that configures a reporting periodicity, an offset, and / or a reporting resource (e.g., PUCCH resource) for sending measurement results obtained by the UE from measurements on the at least one third reference signal. The UE sends the at least one third measurement result based on the third reporting configuration. For example, the UE sends each of the at least one third measurement result on the reporting resource at different periodicities and / or offsets.

[0268] In some implementations, the DU transmits a third measurement activation command to the UE to instruct the UE to start performing measurements on at least one third reference signal. Alternatively, the DU instructs the UE to start performing measurements on at least one second reference signal in the first measurement activation command or the second measurement activation command. The UE starts performing at least one measurement on the at least one third reference signal according to the first measurement configuration upon receiving the first measurement activation command, the second measurement activation command, or the third measurement activation command. The DU can start transmitting the at least one third reference signal on the cell 2 before or after transmitting the first measurement activation command, the second measurement activation command, or the third measurement activation command. Based on the measurements, the UE can obtain at least one third measurement result. In one implementation, the UE transmits the at least one third measurement result according to a third reporting configuration. In other implementations, the UE starts performing at least one measurement on the at least one third reference signal upon receiving the third measurement configuration. In such cases, the DU can not transmit a measurement activation command to instruct the UE to perform measurements on the at least one third reference signal. Based on the measurements, the UE can obtain at least one third measurement result.

[0269] In some implementations, the at least one third measurement result does not include the cell ID 1. In such cases, the DU determines or identifies the at least one third measurement result for the cell 2 based on the third resource configuration and / or the third reporting configuration. Based on the determination or identification, the DU can determine the cell ID 2 or the cell index 2. In other implementations, the at least one third measurement result includes the cell ID 2 or the cell index 2.

[0270] In some implementations, the at least one third measurement result includes at least one of a CSI, an RSRP value, an RSRQ value, an SINR value, and / or an event ID. The RSRP, RSRQ, and / or SINR value can be a L1-RSRP, L1-RSRQ, and / or L1-SINR value, respectively. In one implementation, the event ID indicates an event that the UE detects that the signal strength and / or quality of the cell 2 is above a threshold value. The threshold value can be predetermined by the DU. In another implementation, the event ID indicates an event that the UE detects that the signal strength and / or quality of the cell 2 is above a first threshold value and the signal strength and / or quality of the cell 1 is below a second threshold value. The first threshold value and the second threshold value are predetermined by the first DU. In yet another implementation, the event ID indicates an event that the UE detects that the signal strength and / or quality of the cell 2 is above (the signal strength and / or quality of the cell 1 plus a threshold value). The threshold value can be predetermined by the DU.

[0271] In some implementations, similar to receiving the at least one first measurement result, the DU receives, after block 918, at least one additional measurement result for cell 1 from the UE via cell 1. In some implementations, the DU sends, based on the at least one third measurement result and / or the at least one additional measurement result, an LTM command including cell index 2 to the UE. For example, if the DU determines that the at least one third measurement result (i.e., value) is above a first threshold and the at least one additional measurement result (i.e., value) is below a second threshold, the DU sends or determines to send the LTM command. The first threshold and the second threshold can be predetermined by the DU. Otherwise, if the at least one third measurement result is below the first threshold or the at least one additional measurement result is above the second threshold, the UE does not send or determines not to send the LTM command. In another example, if the DU determines that the at least one third measurement result is above (the at least one additional measurement result plus a threshold), the DU sends or determines to send the LTM command. The threshold can be predetermined by the DU. Otherwise, if the at least one first measurement result is not above (the at least one additional measurement result plus the threshold), the UE does not send or determines not to send the LTM command.

[0272] While the DU performs the actions of blocks 902-918 to prepare cell 1 for a first UE (e.g., the UE described above), the DU can perform similar operations to blocks 902-918 to prepare cell 1 for a second UE. The DU generates a first LTM configuration 1 and a second LTM configuration 1 for the first UE and the second UE, respectively. Depending on the UE capabilities of the first UE and the second UE and / or the serving DU configuration of the first UE and the second UE, the first LTM configuration 1 and the second LTM configuration 1 can be the same or different configurations. In some implementations, the DU sets the cell index 1 of the first LTM configuration 1 and the cell index 1 of the second LTM configuration 1 to the same value. In such cases, the cell index 1 can be cell-specific because the DU uses the same cell index value for LTM configurations of the same cell configured for different UEs when preparing cell 1 for LTM for the UEs. In other implementations, the DU sets the cell index 1 of the first LTM configuration 1 and the cell index 1 of the second LTM configuration 1 to different values. In such cases, the cell index 1 is UE-specific because the DU assigns different values to the cell index 1 when preparing cell 1 for LTM for the first UE and the second UE.

[0273] With method 900A, the CU can coordinate cell index values for LTM of different DUs for a UE, as described for FIG. 10A When the UE receives the LTM command including the cell index, the UE only uses the cell index to identify or determine the corresponding LTM configuration, which simplifies the implementation for LTM in the UE.

[0274] FIG. 9Bis a flowchart of an example method 900A similar to method 900B, except that method 900B includes blocks 902B, 903, 909, and 917 instead of blocks 902, 904, 908, and 916. At block 902B, the DU receives a first CU-to-DU message from the CU, the first CU-to-DU message including cell IDs 1,..., N and an LTM group ID to request preparation of cells 1,..., N for an LTM for a UE, where N is a positive integer and the cell IDs 1,..., N identify cells 1,..., N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 903, the DU generates LTM configurations 1,..., N including cell indices 1,..., N to configure cells 1,..., N for the LTM, respectively (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). The cell indices 1,..., N index the cells 1,..., N, respectively.

