Wireless terminal, wireless access network node, and methods for same

Abstract

This wireless terminal receives, from a network, configuration information indicating that a criterion for triggering a Layer 1 measurement reporting event associated with L1 / L2-triggered Mobility (LTM) from a serving cell to a candidate cell is based on a quality evaluation of each beam of one or more reference signal beams of the candidate cell. The wireless terminal evaluates the criteria in consideration of the quality of a plurality of reference signal beams belonging to a first subset of a first particular number, which is greater than one, of reference signal beams that are selected, in order of good measurement beam quality, from a first set of reference signal beams of the candidate cell. Thus, for example, it is possible to provide details of an event evaluation for an event-triggered layer 1 measurement reporting for a conditional LTM.

Description

Wireless terminal, radio access network node, 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 (registered trademark)) Release 18 specifies mechanisms and procedures for Layer-1 (L1) / Layer-2 (L2) Triggered Mobility (LTM) (see, for example, Section 9.2.3.5 of Non-Patent Document 1 and Section 5.3.5.18 of Non-Patent Document 2). When a wireless terminal (i.e., User Equipment (UE)) in a 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. 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] In 3GPP Release 18, LTM supports both intra-gNB Distributed Unit (gNB-DU) mobility and intra-gNB Central Unit (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] 3GPP plans to consider extensions to LTM for 3GPP Release 19 (see, for example, non-patent documents 3-11). For example, as described in non-patent document 3, the LTM extensions under consideration include conditional LTM (CLTM). CLTM may also be called by other names, such as UE-triggered LTM. 3GPP aims to support CLTM, which includes defining the conditions evaluated by the UE to trigger CLTM (CLTM execution). Further LTM extensions under consideration include inter-CU L2 mobility (LTM), Channel State Information (CSI) Reference Signal (CSI-RS) measurements for LTM procedures, and event-triggered L1 measurement reporting.

[0006] The details of the discussion on event-triggered L1 measurement reporting include use cases, beam-level or cell-level measurements, event definitions, configuration, measurement report content, MAC CE or Uplink Control Information (UCI) for measurement reporting. Non-patent literature 4-11 discloses the agreement, proposal, discussion, and comments on event-triggered L1 measurement reporting.

[0007] Regarding the configuration for event-triggered L1 measurement reporting, Non-Patent Document 4 discloses that it has been agreed that the L1 LTM measurement event configuration is associated with the L1 measurement resource configuration provided in the LTM configuration via RRC signaling.

[0008] Non-Patent Document 5 discloses the following agreement on event-triggered L1 measurement reporting at the 126th meeting of the 3GPP Technical Specification Group (TSG) Radio Access Network (RAN) Working Group #2 (WG2) (RAN2): Regarding use cases, event-triggered L1 measurements should be designed for the LTM purpose of selecting a candidate beam or cell to trigger early synchronization, and selecting a target beam or cell to trigger the LTM cell switch procedure.

[0009] For event-triggered L1 measurements, the baseline is to use beam-level measurements for event evaluation. Further consideration will be given to whether cell-level measurements are used for event evaluation.

[0010] Regarding the event definition, it is further considered which beams of the serving cell and neighboring (or candidate) cells are used for event evaluation. As Layer 1 measurement events, the following LTM events based on the beam quality of the serving cell and candidate cell are supported: - Event LTM2: Beam of serving cell becomes worse than absolute threshold; - Event LTM3: Beam of candidate cell becomes amount of offset better than beam of serving cell; - Event LTM4: Beam of candidate cell becomes better than absolute threshold; - Event LTM5: Beam of serving cell becomes worse than absolute threshold1 AND Beam of candidate cell becomes better than another absolute threshold2.

[0011] Regarding configuration, the L1 measurement resource configuration in LTM configuration supports both Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) block (SSB) and CSI-RS beam configuration. Event LTM3 and Event LTM5 assume that the same reference signal (RS) type is used in both the serving cell and neighboring (or candidate) cells.

[0012] RAN2 assumes that filtering of L1 measurements is required. It is up to RAN Working Group #1 (WG1) (RAN1) to decide whether L1 filtering as specified in the 3GPP specifications is required or whether it is left to the UE implementation.

[0013] LTM event evaluation can apply time to trigger (TTT), entering and leaving hysteresis, and beam-specific offsets. The application of cell-specific offsets is under further consideration. The need for measurement reporting after the leaving condition is met is under further consideration.

[0014] Non-patent documents 6-11 disclose proposals from various companies regarding event-triggered L1 measurement reports at the 126th meeting of 3GPP RAN2.

[0015] Non-Patent Document 6 discloses that cell-level measurement results based on the consolidation of multiple beams of a cell may be used for L1 event evaluation or to trigger L1 measurement reporting events. Specifically, Non-Patent Document 6 states that because reports triggered by L1 events are primarily used for mobility decisions, comprehensive consideration of cell-level measurement results helps select a target cell and improve mobility robustness. In some cases, the quality of a cell's best beam may not fully reflect the quality of the cell. For example, this may be the case when a candidate cell has only one strongest beam that is well above a threshold, while other beams of the candidate cell are well below the threshold. In this case, because the quality of most beams in the candidate cell is low, another cell switch may be triggered soon after the UE switches to this candidate cell, which may result in frequent ping-pong handovers or too short stays in the candidate cell.

[0016] Non-Patent Document 6 discloses that cell-level measurement results can be considered as input for L1 event evaluation to mitigate the ping-pong effect caused by single-beam-level measurement results. Non-Patent Document 6 also discloses that cell-level measurement results may be based on or derived from the consolidation of multiple beams of a cell, similar to existing Layer 3 (L3) Radio Resource Management (RRM) measurements. Non-Patent Document 6 also describes that in existing L3 RRM measurements, the network can configure an absolute threshold (e.g., absThreshSS-BlocksConsolidation) for the consolidation of beam-level measurement results and the maximum number of beams to be averaged (e.g., nrofSS-BlocksToAverage).

[0017] Non-Patent Document 7 states that triggering an L1 event based on the consolidated results of multiple RSs is useful for LTM in terms of use cases and signaling efficiency, similar to cell-level measurement evaluation. Furthermore, Non-Patent Document 7 states that, in principle, two types of L1 event evaluation metrics can be considered: L1 event evaluation based on the consolidated metric of multiple reference signals of a cell, and L1 event evaluation based on individual RS-level metrics. In L1 event evaluation based on the consolidated metric of multiple reference signals of a cell, event evaluation is performed based on the consolidated metric of the measurement results of multiple reference signals configured for a cell (serving cell or candidate cell). For example, if a UE is configured with four reference signals for an L1 event of an LTM candidate cell, all (or a subset) of the reference signals are used to evaluate the event. Such consolidated L1 events are useful for the network to make cell-level decisions.

[0018] Non-Patent Documents 6-11 provide various proposals regarding which beams of the serving cell and candidate cell are used for event evaluation. Non-Patent Document 6 discloses that the beams considered in the evaluation of an L1 measurement report event may be, for example, the best beam of the serving cell and the best beam of the candidate cell, or the considered beam of the serving cell may be the (current) beam associated with an activated Transmission Configuration Indicator (TCI) state.

[0019] Non-Patent Document 8 states that since there may be multiple beams for an LTM candidate cell or a serving cell, it is necessary to clarify which beam of the cell to use for event evaluation. Non-Patent Document 8 states that for a serving cell, if the serving cell is associated with an event, the best beam should be used for event evaluation. Non-Patent Document 8 states that for a candidate cell, the measurement results of each candidate beam should be evaluated for the associated event, and if the measurement results of any candidate beam meet the trigger criteria for the event, the event is triggered. Non-Patent Document 8 proposes that the following events are supported: - A3-like event: at least one candidate beam in the associated resource configuration becomes the amount of offset better than the best beam of the current PCell / PSCell; - A4-like event: at least one candidate beam in the associated resource configuration becomes better than the absolute threshold; - A5-like event: the best beam in the current PCell / PSCell becomes worse than absolute threshold1 AND at least one candidate beam in the associated resource configuration becomes better than another absolute threshold2.

[0020] Non-Patent Document 9 proposes that in evaluating an L1 measurement reporting event, the UE compares the best beam quality of a cell with a certain threshold or with the best beam quality of another cell.

[0021] Non-Patent Document 10 states that the beam of a candidate cell used for event evaluation can be the best beam or any beam detected by the UE in the L1 measurement resource configuration of the candidate cell. Non-Patent Document 10 also states that the beam of a serving cell used for event evaluation is the current beam. The term "current beam" refers to the current serving beam indicated by the TCI state of the latest scheduling Downlink Control Information (DCI) and used for the current transmission.

[0022] Non-Patent Document 11 describes that L1 measurement is based on an RS set, for example, an SSB set or a CSI-RS set, and that the network configures an SSB or CSI-RS resource set for the UE, and the UE performs L1 measurement according to the configured RS set. Non-Patent Document 11 states that events similar to Event A3 and Event A5 among existing L3 measurement report events are useful for triggering early synchronization and LTM cell switch, and proposes the following events: - L1-A3 event: the quality of one or more RSs in the candidate cell RS set is offset better than one or more RSs in the serving cell RS set; - L1-A5 event: the quality of one or more RSs in the serving cell RS set is worse than threshold1 and one or more RSs in the candidate cell RS set is better than threshold2.

