Communication method, user device, and network node

Abstract

This communication method executed by a user device of a mobile communication system comprises: deriving a plurality of measurement values corresponding to one cell by repeatedly performing radio quality measurement of the one cell in a layer 1 (L1); generating a radio resource control (RRC) message including the plurality of measurement values corresponding to the one cell; and transmitting the RRC message to a network.

Description

COMMUNICATION METHOD, USER EQUIPMENT, AND NETWORK NODE

[0001] The present disclosure relates to a communication method, a user equipment, and a network node.

[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 (sometimes simply referred to as a "cell switch") of a user equipment in a radio resource control (RRC) connected state is instructed by transmitting an RRC layer message (a 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 V18.0.0 (2023-12)"

[0005] The present disclosure provides techniques that enable network optimization for 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, comprising: repeatedly performing radio quality measurements for a cell in Layer 1 (L1) to derive a plurality of measurement values ​​corresponding to the cell; generating a Radio Resource Control (RRC) message including the plurality of measurement values ​​corresponding to the cell; and transmitting the RRC message to a network.

[0007] A user equipment according to a second aspect of the present disclosure is a user equipment used in a mobile communication system, and includes: a control unit that repeatedly performs radio quality measurements for a cell in Layer 1 (L1) to derive multiple measurement values ​​corresponding to the cell, and generates a radio resource control (RRC) message including the multiple measurement values ​​corresponding to the cell; and a transmission unit that transmits the RRC message to a network.

[0008] A network node according to a third aspect of the present disclosure is a network node for use in a mobile communication system, and includes a receiver that receives from a user equipment a radio resource control (RRC) message including a plurality of measurements obtained by the user equipment repeatedly performing radio quality measurements for one cell at Layer 1 (L1).

[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. FIG. 7 is a diagram illustrating a filter coefficient of an L3 filter that is set from a gNB to a UE by RRC. FIG. 8 is a diagram illustrating an example of an LTM procedure. FIG. 9 is a diagram illustrating an operation of a UE according to an embodiment. FIG. 10 is a diagram illustrating an example of a first operation pattern according to an embodiment. FIG. 11 is a diagram illustrating a Logged Measurement Configuration message according to the first operation pattern. FIG. 12 is a diagram illustrating a UE Information Response message according to the first operation pattern. FIG. 13 is a diagram illustrating an example of a second operation pattern according to an embodiment. FIG. 14 is a diagram illustrating a HOF report according to the second operation pattern. FIG. 15 is a diagram illustrating SHR according to the second operation pattern. FIG. 16 is a diagram illustrating an operation of a UE according to a modified example of an embodiment.

[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 an embodiment. The mobile communication system 1 conforms to the 3GPP standard 5th Generation System (5GS). While the following description will be given using 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 that is 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 a 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).

[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 illustrating an example configuration of a UE 100 (user equipment) according to an embodiment. The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 configure 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 under the control of 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 an 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 successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has a CRC (Cyclic Redundancy Code) 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) Overview of Radio Quality Measurement by UE The UE 100 in the RRC connected state measures at least one beam of a cell and derives the radio quality of the cell by averaging the measurement results (power values). 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 the measurement report information (RRC message) transmitted from E100 to gNB200.

[0051] Figure 7 is a diagram to explain the filter coefficients of the L3 filter 13 set by RRC from the gNB 200 to the UE 100.

[0052] As shown in Figure 7 (1), the RRC information element QuantityConfigNR includes a list of QuantityConfigNRs. Each QuantityConfigNR includes a QuantityConfigRS. QuantityConfigRS includes a FilterConfig. FilterConfig includes a FilterCoefficient, which defaults to fc4 (filter coefficient k = 4). As shown in Figure 7 (2), FilterCoefficient is specified within the range from fc0 (filter coefficient k = 0) to fc19 (filter coefficient k = 19).

[0053] (3) Overview of LTM Technology The mobile communication system 1 according to this embodiment supports LTM (L1 / L2-triggered mobility).

[0054] 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.

[0055] 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.

[0056] Specifically, in LTM, first, gNB200 prepares an LTM candidate cell configuration for a candidate cell to be switched to, and provides the LTM candidate cell configuration to UE100 via RRC signaling.

[0057] Secondly, the UE 100 performs a synchronization process with the candidate cell by early synchronization (Early sync).

[0058] 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 candidate cell setting) to the UE 100 by MAC CE. The serving cell switch trigger is conveyed in a MAC CE including at least a candidate setting index together with a beam indicator.

[0059] Fourth, UE100 switches the serving cell in response to a cell switching command from gNB200 (source cell).

[0060] In this way, a serving cell switch is triggered by selecting an LTM candidate cell setting as a target setting by gNB200. An LTM candidate cell setting can be added, changed, and released by gNB200 via RRC signaling.

[0061] The following principles apply to LTM:

[0062] Each LTM candidate cell configuration can be provided as a differential configuration (delta configuration) relative to the reference configuration used to form the complete candidate cell configuration.

[0063] If a full candidate cell configuration is applied, it replaces the current UE configuration upon a serving cell switch. The reconfiguration procedure does the replacement but does not necessarily reset the MAC, RLC or PDCP layers.

[0064] The user plane continues without a reset if configured in RRC signaling to avoid additional delays in data recovery.

[0065] - Security is not updated in LTM.

[0066] LTM between subsequent LTM candidate cell configurations can be performed without RRC reconfiguration, i.e., the UE 100 does not release other LTM candidate cell configurations after LTM is triggered.

[0067] 8 is a diagram showing an example of a cell switching procedure using LTM. In the illustrated example, it is assumed that UE 100 performs serving cell switching from a first cell of gNB 200 to a second cell.

[0068] 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 a "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".

[0069] In step S1, UE100 is in an RRC connected state in the cell (first cell, source cell) of gNB200.

[0070] In step S2, UE100 transmits a Measurement Report message, which is an RRC message, to gNB200.

[0071] In step S3, gNB200 decides to use LTM based on the Measurement Report message and starts preparing the candidate cell.

[0072] In step S4, the gNB 200 transmits to the UE 100 an RRC Reconfiguration message including an LTM candidate cell configuration (LTM Candidate Configuration) of one or more candidate cells. The candidate cell configuration may include a random access channel (RACH) configuration used for RA preamble transmission to the corresponding candidate cell, for example, a contention-free random access (CFRA) configuration. 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.

[0073] In step S5, UE100 saves the LTM candidate cell setting and sends an RRC Reconfiguration Complete message to gNB200.