[0275] At block 909, the DU sends a message to the UE including the LTM IDs 1,..., N, the LTM configurations 1,..., N, and the LTM group ID, where the LTM IDs 1,..., N identify the LTM configurations 1,..., N, respectively (e.g., 318, 394, 380, 480, 494, 580, 594, 581, 517, 519, 582, 680, 694, 681, 617, 619, 682, 780, 794, 781, 717, 719, 782, 880, 894, 881, 817, 819, 882). At block 917, the DU sends an LTM command to the UE including the LTM group ID and the cell index 1 (e.g., events 330, 380, 480, 430, 580, 530, 581, 582, 680, 630, 681, 682, 780, 730, 781, 782, 880, 830, 881, 882). In some implementations, the DU sends the LTM command to the UE on the serving cell in response to the determination of block 914.

[0276] When the UE receives the LTM command from the DU on the serving cell, the UE determines or identifies the LTM configuration 1 and the cell ID 1 based on the LTM group ID and the cell index 1. In some implementations, the UE determines or identifies the LTM configuration 1 based on the LTM group ID and the cell index 1, and identifies the cell ID 1 in the LTM configuration 1. The UE accesses the cell 1 identified by the cell ID 1 (e.g., events 332, 380, 432, 480, 580, 532, 581, 582, 680, 632, 681, 682, 780, 732, 781, 782, 880, 832, 881, 882). The UE communicates with the DU via the cell 1 using the LTM configuration 1 (e.g., events 336, 380, 480, 436, 580, 536, 581, 582, 680, 636, 681, 682, 780, 736, 781, 782, 880, 836, 881, 882) as described for block 918.

[0277] In some implementations, the DU is a serving DU for the UE. For example, the DU is the DU 174 in FIG. 3 , FIG. 5A and FIG. 5B , the S-DU 174A in FIG. 4 , FIG. 6A and FIG. 6B , or the S-DU 174B in FIG. 7A , FIG. 7B , FIG. 8A and FIG. 8B . The serving DU can perform blocks 902B-918. In other implementations, the DU is a non-serving DU. For example, the DU is the T-DU 174B in FIG. 4 , FIG. 6A and FIG. 6B , and the T-DU 174C in FIG. 8A and FIG. 8B . The non-serving DU can perform blocks 902B-906, 910, and / or 918. In such cases, a serving DU for the UE can perform blocks 909, 912, 914, and 917. The serving DU can receive the LTM group ID, the cell index 1, …, N, and / or the LTM configuration 1, …, N from the CU, so that the serving DU can send the LTM command to the UE.

[0278] In some implementations, after block 918, the DU receives at least one third measurement result for the cell 2 (identified by the cell ID 2) from the first UE, as described for FIG. 9DThe DU determines to trigger a serving cell change to cell 2 for the UE based on the at least one third measurement result. Similar to block 917, in response to the determination, the DU sends an LTM command including the LTM group ID and cell index 2 to the UE on cell 1 or another serving cell. When the UE receives the LTM command, the UE determines or identifies the LTM configuration 2 and cell ID 2 based on the LTM group ID and cell index 2. In some implementations, the UE determines or identifies the LTM configuration 2 based on the cell index 2 and identifies the cell ID 2 in the LTM configuration 2. The UE accesses the cell 2 identified by the cell ID 2 (e.g., events 332, 380, 432, 480, 580, 532, 581, 582, 680, 632, 681, 682, 780, 732, 781, 782, 880, 832, 881, 882). The UE communicates with the DU via the cell 2 using the LTM configuration 2 (e.g., events 336, 380, 480, 436, 580, 536, 581, 582, 680, 636, 681, 682, 780, 736, 781, 782, 880, 836, 881, 882).

[0279] Unlike the method 900A, the DU (e.g., the first DU) instead of the CU assigns the values to the cell indexes 1, …, N in the method 900B. In some implementations, the LTM group ID can be a DU ID or a cell group ID. In some implementations, the CU sets the LTM group ID to a first value. In some scenarios or implementations, similar to block in the method 900B, an additional DU (e.g., the second DU) can perform an action on the UE using the CU. In such cases, the CU sets the LTM group ID of the second DU to a second value other than the first value.

[0280] With the method 900B, the coordination of the cell index values for the LTM of the UE by different DUs is avoided, which simplifies the implementation of the LTM in the DUs.

[0281] FIG. 3is a flowchart of an example method 900C similar to the methods 900A and 900B, except that the method 900C includes the blocks 902C, 905, and 907 instead of the blocks 902B, 904, and 906. At block 902C, the DU receives, from the CU, a first CU-to-DU message including cell IDs 1, …, N to request the cells 1, …, N for LTM for the UE, where N is a positive integer, and the cell IDs 1, …, N identify the cells 1, …, N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 905, the DU generates an LTM group ID and LTM configurations 1, …, N including cell indexes 1, …, N to configure the cells 1, …, N for LTM (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). The cell indexes 1, …, N index the cells 1, …, N, respectively. At block 907, the DU sends, to the CU, a DU-to-CU message including the LTM configurations 1, …, N and the LTM group ID (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882).