[0023] Furthermore, Non-Patent Documents 6 and 9-11 propose introducing TTT into the evaluation of L1 measurement reporting events. In particular, Non-Patent Document 6 states that if a criterion such as TTT is introduced into event evaluation, it may be necessary to further consider whether a change in the best beam of a cell resets the event evaluation for that cell. For example, if the best beam of a candidate cell (e.g., beam_1) satisfies the entry criteria for an event, the UE starts the TTT timer. However, the best beam of the candidate cell may subsequently be changed to another beam (e.g., beam_2), and beam_1 may no longer satisfy the entry criteria for the event while the timer is running. In this case, if the UE resets the timer, restarts the timer, and reevaluates the new best beam, the triggering of the L1 measurement report may be delayed. Alternatively, the UE may continue evaluating the event as long as at least one candidate beam of the candidate cell satisfies the entry criteria while the TTT timer is running. In other words, a change in the best beam of a cell does not affect the event evaluation for that cell.

[0024] 3GPP TS 38.300 V18.1.0 (2024-03) "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; NR and NG-RAN Overall Description; Stage 2 (Release 18)", March 2024 3GPP TS 38.331 V18.1.0 (2024-03) "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Radio Resource Control (RRC) protocol specification (Release 18)", March 2024 Intel, "New WID: NR mobility enhancements Phase 4", RP-234036, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023 Samsung, "Report from session on V2X / SL, R19 NES and MOB", R2-2403731, 3GPP TSG-RAN WG2 Meeting #125bis, Changsha, China, April 15-19, 2024 Samsung, "Report from session on V2X / SL, R19 NES and MOB", R2-2405701, 3GPP TSG-RAN WG2 Meeting #126, Fukuoka, Japan, May 20-24, 2024 ZTE Corporation, "Discussion on event-triggered L1 measurement reporting", R2-2405063, 3GPP TSG-RAN WG2 Meeting #126, Fukuoka, Japan, May 20-24, 2024 LG Electronics Inc., "Measurement related enhancements for LTM", R2-2405492, 3GPP TSG-RAN WG2 Meeting #126, Fukuoka, Japan, May 20-24, 2024CATT, "Event-triggered L1 measurement reporting", R2-2404166, 3GPP TSG-RAN WG2 Meeting #126, Fukuoka, Japan, May 20-24, 2024MediaTek Inc., "Discussion on event-triggered L1 measurement reporting", R2-2404297, 3GPP TSG-RAN WG2 Meeting #126, Fukuoka, Japan, May 20-24, 2024Apple, "Measurement enhancements for LTM", R2-2404677, 3GPP TSG-RAN WG2 Meeting #126, Fukuoka, Japan, May 20-24, 2024Huawei, HiSilicon, "Event triggered L1 report for LTM", R2-2404779, 3GPP TSG-RAN WG2 Meeting #126, Fukuoka, Japan, May 20-24, 2024.

[0025] The inventors have investigated support for event-triggered L1 measurement reporting related to LTM (and CLTM) and have found various challenges. One of these challenges concerns the evaluation or definition of L1 measurement reporting events. As mentioned above, there have been many proposals regarding the evaluation and definition of L1 measurement reporting events. Essentially, these proposals use criteria and parameters similar to those used in the evaluation of existing L3 measurement reporting events (e.g., events A3 and A5), such as entry and exit conditions, TTT, offset, and hysteresis, but modified to suit beam-level evaluation. In addition, these proposals include the use of integrated metrics from multiple reference signals of a cell for L1 event evaluation (e.g., Non-Patent Documents 6 and 7). Furthermore, Non-Patent Document 6 discusses whether a change in the best beam of a cell during TTT resets the event evaluation for that cell if a TTT-like criterion is introduced for event evaluation. However, the details of the evaluation and definition of L1 measurement reporting events are still unclear at this time.

[0026] One of the objectives that the embodiments disclosed in this specification aim to achieve is to provide an apparatus, a method, and a program that contribute to solving at least one of the problems related to event-triggered L1 measurement reporting. It should be noted that this objective is only one of the objectives that the embodiments disclosed in this specification aim to achieve. Other objectives or objectives and novel features will become apparent from the description of this specification or the accompanying drawings.

[0027] In a first aspect, a wireless terminal is configured to receive configuration information from a network indicating that a criterion for triggering a Layer 1 measurement reporting event related to LTM from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, and further configured to evaluate the criterion by taking into account the quality of a plurality of reference signal beams belonging to a first subset of a first specific number greater than one, selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

[0028] In a second aspect, a method performed by a wireless terminal includes (a) receiving configuration information from a network indicating that a criterion for triggering a Layer 1 measurement reporting event associated with an LTM from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, and (b) evaluating the criterion taking into account the quality of a plurality of reference signal beams belonging to a first subset of a first specific number greater than one, selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

[0029] In a third aspect, a radio access network (RAN) node is configured to transmit, to a wireless terminal, configuration information indicating that a criterion for triggering a Layer 1 measurement reporting event related to LTM from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, the configuration information including a first specific number of configurations greater than 1. The configuration information causes the wireless terminal to evaluate the criterion taking into account the quality of a plurality of reference signal beams belonging to a first subset of the first specific number of reference signal beams selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

[0030] In a fourth aspect, a method performed by a RAN node includes transmitting configuration information to a wireless terminal indicating that a criterion for triggering a Layer 1 measurement reporting event related to LTM from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, the configuration information including a first specific number of configurations greater than 1. The configuration information causes the wireless terminal to evaluate the criterion taking into account the quality of a plurality of reference signal beams belonging to a first subset of the first specific number of reference signal beams selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

[0031] In a fifth aspect, a program includes a group of instructions (software code) that, when loaded into a computer, causes the computer to perform the method according to the second or fourth aspect described above.

[0032] 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 event-triggered L1 measurement reporting, including the above-described problem.

[0033] FIG. 1 illustrates an example configuration of a wireless communication system according to one or more embodiments. FIG. 2 illustrates an example configuration of a wireless communication system according to one or more embodiments. FIG. 3 illustrates an example signaling procedure for LTM according to one or more embodiments. FIG. 4 illustrates an example signaling procedure for conditional LTM according to one or more embodiments. FIG. 5 illustrates a sequence diagram of an example operation of a UE and a RAN node according to one or more embodiments. FIG. 6 illustrates a sequence diagram of an example operation of a UE according to one or more embodiments. FIG. 7 illustrates a sequence diagram of an example operation of a UE according to one or more embodiments. FIG. 8 illustrates a sequence diagram of an example operation of a UE according to one or more embodiments. FIG. 9 illustrates a block diagram of an example configuration of a CU, CU-CP, CU-UP, and DU according to one or more embodiments. FIG. 10 illustrates a block diagram of an example configuration of a UE according to one or more embodiments.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The following embodiments are described primarily for the 3GPP fifth generation mobile communication system (5G system), but may also be applied to future 3GPP Beyond 5G or 6G systems, or other wireless communication systems that support technologies similar to 3GPP LTM.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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).

[0042] 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).

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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, in normal LTM, 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.

[0049] 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 an LTM configuration, including 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., 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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, and the specific reference signal may be, for example, an SSB or a CSI-RS.

[0054] 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.

[0055] LTM (regular LTM and CLTM) supports both intra-gNB-DU mobility and intra-gNB-CU inter-gNB-DU mobility. LTM may also support inter-gNB-CU L2 mobility. LTM supports not only intra-frequency mobility but also inter-frequency mobility. LTM supports the following scenarios: PCell change in non-CA scenarios; PCell change without SCell change in CA scenarios; PCell change with SCell change in CA scenarios; and Dual Connectivity scenarios. PCell change with SCell change in CA scenarios 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.

[0056] 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.

[0057] 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.

[0058] The control plane handling for regular LTM will be described in more detail below. The 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 occur. The UE 40 may perform Contention-based Random Access (CBRA) or Contention-free RA (CFRA) during a cell switch.

[0059] 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, and may further include a Timing Advance Command field, a TCI state ID field, an Uplink (UL) TCI state ID field, and a Random Access Preamble index field.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The Random Access Preamble index field indicates the random access preamble index of the contention-free random access resources.

[0064] 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.

[0065] 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 serving cell may also be referred to as a source cell from a mobility (e.g., LTM) perspective. 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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 containing LTM configuration to UE 40. The LTM configuration includes 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.

[0070] 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.

[0071] 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 transmits 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. The transmission of the L1 measurement reports may be periodic, semi-persistent, or aperiodic. Additionally or alternatively, as described below, the transmission of the L1 measurement reports may be event-triggered. In other words, the transmission of the L1 measurement reports may be triggered when a criterion for an L1 measurement report event is met.

[0072] In step 307, the gNB1 decides to perform an LTM cell switch to one of the prepared candidate cells and transmits 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 and triggers 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 TA is not available, the UE 40 performs a random access procedure toward the target cell.

[0073] 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.

[0074] 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.

[0075] 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 .

[0076] 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 including CLTM configuration to UE 40. The CLTM configuration includes configurations of one or more CLTM candidate cells and CLTM execution conditions for each candidate cell. In step 404, UE 40 stores the CLTM candidate cell configuration and CLTM execution conditions and sends an RRCReconfigurationComplete message to gNB1.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] Step 406 is a CLTM evaluation phase in which the UE 40 evaluates the CLTM execution conditions of each candidate cell.

[0081] 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.

[0082] 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 via 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 transmitted on a PUCCH.

[0083] 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 has been initiated, although step 4071 may be omitted.

[0084] 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.

[0085] Step 409 is the CLTM completion phase, which may be similar to step 311 in FIG.

[0086] The gNB1 and UE 40 may support event-triggered L1 measurement reporting for LTM. For example, the L1 measurement report normally transmitted during the LTM execution phase of LTM (e.g., step 306 in FIG. 3 ) may be an event-triggered L1 measurement report. The event-triggered L1 measurement report may be used by the gNB1 to select a target beam or cell and trigger an LTM cell switch procedure. Additionally or alternatively, the event-triggered L1 measurement report may be used by the gNB1 to select a candidate beam or cell for triggering early synchronization (e.g., step 305 in FIG. 3 ) by a PDCCH order. The event-triggered L1 measurement report may also be used in CLTM. Specifically, even in CLTM, the event-triggered L1 measurement report may be used by the gNB1 to select a candidate beam or cell for triggering early synchronization (e.g., step 405 in FIG. 4 ) by a PDCCH order.

