Distributed unit, central unit, wireless terminal, and methods therefor

Abstract

In the present invention, a distributed unit (DU) of a radio access network (RAN) node receives, from a central unit (CU) of the RAN node, a first message for requesting preparation of a first candidate cell for L1 / L2-triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells that include the first candidate cell. The DU determines, on the basis of whether or not the first message includes a first display which is related to a conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM which has been requested by the first message are the subject of the conditional LTM or the subject of a normal LTM. This is useful for providing, for example, details of the operations of the CU and a candidate DU for preparing the conditional LTM.

Description

Distributed unit, central unit, wireless terminal, and methods thereof

[0001] TECHNICAL FIELD The present disclosure relates to wireless communication systems, and more particularly to mobility of wireless terminals.

[0002] The 3rd Generation Partnership Project (3GPP®) Release 18 specifies mechanisms and procedures for Layer-1 (L1) / Layer-2 (L2) Triggered Mobility (LTM) (see, for example, Non-Patent Documents 1-6). When a wireless terminal (i.e., User Equipment (UE)) in the Radio Resource Control (RRC)_CONNECTED state moves from the coverage area of ​​one cell to another, a serving cell change must be performed at some point. The serving cell change, as specified in 3GPP Release 17 and earlier, is triggered by Layer-3 (L3) measurements and involves reconfiguration with synchronization triggered by RRC signaling for the change of Primary Cell (PCell) and Primary Secondary Cell Group (SCG) Cell (PSCell), and the release and addition of Secondary Cells (SCells), if applicable.

[0003] In contrast, LTM is a procedure in which a base station (i.e., gNB) receives L1 measurement reports from a UE and, based on these, the gNB changes one or more serving cells of the UE through L2 signaling, specifically, Medium Access Control (MAC) Control Element (MAC CE). The gNB prepares one or more candidate cells and provides the candidate cell configurations to the UE through an RRC message. An LTM cell switch is triggered when the gNB selects one of the candidate cell configurations as the target configuration for LTM. The gNB then sends a Cell Switch Command MAC CE to the UE. The Cell Switch Command MAC CE indicates the target configuration selected by the gNB (which corresponds to one target cell). In response to receiving the Cell Switch Command MAC CE, the UE initiates a cell switch to the target cell. The UE performs a Random Access Channel (RACH)-less LTM cell switch or a RACH-based LTM cell switch. Subsequent LTM between candidate cells (i.e., after LTM is triggered, the UE does not release other candidate cell configurations) can be performed without RRC reconfiguration. Candidate cell configurations can be added, modified, or released only by the network (i.e., gNB) via RRC signaling.

[0004] LTM supports both intra-gNB Distributed Unit (gNB-DU) mobility and intra-gNB-CU inter-gNB-DU mobility. LTM supports not only intra-frequency mobility but also inter-frequency mobility. LTM supports the following scenarios: PCell change in non-Carrier Aggregation (CA) scenario; PCell change without SCell change in CA scenario; PCell change with SCell change in CA scenario; and Dual Connectivity scenario. PCell change with SCell change in CA scenario includes a) the case where the target PCell or target SCell(s) is not the current serving cell (i.e., CA-to-CA scenario with PCell change), b) the case where the target PCell is the current SCell, and c) the case where the target SCell is the current PCell. The Dual Connectivity scenario includes at least a PSCell change without MN involvement.

[0005] Non-Patent Document 2 discloses inter-gNB-DU LTM, i.e., a procedure for LTM in which a UE moves from one gNB-DU to another within the same gNB-CU. The gNB-CU receives an L3 measurement report from the UE and decides to initiate LTM preparation (or LTM configuration). The gNB-CU sends one or more UE CONTEXT SETUP REQUEST messages to a candidate gNB-DU regarding the preparation of one or more candidate cells. If multiple candidate cells are prepared, the gNB-CU uses multiple UE Context Setup procedures, each for one candidate cell. If the candidate gNB-DU accepts the LTM configuration request, it responds to the gNB-CU with one or more UE CONTEXT SETUP RESPONSE messages. Each of the one or more UE CONTEXT SETUP RESPONSE messages contains RRC configuration for a corresponding accepted candidate cell.

[0006] Non-Patent Document 6 proposes an improvement to support LTM for F1 Application Protocol (F1AP) messages sent from a gNB-CU to a gNB-DU. Specifically, Non-Patent Document 6 discloses that a UE CONTEXT SETUP REQUEST message sent from a gNB-CU to a gNB-DU may include an LTM Information Setup information element (IE), an LTM Configuration ID Mapping List IE, an Early Sync Information Request IE, and a Source gNB-DU ID IE. In addition, Non-Patent Document 6 discloses that a UE CONTEXT MODIFICATION REQUEST message sent from a gNB-CU to a gNB-DU may include an LTM Information Modify IE, an LTM Configuration ID Mapping List IE, an Early Sync Information Request IE, an Early Sync Information List IE, and an LTM Cells To Be Released List IE. Furthermore, non-patent document 6 discloses that the UE CONTEXT SETUP RESPONSE and UE CONTEXT SETUP RESPONSE messages sent from the gNB-DU to the gNB-CU may include an Early Sync Information IE and an LTM Configuration IE.

[0007] 3GPP plans to consider extensions to LTM for 3GPP Release 19 (see, for example, Non-Patent Document 7). LTM extensions under consideration include conditional LTM (CLTM), which may also be called by other names such as UE triggered LTM. 3GPP aims to support CLTM, which includes defining the conditions to be evaluated by the UE to trigger CLTM (CLTM execution).

[0008] Non-Patent Documents 8-11 disclose findings and proposals regarding CLTM. Non-Patent Document 8 states that when CLTM is introduced, the LTM mechanisms of 3GPP Release 18, such as UE-based TA (not early TA) and RACH-less operation, can be reused to perform handover with low latency.

[0009] Non-Patent Document 9 describes the features and advantages of conditional reconfiguration, i.e., L3 conditional mobility, and states that CLTM can be considered to improve robustness. Non-Patent Document 9 discloses that potential enhancements for CLTM include L1 measurement-based execution conditions and enhanced procedures such as early TA acquisition.

[0010] Non-Patent Document 10 states that CLTM, i.e., UE-initiated LTM execution based on configured conditions, can be effective in improving the robustness of LTM. Non-Patent Document 10 includes the following description regarding CLTM: The UE autonomously executes LTM when configured conditions are met. The configured conditions relate to, for example, L1 / L2-based triggers and Beam Failure Detection (BFD). For CLTM execution, resources to be used in the target cell may be specified regardless of whether source cell notification is received. The resources to be used in the target cell include, for example, configured Scheduling Request (SR), Sunding Reference Signal (SRS), or Configured Grant (CG), and Dynamic Grant (DG) for the intra-DU case. For target cell synchronization, early synchronization (before conditional LTM is performed) may be required, which can be UE-based synchronization or an early LTM RACH with a Random Access Response (RAR) or MAC CE providing TA.

[0011] Non-Patent Document 11 includes the following description regarding CLTM: Applicable CLTM scenarios include Contention-Based Random Access (CBRA)-based CLTM, Contention-Free RA (CFRA)-based CLTM, and RACH-less CLTM. For CFRA-based CLTM, provisioning and validity management of CFRA resources need to be considered. For RACH-less CLTM, both RA-based and UE-based TA acquisition are supported for early TA acquisition. For RA-based early TA acquisition, RA including RAR is used as the baseline. For beam indication, pre-beam indication from the network is considered. In CLTM, it is important to reduce candidate cell management operations. For example, it is possible to reduce Channel State Information (CSI)-related operations and TA acquisition operations based on L3 measurements of candidate cells. Regarding the coexistence of 3GPP Release 18 LTM and CLTM, dynamic activation of CLTM evaluation for configured candidate cells is considered.

[0012] MediaTek Inc., vivo, "Introduction of NR further mobility enhancements in TS 38.300", R2-2313832, 3GPP TSG-RAN WG2 Meeting #124, Chicago, USA, November 13-17, 2023Huawei, Ericsson, Nokia, Nokia Shanghai Bell, ZTE, NEC, LG Electronics, Lenovo, Samsung, CATT, Google, "Introduction of L1L2Mob and S-CPAC", R3-238088, 3GPP TSG-RAN WG3 Meeting #122, Chicago, USA, November 13-17, 2023ZTE Corporation, Sanechips, CATT, "Introduction of NR further mobility enhancements in TS 37.340", R2-2313647, 3GPP TSG-RAN WG2 Meeting #124, Chicago, USA, November 13-17, 2023Ericsson, "Introduction of further NR mobility enhancements", R2-2314056, 3GPP TSG-RAN WG2 Meeting #124, Chicago, USA, November 13-17, 2023Huawei, HiSilicon, "Introduction of NR further mobility enhancements in TS 38.321", R2-2314040, 3GPP TSG-RAN WG2 Meeting #124, Chicago, USA, November 13-17, 2023Ericsson, Huawei, Nokia, Nokia Shanghai Bell, ZTE, NEC, LG Electronics Inc., Lenovo, CATT, Samsung, Qualcomm Incorporated, "Additions for L1 / L2 triggered mobility", R3-238152, 3GPP TSG-RAN WG3 Meeting #122, Chicago, USA, November 13-17, 2023Intel, "New WID: NR mobility enhancements Phase 4", RP-234036, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023Samsung, "Scope of Mobility Enhancements in Rel-19", RP-232916, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023vivo, "Views on Rel-19 Mobility enhancements (RAN2-led)", RP-233056, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023Qualcomm Incorporated, "Views on scope for NR Mobility enhancements in Rel-19", RP-233214, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023LG Electronics, " Work scope of mobility enhancements in Rel-19", RP-233466, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023.

[0013] The inventors have considered supporting CLTM in cellular networks and have found various challenges. One of these challenges relates to signaling between a CU (e.g., gNB-CU) and a DU (e.g., gNB-DU) for CLTM. It is currently unclear how a CU and one or more DUs operate to prepare for CLTM between multiple candidate cells.

[0014] One of the objectives of the embodiments disclosed herein is to provide an apparatus, a method, and a program that contribute to solving at least one of the problems related to CLTM, including the problems described above. It should be noted that this objective is only one of the objectives of the embodiments disclosed herein. Other objectives or objectives and novel features will become apparent from the description of this specification or the accompanying drawings.

[0015] A first aspect is directed to a distributed unit (DU) of a Radio Access Network (RAN) node, the DU being configured to receive, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for a long-term mobile station (LTM) of a wireless terminal among multiple candidate cells including the first candidate cell, and to determine whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.

[0016] A second aspect is directed to a method performed by a DU of a RAN node, the method including the steps of: (a) receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for LTM of a wireless terminal among a plurality of candidate cells including the first candidate cell; and (b) the DU determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM.

[0017] A third aspect is directed to a CU of a RAN node, configured to send a first message to a DU of the RAN node requesting preparation of a first candidate cell for LTM of a wireless terminal among multiple candidate cells including the first candidate cell, the first message indicating to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.

[0018] A fourth aspect is directed to a method performed by a CU of a RAN node, the method including sending a first message to a DU of the RAN node requesting preparation of a first candidate cell for LTM of a radio terminal among a plurality of candidate cells including the first candidate cell, the first message indicating to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.

[0019] A fifth aspect is directed to a wireless terminal configured to evaluate an execution condition for conditional LTM for each of one or more candidate cells. The wireless terminal is configured to perform a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell. For the cell switch, the wireless terminal is configured to determine whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for the one candidate cell for which the execution condition is determined to be met was used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.

[0020] A sixth aspect is directed to a method performed by a wireless terminal, the method including: (a) evaluating an execution condition for conditional LTM for each of one or more candidate cells; and (b) performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell, wherein performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for the one candidate cell for which the execution condition is determined to be met was used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.

[0021] A seventh aspect is directed to a program, which includes a set of instructions (software code) that, when loaded into a computer, causes the computer to perform the method according to the second, fourth, or sixth aspect.