[0282] In some implementations, the DU is a serving DU for the UE. For example, the DU is the DU 174 in FIG. 5A , FIG. 5B and FIG. 4 , the S-DU 174A in FIG. 6A , FIG. 6B and FIG. 7A , or the S-DU 174B in FIG. 7B , FIG. 8A , FIG. 8B and FIG. 4 . The serving DU can perform the blocks 902C through 918. In other implementations, the DU is a non-serving DU. For example, the DU is the T-DU 174B in FIG. 6A , FIG. 6B and FIG. 8A , and the T-DU 174B in FIG. 8B and FIG. 10AThe non-serving DU can perform blocks 902C-907, 910, and / or 918. In such cases, the serving DU for the UE can perform blocks 909, 912, 914, and 917. The serving DU can receive the LTM group ID, cell indices 1,..., N, and / or LTM configurations 1,..., N from the CU, so that the serving DU can send LTM commands to the UE.

[0283] Unlike method 900B where the CU manages (e.g., assigns) the LTM group ID, in method 900C, the DU manages (e.g., assigns) the LTM group ID. In some scenarios or implementations, similar to block in method 900C, an additional DU (e.g., a second DU) can perform actions on the UE using the CU. In such cases, the LTM group ID configured by the first DU (i.e., a first LTM group ID) and the LTM group ID configured by the second DU (i.e., a second LTM group ID) are set to different values. In some implementations, the first DU and the second DU are pre-configured with the first LTM group ID (value) and the second LTM group ID (value). In other implementations, an operations, administration, and maintenance (OAM) node sends a first message to configure the first LTM group ID (value) and a second message to the second DU to configure the LTM group ID (value). In yet another implementation, the CU sends a CU-to-DU message to the first DU to configure the first LTM group ID value and a CU-to-DU message to the second DU to configure the second LTM group ID value. In yet another implementation, the first DU obtains the first LTM group ID (value) from a mathematical function with at least one first input value and the second DU obtains the second LTM group ID (value) from a mathematical function with at least one second input value. At least one of the first input value is different from at least one of the second input value. For example, the first input value is the gNB-DU ID of the first DU and the second input is the gNB-DU ID of the second DU.

[0284] With method 900C, coordination of the cell index values for LTM of a UE by different DUs is avoided, which simplifies the implementation of LTM in the DUs.

[0285] FIG. 10Ais a flowchart of an example method 900D similar to the methods 900A, 900B, and 900C, except that the method 900D includes the block 902D instead of the blocks 902A, 902B, and 902C. At the block 902D, the DU receives, from the CU, a first CU-to-DU message including a first set of IDs, cell IDs 1, …, N, and cell indexes 1, …, N to request cell 1, …, N for the UE to prepare for LTM, where N is a positive integer, the cell IDs 1, …, N identify the cells 1, …, N, respectively, and the cell indexes 1, …, N index the cells 1, …, N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882).

[0286] In some implementations, the DU is a serving DU for the UE. For example, the DU is the DU 174 in FIG. 9A , FIG. 9A and FIG. 10A , the S-DU 174A in FIG. 10A , FIG. 9A and FIG. 9A , or the S-DU 174B in FIG. 10B , FIG. 10B , FIG. 9B and FIG. 9B . The serving DU can perform the blocks 902D through 918. In other implementations, the DU is a non-serving DU. For example, the DU is the T-DU 174B in FIG. 10B , FIG. 10B and FIG. 9B , and the T-DU 174C in FIG. 10C and FIG. 10C . The non-serving DU can perform the blocks 902D through 906, 910, and / or 918. In such cases, a serving DU for the UE can perform the blocks 909, 912, 914, and 917. The serving DU can receive, from the CU, the LTM set of IDs, the cell indexes 1, …, N, and / or the LTM configurations 1, …, N, so that the serving DU can send the LTM commands to the UE.

[0287] With the method 900D, coordination of cell index values for LTM for the UE by different DUs is avoided, which simplifies implementation of LTM in the DUs.

[0288] FIG. 9C An example method 1000A is shown that can be implemented by a CU (e.g., the CU 172 of the base station 104 or 106) for configuring LTM for a UE (e.g., the UE 102).

[0289] Method 1000A begins at block 1002A where the CU sends a first CU-to-DU message to the first DU, the first CU-to-DU message including cell IDs 1,..., N and cell indexes 1,..., N to request cells 1,..., N for the UE to prepare for LTM, where N is a positive integer, the cell IDs 1,..., N identify the cells 1,..., N, respectively, and the cell indexes 1,..., N index the cells 1,..., N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 1004A, the CU receives a first DU-to-CU message from the first DU, the first DU-to-CU message including LTM configurations 1,..., N, where the LTM configurations 1,..., N include the cell indexes 1,..., N, respectively (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 1006, the CU generates a first message, the first message including LTM IDs 1,..., N and the LTM configurations 1,..., N, where the LTM IDs 1,..., N identify the LTM configurations 1,..., N, respectively. At block 1008, the CU sends the first message to the UE via the first RAN node (e.g., events 316, 318, 394, 380, 480, 494, 580, 594, 581, 517, 519, 582, 680, 694, 681, 617, 619, 682, 780, 794, 781, 717, 719, 782, 880, 894, 881, 817, 819, 882).