[0087] The UE 40 evaluates criteria for triggering an L1 measurement reporting event. Alternatively, or in other words, the UE 40 determines whether to trigger an L1 measurement report or an L1 measurement reporting event based on (or using) the criteria for triggering an L1 measurement reporting event. The term "criterion" may be rephrased as one or more conditions, one or more trigger conditions, one or more trigger states, etc. The term "criterion for triggering an L1 measurement reporting event" may be rephrased as criteria for an L1 measurement reporting event, criteria for triggering an L1 measurement report, or criteria for an event-triggered L1 measurement report, etc.

[0088] The criteria for triggering an L1 measurement reporting event may include an entry (or entering) condition that is considered to start the L1 measurement reporting. Additionally, the criteria may include a leaving (or exit) condition that is considered to stop the L1 measurement reporting. Similar to existing L3 measurement reporting (e.g., events A2, A3, A4, and A5), the entry and exit conditions may be defined with hysteresis. Similar to existing L3 measurement reporting (e.g., event A3), the entry and exit conditions may be defined with an offset.

[0089] Similar to existing L3 measurement report triggering, UE 40 may use the TTT to determine entry and exit conditions associated with an L1 measurement report event. For example, UE 40 may initiate a procedure for transmitting an L1 measurement report for a candidate cell or a candidate reference signal beam to gNB1 if the entry condition applied to the L1 measurement report event is continuously satisfied for the candidate cell or candidate reference signal beam during a predetermined first period (e.g., TTT period). In other words, UE 40 may initiate or trigger an L1 measurement report if the entry condition applied to the L1 measurement report event is satisfied for all L1 measurements (or filtered L1 measurement results) performed during the predetermined first period (e.g., TTT period).

[0090] The UE 40 may stop transmitting L1 measurement reports for a candidate cell if the opt-out condition applied to the L1 measurement reporting event is continuously satisfied for the candidate cell for a predetermined second period. In other words, the UE 40 may stop transmitting L1 measurement reports if the opt-out condition applied to the L1 measurement reporting event is satisfied for all L1 measurements (or filtered L1 measurement results) performed during a predetermined second period (e.g., TTT period). The length of the second period may be the same as or different from the length of the first period.

[0091] Alternatively, the UE 40 may initiate a procedure for transmitting an L1 measurement report to the gNB 1 if an entry condition applicable to the L1 measurement reporting event is satisfied a predetermined number of times within a predetermined first period of time. The UE 40 may stop transmitting the L1 measurement report if a departure condition applicable to the L1 measurement reporting event is satisfied a predetermined number of times within a predetermined second period of time.

[0092] Alternatively, the UE 40 may initiate a procedure for transmitting an L1 measurement report to the gNB 1 when an entry condition applied to the L1 measurement reporting event is satisfied a predetermined number of times in succession. The UE 40 may stop transmitting an L1 measurement report when a departure condition applied to the L1 measurement reporting event is satisfied a predetermined number of times in succession.

[0093] In response to the entry condition applicable to the L1 measurement reporting event being satisfied, the UE 40 may transmit the L1 measurement report periodically at a predetermined interval until the exit condition applicable to that L1 measurement reporting event is satisfied. Alternatively, in response to the entry condition applicable to the L1 measurement reporting event being satisfied, the UE 40 may transmit the L1 measurement report only once or a predetermined number of times.

[0094] The gNB1 and UE40 may support at least one of the following LTM events as L1 measurement events based on the beam quality of the serving cell and candidate cell: - Event LTM2: Beam of serving cell becomes worse than absolute threshold; - Event LTM3: Beam of candidate cell becomes amount of offset better than beam of serving cell; - Event LTM4: Beam of candidate cell becomes better than absolute threshold; - Event LTM5: Beam of serving cell becomes worse than absolute threshold1 AND Beam of candidate cell becomes better than another absolute threshold2.

[0095] The beam considered in the evaluation of the L1 measurement event may be SSB (ie, SSB beam) or CSI-RS (ie, CSI-RS beam).

[0096] If the serving cell is associated with the L1 measurement event, the best beam of the serving cell, i.e., the reference signal beam with the best quality (e.g., L1-RSRP), may be used for event evaluation. Alternatively, the reference signal beam of the serving cell considered in the event evaluation may be the current reference signal beam associated with an activated or designated TCI state. Alternatively, the measurement results of each of multiple reference signal beams of the serving cell may be evaluated for the L1 measurement event. In other words, if the measurement results of any of multiple reference signal beams (or beams to be measured) of the serving cell meet the criteria applied to the event, UE 40 may trigger the event and start or stop transmitting L1 measurement reports for the candidate cell.

[0097] For a candidate cell, the measurement results of each candidate reference signal beam may be evaluated for an L1 measurement event. In other words, if the measurement results of any of multiple candidate beams (or measurement beams) of the candidate cell satisfy the criteria applied to the event, UE 40 may trigger the event for the candidate cell and start or stop transmitting L1 measurement reports for the candidate cell. Alternatively, the beam of the candidate cell considered in the event evaluation may be the best beam, i.e., the beam with the best quality (e.g., L1-RSRP), among the candidate beams (or measurement beams) of the candidate cell configured in UE 40.

[0098] In evaluating an L1 measurement report event, a consolidated metric derived from a set of quality measurements of multiple reference signal beams of a candidate cell may be used in addition to a beam-level metric, such as the L1-RSRP for each reference signal beam. Similarly, if a serving cell is associated with the L1 measurement event, in evaluating the L1 measurement report event, a consolidated metric derived from a set of quality measurements of multiple reference signal beams of the serving cell may be used in addition to a beam-level metric. Alternatively, a consolidated metric derived from a set of quality measurements of multiple reference signal beams of the serving cell may be used instead of a beam-level metric. The consolidated metric may be, for example, an average of the quality measurements of multiple reference signal beams. The beam-level metric may also be referred to as beam quality, beam-level quality, or beam measurement result. The consolidated metric may also be referred to as a cell-level metric, cell-level quality, or cell quality.

[0099] 5 shows an example of the operation of the gNB1 and the UE 40 regarding event-triggered L1 measurement reporting. In step 501, the gNB1 transmits a configuration for event-triggered L1 measurement reporting to the UE 40. The gNB1 may transmit the configuration for event-triggered L1 measurement reporting to the UE 40 using an RRC message (e.g., an RRC Reconfiguration message).

[0100] The configuration of event-triggered L1 measurement reporting may include a reporting configuration including an event definition and a resource configuration associated with the reporting configuration. The resource configuration indicates a set of reference signals to be measured for the candidate cell. In other words, the resource configuration indicates which reference signal beams (e.g., one or more SSBs or one or more CSI-RSs) are to be measured. The gNB1 may transmit the configuration of event-triggered L1 measurement reporting to the UE 40 together with or in association with the LTM configuration by including it in the LTM configuration. For example, the reporting configuration for event-triggered L1 measurement reporting may be included in the CSI measurement configuration (e.g., CSI-MeasConfig or LTM-CSI-ReportConfig included in the RRC Reconfiguration message). Meanwhile, the resource configuration for event-triggered L1 measurement reporting may be included in the LTM configuration (e.g., LTM-Config included in the RRC Reconfiguration message).

[0101] In step 502, the UE 40 evaluates criteria for triggering an L1 measurement report. As described above, the criteria may include entry conditions that are considered to initiate an L1 measurement report, and may further include exit conditions. The UE 40 may evaluate the criteria for triggering an L1 measurement report as shown in FIG. 6.

[0102] FIG. 6 illustrates an example of event evaluation for an L1 measurement report. In step 601, UE 40 determines that the entry condition applicable to the L1 measurement report event is satisfied for the candidate cell or candidate reference signal beam for the configured TTT period. In step 602, UE 40 transmits an L1 measurement report associated with the event in response to the determination in step 601. According to the configuration of the event-triggered L1 measurement report, UE 40 may periodically transmit the L1 measurement report at a predetermined interval. The L1 measurement report may be transmitted via Layer 1 signaling (e.g., UCI) or Layer 2 signaling (e.g., MAC / CE). The L1 measurement report may indicate not only the quality of the reference signal beam (e.g., L1-RSRP) for which the entry condition is satisfied, but also the quality of other reference signals of the candidate cell. In addition, the L1 measurement report may indicate an aggregate metric derived from a set of quality measurements of multiple reference signal beams of the candidate cell.

[0103] In step 603, UE 40 determines that the exit condition applicable to the L1 measurement report event has been satisfied for the candidate cell or candidate reference signal beam for the configured TTT period. The length of the TTT period applicable to the exit condition may be the same as or different from the length of the TTT period applicable to the entry condition. In step 604, UE 40 stops transmitting the L1 measurement report associated with the event in response to the determination in step 603.

[0104] In one example, UE 40 may determine whether the entry condition is satisfied and whether the TTT period for the entry condition is satisfied for each candidate beam of a candidate cell. UE 40 may independently and in parallel evaluate whether the entry condition is satisfied during the TTT period for a first and second candidate beam of a candidate cell. In other words, UE 40 may independently and in parallel evaluate whether the entry condition is satisfied during the TTT period for a first candidate beam, while evaluating whether the entry condition is satisfied during the TTT period for a second candidate beam. UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to the first candidate beam of a candidate cell satisfying the entry condition for the first time. Then, in response to the first candidate beam continuously satisfying the entry condition until the expiration of the TTT timer (i.e., the TTT period has elapsed), UE 40 may trigger an L1 measurement report for the first candidate beam. If the first candidate beam no longer satisfies the entry condition before the TTT period has elapsed, the UE 40 may restart evaluating the entry condition for the first candidate beam. The UE 40 may also perform evaluation of the second candidate beam in a similar manner.

