Communication method, user device, and network node

Abstract

A communication method executed by a user device in a mobile communication system that supports L1 / L2 Triggered Mobility (LTM) includes: receiving, from a network node, setting of an L1 event condition for triggering a report of a layer 1 (L1) measurement result and setting of a stop event condition; performing event evaluation to evaluate whether the L1 event condition is satisfied on the basis of a result of L1 measurement, the L1 measurement being a radio quality measurement in L1; triggering transmission of the L1 measurement report to the network node in response to the L1 event condition being satisfied; and stopping the event evaluation and / or periodic transmission of the L1 measurement report in response to the stop event condition being satisfied.

Description

COMMUNICATION METHOD, USER EQUIPMENT, AND NETWORK NODE

[0001] The present disclosure relates to a communication method, a user equipment, and a network node for use in a mobile communication system.

[0002] The 3rd Generation Partnership Project (3GPP) (registered trademark; the same applies hereinafter) defines technical specifications for NR (New Radio), a fifth-generation (5G) radio access technology. In a 3GPP mobile communication system, a serving cell switch (serving cell change) of a user equipment in a radio resource control (RRC) connected state is instructed by transmitting an RRC layer message (so-called handover command), which corresponds to Layer 3 (L3), from a network node to the user equipment.

[0003] Meanwhile, Release 18 of the 3GPP standard (3GPP Release 18) defines technical specifications for LTM (L1 / L2-Triggered Mobility), a new procedure for serving cell switching. LTM is a procedure in which a network node receives a Layer 1 (L1) measurement report from a user equipment, and based on the report, the network node signals a cell switch command to the user equipment via a medium access control (MAC) control element (CE), thereby causing the network node to change the serving cell of the user equipment.

[0004] 3GPP technical specification "3GPP TS 38.300 V18.2.0"

[0005] This disclosure provides techniques for improving LTM.

[0006] A communication method according to a first aspect of the present disclosure is a communication method executed by a user equipment in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), and includes receiving, from a network node, a setting of an L1 event condition that triggers reporting of Layer 1 (L1) measurement results and a setting of a stop event condition; performing an event evaluation that evaluates whether the L1 event condition is satisfied based on a result of an L1 measurement, which is a radio quality measurement in L1; triggering transmission of the L1 measurement report to the network node in response to the L1 event condition being satisfied; and stopping the event evaluation and / or periodic transmission of the L1 measurement report in response to the stop event condition being satisfied.

[0007] A user equipment according to a second aspect of the present disclosure is a user equipment used in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), and includes: a receiver that receives from a network node a setting of an L1 event condition that triggers a report of a Layer 1 (L1) measurement result and a setting of a stop event condition, a controller that performs event evaluation that evaluates whether the L1 event condition is satisfied based on a result of an L1 measurement that is a radio quality measurement in L1, and a transmitter that triggers transmission of the L1 measurement report to the network node in response to the L1 event condition being satisfied. The controller stops the event evaluation and / or the periodic transmission of the L1 measurement report in response to the satisfaction of the stop event condition.

[0008] A network node according to a third aspect of the present disclosure is a network node for use in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), and includes: a transmitter that transmits to a user equipment (UE) an L1 event condition setting that triggers a report of a Layer 1 (L1) measurement result and a stop event condition setting, and a receiver that receives, from the user equipment, the L1 measurement report in response to the L1 event condition being satisfied, the L1 event condition being evaluated based on a result of an L1 measurement that is a radio quality measurement in L1. The setting of the stop event condition causes the user equipment to stop the event evaluation and / or the periodic transmission of the L1 measurement report in response to the stop event condition being satisfied.

[0009] 1 is a diagram illustrating an example of the configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a UE (user equipment) according to an embodiment. FIG. 3 is a diagram illustrating an example of the configuration of a gNB (network node) according to an embodiment. FIG. 4 is a diagram illustrating a protocol stack configuration of a radio interface of a user plane that handles data. FIG. 5 is a diagram illustrating a protocol stack configuration of a radio interface of a control plane that handles signaling (control signals). FIG. 6 is a diagram illustrating a configuration related to measurements by a UE according to an embodiment. FIG. 7 is a diagram illustrating an example of a cell switching procedure by LTM in intra-CU (i.e., within the same gNB) according to an embodiment. FIG. 8 is a diagram illustrating an example of operation of inter-CU LTM according to an embodiment. FIG. 9 is a diagram illustrating an example of an event-triggered L1 measurement report according to an embodiment. FIG. 10 is a diagram illustrating an overview of the operation of a UE according to an embodiment. FIG. 11 is a diagram illustrating a specific example of the operation of a mobile communication system according to an embodiment. FIG. 12 is a diagram for explaining beams (reference signals) measured by a UE according to an embodiment. FIG. 13 is a diagram illustrating operations related to stopping an L1 measurement report procedure according to an embodiment. FIG. 14 is a diagram illustrating an example of the operation of a mobile communication system according to a first operation pattern. FIG. 15 is a diagram illustrating an example of the operation of a mobile communication system according to a second operation pattern. FIG. 16 is a diagram illustrating derivation of L3 cell-level measurement results (when a "threshold" and a "number" are set). FIG. 17 is a diagram illustrating different measurement results for different numbers of beams. A diagram showing the number of beams that satisfy an event condition (e.g., "RSRP is greater than or equal to a threshold").

[0010] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0011] (1) Configuration of a Mobile Communication System FIG. 1 is a diagram showing an example of the configuration of a mobile communication system 1 according to this embodiment. The mobile communication system 1 conforms to the 3GPP standard 5th Generation System (5GS). While the following description uses 5GS as an example, the mobile communication system may also be at least partially based on an LTE (Long Term Evolution) system. The mobile communication system may also be at least partially based on a 6th Generation (6G) system.

[0012] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN: Next Generation Radio Access Network) 10, and a 5G core network (5GC: 5G Core Network) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10. Furthermore, the 5GC 20 may be simply referred to as the core network (CN) 20. The RAN 10 and the CN 20 constitute a network 5 of the mobile communication system 1.

[0013] The UE 100 is a mobile wireless communication device. The UE 100 may be any device used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone) and / or a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE). A link in the transmission direction from the UE 100 to the network 5 is referred to as an uplink (UL), and a link in the transmission direction from the network 5 to the UE 100 is referred to as a downlink (DL).

[0014] The NG-RAN 10 includes a base station (referred to as "gNB" in the 5G system) 200, which is a type of network node. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, etc. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource that performs wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0015] In addition, gNBs can also be connected to the Evolved Packet Core (EPC), which is the core network of LTE. LTE base stations can also be connected to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0016] The 5GC20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and the UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0017] 2 is a diagram showing an example of the configuration of a UE 100 (user equipment) according to this embodiment. The UE 100 has a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit 140 that performs wireless communication with the gNB 200.

[0018] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0019] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0020] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer described below. The operations of the UE 100 described above and below may be operations controlled by the control unit 230. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0021] 3 is a diagram showing an example configuration of a gNB 200 (network node) according to this embodiment. The gNB 200 has a transmitter 210, a receiver 220, a controller 230, and a network communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit 250 that performs wireless communication with the UE 100. The network communication unit 240 has a transmitter 241 that transmits and a receiver 242 that receives.

[0022] The transmitting unit 210 performs various transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0023] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0024] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes for each layer described below. The operations of the gNB 200 described above and below may be operations under the control of the control unit 230. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0025] The network communication unit 240 is connected to adjacent base stations via an Xn interface, which is an interface between base stations. The network communication unit 240 is connected to the AMF / UPF 300 via an NG interface, which is an interface between a base station and a core network. The gNB 200 is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and the two units may be connected by an F1 interface, which is a fronthaul interface.

[0026] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0027] The user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0028] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires the successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has a CRC parity bit scrambled by the RNTI added.

[0029] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of the UE 100 and the MAC layer of the gNB 200 via a transport channel. The MAC layer of the gNB 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to the UE 100.

[0030] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via a logical channel.

[0031] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0032] The SDAP layer maps IP flows, which are units for Quality of Service (QoS) control by the core network, to radio bearers, which are units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP may not be required.

[0033] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0034] The protocol stack of the radio interface of the control plane has an RRC (Radio Resource Control) layer and an NAS (Non-Access Stratum) layer instead of the SDAP layer shown in FIG.

[0035] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0036] The NAS layer (also simply referred to as "NAS") located above the RRC layer performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300A. Note that the UE 100 has an application layer and the like in addition to the radio interface protocol. Also, a layer lower than the NAS layer is referred to as the AS layer (also simply referred to as "AS").

[0037] (2) Measurement by UE The UE 100 in the RRC connected state measures at least one beam of a cell and averages the measurement results (power values) to derive the radio quality of the cell. At this time, the UE 100 is configured to consider a subset of the detected beams.

[0038] Here, filtering, which is measurement averaging, is performed at two different levels. UE100 first derives beam quality by L1 filtering, which is filtering at the physical layer (PHY, Layer 1 (L1)), and then derives cell quality from multiple beams by L3 filtering, which is filtering at the RRC layer (Layer 3 (L3)) level. Note that cell quality from beam measurements is derived in the same way for serving and non-serving cells. UE100 may include measurement results of the X best beams in the L3 measurement report, depending on the configuration by gNB200.

[0039] FIG. 6 is a diagram showing a configuration related to measurements by UE 100.

[0040] The control unit 130 of the UE 100 has an L1 filter 11 , a beam combining / selecting unit 12 , an L3 filter 13 , an evaluation unit 14 , an L3 beam filter 15 , and a beam selecting unit 16 .

[0041] The L1 filter 11 includes K L1 filters 11 corresponding to the K beams. K measurement values ​​A obtained by the UE 100 (receiving unit 110) measuring the radio quality for each of the K beams are input to the L1 filter 11. The K measurement values ​​A for the K beams are measurement values ​​(beam-specific samples) within the physical layer, and are measurement values ​​of an SSB (SS / PBCH block) or CSI (Channel State Information) reference signal resource detected by the UE 100 (receiving unit 110) in L1. The L1 filter 11 performs L1 filtering on the K measurement values ​​A for the K beams in L1, and outputs the beam-specific measurement values ​​A after the L1 filtering. １ are output to the beam combining / selecting unit 12 and the L3 beam filter 15.

[0042] The beam integration / selection unit 12 calculates beam-specific measurements A １ to derive the cell radio quality (Cell quality) B, and output the cell quality B to the L3 filter 13. The operation setting of the beam combining / selecting unit 12 is provided by RRC signaling from the gNB 200.

[0043] The L3 filter 13 filters the measurement value (cell quality B) output by the beam combining / selecting unit 12 at L3 and outputs the measurement value C after L3 filtering to the evaluation unit 14. The configuration of the operation of the L3 filter 13 is provided by RRC signaling from the gNB 200. The measurement value C after L3 filtering is used as input for one or more evaluations of an L3 measurement report from the UE 100 to the gNB 200.

[0044] The L3 filter 13 filters the measurement results for each cell measurement and each beam measurement by the following equation (1) before using them for evaluation of reporting criteria or for L3 measurement reporting: F ｎ = (1 - a) x F ｎ－１ + a × M ｎ ...(1) where M ｎ is the latest measurement result from the physical layer (L1). ｎ F is the updated filtered measurement result, which is used for evaluation of reporting criteria or L3 measurement reporting. ｎ－１ is the old filtered measurement, F is the measurement result when the first measurement is received from the physical layer (L1). ０ M １ is set to

[0045] When MeasObjectNR is set in RRC, a = 1 / 2 （ｋｉ／４） Here, k ｉ is the filter coefficient of the corresponding measurement of the ith QuantityConfigNR in the quantityConfigNR-List, where i is indicated by the quantityConfigIndex in the MeasObjectNR. For other measurements, a=½ （ｋ／４） where k is the filter coefficient of the corresponding measurement received by quantityConfig.

[0046] The L3 filter 13 adapts the filter so that its time characteristics are preserved at different input rates, while the filter coefficient k assumes a sample rate equal to X ms, where the value of X corresponds to one intra-frequency L1 measurement period assuming non-DRX operation and is frequency range dependent.

[0047] Note that if the filter coefficient k is set to 0 (zero), no L3 filtering is applied.

[0048] The evaluation unit 14 evaluates whether an L3 measurement report D to the gNB 200 is necessary. This evaluation can be performed based on a comparison of multiple measurement flows at the reference point C, for example, different measurement values. This is done by comparing input C and input C １ The evaluation unit 14 determines whether at least the new measurement results are at points C, C １ Each time a measurement is reported, an event evaluation corresponding to the reporting criteria is performed. The reporting criteria setting is provided by RRC signaling from the gNB 200. The L3 measurement report D represents measurement report information (RRC message) transmitted from the UE 100 to the gNB 200. The L3 measurement report D includes the measurement ID of the associated measurement setting that triggered the report.

