Communication method, user equipment, chip set, program, and mobile communication system

Abstract

This communication method, which is executed by a user equipment of a mobile communication system that assists in L1 / L2 triggered mobility (LTM), involves: receiving, from a network node, information indicating a radio quality condition to be satisfied in order to perform LTM cell switching; performing, in layer 1 (L1), L1 filtering on the measured value obtained by measuring the radio quality; and performing, in layer 3 (L3), specific L3 filtering, which is different from L3 filtering used for L3 handover, on the measured value after the L1 filtering, then evaluating whether the radio quality condition is satisfied.

Description

COMMUNICATION METHOD, USER EQUIPMENT, CHIPSET, PROGRAM, AND MOBILE COMMUNICATION SYSTEM

[0001] The present disclosure relates to a communication method, a user device, a chipset, a program, and 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 V18.0.0 (2023-12)"

[0005] The present disclosure relates to a communication method that enables conditional LTM to be performed appropriately.

[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 that supports LTM (L1 / L2 Triggered Mobility), and includes receiving, from a network node, information indicating a radio quality condition that must be satisfied in order to perform cell switching by the LTM; performing, in Layer 1 (L1), L1 filtering on measurement values ​​obtained by radio quality measurement; and, in Layer 3 (L3), performing specific L3 filtering, which is different from L3 filtering used for L3 handover, on the measurement values ​​after the L1 filtering, and then evaluating whether the radio quality condition is satisfied.

[0007] A user equipment according to a second aspect of the present disclosure is a user equipment for a mobile communication system supporting L1 / L2 Triggered Mobility (LTM), comprising: a receiver that receives, from a network node, information indicating a radio quality condition that must be satisfied in order to perform cell switching by the LTM; and a controller that performs L1 filtering on measurement values ​​obtained by radio quality measurement in Layer 1 (L1). The controller performs specific L3 filtering on the measurement values ​​after the L1 filtering, which is different from the L3 filtering used for L3 handover, in Layer 3 (L3), and then evaluates whether the radio quality condition is satisfied.

[0008] A chipset according to a third aspect of the present disclosure includes a circuit for performing the communication method according to the first aspect.

[0009] A program according to a fourth aspect of the present disclosure causes a user device to execute the communication method according to the first aspect.

[0010] A mobile communication system according to a fifth aspect of the present disclosure includes a user equipment according to the second aspect and a network node.

[0011] 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. FIG. 7 is a diagram for explaining filter coefficients of an L3 filter that is set from a gNB to a UE by RRC. FIG. 8 is a diagram showing an example of an LTM procedure. FIG. 9 is a diagram showing an example of UE operation related to C-LTM. FIG. 10 is a diagram showing a specific example of C-LTM operation in a mobile communication system. FIG. 11 is a diagram showing an overview of UE operation according to an embodiment. FIG. 12 is a diagram for explaining an example of a first operation pattern according to an embodiment. FIG. 13 is a diagram for explaining another example of the first operation pattern according to an embodiment. FIG. 14 is a diagram for explaining a second operation pattern according to an embodiment. FIG. 15 is a diagram for explaining a third operation pattern according to an embodiment.

[0012] 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.

[0013] (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 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.

[0014] 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.

[0015] 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).

[0016] 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").

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0034] 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.

[0035] 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).

[0036] 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.

[0037] 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.

[0038] 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").

[0039] (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.

[0040] 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.

[0041] FIG. 6 is a diagram showing a configuration related to measurements by UE 100.

[0042] 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 .

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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

[0047] 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.

[0048] 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.

[0049] Note that if the filter coefficient k is set to 0 (zero), no L3 filtering is applied.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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).

[0055] (3) Overview of LTM The mobile communication system according to the embodiment supports LTM (L1 / L2-triggered mobility).

[0056] In a typical handover procedure, a serving cell switch is triggered by signaling in the upper layer L3, specifically the RRC layer. Hereinafter, 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 a handover of the UE 100 based on the Measurement Report message, and instructs the cell switch by transmitting a handover command, which is an RRC message (specifically, an RRC Reconfiguration message), from the gNB 200 to the UE 100.

[0057] 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.

[0058] 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.

[0059] Secondly, the UE 100 performs a synchronization process with the candidate cell by early synchronization (Early sync).

[0060] 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.

[0061] Fourth, UE100 switches the serving cell in response to a cell switching command from gNB200 (source cell).

[0062] 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.

[0063] The following principles apply to LTM:

[0064] 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.

[0065] 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.

[0066] The user plane continues without a reset if configured in RRC signaling to avoid additional delays in data recovery.

[0067] - Security is not updated in LTM.

[0068] 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.

[0069] 8 is a diagram showing an example of an LTM procedure. In the illustrated example, it is assumed that the UE 100 performs a serving cell switch from the first cell of the gNB 200 to the second cell.

[0070] 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".

[0071] In step S1, UE100 is in an RRC connected state in the cell (first cell, source cell) of gNB200.

[0072] In step S2, UE100 transmits a Measurement Report message, which is an RRC message, to gNB200.

[0073] In step S3, gNB200 decides to use LTM based on the Measurement Report message and starts preparing the candidate cell.

[0074] In step S4, gNB200 sends an RRC Reconfiguration message to UE100, which includes LTM candidate cell configurations (LTM Candidate Configurations) for one or more candidate cells.

[0075] In step S5, UE100 saves the LTM candidate cell setting and sends an RRC Reconfiguration Complete message to gNB200.

[0076] In step S6, the UE 100 may perform synchronization processing with the candidate cell before receiving the cell switch command. Such synchronization processing is called early synchronization (Early sync). Here, the UE 100 may perform early timing advance (TA) acquisition in the candidate cell requested by the gNB 200 (source cell) before receiving the cell switch command of step S9. This is performed by contention-free random access (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. The UE 100 transmits a random access preamble (RA preamble) to the specified candidate cell. In order to minimize communication interruption of the source cell due to 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. The TA value is a value for adjusting the uplink transmission timing of the UE 100.

[0077] 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).

[0078] In step S8, gNB200 decides to switch the serving cell to the target cell (second cell).

[0079] In step S9, gNB200 transmits a Cell Switch Command (MAC CE) including a candidate configuration index of the target cell to UE100. The Cell Switch Command may include a TA value obtained by early synchronization.

[0080] 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.