[0105] In another example, UE 40 may determine whether the entry condition is satisfied and whether the TTT for the entry condition is satisfied for all or a subset of candidate beams of a candidate cell. For example, UE 40 may evaluate whether the entry condition is satisfied for a best beam among multiple candidate beams of a candidate cell. UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to the best beam of the candidate cell first satisfying the entry condition. UE 40 may then continue the started TTT timer even if the best beam of the candidate cell changes during the TTT period. UE 40 may trigger an L1 measurement report for the candidate cell in response to the best beam of the candidate cell continuously satisfying the entry condition during the TTT period, even if the best beam of the candidate cell changes during the TTT period.

[0106] If the serving cell is associated with the L1 measurement event, the UE 40 may determine whether the entry condition is satisfied and whether the TTT for the entry condition is satisfied for all or a subset of the reference signal beams to be measured of the serving cell. For example, the UE 40 may evaluate whether the entry condition is satisfied for a best beam among multiple reference signal beams of the serving cell. The UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to the best beam of the serving cell first satisfying the entry condition. The UE 40 may then continue the TTT timer even if the best beam of the serving cell changes during the TTT period. Even if the best beam of the serving cell changes during the TTT period, the UE 40 may trigger an L1 measurement report in response to the best beam of the serving cell continuously satisfying the entry condition during the TTT period.

[0107] If the serving cell is associated with the L1 measurement event, the UE 40 may perform a beam-by-beam determination of whether the entry condition is satisfied and a TTT period for the entry condition is satisfied for each of all or a subset of the reference signal beams to be measured of the serving cell. The UE 40 may independently and in parallel evaluate whether the entry condition is satisfied during the TTT period for each reference signal beam to be measured of the serving cell. The UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to at least one of the multiple serving cell reference signal beams first satisfying the entry condition. The UE 40 may then trigger an L1 measurement report in response to any serving cell reference signal beam continuously satisfying the entry condition until the expiration of the TTT timer (i.e., the TTT period has elapsed).

[0108] First Embodiment A configuration example of a wireless communication system according to this embodiment is similar to the configuration example described with reference to Figures 1 and 2. This embodiment provides details of event evaluation or event definition for event-triggered L1 measurement reporting.

[0109] In this embodiment, UE 40 receives configuration information regarding LTM from the serving cell to the candidate cell, such as a configuration for event-triggered L1 measurement reporting (e.g., step 501 in FIG. 5 ), from the network (e.g., gNB1). The configuration information, or the configuration for event-triggered L1 measurement reporting, indicates that the criteria for triggering an L1 measurement reporting event are based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell. Furthermore, UE 40 evaluates the criteria for triggering an L1 measurement reporting event (e.g., step 502 in FIG. 5 ). In evaluating the criteria, UE 40 considers the quality of multiple reference signal beams belonging to a first subset of a first specific number (greater than one) of reference signal beams selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

[0110] The first specific number defining or specifying the size of the first subset may be referred to as a specified, certain, predetermined, preset, or preconfigured number. The first specific number may be provided to the UE 40 by the gNB1 and may be included in configuration information or a configuration (e.g., reporting configuration) of event-triggered L1 measurement reporting.

[0111] In one example, the UE 40 may perform a beam-by-beam determination of whether the entry condition is satisfied and a TTT period for the entry condition for each of a plurality of candidate beams belonging to the first subset. The UE 40 may independently and in parallel evaluate whether the entry condition is satisfied during the TTT period for each reference signal beam belonging to the first subset. The UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to the first candidate beam belonging to the first subset first satisfying the entry condition. Then, in response to the first candidate beam continuously satisfying the entry condition until the TTT timer expires (i.e., the TTT period has elapsed), the UE 40 may trigger an L1 measurement report for the first candidate beam. If the first candidate beam no longer satisfies the entry condition before the TTT period has elapsed, the UE 40 may restart the evaluation of the entry condition for the first candidate beam. The UE 40 may perform a similar evaluation for each of the remaining one or more beams belonging to the first subset. Note that if a candidate beam in the first subset initially satisfies the entry condition but leaves the first subset before the expiration of the TTT period, UE 40 may stop evaluating the entry condition for the candidate beam. Then, if the candidate beam again belongs to the first subset, UE 40 may restart evaluating the entry condition for the candidate beam. For example, if the quality of the candidate beam becomes worse than the quality of at least one other reference signal beam that is not included in the first subset, the candidate beam is considered to have left the first subset.

[0112] In another example, UE 40 may determine whether the entry condition is satisfied and whether the TTT related to the entry condition is satisfied on a subset-by-subset basis for all of a plurality of candidate beams belonging to the first subset. For example, UE 40 may evaluate whether the entry condition is satisfied for a best beam among a plurality of candidate beams belonging to the first subset. UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to the best beam in the first subset first satisfying the entry condition. UE 40 may then continue the started TTT timer even if the best beam in the first subset changes during the TTT period. UE 40 may trigger an L1 measurement report for the candidate cell in response to the best beam in the first subset continuously satisfying the entry condition during the TTT period, even if the best beam in the first subset changes during the TTT period. In addition, if a beam (e.g., beam #1) that was the best beam when the entry conditions were first satisfied is removed from the first subset, UE 40 may stop evaluating the entry conditions for that beam (e.g., beam #1). UE 40 may then start evaluating the entry conditions for the best beam (e.g., beam #2) in the first subset at that time. For example, if the quality of a candidate beam (e.g., beam #1) becomes worse than the quality of at least one other reference signal beam that is not included in the first subset, the candidate beam is considered to have been removed from the first subset.

[0113] Furthermore, in evaluating the criteria for triggering an L1 measurement reporting event, UE 40 may consider the quality of multiple reference signal beams belonging to a second subset of a second specific number greater than one, selected from a second set of reference signal beams of the serving cell in order of best measured beam quality.

[0114] The second specific number defining or specifying the size of the second subset may be referred to as a specified, certain, predetermined, preset, or preconfigured number. The second specific number may be provided to the UE 40 by the gNB1 and may be included in configuration information or a configuration (e.g., reporting configuration) of the event-triggered L1 measurement report.

[0115] If the serving cell is associated with the L1 measurement event, the UE 40 may determine whether the entry condition is satisfied and whether the TTT for the entry condition is satisfied for all of the reference signal beams belonging to the second subset on a subset-by-subset basis. The entry condition may be the entry condition for Event LTM2, Event LTM3, or Event LTM5 described above. For example, the UE 40 may evaluate whether the entry condition is satisfied for the best beam among the reference signal beams belonging to the second subset. The UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to the best beam in the second subset first satisfying the entry condition. The UE 40 may then continue the TTT timer even if the best beam in the second subset changes during the TTT period. Even if the best beam in the second subset changes during the TTT period, the UE 40 may trigger an L1 measurement report in response to the best beam in the second subset continuously satisfying the entry condition during the TTT period.

[0116] In another example, when the serving cell is associated with the L1 measurement event, UE 40 may evaluate the initial satisfaction of the entry condition with respect to the best beam among multiple reference signal beams belonging to the second subset. UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to the best beam (e.g., beam #1) in the second subset first satisfying the entry condition. UE 40 may then continue the TTT timer as long as the beam (e.g., beam #1) that was the best beam when the entry condition was first satisfied continues to satisfy the entry condition during the TTT period, even if the best beam in the second subset changes to another beam (e.g., beam #2) during the TTT period. UE 40 may trigger an L1 measurement report in response to the beam (e.g., beam #1) that was the best beam when the entry condition was first satisfied continuously satisfying the entry condition during the TTT period.

[0117] In yet another example, when the serving cell is associated with the L1 measurement event, the UE 40 may perform a beam-by-beam determination of whether the entry condition is satisfied and a TTT period for the entry condition for each of a plurality of reference signal beams belonging to the second subset. The UE 40 may independently and in parallel evaluate whether the entry condition is satisfied during the TTT period for each reference signal beam belonging to the second subset. The entry condition may be the entry condition for Event LTM2, Event LTM3, or Event LTM5 described above. The UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to at least one of the plurality of reference signal beams belonging to the second subset first satisfying the entry condition. Then, the UE 40 may trigger an L1 measurement report in response to any reference signal beam belonging to the second subset continuously satisfying the entry condition until the expiration of the TTT timer (i.e., the TTT period has elapsed). For example, if the beam with the worst quality (worst beam) among the serving cell reference signal beams belonging to the second subset satisfies the entry condition for the TTT, the UE 40 may trigger an L1 measurement report. The UE 40 may evaluate whether the entry condition is satisfied for the worst beam in the second subset. The UE 40 may start a TTT timer for measuring the expiration of the TTT period in response to the worst beam in the second subset first satisfying the entry condition. The UE 40 may then continue the TTT timer even if the worst beam in the second subset changes during the TTT period. The UE 40 may trigger an L1 measurement report in response to the worst beam in the second subset continuously satisfying the entry condition for the TTT period, even if the worst beam in the second subset changes during the TTT period.

[0118] The UE 40 may perform event evaluation taking into account both a first subset of reference signal beams of the candidate cell and a second subset of reference signal beams of the serving cell. The UE 40 may perform the determination of whether the entry condition is satisfied and the determination of whether the TTT for the entry condition is satisfied for each of the plurality of reference signal beams belonging to the first subset, beam by beam, and for each of the plurality of reference signal beams belonging to the second subset. The entry condition may be the entry condition for the above-mentioned Event LTM3 or Event LTM5. For example, if any one of the serving cell reference signal beams belonging to the second subset satisfies the entry condition for the TTT for one of the candidate cell reference signal beams belonging to the first subset, the UE 40 may trigger an L1 measurement report. This L1 measurement report may be for the candidate cell or the one candidate cell reference signal beam. For example, if the beam with the worst quality (worst beam) among the serving cell reference signal beams belonging to the second subset satisfies the entry condition for one of the candidate cell reference signal beams belonging to the first subset during the TTT, the UE 40 may trigger an L1 measurement report for the candidate cell or the one candidate cell reference signal beam.