[0022] According to the above-described aspects, it is possible to provide an apparatus, a method, and a program that contribute to solving at least one of a plurality of problems related to CLTM, including the above-described problems.

[0023] 1 illustrates an example configuration of a wireless communication system according to one or more embodiments. 2 illustrates an example configuration of a wireless communication system according to one or more embodiments. 3 illustrates an example signaling procedure for LTM according to one or more embodiments. 4 illustrates an example signaling procedure for conditional LTM according to one or more embodiments. 5 illustrates a flowchart of an example DU operation according to one or more embodiments. 6 illustrates a flowchart of an example CU operation according to one or more embodiments. 7 illustrates an example signaling between a CU and a candidate DU according to one or more embodiments. 8 illustrates an example format of a UE CONTEXT SETUP REQUEST message according to one or more embodiments. 9 illustrates an example format of a UE CONTEXT SETUP REQUEST message according to one or more embodiments. 10 illustrates an example format of a UE CONTEXT SETUP REQUEST message according to one or more embodiments. 11 illustrates an example format of a UE CONTEXT SETUP REQUEST message according to one or more embodiments. 12 illustrates an example format of a DU to CU RRC Information information element according to one or more embodiments. 13 illustrates an example format of a UE CONTEXT SETUP RESPONSE message according to one or more embodiments.

[0023] Figure 1 illustrates an example of signaling between a CU, a source DU, and a candidate DU, in accordance with one or more embodiments.

[0024] Figure 2 illustrates an example of signaling between a CU and a candidate DU, in accordance with one or more embodiments.

[0025] Figure 3 illustrates a flowchart of an example of UE operation, in accordance with one or more embodiments.

[0026] Figure 4 illustrates a block diagram of an example configuration of a CU, a CU-CP, a CU-UP, and a DU, in accordance with one or more embodiments.

[0027] Figure 5 illustrates a block diagram of an example configuration of a UE, in accordance with one or more embodiments.

[0024] Hereinafter, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary.

[0025] The multiple embodiments described below may be used independently, or two or more embodiments may be combined as appropriate. These multiple embodiments may have different novel features. Therefore, these multiple embodiments may contribute to achieving different objectives or solving different problems, and may contribute to achieving different effects.

[0026] Each drawing is merely an example for describing one or more embodiments. Each drawing may not relate to only one particular embodiment, but may also relate to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0027] The following embodiments are described primarily for the 3GPP 5th generation mobile communication system (5G system), but may also be applied to other wireless communication systems that support technologies similar to 3GPP LTM.

[0028] As used herein, depending on the context, "if" may be interpreted to mean "when," "while," "at or around the time," "after," "upon," "in response to determining," "in accordance with a determination," or "in response to detecting." These expressions may be interpreted to have the same meaning, depending on the context.

[0029] First, the configurations and operations of several network elements common to several embodiments will be described. Figure 1 shows an example configuration of a wireless communication system related to several embodiments. In the example of Figure 1, the wireless communication system includes a gNB-CU 10, gNB-DUs 21 and 22, TRPs 31 to 34, and a UE 40. The UE 40 may also be referred to by other terms such as a radio terminal, a mobile terminal, a mobile station, or a wireless transmit receive unit (WTRU). Each element (network function) shown in Figure 1 can be implemented, for example, as a network element on dedicated hardware, as a software instance running on dedicated hardware, or as a virtualized function instantiated on an application platform.

[0030] The gNB-CU10 and gNB-DUs 21 and 22 correspond to one gNB1. In other words, the gNB1 includes the gNB-CU10 and the gNB-DUs 21 and 22. Alternatively, the gNB1 includes the TRPs 31 to 34 in addition to the gNB-CU10 and the gNB-DUs 21 and 22. The gNB1 is an NG-RAN node. The gNB1 may also be referred to as a RAN node, a base station, a radio station, or an access point. The gNB-CU10, the gNB-DUs 21 and 22, and the TRPs 31 to 34 may also be referred to as a RAN node.

[0031] The gNB1 may be an en-gNB, which provides NR user plane and control plane protocol termination to the UE and operates as a secondary node for Evolved Universal Terrestrial Radio Access (E-UTRA)-NR Dual Connectivity (EN-DC).

[0032] The gNB-CU10 is a logical node that controls the operation of one or more gNB-DUs (e.g., gNB-DUs 21 and 22). The gNB-CU10 hosts the RRC, Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols of the gNB1 (or the RRC and PDCP protocols of the gNB). If the gNB1 is an en-gNB, the gNB-CU10 hosts the RRC and PDCP protocols of the en-gNB. The gNB-CU10 may include a Control Plane (CP) Unit (i.e., gNB-CU-CP) and one or more User Plane (UP) Units (i.e., gNB-CU-UPs).

[0033] Each of the gNB-DUs 21 and 22 is a logical node that hosts the Radio Link Control (RLC) layer and MAC layer of the gNB1 and hosts part of the gNB1's Physical (PHY) layer, i.e., the upper PHY layer. The remaining PHY layer signal processing, i.e., the lower PHY layer, is located in the TRPs 31 to 34. One gNB-DU supports one or more cells. One cell is supported by only one gNB-DU. In the example of FIG. 1, the gNB-DU 21 is connected to the TRPs 31 and 32, while the gNB-DU 22 is connected to the TRPs 33 and 34. The TRPs 31 to 34 provide separate cells 51 to 54, respectively. In other words, the gNB-DU 21 provides multiple cells 51 and 52, and the TRPs 31 and 32 correspond to the cells 51 and 52, respectively. Similarly, gNB-DU 22 provides multiple cells 53 and 54, and TRPs 33 and 34 correspond to cells 53 and 54, respectively.

[0034] Each of the TRPs 31-34 can communicate with the UE 40 using a beam. The TRPs 31-34 may also be referred to as Radio Units (RUs) or Remote Radio Heads (RRHs). Each of the TRPs 31-34 provides lower PHY layer signal processing and analog Radio Frequency (RF) signal processing. Each TRP includes or is connected to one or more antenna arrays. Each TRP has multiple RF chains equal to or less than the total number of antenna elements included in the one or more antenna arrays. Each TRP also includes a Digital Front End (DFE). The DFE provides lower PHY layer signal processing and digital radio signal processing. The lower PHY layer signal processing includes, for example, fast Fourier transform (FFT) and inverse FFT (IFFT). The lower PHY layer signal processing may further include cyclic prefix (CP) addition and removal, and physical RACH (PRACH) extraction or filtering. Digital radio signal processing may include, for example, digital pre-distortion (DPD), crest factor reduction (CFR), digital up-conversion (DUC), digital down-conversion (DDC), and transmit and receive baseband channel filters. The DFE may perform digital baseband precoding for beamforming. If a hybrid beamforming scheme is employed, an analog beamformer circuit or analog precoder (e.g., a phase shifter matrix) may be located between one or more antenna arrays and multiple RF chains.

[0035] The interface between the gNB-CU 10 and each of the gNB-DUs 21 and 22 is an F1 interface. A direct interface, connection, or backhaul may be provided to communicatively connect the gNB-DU 21 and the gNB-DU 22. Similarly, a direct interface, connection, or backhaul may be provided to communicatively connect two TRPs serving adjacent cells, for example, between TRPs 31 and 32, between TRPs 32 and 33, and between TRPs 33 and 34.

[0036] Figure 2 shows an example configuration of a gNB1. In the example of Figure 2, the gNB-CU10 includes a gNB-CU-CP11 and one or more gNB-CU UPs 12. The gNB-CU-CP11 is a logical node that hosts the control plane portion of the gNB-CU10's RRC and PDCP protocols. The gNB-CU-CP11 terminates an E1 interface connected to each gNB-CU-UP and an F1-C interface connected to each gNB-DU. The E1 interface uses the E1 Application Protocol (E1AP). The F1-C interface uses the F1 Application Protocol (F1AP). The gNB-CU-CP11 also terminates an NG-C interface connected to a control plane node (i.e., Access and Mobility management Function (AMF)) in the core network.

[0037] The gNB-CU-UP 12 is a logical node that hosts the user plane portion of the PDCP protocol of the gNB-CU 10 for the en-gNB, or the user plane portion of the PDCP protocol and the SDAP protocol of the gNB-CU 10 for the gNB. The gNB-CU-UP 12 terminates the E1 interface connected to the gNB-CU-CP 11 and the F1-U interface connected to each gNB-DU. The F1-U interface uses a General Packet Radio Service Tunneling Protocol User Plane (GTP-U) tunnel. The gNB-CU-UP 12 also terminates the NG-U interface connected to a user plane node (i.e., User Plane Function (UPF)) in the core network.

[0038] The gNB1 and the UE 40 support LTM (normal LTM and CLTM). In this specification, the term "LTM" refers to a broad concept that includes both normal LTM (normal LTM) and conditional LTM. The term "normal LTM (or normal LTM)" refers to non-conditional LTM as defined in 3GPP Release 18. Specifically, normal LTM is an LTM in which the UE 40 performs an LTM cell switch in response to the UE 40 receiving a layer 1 or layer 2 cell switch command from a source DU. In contrast, in CLTM, the UE 40 evaluates an execution condition set by the network, and performs an LTM cell switch in response to the UE 40 determining that the execution condition is met.

[0039] Regular LTM is a procedure in which the gNB1 receives L1 measurement reports from the UE 40 and, based on the reports, changes one or more serving cells (e.g., cell groups) of the UE 40 through L1 or L2 signaling (e.g., MAC CE). The gNB1 prepares one or more candidate cells and provides candidate cell configurations to the UE 40 through an RRC message. Then, the gNB1 selects one of the candidate cell configurations as a target configuration for regular LTM, triggering an LTM cell switch. Candidate cell configurations can only be added, changed, or released by the network (i.e., the gNB1) via RRC signaling. However, as an exception, the UE 40 may autonomously release or remove at least some of the candidate cell configurations only in certain circumstances or when certain conditions are met.

[0040] In both regular LTM and CLTM, the LTM candidate cell configuration may be provided on top of the reference configuration or as a delta configuration to the reference configuration. The reference configuration is managed separately from the delta configuration of each candidate cell, and the UE 40 stores the reference configuration as a configuration separate from the delta configuration of each candidate cell. In both regular LTM and CLTM, security is not updated during LTM (or LTM execution or LTM cell switch execution). In both regular LTM and CLTM, subsequent LTM between candidate cells (i.e., after LTM is triggered, the UE 40 does not release other candidate cell configurations) can be performed without RRC reconfiguration.

[0041] In both normal LTM and CLTM, the LTM candidate cell configuration includes multiple candidate Transmission Configuration Indicator (TCI) state configurations. Each candidate TCI state configuration indicates a reference signal that serves as a path loss reference for at least one of the Physical Downlink Control Channel (PDCCH), Physical Downlink Shared Channel (PDSCH), Physical Uplink Control Channel (PUCCH), and Physical Uplink Sheared Channel (PUSCH) in the corresponding candidate TCI state.

[0042] The TCI state (or TCI state ID or TCI state setting) indicates the Quasi Co-Location (QCL) relationship between the antenna port used for downlink or uplink transmission and the antenna port used for transmitting a specific reference signal. Two antenna ports are said to be QCLed (Quasi Co-located) if the characteristics of the channel through which symbols on one antenna port are transmitted can be inferred from the channel through which symbols on the other antenna port are transmitted. QCL is an index that indicates the statistical properties of a signal or channel. If two antenna ports or two signals transmitted on these two antenna ports are QCLed, it means that these two signals have passed through similar wireless channels that share similar characteristics in at least one of Doppler shift, Doppler spread, average delay, delay spread, and spatial reception (Rx) parameters. If two antenna ports are QCLed, the two signals transmitted on these two antenna ports can be considered to arrive at the receiver through similar channels. Therefore, if the receiver can detect one signal and know the channel characteristics of that signal, the channel characteristics can help it detect the other signal.

[0043] The specific downlink transmission may be, for example, a PDCCH transmission or a PDSCH transmission. The specific uplink transmission may be, for example, a PUCCH transmission or a PUSCH transmission. The specific reference signal may be, for example, a Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) block (SSB) or a Channel State Information (CSI) Reference Signal (CSI-RS).