[0074] In step S6, the UE 100 may perform synchronization processing with the candidate cell before receiving the cell switching command. Such synchronization processing may be referred to as early synchronization (Early sync). Here, the UE 100 may perform downlink synchronization processing (DL synchronization processing) for the candidate cell, and then perform early timing advance (TA) acquisition in the candidate cell requested by the gNB 200 (source cell). This is performed by a CFRA triggered by a PDCCH command (PDCCH order) from the source 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 UE 100, the PDCCH order may include a cell indicator indicating a corresponding RACH transmission cell, i.e., a candidate cell to which UE 100 should transmit a random access preamble (RA preamble).

[0075] The UE 100 transmits an RA preamble to the designated candidate cell. In order to minimize communication interruption of the source cell due to the CFRA for the 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 candidate cell. The TA value of the candidate cell (target cell) is indicated in the cell switching command in step S9. Note that the TA value is a value for adjusting the uplink transmission timing of the UE 100.

[0076] In step S7, the UE 100 performs layer 1 (L1) measurement in the configured candidate cell and transmits a physical layer measurement report (L1 measurement report) to the gNB 200. 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).

[0077] In step S8, gNB200 decides to switch the serving cell to the target cell (second cell).

[0078] In step S9, the gNB 200 transmits a cell switch command (MAC CE) including a candidate configuration index of the target cell to the UE 100. The cell switch command may include the TA value obtained by early synchronization.

[0079] In step S10, the UE 100 switches to the configuration of the target cell. Specifically, the UE 100 detaches from the source cell (first cell) and applies the configuration of the target cell.

[0080] In step S11, if the serving cell switch needs to include execution of a random access procedure (for example, if the cell switch command does not include a valid TA value), the UE 100 executes a random access procedure for the target cell (RACH (Random Access Channel)-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 includes a valid TA value), it can skip the random access procedure (RACH-less LTM cell switch).

[0081] In step S12, the UE 100 indicates that the serving cell switch to the target cell has been successfully completed. 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.

[0082] In addition, in 3GPP Release 19, the introduction of a conditional LTM (C-LTM: Conditional LTM) procedure is planned to be considered. For example, the gNB 200 sets in advance in the UE 100 an execution condition (trigger condition, CondEvent), which is a radio quality condition for performing LTM cell switching, in the RRC Reconfiguration message of step S4. The UE 100 performs cell switching by LTM (also referred to as "LTM cell switching") when the radio quality condition is satisfied. This makes it possible to skip the operations from the L1 Measurement Report in step S7 to the Cell Switch Command (MAC CE) in step S9. As a result, it is possible to speed up cell switching and minimize interruptions in data communication. In the following description of the embodiments, LTM may be read as conditional LTM (C-LTM).

[0083] (4) Overview of SON Technology The mobile communication system 1 according to this embodiment supports SON (Self-Organizing Network).

[0084] SON is a technology that automatically optimizes parameters of the network 5, particularly configuration parameters of the gNB 200. SON includes Mobility Robustness Optimization (MRO) and RACH optimization. MRO is a technology for adjusting handover-related parameters to minimize handover failures. RACH optimization is a technology for adjusting RACH-related parameters to improve the probability of successful access and reduce access delay. Furthermore, Minimization of Drive Tests (MDT) technology is used to support the SON technology. MDT is a technology for collecting measurement information and location information for network optimization from the UE 100 to reduce the need for manual drive tests.

[0085] Functions in such technology include, for example, Immediate MDT, Logged MDT, Handover Failure (HOF) Report, and Successful Handover Report (SHR).

[0086] In Immediate MDT, UE 100 in an RRC connected state performs radio quality measurements and reports the measurement results to the network 5 (gNB 200) together with location information indicating the geographical location of UE 100. In Immediate MDT, measurement configuration and reporting procedures for L3 handover are applied, and UE 100 transmits an RRC message (L3 measurement report) including location information to the network 5.

[0087] In the logged MDT, the UE 100 in an RRC idle state or an RRC inactive state performs radio quality measurement and records the measurement result together with location information of the UE 100 as log information, and then the UE 100 transmits an RRC message (UE Information Response message) including the log information in response to a request from the network 5.

[0088] In the HOF report, the UE 100 records related information (including a radio quality measurement result) as log information when the HOF occurs, and then transmits an RRC message (UE Information Response message) including the log information in response to a request from the network 5.

[0089] In SHR, when handover is barely successful, the UE 100 records related information (including radio quality measurement results) as log information, and then transmits an RRC message (UE Information Response message) including the log information in response to a request from the network 5. A barely successful handover generally means a state in which handover is successful but there is still room for optimization, and for example means a state in which handover is successful just before various timers related to handover expire.

[0090] These functions enable the network 5 to collect information for automatically adjusting various parameters from the UE 100 and perform network optimization.

[0091] (5) Operation According to the Embodiment Conventional SON technology does not take into account LTM, which is a newly introduced serving cell switching technology, and therefore has a problem in that it is difficult to perform network optimization related to LTM.

[0092] Specifically, in conventional SON technology, the UE 100 reports one measurement value (i.e., L3 measurement value) after L3 filtering for each cell (serving cell and / or neighboring cell). For example, in MDT, the UE 100 associates one L3 measurement value for each cell (serving cell and / or neighboring cell) with one piece of location information and reports the result to the network 5. In addition, in HOF reporting, the UE 100 reports only one L3 measurement value for each cell (serving cell and / or neighboring cell) at the time of HOF occurrence.

[0093] On the other hand, one of the features of LTM is high-speed cell switching decision using L1 measurement reports, which allows cell switching decision to follow instantaneous fluctuations in the radio environment (radio quality). Such instantaneous fluctuation-responsive cell switching decision is considered to be particularly effective in environments with severe fading and / or shadowing, such as FR (Frequency Range) 2.

[0094] However, in conventional SON technology, the UE 100 reports only one L3 measurement value per cell, so the network 5 cannot grasp the situation of instantaneous fluctuations in the radio environment (radio quality), making it difficult to perform network optimization related to LTM. For example, if the transmission timing of the cell switching command from the gNB 200 cannot be optimized, the instantaneous fluctuations cannot be tracked, and the possibility of cell switching failure (for example, cell switching that is too late) increases.

[0095] Therefore, in this embodiment, the UE 100 transmits to the network 5 an RRC message including time-series data consisting of a plurality of L1 measurement values ​​for each cell (serving cell and / or neighboring cell). Each L1 measurement value is a radio quality measurement value to which L3 filtering (L3 filter 13) has not been applied. Each L1 measurement value is a beam measurement value A output by the L1 filter 11. １ Each L1 measurement value may be a cell quality B output by the beam combining / selecting unit 12. Alternatively, each L1 measurement value may be an output C of the L3 filter 13 with a filter coefficient k set to zero.