[0119] The above-described operations of UE 40 and gNB 1 can provide examples of event evaluation or event definition for event-triggered L1 measurement reporting.

[0120] Second Embodiment A configuration example of a wireless communication system according to this embodiment is similar to the configuration example described with reference to Figures 1 and 2. This embodiment provides details of event evaluation or event definition for event-triggered L1 measurement reporting.

[0121] In this embodiment, UE 40 evaluates criteria for triggering a Layer 1 measurement reporting event related to LTM from the serving cell to the candidate cell by considering the replacement of at least one beam belonging to a first subset of a first specific number of reference signal beams greater than one selected from a first set of reference signal beams of the candidate cell in order of measurement beam quality. The first set is a set of reference signals to be measured of the candidate cell. The first set is configured in UE 40 by gNB1 (e.g., step 501 of FIG. 5). UE 40 selects the first specific number of beams from the best beams in order of quality (e.g., L1-RSRP) based on L1 measurements (or filtered L1 measurement results) of the first set of reference signal beams of the candidate cell.

[0122] The first particular number defining or specifying the size of the first subset may be referred to as a specified, certain, predetermined, preset, or preconfigured number. The first particular number may be provided to the UE 40 by the gNB1 and may be included in an event-triggered L1 measurement reporting configuration (e.g., reporting configuration).

[0123] 7 shows an example of an evaluation by UE 40 of the entry conditions that apply to an L1 measurement reporting event. In step 701, UE 40 determines whether the entry conditions are continuously met for a candidate cell (or a candidate reference signal beam of the candidate cell) for a predetermined first period (e.g., TTT period).

[0124] In step 702, UE 40 determines whether, after the entry condition is first satisfied and before the first period of time has elapsed, at least one beam belonging to a first subset of a first specific number (greater than one) of reference signal beams selected from a first set of reference signal beams of the candidate cell in descending order of measured beam quality has been replaced. For example, UE 40 determines whether an event has occurred in which the measured beam quality of another beam not belonging to the first subset has become better than the beam quality of a certain beam belonging to the first subset, and the other beam has instead belonged to the first subset. If such a beam replacement has occurred, UE 40 discards the current evaluation of the entry condition for the candidate cell and restarts evaluation of the entry condition using the new first subset after the beam replacement.

[0125] 7, there is no particular limitation on the entry condition. For example, the entry condition may be the entry condition for the above-mentioned Event LTM3, Event LTM4, or Event LTM5. The entry condition may include comparing the quality of the reference signal beam of the candidate cell with a threshold or comparing the quality of the reference signal beam of the serving cell. The entry condition may include comparing the quality of the reference signal beam included in the first subset with a threshold or comparing the quality of the reference signal beam of the serving cell.

[0126] 7 may be modified, for example, as follows: In step 701, UE 40 may determine whether the entry condition is satisfied a predetermined number of times during a predetermined first period. In this case, in step 702, UE 40 may determine whether there has been a change in at least one beam belonging to the first subset after the entry condition is satisfied for the first time and before the entry condition is satisfied the predetermined number of times during the first period.

[0127] Alternatively, UE 40 may determine whether the entry condition is satisfied a predetermined number of times in succession in step 701. In this case, UE 40 may determine whether at least one beam belonging to the first subset has been replaced after the entry condition is satisfied for the first time and before the entry condition is satisfied a predetermined number of times in succession in step 702.

[0128] 8 shows an example of signaling related to event-triggered L1 measurement reporting between gNB1 and UE 40. In step 801, gNB1 transmits a configuration for event-triggered L1 measurement reporting to UE 40. This configuration includes a first specific number that defines or specifies the size of a first subset. As described above, the first subset is a set of beams selected from a set of reference signal beams of candidate cells measured by UE 40 in order of best measured beam quality.

[0129] As can be seen from the above description, in this embodiment, the UE 40 takes into account the change of at least one beam belonging to the first subset of reference signal beams of the candidate cell in the evaluation of the Layer 1 measurement report event. As an example, a case may be considered in which the beams belonging to the first subset of reference signal beams of the candidate cell change frequently. This may mean that the beam quality of the candidate cell fluctuates rapidly and that frequent beam switches are required at the candidate cell if the UE 40 switches to the candidate cell. From the perspective of mobility robustness, it may be appropriate to delay the triggering of the L1 measurement report for a candidate cell with such characteristics. The operation described with reference to FIG. 7 may help address this issue.

[0130] Third Embodiment A configuration example of a wireless communication system according to this embodiment is similar to the configuration example described with reference to Figures 1 and 2. This embodiment provides details of event evaluation or event definition for event-triggered L1 measurement reporting.

[0131] In this embodiment, UE 40 evaluates criteria for triggering a Layer 1 measurement reporting event related to LTM from the serving cell to the candidate cell by considering the replacement of at least one beam belonging to a second subset of a second specific number of reference signal beams (greater than one) selected from a second set of reference signal beams of the serving cell in order of measurement beam quality. The second set is a set of reference signals to be measured of the serving cell. The second set may be configured in UE 40 by gNB1 (e.g., step 501 of FIG. 5). UE 40 selects the second specific number of beams from the best beams in order of quality (e.g., L1-RSRP) based on L1 measurements (or filtered L1 measurement results) of the second set of reference signal beams of the serving cell.

[0132] The second specific number defining or specifying the size of the second subset may be referred to as a specified, certain, predetermined, preset, or preconfigured number. The second specific number may be provided to the UE 40 by the gNB1 and may be included in an event-triggered L1 measurement reporting configuration (e.g., reporting configuration).

[0133] 9 shows an example of evaluation by UE 40 of the departure condition applied to the L1 measurement report event. In step 901, UE 40 determines whether the departure condition is continuously met for a candidate cell (or a candidate reference signal beam of the candidate cell) for a predetermined second period (e.g., TTT period).

[0134] In step 902, UE 40 determines whether there has been a change in at least one beam belonging to a second subset of a second specific number (greater than one) of reference signal beams selected from the second set of reference signal beams of the serving cell in descending order of measured beam quality after the first satisfaction of the departure condition and before the second period has elapsed. If there has been such a change in beam, UE 40 discards the current evaluation of the departure condition for the candidate cell and restarts the evaluation of the departure condition using the new second subset after the beam change.

[0135] 9, there is no particular limitation on the departure condition. For example, the departure condition may be the departure condition for Event LTM3, Event LTM4, or Event LTM5 described above. The departure condition may include comparing the quality of the serving cell with a threshold or comparing the quality of a reference signal beam of a candidate cell. The departure condition may include comparing the quality of a reference signal beam included in the second subset with a threshold or comparing the quality of a reference signal beam of a candidate cell.

[0136] 9 may be modified as follows, for example: In step 901, UE 40 may determine whether the departure condition is satisfied a predetermined number of times during a predetermined second period. In this case, in step 902, UE 40 may determine whether there has been a change in at least one beam belonging to the second subset after the departure condition is satisfied for the first time and before the departure condition is satisfied the predetermined number of times during the second period.

[0137] Alternatively, in step 901, UE 40 may determine whether the departure condition is satisfied a predetermined number of times in succession. In this case, in step 702, UE 40 may determine whether there has been a change in at least one beam belonging to the second subset after the departure condition is satisfied for the first time and before the departure condition is satisfied a predetermined number of times in succession.

[0138] 10 shows an example of signaling related to event-triggered L1 measurement reporting between gNB1 and UE 40. In step 1001, gNB1 transmits a configuration for event-triggered L1 measurement reporting to UE 40. This configuration includes a second specific number that defines or specifies the size of the second subset. As described above, the second subset is a set of beams selected from the set of reference signal beams of the serving cell measured by UE 40 in order of best measured beam quality.

[0139] As can be seen from the above description, in this embodiment, the UE 40 takes into account the change of at least one beam belonging to the second subset of reference signal beams of the serving cell in its evaluation of Layer 1 measurement report events. As an example, consider a case where the beams belonging to the second subset of reference signal beams of the serving cell change frequently. This may mean that the beam quality of the serving cell fluctuates rapidly, and frequent beam switches are required in the serving cell if the UE 40 is to remain in the serving cell. From the perspective of mobility robustness, if the serving cell has such beam quality characteristics, it may be preferable for the UE 40 to continue transmitting L1 measurement reports to facilitate switching to a candidate cell that may provide more stable beam quality. The operations described with reference to FIG. 9 may help address this issue.

[0140] <Other Embodiments> The second embodiment and the third embodiment may be used in combination. For example, in evaluating the entry condition in step 601 of Fig. 6, the UE 40 may perform the operation described in the second embodiment (e.g., the operation shown in Fig. 7). In addition, in evaluating the departure condition in step 603 of Fig. 6, the UE 40 may perform the operation described in the third embodiment (e.g., the operation shown in Fig. 9).

[0141] The first embodiment may be used in combination with the second embodiment or with the second and third embodiments. In this case, the "first subset" of reference signal beams of the candidate cell described in the first embodiment may be the same as or common to the "first subset" of reference signal beams of the candidate cell described in the second embodiment. Similarly, the "second subset" of reference signal beams of the serving cell described in the first embodiment may be the same as or common to the "second subset" of reference signal beams of the serving cell described in the third embodiment.