[0049] The L3 beam filter 15 receives k measured values ​​A １ (i.e., beam-specific measurements) are filtered on a per-beam basis and k measurements E (i.e., beam-specific measurements) are output to the beam selector 16. The measurements E are used as input to select the X measurements to be reported.

[0050] The beam selection unit 16 selects X measurement values ​​F from the k measurement values ​​E and outputs the X measurement values ​​F. The X measurement values ​​F are beam measurement information included in measurement report information (RRC message) transmitted from the UE 100 to the gNB 200.

[0051] (3) Overview of LTM The mobile communication system 1 supports LTM (L1 / L2-triggered mobility).

[0052] In a typical handover procedure, a serving cell switch is triggered by signaling in the upper layer L3, specifically, the RRC layer. Such a typical handover is also referred to as an L3 handover. In an L3 handover, an L3 measurement report message, which is an RRC message, is transmitted from the UE 100 to the gNB 200. The gNB 200 determines the handover of the UE 100 based on the Measurement Report message, and instructs the cell switch by transmitting a handover command (specifically, an RRC Reconfiguration message) which is an RRC message from the gNB 200 to the UE 100.

[0053] On the other hand, LTM is a technology for shortening mobility delay (specifically, serving cell switching delay) compared to a typical handover procedure by triggering a serving cell switch by signaling of a lower layer, Layer 1 (L1) and / or Layer 2 (L2). In LTM, the gNB 200 receives an L1 measurement report from the UE 100, and based on the L1 measurement report, the gNB 200 signals the UE 100 via a MAC CE to instruct the serving cell switch by a cell switch command.

[0054] Specifically, in LTM, first, gNB200 prepares LTM settings for candidate cells to be switched to, and provides the LTM settings to UE100 via RRC signaling.

[0055] Secondly, the UE 100 performs a synchronization process with the LTM candidate cell by early synchronization (Early sync).

[0056] Third, the gNB 200 receives an L1 measurement report from the UE 100, determines a serving cell switch to the target cell based on the L1 measurement report, and transmits a cell switch command (Cell Switch Command) indicating the target cell (LTM setting) to the UE 100 via a MAC control element (CE). The serving cell switch trigger is conveyed in a MAC CE including at least a candidate setting index (ID) together with a beam indicator.

[0057] Fourth, the UE 100 switches the serving cell in response to a cell switch command MAC CE from the gNB 200 (source cell).

[0058] In this way, a serving cell switch is triggered by selecting the LTM configuration as the target configuration by gNB200. The LTM configuration can be added, changed, and released by gNB200 via RRC signaling.

[0059] The following principles apply to LTM:

[0060] Each LTM setting can be provided as a delta setting relative to a reference setting that is used to form the complete LTM setting.

[0061] If a full LTM configuration is applied, the current UE configuration is replaced upon a serving cell switch. The reconfiguration procedure does this but does not necessarily reset the MAC, RLC or PDCP layers.

[0062] The user plane continues without a reset if configured in RRC signaling to avoid additional delays in data recovery.

[0063] - Security is not updated in LTM.

[0064] LTM between subsequent LTM configurations can be performed without RRC reconfiguration, i.e., the UE 100 does not release other LTM configurations after an LTM is triggered.

[0065] (3.1) LTM for Intra-CU Figure 7 is a diagram showing an example of a cell switching procedure using LTM in intra-CU (i.e., within the same gNB 200). In the illustrated example, UE 100 performs a serving cell switch from a first cell of gNB 200 to a second cell.

[0066] Here, the first cell and the second cell may be formed by different TRPs (Transmission and Reception Points). In the following description of the embodiment, the second cell is also referred to as an "LTM candidate cell (or LTM candidate cell)" until a serving cell switch by LTM is determined, and after a serving cell switch by LTM is determined, the second cell is also referred to as a "target cell". The first cell is also referred to as a "source cell" or a "(current) serving cell".

[0067] In step S1, UE100 is in an RRC connected state in the cell (first cell) of gNB200.

[0068] In step S2, the UE 100 transmits a Measurement Report message, which is an RRC message, to the gNB 200 (first cell). The measurement report transmitted by the RRC message is also referred to as an "L3 measurement report."

[0069] In step S3, gNB200 decides to use LTM based on the Measurement Report message and starts preparing an LTM candidate cell.

[0070] In step S4, the gNB 200 (first cell) transmits an RRC message, specifically an RRC Reconfiguration message, to the UE 100, including LTM configurations (LTM Candidate Configurations) of one or more LTM candidate cells. The LTM configurations may include a random access channel (RACH) configuration, such as a contention-free random access (CFRA) configuration, used to transmit RA preambles to the corresponding LTM candidate cells. Such a RACH configuration may be referred to as an early UL synchronization configuration (EarlyUlSyncConfig). CFRA is a random access procedure in which a dedicated RACH resource (e.g., a dedicated preamble sequence and / or a dedicated time-frequency resource) is assigned to the UE 100, and no RACH contention occurs between the UEs 100.

[0071] In step S5, UE100 saves the LTM setting and sends an RRC Reconfiguration Complete message to gNB200 (first cell).

[0072] In step S6, the UE 100 may perform synchronization processing with the LTM candidate cell (second cell) before receiving the cell switch command MAC CE from the first cell. Such synchronization processing may be referred to as early synchronization. Here, the UE 100 may perform downlink synchronization processing (DL synchronization processing) for the LTM candidate cell, and then perform early timing advance (TA) acquisition (i.e., UL early synchronization) in the LTM candidate cell requested by the gNB 200 (serving cell). This is performed by CFRA triggered by a PDCCH order (PDCCH order) from the first cell. Note that when DCI Format 1_0 is used and all "Frequency domain resource assignment" fields in the DCI are set to "1", the DCI is treated as a PDCCH order. In addition, when early UL synchronization setting (EarlyUlSyncConfig) is configured in UE100, the PDCCH order may include a cell indicator indicating the corresponding RACH transmission cell, i.e., to which LTM candidate cell UE100 should transmit a random access preamble (RA preamble).

[0073] The UE 100 transmits an RA preamble to the designated LTM candidate cell (second cell). In order to minimize communication interruption of the serving cell due to CFRA for the LTM candidate cell, in early synchronization, the UE 100 does not receive a random access response (RAR) for the purpose of acquiring a TA value from the LTM candidate cell. The TA value of the LTM candidate cell (target cell) is indicated in the cell switching command MAC CE in step S9. Note that the TA value is a value for adjusting the uplink transmission timing of the UE 100.

[0074] In step S7, the UE 100 performs layer 1 (L1) measurement in the configured LTM candidate cell and transmits a physical layer measurement report (also referred to as an "L1 measurement report") to the gNB 200 (first cell). The L1 measurement report is transmitted and received at L1, which is the PHY layer. For example, the UE 100 transmits L1-RSRP and / or L1-SINR to the gNB 200 via a PUCCH (Physical Uplink Control Channel) and / or a PUSCH (Physical Uplink Shared Channel).

[0075] In step S8, gNB200 decides to switch the serving cell to the target cell (second cell).

[0076] In step S9, the gNB 200 (first cell) transmits a cell switch command MAC CE including a candidate configuration index of the target cell to the UE 100. The cell switch command MAC CE may include a TA value determined by UL early synchronization (i.e., a TA value derived based on the RA preamble).

[0077] In step S10, the UE 100 switches to the configuration of the target cell (second cell). Specifically, the UE 100 detaches from the first cell and applies the configuration of the target cell (second cell).

[0078] In step S11, if the serving cell switch needs to include execution of a random access procedure (for example, if the cell switch command MAC CE does not include a valid TA value), the UE 100 executes the random access procedure for the target cell (RACH-based LTM cell switch). Note that, if the UE 100 does not need to acquire the TA of the target cell at the time of serving cell switch (for example, if the cell switch command MAC CE includes a valid TA value), it can skip the random access procedure (RACH-less LTM cell switch).

[0079] In step S12, the UE 100 indicates that the serving cell switch to the target cell has been successfully completed, for example, by sending an RRC Reconfiguration Complete message to the target cell (second cell). Thereafter, the UE 100 may perform steps S6 to S12 multiple times for subsequent LTM serving cell switches based on the configuration provided in step S4.

[0080] (3.2) Inter-CU LTM The LTM introduced in 3GPP Release 18 only supports intra-CU and does not support inter-CU (i.e., between different gNBs 200) LTM. In other words, in conventional LTM, it is possible to perform LTM cell switching between cells under the same CU (same gNB 200), but it is not possible to perform LTM cell switching between cells under different CUs (different gNBs 200).

[0081] Meanwhile, inter-CU LTM is scheduled to be newly introduced in 3GPP Release 19. In inter-CU LTM, the UE 100 performs LTM cell switching from a first cell of one gNB 200 to a second cell of another gNB 200.

[0082] An example of the operation of the Inter CU LTM will be described based on the operation of Fig. 7. Fig. 8 is a diagram showing an example of the operation of the Inter CU LTM.

[0083] In step S101, the UE 100 transmits an L3 measurement report to the gNB 200a. The gNB 200a receives the L3 measurement report.

[0084] In step S102, gNB200a determines to use inter-gNB (inter-CU) LTM based on the L3 measurement report in step S101 and starts preparing an LTM candidate cell. Here, it is assumed that the second cell of gNB200b has been determined as the LTM candidate cell.

[0085] In step S103, the gNB 200a transmits a request message (LTM HO Request) indicating a serving cell change by LTM to the gNB 200b. The gNB 200b receives the request message (LTM HO Request). The request message (LTM HO Request) includes an LTM indicator and may be a Handover Request message used in a general handover. Alternatively, the request message (LTM HO Request) may be a new message different from the Handover Request message, for example, an LTM Handover Request message. Note that the request message (LTM HO Request) may include, similarly to a general handover, the RRC setting information of the UE 100, a cell identifier indicating the second cell, and the like.

[0086] In step S104, the gNB200b determines whether or not to accept the request of step S103 (Admission control). Here, the description will proceed assuming that the request of step S103 is accepted. In this case, the gNB200b may configure a CFRA resource for early synchronization in the second cell. Note that, if the request of step S103 is rejected, the gNB200b may send a rejection message to the gNB200a. The rejection message may include information indicating that inter-gNB LTM cannot be used.

[0087] In step S105, the gNB200b transmits an acknowledgement message (LTM HO Request Ack) indicating acceptance of the request of step S103 to the gNB200a. The gNB200a receives the acknowledgement message (LTM HO Request Ack). The acknowledgement message (LTM HO Request Ack) may include an LTM indicator and may be a Handover Request Ack message used in general handover. Alternatively, the acknowledgement message (LTM HO Request Ack) may be a new message different from the Handover Request Ack message, for example, an LTM Handover Request Ack message. The acknowledgement message (LTM HO Request Ack) may include information indicating an early synchronization CFRA resource (e.g., an RA preamble and / or a PRACH (Physical Random Access Channel) resource) configured by the gNB200b for the second cell. Note that the acknowledgement message (LTM HO Request Ack) may include RRC reconfiguration information (RRC Reconfiguration) of the UE100 to be applied in the second cell, as in a general handover. The acknowledgement message (LTM HO Request Ack) may include a notification indicating that the second cell will transmit (reply) an RAR in response to the RA preamble transmission, and / or information indicating an RAR reception window.

[0088] In step S106, the gNB 200a transmits an RRC Reconfiguration message including the LTM configuration (LTM Candidate Configuration, LTM-Candidate) of the second cell to the UE 100. The UE 100 receives the RRC Reconfiguration message. The RRC Reconfiguration message may include information indicating the CFRA resource for early synchronization configured by the gNB 200b for the second cell. The RRC Reconfiguration message may include a notification indicating that the second cell will transmit (reply) an RAR in response to the RA preamble transmission, and / or information indicating an RAR reception window.

[0089] In step S107, the UE 100 saves the LTM setting and transmits an RRC Reconfiguration Complete message to the gNB 200a. The gNB 200a receives the RRC Reconfiguration Complete message.

[0090] In step S108, the UE 100 may transmit an L1 measurement report (or an L3 measurement report) to the gNB 200a for the gNB 200a to determine early synchronization. The gNB 200a may receive the L1 measurement report (or the L3 measurement report).

[0091] In step S109, gNB200a may make a decision to perform early synchronization.