[0096] FIG. 9 is a diagram showing the operation of the UE 100 according to this embodiment.

[0097] In step S101, the UE 100 derives a plurality of measurement values ​​corresponding to one cell by repeatedly performing radio quality measurement for one cell in Layer 1 (L1). In this embodiment, each of the plurality of measurement values ​​is an L1 measurement value to which the L3 filter 13 has not been applied. The radio quality measurement may be a measurement of the received power of a synchronization signal (SS-RSRP: SS Reference Signal Received Power) or a measurement of the received power of a channel state information reference signal (CSI-RSRP: CSI Reference Signal Received Power). The L1 measurement value (L1 measurement result) is not limited to such L1-RSRP, and may be other L1 measurement results (for example, CSI such as RSRQ (Reference Signal Received Quality), SINR (Signal-to-Interference-plus-Noise Ratio), CQI (Channel Quality Indicator), etc.).

[0098] In step S102, the UE 100 generates an RRC message including a plurality of L1 measurement values ​​corresponding to one cell obtained in step S101. The RRC message may include an L1 measurement list in which a plurality of L1 measurement values ​​are configured in a list format. The RRC message may include location information indicating the geographical location of the UE 100 and a plurality of L1 measurement values ​​(L1 measurement list) associated with the location information. The RRC message may include a set of a cell ID and an L1 measurement list for each of a plurality of cells (e.g., a serving cell and neighboring cells including an LTM candidate cell). Note that each entry (L1 measurement value) in the L1 measurement value list may use the L1 measurement value as is, or may be an index value obtained by quantizing the L1 measurement value. Each entry (L1 measurement value) in the L1 measurement value list may be a difference value (offset value) based on one L1 measurement value.

[0099] In step S103, the UE 100 transmits the RRC message obtained in step S102 to the network 5 (gNB 200). The network 5 (gNB 200) receives the RRC message. The RRC message may be a Measurement Report message or a UE Information Response message. The Measurement Report message may be a Measurement Report message used in Immediate MDT. The UE Information Response message may be a logged MDT, HOF report, or a UE Information Response message used to transmit SHR log information.

[0100] According to such an operation, the network 5 can grasp the situation of instantaneous fluctuations in the radio environment (radio quality), and it becomes possible to perform network optimization related to LTM. Note that the UE 100 that performs such an operation has a control unit 130 that derives multiple measurement values ​​corresponding to one cell by repeatedly performing radio quality measurements for one cell in L1, and generates an RRC message including the multiple measurement values ​​corresponding to one cell, and a transmission unit 120 that transmits the RRC message to the network 5. On the other hand, the gNB 200 has a receiving unit 220 that receives the RRC message.

[0101] (5.1) Specific Examples of Operations According to the Embodiment A first operation pattern and a second operation pattern will be described as specific examples of operations according to the embodiment.

[0102] (5.1.1) First Operation Pattern The first operation pattern is an operation pattern that mainly assumes immediate MDT and logged MDT (also simply referred to as "MDT").

[0103] In conventional MDT, the measurement results reported by the UE 100 to the network 5 are L3 measurements after L3 filtering.

[0104] Furthermore, in conventional Immediate MDT, the UE 100 transmits an L3 Measurement Report message including location information and one measurement value per measurement cell to the network 5. The time interval (periodicity) of the L3 measurement report is set by the network 5 to the UE 100, and is 120 ms or more in the 3GPP technical specifications.

[0105] Furthermore, in conventional logged MDT, the UE 100 records (also referred to as "logging") location information, a timestamp, and one measurement value per measurement cell as log information, and transmits a UE Information Response message including the log information to the network 5. The logging time interval (logging interval) is set in the UE 100 by the network 5, and is 320 ms or more in the 3GPP technical specifications.

[0106] Here, when considering applying MDT to LTM (especially optimization of cell switching commands based on L1 measurement reports) and / or future model learning on the network 5 side (e.g., AI (Artificial Intelligence) / ML (Machine Learning) for mobility), the low resolution of the radio quality measurement data, i.e., the long period on the time axis and averaging by L3 filtering, become problems.

[0107] The UE 100 derives L1 measurement values ​​by measuring radio quality in L1 at time intervals shorter than the time interval (periodicity) of L3 measurement reports and the time interval (logging interval) of logging. Therefore, in the first operation pattern, the UE 100 reports the L1 measurement values ​​derived at such short time intervals (specifically, L1 measurement values ​​to which L3 filtering has not been applied) to the network 5.

[0108] However, if location information (and a timestamp in the case of logged MDT) is assigned to each of these L1 measurement values, there is a problem in that the amount of data that UE 100 needs to report in an RRC message to network 5 increases (i.e., overhead increases). Therefore, in the first operation pattern, UE 100 transmits to network 5 an RRC message including location information (and a timestamp in the case of logged MDT) and an L1 measurement value list associated with the location information. This makes it possible to associate multiple L1 measurement values ​​with one piece of location information (and one timestamp), thereby reducing overhead.

[0109] As described above, in operation pattern 1, in MDT, UE 100 reports the L1 measurement values ​​in the form of a list to network 5. Specifically, UE 100 reports an L1 measurement value list for one cell to network 5 in association with one piece of location information (and one timestamp).

[0110] In the first operation pattern, the network 5 (gNB200) transmits to the UE100 configuration information for configuring the UE100 with at least one of MDT measurement, reporting, and logging. The UE100 receives the configuration information from the network 5. The configuration information includes information for configuring a measurement interval, which is a time interval at which the UE100 performs radio quality measurements (at least one of MDT measurement, reporting, and logging). The information for configuring the measurement interval includes information indicating a reference measurement interval and information indicating how many times radio quality measurements should be performed within the reference measurement interval. For example, the network 5 configures the UE100 with how many L1 measurements to report / log within the conventional measurement / reporting / logging interval.

[0111] Fig. 10 is a diagram illustrating an example of a first operation pattern according to an embodiment. Here, explanation will be given using a logged MDT as an example. Fig. 11 is a diagram illustrating a Logged Measurement Configuration message according to the first operation pattern. Fig. 12 is a diagram illustrating a UE Information Response message according to the first operation pattern.

[0112] As shown in Figure 10, in step S201, UE100 is in an RRC connected state in a cell of network 5 (gNB200).

[0113] In step S202, the network 5 (gNB 200) transmits a Logged Measurement Configuration message, which is an RRC message including configuration information for configuring logged MDT measurement and logging, to the UE 100. The UE 100 receives the Logged Measurement Configuration message.

