Communication method

Abstract

In this communication method that is used in a mobile communication system supporting L1 / L2-Triggered Mobility (LTM), a user device that has configuration information for conditional LTM cell switching from a cell of a network node to a candidate cell receives, from the network node, an LTM cell switching command Medium Access Control (MAC) Control Element (CE) that directs the execution of the LTM cell switching to the candidate cell, and in response to receiving the LTM cell switching command MAC CE, the user device applies a candidate cell configuration that is included in the configuration information for the conditional LTM cell switching, and executes the LTM cell switching to the candidate cell.

Description

Communication method

[0001] The present disclosure relates to a communication method used in a mobile communication system.

[0002] In 3GPP (3rd Generation Partnership Project) (registered trademark; the same applies hereinafter), the technical specifications of NR (New Radio), which is a 5th generation (5G) radio access technology, are defined. In a 3GPP mobile communication system, the serving cell switching (serving cell change) of a user equipment in the RRC (Radio Resource Control) connected state is instructed by transmitting a message (so-called handover command) of the RRC layer corresponding to layer 3 (L3) from a network node to the user equipment.

[0003] On the other hand, in 3GPP Release 18 (3GPP Release 18), the technical specifications of LTM (L1 / L2-Triggered Mobility), which is a new procedure for serving cell switching, are formulated. LTM is a procedure in which a network node receives a layer 1 (L1) measurement report from a user equipment, and based on this, the network node changes the serving cell of the user equipment by a cell switching command signaled to the user equipment by a MAC (Medium Access Control) CE (Control Element).

[0004] 3GPP Technical Specification "3GPP TS 38.300 V18.4.0"

[0005] The present disclosure provides a technology for improving LTM.

[0006] A communication method according to a first aspect of this disclosure is a communication method used in a mobile communication system that supports LTM (L1 / L2-Triggered Mobility), comprising: a user device having setting information for conditional LTM cell switching from a network node cell to a candidate cell receiving an LTM cell switching command MAC (Medium Access Control) CE (Control Element) from the network node instructing the execution of LTM cell switching to the candidate cell; and the user device, in response to receiving the LTM cell switching command MAC CE, applying the candidate cell setting included in the setting information for conditional LTM cell switching and executing the LTM cell switching to the candidate cell.

[0007] A second aspect of the present disclosure is a communication method for use in a mobile communication system that supports LTM (L1 / L2-Triggered Mobility), comprising: a user device having set a plurality of execution conditions associated with a plurality of candidate cells, evaluating whether any of the plurality of execution conditions are met, wherein each of the plurality of execution conditions indicates a condition for performing a switch from the current serving cell; and, in response to the fulfillment of one of the plurality of execution conditions and the fulfillment of another of the plurality of execution conditions, selecting a candidate cell corresponding to the one execution condition and one of the other execution conditions based on a predetermined priority order or a setting from the network node; and switching from the current serving cell to the selected candidate cell.

[0008] This figure shows an example configuration of a mobile communication system according to an embodiment. This figure shows an example configuration of a UE (User Equipment) according to an embodiment. This figure shows an example configuration of a gNB (Network Node) according to an embodiment. This figure shows the configuration of the protocol stack of the wireless interface of the user plane that handles data. This figure shows the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals). This figure shows an example of a cell switching procedure by LTM in an intraCU (i.e., within the same gNB) according to an embodiment. This figure is for explaining LTM cell switching of an interCU according to an embodiment. This figure shows the operation of a UE according to the first embodiment. This figure shows Example 1 of the first embodiment. This figure shows Example 2 of the first embodiment. This figure shows Example 1 of the second embodiment. This figure shows Example 2 of the second embodiment. This figure shows Example 3 of the second embodiment. This figure shows the operation of a UE according to the third embodiment. This figure shows an example of priority information related to Scenario 1 of the third embodiment. This figure shows an embodiment of the third embodiment. This figure shows two scenarios in which C-LTM and LTM coexist. This figure shows a scenario in which multiple execution conditions are triggered. This figure shows an example configuration of an Information Element for LTM settings according to an embodiment.

