Communication method, user equipment, and network node

Abstract

This communication method to be executed by user equipment in a mobile communication system supporting L1 / L2 Triggered Mobility (LTM) comprises: performing an L1 measurement that is a radio quality measurement in a layer 1 (L1); transmitting, in response to satisfaction of a first radio quality condition for triggering a report of an L1 measurement result, an L1 measurement report including the L1 measurement result at least once to a network node in the L1 or a layer 2 (L2); and transmitting, in response to satisfaction of a second radio quality condition for stopping the report, notification information indicating that the second radio quality condition is satisfied to the network node in the L1 or the L2.

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 method executed by a user equipment in a mobile communication system supporting L1 / L2 Triggered Mobility (LTM). The communication method includes: performing a radio quality measurement in Layer 1 (L1) that is an L1 measurement; transmitting an L1 measurement report including the L1 measurement result to a network node at least once in the L1 or Layer 2 (L2) in response to a first radio quality condition being satisfied that triggers a report of the L1 measurement result; and transmitting notification information indicating that the second radio quality condition is satisfied to the network node in the L1 or Layer 2 in response to a second radio quality condition being satisfied that stops the report.

[0007] A user equipment according to a second aspect of the present disclosure is an equipment used in a mobile communication system supporting L1 / L2 Triggered Mobility (LTM). The user equipment includes: a control unit that performs L1 measurement, which is radio quality measurement in Layer 1 (L1); and a transmission unit that, in response to a first radio quality condition that triggers a report of an L1 measurement result being satisfied, transmits an L1 measurement report including the L1 measurement result to a network node at least once in the L1 or Layer 2 (L2). In response to a second radio quality condition that stops the report being satisfied, the transmission unit transmits notification information indicating that the second radio quality condition has been satisfied to the network node in the L1 or L2.

[0008] A network node according to a third aspect of the present disclosure is a device used in a mobile communication system supporting L1 / L2 Triggered Mobility (LTM). The network node includes a receiving unit that receives, from a user equipment (UE) performing L1 measurement, which is radio quality measurement in Layer 1 (L1), an L1 measurement report that is transmitted at least once in Layer 1 (L1) or Layer 2 (L2) in response to satisfaction of a first radio quality condition that triggers a report of the L1 measurement result and that includes the L1 measurement result. The receiving unit receives, from the user equipment, notification information that is transmitted in Layer 1 or L2 in response to satisfaction of a second radio quality condition that stops the report and indicates that the second radio quality condition has been satisfied.

[0009] 1 is a diagram showing an example of the configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram showing an example of the configuration of a UE (user equipment) according to an embodiment. FIG. 3 is a diagram showing an example of the configuration of a gNB (network node) according to an embodiment. FIG. 4 is a diagram showing a protocol stack configuration of a radio interface of a user plane that handles data. FIG. 5 is a diagram showing a protocol stack configuration of a radio interface of a control plane that handles signaling (control signals). FIG. 6 is a diagram showing a configuration related to measurements by a UE according to an embodiment. FIG. 7 is a diagram showing 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 showing an example of the operation of inter-CU LTM according to an embodiment. FIG. 9 is a diagram showing an example of an event-triggered L1 measurement report according to an embodiment. FIG. 10 is a diagram showing an overview of the operation of a UE according to an embodiment. FIG. 11 is a diagram showing a specific example of the operation of a mobile communication system according to an embodiment. FIG. 12 is a diagram for explaining another example of operation according to an embodiment. FIG. 13 is a diagram showing an example of the operation of a UE according to 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 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 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) 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 A１ 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 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) Operation of the Mobile Communication System Based on the above-described configuration and operation, the operation of the mobile communication system 1 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 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.

[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. 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 transmitting 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) transmitting 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 embodiment, when an event-triggered L1 measurement is introduced, an operation is described that enables gNB200 to accurately determine that the leaving condition (second radio quality condition) has been met in UE100, thereby enabling improvement of LTM.

[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 S11, 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 S12, 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 met (step 12: YES), in step S13, the UE 100 transmits an L1 measurement report including an L1 measurement result to the gNB 200 at least once over L1 or L2. For example, when transmitting the L1 measurement report over 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 over 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 S13, the UE 100 may start transmitting periodic L1 measurement reports.