[0114] 11 , the Logged Measurement Configuration message includes a setting for the logging period (LoggingInterval). In the first operation pattern, the Logged Measurement Configuration message further includes information indicating the number of divisions of the logging period (IntervalDivision). This information may be the number of entries in the L1 measurement result list. Note that instead of (or in addition to) the number of divisions of the logging period, the information may be the acquisition period of the L1 measurement results (i.e., the storage period for entries in the L1 measurement result list).

[0115] As shown in FIG. 10, in step S203, the UE 100 transitions from the RRC connected state to the RRC idle state or the RRC inactive state.

[0116] In step S204, the UE 100 starts a periodic logging process of the L1 measurement result in accordance with the contents set in the Logged Measurement Configuration message. When an event is set in the Logged Measurement Configuration message, the UE 100 may start the periodic logging process when the event is satisfied as a trigger.

[0117] The UE 100 may perform L1 measurement at a period determined by "measurement period (Logging Interval) ÷ ​​division number information (Interval Division)" and log the L1 measurement values. As shown in FIG. 12, the UE 100 stores one L1 measurement report result (resultsSSB-Cell) in each entry of a list (resultsSSB-Cell-L1MeasList) that stores L1 measurement results. One piece of location information (locationInfo) and one timestamp (relativeTimeStamp) are associated with the list.

[0118] Thereafter, as shown in FIG. 10, in step S205, the UE 100 transmits a notification (Availability Indicator) indicating that the log information is held to the network 5 (gNB 200). The network 5 (gNB 200) receives the notification (Availability Indicator). For example, when the UE 100 transitions from the RRC idle state to the RRC connected state, the UE 100 may include the notification (Availability Indicator) in an RRC Setup Complete message and transmit it to the network 5 (gNB 200). When the UE 100 transitions from the RRC inactive state to the RRC connected state, the UE 100 may include the notification (Availability Indicator) in an RRC Resume Complete message and transmit it to the network 5 (gNB 200). The UE 100 in the RRC connected state may transmit the notification (Availability Indicator) to the network 5 (gNB 200) when RRC is re-established or when handover is successful.

[0119] In step S206, the UE 100 transitions to an RRC connected state.

[0120] In step S207, the network 5 (gNB 200) transmits a message (UE Information Request message) requesting the transmission of log information to the UE 100. The UE 100 receives the message (UE Information Request message).

[0121] In step S208, UE100 transmits a message (UE Information Response message or another RRC message) including log information to network 5 (gNB200). Network 5 (gNB200) receives the message. Network 5 (gNB200) acquires the log information in the message and may transmit the acquired log information to CN20 or OAM (Operations, Administration, Maintenance). Network 5 may optimize various network parameters related to LTM based on the log information.

[0122] In the illustrated operation example, the logged MDT has been described as an example, but such an operation may be applied to the immediate MDT. In this case, the UE 100 performs measurement and reporting while maintaining the RRC connected state. In addition, the above-mentioned setting information is replaced with measurement setting, the logging interval is replaced with a reporting interval (periodicity, report interval), and the UE Information Response message is replaced with a Measurement Report message.

[0123] (5.1.2) Second Operation Pattern The second operation pattern will be described, focusing mainly on differences from the first operation pattern. The second operation pattern is an operation pattern that mainly assumes HOF reporting and SHR. In the first operation pattern, the UE 100 periodically performs measurement reporting or logging. In the second operation pattern, the UE 100 performs logging only once when a predetermined event (e.g., cell switching failure or cell switching success) occurs.

[0124] In conventional HOF reporting and SHR, the UE 100 reports a snapshot of the L3 measurement results at the time of event occurrence to the network 5. For example, the UE 100 reports only one L3 measurement result for each of the serving cell and the neighboring cell at the time of HOF occurrence to the network 5.

[0125] On the other hand, in LTM, the gNB 200 determines the LTM cell switching based on the L1 measurement report. The UE 100 performs L1 measurements at short intervals, and the L1 measurement values ​​vary greatly from measurement to measurement. Therefore, in order to perform network optimization related to LTM, time series data of L1 measurements over a certain period when an event occurs can be useful.

[0126] Therefore, in the second operation pattern, the UE 100 records time-series data of the L1 measurement values ​​for a certain period before and after the occurrence of an event as log information. Specifically, the UE 100 detects an event related to a serving cell switch, records a plurality of L1 measurement values ​​(L1 measurement value list) for a certain period before and / or after the occurrence of the event as log information, generates an RRC message (UE Information Response message) including the log information, and transmits the RRC message to the network 5 (gNB 200). The event may be any of a failure of cell switch, a success of cell switch, or a satisfaction of a trigger condition for cell switch.

[0127] Fig. 13 is a diagram illustrating an example of a second operation pattern according to an embodiment. Fig. 14 is a diagram illustrating a HOF report according to the second operation pattern. Fig. 15 is a diagram illustrating an SHR according to the second operation pattern. While LTM cell switching is primarily assumed here, L3 handover may also be assumed.

[0128] As shown in Figure 13, in step S301, UE100 is in an RRC connected state in a cell of network 5 (gNB200).

[0129] In step S302, the network 5 (gNB 200) may transmit an RRC message (RRC Reconfiguration message) including configuration information for configuring the HOF report and / or SHR to the UE 100. The UE 100 may receive the RRC message.

[0130] The configuration information may include a logging event configuration and / or a logging period configuration.

[0131] The logging event setting is information specifying an event to be logged. The specified event may be at least one of a successful cell switch and a failed cell switch. The specified event may be a cell switch trigger condition being satisfied. When the setting is implemented, the UE 100 may start provisionally storing the L1 measurement results. Alternatively, the UE 100 may start provisionally storing the L1 measurement results when a measurement start trigger included in the setting is detected. The measurement start trigger may be Early TA (i.e., when CFRA is executed and / or when UE-based TA measurement is executed), a radio quality threshold (e.g., when the RSRP of the serving cell falls below a threshold and / or when the RSRP of the LTM candidate cell and / or neighbor cell exceeds a threshold, or may be an existing Event A3 trigger condition, etc.). When the UE 100 provisionally stores the L1 measurement results, the UE 100 sequentially stores the L1 measurement results in internal variables (list entries). The UE 100 may sequentially delete the L1 measurement results that exceed the logging period (a certain period in the past) from the internal variables (list entries). Also, when the occurrence of a logging event is detected in S304 described later, the UE 100 may extract the past L1 measurement results from the internal variables, store them in the L1 measurement value list, and report them to the network.