[0092] In step S110, the gNB 200a may transmit an Early sync CFRA Request message to the gNB 200b, which is a request message requesting preparation of a CFRA resource for early synchronization, specifically, configuration and / or activation (validation) of a CFRA resource for early synchronization. The gNB 200b may receive the request message (Early sync CFRA Request message). The request message (Early sync CFRA Request message) may include an identifier (Xn-AP UE ID) for identifying the UE 100 and / or an identifier (cell ID) for identifying the second cell.

[0093] In step S111, gNB200b may prepare CFRA resources for early synchronization.

[0094] In step S112, the gNB 200b may transmit a notification message indicating that the CFRA resource for early synchronization has been prepared, for example, an Early sync CFRA Request Ack message, to the gNB 200a. The gNB 200a may receive the notification message (Early sync CFRA Request Ack message).

[0095] In step S113, the gNB 200a may transmit a PDCCH order to the UE 100 and instruct the UE 100 to perform CFRA for early synchronization. The UE 100 receives the PDCCH order. The PDCCH order may include information (Target cell indicator) for identifying the second cell as a target of the CFRA. The PDCCH order may include a notification indicating that the second cell will transmit (reply) an RAR in response to the RA preamble transmission, and / or information indicating an RAR reception window.

[0096] In step S114, the UE 100 may perform early synchronization of the downlink (DL) with the second cell. For example, the UE 100 performs timing synchronization using the SSB (PSS / SSS) of the second cell. Note that the UE 100 may have performed DL synchronization before this point.

[0097] In step S115, the UE 100 transmits a CFRA, specifically, an RA preamble on a PRACH, to the second cell specified in the PDCCH order in order to perform early synchronization of the uplink (UL) with the second cell. The gNB 200b receives the RA preamble. The UE 100 identifies the CFRA resource (for example, an RA preamble and / or a PRACH resource) based on information set in the SIB or the like and information such as a "Random Access Preamble Index" and a "PRACH Mask Index" in the PDCCH order.

[0098] In step S116, the gNB 200b may transmit an RAR including a TA value derived based on the RA preamble to the UE 100. The UE 100 may receive the RAR. Step S116 may be an optional step that is executed only if there is a setting from the gNB 200a (e.g., the setting in step S106).

[0099] The UE 100 may transmit a notification (Early Sync Complete) indicating that the UL early synchronization with the second cell has been completed to the gNB 200a (step S117). The notification (Early Sync Complete) may include the TA value notified by the RAR.

[0100] In step S118, the gNB 200b may transmit to the gNB 200a a notification message (Early Sync Complete) indicating that UL early synchronization with the UE 100 has been completed. The gNB 200a may receive the notification message (Early Sync Complete). The notification message (Early Sync Complete) may include the TA value derived based on the RA preamble of step S115.

[0101] In step S119, the UE 100 transmits an L1 measurement report to the gNB 200a. The gNB 200a receives the L1 measurement report.

[0102] In step S120, when gNB200a determines that the possibility of LTM execution has increased, for example, based on the L1 measurement report of step S119, it may transmit a UL resource request message to gNB200b. gNB200b may receive the request message. The UL resource request may be a request for preparation or activation of CFRA resources. The UL resource request may be a request for preparation or execution of UL grant transmission to UE100. The UL resource request may be a request for preparation or activation of UL configured grant (CG) resources. Note that the transmission of the request message in step S120 may be simultaneous with the LTM execution decision in step S121. The transmission may be after the LTM execution decision in step S121.

[0103] In step S121, gNB200a decides to perform LTM based on the L1 measurement report of step S119.

[0104] In step S122, in response to the LTM execution decision, the gNB 200a transmits a cell switching command (MAC CE) to the UE 100. The UE 100 receives the cell switching command. The cell switching command may include the TA value notified to the gNB 200a in step S117 or S118.

[0105] In step S123, in response to the reception of the cell switching command, the UE 100 detaches from the first cell (source cell) and applies the LTM setting of the second cell (target cell).

[0106] In step S124, if the cell switch command does not include a TA value (a valid TA value), the UE 100 may perform a random access procedure for the second cell.

[0107] In step S125, the UE 100 transmits an RRC Reconfiguration Complete message to the second cell. The gNB 200b receives the RRC Reconfiguration Complete message.

[0108] In step S126, the gNB 200b transmits DCI including a CRC (Cyclic Redundancy Code) scrambled with the C-RNTI assigned to the UE 100 to the UE 100 on the PDCCH, and may transmit a Contention Resolution MAC CE to the UE 100 on the PDSCH assigned by the DCI. The UE 100 may receive the DCI and the Contention Resolution MAC CE.

[0109] In step S127, gNB200b may transmit a notification message (LTM HO Success) to gNB200a indicating that the inter-network node LTM to the second cell has been completed. gNB200a may receive the notification message (LTM HO Success).

[0110] (4) Basic Operation Example Regarding L1 Measurement Reporting Based on the above-described configuration and operations, a basic operation example regarding L1 measurement reporting according to the embodiment will be described.

[0111] As described above, in LTM, gNB200 performs control related to LTM (also referred to as "LTM control") based on an L1 measurement report from UE100. For example, gNB200 selects a target beam (and / or target cell) based on the L1 measurement report and triggers an LTM cell switch for the selected target. Furthermore, gNB200 may select a candidate beam (and / or target cell) for triggering early synchronization based on the L1 measurement report.

[0112] The L1 measurement results included in the L1 measurement report include reference signal received power (RSRP). Such RSRP is also referred to as L1-RSRP. Types of L1-RSRP include SS-RSRP, which is obtained by measuring SSB as a reference signal, and CSI-RSRP, which is obtained by measuring CSI-RS as a reference signal. SS-RSRP is defined as the linear average of the power levels (in watts) of resource elements carrying the secondary synchronization signal (SSS). The measurement time resource of SS-RSRP is limited to the SS / PBCH Block Measurement Time Configuration (SMTC) window period. When SS-RSRP is used as L1-RSRP by the report configuration, the measurement time resource limitation due to the SMTC window period may not apply. On the other hand, CSI-RSRP is defined as the linear average of the power levels (in [W]) of the resource elements of the antenna port carrying the CSI reference signal configured for RSRP measurement over the configured CSI-RS opportunities within the considered measurement frequency band.

[0113] In 3GPP Release 18, it is assumed that periodic L1 measurement reports will be used as L1 measurement reports. Such periodic L1 measurement reports may require the UE 100 to transmit L1 measurement reports at a high transmission frequency, which may increase the load (power consumption, etc.) on the UE 100. On the other hand, in 3GPP Release 19, the introduction of event-triggered L1 measurement reports (also referred to as "event-triggered L1 measurement") is being considered.

[0114] In event-triggered L1 measurements, the measurement results at the beam level are basically used for event evaluation. However, event-triggered L1 measurements may also be measurements at the cell level. In event-triggered L1 measurement reports, the UE 100 transmits an L1 measurement report to the gNB 200 when a radio quality condition (also referred to as an "entering condition" or "first radio quality condition") corresponding to an L1 LTM measurement event is satisfied. In other words, in event-triggered L1 measurement reports, the UE 100 does not need to transmit an L1 measurement report during a period in which the set radio quality condition is not satisfied, thereby reducing the load on the UE 100. Note that the UE 100 performs LTM event evaluation, which is an evaluation of whether the L1 LTM measurement event is satisfied, on L1 or L2. The UE 100 also transmits the L1 measurement report on L1 or L2.

[0115] As L1 LTM measurement events, the following events based on beam-specific quality may be supported: - Event LTM1: The beam of the serving cell becomes better than an absolute threshold; - Event LTM2: The beam of the serving cell becomes worse than an absolute threshold; - Event LTM3: The beam of the LTM candidate cell becomes better than the beam of the serving cell by a certain offset; - Event LTM4: The beam of the LTM candidate cell becomes better than an absolute threshold; - Event LTM5: The beam of the serving cell becomes worse than absolute threshold 1 and the beam of the LTM candidate cell becomes better than another absolute threshold 2.

[0116] In addition, the UE 100 uses any beam for event evaluation for each of the serving cell and the neighboring cell. The L1 measurement resource configuration in the LTM configuration supports beam configuration of SSB and CSI-RS. For the events LTM3 and LTM5, the same reference signal type is used for the serving cell and the neighboring cell (LTM candidate cell). In addition, the L1 measurement result included in the L1 measurement report is, as shown in FIG. 6, a beam-specific measurement value A after L1 filtering. １ may be.

[0117] 9 is a diagram illustrating an example of an event-triggered L1 measurement report according to the embodiment. In the illustrated example, it is assumed that the event LTM4 is set from the gNB 200 to the UE 100 as an L1 LTM measurement event.

[0118] The UE 100 evaluates (determines) whether the L1 radio quality conditions (entering conditions, leaving conditions) corresponding to the set L1 LTM measurement event are satisfied. Hereinafter, such L1 radio quality conditions are also referred to as "L1 event conditions" or "L1 events." Note that "satisfying the event conditions" is synonymous with "satisfying the entering conditions" or "entering an event," and "not satisfying the event conditions" is synonymous with "satisfying the leaving conditions" or "leaving from an event." A state in which the event conditions are satisfied (i.e., a state in which the entering conditions are satisfied) is also referred to as an "enter state," and a state in which the event conditions are not satisfied (i.e., a state in which the leaving conditions are satisfied) is also referred to as a "leaving state."

[0119] When an entering condition according to the L1 LTM measurement event is satisfied, the UE 100, in which an L1 LTM measurement event is set by the gNB 200, transmits an L1 measurement report to the gNB 200. The entering condition may be a condition in which a hysteresis value (offset value) is assigned to a reference value (threshold) in the L1 LTM measurement event.

[0120] Such an L1 measurement report may be a periodic L1 measurement report, i.e., the UE 100 may start transmitting the periodic L1 measurement report when an entering condition according to a configured L1 LTM measurement event is met.

[0121] By receiving such an event-triggered L1 measurement report, gNB200 can determine that the entering condition is met in UE100, and can start LTM control, for example. It is also desirable that gNB200 can determine that the L1 LTM measurement event is no longer met in UE100. If gNB200 can determine that the L1 LTM measurement event is no longer met in UE100, gNB200 can, for example, discontinue LTM control, which may enable appropriate and efficient LTM control.

[0122] When the entering condition is satisfied, the UE 100 starts (triggers) the transmission of periodic L1 measurement reports. At least one of a hysteresis value (offset value), a TTT (Time To Trigger), a report interval (reportInterval), and a report amount (reportAmount) may be configured in the UE 100. When the TTT is configured, the UE 100 may start (trigger) the transmission of the L1 measurement report in response to a state in which the first radio quality condition (entering condition) is satisfied continuing for a time period of the TTT. When the report interval (reportInterval) is configured, the UE 100 may transmit the L1 measurement report at a period corresponding to the report interval (reportInterval). When the report amount (reportAmount) is set, the UE 100 may transmit the L1 measurement report a number of times according to the report amount (reportAmount).

[0123] On the other hand, when a radio quality condition (also referred to as a "leaving condition" or "second radio quality condition") corresponding to the L1 LTM measurement event is satisfied, the periodic transmission of the L1 measurement report may be terminated. The leaving condition may be a condition in which a hysteresis value (offset value) is assigned to a reference value (threshold value, etc.) in the L1 LTM measurement event. Therefore, when the gNB200 can no longer receive periodic L1 measurement reports from the UE100, it can be estimated that the leaving condition has been satisfied in the UE100.

[0124] However, if gNB200 is temporarily unable to receive the L1 measurement report due to a deterioration in radio conditions, etc., there is a problem that gNB200 may mistakenly determine that the leaving condition is met at UE100, even though the leaving condition is not met at UE100.

[0125] In addition, since the L1 measurement results may be subject to large instantaneous fluctuations, it is assumed that the gNB200 side, which receives the periodic L1 measurement reports, averages (filters) the L1 measurement results before using them for LTM control. If the gNB200 is no longer able to receive periodic L1 measurement reports from the UE100, the input data to the filter on the gNB200 side will be zero. If the filter on the gNB200 side continues to operate in such a situation, the filtering result on the gNB200 side will be significantly worse than the actual radio conditions, which may cause an erroneous determination on the gNB200 side.

[0126] Therefore, in the following embodiments (4.1) and (4.2), when event-triggered L1 measurements are introduced, operations are described that enable gNB200 to accurately determine that the leaving condition (second radio quality condition) has been met in UE100, thereby enabling LTM to be improved.