[0131] In step S14, 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 set L1 LTM measurement event is no longer satisfied. For example, when the event LTM4 is set 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 14: YES), in step S15, 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 S13, 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 S15, 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 S15, 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. The leave notification information may be only an LCID without a MAC CE body. The 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 S20, UE100 is in an RRC connected state in the cell (serving cell) of gNB200.

[0140] In step S21, the gNB 200 transmits an L1 measurement report configuration, which is a configuration related to L1 measurement reporting, to the UE 100. The gNB 200 may transmit an RRC message (RRC Reconfiguration message) including the L1 measurement report configuration to the UE 100. The UE 100 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 S22, UE100 performs L1 measurements (beam measurements) for the serving cell and / or LTM candidate cell according to the L1 measurement report configuration in step S21.

[0146] In step S23, 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 S24a, the UE 100 starts transmitting an L1 measurement report. If the TTT is set, the UE 100 may start (trigger) transmitting 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 S24a, S24b, S24c, ..., the UE 100 periodically transmits L1 measurement reports. 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 S25, 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 S26, 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. The 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] (4.3) Other Operation Examples FIG. 12 is a diagram for explaining other operation examples according to the embodiment.

[0155] The gNB 200 forms multiple beams within one of its own cells. In the illustrated example, the gNB 200 forms five beams #1 to #5 within one of its own cells. Each beam can be identified by SSB or CSI-RS. The UE 100 moves through the cell.

[0156] First, in the situation shown in (a) of Figure 12, beam #1 is the beam with the highest radio quality (RSRP) (also referred to as the "best beam"). Here, the radio quality of beam #1 exceeds the threshold (Configured threshold) corresponding to the LTM measurement event configured in UE 100. In this case, UE 100 enters the LTM measurement event by event evaluation and triggers the transmission of an L1 measurement report.

[0157] Next, in the situation shown in (b) of Figure 12, the best beam has been changed to beam #3 due to the movement of UE 100. The radio quality of beam #3 exceeds the threshold value corresponding to the LTM measurement event set in UE 100.

[0158] Next, in the situation shown in (c) of Figure 12, the best beam has been changed to beam #5 due to the movement of UE 100. The radio quality of beam #5 exceeds the threshold value corresponding to the LTM measurement event set in UE 100.

[0159] In the scenario shown in Fig. 12, UE 100 performs radio quality measurement on a beam-by-beam basis in L1 measurement, and enters an LTM measurement event and transmits an L1 measurement report when the first radio quality condition (entering condition) is satisfied for at least one beam in the cell. However, in the scenario shown in Fig. 12, the timing to leave the LTM measurement event is not specified in the 3GPP technical specifications.

[0160] In the first operation pattern, the UE 100 leaves the LTM measurement event and transmits leave notification information each time the second radio quality condition (leaving condition) is not satisfied for each beam in the cell. That is, the UE 100 evaluates the entry and leaving of the LTM measurement event at the beam level in the event evaluation.

[0161] For example, in the example of Figure 12, in the situation (a), when the radio quality of beam #1 exceeds a threshold, UE 100 enters an LTM measurement event and transmits an L1 measurement report, and when the radio quality of beam #1 falls below the threshold, UE 100 leaves the LTM measurement event and transmits leave notification information. In the situation (b), when the radio quality of beam #3 exceeds a threshold, UE 100 enters an LTM measurement event and transmits an L1 measurement report, and when the radio quality of beam #3 falls below the threshold, UE 100 leaves the LTM measurement event and transmits leave notification information. In the situation (c), when the radio quality of beam #5 exceeds a threshold, UE 100 enters an LTM measurement event and transmits an L1 measurement report, and when the radio quality of beam #5 falls below the threshold, UE 100 leaves the LTM measurement event and transmits leave notification information. Such leaving event evaluation is also referred to as "beam-level leaving event evaluation."

[0162] In this way, by evaluating the entry and leaving of LTM measurement events at the beam level, gNB200 can obtain detailed information about the entry and leaving of LTM measurement events at the beam level.

[0163] In the first operation pattern, the UE 100 may receive configuration information from the gNB 200 that configures the transmission of leave notification information indicating that the second radio quality condition has been met at the beam level (i.e., leaving from the LTM measurement event). In other words, the gNB 200 may configure the UE 100 to perform beam-level leaving event evaluation.