[0044] The TCI state indicates, for example, the QCL relationship between the antenna port used for PDSCH transmission and the antenna port used for transmitting a specific SSB or a specific CSI-RS. Additionally or alternatively, the TCI state indicates the QCL relationship between the antenna port used for PDCCH transmission and the antenna port used for transmitting a specific SSB or a specific CSI-RS. In other words, the TCI state indicates, for example, the QCL relationship between the Demodulation Reference Signal (DMRS) port used for demodulating the PDSCH or PDCCH and a specific downlink SSB or CSI-RS port.

[0045] LTM (regular LTM and CLTM) supports both intra-gNB-DU mobility and intra-gNB-CU inter-gNB-DU mobility. LTM supports not only intra-frequency mobility but also inter-frequency mobility. LTM supports the following scenarios: PCell change in a non-CA scenario; PCell change without SCell change in a CA scenario; PCell change with SCell change in a CA scenario; and Dual Connectivity scenario. PCell change with SCell change in a CA scenario includes a) the case where the target PCell or target SCell(s) is not the current serving cell (i.e., CA-to-CA scenario with PCell change), b) the case where the target PCell is the current SCell, and c) the case where the target SCell is the current PCell. Dual Connectivity scenarios include at least a PSCell change without MN involvement.

[0046] The mobility 120 shown in Fig. 1 is intra-DU (intra-DU) LTM. Specifically, the UE 40 moves from the beam of the cell 52 of the TRP32 associated with the same gNB-DU21 to the beam of the cell 51 of the TRP31. In contrast, the mobility 140 shown in Fig. 1 is inter-DU (inter-DU) LTM. Specifically, the UE 40 moves from the beam of the cell 52 of the TRP32 associated with the gNB-DU21 to the beam of the cell 53 of the TRP33 associated with another gNB-DU22.

[0047] Before and after the LTM cell switch, the termination points of radio bearers (e.g., Signaling Radio Bearers (SRBs), Data Radio Bearers (DRBs)) for the UE 40 are fixed at the gNB-CU10 and remain unchanged. One or more QoS flows belonging to the PDU session of the UE 40 pass through the same gNB-CU10 (e.g., gNB-CU-UP) after the LTM cell switch as before the switch. Therefore, radio bearer configurations may be inherited or maintained in the UE 40 and the gNB1 (i.e., gNB-CU10, or gNB-CU10 and the (target) gNB-DU 21 or 22) before and after the LTM. Alternatively, the target gNB-DU (e.g., gNB-DU 22) or gNB-CU10 may have transmitted radio bearer configurations for the target cell to the UE 40 via the source gNB-DU (e.g., gNB-DU 21) during LTM preparation. If UE 40 does not receive explicit radio bearer configuration for after the LTM cell switch from gNB1 (e.g., gNB-CU10 or target gNB-DU), UE 40 may carry over the radio bearer configuration in the serving cell to the target cell after the LTM cell switch. In other words, UE 40 may continue to use the radio bearer configuration in the serving cell in the target cell after the LTM cell switch.

[0048] The control plane handling for normal LTM will be described in more detail below. A cell switch command (or cell switch trigger information) sent by the gNB1 to the UE 40 may be conveyed in a MAC CE (i.e., LTM Cell Switch Command MAC CE). This MAC CE includes at least an index (i.e., Target Configuration ID) of a candidate target configuration associated with a target cell selected by the gNB1 from one or more prepared LTM candidate cells. Simultaneously with the LTM triggered by the MAC CE, activation of one or more SCells associated with the candidate target configuration may be performed. The UE 40 may perform CBRA or CFRA during a cell switch.

[0049] The Cell Switch Command MAC CE is sent by gNB1 to UE 40 to trigger an LTM cell switch by UE 40 to a target cell selected by gNB1. The Cell Switch Command MAC CE includes, among other fields, a Target Configuration ID field, a Timing Advance Command field, a TCI state ID field, an Uplink (UL) TCI state ID field, and a Random Access Preamble index field.

[0050] The Target Configuration ID field indicates the index of the candidate target configuration to be applied to the LTM cell switch. The candidate target configuration is the candidate cell configuration of the target cell selected by gNB1.

[0051] The Timing Advance Command field indicates whether Timing Advance (TA) is valid for the LTM target cell (i.e., the Special Cell (SpCell) corresponding to the target configuration indicated in the Target Configuration ID field). If the value of the Timing Advance Command field is set to FFF, this field indicates that valid timing adjustment is not available for the TA Group (TAG) of the LTM target cell. Otherwise, this field indicates a TA value used to control the amount of timing adjustment that the MAC entity of UE 40 must apply, and indicates that UE 40 can skip the random access procedure for this LTM cell switch.

[0052] The TCI state ID field indicates and activates the TCI state of the LTM target cell (i.e., the SpCell of the target configuration indicated in the Target Configuration ID field). The TCI state indicated by the TCI state ID field is for a joint TCI state or a downlink TCI state. The UL TCI state ID field indicates and activates the uplink TCI state of the LTM target cell.

[0053] The Random Access Preamble index field indicates the random access preamble index of the contention-free random access resources.

[0054] If the UE 40 has a valid Timing Advance (TA) of the target cell and does not need to acquire the TA of the target cell during an LTM cell switch, the UE 40 can skip the random access procedure. An LTM cell switch procedure in which the UE skips the random access procedure is called RACH-less LTM. The UE 40 can acquire the TA through early TA acquisition. Early TA acquisition is triggered by a Physical Downlink Control Channel (PDCCH) order or achieved by UE-based TA measurement.

[0055] In early TA acquisition via a PDCCH order, the gNB1 (e.g., source DU) triggers the UE 40 to perform CFRA to a candidate cell via a PDCCH order via the serving cell. The UE 40 transmits a first random access message (e.g., a random access preamble) to the candidate cell. To minimize data interruption in the serving cell due to the CFRA to the candidate cell, the UE 40 does not monitor or receive a random access response from the candidate cell. The candidate cell does not transmit a random access response to the CFRA. The TA value of the candidate cell is indicated to the UE 40 by the LTM Cell Switch Command MAC CE. Note that the TA value of the candidate cell is indicated in the LTM Cell Switch Command MAC CE only when the candidate cell is selected as a target cell for cell switch. Alternatively, the TA value of the candidate cell may be refined as indicated in the LTM Cell Switch Command MAC CE regardless of whether the candidate cell is selected as a target cell for cell switch.

[0056] UE-based TA measurement is configured by RRC in the UE 40. In UE-based TA measurement, the UE 40 derives the TA of the candidate cell based on the reception timing difference between the current serving cell and the candidate cell and the TA value of the current serving cell.

[0057] 3 shows an example of the overall procedure of normal LTM. Subsequent LTMs are performed by repeating the procedures of early synchronization, LTM execution, and LTM completion without releasing other candidate cell settings after each LTM completion. Note that early synchronization is intended to allow UE 40 to synchronize with a candidate cell before the LTM execution phase and skip the random access procedure in the LTM execution phase. However, early synchronization is optional and does not necessarily have to be performed.

[0058] Steps 301 to 304 are the LTM preparation phase. In step 301, UE 40 in an RRC_CONNECTED state sends an L3 measurement report to gNB1. Specifically, UE 40 transmits a MeasurementReport message to gNB1. The MeasurementReport message indicates L3 measurement results. The MeasurementReport message may indicate measurement results of the serving cell and neighboring cells. The measurement results for each cell include Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), or Signal-to-Interference and Noise Ratio (SINR), or any combination thereof.

[0059] In step 302, based on the L3 measurement report, gNB1 decides to use LTM and starts preparing one or more LTM candidate cells. An LTM candidate cell may also be referred to as an LTM candidate target cell. In step 303, gNB1 sends an RRCReconfiguration message to UE 40, including the configuration of one or more LTM candidate cells. In step 304, UE 40 stores the configuration of one or more LTM candidate cells and sends an RRCReconfigurationComplete message to gNB1.

[0060] Step 305 is the early synchronization phase, in which UE 40 may perform downlink (DL) synchronization and uplink (UL) TA acquisition with one or more candidate cells before receiving the LTM cell switch command.

[0061] Steps 306 to 310 are the LTM execution phase. In step 306, the UE 40 performs L1 measurements on the configured LTM candidate cells and sends L1 measurement reports to the gNB1. The L1 measurement reports may be carried by L1 signaling (e.g., Uplink Control Information (UCI)) or MAC CE. In step 307, the gNB1 decides to perform an LTM cell switch to one of the prepared candidate cells and sends an LTM cell switch command (i.e., LTM Cell Switch Command MAC CE) including an identifier of the target cell (e.g., LTM candidate ID) to the UE 40 (step 308). The LTM switch command includes a Target Configuration ID associated with the target cell, triggering the UE 40 to perform an LTM cell switch. In step 309, the UE 40 switches to the target cell configuration specified by the gNB1. In other words, the UE 40 detaches from the source cell and applies the target cell configuration. In step 310, if a TA is not available, the UE 40 performs a random access procedure towards the target cell.

[0062] Step 311 is the LTM completion phase. The UE 40 completes the LTM cell switch procedure by sending an RRCReconfigurationComplete message to the target cell. Alternatively, if the UE 40 performs a random access procedure in the LTM execution phase, the UE 40 determines that the execution of the LTM cell switch has been successfully completed when the random access procedure has been successfully completed. In the case of RACH-less LTM, the UE 40 determines that the execution of the LTM cell switch has been successfully completed when the UE 40 determines that the network has successfully received the first uplink data.

[0063] 4 shows an example of the overall procedure of CLTM. Subsequent CLTMs are performed by repeating the procedure of early synchronization, CLTM execution, and CLTM completion without releasing other candidate cell settings after each CLTM completion. Note that early synchronization is intended to allow UE 40 to synchronize with a candidate cell before the CLTM execution phase and skip the random access procedure during the CLTM execution phase. However, early synchronization is optional and does not necessarily have to be performed.

[0064] Steps 401 to 404 are the CLTM preparation phase. In step 401, UE 40 in RRC_CONNECTED state sends an L3 measurement report to gNB 1. Step 401 may be the same as step 301 in FIG. 3 .

[0065] In step 402, based on the L3 measurement report, gNB1 decides to use CLTM and starts preparing one or more CLTM candidate cells. A CLTM candidate cell may also be called a CLTM candidate target cell. In step 403, gNB1 sends an RRCReconfiguration message to UE 40, which includes the configuration of one or more CLTM candidate cells and the CLTM execution condition for each candidate cell. In step 404, UE 40 stores the CLTM candidate cell configuration and the CLTM execution condition, and sends an RRCReconfigurationComplete message to gNB1.

[0066] Note that gNB1 may decide to use both regular LTM and CLTM. CLTM cell switch may be used for some of the multiple candidate cells prepared in steps 402 and 403, and regular LTM cell switch may be used for the remaining cells. For example, a CLTM cell switch triggered by UE 40 determining that an execution condition is met may be applied to a cell switch from a source cell (serving cell) or a first candidate cell to another candidate cell, while a regular LTM cell switch triggered by an LTM cell switch command by gNB1 may be applied to a cell switch from a second candidate cell to another candidate cell. In another example, a CLTM cell switch may be applied to a cell switch from a source cell to a first candidate cell, while a regular LTM cell switch may be applied to a cell switch from a source cell to a second candidate cell.

[0067] Additionally or alternatively, CLTM cell switch and normal LTM may be used for the purpose of cell switch from a source cell to the same candidate cell or cell switch between the same candidate cell pair. In this case, UE 40 may perform cell switch triggered by either the satisfaction of a CLTM execution condition or the receipt of an LTM cell switch command from gNB1, whichever occurs first. Note that even when UE 40 performs LTM cell switch triggered by the LTM cell switch command received from gNB1, it also retains CLTM-specific settings (e.g., CLTM execution conditions) for subsequent CLTM.