[0127] (4.1) Overview of UE Operation Based on the above-described configuration and operation, an overview of the operation of the UE 100 according to the embodiment will be described. Fig. 10 is a diagram showing an overview of the operation of the UE 100 according to the embodiment.

[0128] In step S201, the UE 100 for which the L1 LTM measurement event is set performs L1 measurement, which is radio quality measurement in L1 (starts L1 measurement).

[0129] In step S202, the UE 100 evaluates (determines) whether a first radio quality condition (entering condition) that triggers an L1 measurement report, which is a report of the L1 measurement result, is satisfied based on the L1 measurement result. The first radio quality condition (entering condition) may be a condition that determines whether a set L1 LTM measurement event is satisfied. For example, when the event LTM4 is set in the UE 100, the UE 100 evaluates that the first radio quality condition (entering condition) is satisfied when the beam quality (L1-RSRP) of the LTM candidate cell becomes better than an absolute threshold plus a hysteresis value (offset value).

[0130] If the first radio quality condition (entering condition) is satisfied (step S202: YES), in step S203, the UE 100 transmits an L1 measurement report including an L1 measurement result to the gNB 200 at least once on L1 or L2. For example, when transmitting the L1 measurement report on L1, the UE 100 may transmit the L1 measurement report as uplink control information (UCI) on a physical uplink control channel (PUCCH). Alternatively, when transmitting the L1 measurement report on L2, the UE 100 may transmit the L1 measurement report as a medium access control and control element (MAC CE) on a physical uplink shared channel (PUSCH). In step S203, the UE 100 may start transmitting periodic L1 measurement reports.

[0131] In step S204, the UE 100 evaluates (determines) whether a second radio quality condition (leaving condition) for suspending L1 measurement reporting is satisfied based on the L1 measurement result. The second radio quality condition (leaving condition) may be a condition for determining that the configured L1 LTM measurement event is no longer satisfied. For example, when the event LTM4 is configured in the UE 100, the UE 100 evaluates that the second radio quality condition (leaving condition) is satisfied when the beam quality (L1-RSRP) of the LTM candidate cell becomes worse than the absolute threshold minus the hysteresis value (offset value).

[0132] If the second radio quality condition (leaving condition) is satisfied (step S204: YES), in step S205, the UE 100 transmits notification information (also referred to as "leave notification information") indicating that the second radio quality condition is satisfied to the gNB 200 on L1 or L2. If the UE 100 has started transmitting periodic L1 measurement reports in step S203, the UE 100 terminates (cancels) the transmission of the periodic L1 measurement reports in response to the second radio quality condition (leaving condition) being satisfied. The UE 100 may transmit the leave notification information on the PUCCH by UCI on L1. Alternatively, the UE 100 may transmit the leave notification information on the PUSCH by MAC CE on L2. The leave notification information may include information indicating the type of the L1 LTM measurement event that satisfied the leaving condition.

[0133] According to this operation, UE100 transmits leave notification information indicating that the second radio quality condition (leaving condition) has been satisfied to gNB200 on L1 or L2, and can therefore explicitly notify gNB200 that the second radio quality condition has been satisfied. Thus, gNB200 can accurately determine that the second radio quality condition has been satisfied in UE100. In other words, UE100 can explicitly notify gNB200 that the configured L1 LTM measurement event is no longer satisfied. Thus, gNB200 can accurately determine that the L1 LTM measurement event is no longer satisfied in UE100.

[0134] The UE 100 that performs such an operation has a control unit 130 that performs L1 measurement, and a transmission unit 120 that, in response to the first wireless quality condition being satisfied, transmits an L1 measurement report including an L1 measurement result to the gNB 200 at least once via L1 or L2. In response to the second wireless quality condition being satisfied, the transmission unit 120 transmits leave notification information indicating that the second wireless quality condition is satisfied to the gNB 200 via L1 or L2.

[0135] On the other hand, the gNB 200 has a receiver 220 that receives an L1 measurement report that is transmitted at least once on L1 or L2 from the UE 100 performing the L1 measurement in response to the first wireless quality condition being satisfied, and that includes the L1 measurement result. The receiver 220 receives leave notification information from the UE 100 that is transmitted on L1 or L2 in response to the second wireless quality condition being satisfied, and that indicates that the second wireless quality condition is satisfied.

[0136] In step S205, the UE 100 may transmit an L1 measurement report including leave notification information to the gNB 200 via L1 or L2. For example, the UE 100 may transmit an L1 measurement report including leave notification information to the gNB 200 at the first transmission timing according to the reporting interval of the L1 measurement report after the second radio quality condition is satisfied. That is, the UE 100 may transmit the L1 measurement report including leave notification information (e.g., a leave flag) at the L1 measurement report timing immediately after the leaving condition is satisfied. In this case, the UE 100 may transmit at least one L1 measurement report after the leaving condition is satisfied. Note that the L1 measurement report including the leave notification information does not need to include the L1 measurement result. The L1 measurement report may include the L1 measurement result.

[0137] Alternatively, in step S205, when the second radio quality condition is satisfied, the UE 100 may transmit leave notification information to the gNB 200 on L1 or L2 using signaling different from the L1 measurement report. For example, when the second radio quality condition is satisfied, the UE 100 may transmit leave notification information to the gNB 200 on L1 or L2 before the first transmission timing according to the reporting interval of the L1 measurement report. That is, when the leaving condition is satisfied, the UE 100 may immediately transmit leave notification information. Such leave notification information may be a MAC CE. Such leave notification information may be only an LCID without a MAC CE body. Such leave notification information may be flag information in the UCI.

[0138] (4.2) Specific Example of System Operation Based on the above-described configuration and operation, a specific example of the operation of the mobile communication system 1 according to the embodiment will be described. Fig. 11 is a diagram showing a specific example of the operation of the mobile communication system 1 according to the embodiment.

[0139] In step S300, UE100 is in an RRC connected state in the cell (serving cell) of gNB200.

[0140] In step S301, gNB200 transmits an L1 measurement report configuration, which is a configuration related to L1 measurement reporting, to UE100. gNB200 may transmit an RRC message (RRC Reconfiguration message) including the L1 measurement report configuration to UE100. UE100 receives the L1 measurement report configuration.

[0141] The L1 measurement reporting configuration may include at least one of the following information:

[0142] a: Configuration information related to L1 LTM measurement event The configuration information a is information specifying, for example, any one of events LTM1 to LTM5. The configuration information a may include at least one of a threshold value used in the specified event, a hysteresis value (offset value), a TTT (Time To Trigger), a report interval (reportInterval), and a report amount (reportAmount). A plurality of L1 LTM measurement events may be configured in the UE 100.

[0143] b: Setting information regarding whether transmission of leave notification information is requested (permitted) The setting information b may be information indicating that transmission of leave notification information is requested (permitted). The setting information b may be information indicating that transmission of leave notification information is not requested (permitted). The UE 100 may transmit the leave notification information only when transmission of leave notification information is requested (permitted) based on the setting information b.

[0144] These pieces of configuration information may be included in an LTM configuration (LTM candidate configuration), and may be configured for each LTM candidate cell.

[0145] In step S302, UE100 performs L1 measurements (beam measurements) for the serving cell and / or LTM candidate cell according to the L1 measurement report configuration in step S301.

[0146] In step S303, the UE 100 evaluates (determines) whether or not a first radio quality condition (entering condition) corresponding to the set L1 LTM measurement event is satisfied, based on the L1 measurement result.

[0147] If the first radio quality condition (entering condition) is satisfied (step S23: YES), in step S304a, the UE 100 starts (trigger) transmission of the L1 measurement report. If the TTT is set, the UE 100 may start (trigger) transmission of the L1 measurement report in response to the state in which the first radio quality condition (entering condition) is satisfied continuing for the time of the TTT.

[0148] In steps S304a, S304b, S304c, ..., the UE 100 transmits L1 measurement reports periodically. The period is determined according to a report interval (reportInterval) set in the UE 100. When a report amount (reportAmount) is set, the UE 100 may transmit the L1 measurement reports a number of times according to the report amount (reportAmount).

[0149] In step S305, the UE 100 evaluates (determines) whether or not a second radio quality condition (leaving condition) corresponding to the set L1 LTM measurement event is satisfied, based on the L1 measurement result.

[0150] If the second radio quality condition (leaving condition) is satisfied (step 25: YES), in step S306, the UE 100 transmits leave notification information indicating that the second radio quality condition is satisfied to the gNB 200 via L1 or L2. The gNB 200 receives the leave notification information.

[0151] When the second radio quality condition (leaving condition) is satisfied, if the transmission of the L1 measurement report is continuing, the UE 100 may transmit an L1 measurement report including leaving notification information to the gNB 200 at the timing of transmitting the first L1 measurement report after the second radio quality condition (leaving condition) is satisfied. The leaving notification information may include information indicating that the leaving condition has been satisfied and / or information indicating the type of the L1 LTM measurement event that satisfied the leaving condition.

[0152] On the other hand, when the transmission of the L1 measurement report has been completed, for example, when the transmission of the L1 measurement report for the report amount (reportAmount) has been completed, the UE 100 may immediately transmit leaving notification information to the gNB 200 when the second radio quality condition (leaving condition) is satisfied. In this case, the UE 100 may transmit only the leaving notification information to the gNB 200 without including the leaving notification information in the L1 measurement report. Such leaving notification information may be information in the UCI. Such leaving notification information may be information in the MAC CE. When transmitting leaving notification information in the MAC CE, only the corresponding LCID (i.e., the LCID indicating that it is leaving notification information) may be transmitted, and the main body (payload portion) of the MAC CE may not be transmitted.

[0153] The gNB 200 that has received the leave notification information may stop (suspend) the transmission of the cell switching command MAC CE based on the leave notification information, for example, in response to notification of the leaving condition of the event LTM3. For example, the gNB 200 may recognize that there will be no more input to the filter of the L1 measurement report value, and may stop processing its own filter and / or clear (reset) the filter output value.

[0154] 12 is a diagram for explaining a beam (reference signal) measured by the UE 100 according to the embodiment. In the illustrated example, there is a gNB 200a that manages the serving cell of the UE 100 and a gNB 200b that manages the LTM candidate cell of the UE 100, but the serving cell and the LTM candidate cell may be managed by the same gNB 200.

[0155] Each gNB 200 transmits an SSB in its own cell. The SSB is transmitted by a beam with a wide beam width using an analog beam former and is a reference signal that is not specific to a specific UE 100 (UE-specific). The UE 100 can measure the SSB as a reference signal to obtain the SS-RSRP.

[0156] In addition, each gNB 200 transmits CSI-RS in its own cell. The CSI-RS is transmitted by a narrow beam width beam formed by a digital beam former and may be a reference signal for a specific UE 100 (UE-specific). The UE 100 can measure the CSI-RS as a reference signal to obtain the CSI-RSRP.

[0157] The UE 100 receives K beam-specific measurement values ​​A of the K beams output by the L1 filter 11 in FIG. １ Alternatively, K beam-specific measurement values ​​A of K beams input to the L1 filter 11 in FIG. 6 may be used as L1 measurement results for L1 event evaluation. １ or A is also called the "beam measurement value", and measurement value A １ Or the process of deriving A is also referred to as "beam quality measurement". The "beam measurement value" may be SS-RSRP or CSI-RSRP. Note that the beam measurement value may be read as a reference signal measurement value, and the beam quality measurement may be read as a reference signal quality measurement. The UE 100 measures each beam (reference signal) of the serving cell and / or the LTM candidate cell according to the configured L1 LTM measurement event to derive each beam measurement value.

[0158] (5) Operation Regarding Stopping of L1 Measurement Report Procedure An operation regarding stopping of the L1 measurement report procedure according to the embodiment will be described.

[0159] In the above-described embodiment, the UE 100 leaves the L1 LTM measurement event and stops transmitting the L1 measurement report when the second radio quality condition (leaving condition) corresponding to the configured L1 LTM measurement event (L1 event condition) is satisfied. Therefore, the UE 100 may need to periodically transmit the L1 measurement report between entering the L1 LTM measurement event and leaving it. In this case, the load (power consumption, etc.) of the UE 100 increases.

[0160] When the report amount (reportAmount) is set in the UE 100, the UE 100 transmits the L1 measurement report a number of times according to the report amount (reportAmount). Therefore, by setting the report amount (reportAmount) in the UE 100, the load (power consumption, etc.) of the UE 100 can be reduced.