[0132] The setting of the logging period may include information indicating a certain period in the past and / or information indicating a certain period in the future, based on the time when the logging event is satisfied.

[0133] In step S303, the UE 100 triggers (attempts) cell switching. The UE 100 may trigger cell switching in response to receiving a cell switching command from the network 5 (gNB 200). In the case of C-LTM (or conditional L3 handover (CHO)), the UE 100 may trigger cell switching in response to the trigger condition set by the network 5 (gNB 200) being satisfied.

[0134] In step S304, the UE 100 detects the occurrence of a logging event. The logging event is set by the network 5 (gNB 200) and may be at least one of a successful cell switch and a failed cell switch. The logging event may be that a trigger condition for cell switch is satisfied.

[0135] In step S305, the UE 100 generates and records log information in response to the occurrence of a logging event. The log information includes a plurality of L1 measurement results (L1 measurement value list) for a certain period before and after the logging event.

[0136] The log information may further include information indicating an event type. The information indicating the event type may be information indicating success or failure of LTM cell switching (the state at the time of completion of the LTM procedure). The information may be procedure-specific information such as L3 handover or LTM. The information may be function-specific information such as a C-LTM execution trigger or a CHO execution trigger. The information may be event details (trigger type such as an A3 trigger).

[0137] In the case of C-LTM, the log information may further include information indicating the time between when C-LTM is set by gNB200 and when the set event occurs.

[0138] As shown in FIG. 14, in the case of cell switching failure, the UE 100 may include an L1 measurement value list as the measurement result of the serving cell (measResultLastServCell) in the log information. The UE 100 may include an L1 measurement value list in each entry of the list of measurement results of neighboring cells (measResultListNR). In addition, in the case of LTM cell switching failure, the UE 100 may set "hof" as the connection failure type (connectionFailureType) in the log information. The UE 100 may set "LTM" (or "C-LTM") as the type of failed handover (lastHO-Type). The UE 100 may set information specific to the LTM cell switching as the cause (rlf-Cause) of the radio link failure (RLF) due to the LTM cell switching in the log information (see a third modified example described later).

[0139] As shown in FIG. 15, in the case of successful cell switching, the UE 100 may include an L1 measurement list as the measurement result (sourceCellMeas) of the source cell in the log information. The UE 100 may include an L1 measurement list as the measurement result (targetCellMeas) of the target cell. Also, the L1 measurement list may be included as the measurement result of a candidate cell (LTM candidate cell, C-LTM candidate cell, CHO candidate cell, CPAC candidate cell, etc.). When there are multiple candidate cells, an L1 measurement list may be included for each candidate cell. Among the candidate cells, an L1 measurement list of a cell that did not become a target cell (a cell corresponding to a candidate cell configuration held other than the target cell configuration applied by the UE 100) may be included. Note that in the case of successful cell switching, the UE 100 may set "LTM" (or "C-LTM") as the type of successful handover in the log information.

[0140] Thereafter, as shown in FIG. 13, in step S306, the UE 100 may transition to an RRC idle state if the cell switching fails.

[0141] In step S307, the UE 100 transmits a notification (Availability Indicator) indicating that the log information is held to the network 5 (gNB 200). The network 5 (gNB 200) receives the notification (Availability Indicator). For example, the UE 100 may transmit the notification (Availability Indicator) to the network 5 (gNB 200) by including it in an RRC Setup Complete message when transitioning from the RRC idle state to the RRC connected state. When the UE 100 transitions from the RRC inactive state to the RRC connected state, the UE 100 may include the notification (Availability Indicator) in an RRC Resume Complete message and transmit it to the network 5 (gNB 200). The UE 100 in the RRC connected state may transmit the notification (Availability Indicator) to the network 5 (gNB 200) when RRC is re-established or when handover is successful.

[0142] In step S308, UE 100 may transition to an RRC connected state.

[0143] In step S309, the network 5 (gNB200) transmits a message (UE Information Request message) requesting the transmission of log information to the UE 100. The UE 100 receives the message (UE Information Request message).

[0144] In step S310, UE100 transmits a message (UE Information Response message or another RRC message) including log information to network 5 (gNB200). Network 5 (gNB200) receives the message. Network 5 (gNB200) may acquire the log information in the message and transmit the acquired log information to CN20 or OAM. Network 5 may optimize various network parameters related to LTM based on the log information.

[0145] (6) Modifications Modifications of the embodiments will be described, focusing on differences from the above-described embodiments. The following modifications may or may not be based on the operation of including the L1 measurement value list in an RRC message (Measurement Report message or UE Information Response message) as in the above-described embodiment.

[0146] In the above-described second operation pattern, an example has been described in which, assuming a HOF report and an SHR, when a predetermined event for logging (for example, a handover failure or a handover success) occurs, the UE 100 includes in the log information a plurality of L1 measurement results (an L1 measurement value list) for a certain period before and after the event. In contrast, in the modified example, when the event occurs, the UE 100 includes in the log information information related to LTM cell switching, which is information different from the L1 measurement value list.

[0147] FIG. 16 is a diagram showing the operation of UE 100 according to the modified example.

[0148] In step S401, the UE 100 records log information including information about the LTM cell switching in response to detecting an event (logging event) related to the LTM cell switching. The logging event is set by the network 5 (gNB 200) and may be at least one of a successful cell switching and a failed cell switching. The logging event may be that a trigger condition for the cell switching is satisfied. The log information may include information about the source cell (such as a cell ID and a measurement result) and / or information about the target cell (such as a cell ID and a measurement result).

[0149] In the first modified example, the log information includes information indicating that the subsequent cell switch is a cell switch that switches the serving cell without RRC reconfiguration from the network 5, after the cell switch based on the RRC configuration from the network 5. The subsequent cell switch may be a subsequent LTM cell switch (Sequent LTM).

[0150] In a second modified example, the log information includes information regarding the optimal cell switching timing estimated by UE100, and / or information indicating the time from when UE100 detects a reporting event of a measurement report for LTM cell switching to when the measurement report is transmitted to network 5.

[0151] In a third modified example, the log information includes at least one of information indicating whether UE-based TA measurement, in which UE 100 itself derives a TA value to be applied to a target cell for LTM cell switching, was successful, information regarding the TA value applied to the target cell, and information indicating whether the random access procedure performed for the target cell was contention-free random access (CFRA) or contention-based random access (CBRA).

[0152] In step S402, the UE 100 transmits an RRC message including log information to the network 5 (gNB 200). The RRC message may be a UE Information Response message.