[0068] Step 405 is an early synchronization phase in which UE 40 may perform DL synchronization and UL TA acquisition with one or more candidate cells. Step 405 may be performed in parallel with step 406, which will be described below.

[0069] Step 406 is a CLTM evaluation phase in which the UE 40 evaluates the CLTM execution conditions of each candidate cell.

[0070] Steps 407 and 408 are CLTM execution phases. In step 407, UE 40 determines that the execution conditions are met for any of the candidate cells and decides to execute a cell switch to the candidate cell. UE 40 detaches from the source cell and applies the target cell configuration. In step 408, if TA is not available, UE 40 executes a random access procedure toward the target cell.

[0071] In some implementations, in step 4071, after determining that an execution condition is met for any candidate cell (i.e., target cell) (and before detaching from the source cell), the UE 40 may transmit L1 or L2 (L1 / L2) signaling to the gNB1 (e.g., source DU) in the source cell. The L1 / L2 signaling includes an identifier or index (e.g., Target Configuration ID) indicating the target cell or a candidate target configuration associated with the target cell. The L1 / L2 signaling in step 4071 may further indicate that the cell switch by the UE 40 using CLTM is performed in a RACH-less or CFRA-based manner. The L1 / L2 signaling may be a MAC CE. The name of the MAC CE may be, for example, CLTM Indication MAC CE or CLTM Triggering Indication MAC CE. Alternatively, the L1 / L2 signaling may be UCI on the PUCCH.

[0072] The L1 / L2 signaling in step 4071 enables UE 40 to inform gNB1 that the CLTM execution condition has been met for the target cell or that a CLTM cell switch to the target cell will be initiated, although step 4071 may be omitted.

[0073] After or in response to receiving the L1 / L2 signaling in step 4071, the source DU may notify the CU of the initiation of a CLTM cell switch. This notification may include the target cell ID. This notification may be performed using an F1AP message, such as a DU-CU CELL SWITCH NOTIFICATION message. Furthermore, the CU may notify a candidate DU (i.e., target DU) serving the target cell of the initiation of a CLTM cell switch to the target cell. The notification from the CU to the target DU may include the target cell ID. This notification may be performed using an F1AP message, such as a CU-DU CELL SWITCH NOTIFICATION message. In other words, the source DU may notify the target DU via the CU of the initiation of a CLTM cell switch to the target cell. These signalings allow the target DU to know that the UE 40 has initiated a CLTM cell switch to the target cell. In other words, these signalings allow the target DU to know that the cell switch to the target cell initiated by the UE 40 is based on CLTM rather than normal LTM.

[0074] Step 409 is the CLTM completion phase, which may be similar to step 311 in FIG.

[0075] <First embodiment> A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Figures 1 and 2. This embodiment provides details of signaling between a CU (e.g., gNB-CU 10) and a DU (e.g., gNB-DUs 21 or 22) performed to prepare CLTM between multiple candidate cells.

[0076] 5 shows an example of the operation of a candidate DU (e.g., gNB-DU 21 or 22) that serves a candidate cell for CLTM. In the case of intra-DU CLTM, the candidate DU is naturally the same as the DU that serves the source cell. In addition, even in the case of intra-CU inter-DU CLTM, the DU that serves the source cell may further serve other candidate cells. Furthermore, the source cell may be prepared as one of the candidate cells for a subsequent CLTM. Therefore, in the case of intra-CU inter-DU CLTM, the candidate DU may be different from or the same as the DU that serves the source cell.

[0077] In step 501, the candidate DU receives a first message from the CU requesting preparation of a first candidate cell. The first message is a message from the CU requesting preparation of the first candidate cell for LTM of the UE 40 among multiple candidate cells including the first candidate cell. The first candidate cell may be the same as the source cell. Alternatively, one of the multiple candidate cells excluding the first candidate cell may be the same as the source cell. In other words, the first candidate cell or another candidate cell included in the multiple candidate cells may be the same as the source cell of the first LTM in the LTM requested by the first message. The first message may include a first indication related to CLTM. The first message may be an F1AP message, specifically a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message.

[0078] In step 502, the candidate DU determines whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to CLTM or normal LTM based on whether the first message includes a first indication related to CLTM. Specifically, if the first message in step 501 includes the above-mentioned first indication, the candidate DU may consider one or more cell switches from the first candidate cell to one or more other candidate cells to be subject to CLTM. On the other hand, if the first message does not include the first indication, the candidate DU may consider these one or more cell switches to be subject to normal LTM.

[0079] FIG. 6 shows an example of the operation of a CU (e.g., gNB-CU 10). In step 601, the CU decides to initiate LTM configuration. As described with reference to step 302 of FIG. 3 and step 402 of FIG. 4, the CU may decide to use regular LTM, CLTM, or both based on one or more L3 measurement reports from the UE 40. As described above, the CU may decide to use both regular LTM and CLTM. CLTM cell switch may be used for some of multiple candidate cells, and regular LTM cell switch may be used for the remaining candidate cells. For example, CLTM cell switch may be applied to a cell switch from a source cell or a first candidate cell to another candidate cell, while regular LTM cell switch may be applied to a cell switch from a second candidate cell to another candidate cell.

[0080] In step 602, the CU sends a first message to a candidate DU (e.g., gNB-DU 21 or 22) requesting preparation of a first candidate cell for LTM of the UE 40 among multiple candidate cells, including the first candidate cell. The first message indicates to the candidate DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to CLTM or normal LTM, based on whether the first message includes a first indication related to CLTM. Specifically, if the first message includes the above-mentioned first indication, the first message may cause the candidate DU to consider one or more cell switches from the first candidate cell to one or more other candidate cells as subject to CLTM. On the other hand, if the first message does not include the first indication, the first message may cause the candidate DU to consider these one or more cell switches as subject to normal LTM.

[0081] The operations of the CU and candidate DU described with reference to Figures 5 and 6 can provide details of the operations of the CU and candidate DU for preparing a CLTM. Furthermore, these operations of the CU and candidate DU help to reuse the first message for both preparing a normal LTM and preparing a CLTM. In other words, these operations of the CU and candidate DU make it possible to reuse the first message for preparing a normal LTM for preparing a CLTM.

[0082] The operations of the CU and candidate DU described with reference to Figures 5 and 6 may be modified as follows: The first message received by the candidate DU in step 501 of Figure 5 may include a second indication related to CLTM for a cell switch (inbound) from a candidate cell of another candidate DU to a first candidate cell of the candidate DU. Similarly, the first message sent by the CU to the candidate DU in step 602 of Figure 6 may include a second indication related to CLTM for a cell switch (inbound) from a candidate cell of another candidate DU to a first candidate cell of the candidate DU. The second indication may indicate whether CLTM, normal LTM, or both are scheduled or configured for the cell switch from the other candidate cell to the first candidate cell.

[0083] The first message in step 501 of Figure 5 and step 602 of Figure 6 may include a second indication in addition to the first indication described above. Alternatively, the first message in step 501 of Figure 5 and step 601 of Figure 6 may include the second indication without including the first indication. Alternatively, the first message in step 501 of Figure 5 and step 602 of Figure 6 may include a single common indication that serves as both the first indication and the second indication. The second indication may be included in a subsequent message (not shown) sent from the CU to the candidate DU, which is different from the first message.

[0084] The candidate DU may determine whether an (inbound) cell switch from another cell (i.e., another candidate cell or source cell) to the first candidate cell provided by the candidate DU is subject to normal LTM, CLTM, or both, based on whether the received message includes the second indication. Alternatively, the candidate DU may determine this based on the content of the second indication. This allows the candidate DU to know in advance whether CLTM or normal LTM is scheduled for the subsequent (inbound) cell switch from the candidate DU to the first candidate cell, and to make necessary preparations in advance (e.g., a standby method for access from the UE 40 to the first candidate cell). Note that a node managing the other cell (e.g., another candidate DU or source DU) may generate an execution condition to be evaluated by the UE 40 for a CLTM cell switch from the other cell (i.e., another candidate cell or source cell) to the first candidate cell.

[0085] The candidate DU may generate a second message based on the first message and send the second message to the CU. The second message typically includes cell configuration of the first candidate cell prepared for LTM or CLTM. The second message may be an F1AP message, specifically a UE CONTEXT SETUP RESPONSE message or a UE CONTEXT MODIFICATION RESPONSE message.

[0086] In one implementation, the candidate DU may generate execution conditions to be evaluated by the UE 40 for a CLTM cell switch from a first candidate cell to another candidate cell. In this case, if one or more cell switches from the first candidate cell to one or more other candidate cells are subject to CLTM, the candidate DU may include one or more CLTM execution conditions for these one or more cell switches in the second message in addition to the LTM configuration for the first candidate cell. On the other hand, if these one or more cell switches are subject to normal LTM, the candidate DU may include the LTM configuration for the first candidate cell in the second message without including one or more CLTM execution conditions in the second message. According to this operation, the candidate DU can determine whether or not it is necessary to generate a CLTM execution condition based on whether or not the first message includes a specific indication.

[0087] In another implementation, the CU may generate execution conditions to be evaluated by the UE 40 for a CLTM cell switch from a first candidate cell to another candidate cell. In this case, the candidate DU may provide the CU with suggestion information (or assist information) used, useful, or supporting the CU in generating the execution conditions. If one or more cell switches from the first candidate cell to one or more other candidate cells are subject to CLTM, the candidate DU may include suggestion information for CLTM in the second message in addition to the LTM configuration for the first candidate cell. On the other hand, if these one or more cell switches are subject to normal LTM, the candidate DU may include the LTM configuration for the first candidate cell in the second message without including suggestion information in the second message. According to this operation, the candidate DU can determine whether or not it is necessary to generate suggestion information based on whether the first message includes a specific indication.

[0088] The proposal information may be considered by the CU to determine one or more execution conditions for one or more cell switches from the first candidate cell to one or more other candidate cells. The CU may determine one or more execution conditions for these one or more cell switches based on the proposal information. The proposal information may indicate, for example, one or more proposed events (i.e., events that trigger CLTM), proposed parameters (e.g., offsets or thresholds), or a combination thereof. The one or more proposed parameters may include, for example, an offset or threshold to be applied to radio quality (e.g., RSRP) for a radio quality-related execution condition.

[0089] In some implementations, CLTM may be applied to only one or more cell pairs among a plurality of candidate cells configured for LTM, and normal LTM may be applied to the remaining one or more cell pairs. In this case, the first message or the above-described indication included in the first message (i.e., the first indication, the second indication, or both) may explicitly indicate which cell pairs among the plurality of candidate cells are subject to CLTM. In other words, or alternatively, the first message or the above-described first indication may explicitly indicate which one or more of the plurality of candidate cells, excluding the first candidate cell, are subject to CLTM in a cell switch from the first candidate cell. This allows the candidate DU to know which candidate cells will be subject to CLTM in a cell switch from the first candidate cell, and can assist the candidate DU in generating the CLTM execution condition (or the above-described proposal information).

[0090] In some implementations, the first indication included in the first message may indicate to the candidate DU whether one or more cell switches from the first candidate cell to one or more other candidate cells are subject to CLTM. Furthermore, the first message or the first indication may further indicate to the candidate DU whether generation of execution conditions is required if these one or more cell switches are subject to CLTM. This enables the candidate DU to know whether it is necessary to generate CLTM execution conditions for CTLM cell switches from the first candidate cell to other cells.

[0091] The indication (i.e., the first indication or the second indication, or both) included in the first message may be an indication of one or more execution condition requests for one or more cell switches. Alternatively, the indication (i.e., the first indication or the second indication, or both) may be an indication of CLTM.

[0092] As described above, the first message may be a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message. In this case, the above-mentioned indication (i.e., the first indication, the second indication, or both) may be included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message. The above-mentioned indication may be included in an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message. Alternatively, the above-mentioned indication (i.e., the first indication, the second indication, or both) may be included in an information element, separate from the LTM Information Setup information element or the LTM Information Modify information element, in the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message.