[0081] In step S11, if the serving cell switch needs to include the execution of a random access procedure (for example, if the Cell Switch Command does not include a valid TA value), the UE 100 executes the random access procedure for the target cell. Note that, if the UE 100 does not need to acquire the TA of the target cell at the time of the serving cell switch (for example, if the Cell Switch Command includes a valid TA value), the random access procedure can be skipped.

[0082] 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.

[0083] (4) Conditional LTM In 3GPP Release 19, the introduction of a conditional LTM (C-LTM) procedure is planned to be considered. The cell switching procedure using LTM as shown in Fig. 8 can be applied to the C-LTM procedure, as well as the conditional L3 handover. C-LTM may also be referred to as RACH (Random Access Channel)-less conditional handover (RL-CHO).

[0084] For example, the gNB 200 sets in advance in the UE 100 an execution condition (trigger condition), which is a radio quality condition for cell switching, in the RRC Reconfiguration message of step S4. This makes it possible to skip the operations from the L1 Measurement Report of step S7 to the Cell Switch Command (MAC CE) of step S9, and as a result, it is thought that it is possible to speed up cell switching and minimize interruptions in data communication.

[0085] Also, one of the features of LTM is early synchronization (Early sync). Early synchronization allows the random access procedure to be skipped when performing cell switching. Such early synchronization may also be applicable to conditional handover. Here, in conventional LTM early synchronization, the UE 100 triggers CFRA by receiving a PDCCH order from the source cell before receiving a Cell Switch Command (MAC CE) from the current serving cell (source cell). However, in C-LTM, since the UE 100 voluntarily triggers cell switching, the gNB 200 cannot determine the timing at which the UE 100 should perform early synchronization. Therefore, there is a concern that the PDCCH order cannot be used and the CFRA cannot be used either. Although it is possible to reserve resources for CFRA for UE 100 in a candidate cell, gNB 200 cannot determine when UE 100 will trigger CFRA, which may result in wasted CFRA resources. Also, in C-LTM, gNB 200 does not transmit a Cell Switch Command (MAC CE) to UE 100 as in conventional LTM, so the TA value cannot be notified to UE 100 by the Cell Switch Command (MAC CE).

[0086] In an embodiment, in addition to setting the cell switch with a trigger condition in the UE 100, the early synchronization with a trigger condition may be set in the UE 100, so that the UE 100 can spontaneously trigger each of the early synchronization and the cell switch. Here, in the early synchronization, contention-based random access (CBRA) may be used instead of CFRA.

[0087] 9 is a diagram showing an example of an operation of UE 100 related to C-LTM. The illustrated operation is an operation for performing cell switching to change the serving cell of UE 100 in an RRC connected state from a first cell #a to a second cell #b. Specifically, the illustrated operation is an operation for realizing C-LTM.

[0088] In step S21, the UE 100 receives setting information from the first cell #a (gNB 200) including first information for specifying a first condition (radio quality condition) for triggering early synchronization related to cell switching and second information for specifying a second condition (radio quality condition) for triggering cell switching. As a result, the trigger condition for early synchronization and the trigger condition for cell switching are each set in the UE 100. Hereinafter, such setting information may be referred to as "C-LTM setting".

[0089] The first information and / or the second information may include information indicating radio quality conditions to be satisfied for the first cell #a (serving cell) and / or the second cell #b (candidate cell) to trigger early synchronization and / or cell switching. The radio quality may be at least one measurement value of a reference signal received power (RSRP), a reference signal received quality (RSRQ), a signal-to-interference-and-noise ratio (SINR), and a received signal strength indicator (RSSI). The radio quality conditions may be threshold values ​​to be compared with these measurements. The information indicating the radio quality conditions may include a threshold value for the first cell #a (serving cell) and a threshold value for the second cell #b (candidate cell).

[0090] The configuration information of step S21 may include a TA value for the second cell #b. In step S22, the UE 100 may perform early synchronization (specifically, uplink early synchronization) only when the TA value for the second cell #b is not included in the configuration information. When the TA value for the second cell #b is included in the configuration information, the UE 100 may skip the early synchronization of step S22 (specifically, uplink early synchronization).

[0091] In step S22, the UE 100 performs early synchronization including a random access procedure for the second cell #b in response to the first condition set in step S21 being satisfied. Here, the early synchronization includes downlink early synchronization and uplink early synchronization. The UE 100 performs the random access procedure for uplink early synchronization (i.e., acquisition of a TA value).

[0092] The random access procedure in the early synchronization of step S22 may be a contention-based random access (CBRA) procedure. This allows the UE 100 to perform the random access procedure even if it does not receive a PDCCH order from the first cell #a (serving cell). Information indicating candidates for PRACH (Physical Random Access Channel) resources to be applied to CBRA (specifically, candidates for random access preambles and / or candidates for PRACH time / frequency resources) may be included in system information (SIB: System Information Block) broadcast from the second cell #b (candidate cell). This information may be included in the configuration information of step S21. The configuration information of step S21 may explicitly or implicitly specify the CBRA procedure to the UE 100 as the random access procedure in the early synchronization. Unlike CFRA in which a dedicated random access preamble is assigned to the UE 100, in CBRA, the UE 100 selects a random access preamble by itself from random access preamble candidates (a group of random access preambles). Therefore, in CFRA, no contention of random access preambles occurs between UEs, but in CBRA, contention of random access preambles may occur between UEs.

[0093] The CBRA procedure in early synchronization in step S22 includes transmitting a random access preamble (RA preamble) from UE 100 to the second cell #b, and UE 100 receiving a random access response (RAR) from the second cell #b.

[0094] In step S22, the UE 100 identifies a PRACH resource to be used exclusively for transmitting a random access preamble for early synchronization. For example, some of the candidates for the PRACH resource for CBRA are prepared (designated) as PRACH resources dedicated to early synchronization. The UE 100 transmits the random access preamble using the identified PRACH resource (the random access preamble dedicated to early synchronization and / or the PRACH time-frequency resource dedicated to early synchronization).

[0095] The RAR includes a TA value for the second cell #b. The RAR may include a temporary identifier of the UE 100 in the second cell #b, for example, a Cell Radio Network Temporary Identifier (C-RNTI). Such a C-RNTI is also referred to as a Temporary C-RNTI. In step S23, the UE 100 may transmit an RRC message (for example, an RRC Reconfiguration Complete message) including the Temporary C-RNTI to the second cell #b as the first transmission to the second cell #b.