[0142] In the above-described embodiments, or a combination thereof, the current reference signal beam associated with the activated or designated TCI state may be used instead of the best beam of the serving cell. For example, the best beam of the serving cell in the above-described embodiments may be replaced with the current reference signal beam. In this case, the "second subset" of reference signal beams of the serving cell described in the above-described embodiments may be considered as a set of beams selected from the set of reference signal beams excluding the current reference signal beam in order of best measured beam quality. Considering a case where the second subset is composed of N (N>1) reference signal beams, the second subset may be composed of the current reference signal beam and N-1 reference signal beams (excluding the current reference signal beam) in order of best measured beam quality.

[0143] Furthermore, in the above-described embodiments or a combination thereof, when the current reference signal beam associated with the activated or specified TCI state is used instead of the best beam of the serving cell, the UE 40 may operate as follows: Even after the current reference signal beam is switched (or changed) to any of the other reference signal beams in the second subset, the UE 40 may continue to evaluate the entry conditions for the switched (or changed) current reference signal beam. On the other hand, if the current reference signal beam is switched (or changed) to any of the other reference signal beams not belonging to the second subset, the UE 40 may restart evaluating the entry conditions for the switched (or changed) current reference signal beam.

[0144] The content of the Layer 1 measurement report may include an aggregate metric (e.g., average) derived from a set of quality measurements of a first specific number of reference signal beams included in a first subset of reference signal beams of the candidate cell, which may facilitate the gNB1 knowing the cell-level quality of the candidate cell. Additionally or alternatively, the content of the Layer 1 measurement report may include an aggregate metric (e.g., average) derived from a set of quality measurements of a second specific number of reference signal beams included in a second subset of reference signal beams of the serving cell, which may facilitate the gNB1 knowing the cell-level quality of the serving cell.

[0145] UE 40 may use an integrated metric derived from a set of quality measurements of a first specific number of reference signal beams included in a first subset of reference signal beams of the candidate cell in evaluating criteria (e.g., entry and departure conditions) for an L1 measurement reporting event. This facilitates UE 40 to consider the cell-level quality of the candidate cell in evaluating the L1 measurement reporting event for LTM. Additionally or alternatively, UE 40 may use an integrated metric derived from a set of quality measurements of a second specific number of reference signal beams included in a second subset of reference signal beams of the serving cell in evaluating criteria (e.g., entry and departure conditions) for an L1 measurement reporting event. This facilitates UE 40 to consider the cell-level quality of the serving cell in evaluating the L1 measurement reporting event for LTM.

[0146] The UE 40 may report to the gNB1 frequent fluctuations in the quality of one or more reference signal beams of LTM candidate cells. The UE 40 may also report to the gNB1 frequent fluctuations in the quality of one or more reference signal beams of the serving cell. Similarly, the UE 40 may report to the gNB1 frequent fluctuations in the quality of one or more reference signal beams of neighboring cells. These reports may be periodic, semi-persistent, aperiodic, or event-triggered. When event-triggered reporting is used, a trigger condition may be configured in the UE 40 that takes into account a parameter representing the speed of quality fluctuations in the quality of the reference signal beam. The UE 40 may transmit an L1 measurement report in response to the trigger condition being satisfied. Such an L1 measurement report can be used, for example, for downlink beam adjustment by the RAN (e.g., the gNB1 or another controller). Additionally or alternatively, such L1 measurement reports may be used as training data for training artificial intelligence (AI) or machine learning (ML) models, or as input for inference in AI / ML models.

[0147] Next, a description will be given below of configuration examples of the gNB-CU10, gNB-CU-CP11, gNB-CU-UP12, gNB-DUs 21 and 22, and UE 40. Fig. 11 is a block diagram showing a configuration example 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 Fig. 11.

[0148] 11 , the gNB-CU 10 includes a network interface 1101, a processor 1102, and a memory 1103. The network interface 1101 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 1101 may include multiple interfaces. The network interface 1101 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.

[0149] The processor 1102 may include multiple processors. If the gNB-CU10 is a gNB-CU-CP, the processor 1102 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 1102 performs, for example, termination of the NG-U interface, termination of the F1-U interface, and data processing for the SDAP and PDCP layers.

[0150] In the case of the gNB-DUs 21 and 22, the processor 1102 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. For example, the processor 1102 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 1102 may include a digital beamformer module for beamforming. The digital beamformer module may include a multiple-input multiple-output (MIMO) encoder and precoder.

[0151] The memory 1103 is configured by a combination of volatile memory and non-volatile memory. The volatile memory is, for example, Static Random Access Memory (SRAM) or 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 1103 may include storage located remotely from the processor 1102. In this case, the processor 1102 may access the memory 1103 via the network interface 1101 or another I / O interface.

[0152] The memory 1103 may store one or more software modules (computer programs) 1104 including instructions and data for performing the processing by the gNB-CU 10 described in the above-described embodiments. In some implementations, the processor 1102 may be configured to read and execute the one or more software modules 1104 from the memory 1103, thereby performing the processing by the gNB-CU 10 described in the above-described embodiments.

[0153] FIG. 12 is a block diagram showing an example configuration of a UE 40. An RF transceiver 1201 performs analog RF signal processing for communication with TRPs. The RF transceiver 1201 may include multiple transceivers. The analog RF signal processing performed by the RF transceiver 1201 includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver 1201 is coupled to an antenna array 1202 and a baseband processor 1203. The RF transceiver 1201 receives modulation symbol data (or OFDM symbol data) from the baseband processor 1203, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 1202. The RF transceiver 1201 also generates a baseband receive signal based on the receive RF signal received by the antenna array 1202 and provides the baseband receive signal to the baseband processor 1203. The RF transceiver 1201 may include an analog beamformer circuit for beamforming. The analog beamformer circuitry includes, for example, multiple phase shifters and multiple power amplifiers.

[0154] The baseband processor 1203 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).

[0155] For example, the digital baseband signal processing by the baseband processor 1203 may include signal processing of the SDAP layer, PDCP layer, RLC layer, MAC layer, and PHY layer. Also, the control plane processing by the baseband processor 1203 may include processing of the Non-Access Stratum (NAS) protocol, the RRC protocol, MAC CEs, and DCIs.

[0156] The baseband processor 1203 may perform MIMO encoding and precoding for beamforming.

[0157] The baseband processor 1203 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 1204, which will be described later.

[0158] The application processor 1204 is also referred to as a CPU, MPU, microprocessor, or processor core. The application processor 1204 may include multiple processors (multiple processor cores). The application processor 1204 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 1206 or a memory not shown, thereby realizing various functions of the UE 40.

[0159] In some implementations, the baseband processor 1203 and the application processor 1204 may be integrated on a single chip, as indicated by the dashed line (1205) in Figure 12. In other words, the baseband processor 1203 and the application processor 1204 may be implemented as a single System on Chip (SoC) device 1205. An SoC device is sometimes called a system Large Scale Integration (LSI) or chipset.

[0160] The memory 1206 is volatile memory, nonvolatile memory, or a combination thereof. The memory 1206 may include multiple physically independent memory devices. The volatile memory may be, for example, SRAM, DRAM, or a combination thereof. The nonvolatile memory may be MROM, EEPROM, flash memory, a hard disk drive, or any combination thereof. For example, the memory 1206 may include an external memory device accessible from the baseband processor 1203, the application processor 1204, and the SoC 1205. The memory 1206 may also include an internal memory device integrated within the baseband processor 1203, the application processor 1204, or the SoC 1205. Furthermore, the memory 1206 may include memory within a Universal Integrated Circuit Card (UICC).

[0161] The memory 1206 may store one or more software modules (computer programs) 1207 including instructions and data for performing the processing by the UE 40 described in the above-described embodiments. In some implementations, the baseband processor 1203 or the application processor 1204 may be configured to read and execute the software modules 1207 from the memory 1206, thereby performing the processing by the UE 40 described in the above-described embodiments using the drawings.

[0162] 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 1201 and antenna array 1202, namely, at least one of baseband processor 1203 and application processor 1204, and memory 1206 storing software module 1207.

[0163] As described with reference to Figures 11 and 12, each of the processors included in the gNB-CU, gNB-CU-CP, gNB-CU-UP, gNB-DU, and UE 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.

[0164] 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.

[0165] 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., wireless terminals, RAN nodes) may naturally also be described as appendices directed to methods and programs. For example, some or all of the elements described in appendices 2-21, which are dependent on appendices 1, may also be described as appendices dependent on appendices 22 and 23, due to the same dependency relationship as appendices 2-21. Similarly, some or all of the elements described in appendices 25-33, which are dependent on appendices 24, may also be described as appendices dependent on appendices 34 and 35, due to the same dependency relationship as appendices 25-33. 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.