[0164] Also, in the first operation pattern, the UE 100 may transmit leave notification information indicating that the second radio quality condition is satisfied at the beam level to the gNB 200. In other words, information indicating that the leave notification information is due to a leaving event evaluation at the beam level may be included in the leave notification information and transmitted.

[0165] On the other hand, in the second operation pattern, UE100 leaves from the LTM measurement event and transmits leave notification information in response to the second radio quality condition (leaving condition) being satisfied for the beam (best beam) with the best radio quality in the cell. That is, UE100 leaves from the LTM measurement event in response to all observable beams in the cell not satisfying the leaving condition. Such leaving event evaluation is also referred to as "cell-level leaving event evaluation."

[0166] For example, in the example of FIG. 12 , in the situation (a), when the radio quality of beam #1 exceeds a threshold, UE 100 enters an LTM measurement event and transmits an L1 measurement report. Even if the radio quality of beam #1 falls below the threshold, UE 100 does not leave the LTM measurement event if the radio qualities of other beams exceed the threshold. In the situation (b), UE 100 maintains the state in which it has entered the LTM measurement event. In the situation (c), when the radio quality of beam #5 falls below the threshold, all beams in the cell fall below the threshold, and UE 100 leaves the LTM measurement event and transmits leave notification information. Such leaving event evaluation is also referred to as "cell-level leaving event evaluation."

[0167] In this way, by evaluating the entry of the LTM measurement event at the beam level while evaluating the leave of the LTM measurement event at the cell level, UE100 can avoid frequently sending leave notification information. Also, from the perspective of LTM cell switching, gNB200 does not need to understand the event leave at the beam level, and it is considered sufficient to understand the event leave at the cell level. Therefore, UE100 can provide leave notification information that is useful for gNB200 to perform LTM control by evaluating the leave of the LTM measurement event at the cell level.

[0168] In the second operation pattern, the UE 100 may receive configuration information from the gNB 200 that configures the transmission of leave notification information indicating that the second radio quality condition has been met at the cell level (i.e., leaving from the LTM measurement event). In other words, the gNB 200 may configure the UE 100 to perform cell-level leaving event evaluation.

[0169] Also, in the second operation pattern, the UE 100 may transmit leave notification information indicating that the second radio quality condition is satisfied at the cell level to the gNB 200. In other words, information indicating that the leave notification information is due to a leaving event evaluation at the cell level may be included in the leave notification information and transmitted.

[0170] 13 is a diagram showing an example of the operation of the UE 100 according to the embodiment. Here, differences from the operation according to the above-described embodiment will be mainly described, and overlapping descriptions will be omitted.

[0171] In step S30, the UE 100 receives an RRC Reconfiguration message including an LTM setting from the gNB 200. The RRC Reconfiguration message may include information for setting whether to perform leaving event evaluation (sending leave notification information). The RRC Reconfiguration message may include information for setting whether to perform leaving event evaluation (sending leave notification information) at 1) the beam level, 2) the cell level, or 3) both of these. In the following operation example, it is assumed that the information in 1) or 2) is set in the UE 100.

[0172] In step S31, the UE 100 performs (starts) L1 measurement.

[0173] In step S32, the UE 100 performs an entering event evaluation of the LTM measurement event. The UE 100 determines that the event has entered if at least one beam satisfies the entering condition (first wireless quality condition).

[0174] In step S33, the UE 100 transmits an L1 measurement report upon entering the event.

[0175] In step S34, UE 100 checks whether the leaving event evaluation of the LTM measurement event is at the cell level (beam level) based on the configuration information.

[0176] If beam-level leaving event evaluation is configured (step S34: NO), in step S35, UE100 performs beam-level leaving event evaluation. Every time each beam no longer satisfies the event condition (step S35: YES), in step S37, UE100 transmits an L1 measurement report. The L1 measurement report may include information indicating that the beam-level event condition no longer satisfies the event condition. The L1 measurement report may include an identifier (e.g., a reference signal identifier) ​​indicating the beam that no longer satisfies the event condition.

[0177] On the other hand, if leaving event evaluation at the cell level is configured (step S34: YES), in step S36, UE100 performs leaving event evaluation at the cell level. If the best beam in the cell no longer satisfies the event condition (step S36: YES), in step S37, UE100 transmits an L1 measurement report. The L1 measurement report may include information indicating that the event condition at the cell level no longer satisfies the event condition. The L1 measurement report may include an identifier indicating the beam or cell that no longer satisfies the event condition.