[0093] FIG. 7 shows an example of signaling between a CU and a candidate DU for preparing LTM (CLTM or CLTM and normal LTM). The CU 701 shown in FIG. 7 may be the gNB-CU 10 in FIGS. 1 and 2, and the candidate DU 702 shown in FIG. 7 may be the gNB-DU 21 or 22 in FIGS. 1 and 2. In step 721, the CU 701 decides to initiate CLTM configuration. In other words, the CU 701 decides to use CLTM and initiates preparation of one or more CLTM candidate cells. The CU 701 may decide to initiate CLTM configuration based on one or more L3 measurement reports from the UE 40. Step 721 may correspond to step 601 in FIG. 6.

[0094] In step 722, the CU 701 sends a UE CONTEXT SETUP REQUEST message to the candidate DU 702. The UE CONTEXT SETUP REQUEST message includes an LTM Information Setup IE and further includes a new field or IE. This new field or IE indicates that the message or LTM preparation is for CLTM. This new field or IE may be included in the LTM Information Setup IE or may be included in the UE CONTEXT SETUP REQUEST message separately from the LTM Information Setup IE. Step 722 may correspond to step 501 in Figure 5 and step 602 in Figure 6.

[0095] In step 723, the candidate DU 702 sends a UE CONTEXT SETUP RESPONSE message to the CU 701. The UE CONTEXT SETUP RESPONSE message includes a DU To CU RRC Information IE. The DU To CU RRC Information IE contains RRC information sent from the candidate DU 702 to the CU 701. The RRC information includes the configuration of the candidate cell or the configuration of a cell group (CellGroupConfig) including the candidate cell. The UE CONTEXT SETUP RESPONSE message further includes an LTM Configuration IE. The LTM Configuration IE contains the time and frequency configuration of SSB or CSI-RS. In addition, the UE CONTEXT SETUP RESPONSE message includes a new F1AP IE or a new field or IE in the DU To CU RRC Information IE (RRC Container). This new F1AP IE or the new field or IE in the DU To CU RRC Information IE contains one or more CLTM execution conditions. These one or more CLTM execution conditions are used and evaluated by the UE 40 to determine whether to perform one or more subsequent CLTM cell switches from the candidate cell for which preparation was requested in the UE CONTEXT SETUP REQUEST message to one or more other candidate cells.

[0096] Note that if the candidate DU 702 is the same as the source DU that provides the source cell, a UE CONTEXT MODIFICATION REQUEST message is used instead of the UE CONTEXT SETUP REQUEST message (step 722), and a UE CONTEXT MODIFICATION RESPONSE message is used instead of the UE CONTEXT SETUP RESPONSE message (step 723). The UE CONTEXT MODIFICATION REQUEST message may include an LTM Information Modify IE instead of the LTM Information Setup IE. The new fields or IEs described with respect to step 722 may be included in the LTM Information Modify IE or may be included in the UE CONTEXT MODIFICATION REQUEST message separately from the LTM Information Modify IE.

[0097] The operations of the CU 701 and the candidate DU 702 described with reference to Figure 7 can provide details of the operations of the CU 701 and the candidate DU 702 for preparing a CLTM. Furthermore, these operations of the CU 701 and the candidate DU 702 help to use the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message for both normal LTM preparation and CLTM preparation. In other words, these operations of the CU 701 and the candidate DU 702 enable the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message for normal LTM preparation to be reused for CLTM preparation.

[0098] 8 to 11 show specific examples of new fields or IEs included in the UE CONTEXT SETUP REQUEST message described with respect to step 722. In the example of FIG. 8, the UE CONTEXT SETUP REQUEST message includes a Conditional LTM Information Request IE 801 in addition to the LTM Information Setup IE. The Conditional LTM Information Request IE 801 can optionally include a Request for Execution Condition IE 802. If the Request for Execution Condition IE 802 set to "true" is included in the Conditional LTM Information Request IE 801 included in the UE CONTEXT SETUP REQUEST message, the candidate DU 702 considers the request to be related to CLTM and that the generation of a CLTM execution condition is required. The candidate DU 702 then includes the CLTM execution condition in the UE CONTEXT SETUP RESPONSE message.

[0099] In the example of Figure 9, the UE CONTEXT SETUP REQUEST message can include a Request for Execution Condition IE 901 in the LTM Information Setup IE. If the Request for Execution Condition IE 901 set to "true" is included in the LTM Information Setup IE included in the UE CONTEXT SETUP REQUEST message, the candidate DU 702 considers the request to be related to CLTM and that the generation of a CLTM execution condition is required. The candidate DU 702 then includes the CLTM execution condition in the UE CONTEXT SETUP RESPONSE message.

[0100] In the example of FIG. 10 , the UE CONTEXT SETUP REQUEST message may include a Conditional LTM Indicator IE 1001 in the LTM Information Setup IE. If the Conditional LTM Indicator IE 1001 set to “true” is included in the LTM Information Setup IE included in the UE CONTEXT SETUP REQUEST message, the candidate DU 702 considers the request to be related to CLTM. Specifically, the candidate DU 702 may recognize that an LTM cell switch (outbound) from a candidate cell provided by the candidate DU 702 to another candidate cell is subject to CLTM. Additionally or alternatively, the candidate DU 702 may recognize that CLTM is scheduled or configured in an LTM cell switch (inbound) from another candidate cell to the candidate cell provided by the candidate DU 702. The candidate DU 702 may include a CLTM execution condition in the UE CONTEXT SETUP RESPONSE message. Alternatively, the candidate DU 702 may include the above-mentioned proposal information in the UE CONTEXT SETUP RESPONSE message.

[0101] In the example of FIG. 11 , the LTM Indicator IE 1101 included in the UE CONTEXT SETUP REQUEST message is extended compared to that in 3GPP Release 18. The LTM Indicator IE 1101 may be set to the value “CLTM.” If the LTM Indicator IE 1101 set to “CLTM” is included in the LTM Information Setup IE included in the UE CONTEXT SETUP REQUEST message, the candidate DU 702 considers the request to be related to CLTM. Specifically, the candidate DU 702 may recognize that an LTM cell switch (outbound) from a candidate cell provided by the candidate DU 702 to another candidate cell is subject to CLTM. Additionally or alternatively, the candidate DU 702 may recognize that a CLTM is scheduled for an LTM cell switch (inbound) from another candidate cell to the candidate cell provided by the candidate DU 702. The candidate DU 702 may include a CLTM execution condition in the UE CONTEXT SETUP RESPONSE message. Alternatively, the candidate DU 702 may include the above-mentioned proposal information in the UE CONTEXT SETUP RESPONSE message.

[0102] 12 and 13 show specific examples of new fields or IEs included in the UE CONTEXT SETUP RESPONSE message described with respect to step 723. Figure 12 shows an example of a DU To CU RRC Information IE included in the UE CONTEXT SETUP RESPONSE message. In the example of Figure 12, the DU To CU RRC Information IE may include a ConditionalLTM-Configuration field or IE 1201. The ConditionalLTM-Configuration field or IE 1201 includes or indicates one or more CLTM execution conditions generated by the candidate DU.

[0103] In the example of Figure 13, the UE CONTEXT SETUP RESPONSE message may include, within the LTM Configuration IE, a Conditional LTM Configuration IE 1301. The Conditional LTM Configuration IE 1301 includes or indicates one or more CLTM execution conditions generated by the candidate DU.

[0104] Similar to the examples described with reference to Figures 8 to 11, the UE CONTEXT MODIFICATION REQUEST message may be extended to include the new fields or IEs described with reference to step 722. Similar to the examples described with reference to Figures 12 and 13, the UE CONTEXT MODIFICATION RESPONSE message may be extended to include the new fields or IEs described with reference to step 723.

[0105] Figure 14 shows an example of signaling between a CU, a source DU, and a candidate DU for preparing for LTM (CLTM or CLTM and regular LTM). CU 1401 shown in Figure 14 may be gNB-CU 10 in Figures 1 and 2. Source DU 1402 shown in Figure 14 may be gNB-DU 21 in Figures 1 and 2. Two candidate DUs 1403 and 1404 shown in Figure 14 may be gNB-DU 22 in Figures 1 and 2.

[0106] In step 1421, source DU 1402 sends a UL RRC MESSAGE TRANSFER message carrying the L3 measurement report received from the UE to CU 1401. In step 1422, CU 1401 decides to initiate CLTM configuration. In other words, CU 1401 decides to use CLTM and starts preparing one or more CLTM candidate cells. CU 1401 may decide to initiate CLTM configuration based on one or more L3 measurement reports from UE 40. Step 1422 may correspond to step 601 in FIG. 6 .

[0107] In step 1423, the CU 1401 sends a UE CONTEXT SETUP REQUEST message to each of the candidate DUs 1403 and 1404. Step 1423 is similar to step 722 in Figure 7. Step 1423 may correspond to step 501 in Figure 5 and step 602 in Figure 6.

[0108] In step 1424, each of the candidate DUs 1403 and 1404 sends a UE CONTEXT SETUP RESPONSE message to the CU 1401. Step 1424 is similar to step 723 in FIG.

[0109] In step 1425, the CU 1401 sends a UE CONTEXT MODIFICATION REQUEST message to the source DU 1402. The UE CONTEXT MODIFICATION REQUEST message requests the source DU 1402 to prepare the source cell or another cell provided by the source DU 1402 as a CLTM candidate cell. Step 1425 is similar to step 722 in FIG. 7. The new fields or IEs described with respect to step 722 may be included in the LTM Information Modify IE or may be included in the UE CONTEXT MODIFICATION REQUEST message separately from the LTM Information Modify IE. Furthermore, the UE CONTEXT MODIFICATION REQUEST message may include information indicating whether CLTM, normal LTM, or both are planned or configured for a cell switch from a candidate cell of another candidate DU to the source cell or another cell provided by the source DU 1402.

[0110] In step 1426, the source DU 1402 sends a UE CONTEXT MODIFICATION RESPONSE message to the CU 1401. The UE CONTEXT MODIFICATION RESPONSE message includes a DU To CU RRC Information IE. The DU To CU RRC Information IE contains RRC information sent from the source DU 1402 to the CU 1401. The RRC information includes the configuration of candidate cells (i.e., the source cell or other cells served by the source DU 1402) or the configuration of a cell group (CellGroupConfig) including candidate cells. Step 1426 is similar to step 723 in FIG. 7. The UE CONTEXT MODIFICATION RESPONSE message of step 1426 is extended to include the new fields or IEs described with respect to step 723. Furthermore, the UE CONTEXT MODIFICATION RESPONSE message (or the DU To CU RRC Information IE) may include an execution condition for CLTM to the source cell or other cells served by the source DU 1402.

[0111] 14, after steps 1425 and 1426, the CU 1401 further sends a UE CONTEXT MODIFICATION REQUEST message to the source DU 1402, and the source DU 1402 further sends a UE CONTEXT MODIFICATION RESPONSE message to the CU 1401. The additional UE CONTEXT MODIFICATION REQUEST message (not shown) includes information collected from the candidate DUs 1403 and 1404 (e.g., collected CSI reporting settings and RACH configuration settings, and TCI state settings of the candidate cells accepted by other DUs). The additional UE CONTEXT MODIFICATION RESPONSE message (not shown) may include updated lower layer settings (e.g., including CSI reporting settings).

[0112] An additional UE CONTEXT MODIFICATION REQUEST message (not shown) may indicate, on a candidate cell-by-candidate cell basis, whether normal LTM or CLTM is to be applied to each cell switch from the source cell to one or more candidate cells. This enables the source DU 1402 to recognize the type of cell switch (i.e., normal LTM or CLTM) to be applied to each candidate cell and to perform operations according to the cell switch type for each candidate cell. Furthermore, an additional UE CONTEXT MODIFICATION REQUEST message (not shown) may include information indicating whether CLTM, normal LTM, or both are planned or configured for a cell switch from a candidate cell of another candidate DU to the source cell or another cell served by the source DU 1402.