[0009] A mobile communication system according to an embodiment will be described with reference to the drawings. In the drawings, identical or similar parts are denoted by the same or similar reference numerals.

[0010] (1) The mobile communication system configuration diagram 1 is a diagram showing an example of the configuration of the mobile communication system 1 according to the embodiment. The mobile communication system 1 conforms to the 5th Generation System (5GS) of the 3GPP standard. In the following explanation, 5GS will be used as an example, but the mobile communication system may also have an LTE (Long Term Evolution) system applied to it at least partially. The mobile communication system may also have a 6th Generation (6G) system applied to it at least partially.

[0011] The mobile communication system 1 comprises User Equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereinafter, NG-RAN 10 may be simply referred to as RAN 10, and 5GC 20 may be simply referred to as core network (CN) 20. RAN 10 and CN 20 constitute the network 5 of the mobile communication system 1.

[0012] UE100 is a mobile wireless communication device. UE100 can be any device used by a user. For example, UE100 can 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 attached to a sensor, a vehicle or a device attached to a vehicle (Vehicle UE), or an aircraft or a device attached to an aircraft (Aerial UE). The link from UE100 to network 5 in the transmission direction is called the uplink (UL), and the link from network 5 to UE100 in the transmission direction is called the downlink (DL).

[0013] NG-RAN10 includes a base station (referred to as "gNB" in the 5G system) 200, which is a type of network node. The gNBs 200 are interconnected via the Xn interface, which is an inter-base station interface. The gNBs 200 manage one or more cells. The gNBs 200 perform wireless communication with UEs 100 that have established a connection with their own cell. The gNBs 200 have radio resource management (RRM) functions, user data (hereinafter simply referred to as "data") routing functions, measurement and control functions for mobility control and scheduling, etc. "Cell" is used as a term to indicate the smallest unit of a wireless communication area. "Cell" is also used as a term to indicate a function or resource that performs wireless communication with a UE 100. "Cell" is identified by a cell identifier (cell ID). One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0014] Furthermore, gNBs can also connect to the Evolved Packet Core (EPC), which is the core network of LTE. LTE base stations can also connect to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0015] 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 UE100. The AMF manages the mobility of the UE100 by communicating with it using NAS (Non-Access Stratum) signaling. The UPF controls data transfer. The AMF and UPF are connected to the gNB200 via the NG interface, which is the base station-core network interface.

[0016] Figure 2 shows an example configuration of UE100 (user device) according to an embodiment. UE100 includes 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 gNB200.

[0017] 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 the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130.

[0018] The transmitting unit 120 performs various types of transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 130 into a wireless signal and transmits it from the antenna.

[0019] The control unit 130 performs various control and processing operations in the UE 100. Such processing includes processing in each layer described later. The operation of the UE 100 described above and later may also be controlled by the control unit 130. 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 for processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processing operations.

[0020] Figure 3 shows an example configuration of a gNB200 (network node) according to an embodiment. The gNB200 includes a transmitting unit 210, a receiving unit 220, a control unit 230, and a network communication unit 240. The transmitting unit 210 and the receiving unit 220 constitute a wireless communication unit 250 that performs wireless communication with the UE100. The network communication unit 240 includes a transmitting unit 241 that performs transmission and a receiving unit 242 that performs reception.

[0021] The transmitting unit 210 performs various types of transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a wireless signal and transmits it from the antenna.

[0022] 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 the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 230.

[0023] The control unit 230 performs various control and processing operations in the gNB 200. Such processing includes processing in each layer described later. The operation of the gNB 200 described above and later may also be controlled by 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 for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, decoding, etc. of the baseband signal. The CPU executes programs stored in memory and performs various processing operations.