[0096] In step S23, after the early synchronization is completed, the UE 100 performs cell switching without a random access procedure in response to the second condition set in step S21 being satisfied.

[0097] In step S23, when the second condition is satisfied, the UE 100 may check whether the TA value notified in the RAR is valid. If the TA value is valid, the UE 100 performs cell switching without a random access procedure. On the other hand, if the TA value is invalid when the second condition is satisfied, the UE 100 may perform cell switching with a random access procedure in step S23.

[0098] According to this operation, the UE 100 can spontaneously trigger early synchronization when the first condition is set by the gNB 200 and the first condition is met. Therefore, the UE 100 can trigger early synchronization even without receiving a PDCCH order from the first cell #a (source cell). Then, after the early synchronization is completed, the UE 100 performs cell switching to the second cell #b (target cell) without a random access procedure when the set second condition is met. This enables C-LTM to be realized, and the time from when the second condition is met to when the cell switching is completed can be shortened.

[0099] FIG. 10 is a diagram showing a specific example of the C-LTM operation of the mobile communication system 1.

[0100] In step S101, UE100 is in an RRC connected state (RRC Connected) in the first cell #a (serving cell) of gNB200. UE100 may transmit capability information (UE capability) indicating that it supports C-LTM to gNB200. gNB200 may receive the capability information (UE capability).

[0101] In step S102, the UE 100 transmits a Measurement Report message, which is an RRC message, to the gNB 200 (serving cell). The gNB 200 receives the Measurement Report message. The Measurement Report message includes a measurement value of at least one of the radio quality of the first cell #a (serving cell) and the radio quality of the second cell #b (candidate cell).

[0102] In step S103, gNB200 decides to configure C-LTM for UE100 and identifies a candidate cell.

[0103] In step S104, gNB200 transmits the C-LTM configuration to UE100. gNB200 may transmit an RRC message (specifically, an RRC Reconfiguration message) including the C-LTM configuration to UE100. UE100 receives the C-LTM configuration from gNB200 (serving cell).

[0104] The C-LTM configuration includes a) configuration information related to conditional early synchronization, and b) other mobility-related configuration information. The configuration information related to the conditional early synchronization in a) may include at least one piece of information from the following a1) to a4). Note that if the configuration related to the conditional early synchronization in a) is not included in the C-LTM configuration, the UE 100 may not perform the conditional early synchronization.

[0105] a1) First Condition: Such configuration information (Early sync trigger config.) explicitly indicates the first condition. The first condition may be a wireless quality threshold such as RSRP / RSRQ / SINR. The first condition may be a data reception quality threshold such as BLER. The first condition may be location information indicating a geographical range determined by latitude, longitude, altitude, etc. The first condition may be an event (e.g., a measurement event or a conditional event) defined in the RRC protocol. The first condition may be information indicating the use of model inference using an AI (Artificial Intelligence) / ML (Machine Learning) model, such as a model ID or function ID of the AI / ML model.

[0106] a2) Information specifying execution of conditional early synchronization: Such configuration information (Early sync trigger config.) implicitly indicates the first condition. When this information is included in the C-LTM configuration, the UE 100 determines to execute conditional early synchronization. In this case, the UE 100 may determine the trigger timing of early synchronization by referring to the C-LTM execution condition (second condition). For example, the UE 100 adds an offset to the radio quality or its threshold used in the conditional event (for example, adds +3 dB to the RSRP value of the serving cell). The UE 100 triggers early synchronization when such a first condition is satisfied. Alternatively, the UE 100 may immediately trigger early synchronization when it receives an RRC Reconfiguration message including configuration information for conditional early synchronization.

[0107] a3) Configuration information for PRACH resources dedicated to early synchronization: By defining a PRACH resource dedicated to early synchronization, the gNB 200 can distinguish between PRACH transmission for initial access that is not a cell switch and PRACH transmission for early synchronization. Based on the configuration information in a3), the UE 100 selects a PRACH resource to be used for early synchronization from among PRACH resource candidates dedicated to early synchronization among PRACH resource candidates for CBRA. This division of PRACH resources is also referred to as PRACH partitioning. In PRACH partitioning, a portion of the PRACH time-frequency resources and / or a portion of the random access preamble (preamble sequence) is designated (prepared) for a specific use. For example, the UE 100 selects a PRACH resource to be used for early synchronization from among PRACH resource candidates dedicated to early synchronization among random access preamble candidates for CBRA. By using such a PRACH resource dedicated to early synchronization, the gNB 200 that received the random access preamble from the UE 100 can identify that it is an RA transmission (access) by early synchronization of C-LTM based on the PRACH resource applied to the received random access preamble. Note that the setting information of the PRACH resource dedicated to early synchronization is not limited to the case where it is signaled individually to the UE in the C-LTM setting, but the first cell #a or the second cell #b may be signaled commonly to multiple UEs in the SIB. Note that the PRACH resource dedicated to early synchronization may be a CFRA resource.

[0108] a4) Configuration information regarding the validity period of the TA value: The TA value for the second cell #b, which is a candidate cell, can change its optimal value depending on the positional relationship (propagation distance) between the UE 100 and the second cell #b, so the validity period of the TA value is determined. The configuration information of a4) may indicate the validity period of the TA value as any of the following.

[0109] Time length: In this case, the configuration information of a4) indicates the time length of the validity period of the TA value acquired by the UE 100. For example, the configuration information may be a timer value set in a timer that measures the validity period of the TA value.

[0110] UE movement distance: In this case, the setting information of a4) is the movement distance of the UE 100 after the UE 100 acquires the TA value, and indicates the upper limit of the movement distance of the UE 100 for which the TA value is valid. The setting information may be a movement distance threshold. In other words, the setting information may be information on the area range for which the TA value is valid.

[0111] UE location: In this case, the configuration information of a4) indicates the geographical location (for example, latitude, longitude, and altitude) of the UE 100 for which the TA value is valid.

[0112] Radio quality of second cell #b: In this case, the configuration information of a4) may be a radio quality threshold (RSRP threshold, etc.) of second cell #b, which is a candidate cell. UE 100 considers the TA value to be valid if the radio quality of second cell #b is within a radio quality range specified by the configuration information. When multiple candidate cells exist, the configuration information of a4) may be specified separately for each candidate cell. That is, the configuration information may be associated with the cell ID of the candidate cell.