[0290] At block 1010A, the CU sends a second CU-to-DU message to the second DU, the second CU-to-DU message including cell IDs N+l,..., N+M and cell indexes N+l,..., N+M to request the UE to prepare for the cells N+l,..., N+M for LTM, where M is a positive integer, and the cell IDs N+l,..., N+M identify the cells N+l,..., N+M, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 1012, the CU receives a second DU-to-CU message from the second DU including LTM configurations N+l,..., N+M, where the LTM configurations N+l,..., N+M include the cell indexes N+l,..., N+M (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). The cell indexes N+l,..., N+M index the cells 1,..., N, respectively. At block 1014, the CU generates a second message including LTM IDs N+l,..., N+M and the LTM configurations N+l,..., N+M, where the LTM IDs N+l,..., N+M identify the LTM configurations N+l,..., N+M, respectively. At block 1016, the CU sends the second message to the UE via the first DU or the RAN node (e.g., the second DU, the second CU, or the base station) (e.g., events 316, 318, 394, 380, 480, 494, 580, 594, 581, 517, 519, 582, 680, 694, 681, 617, 619, 682, 780, 794, 781, 717, 719, 782, 880, 894, 881, 817, 819, 882).

[0291] In some implementations, FIG. 9C The CU and the first DU in FIG. 10C The CU, the first DU, and the second DU described above. Thus, the description for FIG. 10C may apply to FIG. 9C and the description for FIG. 10D may apply to FIG. 10DIn some implementations, the first message and the second message are RRC reconfiguration messages. In some implementations, the first RAN node is a serving DU (e.g., the first DU, the second DU, or the third DU), another CU, or a base station for the UE. In other implementations, the first RAN node is a serving DU (e.g., the first DU, the second DU, or the third DU), another CU, or a base station for the UE. In some implementations, the first RAN node and the second RAN node are the same RAN node. In other implementations, the first RAN node and the second RAN node are different RAN nodes. In some implementations, the second RAN node is a new serving RAN node for the UE, and the first RAN node is an old serving RAN node for the UE.

[0292] In some implementations, the maximum number of cells for the LTM for the UE is 7, 8, 15, 16, 31, 32, 63, or 64. For example, the number N can be less than 8, 9, 16, 17, 32, 33, 64, or 65 cells. In another example, the number N+M can be less than 8, 9, 16, 17, 32, 33, 64, or 65 cells.

[0293] In some implementations, the CU includes the cell IDs 1,..., N, the cell indexes 1,..., N, and / or the LTM configurations 1,..., N in the second CU-to-DU message. In other implementations, the CU sends a third CU-to-DU message to the second DU, the third CU-to-DU message including the cell IDs 1,..., N, the cell indexes 1,..., N, and / or the LTM configurations 1,..., N. Thus, when the second DU is / is becoming a serving DU for the UE, the second DU communicates with the UE via a serving cell (e.g., one of the cells N+1,..., N+M). The second DU (i.e., the serving DU) can receive at least one measurement from the UE for the serving cell and / or the cell 1. Based on the at least one measurement, the second DU sends an LTM command including the cell index 1 to the UE to command the UE to perform a serving cell change from the serving cell to the cell 1, as described for FIG. 9A .

[0294] In some implementations, the CU sends a fourth CU-to-DU message to the first DU, the fourth CU-to-DU message including the cell indexes N+1,..., N+M and / or the LTM configurations N+1,..., N+M. Thus, when the first DU is / becomes a serving DU for the UE, the first DU communicates with the UE via a serving cell (i.e., one of the cells N+1,..., N+M). The first DU (i.e., the serving DU) can receive from the UE at least one measurement result for the serving cell and / or the cell N+1. Based on the at least one measurement result, the first DU sends to the UE an LTM command including the cell index N+1 to command the UE to perform a serving cell change from the serving cell to the cell N+1.

[0295] In some implementations, the CU sets the cell indexes 1,..., N+M to different values. When the UE receives an LTM command including a cell index among the cell indexes 1,..., N+M, the UE uniquely determines or identifies an LTM configuration according to the cell index (e.g., the cell index 1), where the LTM configuration (e.g., the LTM configuration 1) includes the cell index (e.g., the cell index 1). In other words, among the multiple DUs that are prepared for LTM for the UE, the cell index (value) of the UE is unique. When the CU has already used a cell index (value) to prepare a cell for LTM for a UE with a DU, the CU avoids using the cell index (value) to prepare a cell for LTM for a UE with another DU.

[0296] FIG. 9Bis a flowchart of an example method 1000B similar to the method 1000A, except that the method 1000B includes blocks 1002B, 1004B, 1007, 1010B, and 1015 instead of blocks 1002A, 1004A, 1006, 1010A, and 1014. At block 1002B, the CU sends a first CU-to-DU message to the first DU, the first CU-to-DU message including cell IDs 1, …, N and a first LTM group ID to request preparation of cells 1, …, N for LTM, where N is a positive integer and the cell IDs 1, …, N identify cells 1, …, N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 1004B, the CU receives a first DU-to-CU message from the first DU, the first DU-to-CU message including LTM configurations 1, …, N, where the LTM configurations 1, …, N include cell indices 1, …, N, respectively (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). The cell indices 1, …, N index the cells 1, …, N, respectively. At block 1007, the CU generates a first message including the first LTM group ID, LTM IDs 1, …, N, and the LTM configurations 1, …, N, where the LTM IDs 1, …, N identify the LTM configurations 1, …, N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 1010B, the CU sends a second CU-to-DU message to a second DU, the second CU-to-DU message including cell IDs N+1, …, N+M and a second LTM group ID to request preparation of cells N+1, …, N+M for LTM for the UE, where M is a positive integer and the cell IDs N+1, …, N+M identify cells N+1, …, N+M, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882).At block 1015, the CU generates a second message including the second LTM group ID, LTM ID N+1, …, N+M, and LTM configuration N+1, …, N+M, where LTM ID N+1, …, N+M identify LTM configuration N+1, …, N+M, respectively (e.g., events 316, 318, 394, 380, 480, 494, 580, 594, 581, 517, 519, 582, 680, 694, 681, 617, 619, 682, 780, 794, 781, 717, 719, 782, 880, 894, 881, 817, 819, 882).