[0024] The network communication unit 240 is connected to an adjacent base station via the Xn interface, which is an inter-base station interface. The network communication unit 240 is connected to the AMF / UPF 300 via the NG interface, which is an inter-base station-core network interface. The gNB 200 may consist of a central unit (CU) and a distributed unit (DU) (i.e., functionally divided), and the two units may be connected by the F1 interface, which is a front-haul interface. In this case, each of the gNB-DU and gNB-CU may have a functional block configuration similar to the one shown in Figure 3. However, the gNB-CU is assumed not to have a wireless communication unit 250.

[0025] Figure 4 shows the configuration of the protocol stack for the user plane's wireless interface that handles data.

[0026] The user plane radio interface protocol consists of a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0027] 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 the physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a Radio Network Temporary Identifier (RNTI) and acquires the successfully decoded DCI as the DCI addressed to its own UE. The DCI transmitted from gNB200 has a CRC (Cyclic Redundancy Check) parity bit added, which is scrambled by the RNTI.

[0028] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ: Hybrid Automatic Repeat reQuest), and random access procedures. Data and control information are transmitted between the MAC layer of UE100 and the MAC layer of gNB200 via the transport channel. The MAC layer of gNB200 includes a scheduler. The scheduler determines the transport format for the up and down links (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to UE100.

[0029] 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 UE100 and the RLC layer of gNB200 via a logical channel.

[0030] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0031] The SDAP layer maps IP flows, which are the units under which the core network performs QoS (Quality of Service) control, to wireless bearers, which are the units under which the AS (Access Stratum) performs QoS control. Note that if the RAN is connected to the EPC, the SDAP is not required.

[0032] Figure 5 shows the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals).

[0033] The control plane's wireless interface protocol stack includes an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer, instead of the SDAP layer shown in Figure 4.

[0034] RRC signaling for various settings is transmitted between the RRC layer of the UE100 and the RRC layer of the gNB200. The RRC layer controls the logical channel, transport channel, and physical channel in response to the establishment, re-establishment, and release of the radio bearer. If there is a connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC connected state. If there is no connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC idle state. If the connection between the RRC of the UE100 and the RRC of the gNB200 is suspended, the UE100 is in the RRC inactive state.

[0035] The NAS layer (also simply referred to as "NAS"), located above the RRC layer, handles session management and mobility management, among other things. NAS signaling is transmitted between the NAS layer of the UE100 and the NAS layer of the AMF300A. The UE100 also has an application layer in addition to the wireless interface protocol. Furthermore, the layer below the NAS layer is called the AS layer (also simply referred to as "AS").

[0036] (2) Overview of LTM The mobile communication system 1 according to the embodiment supports LTM (L1 / L2-Triggered Mobility).

[0037] In a typical handover procedure, the serving cell switch is triggered by signaling at the higher layer, L3, specifically the RRC layer. This type of typical handover is also called an L3 handover. In an L3 handover, an RRC message, specifically an L3 Measurement Report message, is sent from UE100 to gNB200. Based on this Measurement Report message, gNB200 decides to hand over UE100 and instructs the cell switch by sending a handover command (specifically, an RRC Reconfiguration message) from gNB200 to UE100.

[0038] On the other hand, LTM is a technique for reducing mobility delays (specifically, serving cell switching delays) compared to general handover procedures by triggering serving cell switching through signaling at the lower layers, Layer 1 (L1) and / or Layer 2 (L2). In LTM, the gNB200 receives an L1 measurement report from the UE100, and based on this, the gNB200 instructs the UE100 to switch serving cells by signaling a cell switching command via MAC CE.

[0039] Specifically, in LTM, firstly, gNB200 prepares an LTM candidate cell setting for the candidate cell to be switched to, and provides the LTM candidate cell setting to UE100 via RRC signaling.

[0040] Secondly, UE100 performs synchronization with LTM candidate cells through early sync.

[0041] Thirdly, the gNB 200 receives the L1 measurement report from the UE 100, determines the 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 means of a MAC CE. The serving cell switch trigger is transmitted by a MAC CE including at least a candidate setting index (setting ID) together with a beam indicator.