[0161] However, if the number of L1 measurement report transmissions set by the report amount (reportAmount) is too small, there is a concern that gNB200 may not be able to properly perform LTM control, such as selecting a candidate beam (and / or target cell) for early synchronization and / or determining LTM cell switching. For example, after the transmission of L1 measurement reports for the report amount (reportAmount) has been completed, gNB200 may not be able to perform LTM control based on the L1 measurement reports.

[0162] On the other hand, if the number of L1 measurement report transmissions set by the report amount (reportAmount) is too high, the UE 100 will continue to transmit the L1 measurement report even if the gNB 200 does not require the L1 measurement report. That is, there is a concern that the transmission of the L1 measurement report will continue more than necessary. In this case, there is a problem that the load on the UE 100 (power consumption, etc.) will increase unnecessarily. In addition, if the transmission of the L1 measurement report continues more than necessary, the gNB 200 can stop the transmission of the L1 measurement report by deleting (de-configuring) the corresponding report setting using RRC layer signaling. However, there is a problem that the overhead related to RRC signaling increases and / or the UE processing and communication delay related to RRC reconfiguration occur.

[0163] In addition, it is difficult for the gNB 200 to pre-set an optimal report amount (reportAmount) based on prediction to the UE 100. Therefore, there is a problem in that it is difficult to appropriately control L1 measurement reporting.

[0164] In the following embodiment, an operation for enabling appropriate control of L1 measurement reporting will be described. Fig. 13 is a diagram showing an operation related to stopping an L1 measurement reporting procedure according to the embodiment. Note that this operation can be performed in combination with the operation according to the above embodiment.

[0165] In step S400, the UE 100 receives an RRC message (RRC Reconfiguration message) from the gNB 200, which includes a setting of an L1 event condition (L1 LTM measurement event) that triggers reporting of the L1 measurement result and a setting of a stop event condition. The L1 event condition may be any of the above-mentioned events LTM1 to LTM5. On the other hand, the stop event condition is a condition for stopping event evaluation and / or periodic transmission of L1 measurement reports. The stop event condition is a condition different from the L1 event condition and is also a condition different from the above-mentioned leaving condition (second radio quality condition). The stop event condition may be a condition that specifies an event related to LTM control by the gNB 200.

[0166] In step S401, the UE 100 performs L1 measurement, which is radio quality measurement in L1 (starts L1 measurement).

[0167] In step S402, the UE 100 performs an event evaluation to evaluate whether the L1 event condition set in step S400 is satisfied, based on the L1 measurement result.

[0168] In step S403, UE100 triggers (starts) periodic transmission of L1 measurement reports to gNB200 in response to the L1 event condition being met (step S402: YES).

[0169] In step S404, the UE 100 evaluates whether the stop event condition set in step S400 is satisfied.

[0170] In step S405, the UE 100 stops the event evaluation and / or the periodic transmission of the L1 measurement report in response to the stop event condition being satisfied (step S404: YES).

[0171] In this way, the UE 100 that has started transmitting periodic L1 measurement reports stops the transmission of event evaluation and / or periodic L1 measurement reports in response to the satisfaction of a stop event condition preset by the gNB 200. Therefore, the event evaluation and / or transmission of periodic L1 measurement reports in the UE 100 can be stopped at an appropriate timing. Therefore, the load on the UE 100 required for L1 measurement reports can be reduced while enabling the gNB 200 to perform appropriate LTM control.

[0172] The UE 100 that performs such operations includes a receiver 110 that receives an L1 event condition setting and a stop event condition setting from the gNB 200, a control unit 130 that performs event evaluation that evaluates whether the L1 event condition is met based on the result of the L1 measurement, and a transmitter 120 that triggers the transmission of an L1 measurement report to the gNB 200 in response to the L1 event condition being met (see FIG. 2). The control unit 130 stops the event evaluation and / or the periodic transmission of the L1 measurement report in response to the stop event condition being met. Meanwhile, the gNB 200 includes a transmitter 210 that transmits the L1 event condition setting and the stop event condition setting to the UE 100, and a receiver 220 that receives an L1 measurement report in response to the L1 event condition being met from the UE 100 that performs event evaluation that evaluates whether the L1 event condition is met based on the result of the L1 measurement. Setting a stop event condition causes the UE 100 to stop event evaluation and / or periodic transmission of L1 measurement reports in response to the stop event condition being met.

[0173] In step S405, the UE 100 may stop the periodic transmission of the L1 measurement report in response to the suspension event condition being satisfied. For example, the UE 100 may temporarily suspend the transmission of the periodic L1 measurement report in response to the suspension event condition being satisfied, and may resume the transmission of the periodic L1 measurement report in response to receiving a resume instruction from the gNB 200. In this case, the UE 100 may suspend the transmission of the periodic L1 measurement report in response to the suspension event condition being satisfied, while retaining the configuration related to the L1 event condition (such as the L1 measurement configuration). As a result, the UE 100 that has suspended the event evaluation and / or the periodic L1 measurement report can resume the suspension of the event evaluation and / or the periodic L1 measurement report using the retained configuration. When performing such an operation, the suspension event condition may be referred to as a "deactivation condition" or a "suspend condition."

[0174] In step S405, the UE 100 may stop the event evaluation in response to the stop event condition being satisfied. For example, the UE 100 may stop the periodic transmission of the L1 measurement report by leaving the event in response to the stop event condition being satisfied.

[0175] In step S405, the UE 100 may delete a configuration related to the L1 event condition (e.g., an LTM configuration and / or an L1 measurement configuration) in response to the occurrence of an event set as a stop event condition. Deletion of the configuration stops L1 event evaluation and periodic transmission of L1 measurement reports. Such deletion of the configuration may be referred to as release, discard, or deconfiguration. When such an operation is performed, the stop event condition may be referred to as a "deletion condition," "release condition," "discard condition," or "deconfiguration condition."

[0176] The stop event condition set in UE 100 may be a condition that a physical downlink control channel (PDCCH) order that triggers a physical random access channel (PRACH) transmission for early synchronization to the LTM candidate cell is received from the serving cell, or a condition that a PRACH transmission for early synchronization to the LTM candidate cell is performed.

[0177] The stop event condition set in the UE 100 may be a condition that a cell switching command (cell switching command MAC CE) instructing LTM cell switching to the LTM candidate cell is received from the serving cell, or a condition that LTM cell switching to the LTM candidate cell is started or completed.

[0178] The stop event condition set in UE100 may be a condition that at least one of the settings of L1 measurement, event evaluation, and transmission of periodic L1 measurement reports has been changed by gNB200.

[0179] The stop event condition set in UE 100 may be a condition that a measurement value of the serving cell becomes better than a threshold. The condition may be the above-mentioned event LTM1 (a condition that a beam measurement value of the serving cell becomes better than a threshold). Alternatively, the condition may be event A3 (a condition that a measurement value of the serving cell becomes better than a threshold) specified in the RRC specifications. In such a case, the L1 event condition set in UE 100 may be an L1 LTM measurement event other than the above-mentioned event LTM1, for example, any of events LTM2 to LTM5.

[0180] In response to the stop event condition being satisfied, the UE 100 may transmit a report to the gNB 200. In response to receiving an acknowledgement (Ack) for the report from the gNB 200, the UE 100 may delete the setting related to the L1 event condition.

[0181] (5.1) First Operation Pattern In the first operation pattern, the UE 100 stops the periodic transmission of the L1 measurement report in response to a stop event condition being satisfied.

[0182] 14 is a diagram showing an example of operation of the mobile communication system 1 according to the first operation pattern. This example of operation can be implemented in combination with the operation according to the above-described embodiment.

[0183] In step S500, the gNB 200 that manages the serving cell of the UE 100 transmits an RRC Reconfiguration message including an LTM setting and / or an L1 measurement setting to the UE 100. The UE 100 receives the RRC Reconfiguration message. The LTM setting and / or the L1 measurement setting includes a setting of an L1 event condition (L1 LTM measurement event) and a setting of a stop event condition. In the RRC Reconfiguration message, the L1 event condition and the stop event condition may be associated with each other, for example, by a measurement ID and / or an LTM setting ID.

[0184] The L1 event condition setting may be associated with an L1 measurement report setting in the L1 measurement setting. The L1 measurement report setting may include information for setting transmission of L1 measurement reports periodically or for a long period of time after an event is entered. The information may be a report amount (reportAmount) set to a large number or infinity. Alternatively, the concept of report amount (reportAmount) may not be introduced, and it may be specified in advance that L1 measurement reports are transmitted periodically after an event is entered.

[0185] The setting of the stop event condition associated with the L1 event condition includes, for example, information specifying one of the following LTM-related events: - Execution of early synchronization, such as reception of a PDCCH order or transmission of a PRACH to an LTM candidate cell; - Execution of an LTM cell switch, such as reception of a cell switch command or start / completion of access to a candidate cell; - LTM setting change, such as modifying or removing the settings of an LTM candidate cell.

[0186] In step S501, UE100 performs beam measurement (L1 measurement) on the serving cell and / or the LTM candidate cell according to the setting of step S500. For example, UE100 may measure the quality of each beam (each reference signal) observable in the serving cell. UE100 may measure the quality of each beam (each reference signal) observable in the LTM candidate cell.

[0187] In step S502, the UE 100 evaluates whether the L1 event condition (quality condition) set in step S500 is satisfied based on the L1 measurement result obtained in step S501 (event evaluation). If the L1 event condition is not satisfied (step S502: NO), the UE 100 returns the process to step S501.

[0188] If the L1 event condition is satisfied (step S502: YES), in step S503, the UE 100 enters the L1 event (L1 LTM measurement event) set in step S500.

[0189] In step S504, UE100 starts (trigger) periodic transmission of an L1 measurement report to gNB200 and transmits the L1 measurement report to gNB200. gNB200 receives the L1 measurement report. The L1 measurement report may include an L1 measurement result (beam measurement value), beam identification information, and / or information on the event type triggered in step S502. The beam identification information may be an SSB index, a CSI-RS index, and / or a TCI (Transmission Configuration Indication) state index. The beam identifier may be a reference signal identifier.

[0190] In step S505, gNB200 may transmit an LTM-related instruction to UE100. For example, when gNB200 determines to perform early synchronization, to perform LTM cell switching, or to change LTM-related settings (LTM settings or L1 measurement settings) based on the L1 measurement report from UE100, it transmits an LTM-related instruction to UE100 instructing the execution of early synchronization, the execution of LTM cell switching, or the change of LTM-related settings. When UE100 receives an LTM-related instruction from gNB200, it performs the operation (processing) instructed by the LTM-related instruction.

[0191] In step S506, UE100, which transmits periodic L1 measurement reports, checks whether the stop event condition corresponding to the LTM-related instruction is met based on whether or not it received an LTM-related instruction from gNB200 in step S505.

[0192] If the stop event condition is satisfied (step S506: YES), in step S507, the UE 100 stops transmitting the periodic L1 measurement report. The UE 100 may maintain the entered state of the L1 event while stopping the transmission of the periodic L1 measurement report. Alternatively, the UE 100 may stop transmitting the periodic L1 measurement report by stopping event evaluation (i.e., leaving the L1 event). Here, the description will proceed assuming that the entered state of the L1 event is maintained.

[0193] In step S508, the gNB 200 may transmit a resume instruction to the UE 100 to instruct the UE 100 to resume transmission of periodic L1 measurement reports. The resume instruction may be transmitted by a MAC CE or a DCI. The resume instruction may be transmitted by an RRC message. For example, when the gNB 200 needs to determine whether to perform early synchronization, whether to perform an LTM cell switch, or whether to change a setting (LTM setting or L1 measurement setting), the gNB 200 may decide to resume transmission of periodic L1 measurement reports and transmit a resume instruction to the UE 100. The resume instruction may include an identifier for identifying the setting related to the L1 measurement report, for example, a candidate cell ID, an LTM setting ID, and / or an L1 measurement setting ID (which may be an event ID, a report setting ID, or the like), and / or beam identification information.

[0194] If a resume instruction is received from gNB200 (step S509: YES), in step S510, UE100 may resume transmitting periodic L1 measurement reports.

[0195] Thus, in the first operation pattern, UE100 stops L1 measurement report transmission (or event evaluation) upon receiving an LTM-related instruction from gNB200 that is pre-set as a stop event condition.

[0196] In this operation pattern, an example has been described in which an event related to receiving an LTM-related instruction from the gNB 200 is used as a stop event condition. However, the stop event condition may be a condition in which the measurement value of the serving cell becomes better than a threshold.