[0113] Meanwhile, the other mobility-related configuration in b) may include at least one of the following information in b1) to b4). Note that the configuration information in b) may be similar to configuration information for general CHO (conditional reconfiguration) that does not use conditional early synchronization. When multiple candidate cells exist, the other mobility-related configuration in b) may be specified separately for each candidate cell.

[0114] b1) Candidate Cell ID: The cell ID of the candidate cell.

[0115] b2) Second Condition (CondEvent): Information indicating a radio quality condition that must be satisfied for the serving cell and / or candidate cell to trigger a cell switch.

[0116] b3) RRC configuration: The RRC configuration applied in the candidate cell.

[0117] b4) Configured Grant (CG) Configuration: This is configuration information for configuring uplink radio resources (e.g., PUSCH resources) available for initial uplink transmission in a candidate cell.

[0118] In step S105, the UE 100 transmits an RRC Reconfiguration Complete message indicating that the configuration by the RRC Reconfiguration message of step S104 has been completed to the gNB 200 (serving cell). The gNB 200 receives the RRC Reconfiguration Complete message.

[0119] In step S106, the UE 100 performs radio quality measurement based on the setting in step S104 (particularly, setting information related to the conditional early synchronization), evaluates whether or not a first condition (Early sync trigger condition) is satisfied, detects that the condition is satisfied, and triggers early synchronization.

[0120] In step S107, the UE 100 performs downlink early synchronization (DL synchronization) with the second cell #b. The UE 100 may establish downlink synchronization with the second cell #b by using synchronization signals (primary synchronization signal and secondary synchronization signal) included in a synchronization signal (SSB) received from the second cell #b, which is a candidate cell.

[0121] In step S108, the UE 100 performs early synchronization (UL synchronization) of the uplink with the second cell #b.

[0122] Specifically, in step S108a, UE100 performs PRACH transmission (random access preamble transmission) using a PRACH resource dedicated to early synchronization among CBRA resources. gNB200 receives a random access preamble from UE100. gNB200 recognizes that PRACH transmission has been performed using a PRACH resource dedicated to early synchronization and determines that it is a C-LTM RACH procedure. gNB200 may recognize that transmitting the RAR in step S108b and receiving Msg3 (RRC Reconfiguration Complete message) in step S111 will be delayed. In addition, in step S108a, PRACH transmission (random access preamble transmission) may be performed using a CFRA resource based on the setting in step S104. gNB200 may determine that the PRACH procedure is C-LTM because a PRACH transmission was performed on the CFRA resource.

[0123] In step S108b, gNB200 transmits an RAR (Random Access Response) to UE100. UE100 receives the RAR. As with a normal CBRA procedure, the RAR may include at least one of a TA value, a Temporary C-RNTI, and an UL grant indicating the uplink radio resource (e.g., a PUSCH resource) used in step S111. Note that in step S108b, gNB200 may notify the TA value by other signaling instead of the RAR. For example, a MAC PDU (Protocol Data Unit) or MAC CE different from the RAR may be used, or an RRC message may be used. When the MAC CE is used, the TA value may be notified by a MAC CE dedicated to early synchronization (for example, an Early Sync TA notification MAC CE). When the UE 100 receives the MAC CE, the UE 100 does not immediately apply the notified TA value but stores it in a memory, and when a trigger condition is satisfied in step S110, the UE 100 reads out the TA value from the memory and applies it.

[0124] In step S109, the UE 100 starts a TA validity check based on the setting in step S104 (particularly, setting information related to conditional early synchronization). For example, the UE 100 may start a timer (TAT (Time Alignment Timer)).

[0125] In step S110, the UE 100 evaluates whether or not a trigger condition (Execution condition) for cell switching by C-LTM is satisfied based on the settings in step S104 (particularly, other mobility-related settings), and detects that the condition is satisfied. For example, the UE 100 detects that CondEvent A3 is satisfied. Note that CondEvent A3 is a trigger condition indicating that the radio quality of a neighboring cell (which may be a candidate cell or a target cell) is improved by an offset amount relative to the radio quality of a special cell (which may be an SpCell or a source cell), and corresponds to an event that triggers the execution of a conditional handover (here, C-LTM).

[0126] In step S111, if the TA value is valid, the UE 100 transmits an RRC Reconfiguration Complete message (Msg3) to the second cell #b (target cell). The UE 100 may determine that the TA value is valid if the timer (TAT) is running. The gNB 200 receives the RRC Reconfiguration Complete message.

[0127] Here, the UE 100 may transmit the RRC Reconfiguration Complete (Msg3) using uplink resources (PUSCH transmission) allocated by either a CG (configured grant) or a UL grant. For example, if the CG setting has been performed in step S104, the UE 100 performs PUSCH transmission using the CG resource. If the CG setting has not been performed in step S104, the UE 100 monitors the PDCCH of the second cell #b (target cell), and when receiving a PDCCH (UL grant, also referred to as "Dynamic grant") scrambled with the Temporary C-RNTI, the UE 100 may perform PUSCH transmission according to the UL grant. When the UE 100 receives the UL grant in step S108b, the UE 100 may perform PUSCH transmission in accordance with the UL grant.

[0128] On the other hand, if the TA value is not valid, the UE 100 performs a new RACH procedure (CBRA) for the second cell #b and transmits an RRC Reconfiguration Complete message to the second cell #b. For example, if the timer (TAT) has expired, the UE 100 determines that the TA value is invalid. Alternatively, if the TA value is not valid, the UE 100 may perform early synchronization again. Whether to perform early synchronization when the TA expires may be configured in the UE 100 by the gNB 200.

[0129] In step S108, UE 100 may perform CFRA using the PDCCH order, similar to step S6 in Fig. 8. Furthermore, when the timer (TAT) expires (i.e., before step S111), UE 100 may discard the currently acquired TA value and may perform the UL synchronization process (CBRA) of step S108 again. Furthermore, UE 100 may stop (or discard) the timer (TAT) when cell switching is completed in step S113.

[0130] In step S112, gNB200 transmits Msg4 to UE100. UE100 receives Msg4 from gNB200 (target cell). UE100 may determine that C-LTM is completed when it receives PDCCH (DCI including CRC scrambled with Temporary C-RNTI) from the target cell (step S113). The DL transmission from gNB200 may be accompanied by PDSCH (Contention Resolution MAC CE).

[0131] If a contention occurs and contention resolution fails, the UE 100 may perform the RACH procedure (CBRA) again. The UE 100 may consider such a failure as a handover failure (HOF). The UE 100 may initiate access (CBRA) to another candidate cell.