[0178] (5) Other embodiments 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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).

[0183] 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.

[0184] 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.

[0185] 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.

[0186] This application claims priority from Japanese Patent Application No. 2024-128106 (filed August 2, 2024), the entire contents of which are incorporated herein by reference.

[0187] (6) Supplementary Notes The following are additional notes regarding the features of the above-described embodiment.

[0188] Supplementary Note 1: A communication method executed by a user equipment in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: performing L1 measurement, which is a radio quality measurement in Layer 1 (L1); transmitting an L1 measurement report including the L1 measurement result to a network node in the L1 or Layer 2 (L2) at least once in response to a first radio quality condition that triggers a report of the L1 measurement result being satisfied; and transmitting notification information indicating that the second radio quality condition has been satisfied to the network node in the L1 or L2 in response to a second radio quality condition that stops the report being satisfied.

[0189] Supplementary Note 2: The communication method according to Supplementary Note 1, wherein the user equipment transmits an L1 measurement report including the notification information to the network node on the L1 or L2 in response to the second radio quality condition being satisfied.

[0190] Supplementary Note 3: The communication method according to Supplementary Note 2, wherein the user equipment transmits the L1 measurement report including the notification information to the network node at a first transmission timing in accordance with a reporting interval of the L1 measurement report after the second radio quality condition is satisfied.

[0191] Supplementary Note 4: The communication method according to Supplementary Note 1, wherein the user equipment transmits the notification information to the network node on the Layer 1 or the Layer 2 using signaling different from the Layer 1 measurement report when the second radio quality condition is satisfied.

[0192] Supplementary Note 5: The communication method according to Supplementary Note 4, wherein the user equipment transmits the notification information to the network node on the L1 or L2 before a first transmission timing according to a reporting interval of the L1 measurement report when the second radio quality condition is satisfied.

[0193] Supplementary Note 6: The communication method according to any one of Supplementary Notes 1 to 5, wherein the user equipment transmits the notification information in uplink control information (UCI) on the Layer 1.

[0194] Supplementary Note 7: The communication method according to any one of Supplementary Notes 1 to 5, wherein the user equipment transmits the notification information in the Layer 2 by a Medium Access Control Element (MAC CE).

[0195] Supplementary Note 8: The communication method according to any one of Supplementary Notes 1 to 7, wherein the user equipment performs radio quality measurement on a beam-by-beam basis in the L1 measurement, and transmits the L1 measurement report to the network node when the first radio quality condition is satisfied in at least one beam within a cell.

[0196] Supplementary Note 9: The communication method according to Supplementary Note 8, wherein the user equipment transmits the notification information to the network node each time the second radio quality condition becomes unsatisfied for each beam in the cell.

[0197] Supplementary Note 10: The communication method according to Supplementary Note 9, wherein the user equipment receives from the network node configuration information that configures transmission of the notification information indicating that the second radio quality condition is satisfied at a beam level.

[0198] Supplementary Note 11: The communication method according to Supplementary Note 9 or 10, wherein the user equipment transmits the notification information indicating that the second radio quality condition is satisfied at a beam level to the network node.

[0199] Supplementary Note 12: The communication method according to Supplementary Note 8, wherein the user equipment transmits the notification information to the network node on the Layer 1 or the Layer 2 in response to the second radio quality condition being satisfied for a beam having the best radio quality in the cell.

[0200] Supplementary Note 13. The communication method according to Supplementary Note 12, wherein the user equipment receives from the network node configuration information for configuring transmission of the notification information indicating that the second radio quality condition is satisfied at a cell level.

[0201] Supplementary Note 14. The communication method according to Supplementary Note 12 or 13, wherein the user equipment transmits the notification information indicating that the second radio quality condition is satisfied at a cell level to the network node.

[0202] Supplementary Note 15: A user equipment used in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: a control unit that performs L1 measurement, which is a radio quality measurement in Layer 1 (L1); and a transmission unit that, in response to a first radio quality condition that triggers a report of an L1 measurement result, transmits an L1 measurement report including the L1 measurement result to a network node in the L1 or Layer 2 (L2) at least once, and in response to a second radio quality condition that stops the report being satisfied, the transmission unit transmits notification information indicating that the second radio quality condition has been satisfied to the network node in the L1 or L2.