[0197] (5.2) Second Operation Pattern In the second operation pattern, the UE 100 deletes the settings related to the L1 event condition (e.g., the LTM setting and / or the L1 measurement setting) in response to the occurrence of an event set as the stop event condition. In the following second operation pattern, an example will be described in which the stop event condition is a condition in which the measurement value of the serving cell becomes better than a threshold. However, an event related to receiving an LTM-related instruction from the gNB 200 may also be used as the stop event condition.

[0198] 15 is a diagram showing an example of operation of the mobile communication system 1 according to the second operation pattern. This operation example can be implemented in combination with the operation according to the above-described embodiment. Here, differences from the first operation pattern will be mainly described.

[0199] In step S600, gNB200, which manages the serving cell of UE100, transmits an RRC Reconfiguration message including LTM configuration and / or L1 measurement configuration to UE100. UE100 receives the RRC Reconfiguration message.

[0200] The LTM setting and / or L1 measurement setting includes a setting of an L1 event condition (L1 LTM measurement event) a that triggers the reporting of the L1 measurement result, and a setting of an event condition b (stop event condition) that deletes the setting related to the L1 event condition a. For example, the L1 event condition a that triggers the reporting of the L1 measurement result may be any one of the events LTM2 to LTM5. Meanwhile, the event condition b that deletes the setting related to the L1 event condition a may be the event LTM1 or the event A1, but here it is assumed that the event LTM1 is specified as the event condition b.

[0201] In the RRC Reconfiguration message, the L1 event condition a and the event condition b may be associated with each other by, for example, a measurement ID and / or an LTM configuration ID. That is, the RRC Reconfiguration message in step S600 includes an ID (index) of a configuration to be deleted when the event condition b is satisfied, such as a measurement ID and / or an LTM configuration ID. For example, assume that the L1 event condition a is identified by measurement ID #1, the event condition b is identified by measurement ID #2, and the LTM configuration is identified by LTM configuration ID #3. In this case, automatic deletion of the measurement ID #3 and the LTM configuration #3 may be configured (associated) within the configuration of measurement ID #1.

[0202] In step S601, UE100 performs beam measurement (L1 measurement) on the serving cell and / or LTM candidate cell according to the setting in step S600.

[0203] In step S602, the UE 100 evaluates whether the L1 event condition a set in step S600 is satisfied based on the L1 measurement result obtained in step S601. If the L1 event condition a is not satisfied (step S602: NO), the UE 100 returns the process to step S601.

[0204] If the L1 event condition a is satisfied (step S602: YES), in step S603, the UE 100 enters the L1 event a set in step S600.

[0205] In step S604, UE100 starts (trigger) periodic transmission of L1 measurement report a to gNB200 and transmits L1 measurement report a to gNB200. gNB200 receives L1 measurement report a. L1 measurement report a may include L1 measurement results (beam measurement values), beam identification information, and / or information on the event type triggered in step S602 (event ID and / or measurement ID).

[0206] In step S605, the UE 100 that periodically transmits the L1 measurement report a evaluates whether or not the event condition b corresponding to the L1 event condition a is satisfied, based on the L1 measurement result.

[0207] If the event condition b is satisfied (step S605: YES), in step S606, the UE 100 enters the event b.

[0208] In step S607, UE100 starts (trigger) the transmission of L1 measurement report b to gNB200 and transmits L1 measurement report b to gNB200. gNB200 receives L1 measurement report b. L1 measurement report b may include L1 measurement results (beam measurement values), beam identification information, and / or information on the event type triggered in step S605 (event ID and / or measurement ID). Based on the event type information, gNB200 may recognize that UE100 deletes event condition b and LTM setting.

[0209] In step S608, gNB200 may send an acknowledgement response (HARQ Ack) to UE100 for L1 measurement report b.

[0210] In step S609, UE100 deletes L1 event condition a and LTM setting in response to receiving the confirmation response (HARQ Ack). Note that this deletion may be performed at the timing of step S606 or step S607, but deleting at the time of the confirmation response can prevent discrepancies in recognition between gNB200 and UE100.

[0211] In this way, in the second operation pattern, the UE 100 deletes the setting related to the L1 event condition a in response to the event condition b being satisfied.

[0212] (6) Other Embodiments In the above-described embodiments, cell-level measurements may be used in addition to beam-level measurements for L1 event evaluation. Cell-level L1 measurements are more stable than beam-level measurements. There are two types of cell-level measurements: measurements derived from beams but without L3 filtering; legacy L3 measurements, i.e., measurements after L3 filtering.

[0213] In either case, event evaluation based on both beam-level and cell-level measurement results is considered to contribute to the stability of the evaluation results. For example, when beam-level event LTM3 and cell-level event LTM4 (or event A4) are combined, the LTM decision (i.e., cell switching) based on event LTM3 occurs only after event LTM4 is satisfied (i.e., the quality of this LTM candidate cell is better than a certain level). Therefore, the combined event based on both beam-level and cell-level measurements can improve the stability of event evaluation.

[0214] In the above-described embodiment, there are three possible options for the layer that performs one-event evaluation (i.e., evaluation of enter and leave conditions): L1 (PHY layer): This is a viable option because conventional L1 measurement reporting is performed at the PHY layer. The drawback is that a large impact on the PHY layer specifications is expected; L2 (MAC layer): This is a viable option because the LTM decision is made in the DU of the gNB 200 and the cell switch command is sent as a MAC CE. The drawback is a large impact on the MAC specifications, including some inter-layer interactions. For example, MAC needs to control the start / stop of L1 measurement reporting for the PHY; L3 (RRC layer): The functionality for event-triggered L3 measurement reporting is available at the RRC layer, so it may be possible to reuse it with relatively little effort / modification. The drawback is that inter-layer interactions are required, for example, RRC instructing the PHY to start / stop L1 measurement reporting.

[0215] These three options have their advantages and disadvantages, and all options are technically feasible, but the MAC layer is the appropriate layer because the cell switch command is processed at the MAC layer, and the impact on the PHY can be minimized.

[0216] In the above-described embodiment, there are three possible options for the layer that performs the L1 measurement report: L1 (UCI): This is a valid option because there is an existing periodic L1 measurement report. Therefore, from the perspective of the reporting mechanism, it may be necessary to change the specification, such as turning on / off the periodic L1 measurement report when entering / leaving the event state. The disadvantage is that it may be unclear whether this can contribute to a significant improvement in radio resource efficiency; L2 (MAC CE): This is a reasonable option because the subsequent cell switch command is sent by the MAC layer, so the procedure including the LTM decision can be processed at the same layer. Furthermore, the MAC CE is fast enough for the gNB 200 to make the LTM decision. The disadvantage is that it is expected that a new MAC CE will be specified; L3 (RRC message): This is a possible option because the L3 measurement reporting framework already exists. However, since LTM is a low-latency cell switching mechanism and LTM decisions are made by the DU of gNB200, RRC messages incur significant delays on both the radio interface and the network interface (i.e., F1-AP).

[0217] Therefore, either UCI or MAC CE are viable options since RRC messages are difficult to apply to LTM from a latency perspective, but MAC CE is preferable due to the lack of complexity regarding inter-layer interactions and the minimal impact of PHY specifications.

[0218] In the above-described embodiment, it is preferable that UE100 includes at least one of the following information in the L1 measurement report: - Beam measurement results (i.e., L1 measurement results, which may be measurement results for multiple beams and multiple cells); - Beam information (i.e., reference signal identifier, e.g., SSB index or CSI-RS index); - Triggered event information (event ID, e.g., information indicating event LTM3).

[0219] The LTM in the above-described embodiments may be read as conditional LTM. For example, the above-described LTM of an inter-CU or intra-CU may be conditional LTM of an inter-CU or intra-CU. In conditional LTM, for example, the RRC Reconfiguration message in step S4 of FIG. 6 includes information indicating the execution conditions (e.g., radio quality conditions) of LTM cell switching for each LTM candidate cell. The UE 100 performs LTM cell switching to an LTM candidate cell that satisfies the preset execution conditions (radio quality conditions) instead of the cell switching command MAC CE transmitted from the gNB 200. This enables faster LTM cell switching.

[0220] The above-described operational flows are not limited to being implemented independently, but can be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow. In each flow, it is not necessary to execute all steps, and only some steps may be executed. Furthermore, the order of steps in each flow may be changed as appropriate.

[0221] In the above-described embodiments and examples, an example in which the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB) or a 6G base station. The base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of the IAB node. The UE 100 may also be an MT (Mobile Termination) of the IAB node. That is, the UE 100 may be a terminal function unit (a type of communication module) for the base station to control a relay that relays signals. Such a terminal function unit is referred to as an MT. Examples of MTs include, in addition to IAB-MT, NCR (Network Controlled Repeater)-MT and RIS (Reconfigurable Intelligent Surface)-MT.

[0222] The term "network node" primarily refers to a base station, but may also refer to a core network device or a part of a base station (CU, DU, or RU). A network node may also be configured by a combination of at least a part of a core network device and at least a part of a base station.

[0223] A program that causes a computer to execute each process performed by the UE 100 or the gNB 200 may be provided. The program may be recorded on a computer-readable medium. Using a computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM and / or a DVD-ROM. Furthermore, circuits that execute each process performed by the UE 100 or the gNB 200 may be integrated, and at least a portion of the UE 100 or the gNB 200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0224] The functions performed by the above-described communication device (such as the UE 100 or the gNB 200) may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a CPU (Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to perform the described functions. A processor includes transistors and / or other circuits and is considered to be circuitry or processing circuitry. A processor may be a programmed processor that executes a program stored in a memory. In this specification, a circuitry, unit, or means is hardware that is programmed to realize or executes a described function. The hardware may be any hardware disclosed herein or any hardware known to be programmed to realize or execute the described function. If the hardware is a processor, which is considered to be a type of circuitry, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0225] As used in this disclosure, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Additionally, as used in this disclosure, the term "or" is not intended to mean an exclusive or. Furthermore, as used in this disclosure, any reference to an element using a designation such as "first," "second," etc. does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein, or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles are intended to include the plural unless the context clearly indicates otherwise.

[0226] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0227] This application claims priority to U.S. Provisional Application No. 63 / 679,778 (filed August 6, 2024), the entire contents of which are incorporated herein by reference.

[0228] (7) First Supplementary Note: The following is a supplementary note regarding the features of the above-described embodiment.

[0229] Supplementary Note 1: A communication method executed by a user equipment in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: receiving, from a network node, a setting of an L1 event condition that triggers a report of a Layer 1 (L1) measurement result and a setting of a stop event condition; performing event evaluation that evaluates whether the L1 event condition is satisfied based on a result of an L1 measurement that is a radio quality measurement in L1; triggering transmission of the L1 measurement report to the network node in response to the L1 event condition being satisfied; and stopping the event evaluation and / or the periodic transmission of the L1 measurement report in response to the stop event condition being satisfied.

[0230] Supplementary Note 2: The communication method according to Supplementary Note 1, wherein the user equipment stops periodic transmission of the L1 measurement report in response to an occurrence of an event set as the stop event condition, even when the L1 event condition is satisfied.

[0231] Supplementary Note 3: The communication method according to Supplementary Note 1 or 2, wherein the user device deletes a setting related to the L1 event condition in response to an occurrence of an event set as the stop event condition.

[0232] Supplementary Note 4: The communication method according to any one of Supplementary Notes 1 to 3, wherein the stop event condition is a condition that a Physical Downlink Control Channel (PDCCH) order that triggers a Physical Random Access Channel (PRACH) transmission for early synchronization to an LTM candidate cell has been received from a serving cell, or a condition that the PRACH transmission for the early synchronization to the LTM candidate cell has been performed.

[0233] Supplementary Note 5: The communication method according to any one of Supplementary Notes 1 to 3, wherein the stop event condition is a condition that a cell switch command instructing an LTM cell switch to an LTM candidate cell is received from a serving cell, or a condition that the LTM cell switch to the LTM candidate cell has been started or completed.

[0234] Supplementary Note 6: The communication method according to any one of Supplementary Notes 1 to 3, wherein the stop event condition is that at least one of the settings of the L1 measurement, the event evaluation, and the transmission of periodic L1 measurement reports has been changed by the network node.

[0235] Supplementary Note 7: The communication method according to any one of Supplementary Notes 1 to 3, wherein the stop event condition is that a measurement value of a serving cell becomes better than a threshold.

[0236] Supplementary Note 8: The communication method of Supplementary Note 7, wherein the user equipment transmits a report to the network node in response to the stop event condition being satisfied, and deletes a configuration related to the L1 event condition in response to receiving an acknowledgement response to the report from the network node.