[0153] (6.1) First Modification In conventional conditional L3 handover (CHO) and conditional PSCell addition / modification (CPAC), RRC settings including trigger conditions etc. are configured for UE 100 from network 5 (gNB 200), but UE 100 erases the settings when it successfully accesses the target cell. Therefore, in order to perform the next CHO / CPAC etc., it is necessary to perform RRC reconfiguration (RRC Reconfiguration) from network 5 (gNB 200) to UE 100.

[0154] On the other hand, conventionally, in LTM (and CPAC), a method has been specified in which the RRC setting including the trigger condition and the like is maintained even after the UE 100 accesses the target cell, and the RRC setting can be used to switch to another cell. (In the case of LTM, this is also referred to as "Subsequent LTM"). This eliminates the need to perform RRC reconfiguration to perform the next LTM (and CPAC), reduces signaling, and speeds up LTM cell switching (and CPAC).

[0155] Here, if the subsequent LTM cell switching fails, it is possible that the cell switching failed because the retained RRC configuration was inappropriate (for example, too old). In such a case, it was necessary for the network 5 (gNB 200) to perform RRC reconfiguration on the UE 100. However, in conventional SON technology, the network 5 cannot determine whether the cell switching failure / success is the failure / success of the first cell switching or the failure / success of the subsequent LTM cell switching. Therefore, there is a problem that it is difficult to perform network optimization for the subsequent LTM.

[0156] Therefore, in the first modification, when a logging event (cell switching failure / success) occurs in the subsequent cell switching, the UE 100 includes information indicating the subsequent cell switching in the log information.

[0157] A specific example of the operation according to the first modification will be described with reference to Fig. 13. Here, the case of subsequent LTM will be described as an example, but similar operations may be applied to subsequent PSCell change (Subsequent CPC) or subsequent PSCell addition (Subsequent CPA).

[0158] In step S301, UE100 is in an RRC connected state in a cell of network 5 (gNB200).

[0159] In step S302, the network 5 (gNB 200) may transmit to the UE 100 an RRC message (RRC Reconfiguration message) including configuration information for configuring the HOF report and / or SHR. The UE 100 may receive the RRC message. The configuration information may include a logging event configuration. The logging event configuration is information that specifies an event to be logged. The specified event may be at least one of a cell switch success and a cell switch failure. The specified event may be that a trigger condition for cell switch is satisfied. The configuration information may include information that configures logging for a subsequent LTM.

[0160] In step S303, UE 100 triggers (attempts) a subsequent LTM cell switch. The subsequent LTM cell switch is an operation of performing an LTM cell switch without RRC reconfiguration from the network 5 after an LTM cell switch based on the RRC configuration from the network 5 (the LTM candidate cell configuration in step S4 of FIG. 8 ). That is, UE 100 performs (attempts) a subsequent LTM cell switch by reusing the RRC configuration (LTM candidate cell configuration) from the network 5. For example, UE 100 holds the LTM candidate cell configuration, and performs (attempts) an LTM cell switch based on the LTM candidate cell configuration in response to receiving a cell switch command from the serving cell.

[0161] In step S304, the UE 100 detects the occurrence of a logging event. The logging event may be at least one of a success of a subsequent LTM cell switch and a failure of a subsequent LTM cell switch.

[0162] In step S305, the UE 100 generates log information in response to the occurrence of a logging event and records the log information. In this modified example, the log information includes information indicating a subsequent LTM cell switch. The information may be 1-bit information (true / false) indicating a failure / success of the subsequent LTM cell switch. The information may be information indicating the number of times the subsequent LTM cell switch has failed / succeeded (for example, "second time"). For example, in the case of a failure of the subsequent LTM cell switch, the UE 100 may set "hof" as the connection failure type (connectionFailureType) in the log information. The UE 100 may set "subsequent LTM" as the type of the failed handover (lastHO-Type). In the case of a success of the subsequent LTM cell switch, the UE 100 may set "subsequent LTM" as the type of the successful handover in the log information.

[0163] The subsequent operation is the same as that of the second operation pattern described above.

[0164] (6.2) Second Modification In the LTM, the network 5 issues a cell switching instruction to the UE 100 by a cell switching command based on the L1 measurement report (see steps S7 to S9 in FIG. 8 ). Since the LTM aims to respond to instantaneous fluctuations in the radio environment, there is a risk that a cell switching failure (particularly, a cell switching that is too late) will occur because the transmission timing of the cell switching command from the network 5 is not able to keep up with the fluctuations in the radio environment.

[0165] Furthermore, an event-triggered L1 measurement report may be set in the UE 100 from the network 5. For example, a trigger condition (reporting event) for the L1 measurement report is set in the UE 100 from the network 5, and the UE 100 transmits the L1 measurement report to the network 5 in response to the set trigger condition being satisfied (the set reporting event occurring). Here, if there is a large delay in the UE 100 from the occurrence of a reporting event to the transmission of the L1 measurement report to the network 5, there is a risk that a cell switching failure (particularly, a cell switching that is too late) may occur.

[0166] However, with conventional SON technology, the network 5 cannot grasp such a situation, which makes it difficult to perform network optimization related to LTM.

[0167] Therefore, in the second modified example, UE100 includes in the log information information regarding the optimal cell switching timing estimated by UE100, and / or information indicating the time (i.e., delay time) from when UE100 detects a reporting event of an L1 measurement report to when the L1 measurement report is transmitted to network 5.

[0168] A specific example of the operation according to the second modification will be described with reference to FIG. 13, focusing mainly on the differences from the operation according to the first modification.

[0169] In step S301, UE100 is in an RRC connected state in a cell of network 5 (gNB200).

[0170] In step S302, the network 5 (gNB 200) may transmit to the UE 100 an RRC message (RRC Reconfiguration message) including configuration information for configuring the HOF report and / or SHR. The UE 100 may receive the RRC message. The configuration information may include a logging event configuration. The logging event configuration is information that specifies an event to be logged. The specified event may be at least one of a successful cell switch and a failed cell switch. The specified event may be that a trigger condition for cell switch is satisfied.

[0171] The RRC message may include information for configuring logging of the optimal cell switch timing and / or the delay time of the L1 measurement report. The configuration information may include information for configuring model inference using an AI / ML model for deriving the optimal cell switch timing, for example, a model ID or a function ID of the AI / ML model. The AI / ML model may be an AI / ML model that derives the optimal cell switch timing based on an L1 measurement result. The UE 100 may estimate the optimal cell switch timing using the AI / ML model.

[0172] The RRC message may include information for setting a trigger condition (event) for transmitting an L1 measurement report to the network 5 (gNB 200). The UE 100 may trigger an LTM cell switch by transmitting an L1 measurement report to the network 5 (gNB 200) in response to the occurrence of the event, and receiving a cell switch command from the network 5 (gNB 200).