[0132] In the above-described operating scenario, cell switching (C-LTM) between cells within the same gNB (within the same CU), i.e., intra-gNB C-LTM, was assumed. However, cell switching (C-LTM) between cells of different gNBs (different CUs), i.e., inter-gNB C-LTM may also be applied.

[0133] (5) Operation according to the embodiment As described above, in C-LTM, a second condition (CondEvent) indicating the radio quality condition to be met for the serving cell and / or candidate cell to trigger cell switching is set from gNB200 to UE100.

[0134] In the conventional conditional L3 handover, the L3 (RRC) of the UE 100 evaluates whether or not the trigger condition (CondEvent) for cell switching is satisfied using the measurement value after L3 filtering. In the embodiment, it is assumed that the evaluation of whether or not the trigger condition (CondEvent) for cell switching in C-LTM is satisfied is performed in the L3 (RRC) in the same way as in the conventional conditional L3 handover.

[0135] One of the features of conventional LTM is the fast cell switching decision using L1 measurement reports, which allows the cell switching decision to follow instantaneous fluctuations in the radio environment. 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.

[0136] However, when evaluating whether the trigger condition for cell switching in C-LTM is satisfied, if the measurement value after L3 filtering is used, there is a concern that it will not be possible to respond to instantaneous fluctuations in the radio environment. That is, in C-LTM, when the UE 100 evaluates a Cond Event, if the measurement value after L3 filtering is applied in the same way as in the conventional L3 handover, there is a risk that it will not be possible to follow instantaneous fluctuations in the radio environment. As a result, it is not possible to follow instantaneous fluctuations, and the possibility of handover failure (for example, too late handover) increases.

[0137] Therefore, in the embodiment, the UE 100 performs specific L3 filtering, which is different from the L3 filtering used for L3 handover, on the measurement values ​​after L1 filtering in C-LTM, and then evaluates whether the radio quality condition (CondEvent) that must be satisfied to perform cell switching by LTM is satisfied. The specific L3 filtering may be L3 filtering used exclusively for C-LTM. This makes it possible to respond to instantaneous fluctuations in the radio environment and to perform C-LTM appropriately.

[0138] In the following description of the embodiment, an example of applying specific L3 filtering to the evaluation of CondEvent (second condition) that must be satisfied in order to perform cell switching is described, but specific L3 filtering may also be applied to the evaluation of the second condition that must be satisfied in order to perform early synchronization.

[0139] FIG. 11 is a diagram illustrating an overview of the operation of the UE 100 according to the embodiment.

[0140] In step S31, the UE 100 receives information indicating a radio quality condition (CondEvent) that must be satisfied to perform cell switching by LTM (C-LTM) from the gNB 200. Step S31 may be included in step S4 of FIG.

[0141] Specifically, the UE 100 receives an RRC Reconfiguration message from the gNB 200, and C-LTM configuration is performed. The C-LTM configuration includes an LTM CondEvent (e.g., Event A3).

[0142] In step S32, the L1 of the UE 100 performs L1 filtering on the measurement value obtained by the radio quality measurement.

[0143] In step S33, the L3 of the UE 100 performs specific L3 filtering different from the L3 filtering used for L3 handover on the measurement values ​​after L1 filtering, and then evaluates whether or not the radio quality condition (CondEvent) is satisfied. Step S33 may be included in step S110 of FIG. 8.

[0144] In step S34, the UE 100 performs cell switching by LTM in response to the wireless quality condition (CondEvent) being satisfied. For example, the UE 100 triggers cell switching and starts the process of step S111 in FIG.

[0145] In the first operation pattern of the embodiment, the specific L3 filtering is L3 filtering by an L3 filter 13 in which the filter coefficient k is set to zero. This makes it possible to not apply L3 filtering when evaluating CondEvent in C-LTM. Specifically, measurement averaging by L3 filtering is not performed. That is, without performing a weighted average (see equation (1)) of the latest measurement value from L1 and the measurement value after past L3 filtering, CondEvent is evaluated in C-LTM using the latest measurement value from L1. This makes it possible to respond to instantaneous fluctuations in the wireless environment.

[0146] In the first operation pattern of the embodiment, in step S33, UE100 may consider the filter coefficient k to be zero regardless of the filter coefficient k (Quantity Config setting) set by gNB200.

[0147] Alternatively, in the first operation pattern of the embodiment, the UE 100 may receive information from the gNB 200 to set zero as the filter coefficient k used for CondEvent evaluation in C-LTM. That is, the gNB 200 may be restricted to set zero as the filter coefficient k used for CondEvent evaluation in C-LTM.

[0148] In the first operation pattern of the embodiment, the specific L3 filtering may be skip filtering that does not apply the L3 filter 13. This may be achieved by skipping (bypassing) the L3 filter 13 instead of setting the filter coefficient k to zero.

[0149] In the second operation pattern of the embodiment, the specific L3 filtering is L3 filtering by the L3 filter 13 in which the filter coefficient k is adaptively changed according to the situation of the UE 100. As a result, the filter coefficient k used for CondEvent evaluation in C-LTM is adapted to the situation of the UE 100, and it becomes possible to perform C-LTM more appropriately.

[0150] In the second operation pattern of the embodiment, in step S33, the UE 100 may change the filter coefficient k according to a value indicating a moving speed of the UE 100. Alternatively, in step S33, the UE 100 may change the filter coefficient k according to a value indicating a frequency of a cell to be measured.

[0151] In the third operation pattern of the embodiment, the specific L3 filtering may be a process of applying a plurality of types of L3 filtering. In step S33, the UE 100 performs CondEvent evaluation in C-LTM using the processing results of each of the plurality of types of L3 filtering. This makes it possible to perform C-LTM more appropriately.

[0152] In the third operation pattern of the embodiment, the multiple types of L3 filtering may include L3 filtering using a first L3 filter 13 to which a first filter coefficient k is set, and L3 filtering using a second L3 filter 13 to which a second filter coefficient k different from the first filter coefficient k is set.

[0153] (5.1) First Operation Pattern Fig. 12 is a diagram for explaining the first operation pattern of the embodiment. In the following, redundant explanations of operations similar to those described above will be omitted.

[0154] In the illustrated example, when evaluating a C-LTM CondEvent, the UE 100 (control unit 130) regards the filter coefficient of the L3 filter 13 as zero, regardless of the Quantity Config setting. In other words, when evaluating a C-LTM CondEvent, the UE 100 (control unit 130) automatically cancels the application of the L3 filter 13.