[0237] Supplementary Note 9: A user equipment for use in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: a receiver that receives from a network node a setting of an L1 event condition that triggers a report of a Layer 1 (L1) measurement result and a setting of a stop event condition; a controller that performs event evaluation that evaluates whether the L1 event condition is satisfied based on a result of L1 measurement that is a radio quality measurement in L1; and a transmitter that triggers transmission of the L1 measurement report to the network node in response to the L1 event condition being satisfied, wherein the controller stops the event evaluation and / or the periodic transmission of the L1 measurement report in response to the stop event condition being satisfied.

[0238] Supplementary Note 10: A network node used in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: a transmitter that transmits to a user equipment a setting of an L1 event condition that triggers a report of a Layer 1 (L1) measurement result and a setting of a stop event condition; and a receiver that receives, from the user equipment, the L1 measurement report in response to the L1 event condition being satisfied, the L1 measurement report that performs event evaluation that evaluates whether the L1 event condition is satisfied based on a result of L1 measurement that is a radio quality measurement in L1, wherein the setting of the stop event condition causes the user equipment to stop the event evaluation and / or the periodic transmission of the L1 measurement report in response to the stop event condition being satisfied.

[0239] (8) Appendix 2 1. Introduction In RAN #102, a new work item for NR mobility extension phase 4 was approved, which includes the objective of specifying event-triggered L1 measurement reporting. The detailed objectives are described as follows:

[0240] Measurement-related extensions to support LTM:

[0241] Measurement-related extensions are applicable to Intra-CU MCG / SCG LTM and Inter-CU MCG / SCG LTM.

[0242] Specifies the components required to support event-triggered L1 measurement reporting.

[0243] RAN1 and RAN2 will work independently on their respective MIMO and mobility enhanced WI event triggered measurement objectives, with RAN#105 reviewing progress to determine if objective modifications are required to avoid / manage duplication of work.

[0244] It specifies support for CSI-RS measurements for LTM procedures, enabling CSI-RS based beam management and / or other necessary physical layer operations on candidate cells before LTM.

[0245] This appendix presents further observations on the open issue of measurement event evaluation in event-triggered L1 measurement reporting.

[0246] 2. Discussion 2.1 Additional Events RAN2 has agreed on two use cases for event-triggered L1 measurement reporting, which are related to the early synchronization phase and the LTM cell switch execution phase.

[0247] 1. Event-triggered L1 measurements should be designed for the following LTM purposes: - Select a candidate beam / cell to trigger early synchronization. - Select a target beam / cell and trigger the LTM cell switch procedure.

[0248] RAN2 also agreed to introduce events LTM2, 3, 4, and 5, which are similar to events A2, A3, A4, and A5, respectively, but further consideration is needed as to whether to support event LTM1, which is similar to event A1 (for further study).

[0249] 3. The following LTM events based on the beam-specific qualities of the serving cell and candidate cell are supported as L1 LTM measurement events: - Event LTM2: The beam of the serving cell becomes worse than an absolute threshold; - Event LTM3: The beam of the candidate cell becomes better than the beam of the serving cell by a certain offset; - Event LTM4: The beam of the candidate cell becomes better than an absolute threshold; - Event LTM5: The beam of the serving cell becomes worse than absolute threshold 1 and the beam of the candidate cell becomes better than another absolute threshold 2.

[0250] Further study is required as to whether to use the beam of the serving cell or the neighboring cell for event evaluation. Further study is required as to the necessity of event LTM1.

[0251] For the L3 handover procedure, event A1, i.e. "serving cell becomes better than threshold", is used to remove the measurement configuration from the UE when it moves back from the cell edge to the cell center. In the LTM procedure, event LTM1 is assumed to be used for the same purpose, i.e. to deconfigure LTM-Config, which is rather related to the LTM preparation phase.

[0252] Observation 1: As a potential application, event LTM1 is expected to be used to remove LTM configuration during the LTM preparation phase, which is different from the agreed LTM purpose (i.e., early synchronization and LTM cell switch execution phase).

[0253] LTM is a low-latency mobility mechanism that utilizes L1 measurement reports, early synchronization, and cell switch command MAC CE, but as noted in Remark 1, these phases do not involve event LTM1. On the other hand, the LTM preparation phase, which may involve event LTM1, does not require such rapid operations. In fact, the LTM preparation phase can be based on L3 measurement reports, and an RRC Reconfiguration is involved anyway to configure / deconfigure LTM-Config for the UE. Therefore, L1 measurement reports, especially event LTM1, are not mandatory during the LTM preparation phase; i.e., the existing L3 measurement reporting event A1 can still be used for this purpose.

[0254] Proposal 1: RAN2 should agree not to introduce event LTM1 for L1 measurement reporting.

[0255] Since LTM is also considered beneficial for aerial UEs (aircraft UEs) that require low latency mobility, it is worth discussing whether to define H1 / H2-like events to support vertical LTM. In this case, other events such as A3H1 may be beneficial as well. Note that height-dependent events will be used in the early synchronization and LTM cell switch execution phases, which is consistent with the purpose of event-triggered L1 measurement reporting agreed by RAN2. Therefore, RAN2 should discuss whether these AxHx events will be supported in L1 measurement reporting.

[0256] Proposal 2: RAN2 should discuss whether event AxHx-like triggers for Aerial UEs are also supported in L1 measurement reports.

[0257] 2.2 Event Evaluation 2.2.1 Beam-Level and Cell-Level Measurements RAN2 agreed that event evaluation will be based on beam-level measurements including both SSB and CSI-RS, but the details of the beams and cell-level measurements used in the evaluation still need further consideration.

[0258] 2. For event-triggered L1 measurements, the baseline is to use beam-level measurements for event evaluation. Further study is needed for cell-level measurements.

[0259] Further study is required as to whether to use the beam of the serving cell or the neighboring cell for event evaluation. Further study is required as to the necessity of event LTM1.

[0260] 4. Support both SSB and CSI-RS beam configuration in L1 measurement resource configuration within LTM configuration. Working assumption: For events LTM3 and LTM5, the same RS type should be used in both the serving cell and neighboring cells.

[0261] In legacy L3 event evaluation, cell-level measurements, whether SSB or CSI-RS, are derived from the "highest beam measurement quality value" or "linear power-scaled average of the highest beam measurement value above a set threshold (provided the total number of averaged beams does not exceed a set number)" before applying L3 filtering. This is shown in Figure 16.

[0262] For beam-based event evaluation, it is straightforward to follow the same mechanism with configuration, i.e., section 5.5.3.3 of the current RRC specification (see Annex) is reused, but the measurement results should be "before" applying "L3 cell filtering". Note that, as today, it is configurable whether to use beam-level measurements with the best 1 beam or cell-level measurements with the best N beams.

[0263] Proposal 3: RAN2 should agree that the beam level measurement result for event evaluation is the linear power scale average of the highest beam measurement value that exceeds a set threshold (provided that the total number of beams averaged does not exceed a set number), otherwise it is the highest beam measurement quality value, i.e., the same as the existing L3 cell measurement derivation except for applying L3 cell filtering.

[0264] For event LTM3, its condition is defined by comparing beam level measurements from the serving cell and the LTM candidate cell; for other events, absolute thresholds are used for each condition. If Proposal 3 is agreeable and a "threshold" is set, the UE may obtain measurements from a different number of beams, which may make measurement configuration difficult or introduce some errors in the event evaluation process. For example, as shown in Figure 17, the average value of more beams may be weaker than the single value of the "Top-1" beam. Therefore, especially for event LTM3, it is worth discussing whether measurements from a different number of beams can be simply compared.

[0265] Proposal 4: RAN2 should discuss whether measurement results from different numbers of beams are comparable, especially for event LTM3.

[0266] 2.2.2 Stability Aspects At the previous meeting, many companies expressed concerns about the stability of event evaluation, such as false alarms and / or ping-pong events. As a result, it was agreed to introduce TTT, hysteresis, and beam-specific offsets into LTM event evaluation.

[0267] 2. For event-triggered L1 measurements, the baseline is to use beam-level measurements for event evaluation. Further study is needed for cell-level measurements.

[0268] 5. RAN2 assumes that filtering of L1 measurements is required. It is up to RAN1 whether specified L1 filtering is required or can be left to the UE implementation.

[0269] 6. LTM event evaluation can apply hysteresis for TTT, entering / leaving, and / or beam-specific (cell-specific needs further study) offsets. Whether measurement reporting is required once the leaving condition is met needs further study.

[0270] For further stability considerations, it may be considered to use cell-level measurements in addition to beam-level measurements, since cell-level measurements are more stable. So far there are at least two interpretations of "cell-level measurements", namely: - Interpretation 1: Measurements derived from the beam but without applying L3 filtering. This is discussed in proposal 3 above. - Interpretation 2: Legacy L3 measurements, i.e., interpretation 1 with L3 filtering applied.

[0271] Regardless of the interpretation, it may be worth considering whether event evaluation based on both beam-level and cell-level measurements can contribute to the stability of the evaluation results. For example, when beam-level event LTM3 and cell-level event LTM4 (or event A4) are combined, the LTM decision (i.e., cell switch) based on event LTM3 occurs only after event LTM4 is met (i.e., the quality of this LTM candidate cell is better than a certain level). Therefore, it may be beneficial to discuss whether further improvement of the stable evaluation is necessary.

[0272] Proposal 5: RAN2 should discuss whether composite events based on both beam-level and cell-level measurements can improve the stability of event evaluation.

[0273] From another perspective, the stability of event evaluation is considered to depend on the received beam type, i.e., SSB or CSI-RS, for event LTM3 and / or event LTM5. RAN2 agreed to support both SSB and CSI-RS configurations and concluded the working assumption that the same RS type should be used in both the serving cell and neighboring cells.

[0274] 4. Support both SSB and CSI-RS beam configuration in L1 measurement resource configuration within LTM configuration. Working assumption: For events LTM3 and LTM5, the same RS type should be used in both the serving cell and neighboring cells.

[0275] In the process of event evaluation at the UE, in the context of handover / cell switch, SSB should always be available from both the serving cell and the LTM candidate cell, but CSI-RS may not be available from both cells (e.g., CSI-RS is not transmitted from the cell, the UE cannot receive CSI-RS normally, no CSI-RS configuration for measurement is provided, some measurement difficulties in case of inter-frequency scenarios, etc.). In this case, there may be potential issues that should be further discussed. For example, - whether the network needs to adjust the RS type between the serving cell and the LTM candidate cell to match; - whether the event LTM3 / 5 configured with CSI-RS can fall back to one using SSB when CSI-RS from the serving cell or the LTM candidate cell is unavailable; - whether it is allowed to evaluate the event LTM3 / 5 using different RS types, for example, CSI-RS from the serving cell and SSB from the LTM candidate cell.

[0276] Therefore, RAN2 should consider in more detail the implications behind their working assumptions.

[0277] Proposal 6: RAN2 should discuss how to align RS types for measurements during the LTM preparation phase and / or LTM execution phase.

[0278] 2.2.3 Layer that handles evaluation and triggering It has not yet been discussed which layer should handle event evaluation and measurement reporting triggering, i.e., the satisfaction of entering / leaving conditions. Three options are considered:

[0279] L1 (PHY Layer): Legacy L1 measurement reporting is a viable option as it is done within the PHY layer. The drawback is that it is expected to have a significant impact on the RAN1 specification.

[0280] L2 (MAC layer): This is also an option to consider, since the MAC layer already has a large responsibility in LTM. That is, since LTM decisions are made in the source DU and cell switch commands are sent via the MAC, it is consistent that the same layer also handles event evaluation. The drawback is the large impact on the MAC specification, which includes several inter-layer interactions. For example, the MAC needs to control the start / stop of L1 measurement reporting to the PHY.

[0281] L3 (RRC layer): This is a possible option since all functionality for event-triggered L3 measurement reporting is already available in the RRC layer and therefore these can potentially be reused with relatively little effort / modification. The drawback of this option is that it requires interaction between layers, e.g. RRC instructing the PHY to start / stop L1 measurement reporting.

[0282] All three options have advantages and disadvantages, and all are technically feasible, so RAN2 should discuss which layer handles this modeling issue. MAC is the appropriate layer, since cell switch commands are also handled by the MAC layer. However, this is similar to the legacy HO process, where RRC handles L3 measurement reporting including event evaluation and L3 handover decisions. In addition, mobility functions are the responsibility of RAN2, maximizing maintenance and expansion capabilities and minimizing impact on RAN1. This is desirable for this purpose and because RAN2 is the leading WG for this WI.

[0283] Proposal 7: RAN2 should agree that the MAC layer handles event evaluation and measurement reporting triggers.