[0113] In step 1427, the CU 1401 may send a UE CONTEXT MODIFICATION REQUEST message to each candidate DU. The message includes CSI reporting configuration, TCI status information, RACH configuration, and LTM configuration IDs of the candidate cells of the other candidate DUs. The CU 1401 may further provide the lower layer portion of the reference configuration to each candidate DU. The CU 1401 may further provide the updated CSI resource configuration to each candidate DU. The message may further include information indicating whether CLTM, normal LTM, or both are planned or configured for the cell switch from the candidate cell of the other candidate DU to the candidate cell provided by each candidate DU. In step 1428, each candidate DU responds with a UE CONTEXT MODIFICATION RESPONSE message including the updated lower layer configuration. Each candidate DU may also send the updated CSI reporting configuration. Steps 1427 and 1428 may be omitted.

[0114] In step 1429, the CU 1401 sends a DL RRC MESSAGE TRANSFER message to the source DU 1402. This message includes an RRC Reconfiguration message that includes the CLTM setting. Although not shown, the source DU 1401 forwards the received RRC Reconfiguration message to the UE 40.

[0115] FIG. 15 shows an example of signaling between a CU and a candidate DU for preparing LTM (CLTM or CLTM and normal LTM). The CU 1501 shown in FIG. 15 may be the gNB-CU 10 in FIGS. 1 and 2, and the candidate DU 1502 shown in FIG. 15 may be the gNB-DU 21 or 22 in FIGS. 1 and 2. In step 1521, the CU 1501 determines to initiate CLTM configuration. In other words, the CU 1501 determines to use CLTM and initiates preparation of one or more CLTM candidate cells. The CU 1501 may determine to initiate CLTM configuration based on one or more L3 measurement reports from the UE 40. In the example of FIG. 15, the CU 1501 further determines to generate one or more CLTM execution conditions by the CU 1501. The CU 1501 may generate the CLTM execution conditions based on the L3 measurement report (or the L1 measurement report). Step 1521 may correspond to step 601 in FIG. 6.

[0116] In step 1522, the CU 701 sends a UE CONTEXT SETUP REQUEST message to the candidate DU 1502. The UE CONTEXT SETUP REQUEST message includes an LTM Information Setup IE and further includes a new field or IE. This new field or IE indicates that the message or LTM preparation is for CLTM. This new field or IE may be included in the LTM Information Setup IE or may be included in the UE CONTEXT SETUP REQUEST message separately from the LTM Information Setup IE. Step 1522 may correspond to step 501 in FIG. 5 and step 602 in FIG. 6.

[0117] The UE CONTEXT SETUP REQUEST message of step 1522 may optionally indicate one or more CLTM execution conditions determined by CU 1501. The UE CONTEXT SETUP REQUEST message of step 1522 may optionally indicate one or more cell pairs or a list of cell pairs to which CLTM applies. If one or more cell pairs are not indicated, normal LTM as specified in 3GPP Release 18 may apply to all cell pairs within multiple candidate cells or to all cell switches.

[0118] In step 1523, the candidate DU 1502 sends a UE CONTEXT SETUP RESPONSE message to the CU 1501. The UE CONTEXT SETUP RESPONSE message includes a DU To CU RRC Information IE. The DU To CU RRC Information IE contains RRC information sent from the candidate DU 1502 to the CU 1501. The RRC information includes the configuration of the candidate cell or the configuration of a cell group (CellGroupConfig) including the candidate cell. The UE CONTEXT SETUP RESPONSE message further includes an LTM Configuration IE. The LTM Configuration IE contains the time and frequency configuration of SSB or CSI-RS. In addition, the UE CONTEXT SETUP RESPONSE message includes a new F1AP IE or a new field or IE in the DU To CU RRC Information IE (RRC Container). This new F1AP IE or the new field or IE in the DU To CU RRC Information IE may contain the above-mentioned proposal information.

[0119] Note that if the candidate DU 1502 is the same as the source DU that provides the source cell, a UE CONTEXT MODIFICATION REQUEST message is used instead of the UE CONTEXT SETUP REQUEST message (step 1522), and a UE CONTEXT MODIFICATION RESPONSE message is used instead of the UE CONTEXT SETUP RESPONSE message (step 1523). The UE CONTEXT MODIFICATION REQUEST message may include an LTM Information Modify IE instead of the LTM Information Setup IE. The new field or IE described with respect to step 1522 may be included in the LTM Information Modify IE or may be included in the UE CONTEXT MODIFICATION REQUEST message separately from the LTM Information Modify IE.

[0120] Examples of new fields or IEs included in the UE CONTEXT SETUP REQUEST message described with respect to step 1522 may be similar to those shown in FIGS.

[0121] The operations of the CU 1501 and the candidate DU 1502 described with reference to Figure 15 can provide details of the operations of the CU 1501 and the candidate DU 1502 for preparing a CLTM. Furthermore, these operations of the CU 1501 and the candidate DU 1502 help to use the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message for both normal LTM preparation and CLTM preparation. In other words, these operations of the CU 1501 and the candidate DU 1502 enable the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message for normal LTM preparation to be reused for CLTM preparation.

[0122] Second Embodiment A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Figures 1 and 2. This embodiment provides details of the use of a RACH-less LTM cell switch when UE 40 determines that the CLTM execution condition is met.

[0123] 16 shows an example of the operation of UE 40. In step 1601, UE 40 evaluates the CLTM execution condition for each of one or more candidate cells. In step 1602, UE 40 determines whether the CLTM execution condition is met for one of the one or more candidate cells.

[0124] In step 1603, UE 40 determines whether to use a RACH-less cell switch procedure for a cell switch to the selected candidate cell. Specifically, UE 40 determines whether to use the RACH-less cell switch procedure based at least on whether UE 40 has a valid TA value and whether the reference signal beam for which the execution condition for the candidate cell is determined to be met was used to acquire a valid TA value in the early TA acquisition procedure performed for the candidate cell. The reference signal beam used to determine whether the execution condition for the candidate cell is met may be an SSB beam or a CSI-RS beam. An SSB beam may be referred to as SSB, and a CSI-RS beam may be referred to as CSI-RS. If UE 40 has a valid TA value and the reference signal beam was used to acquire the valid TA value in the early TA acquisition procedure, UE 40 performs the RACH-less cell switch procedure. That is, UE 40 skips the random access procedure and accesses the selected candidate cell (i.e., target cell). Otherwise, UE 40 performs a RACH-based cell switch using the random access procedure.

[0125] The operation of UE 40 described with reference to FIG. 16 can provide details of the use of a RACH-less LTM cell switch when UE 40 determines that the CLTM execution condition is met. Specifically, the operation of UE 40 in FIG. 16 provides, for example, the following advantages: A candidate cell selected as a target cell (or a candidate DU managing the cell) can know in advance which uplink beam associated with which reference signal beam it should use to prepare to receive the (first) uplink signal in the cell switch procedure. In other words, the candidate cell (or the candidate DU managing the cell) can know the beam that UE 40 will use to transmit the (first) uplink signal in the cell switch procedure from information about the reference signal associated with the random access preamble used by UE 40 in the early TA acquisition procedure. These advantages are realized based on the fact that the correspondence between the reference signal beam, the beam of the random access preamble, and the beam of the uplink signal can be known in advance from their settings (or information thereon).

[0126] <Other Embodiments> CLTM may be valid only within a predetermined or specific group of multiple cells. UE 40 may evaluate the CLTM execution conditions only for one or more candidate cells that belong to the same group as the current serving cell. For example, CLTM may be valid only within a group of cells served by the same DU (intra-DU cell group).

[0127] Next, exemplary configurations of the gNB-CU10, gNB-CU-CP11, gNB-CU-UP12, gNB-DUs 21 and 22, and UE 40 will be described below. Figure 17 is a block diagram showing an exemplary configuration of the gNB-CU10. The configurations of the gNB-CU-CP11, gNB-CU-UP12, and gNB-DUs 21 and 22 may also be similar to the configurations shown in Figure 17. In addition, the configurations of the CUs (e.g., CUs 701, 1401, etc.) and DUs (e.g., DUs 702, 1402, 403, 1404, etc.) described in the above-mentioned embodiments may also be similar to the configurations shown in Figure 17.

[0128] 17, the gNB-CU10 includes a network interface 1701, a processor 1702, and a memory 1703. The network interface 1701 is used to communicate with network nodes (e.g., gNB-DUs, and control plane (CP) nodes and / or user plane (UP) nodes in the core network). The network interface 1701 may include multiple interfaces. The network interface 1701 may include, for example, an optical fiber interface for communication between the CU and DU and a network interface compliant with the IEEE 802.3 series.

[0129] The processor 1702 may include multiple processors. If the gNB-CU10 is a gNB-CU-CP, the processor 1702 performs, for example, control plane processing, such as processing related to NGAP, RRC, E1AP, and F1AP signaling. If the gNB-CU10 includes a gNB-CU-UP, the processor 1702 performs, for example, termination of the NG-U interface, termination of the F1-U interface, and data processing for the SDAP and PDCP layers.

[0130] In the case of the gNB-DUs 21 and 22, the processor 1702 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. For example, the processor 1702 may include a modem processor (e.g., a Digital Signal Processor (DSP)) that performs digital baseband signal processing and a protocol stack processor (e.g., a Central Processing Unit (CPU) or a Micro Processing Unit (MPU)) that performs control plane processing. The digital baseband signal processing may include signal processing for the RLC, MAC, and PHY layers. The control plane processing may include processing of MAC CEs and DCIs. The processor 1702 may include a digital beamformer module for beamforming. The digital beamformer module may include a multiple-input multiple-output (MIMO) encoder and precoder.

[0131] The memory 1703 is configured by a combination of volatile memory and non-volatile memory. The volatile memory is, for example, Static Random Access Memory (SRAM), Dynamic RAM (DRAM), or a combination thereof. The non-volatile memory is, for example, Mask Read Only Memory (MROM), Electrically Erasable Programmable ROM (EEPROM), flash memory, or a hard disk drive, or any combination thereof. The memory 1703 may include storage located remotely from the processor 1702. In this case, the processor 1702 may access the memory 1703 via the network interface 1701 or another I / O interface.

[0132] The memory 1703 may store one or more software modules (computer programs) 1704 including instructions and data for performing the processing by the gNB-CU 10 described in the above-described embodiments. In some implementations, the processor 1702 may be configured to read and execute the one or more software modules 1704 from the memory 1703, thereby performing the processing by the gNB-CU 10 described in the above-described embodiments.

[0133] FIG. 18 is a block diagram showing an example configuration of a UE 40. An RF transceiver 1801 performs analog RF signal processing for communication with TRPs. The RF transceiver 1801 may include multiple transceivers. The analog RF signal processing performed by the RF transceiver 1801 includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver 1801 is coupled to an antenna array 1802 and a baseband processor 1803. The RF transceiver 1801 receives modulation symbol data (or OFDM symbol data) from the baseband processor 1803, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 1802. The RF transceiver 1801 also generates a baseband receive signal based on the receive RF signal received by the antenna array 1802 and provides the baseband receive signal to the baseband processor 1803. The RF transceiver 1801 may include an analog beamformer circuit for beamforming. The analog beamformer circuitry includes, for example, multiple phase shifters and multiple power amplifiers.

[0134] The baseband processor 1803 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communications. Digital baseband signal processing includes (a) data compression / decompression, (b) data segmentation / concatenation, (c) transmission format (transmission frame) generation / decomposition, (d) transmission path coding / decoding, (e) modulation (symbol mapping) / demodulation, and (f) generation of OFDM symbol data (baseband OFDM signal) using Inverse Fast Fourier Transform (IFFT). Meanwhile, control plane processing includes communication management for Layer 1 (e.g., transmit power control), Layer 2 (e.g., radio resource management and hybrid automatic repeat request (HARQ) processing), and Layer 3 (e.g., signaling related to attachment, mobility, and call management).

[0135] For example, digital baseband signal processing by the baseband processor 1803 may include signal processing of an SDAP layer, a PDCP layer, an RLC layer, a MAC layer, and a PHY layer. Also, control plane processing by the baseband processor 1803 may include processing of a Non-Access Stratum (NAS) protocol, an RRC protocol, MAC CEs, and DCIs.