[0203] Supplementary Note 16: A network node used in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: a receiving unit that receives, from a user equipment that performs L1 measurement, which is a radio quality measurement in Layer 1 (L1), an L1 measurement report that includes the L1 measurement result and that is transmitted at least once in the L1 or Layer 2 (L2) in response to a first radio quality condition being satisfied that triggers a report of the L1 measurement result; and the receiving unit receives, from the user equipment, notification information that is transmitted in the L1 or the L2 in response to a second radio quality condition being satisfied that stops the report and indicates that the second radio quality condition has been satisfied.

[0204] 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 that supports LTM (L1 / L2 Triggered Mobility), comprising: performing L1 measurement, which is a radio quality measurement in Layer 1 (L1); transmitting an L1 measurement report including the L1 measurement result to a network node in L1 or Layer 2 (L2) at least once in response to a first radio quality condition that triggers a report of the L1 measurement result being satisfied; and transmitting notification information indicating that the second radio quality condition has been satisfied to the network node in L1 or L2 in response to a second radio quality condition that stops the report being satisfied.

2. The communication method according to claim 1, wherein the user equipment transmits an L1 measurement report including the notification information to the network node on the L1 or the L2 in response to the second wireless quality condition being satisfied.

3. The communication method according to claim 2, wherein the user equipment transmits the L1 measurement report including the notification information to the network node at the first transmission timing according to the reporting interval of the L1 measurement report after the second wireless quality condition is satisfied.

4. The communication method according to claim 1, wherein the user equipment transmits the notification information to the network node on the L1 or L2 using signaling different from the L1 measurement report when the second radio quality condition is satisfied.

5. A communication method as described in claim 4, wherein the user equipment transmits the notification information to the network node on the L1 or L2 when the second wireless quality condition is satisfied, prior to the first transmission timing according to the reporting interval of the L1 measurement report.

6. A communication method according to any one of claims 1 to 5, wherein the user equipment transmits the notification information on the Layer 1 by using uplink control information (UCI).

7. A communication method according to any one of claims 1 to 5, wherein the user equipment transmits the notification information in the Layer 2 by a Medium Access Control Element (MAC CE).

8. A communication method according to any one of claims 1 to 5, wherein the user equipment performs radio quality measurements on a beam-by-beam basis in the L1 measurement, and transmits the L1 measurement report to the network node when the first radio quality condition is satisfied in at least one beam within a cell.

9. The communication method according to claim 8, wherein the user equipment transmits the notification information to the network node each time the second radio quality condition becomes unsatisfied for each beam in the cell.

10. The communication method according to claim 9, wherein the user equipment receives from the network node configuration information for configuring the transmission of the notification information indicating that the second radio quality condition is satisfied at a beam level.

11. The communication method according to claim 9, wherein the user equipment transmits the notification information to the network node indicating that the second radio quality condition is satisfied at a beam level.

12. A communication method as described in claim 8, wherein the user equipment transmits the notification information to the network node on L1 or L2 in response to the second wireless quality condition being satisfied for the beam with the best wireless quality within the cell.

13. The communication method according to claim 12, wherein the user equipment receives from the network node configuration information for configuring transmission of the notification information indicating that the second radio quality condition is satisfied at a cell level.

14. The communication method according to claim 12, wherein the user equipment transmits the notification information indicating that the second radio quality condition is satisfied at a cell level to the network node.

15. A user equipment used in a mobile communication system that supports LTM (L1 / L2 Triggered Mobility), comprising: a control unit that performs L1 measurement, which is a radio quality measurement in Layer 1 (L1); and a transmission unit that, in response to a first radio quality condition that triggers a report of an L1 measurement result, transmits an L1 measurement report including the L1 measurement result to a network node in the L1 or Layer 2 (L2) at least once, and in response to a second radio quality condition that stops the report being satisfied, the transmission unit transmits notification information indicating that the second radio quality condition has been satisfied to the network node in the L1 or L2.

16. A network node used in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: a receiving unit that receives, from a user equipment that performs L1 measurement, which is a radio quality measurement in Layer 1 (L1), an L1 measurement report that includes the L1 measurement result and that is transmitted at least once in L1 or Layer 2 (L2) in response to a first radio quality condition that triggers a report of the L1 measurement result being satisfied; and the receiving unit receives, from the user equipment, notification information that is transmitted in L1 or L2 in response to a second radio quality condition that stops the report being satisfied and indicates that the second radio quality condition has been satisfied.

Images