[0155] First, the UE 100 (receiving unit 110) in which the C-LTM CondEvent is set measures the radio quality for each beam of the serving cell and the neighboring cell (candidate cell).

[0156] Second, the UE 100 (L1 filter 11) performs L1 filtering on the measurement values ​​of each beam, and the UE 100 (beam combining / selecting unit 12) derives the cell quality from the measurement values ​​after L1 filtering.

[0157] Third, because of the C-LTM CondEvent, the UE 100 (control unit 130) does not apply the L3 filter 13 to the measurement value (cell quality) after L1 filtering. Specifically, when the RRC layer of the UE 100 receives an L1 measurement value (e.g., a received power value) from a lower layer, it assumes that the filter coefficient k of the L3 filter 13 is set to fc0 (k=0), and sets the filter coefficient k to zero. In other words, even if the filter coefficient k=0 (fc0) is not explicitly set in the RRC, it assumes that the filter coefficient k=0, and does not apply the L3 filter 13.

[0158] Fourth, the UE 100 (evaluation unit 14) evaluates whether or not the C-LTM CondEvent is satisfied. Then, when the C-LTM CondEvent is satisfied, the UE 100 (control unit 130) executes (trigger) cell switching by C-LTM.

[0159] Thus, according to the first operation pattern, when evaluating the CondEvent of C-LTM, the UE 100 regards the filter coefficient k of the L3 filter 13 as 0, and does not apply the L3 filter 13. As a result, the CondEvent in C-LTM is evaluated using the latest measurement value from L1 without performing a weighted average (see equation (1)) of the latest measurement value from L1 and the measurement value after past L3 filtering. This makes it possible to respond to instantaneous fluctuations in the radio environment.

[0160] In the above-described operation example, an example has been described in which the UE 100 side considers the filter coefficient k = 0 of the L3 filter 13. However, as another operation example, when the gNB 200 configures the C-LTM for the UE 100 (for example, in the C-LTM config), there may be a restriction that the filter coefficient of the L3 filter 13 for the UE 100 can only be set to fc0 (k = 0). In this case, the UE 100 may assume that the gNB 200 configures fc0 (k = 0) as the filter coefficient of the L3 filter 13.

[0161] Also, instead of setting the filter coefficient of the L3 filter 13 to fc0 (k=0), in the case of C-LTM, the L3 filter 13 may be skipped (bypassed) as shown in Fig. 13. Specifically, the measurement value before being multiplied by the L3 filter 13 (the measurement value before the L3 filter 13) may be directly input to the evaluation unit 14 to evaluate the Cond Event of C-LTM.

[0162] (5.2) Second Operation Pattern When the L3 filter 13 is not applied as in the first operation pattern described above, the L1 measurement value (cell quality) is used for evaluation as is. However, since the L1 measurement value fluctuates greatly, there is a possibility that cell switching cannot be triggered appropriately. For example, there is a risk that the cell switching will fail if the timing of the cell switching is too early. On the other hand, applying the L3 filter 13 as in the conventional method stabilizes event evaluation, but as described above, there is a possibility that it will not be able to respond to instantaneous fluctuations in wireless quality.

[0163] Therefore, in the second operation pattern, the UE 100 (control unit 130 ) dynamically (adaptively) changes the filter coefficient k of the L3 filter 13 depending on the situation of the UE 100 .

[0164] For example, the UE 100 (control unit 130) may change the filter coefficient k according to a value indicating a movement speed of the UE 100. The value indicating the movement speed of the UE 100 may be the movement speed itself based on UE location information derived using a Global Navigation Satellite System (GNSS), or may be, for example, acceleration, the number of cell changes per unit time, a fading speed, or the like.

[0165] Alternatively, the UE 100 (control unit 130) may change the filter coefficient k according to a value indicating the frequency of the cell to be measured. The value indicating the frequency of the cell to be measured may be a frequency range (FR), a frequency band number, or the like.

[0166] Alternatively, the UE 100 (control unit 130) may change the filter coefficient k according to the identifier (for example, a physical cell identifier) ​​of the cell to be measured.

[0167] In the following description of the second operation pattern, an example will be described in which the change method when the UE 100 (control unit 130) changes the filter coefficient k is specified (set) by the gNB 200. However, the change method when the UE 100 (control unit 130) changes the filter coefficient k may be specified in advance in the technical specifications.

[0168] FIG. 14 is a diagram for explaining the second operation pattern of the embodiment.

[0169] First, a C-LTM CondEvent is set from the gNB 200 to the UE 100. Such a C-LTM setting further includes a change setting of the filter coefficient k of the L3 filter 13. The change setting of the filter coefficient k of the L3 filter 13 includes association information that associates a value indicating the range of the movement speed of the UE 100 with a value indicating the filter coefficient k of the L3 filter 13.

[0170] The association information may be information that associates an absolute value indicating the filter coefficient k of the L3 filter 13 with a value indicating the range of the movement speed of the UE 100 .

[0171] For example, the association information may be information such as fc11 when the speed is 0 km / h to 49 km / h, fc9 when the speed is 50 km / h to 99 km / h, fc7 when the speed is 100 km / h to 149 km / h, etc. Alternatively, using a fading speed (fading frequency), information such as fc11 when the speed is 0 Hz to 49 Hz, fc9 when the speed is 50 Hz to 99 Hz, fc7 when the speed is 100 Hz to 149 Hz, etc. The faster the moving speed of UE 100, the weaker the L3 filter 13 may be modified (i.e., modified so that the influence of past measurement values ​​is reduced) to more easily respond to instantaneous fluctuations. Alternatively, the faster the moving speed of UE 100, the stronger the L3 filter 13 may be modified (i.e., modified so that the influence of past measurement values ​​is increased).

[0172] Alternatively, the association information may be information that associates a relative value (a difference value, an offset value) indicating the filter coefficient k of the L3 filter 13 with a value indicating the range of the movement speed of the UE 100 .

[0173] For example, the association information may specify a reference speed (e.g., 40 km / h) as a standard, and may decrement fc by 1 for every 30 km / h above the reference speed. Alternatively, fc may be decremented by 1 for each state such as "high-mobility," "mid-mobility," or "low-mobility." Alternatively, a reference speed (frequency) may be specified using a fading speed (fading frequency), and fc may be decremented by 1 for every 30 Hz above the reference speed.