[0297] In some implementations, FIG. 9D The CU, the first DU, and the second DU in FIG. 9B may be the CU, the first DU, and the second DU in FIG. 9D respectively. Thus, the description for FIG. 10D may apply to FIG. 10D , and the description for FIG. 9B may apply to .

[0298] In some implementations, the first LTM group ID and the second LTM group ID can be a DU ID. In other implementations, the first LTM group ID and the second LTM group ID can be a cell group ID. In some implementations, the CU sets the first LTM group ID and the second LTM group ID to different values.

[0299] FIG. 9Dis a flowchart of an example method 1000C similar to the methods 1000A and 1000B, except that the method 1000C includes blocks 1002C, 1004C, 1010C, and 1013 instead of blocks 1002B, 1004B, 1010B, and 1012. At block 1002C, the CU sends a first CU-to-DU message to the first DU, the first CU-to-DU message including cell IDs 1, …, N to request preparation of cells 1, …, N for LTM, where N is a positive integer and the cell IDs 1, …, N identify the cells 1, …, N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 1004C, the CU receives a first DU-to-CU message from the first DU, the first DU-to-CU message including LTM configurations 1, …, N and a first LTM group ID, where the LTM configurations 1, …, N include cell indices 1, …, N, respectively (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). The cell indices 1, …, N index the cells 1, …, N, respectively. At block 1010C, the CU sends a second CU-to-DU message to the second DU, the second CU-to-DU message including cell IDs N+1, …, N+M to request preparation of cells N+1, …, N+M for LTM for the UE, where M is a positive integer and the cell IDs N+1, …, N+M identify the cells N+1, …, N+M, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At block 1013, the CU receives a second DU-to-CU message from the second DU, the second DU-to-CU message including a second LTM group ID and LTM configurations N+1, …, N+M, where the LTM configurations N+1, …, N+M include cell indices N+1, …, N+M (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). The cell IDs N+1, …, N+M identify the cells N+1, …, N+M, respectively.

[0300] In some implementations, FIG. 11A The CU and the first and second DUs in FIGS. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274, 275, 276, 277, 278, 279, 280, 281, 282, 283, 284, 285, 286, 287, 288, 289, 290, 291, 292, 293, 294, 295, 296, 297, 298, 299, 300, 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337, 338, 339, 340, 341, 342, 343, 344, 345, 346, 347, 348, 349, 350, 351, 352, 353, 354, 355, 356, 357, 358, 359, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433,FIG. 10A The CU, the first DU, and the second DU in FIG. 10A may be the CU, the first DU, and the second DU in FIG. 10A , respectively. Thus, the description for FIG. 11A may apply to FIG. 11B , and the description for may apply to

[0301] . FIG. 10B

[0302] In some implementations, FIG. 10B the CU, the first DU, and the second DU in FIG. 10B may be the CU, the first DU, and the second DU in FIG. 11B , respectively. Thus, the description for 9A, FIG. 11C may apply to FIG. 10C , and the description for FIG. 10C may apply to 9A, FIG. 10C , and FIG. 11C . FIG. 11D FIG. 10D is a flowchart of an example method 1000D similar to the methods 1000A, 1000B, and 1000C, except that the method 1000D includes the block 1002D and 1010D instead of the blocks 1002A, 1002B, 1002C and the blocks 1010A, 1010B, 1010C, and 1010D. At the block 1002D, the CU sends a first CU-to-DU message to the first DU, the first CU-to-DU message including the cell IDs 1, …, N, the cell indexes 1, …, N, and the first LTM group ID to request the cells 1, …, N for the UE to prepare for the LTM, where N is a positive integer and the cell IDs 1, …, N identify the cells 1, …, N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At the block 1010D, the CU sends a second CU-to-DU message to the second DU, the second CU-to-DU message including the cell IDs N+1, …, N+M, the cell indexes N+1, …, N+M, and the second LTM group ID to request the cells N+1, …, N+M for the UE to prepare for the LTM, where M is a positive integer, the cell IDs N+1, …, N+M identify the cells N+1, …, N+M, respectively, and the cell indexes N+1, …, N+M index the cells N+1, …, N+M, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882).