[0136] The baseband processor 1803 may perform MIMO encoding and precoding for beamforming.

[0137] The baseband processor 1803 may include a modem processor (e.g., DSP) that performs digital baseband signal processing and a protocol stack processor (e.g., CPU or MPU) that performs control plane processing. In this case, the protocol stack processor that performs control plane processing may be shared with the application processor 1804, which will be described later.

[0138] The application processor 1804 is also referred to as a CPU, MPU, microprocessor, or processor core. The application processor 1804 may include multiple processors (multiple processor cores). The application processor 1804 executes a system software program (operating system (OS)) and various application programs (e.g., a call application, a web browser, a mailer, a camera operation application, and a music playback application) read from the memory 1806 or a memory not shown, thereby realizing various functions of the UE 40.

[0139] In some implementations, the baseband processor 1803 and the application processor 1804 may be integrated on a single chip, as shown by the dashed line (1805) in Figure 18. In other words, the baseband processor 1803 and the application processor 1804 may be implemented as a single System on Chip (SoC) device 1805. An SoC device may also be called a system Large Scale Integration (LSI) or chipset.

[0140] The memory 1806 is volatile memory, nonvolatile memory, or a combination thereof. The memory 1806 may include multiple physically independent memory devices. The volatile memory is, for example, SRAM, DRAM, or a combination thereof. The nonvolatile memory is, for example, MROM, EEPROM, flash memory, or a hard disk drive, or any combination thereof. For example, the memory 1806 may include an external memory device accessible from the baseband processor 1803, the application processor 1804, and the SoC 1805. The memory 1806 may also include an internal memory device integrated within the baseband processor 1803, the application processor 1804, or the SoC 1805. Furthermore, the memory 1806 may include memory within a Universal Integrated Circuit Card (UICC).

[0141] The memory 1806 may store one or more software modules (computer programs) 1807 including instructions and data for performing the processing by the UE 40 described in the above-described embodiments. In some implementations, the baseband processor 1803 or the application processor 1804 may be configured to read and execute the software modules 1807 from the memory 1806, thereby performing the processing by the UE 40 described in the above-described embodiments using the drawings.

[0142] It should be noted that the control plane processing and operations performed by UE 40 described in the above embodiment can be realized by elements other than RF transceiver 1801 and antenna array 1802, namely, at least one of baseband processor 1803 and application processor 1804, and memory 1806 storing software module 1807.

[0143] As described with reference to Figures 17 and 18, each of the processors included in the gNB-CUs, gNB-CU-CPs, gNB-CU-UPs, gNB-DUs, and UEs according to the above-described embodiments can execute one or more programs including instructions for causing a computer to perform the algorithms described with reference to the drawings. The programs include instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The programs may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray (registered trademark) disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage device. The programs may also be transmitted on a transitory computer-readable medium or a communication medium. By way of example, and not limitation, transitory computer-readable or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0144] The above-described embodiments are merely examples of application of the technical ideas obtained by the inventors of the present invention. In other words, the technical ideas are not limited to the above-described embodiments, and various modifications are possible.

[0145] For example, some or all of the above embodiments may also be described as, but are not limited to, the following appendices. Some or all of the elements (e.g., configurations and functions) described in appendices directed to devices (e.g., distributed units, central units, wireless terminals) may naturally also be described as appendices directed to methods and programs. For example, some or all of the elements described in appendices 2-16, which are dependent on appendices 1, may also be described as appendices dependent on appendices 17 and 18, due to the same dependency relationship as appendices 2-16. Similarly, some or all of the elements described in appendices 20-34, which are dependent on appendices 19, may also be described as appendices dependent on appendices 35 and 36, due to the same dependency relationship as appendices 20-34. Some or all of the elements described in any appendice may be applicable to various hardware, software, recording means for recording software, systems, and methods.

[0146] (Supplementary Note 1) A distributed unit (DU) of a radio access network (RAN) node, comprising: means for receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and means for determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM. (Supplementary Note 2) The DU of Supplementary Note 1, wherein the determining means is configured to: if the first message includes the first indication, consider the one or more cell switches to be subject to the conditional LTM; and if the first message does not include the first indication, consider the one or more cell switches to be subject to the normal LTM. (Supplementary Note 3) The DU described in Supplementary Note 1 or 2, further comprising: means for generating a second message based on the first message; and means for sending the second message to the CU, wherein the generating means is configured to: if the one or more cell switches are targets of the conditional LTM, include one or more execution conditions for the one or more cell switches in the second message in addition to the LTM settings for the first candidate cell; and if the one or more cell switches are targets of the normal LTM, include the LTM settings for the first candidate cell in the second message without including the one or more execution conditions in the second message.(Supplementary Note 4) The DU according to Supplementary Note 1 or 2, further comprising: means for generating a second message based on the first message; and means for sending the second message to the CU, wherein the generating means is configured to: if the one or more cell switches are targets of the conditional LTM, include proposal information for the conditional LTM in addition to LTM configuration for the first candidate cell; and if the one or more cell switches are targets of the normal LTM, not include the proposal information in the second message, but include LTM configuration for the first candidate cell in the second message. (Supplementary Note 5) The DU according to Supplementary Note 4, wherein the proposal information is taken into account by the CU to determine one or more execution conditions for the one or more cell switches. (Supplementary Note 6) The DU according to any one of Supplements 1 to 5, wherein the first message or the first indication explicitly indicates which one or more of the multiple candidate cells, excluding the first candidate cell, are targets of the conditional LTM at a cell switch from the first candidate cell. (Supplementary Note 7) The DU according to any one of Supplements 1 to 5, wherein the first message or the first indication explicitly indicates which cell pairs included in the plurality of candidate cells are subject to the conditional LTM. (Supplementary Note 8) The DU according to any one of Supplements 1 to 7, wherein the first indication is an indication of a request for one or more execution conditions for the one or more cell switches. (Supplementary Note 9) The DU according to any one of Supplements 1 to 7, wherein the first indication is an indication of the conditional LTM. (Supplementary Note 10) The DU according to any one of Supplements 1 to 9, wherein the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message, and the first indication is included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message or an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message.(Supplementary Note 11) The DU according to any one of Supplements 1 to 9, wherein the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message, and the first indication is an information element included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message separately from an LTM Information Setup information element or an LTM Information Modify information element. (Supplementary Note 12) The DU according to any one of Supplements 1 to 11, wherein the first indication indicates to the DU whether the one or more cell switches are subject to the conditional LTM, and the first message or the first indication further indicates to the DU whether generation of an execution condition is required if the one or more cell switches are subject to the conditional LTM. (Supplementary Note 13) The DU according to any one of Supplements 1 to 12, wherein the first indication or a second indication included in the first message separately from the first indication indicates whether one or more cell switches from other cells to the first candidate cell are subject to conditional LTM. (Supplementary Note 14) The conditional LTM is an LTM in which the radio terminal executes a cell switch from the first candidate cell to other cells in response to the radio terminal determining that an execution condition is met, and the normal LTM is an LTM in which the radio terminal executes a cell switch from the first candidate cell to other cells in response to the radio terminal receiving a Layer 1 or Layer 2 cell switch command from a source DU, independently of the execution condition. (Supplementary Note 15) The DU according to any one of Supplements 1 to 14, wherein the LTM requested by the first message is an intra-DU LTM, and the DU is a DU that serves all of the plurality of candidate cells.(Supplementary Note 16) The DU according to any one of Supplements 1 to 14, wherein the LTM requested by the first message is an inter-DU LTM, the first candidate cell is different from a source cell of a first LTM in the LTM requested by the first message, and the DU is a candidate DU different from a source DU that provides the source cell. (Supplementary Note 17) The DU according to any one of Supplements 1 to 14, wherein the LTM requested by the first message is an inter-DU LTM, the first candidate cell is the same as a source cell of a first LTM in the LTM requested by the first message, and the DU is a source DU that provides the source cell. (Supplementary Note 18) A method performed by a distributed unit (DU) of a radio access network (RAN) node, comprising: receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM.(Supplementary Note 19) A program causing a computer to perform a method for a distributed unit (DU) of a radio access network (RAN) node, the method comprising: receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM. (Supplementary Note 20) A central unit (CU) of a radio access network (RAN) node, comprising: means for sending to a distributed unit (DU) of the RAN node a first message requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell, the first message indicating to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM. (Supplementary Note 21) The CU described in Supplementary Note 20, wherein the first message causes the DU to consider the one or more cell switches to be subject to the conditional LTM if the first message includes the first indication, and the first message causes the DU to consider the one or more cell switches to be subject to the normal LTM if the first message does not include the first indication.(Supplementary Note 22) The CU according to Supplementary Note 20 or 21, further comprising: means for receiving a second message based on the first message from the DU, wherein if the one or more cell switches are targets of the conditional LTM, the second message includes one or more execution conditions for the one or more cell switches in addition to an LTM configuration for the first candidate cell, and if the one or more cell switches are targets of the normal LTM, the second message includes an LTM configuration for the first candidate cell without including the one or more execution conditions. (Supplementary Note 23) The CU according to Supplementary Note 20 or 21, further comprising: means for receiving a second message based on the first message from the DU, wherein if the one or more cell switches are targets of the conditional LTM, the second message includes proposal information for the conditional LTM in addition to an LTM configuration for the first candidate cell, and if the one or more cell switches are targets of the normal LTM, the second message includes an LTM configuration for the first candidate cell without including the proposal information. (Supplementary Note 24) The CU according to Supplementary Note 23, further comprising means for determining one or more execution conditions for the one or more cell switches based on the proposal information. (Supplementary Note 25) The CU according to any one of Supplements 20 to 24, wherein the first message or the first indication explicitly indicates which one or more of the plurality of candidate cells excluding the first candidate cell are targets of the conditional LTM in a cell switch from the first candidate cell. (Supplementary Note 26) The CU according to any one of Supplements 20 to 24, wherein the first message or the first indication explicitly indicates which cell pairs included in the plurality of candidate cells are targets of the conditional LTM. (Supplementary Note 27) The CU according to any one of Supplements 20 to 26, wherein the first indication is an indication of a request for one or more execution conditions for the one or more cell switches. (Supplementary Note 28) The CU according to any one of Supplements 20 to 26, wherein the first indication is an indication of the conditional LTM.(Supplementary Note 29) The CU according to any one of Supplements 20 to 28, wherein the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message, and the first indication is included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message or an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message. (Supplementary Note 30) The CU according to any one of Supplements 20 to 28, wherein the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message, and the first indication is an information element included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message, separately from an LTM Information Setup information element or an LTM Information Modify information element. (Supplementary Note 31) The CU according to any one of Supplements 20 to 30, wherein the indication indicates to the DU whether the one or more cell switches are subject to the conditional LTM, and the first message or the first indication further indicates to the DU whether generation of an execution condition is required if the one or more cell switches are subject to the conditional LTM. (Supplementary Note 32) The CU according to any one of Supplements 20 to 31, wherein the first indication or a second indication included in the first message separately from the first indication indicates whether one or more cell switches from other cells to the first candidate cell are subject to conditional LTM.(Supplementary Note 33) The CU according to any one of Supplements 20 to 32, wherein the conditional LTM is an LTM in which the radio terminal executes a cell switch from the first candidate cell to another cell in response to the radio terminal determining that an execution condition is met, and the normal LTM is an LTM in which the radio terminal executes a cell switch from the first candidate cell to another cell in response to the radio terminal receiving a Layer 1 or Layer 2 cell switch command from a source DU, without depending on the execution condition. (Supplementary Note 34) The CU according to any one of Supplements 20 to 33, wherein the LTM requested by the first message is an intra-DU LTM, and the DU is a DU that serves all of the plurality of candidate cells. (Supplementary Note 35) The CU according to any one of Supplementary Notes 20 to 33, wherein the LTM requested by the first message is an inter-DU LTM, the first candidate cell is different from a source cell of a first LTM in the LTM requested by the first message, and the DU is a candidate DU different from a source DU that provides the source cell. (Supplementary Note 36) The CU according to any one of Supplementary Notes 20 to 33, wherein the LTM requested by the first message is an inter-DU LTM, the first candidate cell is the same as a source cell of a first LTM in the LTM requested by the first message, and the DU is a source DU that provides the source cell.(Supplementary Note 37) A method performed by a central unit (CU) of a radio access network (RAN) node, comprising: sending a first message to a distributed unit (DU) of the RAN node requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell, wherein the first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM. (Supplementary Note 38) A program causing a computer to perform a method for a central unit (CU) of a radio access network (RAN) node, the method comprising: sending a first message to a distributed unit (DU) of the RAN node requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell, the first message indicating to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.(Supplementary Note 39) A wireless terminal comprising: means for evaluating an execution condition for conditional Layer-1 / Layer-2 triggered Mobility (LTM) for each of one or more candidate cells; and means for performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell, wherein the means for performing the cell switch is configured to determine whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for the one candidate cell for which the execution condition is determined to be met was used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell. (Supplementary Note 40) The wireless terminal according to Supplementary Note 39, wherein the means for performing the cell switch is configured to: perform a first cell switch procedure that skips a random access procedure if the wireless terminal has the valid Timing Advance value and if the reference signal beam was used to acquire the valid Timing Advance value in the early Timing Advance acquisition procedure; otherwise, perform a second cell switch procedure that uses a random access procedure. (Supplementary Note 41) The wireless terminal according to Supplementary Note 39 or 40, wherein the reference signal beam is a Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) block (SSB) beam or a Channel State Information (CSI) Reference Signal (CSI-RS) beam.(Supplementary Note 42) A method performed by a wireless terminal, comprising: evaluating an execution condition for conditional Layer-1 / Layer-2 triggered Mobility (LTM) for each of one or more candidate cells; and performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell; wherein performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for the one candidate cell for which the execution condition is determined to be met was used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell. (Supplementary Note 43) A program for causing a computer to perform a method for a wireless terminal, the method comprising: evaluating an execution condition for conditional Layer-1 / Layer-2 triggered Mobility (LTM) for each of one or more candidate cells; and performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell; wherein performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for the one candidate cell for which the execution condition is determined to be met was used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.