[0166] (Supplementary Note 1) A wireless terminal comprising: means for receiving from a network configuration information indicating that a criterion for triggering a layer 1 measurement report event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell; and means for evaluating the criterion by taking into account qualities of a plurality of reference signal beams belonging to a first subset of a first specific number greater than one, selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality. (Supplementary Note 2) The wireless terminal according to Supplementary Note 1, wherein the evaluating means is configured to evaluate the criterion by taking into account replacement of at least one beam belonging to the first subset. (Supplementary Note 3) The wireless terminal of Supplementary Note 2, wherein the criteria include an entry condition applied to the Layer 1 measurement report event, the evaluating means is configured to initiate a procedure for transmitting a Layer 1 measurement report for the candidate cell to the network if the entry condition is satisfied for a first period of time, and the evaluating means is configured to abandon a current evaluation of the entry condition and restart evaluation of the entry condition using a new first subset including the at least one other reference signal beam if at least one of the first particular number of reference signal beams belonging to the first subset is replaced by at least one other reference signal beam after the entry condition is first satisfied and before the first period of time has elapsed. (Supplementary Note 4) The wireless terminal of Supplementary Note 3, wherein the entry condition includes comparing a quality of a reference signal beam of the candidate cell to a threshold or comparing it to a quality of a reference signal beam of the serving cell. (Supplementary Note 5) The wireless terminal according to Supplementary Note 3, wherein the entry condition includes a comparison of a quality of a reference signal beam included in the first subset with a threshold or a comparison with a quality of a reference signal beam of the serving cell. (Supplementary Note 6) The wireless terminal according to any one of Supplementary Notes 2 to 5, wherein the setting information includes the first specific number of settings.(Supplementary Note 7) The wireless terminal of any one of Supplements 2 to 5, wherein the evaluating means is configured to use an integrated metric derived from a set of quality measurements of the first specific number of reference signal beams included in the first subset in evaluating the criterion. (Supplementary Note 8) The wireless terminal of any one of Supplements 2 to 6, wherein content of a Layer 1 measurement report triggered based on the criterion includes an integrated metric derived from the set of quality measurements of the first specific number of reference signal beams included in the first subset. (Supplementary Note 9) The wireless terminal of any one of Supplements 2 to 8, wherein the evaluating means is configured to further take into account, in evaluating the criterion, replacement of at least one beam belonging to a second subset of a second specific number of reference signal beams greater than one selected from a second set of reference signal beams of the serving cell in descending order of measured beam quality. (Supplementary Note 10) The wireless terminal according to Supplementary Note 9, wherein the criteria include a departure condition applied to the Layer 1 measurement report event, the evaluating means is configured to stop transmitting Layer 1 measurement reports for the candidate cell to the network if the departure condition is satisfied for a second period of time, and the evaluating means is configured to abandon a current evaluation of the departure condition and restart evaluation of the departure condition using a new second subset including the at least one other reference signal beam if at least one of the second particular number of reference signal beams belonging to the second subset is replaced by at least one other reference signal beam after the departure condition is first satisfied and before the second period of time has elapsed. (Supplementary Note 11) The wireless terminal according to Supplementary Note 10, wherein the departure condition includes comparing a quality of a reference signal beam of the serving cell to a threshold or comparing a quality of a reference signal beam of the candidate cell to a threshold. (Supplementary Note 12) The wireless terminal according to Supplementary Note 10, wherein the withdrawal condition includes a comparison of a quality of a reference signal beam included in the second subset with a threshold or a comparison with a quality of a reference signal beam of the candidate cell. (Supplementary Note 13) The wireless terminal according to any one of Supplementary Notes 9 to 12, wherein the setting information includes the second specific number of settings.(Supplementary Note 14) The wireless terminal of any one of Supplements 9 to 13, wherein the evaluating means is configured to use an aggregate metric derived from a set of quality measurements of the second specific number of reference signal beams included in the second subset in evaluating the criterion. (Supplementary Note 15) The wireless terminal of any one of Supplements 9 to 13, wherein content of a Layer 1 measurement report triggered based on the criterion includes an aggregate metric derived from a set of quality measurements of the second specific number of reference signal beams included in the second subset. (Supplementary Note 16) The wireless terminal of Supplementary Note 1, wherein the criterion includes an entry condition applied to the Layer 1 measurement report event, and the evaluating means is configured to determine whether the entry condition is satisfied for each of the plurality of reference signal beams belonging to the first subset on a beam-by-beam basis. (Supplementary Note 17) The wireless terminal according to Supplementary Note 1, wherein the criterion includes an entry condition applied to the Layer 1 measurement report event, and the evaluating means is configured to determine whether the entry condition is satisfied for all of the plurality of reference signal beams belonging to the first subset on a subset-by-subset basis. (Supplementary Note 18) The wireless terminal according to Supplementary Note 1, 16, or 17, wherein the evaluating means is configured to, in evaluating the criterion, further consider quality of a plurality of reference signal beams belonging to a second subset of a second specific number of reference signal beams greater than one selected from a second set of reference signal beams of the serving cell in descending order of measured beam quality. (Supplementary Note 19) The wireless terminal according to Supplementary Note 18, wherein the evaluating means is configured to evaluate the criterion for each of the plurality of reference signal beams belonging to the second subset. (Supplementary Note 20) The wireless terminal according to Supplementary Note 18, wherein the evaluating means is configured to evaluate the criterion for a worst beam having the lowest quality among the reference signal beams belonging to the second subset.(Supplementary Note 21) The wireless terminal according to any one of Supplementary Notes 1 to 20, wherein the first set of reference signal beams is a set of Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) block (SSB) beams or a set of Channel State Information (CSI) Reference Signal (CSI-RS) beams. (Supplementary Note 22) A method performed by a wireless terminal, comprising: receiving configuration information indicating that a criterion for triggering a layer 1 measurement report event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell; and evaluating the criterion by taking into account the quality of a plurality of reference signal beams belonging to a first subset of a first specific number greater than one, selected from the first set of reference signal beams of the candidate cell in order of best measured beam quality. (Supplementary Note 23) A program for causing a computer to perform, when loaded into the computer, a method for a wireless terminal, comprising: receiving configuration information indicating that criteria for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell are based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell; and considering and evaluating the quality of multiple reference signal beams belonging to a first subset of a first specific number greater than one, selected from a first set of reference signal beams of the candidate cell in order of best measurement beam quality.(Supplementary Note 24) A radio access network node comprising: means for transmitting, to a radio terminal, configuration information indicating that a criterion for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, the configuration information including a first specific number of configurations greater than 1, and the configuration information causing the radio terminal to evaluate the criterion taking into account qualities of a plurality of reference signal beams belonging to a first subset of the first specific number of reference signal beams selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality. (Supplementary Note 25) A radio access network node according to Supplementary Note 24, wherein the configuration information causes the radio terminal to evaluate the criterion taking into account replacement of at least one beam belonging to the first subset. (Supplementary Note 26) A radio access network node as described in Supplementary Note 25, wherein the criteria include an entry condition that applies to the Layer 1 measurement report event, and the radio terminal is configured to initiate a procedure for transmitting a Layer 1 measurement report for the candidate cell to a network if the entry condition is satisfied for a first period of time, and the configuration information causes the radio terminal to abandon a current evaluation of the entry condition and restart evaluation of the entry condition using a new first subset including the at least one other reference signal beam if at least one of the first specific number of reference signal beams belonging to the first subset is replaced by at least one other reference signal beam after the entry condition is first satisfied and before the first period of time has elapsed. (Supplementary Note 27) A radio access network node as described in Supplementary Note 25 or 26, wherein the configuration information further includes a second specific number of configurations greater than 1, and the configuration information causes the radio terminal to further take into account, in evaluating the criteria, replacement of beams belonging to a second subset of the second specific number of reference signal beams greater than 1 selected from a second set of reference signal beams of the serving cell in order of best measured beam quality.28. The radio access network node of Supplementary Note 27, wherein the criteria include an exit condition applied to the Layer 1 measurement report event, and the radio terminal is configured to stop transmitting Layer 1 measurement reports for the candidate cell to the network if the exit condition is satisfied for a second period of time, and the configuration of the second specific number causes the radio terminal to abandon a current evaluation of the exit condition and restart evaluation of the exit condition using a new second subset including the at least one other reference signal beam if at least one of the second specific number of reference signal beams belonging to the second subset is replaced by at least one other reference signal beam after the exit condition is first satisfied and before the second period of time has elapsed. 29. The radio access network node of Supplementary Note 24, wherein the criteria include an entry condition applied to the Layer 1 measurement report event, and the configuration information causes the radio terminal to determine whether the entry condition is satisfied on a beam-by-beam basis for each of the plurality of reference signal beams belonging to the first subset. (Supplementary Note 30) The radio access network node according to Supplementary Note 24, wherein the criterion includes an entry condition applied to the Layer 1 measurement report event, and the configuration information causes the radio terminal to determine whether the entry condition is satisfied on a subset-by-subset basis for all of the plurality of reference signal beams belonging to the first subset. (Supplementary Note 31) The radio access network node according to Supplementary Note 24, 29 or 30, wherein the configuration information causes the radio terminal to, in evaluating the criterion, further consider quality of a plurality of reference signal beams belonging to a second subset of a second specific number greater than one reference signal beams selected from a second set of reference signal beams of the serving cell in descending order of measured beam quality. (Supplementary Note 32) The radio access network node according to Supplementary Note 31, wherein the configuration information causes the radio terminal to evaluate the criterion on a beam-by-beam basis for each of the plurality of reference signal beams belonging to the second subset.(Supplementary Note 33) The radio access network node according to Supplementary Note 31, wherein the configuration information causes the radio terminal to evaluate the criterion with respect to a worst beam having the lowest quality among reference signal beams belonging to the second subset. (Supplementary Note 34) A method performed by a radio access network node, comprising: transmitting to a radio terminal configuration information indicating that a criterion for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, the configuration information including a first specific number of configurations greater than 1, and the configuration information causes the radio terminal to evaluate the criterion by taking into account the quality of a plurality of reference signal beams belonging to a first subset of the first specific number of reference signal beams selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality. (Supplementary Note 35) A program that, when loaded into a computer, causes a computer to perform a method for a radio access network node, comprising transmitting configuration information to a radio terminal indicating that criteria for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell are based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, wherein the configuration information includes a first specific number of configurations greater than 1, and the configuration information causes the radio terminal to evaluate the criteria by taking into account the quality of a plurality of reference signal beams belonging to a first subset of the first specific number of reference signal beams selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

[0167] This application claims priority based on Japanese Patent Application No. 2024-111650, filed July 11, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0168] 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 1102 Processor 1103 Memory 1203 Baseband processor 1204 Application processor 1206 Memory

Claims

1. A wireless terminal comprising: means for receiving configuration information from a network indicating that a criterion for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell; and means for evaluating the criterion by taking into account the quality of a plurality of reference signal beams belonging to a first subset of a first specific number greater than one, selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

2. The wireless terminal according to claim 1, wherein said evaluating means is configured to evaluate said criterion taking into account a change in at least one beam belonging to said first subset.