[0302] In some implementations, FIG. 10B the CU, the first DU, and the second DU in FIG. 10B may be the CU, the first DU, and the second DU in FIG. 11B , respectively. Thus, the description for 9A, FIG. 11C may apply to FIG. 10C , and the description for FIG. 10C may apply to 9A, FIG. 10C , and FIG. 11C . FIG. 11D FIG. 10D is a flowchart of an example method 1000D similar to the methods 1000A, 1000B, and 1000C, except that the method 1000D includes the block 1002D and 1010D instead of the blocks 1002A, 1002B, 1002C and the blocks 1010A, 1010B, 1010C, and 1010D. At the block 1002D, the CU sends a first CU-to-DU message to the first DU, the first CU-to-DU message including the cell IDs 1, …, N, the cell indexes 1, …, N, and the first LTM group ID to request the cells 1, …, N for the UE to prepare for the LTM, where N is a positive integer and the cell IDs 1, …, N identify the cells 1, …, N, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882). At the block 1010D, the CU sends a second CU-to-DU message to the second DU, the second CU-to-DU message including the cell IDs N+1, …, N+M, the cell indexes N+1, …, N+M, and the second LTM group ID to request the cells N+1, …, N+M for the UE to prepare for the LTM, where M is a positive integer, the cell IDs N+1, …, N+M identify the cells N+1, …, N+M, respectively, and the cell indexes N+1, …, N+M index the cells N+1, …, N+M, respectively (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 682, 780, 790, 781, 782, 880, 890, 881, 882).

[0302] In some implementations, FIG. 10B the CU, the first DU, and the second DU in FIG. 10B may be the CU, the first DU, and the second DU in FIG. 11B , respectively. Thus, the description for 9A, FIG. 11C may apply to FIG. 10C , and the description for FIG. 10C may apply to 9A, FIG. 10C , and FIG. 11C . FIG. 11D FIG. 10D

[0303] FIG. 10D An example method 1100A for configuring LTM for a UE (e.g., UE102) is shown, which can be implemented by a CU (e.g., CU 172 of base station 104 or 106).

[0304] Method 1100A begins with box 1102A, where CU performs... FIG. 10D Boxes 1002A, 1004A, 1006, and 1008 within the range. At box 1104A, the CU performs... FIG. 11D Boxes 1010A, 1012, 1014, and 1016 in the diagram. At box 1106, the CU sends a CU-DU message (e.g., events 412, 493, 480, 680, 693, 880, 893) to the UE's serving DU, including cell indices 1, ..., N. At box 1108, the CU sends a CU-DU message (e.g., events 412, 493, 480, 680, 693, 880, 893) to the second DU, including cell indices 1, ..., N. At box 1110, the CU sends a CU-DU message (e.g., events 412, 493, 480, 680, 693, 880, 893) to the UE's serving DU, including cell indices N+1, ..., N+M. The serving DU in box 1110 may be the same as or different from the serving DU in box 1106. At box 1112, the CU sends a CU-DU message (e.g., events 412, 493, 480, 680, 693, 880, 893) to the first DU, including cell indices N+1, ..., N+M.

[0305] Using method 1100A, the CU can send one or more cell indices for the UE to one or more other DUs. When one of the DUs is or becomes the serving DU, the serving DU can send an LTM command to the UE, including one of the cell indices, to instruct the UE to perform a serving cell change to the cell identified by the cell index included in the LTM command.

[0306] against FIG. 12 The description is applicable to FIG. 9AIf the first DU is the serving DU of block 1106, block 1106 can be omitted. If the serving DU of block 1106 is the second DU, block 1110 is omitted. In such cases, the CU-to-DU message of block 1106 can be the second CU-to-DU message in block 1010A or different from the second CU-to-DU message in block 1010A. If the serving DU of block 1110 is the first DU, block 1112 can be omitted. In such cases, the CU-to-DU message of block 1110 can be the first CU-to-DU message in block 1010A or different from the first CU-to-DU message in block 1010A. If the serving DU of block 1110 is the second DU, block 1110 can be omitted.

[0307] In some implementations, the "cell index" in the blocks can be replaced with an "LTM ID."

[0308] FIG. 11A is a flowchart of an example method 1100B similar to method 1100A. Method 1100B starts at block 1102B, where the CU performs FIG. 9A blocks 1002B, 1004B, 1007, and 1008 in block 1104B. At block 1104B, the CU performs FIG. 11A blocks 1010B, 1012, 1015, and 1016 in block 1107. At block 1107, the CU sends a CU-to-DU message (e.g., events 412, 493, 480, 680, 693, 880, 893) to the serving DU of the UE including the first LTM group ID and cell indexes 1,..., N. At block 1109, the CU sends a CU-to-DU message (e.g., events 412, 493, 480, 680, 693, 880, 893) to the second DU including the first LTM group ID and cell indexes 1,..., N. At block 1111, the CU sends a CU-to-DU message (e.g., events 412, 493, 480, 680, 693, 880, 893) to the serving DU of the UE including the second LTM group ID and cell indexes N+1,..., N+M. The serving DU in block 1111 can be the same or different from the serving DU in block 1106. At block 1113, the CU sends a CU-to-DU message (e.g., events 412, 493, 480, 693, 893) to the first DU including the second LTM group ID and cell indexes N+1,..., N+M.

[0309] With method 1100B, the CU can send one or more LTM group IDs and one or more cell indexes for other DUs of the UE to one or more DUs. Each of the LTM group IDs is associated with a particular DU of the other DUs. When one of the DUs is or becomes the serving DU, the serving DU can send an LTM command including one of the cell indexes to the UE to command the UE to perform a serving cell change to a cell identified by the LTM group ID and the cell index included in the LTM command.

[0310] The description for FIG. 12 may apply to FIG. 13 . If the first DU is the serving DU of block 1107, block 1107 can be omitted. If the serving DU of block 1107 is the second DU, block 1109 is omitted. In such cases, the CU-to-DU message of block 1107 can be or be different from the second CU-to-DU message in block 1010B. If the serving DU of block 1111 is the first DU, block 1113 can be omitted. In such cases, the CU-to-DU message of block 1111 can be or be different from the first CU-to-DU message in block 1010B. If the serving DU of block 1111 is the second DU, block 1111 can be omitted.