[0042] Fourthly, the UE 100 switches the serving cell in response to the cell switch command MAC CE from the gNB 200 (source cell).

[0043] In this way, by selecting the LTM candidate cell setting as the target setting by the gNB 200, the serving cell switch is triggered. The LTM candidate cell setting can be added, changed, and released by the gNB 200 via RRC signaling.

[0044] The following principles apply to LTM.

[0045] - Each LTM candidate cell setting can be provided as a differential setting (delta setting) with respect to a reference setting used to form a complete LTM candidate cell setting.

[0046] - When a complete LTM candidate cell setting is applied, the current UE setting is replaced at the time of serving cell switch. Replacement is performed in the reconfiguration procedure, but the MAC, RLC, or PDCP layer is not necessarily reset.

[0047] - The user plane continues without reset if set by RRC signaling for the purpose of avoiding additional delay in data recovery.

[0048] - In LTM, the security is not updated.

[0049] - Subsequent LTM (Subsequent LTM) between subsequent LTM candidate cell settings can be executed without RRC reconfiguration. That is, the UE 100 does not release other LTM candidate cell settings after LTM is triggered.

[0050] (2.1) IntraCU LTM Figure 6 shows an example of a cell switching procedure using LTM in an intraCU (i.e., within the same gNB200). In the illustrated example, UE100 performs an LTM-based serving cell switch (i.e., LTM cell switch) from the first cell to the second cell of the gNB200.

[0051] Here, the first cell and the second cell may be formed by different TRPs (Transmission and Reception Points). In the following description of the embodiments, the second cell will also be referred to as the "LTM candidate cell (or candidate cell)" until the LTM decides to switch the serving cell, and the second cell will also be referred to as the "target cell" after the LTM decides to switch the serving cell. The first cell will also be referred to as the "source cell" or the "(current) serving cell".

[0052] In step S1, UE100 is in an RRC connected state in the cell (first cell) of gNB200.

[0053] In step S2, UE100 sends a Measurement Report message, which is an RRC message, to gNB200 (first cell). The measurement report containing the L3 measurement result is also called the L3 measurement report (L3 MR).

[0054] In step S3, gNB200 decides to use LTM based on the L3 measurement report and begins preparing LTM candidate cells.

[0055] In step S4, gNB200 (first cell) sends an LTM configuration, including the LTM Candidate Configuration / LTM Candidate for one or more LTM candidate cells, to UE100 in an RRC message, specifically an RRC Reconfiguration message. The LTM candidate configuration may include a random access channel (RACH) configuration used for sending RA preambles to the corresponding LTM candidate cells, such as a conflict-free random access (CFRA) configuration. Such a RACH configuration may be referred to as an EarlyUlSyncConfig. CFRA is a random access procedure in which UE100 is allocated dedicated RACH resources (e.g., dedicated preamble sequences and / or dedicated time and frequency resources) and no RACH conflicts occur between UE100s.

[0056] In step S5, UE100 saves the LTM settings (LTM candidate cell settings) and sends an RRC Reconfiguration Complete message to gNB200 (first cell).

[0057] In step S6, UE100 may perform synchronization with the LTM candidate cell (second cell) before receiving the cell switching command MAC CE from the first cell. Such synchronization may be called early sync. Here, UE100 may perform downlink synchronization (DL synchronization) with the LTM candidate cell and then perform early timing advance (TA) acquisition (i.e., UL early sync) with the LTM candidate cell requested by gNB200 (serving cell). This is done by a CFRA triggered by a PDCCH order from the first cell. Note that if DCI Format 1_0 is used and all "Frequency domain resource assignment" fields within the DCI are set to "1", the DCI is treated as a PDCCH order. Furthermore, if EarlyUlSyncConfig is set on UE100, the PDCCH order may include a cell indicator that shows the corresponding RACH transmission cell, i.e., which LTM candidate cell UE100 should send a random access preamble (RA preamble) to.