[0173] In step S303, the UE 100 triggers (attempts) an LTM cell switch.

[0174] In step S304, the UE 100 detects the occurrence of a logging event. The logging event may be at least one of a success of the LTM cell switch and a failure of the LTM cell switch.

[0175] In step S305, the UE 100 generates log information in response to the occurrence of the logging event, and records the log information.

[0176] In this modification, the log information may include information indicating an optimal cell switching timing estimated by the UE 100. The information indicating the optimal cell switching timing may be an absolute time of the optimal cell switching timing. The information may be a relative time (an offset time based on the time point at which the cell switching command is actually received). The time information may be expressed by a radio frame (SFN), a slot, or a symbol. The log information may include a radio environment, for example, a radio quality measurement value (such as RSRP) for the serving cell and / or a neighboring cell.

[0177] In this modification, the log information may include a measurement value of the delay time from the timing of the event trigger (start timing) of the L1 measurement report to the completion of transmission of the L1 measurement report (end timing).

[0178] The subsequent operation is the same as that of the second operation pattern described above.

[0179] In this modification, the LTM cell switching has been described, but the operation according to this modification may be applied to L3 handover. In this case, an L3 measurement report may be used instead of an L1 measurement report. In addition, the end timing of measuring the delay time may be the timing when the UE 100 receives a delivery confirmation (ACK) for the L3 measurement report from the network 5 (gNB 200).

[0180] (6.3) Third Modification The third modification is an embodiment related to UE-based TA measurement in LTM. In the UE-based TA measurement, the UE 100 itself derives a TA value to be applied to a target cell of LTM cell switching.

[0181] In conventional LTM, UE100 can initiate an uplink TA acquisition (referred to as "early TA") procedure for one or more candidate cells (second cells) different from the current serving cell (first cell), depending on the configuration by gNB200. If the candidate cell has the same TA value as the current serving cell or the TA value = 0, the early TA acquisition procedure is not necessary. gNB200 can request UE100 to perform early TA acquisition of the candidate cell before cell switching. The early TA acquisition procedure is realized by CFRA triggered by a PDCCH order as described above, or by UE-based TA measurements configured by RRC.

[0182] In the case of CFRA triggered by a PDCCH order, the gNB 200 to which the candidate cell belongs calculates the TA value and transmits it to the gNB 200 to which the serving cell belongs. When the serving cell triggers an LTM cell switch, it transmits the TA value in a cell switch command (MAC CE).

[0183] In the case of UE-based TA measurement, the UE 100 performs TA measurement of the candidate cell after being configured by the RRC, but the exact time at which the UE 100 performs the TA measurement depends on the implementation of the UE 100. When the UE 100 receives a cell switch command, it applies the TA value it has measured and performs RACH-less LTM.

[0184] Depending on whether a valid TA value is available, the UE 100 performs either a RACH-less LTM cell switch or a RACH-based LTM cell switch. If a TA value is specified in the cell switch command, the UE 100 applies the TA value according to the specification. If UE-based TA measurement is configured but a TA value is not specified in the cell switch command, the UE 100 applies its own measured TA value, if available. If a valid TA value is not available, the UE 100 performs a RACH-based LTM cell switch.

[0185] In this way, in the conventional LTM, the UE-based TA measurement can be configured in the UE 100. However, in the conventional SON technology, the network 5 cannot know whether the UE-based TA measurement has been successful, and therefore it is difficult to perform network optimization related to the LTM (for example, optimizing whether or not the UE-based TA measurement is configured and its content).

[0186] Furthermore, in the conventional SON technology, in the case of UE-based TA measurement, the network 5 cannot grasp what TA value the UE 100 has applied to the target cell, making it difficult to perform network optimization related to LTM.

[0187] Furthermore, in the conventional LTM, the UE 100 may perform a RACH-based LTM cell switch. In this case, the UE 100 performs either a CFRA or a CBRA type of random access procedure to the target cell. However, in the conventional SON technology, it is difficult to know whether the UE 100 performed either a CFRA or a CBRA type of random access procedure to the target cell, especially when the random access procedure fails, making it difficult to perform network optimization for the LTM.

[0188] Therefore, in the third modified example, UE100 includes in the log information at least one of information indicating whether the UE-based TA measurement was successful, information regarding the TA value applied to the target cell, and information indicating whether the random access procedure performed for the target cell was CFRA or CBRA.

[0189] A specific example of the operation according to the third modified example will be described with reference to FIG. 13, focusing on the differences from the operations according to the first and second modified examples.

[0190] In step S301, UE100 is in an RRC connected state in a cell of network 5 (gNB200).

[0191] In step S302, the network 5 (gNB 200) may transmit to the UE 100 an RRC message (RRC Reconfiguration message) including configuration information for configuring an HOF report and / or SHR. The RRC message may include information for configuring UE-based TA measurement. The UE 100 may receive the RRC message. The configuration information may include a logging event configuration. The logging event configuration is information specifying an event to be logged. The specified event may be at least one of a cell switch success and a cell switch failure. The specified event may be that a trigger condition for cell switch has been satisfied. The configuration information may include information for configuring recording of at least one of information indicating whether the UE-based TA measurement was successful, information about the TA value applied to the target cell, and information indicating whether the random access procedure performed for the target cell was CFRA or CBRA.

[0192] In step S303, the UE 100 performs UE-based TA measurements and triggers (attempts) an LTM cell switch by receiving a cell switch command from the network 5. The LTM cell switch is either a RACH-less LTM cell switch or a RACH-based LTM cell switch.

[0193] In step S304, the UE 100 detects the occurrence of a logging event. The logging event may be at least one of a success of the LTM cell switch and a failure of the LTM cell switch.

[0194] In step S305, the UE 100 generates log information in response to the occurrence of a logging event and records the log information. In this modification, the log information may include information indicating whether the UE-based TA measurement was successful or not. The log information may include information on the TA value applied when accessing the target cell. The information may be the TA value itself. The information may be information on the source of the TA value (any of RRC configuration, cell switch command (MAC CE), and UE-based TA measurement). The log information may include information indicating whether CFRA or CBRA was performed in the RACH-based LTM cell switch.

[0195] The subsequent operation is the same as that of the second operation pattern described above.