[0174] The association information may be information that associates an absolute value indicating the filter coefficient k of the L3 filter 13 with a value indicating the frequency of a cell to be measured by the UE 100 .

[0175] For example, the correspondence information may be information such as fc11 for FR1 and fc9 for FR2, or information such as fc13 for Band1 and fc8 for Band n257.

[0176] The association information may be information that associates a relative value indicating the filter coefficient k of the L3 filter 13 with a value indicating the frequency of a measurement target cell of the UE 100 .

[0177] For example, the association information may be information in which a reference frequency is specified (for example, 2 GHz), and fc is decreased by 1 for every reference frequency + 3 GHz.

[0178] Secondly, the UE 100 (receiving unit 110) measures the radio quality for each beam of the serving cell and the neighboring cell (candidate cell).

[0179] Third, the UE 100 (L1 filter 11) performs L1 filtering on the measurement values ​​of each beam, and the UE 100 (beam combining / selecting unit 12) derives cell quality from the measurement values ​​after L1 filtering.

[0180] Fourth, because of the C-LTM CondEvent, UE 100 (control unit 130) acquires the status of UE 100 (information on movement speed, information on cell frequency, cell identifier, etc.) and changes the filter coefficient k of L3 filter 13 according to the status. For example, UE 100 (control unit 130) determines the filter coefficient k of L3 filter 13 based on the association information and sets the determined filter coefficient k in L3 filter 13. L3 filter 13 applies L3 filter 13 to the measurement value (cell quality) after L1 filtering and outputs the measurement value after L3 filtering to evaluation unit 14.

[0181] Fifth, the UE 100 (evaluation unit 14) evaluates whether the C-LTM CondEvent is satisfied based on the measurement value after L3 filtering. Then, the UE 100 (control unit 130) executes (trigger) cell switching by C-LTM when the C-LTM CondEvent is satisfied.

[0182] (5.3) Third Operation Pattern In the third operation pattern, the UE 100 performs an event (CondEvent) evaluation using a plurality of measurement values ​​after a plurality of L3 filterings using a plurality of filter coefficients k. For example, the UE 100 performs an event evaluation using both the measurement values ​​after L1 filtering (before L3 filtering) and the measurement values ​​after L3 filtering.

[0183] FIG. 15 is a diagram for explaining the third operation pattern of the embodiment.

[0184] In the illustrated example, the UE 100 (control unit 130) includes an L3 filter 13a (first L3 filter) to which a first filter coefficient k1 is set, and an L3 filter 13b (second L3 filter) to which a second filter coefficient k2 different from the first filter coefficient k1 is set. Although two L3 filters 13 are illustrated here, three or more L3 filters 13 may be provided.

[0185] The L3 filter 13a filters the measurement value B from L1 using equation (1) and outputs the measurement value Ca after L3 filtering to the evaluation unit 14. The L3 filter 13b filters the measurement value B from L1 using equation (1) and outputs the measurement value Cb after L3 filtering to the evaluation unit 14. Although an example using two L3 filters 13a and 13b is shown here, it is also possible to use one L3 filter 13 in a time-division manner to achieve the same operation as two L3 filters. Alternatively, in cases such as when the second filter coefficient k2 is set to zero for C-LTM, a detour may be provided instead of the L3 filter 13b, and a signal path that bypasses the L3 filter 13b may be provided.

[0186] First, a C-LTM CondEvent is set from the gNB 200 to the UE 100. In such a C-LTM-configured CondEvent, multiple conditions are set for one event.

[0187] When different filter coefficients k are used, for example, an Event A3 threshold of fc0 (a filter coefficient for obtaining an instantaneous value) and an Event A3 threshold of fc9 (a filter coefficient for obtaining an average value) may be set. When these two conditions are satisfied as an AND condition or an OR condition, the UE 100 (evaluation unit 14) may determine that an event has occurred and trigger cell switching. Here, two conditions are exemplified, but three or more conditions may be combined.

[0188] When different L3 filters 13 are used, for example, an Event A3 threshold after L1 filtering (instantaneous value to which L3 filtering is not applied) and an Event A3 threshold after L3 filtering (filter coefficient for obtaining an average value) may be set. When these two conditions are satisfied as an AND condition or an OR condition, the UE 100 (evaluation unit 14) may determine that an event has occurred and trigger cell switching. Here, two conditions are exemplified, but three or more conditions may be combined.

[0189] A case where these multiple conditions are defined as one event. For example, "Event A3b" may be defined as "'Neighbor becomes offset better than SpCell, with Filter Coefficient1' AND 'Neighbor becomes offset better than SpCell, with Filter Coefficient2'", and this may be set in the UE 100. Here, a different value for "offset" may be set for each condition (two or more information elements), or may be a setting common to the conditions (only one information element). Alternatively, when the condition "Neighbor / SpCell becomes better / worse than threshold" is used, the "threshold" may be set for each condition as described above, or may be a (single) setting common to the conditions.

[0190] Secondly, the UE 100 (receiving unit 110) measures the radio quality for each beam of the serving cell and the neighboring cell (candidate cell).

[0191] Third, the UE 100 (L1 filter 11) performs L1 filtering on the measurement values ​​of each beam, and the UE 100 (beam combining / selecting unit 12) derives cell quality from the measurement values ​​after L1 filtering.

[0192] Fourth, UE100 (control unit 130) filters the measurement value B from L1 using L3 filter 13a, outputs the measurement value Ca after L3 filtering to evaluation unit 14, filters the measurement value B from L1 using L3 filter 13b, and outputs the measurement value Cb after L3 filtering to evaluation unit 14.

[0193] Fifth, the UE 100 (evaluation unit 14) evaluates whether or not the C-LTM CondEvent is satisfied based on each of the measurement values ​​Ca and Cb after L3 filtering. Then, the UE 100 (control unit 130) executes (trigger) cell switching by C-LTM when the C-LTM CondEvent is satisfied.

[0194] (6) Other Embodiments The above-described specific L3 filtering process may be performed in L2 (Layer 2, for example, MAC layer). In this case, the above-described "L3" may be read as "L2". The L2-filtered measurement value may be notified to a higher layer (for example, L3, RRC layer). The higher layer (for example, RRC layer) may obtain the L2-filtered measurement value from a lower layer (i.e., L2) and evaluate the above-described condition evaluation (for example, CondEvent A3). Alternatively, the condition evaluation may also be performed in L2. By performing the condition evaluation in L2, the L2-filtered measurement value can be handled in the same layer, thereby reducing dependency between layers.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] A program may be provided that causes a computer to execute each process performed by the UE 100 or the gNB 200. 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 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).