[0284] (9) Appendix 3 Discussion Document 1. Introduction In RAN # 102, a new work item for NR mobility extension phase 4 was approved, which included the objective of specifying event-triggered L1 measurement reporting. The detailed objectives are described as follows:

[0285] Measurement-related extensions to support LTM:

[0286] Measurement-related extensions are applicable to Intra-CU MCG / SCG LTM and Inter-CU MCG / SCG LTM.

[0287] Specifies the components required to support event-triggered L1 measurement reporting.

[0288] RAN1 and RAN2 will work independently on their respective MIMO and mobility enhanced WI event triggered measurement objectives, with RAN#105 reviewing progress to determine if objective modifications are required to avoid / manage duplication of work.

[0289] It specifies support for CSI-RS measurements for LTM procedures, enabling CSI-RS based beam management and / or other necessary physical layer operations on candidate cells before LTM.

[0290] This appendix presents further observations regarding event-triggered L1 measurement reporting.

[0291] 2. Discussion 2.1 L1 Measurement Report Content According to the current L1 measurement configuration for LTM, the reporting content is configured in CSI-ReportConfig and LTM-CSI-ReportConfig. In CSI-ReportConfig, various reporting quantities can be configured, but L1-RSRP will be the most important quantity in the LTM procedure.

[0292]

[0293] Additionally, the number of reference signals to be reported can be configured in CSI-ReportConfig. If this is 1, RSRP is reported as an absolute value (7 bits). Otherwise (i.e., if it is greater than 1), the largest RSRP is reported as an absolute value (7 bits) and the other RSRPs are reported as differential values ​​(4 bits).

[0294]

[0295] LTM-CSI-ReportConfig further allows configuration of the number of cells to be reported, the number of reference signals to be reported per cell, and whether to include SpCells. The first two IEs are similar to nrofReportedRS above (i.e. absolute or differential values), while spCellInclusion indicates whether the UE should include L1 measurement reports related to the current SpCell if the current SpCell is configured as an LTM candidate cell.

[0296]

[0297] In legacy L3 measurement reporting for L3 handover decisions, MeasResults contains the L3 measurement results plus a measId, which is associated with a ReportConfig that contains an EventTriggerConfig. Thus, the measurement report implicitly indicates which event triggered this report.

[0298]

[0299] Based on the existing reporting content in L1 measurement reporting for LTM and L3 measurement reporting for L3 handover decision, the event-triggered L1 measurement report should include the following information, the details of which need further study: - beam measurement results (potentially multiple beams and multiple cells), - beam information (e.g. SSB index), and - triggered event information (e.g. event LTM3, possibly signaled implicitly, e.g. by including measID).

[0300] Proposal 1: As a baseline, RAN2 should agree that beam measurement results, beam information, and triggered event information are reported in event-triggered L1 measurement reports. Details require further study.

[0301] In addition to the baseline information in Proposal 1, additional information useful for LTM will be further considered. For example, the "number of beams that meet the event condition" may be useful for the gNB's cell switch decision. As shown in Figure 18 below, even if the RSRP of the best beams from two cells is the same, the quality of the other beams may explain which cell is more stable. For example, a cell that offers three good beams or another cell that offers only one beam. It is clear that the UE should stay in a cell with three good beams. Otherwise, the UE may experience RLF or ping-pong handover in other cells that only have one beam.

[0302] Another possible approach would be for the L1 measurement report to include (a linear average of) measurements from multiple beams, which would also allow the gNB to take into account which cell is most stable for the UE when making a cell switch decision.

[0303] Currently, the L1 filter is left to the UE implementation, and Rel-19 states that "RAN2 assumes that filtering of L1 measurement results is necessary. It is up to RAN1 whether specified L1 filtering is required or can be left to the UE implementation." Regardless of whether the L1 filter is standardized or not, the filter coefficients change dynamically depending on, for example, the UE's movement speed. Therefore, it may be useful for gNBs to report "L1 filter information," such as the number of L1-RSRP samples, so that they may optimize their own L1 filter when making cell switch decisions.

[0304] Proposal 2: RAN2 should discuss what additional information would be useful for LTM to report, such as the number of beams that meet the event condition or L1 filter information.

[0305] 2.2. Signaling for L1 Measurement Reporting Here again, three options may be considered:

[0306] L1 (UCI): This is a valid option due to the existing periodic L1 measurement reporting. Therefore, from the perspective of the reporting mechanism, it may require only a small specification effort, e.g., turning on / off periodic L1 measurement reporting when entering / leaving an event condition. The drawback is that it requires RAN1 effort, and it may be unclear whether it can contribute to a significant improvement in radio resource efficiency.

[0307] L2 (MAC CE): This is a reasonable choice since the subsequent cell switch command is sent by the MAC layer, and the same layer can handle the procedure including the LTM decision. In addition, MAC CE is fast enough for the gNB to make the LTM decision. It is assumed that a new MAC CE will be defined, which is a drawback.

[0308] L3 (RRC messages): This is certainly a possible option since there is already a framework for L3 measurement reporting. However, given that LTM is a low latency handover mechanism and the LTM decision is made by the DU, RRC messages incur significant latency not only over the radio interface but also over the network interface (i.e., F1-AP).

[0309] Considering the above discussion, either UCI or MAC CE is a viable option since RRC messages are difficult to apply to LTM from a latency perspective. MAC CE is preferable because it eliminates the complexity of layer interactions and minimizes the impact on the RAN1 specification. In addition, it is also advantageous from the perspective of future specification maintenance, since RAN2 is responsible for mobility-related functions.

[0310] Proposal 3: RAN2 should agree that MAC CE is used for L1 measurement reporting.

[0311] 2.3. Reporting at the time of leaving and the amount of reporting At the previous meeting, it was decided that further consideration was needed as to whether it was necessary to introduce reporting at the time of leaving.

[0312] 6. LTM event evaluation can apply hysteresis for TTT, entering / leaving, and / or beam-specific (cell-specific needs further study) offsets. Whether measurement reporting is required once the leaving condition is met needs further study.

[0313] In L3 measurement reporting, leave-time reporting is supported as follows:

[0314] 2> reportType is set to eventTriggered and the leaving condition applicable to this event is met for all measurements after Layer 3 filtering taken during the timeToTrigger defined in VarMeasConfig for this event for one or more cells included in the cellsTriggeredList defined in VarMeasReportList for this measId:

[0315] 3> Delete the corresponding cell in the cellsTriggeredList defined in the VarMeasReportList for this measId;

[0316] 3> If reportOnLeave is set to true in the corresponding reporting setting:

[0317] 4> The corresponding reportConfig does not contain numberOfTriggeringCells; or

[0318] 4> If the corresponding reportConfig contains numberOfTriggeringCells and a measurement report has previously been sent to the network for at least one of the cells:

[0319] 5>Initiate the measurement reporting procedure as specified in 5.5.5;

[0320] The need for leave-time reporting may depend on whether a reporting amount is introduced into the L1 measurement report. For L3 measurements, reportAmount defines the "number of measurement reports applicable to both event-triggered and periodical reporting types" and is shown in Figure 9. In particular, if periodic L1 measurement reporting is performed after entering the condition (e.g., if the reporting amount is not introduced or is set to "infinite"), the leave-time reporting may be greatly simplified or even unnecessary, since the gNB can predict whether the UE has left the event condition based on past L1 measurement reports.

[0321] Observation 1: The need / details of leave-time reporting will depend on whether reporting quantities are introduced into L1 measurement reporting or not.

[0322] Regarding the amount of reporting, it would be useful to limit the number of measurement reports after entering an event condition, since this would contribute to reducing the UE load and its signaling overhead regarding measurement reporting, which is one of the main motivations for introducing this feature.

[0323] On the other hand, as agreed by RAN2, considering that event-triggered L1 measurement reports are designed for two LTM purposes, namely, "selecting a candidate beam / cell for triggering early synchronization" and "selecting a target beam / cell and triggering an LTM cell switch procedure," the gNB needs a certain amount of L1 measurement reports to make appropriate LTM decisions, such as avoiding ping-pong cell switches. However, since the appropriate amount of reports varies depending on the latest radio conditions and the UE's mobility situation, it would be difficult in practice for the gNB to predict in advance (i.e., at the time of RRC Reconfiguration) how many L1 measurement reports are needed for its stable decision. Therefore, it is unclear whether the amount of reports set by RRC Reconfiguration is useful in LTM.

[0324] Assuming that L1 measurement reports are made periodically while the event is fulfilled, and if the gNB may need to stop receiving them in some cases (e.g., if further reports are no longer needed after deciding to start early synchronization), it is conceivable to introduce a method for deactivating L1 measurement reports related to a particular event (e.g., via MAC CE, without reconfiguring the UE), although this may be a different mechanism from the reporting volume.

[0325] Proposal 4: Before deciding on the need for leave-time reporting, RAN2 should discuss how to limit the number of L1 measurement reports after the event is met, for example, by a mechanism similar to the legacy reporting volume or by a new MAC CE to deactivate periodic reporting.

[0326] 1: Mobile communication system 5: Network 10: RAN 11: L1 filter 12: Beam combining / selection unit 13: L3 filter 14: Evaluation unit 15: L3 beam filter 16: Beam selection unit 20: CN 100: UE 110: Receiving unit 120: Transmitting unit 130: Control unit 140: Wireless communication unit 200: gNB 210: Transmitting unit 220: Receiving unit 230: Control unit 240: Network communication unit 241: Transmitting unit 242: Receiving unit 250: Wireless communication unit 300: AMF / UPF

Claims

1. A communication method executed by a user equipment in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: receiving from a network node a setting of an L1 event condition that triggers reporting of Layer 1 (L1) measurement results and a setting of a stop event condition; performing event evaluation to evaluate whether the L1 event condition is met based on the result of L1 measurement, which is a radio quality measurement in L1; triggering transmission of the L1 measurement report to the network node in response to the L1 event condition being met; and stopping the event evaluation and / or the periodic transmission of the L1 measurement report in response to the stop event condition being met.

2. The communication method according to claim 1, wherein the user equipment stops the periodic transmission of the L1 measurement report in response to the occurrence of an event set as the stop event condition, even when the L1 event condition is satisfied.

3. The communication method according to claim 1, wherein the user device deletes the setting related to the L1 event condition in response to the occurrence of an event set as the stop event condition.

4. A communication method according to any one of claims 1 to 3, wherein the stop event condition is a condition that a Physical Downlink Control Channel (PDCCH) order that triggers a Physical Random Access Channel (PRACH) transmission for early synchronization to an LTM candidate cell has been received from a serving cell, or a condition that the PRACH transmission for the early synchronization to the LTM candidate cell has been performed.

5. A communication method according to any one of claims 1 to 3, wherein the stop event condition is a condition that a cell switching command instructing an LTM cell switching to an LTM candidate cell is received from a serving cell, or a condition that the LTM cell switching to the LTM candidate cell has been initiated or completed.

6. A communication method according to any one of claims 1 to 3, wherein the stop event condition is a condition that at least one setting of the L1 measurement, the event evaluation, and the transmission of the periodic L1 measurement report has been changed by the network node.

7. A communication method according to any one of claims 1 to 3, wherein the stop event condition is a condition in which a measurement value of a serving cell becomes better than a threshold value.

8. The communication method according to claim 7, wherein the user equipment transmits a report to the network node in response to the stop event condition being satisfied, and deletes the configuration related to the L1 event condition in response to receiving an acknowledgement response to the report from the network node.

9. A user equipment used in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: a receiver that receives from a network node an L1 event condition setting that triggers reporting of Layer 1 (L1) measurement results and a stop event condition setting; a controller that performs event evaluation that evaluates whether the L1 event condition is satisfied based on the result of L1 measurement, which is a radio quality measurement in L1; and a transmitter that triggers transmission of the L1 measurement report to the network node in response to the L1 event condition being satisfied, wherein the controller stops the event evaluation and / or the periodic transmission of the L1 measurement report in response to the stop event condition being satisfied.

10. A network node used in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: a transmitter that transmits to a user equipment a setting of an L1 event condition that triggers a report of a Layer 1 (L1) measurement result and a setting of a stop event condition; and a receiver that receives the L1 measurement report from the user equipment in response to the L1 event condition being satisfied, the receiver performing an event evaluation that evaluates whether the L1 event condition is satisfied based on the result of an L1 measurement, which is a radio quality measurement in L1. The setting of the stop event condition causes the user equipment to stop the event evaluation and / or the periodic transmission of the L1 measurement report in response to the stop event condition being satisfied.

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