[0147] This application claims priority based on Japanese Patent Application No. 2024-020584, filed February 14, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0148] 1 gNB 10 gNB-CU 11 gNB-CU-CP 12 gNB-CU-UP 21, 22 gNB-DU 31, 32, 33, 34 TRP 40 UE 51, 52, 53, 54 Cell 120 Intra-DU LTM 140 Inter-DU LTM 1702 Processor 1703 Memory 1803 Baseband processor 1804 Application processor 1806 Memory

Claims

1. A distributed unit (DU) of a radio access network (RAN) node, comprising: means for receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and means for determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM.

2. The DU of claim 1, wherein the determining means is configured to: determine that the one or more cell switches are subject to the conditional LTM if the first message includes the first indication; and determine that the one or more cell switches are subject to the normal LTM if the first message does not include the first indication.

3. The DU of claim 1 or 2, further comprising: means for generating a second message based on the first message; and means for sending the second message to the CU, wherein the generating means is configured to: if the one or more cell switches are targets of the conditional LTM, include one or more execution conditions for the one or more cell switches in the second message in addition to the LTM settings for the first candidate cell; and if the one or more cell switches are targets of the normal LTM, include the LTM settings for the first candidate cell in the second message without including the one or more execution conditions in the second message.

4. The DU of claim 1 or 2, further comprising: means for generating a second message based on the first message; and means for sending the second message to the CU, wherein the generating means is configured to: if the one or more cell switches are targets of the conditional LTM, include proposal information for the conditional LTM in addition to the LTM configuration for the first candidate cell; and if the one or more cell switches are targets of the normal LTM, not include the proposal information in the second message, but include the LTM configuration for the first candidate cell in the second message.

5. The DU of claim 4, wherein the suggestion information is taken into account by the CU to determine one or more performance conditions for the one or more cell switches.

6. The DU described in any one of claims 1 to 5, wherein the first message or the first indication explicitly indicates which one or more of the plurality of candidate cells, excluding the first candidate cell, are subject to the conditional LTM in a cell switch from the first candidate cell.

7. The DU according to any one of claims 1 to 5, wherein the first message or the first indication explicitly indicates which cell pairs included in the plurality of candidate cells are subject to the conditional LTM.

8. The DU according to any one of claims 1 to 7, wherein the first indication is an indication of one or more execution condition requirements for the one or more cell switches.

9. The DU of any one of claims 1 to 7, wherein the first representation is a representation of the conditional LTM.

10. The DU according to any one of claims 1 to 9, wherein the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message, and the first indication is included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message or an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message.

11. The DU according to any one of claims 1 to 9, wherein the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message, and the first indication is an information element included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message, separately from an LTM Information Setup information element or an LTM Information Modify information element.

12. A DU as described in any one of claims 1 to 11, wherein the first indication indicates to the DU whether the one or more cell switches are subject to the conditional LTM, and the first message or the first indication further indicates to the DU whether generation of an execution condition is required if the one or more cell switches are subject to the conditional LTM.

13. The DU of any one of claims 1 to 12, wherein the first indication or a second indication included in the first message separately from the first indication indicates whether one or more cell switches from another cell to the first candidate cell are subject to conditional LTM.

14. The DU described in any one of claims 1 to 13, wherein the conditional LTM is an LTM in which the radio terminal executes a cell switch from the first candidate cell to another cell in response to the radio terminal determining that an execution condition is met, and the normal LTM is an LTM in which the radio terminal executes a cell switch from the first candidate cell to another cell in response to the radio terminal receiving a Layer 1 or Layer 2 cell switch command from a source DU, without depending on the execution condition.

15. The DU according to any one of claims 1 to 14, wherein the LTM requested by the first message is an intra-DU LTM, and the DU is a DU that serves all of the plurality of candidate cells.

16. The DU described in any one of claims 1 to 14, wherein the LTM requested by the first message is an inter-DU LTM, the first candidate cell is different from the source cell of the first LTM in the LTM requested by the first message, and the DU is a candidate DU different from the source DU that serves the source cell.

17. The DU described in any one of claims 1 to 14, wherein the LTM requested by the first message is an inter-DU LTM, the first candidate cell is the same as the source cell of the first LTM in the LTM requested by the first message, and the DU is a source DU that serves the source cell.

18. A method performed by a distributed unit (DU) of a radio access network (RAN) node, comprising: receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM.

19. A program causing a computer to execute a method for a distributed unit (DU) of a radio access network (RAN) node, the method comprising: receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM.

20. A central unit (CU) of a radio access network (RAN) node, comprising: means for sending a first message to a distributed unit (DU) of the RAN node requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell, the first message indicating to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.

21. The CU of claim 20, wherein the first message causes the DU to consider the one or more cell switches to be subject to the conditional LTM if the first message includes the first indication, and the first message causes the DU to consider the one or more cell switches to be subject to the normal LTM if the first message does not include the first indication.

22. The CU of claim 20 or 21, further comprising means for receiving from the DU a second message based on the first message, wherein if the one or more cell switches are subject to the conditional LTM, the second message includes one or more execution conditions for the one or more cell switches in addition to LTM settings for the first candidate cell, and if the one or more cell switches are subject to the normal LTM, the second message includes LTM settings for the first candidate cell without including the one or more execution conditions.

23. The CU of claim 20 or 21, further comprising means for receiving from the DU a second message based on the first message, wherein if the one or more cell switches are targets of the conditional LTM, the second message includes proposal information for the conditional LTM in addition to LTM configuration for the first candidate cell, and if the one or more cell switches are targets of the normal LTM, the second message includes LTM configuration for the first candidate cell without including the proposal information.

24. The CU of claim 23, further comprising: means for determining one or more performance conditions for the one or more cell switches based on the proposal information.

25. A CU as described in any one of claims 20 to 24, wherein the first message or the first indication explicitly indicates which one or more of the plurality of candidate cells, excluding the first candidate cell, are subject to the conditional LTM in a cell switch from the first candidate cell.

26. A CU as described in any one of claims 20 to 24, wherein the first message or the first indication explicitly indicates which cell pairs included in the plurality of candidate cells are subject to the conditional LTM.

27. A CU as claimed in any one of claims 20 to 26, wherein the first indication is an indication of one or more performance condition requirements for the one or more cell switches.

28. The CU of any one of claims 20 to 26, wherein the first representation is a representation of the conditional LTM.

29. The CU according to any one of claims 20 to 28, wherein the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message, and the first indication is included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message or an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message.

30. The CU according to any one of claims 20 to 28, wherein the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message, and the first indication is an information element included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message, separately from an LTM Information Setup information element or an LTM Information Modify information element.

31. A CU as described in any one of claims 20 to 30, wherein the indication indicates to the DU whether the one or more cell switches are subject to the conditional LTM, and the first message or the first indication further indicates to the DU whether generation of an execution condition is required if the one or more cell switches are subject to the conditional LTM.

32. A CU as claimed in any one of claims 20 to 31, wherein the first indication or a second indication included in the first message separately from the first indication indicates whether one or more cell switches from another cell to the first candidate cell are subject to conditional LTM.

33. The CU described in any one of claims 20 to 32, wherein the conditional LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell in response to the wireless terminal determining that an execution condition is met, and the normal LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell in response to the wireless terminal receiving a Layer 1 or Layer 2 cell switch command from a source DU, without depending on the execution condition.

34. The CU according to any one of claims 20 to 33, wherein the LTM requested by the first message is an intra-DU LTM, and the DU is a DU that serves all of the plurality of candidate cells.

35. A CU as described in any one of claims 20 to 33, wherein the LTM requested by the first message is an inter-DU LTM, the first candidate cell is different from the source cell of the first LTM in the LTM requested by the first message, and the DU is a candidate DU different from the source DU that serves the source cell.

36. A CU as described in any one of claims 20 to 33, wherein the LTM requested by the first message is an inter-DU LTM, the first candidate cell is the same as the source cell of the first LTM in the LTM requested by the first message, and the DU is a source DU that serves the source cell.

37. A method performed by a central unit (CU) of a radio access network (RAN) node, comprising: sending a first message to a distributed unit (DU) of the RAN node requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell, wherein the first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.

38. A program causing a computer to perform a method for a central unit (CU) of a radio access network (RAN) node, the method comprising: sending a first message to a distributed unit (DU) of the RAN node requesting preparation of a first candidate cell for Layer-1 / Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell, the first message indicating to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.

39. A wireless terminal comprising: means for evaluating an execution condition for conditional Layer-1 / Layer-2 triggered Mobility (LTM) for each of one or more candidate cells; and means for performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell, wherein the means for performing the cell switch is configured to determine whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for the one candidate cell for which the execution condition is determined to be met was used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.

40. The wireless terminal of claim 39, wherein the means for performing the cell switch is configured to: perform a first cell switch procedure that skips a random access procedure if the wireless terminal has the valid Timing Advance value and if the reference signal beam was used to acquire the valid Timing Advance value in the early Timing Advance acquisition procedure; and otherwise perform a second cell switch procedure that uses a random access procedure.

41. The wireless terminal according to claim 39 or 40, wherein the reference signal beam is a Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) block (SSB) beam or a Channel State Information (CSI) Reference Signal (CSI-RS) beam.

42. A method performed by a wireless terminal, comprising: evaluating an execution condition for conditional Layer-1 / Layer-2 triggered Mobility (LTM) for each of one or more candidate cells; and performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell; wherein performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for the one candidate cell for which the execution condition is determined to be met was used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.

43. A program for causing a computer to execute a method for a wireless terminal, the method comprising: evaluating an execution condition for conditional Layer-1 / Layer-2 triggered Mobility (LTM) for each of one or more candidate cells; and, if the execution condition is met for one of the one or more candidate cells, performing a cell switch to the one candidate cell; wherein performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for the one candidate cell for which the execution condition is determined to be met was used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.

Images