3. The wireless terminal of claim 2, wherein the criteria include an entry condition that applies to the Layer 1 measurement report event, the evaluating means is configured to initiate a procedure for transmitting a Layer 1 measurement report for the candidate cell to the network if the entry condition is satisfied for a first period of time, and the evaluating means is configured to abandon a current evaluation of the entry condition and restart evaluation of the entry condition using a new first subset that includes the at least one other reference signal beam if at least one of the first specific number of reference signal beams belonging to the first subset is replaced by at least one other reference signal beam after the entry condition is first satisfied and before the first period of time has elapsed.

4. The wireless terminal according to claim 3, wherein the entry condition includes a comparison of the quality of the reference signal beam of the candidate cell with a threshold or a comparison of the quality of the reference signal beam of the serving cell.

5. The wireless terminal according to claim 3, wherein the entry condition includes a comparison of the quality of a reference signal beam included in the first subset with a threshold or a comparison with the quality of a reference signal beam of the serving cell.

6. A wireless terminal according to any one of claims 2 to 5, wherein the setting information includes the first specific number of settings.

7. A wireless terminal according to any one of claims 2 to 5, wherein the evaluating means is configured to use an aggregate metric derived from a set of quality measurements of the first particular number of reference signal beams included in the first subset in evaluating the criterion.

8. A wireless terminal as described in any one of claims 2 to 6, wherein the content of the Layer 1 measurement report triggered based on the criteria includes an integrated metric derived from a set of quality measurements of the first specific number of reference signal beams included in the first subset.

9. A wireless terminal according to any one of claims 2 to 8, wherein the evaluating means is configured to further take into account, in evaluating the criteria, replacement of at least one beam belonging to a second subset of a second specific number greater than one of reference signal beams selected from a second set of reference signal beams of the serving cell in order of best measured beam quality.

10. The wireless terminal of claim 9, wherein the criteria include a departure condition applied to the Layer 1 measurement report event, the evaluating means is configured to stop transmitting Layer 1 measurement reports regarding the candidate cell to the network if the departure condition is satisfied for a second period of time, and the evaluating means is configured to discard a current evaluation of the departure condition and restart evaluation of the departure condition using a new second subset including the at least one other reference signal beam if at least one of the second specific number of reference signal beams belonging to the second subset is replaced by at least one other reference signal beam after the departure condition is first satisfied and before the second period of time has elapsed.

11. The wireless terminal according to claim 10, wherein the condition for leaving includes comparing the quality of the reference signal beam of the serving cell with a threshold or comparing the quality of the reference signal beam of the candidate cell with a threshold.

12. The wireless terminal according to claim 10, wherein the condition for leaving includes comparing the quality of a reference signal beam included in the second subset with a threshold or comparing the quality of a reference signal beam of the candidate cell.

13. A wireless terminal according to any one of claims 9 to 12, wherein the setting information includes the second specific number of settings.

14. A wireless terminal according to any one of claims 9 to 13, wherein the evaluating means is configured to use an aggregate metric derived from a set of quality measurements of the second particular number of reference signal beams included in the second subset in evaluating the criterion.

15. A wireless terminal as described in any one of claims 9 to 13, wherein the content of the Layer 1 measurement report triggered based on the criteria includes an integrated metric derived from a set of quality measurements of the second specific number of reference signal beams included in the second subset.

16. The wireless terminal of claim 1, wherein the criteria include an entry condition that applies to the Layer 1 measurement reporting event, and the evaluating means is configured to determine whether the entry condition is satisfied on a beam-by-beam basis for each of the plurality of reference signal beams that belong to the first subset.

17. The wireless terminal of claim 1, wherein the criteria include an entry condition applied to the Layer 1 measurement reporting event, and the evaluating means is configured to determine whether the entry condition is satisfied on a subset-by-subset basis for all of the plurality of reference signal beams belonging to the first subset.

18. The wireless terminal of claim 1, 16, or 17, wherein the evaluating means is configured to further take into account, in evaluating the criteria, the quality of a plurality of reference signal beams belonging to a second subset of a second specific number greater than one of reference signal beams selected from a second set of reference signal beams of the serving cell in order of best measured beam quality.

19. The wireless terminal of claim 18, wherein the evaluating means is configured to evaluate the criterion on a beam-by-beam basis for each of the plurality of reference signal beams belonging to the second subset.

20. The wireless terminal according to claim 18, wherein the evaluating means is configured to evaluate the criterion with respect to a worst beam having the lowest quality among the reference signal beams belonging to the second subset.

21. A wireless terminal according to any one of claims 1 to 20, wherein the first set of reference signal beams is a set of Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) block (SSB) beams or a set of Channel State Information (CSI) Reference Signal (CSI-RS) beams.

22. A method performed by a wireless terminal, comprising: receiving configuration information indicating that a criterion for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell; and evaluating the criterion by taking into account the quality of a plurality of reference signal beams belonging to a first subset of a first specific number greater than one, selected from a first set of reference signal beams of the candidate cell in order of best measurement beam quality.

23. A program for causing a computer to perform, when loaded into the computer, a method for a wireless terminal, comprising: receiving configuration information indicating that criteria for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell are based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell; and considering and evaluating the quality of multiple reference signal beams belonging to a first subset of a first specific number greater than one, selected from a first set of reference signal beams of the candidate cell in order of best measurement beam quality.

24. A radio access network node comprising: means for transmitting configuration information to a radio terminal indicating that a criterion for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, the configuration information including a first specific number of configurations greater than 1, and the configuration information causing the radio terminal to evaluate the criterion taking into account the quality of a plurality of reference signal beams belonging to a first subset of the first specific number of reference signal beams selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

25. A radio access network node according to claim 24, wherein the configuration information causes the radio terminal to evaluate the criterion taking into account a permutation of at least one beam belonging to the first subset.

26. The radio access network node of claim 25, wherein the criteria include an entry condition that applies to the Layer 1 measurement report event, and the radio terminal is configured to initiate a procedure for transmitting a Layer 1 measurement report regarding the candidate cell to the network if the entry condition is satisfied for a first period of time, and the configuration information causes the radio terminal to abandon a current evaluation of the entry condition and restart evaluation of the entry condition using a new first subset that includes the at least one other reference signal beam if at least one of the first specific number of reference signal beams belonging to the first subset is replaced by at least one other reference signal beam after the entry condition is first satisfied and before the first period of time has elapsed.

27. A radio access network node as described in claim 25 or 26, wherein the configuration information further includes a second specific number of configurations greater than 1, and the configuration information causes the radio terminal to further take into account, in evaluating the criteria, replacement of beams belonging to a second subset of the second specific number of reference signal beams greater than 1 selected from a second set of reference signal beams of the serving cell in order of best measured beam quality.

28. The radio access network node of claim 27, wherein the criteria include a departure condition that applies to the Layer 1 measurement report event, and the radio terminal is configured to stop transmitting Layer 1 measurement reports for the candidate cell to the network if the departure condition is satisfied for a second period of time, and the setting of the second specific number causes the radio terminal to abandon a current evaluation of the departure condition and restart evaluation of the departure condition using a new second subset including the at least one other reference signal beam if at least one of the second specific number of reference signal beams belonging to the second subset is replaced by at least one other reference signal beam after the departure condition is first satisfied and before the second period of time has elapsed.

29. A radio access network node as described in claim 24, wherein the criteria include an entry condition that applies to the Layer 1 measurement reporting event, and the configuration information causes the radio terminal to determine whether the entry condition is satisfied on a beam-by-beam basis for each of the plurality of reference signal beams that belong to the first subset.

30. A radio access network node as described in claim 24, wherein the criteria include an entry condition that applies to the Layer 1 measurement reporting event, and the configuration information causes the radio terminal to determine whether the entry condition is satisfied on a subset-by-subset basis for all of the plurality of reference signal beams that belong to the first subset.

31. A radio access network node as described in claim 24, 29, or 30, wherein the configuration information causes the radio terminal to further take into account, in evaluating the criteria, the quality of a plurality of reference signal beams belonging to a second subset of a second specific number greater than one, selected from a second set of reference signal beams of the serving cell in order of best measured beam quality.

32. The radio access network node according to claim 31, wherein the configuration information causes the radio terminal to perform evaluation of the criteria on a beam-by-beam basis for each of the plurality of reference signal beams belonging to the second subset.

33. The radio access network node according to claim 31, wherein the configuration information causes the radio terminal to evaluate the criteria with respect to a worst beam having the lowest quality among reference signal beams belonging to the second subset.

34. A method performed by a radio access network node, comprising: transmitting configuration information to a radio terminal indicating that a criterion for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell is based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, wherein the configuration information includes a first specific number of configurations greater than 1, and the configuration information causes the radio terminal to evaluate the criterion taking into account the quality of a plurality of reference signal beams belonging to a first subset of the first specific number of reference signal beams selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

35. A program that, when loaded into a computer, causes a computer to perform a method for a radio access network node, comprising transmitting configuration information to a radio terminal indicating that criteria for triggering a layer 1 measurement reporting event related to layer-1 / layer-2 triggered mobility (LTM) from a serving cell to a candidate cell are based on a beam-by-beam quality evaluation of one or more reference signal beams of the candidate cell, wherein the configuration information includes a first specific number of configurations greater than 1, and the configuration information causes the radio terminal to evaluate the criteria taking into account the quality of a plurality of reference signal beams belonging to a first subset of the first specific number of reference signal beams selected from a first set of reference signal beams of the candidate cell in order of best measured beam quality.

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