[0199] 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 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 hardware that executes them. 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.

[0200] 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, 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.

[0201] 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.

[0202] This application claims priority from Japanese Patent Application No. 2024-013927 (filed February 1, 2024), the entire contents of which are incorporated herein by reference.

[0203] (7) Supplementary Notes The following are additional notes regarding the features of the above-described embodiment.

[0204] Supplementary Note 1: A communication method executed by a user equipment in a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: receiving, from a network node, information indicating a radio quality condition that must be satisfied in order to perform a cell switch by the LTM; performing, in Layer 1 (L1), L1 filtering on measurement values ​​obtained by radio quality measurement; and, in Layer 3 (L3), performing specific L3 filtering different from the L3 filtering used for L3 handover on the measurement values ​​after the L1 filtering, and then evaluating whether the radio quality condition is satisfied.

[0205] Supplementary Note 2: The communication method according to Supplementary Note 1, wherein the specific L3 filtering is the L3 filtering by an L3 filter whose filter coefficients are set to zero.

[0206] Supplementary Note 3: The communication method according to Supplementary Note 2, wherein said evaluating includes regarding said filter coefficients as zero, regardless of the filter coefficients set by said network node.

[0207] Supplementary Note 4: The communication method according to Supplementary Note 2, further comprising receiving information from the network node to set the filter coefficient used in the evaluation to zero.

[0208] Supplementary Note 5: The communication method according to Supplementary Note 1, wherein the specific L3 filtering is a filtering skip that does not apply an L3 filter.

[0209] Supplementary Note 6: The communication method according to Supplementary Note 1, wherein the specific L3 filtering is the L3 filtering performed by an L3 filter whose filter coefficients are adaptively changed according to the status of the user equipment.

[0210] Supplementary Note 7: The communication method according to Supplementary Note 6, wherein said evaluating includes changing said filter coefficients in response to a value indicating a moving speed of said user device.

[0211] Supplementary Note 8: The communication method according to Supplementary Note 6 or 7, wherein said evaluating includes changing said filter coefficient according to a value indicating a frequency of a cell to be measured.

[0212] Supplementary Note 9: The communication method according to any one of Supplementary Notes 1 to 8, wherein the specific L3 filtering is a process of applying a plurality of types of L3 filtering, and performing the evaluation includes performing the evaluation using processing results of each of the plurality of types of L3 filtering.

[0213] Supplementary Note 10: The communication method according to Supplementary Note 9, wherein the plurality of types of L3 filtering include: L3 filtering by a first L3 filter to which a first filter coefficient is set; and L3 filtering by a second L3 filter to which a second filter coefficient different from the first filter coefficient is set.

[0214] Supplementary Note 11: A user equipment of a mobile communication system supporting LTM (L1 / L2 Triggered Mobility), comprising: a receiver that receives, from a network node, information indicating a radio quality condition that should be satisfied in order to perform cell switching by the LTM; and a controller that performs L1 filtering on measurement values ​​obtained by radio quality measurement in Layer 1 (L1), wherein the controller performs, in Layer 3 (L3), specific L3 filtering different from L3 filtering used for L3 handover on the measurement values ​​after the L1 filtering, and then evaluates whether the radio quality condition is satisfied.

[0215] Supplementary Note 12: A chipset comprising a circuit for executing the communication method according to any one of Supplementary Notes 1 to 10.

[0216] Supplementary Note 13: A program that causes a user device to execute the communication method according to any one of Supplementary Notes 1 to 10.

[0217] Supplementary Note 14: A mobile communication system comprising a user equipment according to Supplementary Note 11 and a network node.

[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 that supports LTM (L1 / L2 Triggered Mobility), comprising: receiving, from a network node, information indicating radio quality conditions that must be satisfied in order to perform cell switching using LTM; in Layer 1 (L1), performing L1 filtering on measurement values obtained by radio quality measurement; and in Layer 3 (L3), performing specific L3 filtering, different from the L3 filtering used for L3 handover, on the measurement values after the L1 filtering, and then evaluating whether the radio quality conditions are satisfied.

2. The communication method according to claim 1, wherein the specific L3 filtering is the L3 filtering by an L3 filter whose filter coefficients are set to zero.

3. The communication method according to claim 2, wherein said evaluating includes regarding said filter coefficients as zero regardless of the filter coefficients set by said network node.

4. The communication method according to claim 2, further comprising receiving information from the network node to set the filter coefficient used in the evaluation to zero.

5. The communication method according to claim 1, wherein the specific L3 filtering is a filtering skip that does not apply an L3 filter.

6. The communication method according to claim 1, wherein the specific L3 filtering is L3 filtering using an L3 filter whose filter coefficients are adaptively changed according to the status of the user equipment.

7. The communication method according to claim 6, wherein said evaluating step includes changing said filter coefficients in response to a value indicating a moving speed of said user device.

8. The communication method according to claim 6, wherein said evaluating includes changing said filter coefficients in accordance with a value indicating the frequency of a cell to be measured.

9. The communication method according to claim 1, wherein the specific L3 filtering is a process of applying multiple types of L3 filtering, and performing the evaluation includes performing the evaluation using the processing results of each of the multiple types of L3 filtering.

10. The communication method according to claim 9, wherein the plurality of types of L3 filtering include L3 filtering using a first L3 filter to which a first filter coefficient is set, and L3 filtering using a second L3 filter to which a second filter coefficient different from the first filter coefficient is set.

11. A user equipment of a mobile communication system that supports LTM (L1 / L2 Triggered Mobility), comprising: a receiver that receives, from a network node, information indicating radio quality conditions that must be satisfied in order to perform cell switching using the LTM; and a controller that performs L1 filtering on measurement values obtained by radio quality measurement in Layer 1 (L1), wherein the controller performs specific L3 filtering in Layer 3 (L3) on the measurement values after the L1 filtering, which is different from the L3 filtering used for L3 handover, and then evaluates whether the radio quality conditions are satisfied.

12. A chipset comprising a circuit for performing the communication method of claim 1.

13. A program that causes a user device to execute the communication method according to claim 1.

14. A mobile communication system comprising a user equipment according to claim 11 and a network node.

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