[0196] (7) Other Embodiments In the above-described embodiments, the LTM (and conditional LTM) has been mainly described. However, the operations according to the above-described embodiments may be applied to L3 handover (and conditional L3 handover). Furthermore, an L3 measurement list consisting of a plurality of L3 measurement values ​​may be used instead of an L1 measurement list consisting of a plurality of L1 measurement values. Furthermore, assuming dual connectivity (DC), the operations may be applied to addition or modification of a primary / secondary cell (PSCell), or to conditional PSCell addition or conditional PSCell modification.

[0197] 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.

[0198] 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.

[0199] 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.

[0200] 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).

[0201] The functions performed by 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 (a 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 also be a programmed processor that executes a program stored in memory. In this specification, circuitry, unit, or means refers to hardware that is programmed to perform the described functions or that executes the described functions. The hardware may be any hardware disclosed herein or any hardware known to be programmed or capable of performing the described functions. If the hardware is a processor, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0202] 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 including additional items in addition to the listed items. Additionally, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure 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 shall include the plural unless the context clearly indicates otherwise.

[0203] 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.

[0204] This application claims priority from Japanese Patent Application No. 2024-020672 (filed February 14, 2024), the entire contents of which are incorporated herein by reference.

[0205] (8) Supplementary Notes The following are additional notes regarding the features of the above-described embodiment.

[0206] Supplementary Note 1: A communication method executed by a user equipment in a mobile communication system, comprising: deriving a plurality of measurement values ​​corresponding to a cell by repeatedly performing radio quality measurements for the cell in Layer 1 (L1); generating a Radio Resource Control (RRC) message including the plurality of measurement values ​​corresponding to the cell; and transmitting the RRC message to a network.

[0207] Supplementary Note 2: The communication method according to Supplementary Note 1, wherein each of the plurality of measurements is a Layer 3 (L3) measurement that has not been filtered.

[0208] Supplementary Note 3: The communication method according to Supplementary Note 2, wherein the RRC message includes an L1 measurement value list in which the plurality of measurement values ​​are configured in a list format.

[0209] Supplementary Note 4: The communication method according to any one of Supplementary Notes 1 to 3, wherein the RRC message includes location information indicating a geographical location of the user equipment and the plurality of measurement values ​​associated with the location information.

[0210] Supplementary Note 5: The communication method according to any one of Supplementary Notes 1 to 4, wherein the radio quality measurement is measurement of received power of a synchronization signal or measurement of received power of a channel state information reference signal.

[0211] Supplementary Note 6: The communication method according to any one of Supplementary Notes 1 to 5, wherein the RRC message is a Measurement Report message or a UE Information Response message.

[0212] Supplementary Note 7: The communication method according to any one of Supplementary Notes 1 to 6, wherein the user equipment receives configuration information related to the wireless quality measurement from the network, and the configuration information includes information for setting a measurement interval, which is a time interval at which the user equipment performs the wireless quality measurement.

[0213] Supplementary Note 8: The communication method according to Supplementary Note 7, wherein the information for setting the measurement interval includes information indicating a reference measurement interval and information indicating how many times the wireless quality measurement should be performed within the reference measurement interval.

[0214] Supplementary Note 9: The communication method according to any one of Supplementary Notes 1 to 8, wherein the user equipment detects an event related to a switch of a serving cell of the user equipment, and generates the RRC message including the plurality of measurement values ​​for a certain period before and / or after the occurrence of the event.

[0215] Supplementary Note 10: The communication method according to Supplementary Note 9, wherein the event is one of a failure of the switching, a success of the switching, and a satisfaction of a trigger condition for the switching.

[0216] Supplementary Note 11: A user equipment for use in a mobile communication system, comprising: a controller configured to repeatedly perform radio quality measurements for one cell in Layer 1 (L1) to derive a plurality of measurement values ​​corresponding to the one cell, and to generate a Radio Resource Control (RRC) message including the plurality of measurement values ​​corresponding to the one cell; and a transmitter configured to transmit the RRC message to a network.

[0217] Supplementary Note 12: A network node for use in a mobile communication system, comprising: a receiver configured to receive, from a user equipment, a Radio Resource Control (RRC) message including a plurality of measurements obtained by the user equipment repeatedly performing radio quality measurements for one cell at Layer 1 (L1).

[0218] 1: Mobile communication system 5: Network 10: RAN 20: CN 11: L1 filter 12: Beam combining / selection unit 13: L3 filter 14: Evaluation unit 15: L3 beam filter 16: Beam selection unit 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, comprising: repeatedly performing radio quality measurements for a cell in Layer 1 (L1) to derive a plurality of measurement values ​​corresponding to the cell; generating a Radio Resource Control (RRC) message including the plurality of measurement values ​​corresponding to the cell; and transmitting the RRC message to a network.

2. The communication method according to claim 1, wherein each of the plurality of measurements is a Layer 3 (L3) measurement without an L1 filter applied.

3. The communication method according to claim 2, wherein the RRC message includes an L1 measurement value list in which the plurality of measurement values ​​are configured in a list format.

4. The communication method according to claim 1, wherein the RRC message includes location information indicating a geographical location of the user equipment and the plurality of measurement values ​​associated with the location information.

5. A communication method according to any one of claims 1 to 4, wherein the radio quality measurement is measurement of the received power of a synchronization signal or measurement of the received power of a channel state information reference signal.

6. The communication method according to any one of claims 1 to 4, wherein the RRC message is a Measurement Report message or a UE Information Response message.

7. A communication method according to any one of claims 1 to 4, wherein the user device receives configuration information relating to the wireless quality measurement from the network, and the configuration information includes information for setting a measurement interval, which is a time interval at which the user device performs the wireless quality measurement.

8. The communication method according to claim 7, wherein the information for setting the measurement interval includes information indicating a reference measurement interval and information indicating how many times the wireless quality measurement should be performed within the reference measurement interval.

9. The communication method according to claim 1, wherein the user equipment detects an event relating to a switch of the serving cell of the user equipment, and generates the RRC message including the plurality of measurement values ​​for a certain period before and / or after the occurrence of the event.

10. The communication method according to claim 9, wherein the event is one of the following: the switchover has failed, the switchover has succeeded, or a trigger condition for the switchover has been satisfied.

11. A user equipment for use in a mobile communication system, comprising: a control unit that derives a plurality of measurement values ​​corresponding to a single cell by repeatedly measuring radio quality for the single cell in Layer 1 (L1), and generates a radio resource control (RRC) message including the plurality of measurement values ​​corresponding to the single cell; and a transmission unit that transmits the RRC message to a network.

12. A network node used in a mobile communication system, comprising: a receiver that receives, from a user equipment, a radio resource control (RRC) message including a plurality of measurement values ​​obtained by the user equipment repeatedly performing radio quality measurements for one cell in Layer 1 (L1).