[0311] FIG. 9B to FIG. 9D is a flowchart of an example method 1100C similar to method 1100B, except that method 1100C includes blocks 1102C and 1104C instead of blocks 1102B and 1104B. In block 1102C, the CU performs blocks 1002C, 1004C, 1007, and 1008 in FIG. 11B to FIG. 11D . At block 1104C, the CU performs blocks 1010C, 1013, 1015, and 1016 in FIG. 9B to FIG. 9D . The description for FIG. 11B to FIG. 11D may apply to FIG. 13 .

[0312] ​ is a flowchart of an example method 1100D similar to method 1100B, except that method 1100D includes blocks 1102D and 1104D instead of blocks 1102B and 1104B. In block 1102D, the CU performs blocks 1002D, 1004A, 1007, and 1008 in ​ . At block 1104D, the CU performs blocks 1010D, 1012, 1015, and 1016 in ​ . The description for ​ may apply to ​ .

[0313] ​An example method 1200 for configuring and triggering LTM for a UE (e.g., UE 102) implementable by a DU (e.g., a DU 174 of a base station 104 or 106) is shown.

[0314] The method 1200 starts with block 1202 where the DU receives, from the CU, at least one CU-to-DU message including cell IDs 1,..., N and cell indexes 1,..., N for the UE, where N is a positive integer, the cell IDs 1,..., N identify cells 1,..., N, respectively, and the cell indexes 1,..., N index the cells 1,..., N, respectively (e.g., events 412, 493, 480, 680, 693, 880, 893). At block 1204, the DU receives, from the UE, at least one measurement result for cell 1 (identified by cell ID 1) (e.g., events 324, 380, 424, 480, 580, 524, 581, 582, 680, 624, 681, 682, 780, 724, 781, 782, 880, 824, 881, 882). At block 1206, the DU sends, to the UE, an LTM command including cell index 1 (e.g., events 330, 380, 480, 430, 580, 530, 581, 582, 680, 630, 681, 682, 780, 730, 781, 782, 880, 830, 881, 882).

[0315] In some implementations, the DU can be a DU described in ​ In some implementations, the DU can be a serving DU, a first DU, or a second DU described in ​ In some implementations, the DU can be a serving DU, a first DU, or a second DU described in ​ The description for ​ may apply to ​ In some implementations, the at least one CU-to-DU message includes a UE context modification request message. In some implementations, the DU sends a DU-to-CU message in response to an instruction of the at least one CU-to-DU message. For example, the DU-to-CU message is a UE context modification response message. In some implementations, the at least one CU-to-DU message includes LTM configurations 1,..., N respectively configuring the cell IDs 1,..., N.

[0316] In some implementations, the at least one CU-to-DU message includes LTM IDs 1,..., N identifying the LTM configurations 1,..., N instead of LTM cell indexes 1,..., N indexing the cell IDs 1,..., N. In such cases, the DU includes the LTM ID 1 instead of the cell index 1 in the LTM command.

[0317] ​An example method 1300 for configuring and triggering LTM for a UE (e.g., UE 102) implementable by a DU (e.g., a DU 174 of a base station 104 or 106) is shown.

[0318] The method 1300 starts from block 1302, where the DU receives, from the CU, at least one CU-to-DU message including a first LTM group ID for the UE, cell IDs 1, …, N, and cell indices 1, …, N, where N is a positive integer, the cell IDs 1, …, N identify cells 1, …, N, respectively, and the cell indices 1, …, N index the cells 1, …, N, respectively (e.g., events 412, 493, 480, 680, 693, 880, 893). At block 1303, the DU receives, from the CU, at least one CU-to-DU message including cell IDs N+1, …, N+M, cell indices 1, …, M, and a second LTM group ID for the LTM of the UE, where M is a positive integer, the cell IDs N+1, …, N+M identify cells N+1, …, N+M, respectively, and the cell indices N+1, …, N+M index the cells N+1, …, N+M, respectively.

[0319] At block 1304, the DU receives, from the UE, at least one measurement result for cell 1 (identified by cell ID 1) (e.g., events 324, 380, 424, 480, 580, 524, 581, 582, 680, 624, 681, 682, 780, 724, 781, 782, 880, 824, 881, 882). At block 1306, the DU sends, to the UE, an LTM command including the first LTM group ID and the cell index 1 (e.g., events 330, 380, 480, 430, 580, 530, 581, 582, 680, 630, 681, 682, 780, 730, 781, 782, 880, 830, 881, 882).

[0320] In some implementations, the DU can be a DU described in ​ In some implementations, the DU can be a serving DU, a first DU, or a second DU described in ​ The descriptions of ​ and ​ may apply to ​ .

[0321] In some implementations, the at least one first CU-to-DU message includes LTM IDs 1,..., N that identify LTM configurations 1,..., N instead of LTM cell indexes 1,..., N that index the cell IDs 1,..., N. In such cases, the DU includes the LTM ID 1 instead of the cell index 1 in the LTM command. In some implementations, the at least one second CU-to-DU message includes LTM IDs N+1,..., N+M that identify LTM configurations N+1,..., N+M instead of LTM cell indexes N+1,..., N+M that index the cell IDs 1,..., N.

[0322] The following description can apply to the above description.

[0323] In general, the description for one of the above figures can apply to another of the above figures. The examples, implementations, and methods described above can be combined if not contradictory. The events or blocks described above can be optional or omitted. For example, events or blocks in dashed lines in the figures can be optional. In some implementations, “message” is used and can be replaced with “information element (IE)” and vice versa. In some implementations, “IE” is used and can be replaced with “field” and vice versa. In some implementations, “configuration” can be replaced by “configurations” or “configuration parameters” and vice versa. In some implementations, “LTM command” can be replaced by “serving cell change command,” “layer 1 / layer 2 handover command,” “lower layer handover command,” or “lower layer serving cell change command.” In some implementations, “some” means “one or more.” In some implementations, “at least one” means “one or more.” In some implementations, “DU configuration” can be replaced by “cell group configuration.” In some implementations, “cell index” can be replaced by “candidate cell index,” “serving cell index,” “LTM cell index,” “special cell (SpCell) index,” “PCell index,” or “PSCell index.” In some implementations, “cell ID” can be replaced by a name such as “candidate cell ID,” “serving cell ID,” “SpCell ID,” “LTM cell ID,” “pCell ID,” or “PSCell ID.” In some implementations, “cell ID” and “cell ID” in CU-to-DU messages can be replaced by different names listed above.

[0324] A user device (e.g., UE 102) in which the techniques of this disclosure can be implemented can be any suitable device capable of wireless communication, such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, in some cases, a user device can be embedded in a host unit such as a vehicle or an electronic system of an advanced driver assistance system (ADAS). Still further, a user device can operate as an Internet of Things (IoT) device or a Mobile Internet Device (MID). Depending on the type, a user device can include one or more general-purpose processors, computer-readable memory, a user interface, one or more network interfaces, one or more sensors, and the like.

[0325] Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules can be software modules (e.g., code, or machine-readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and can be configured or arranged in a certain manner. A hardware module can include dedicated circuitry or logic that is permanently configured to perform certain operations, such as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc. A hardware module can also include programmable logic or circuitry that is temporarily configured by software to perform certain operations, such as

[0326] When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software can be executed by one or more general-purpose processors or one or more special-purpose processors.

[0327] The term “or” as used herein is to be interpreted as an inclusive or, meaning any one or any combination of the listed items. Thus, in the phrase “A or B” recited herein, for example, the phrase means “A, B, or both A and B.” In other words, the phrase “A or B” means “any of the following: A, B, or both A and B.”

[0328] Those skilled in the art will appreciate that additional and alternative structural and functional designs for handling mobility between base stations by the principles disclosed herein will occur to those skilled in the art upon reading the present disclosure. Accordingly, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations which will be obvious to those skilled in the art can be made in the arrangement, operation and details of the methods and devices disclosed herein without departing from the spirit and scope defined in the following claims.

Claims

1. A method implemented in a central unit, CU, of a distributed base station, the method comprising: sending, to a distributed unit, DU, of the distributed base station, a CU-to-DU message related to lower tier triggered mobility, LTM, for a user equipment, UE, connected to the distributed base station, the CU-to-DU message comprising a cell identifier, ID, of a candidate cell; receiving, from the DU, a DU-to-CU message in response to the CU-to-DU message, the DU-to-CU message comprising (i) an LTM configuration for the candidate cell and (ii) the cell ID; and sending, to the UE via the DU, the LTM configuration.

2. The method of claim 1, wherein the candidate cell is associated with the DU.

3. The method of claim 2, wherein: the CU-to-DU message comprises a UE context modification request message; and the DU-to-CU message comprises a UE context modification response message.

4. The method of claim 1, wherein: the DU is a first DU, and the candidate cell is associated with a second DU of the distributed base station.

5. The method of claim 4, wherein: the CU-to-DU message comprises a UE context setup request message; and the DU-to-CU message comprises a UE context setup response message.

6. The method of any of the preceding claims, wherein the CU-to-DU message further comprises: an index of the candidate cell.

7. The method of claim 6, wherein the index is a serving cell index.

8. The method of any of claims 1-5, wherein the CU-to-DU message further comprises an LTM ID identifying the LTM configuration.

9. The method of any of claims 1-5, further comprising: sending, to the UE via the DU, an LTM ID.

10. The method of claim 9, wherein: the LTM configuration and the LTM ID are included in a radio resource control, RRC, reconfiguration message.

11. A method implemented in a distributed unit, DU, of a distributed base station, the method comprising: receiving, from a central unit, CU, of the distributed base station, a CU-to-DU message related to lower tier triggered mobility, LTM, for a user equipment, UE, connected to the distributed base station, the CU-to-DU message comprising a cell identifier, ID, of a candidate cell associated with the DU; sending, from the DU, a DU-to-CU message in response to the CU-to-DU message, the DU-to-CU message comprising (i) an LTM configuration for the candidate cell and (ii) the cell ID; receiving, from the CU, the LTM configuration for the UE; and sending, to the UE, the LTM configuration.

12. The method of claim 11, wherein: the CU-to-DU message comprises a UE context modification request message; and the DU-to-CU message comprises a UE context modification response message.

13. The method of claim 11, wherein: the CU-to-DU message comprises a UE context setup request message; and the DU-to-CU message comprises a UE context setup response message. The DU-to-CU message comprises a UE context setup response message.

14. The method of any one of claims 11 to 13, wherein the CU-to-DU message further comprises an LTM ID identifying the LTM configuration.

15. A radio access network, RAN, node comprising processing hardware and configured to implement the method of any one of the preceding claims.

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