[0058] UE100 transmits an RA preamble to the designated LTM candidate cell (second cell). To minimize the interruption of serving cell communication by CFRA to the LTM candidate cell, during early synchronization, UE100 does not receive a Random Access Response (RAR) from the LTM candidate cell for the purpose of obtaining the TA value. The TA value of the LTM candidate cell (target cell) is indicated by the cell switching command MAC CE in step S9. The TA value is used to adjust the uplink transmission timing of UE100.

[0059] In step S7, UE100 performs a Layer 1 (L1) measurement on the configured LTM candidate cell and transmits a measurement report (also referred to as "L1 measurement report (L1 MR)") including the L1 measurement result to gNB200 (first cell). The L1 measurement result may be, for example, L1-RSRP and / or L1-SINR.

[0060] In step S8, the gNB200 decides to switch the serving cell to the target cell (second cell).

[0061] In step S9, the gNB200 (first cell) sends a cell switching command MAC CE (also referred to as the "LTM cell switching command MAC CE") to the UE100, which includes the candidate setting index (setting ID) of the target cell. The cell switching command MAC CE may include the TA value obtained by UL early synchronization (i.e., the TA value derived based on the RA preamble).

[0062] In step S10, UE100 switches to the settings for the target cell (second cell). Specifically, UE100 detaches from the first cell and applies the settings for the target cell (second cell).

[0063] In step S11, if the serving cell switch requires the execution of a random access procedure (for example, if the cell switch command MAC CE does not contain a valid TA value), UE 100 executes a random access procedure on the target cell (RACH-based LTM cell switch). However, if UE 100 does not need to obtain the TA of the target cell during the serving cell switch (for example, if the cell switch command MAC CE contains a valid TA value), the random access procedure can be skipped (RACH-less LTM cell switch).

[0064] In step S12, UE100 indicates that the serving cell switch to the target cell has been successfully completed by sending, for example, an RRC Reconfiguration Complete message to the target cell (second cell). Subsequently, UE100 may perform steps S6 to S12 multiple times for subsequent LTM serving cell switches based on the settings provided in step S4.

[0065] (2.2) InterCU LTM The LTM in 3GPP Release 18 supports intraCU cell switching, but does not support interCU cell switching. In 3GPP Release 19, an extension to the LTM specification is being considered to support interCU cell switching.

[0066] Figure 7 is a diagram illustrating the LTM cell switching of the interCU according to the embodiment.

[0067] In the illustrated example, gNB200a has gNB-CU201a and gNB-DU202a. gNB-CU201a and gNB-DU202a are interconnected via the F1 interface. gNB200b has gNB-CU201b and gNB-DU202b. gNB-CU201b and gNB-DU202b are interconnected via the F1 interface. Also, gNB-CU201a and gNB-CU201b are interconnected via the Xn interface. gNB-DU202a manages one or more cells a, and gNB-DU202b manages one or more cells b. UE100 is in an RRC connected state in cell a and is performing lower-layer communication with gNB-DU202a and upper-layer communication with gNB-CU201a. In this scenario, gNB200a performs an LTM cell switchover to switch the serving cell of UE100 from cell a to cell b.

[0068] In the InterCU's LTM cell switching, the LTM cell switching may be performed using a procedure such as the following:

[0069] 1) UE100 performs L1 measurement on the configured LTM candidate cell and sends an L1 measurement report (L1 MR) including the L1 measurement result to gNB-DU202a (cell a).

[0070] 2) Based on the L1 measurement results from UE100, gNB-DU202a decides to switch to LTM cell b.

[0071] 3) gNB-DU202a sends a cell switching command MAC CE to UE100 to instruct the LTM cell to switch to cell b, and UE100 performs the cell switching from cell a to cell b upon receiving the cell switching command MAC CE.

[0072] (2.3) C-LTM In 3GPP Release 19, the introduction of a Conditional LTM (C-LTM) cell switching procedure is being considered. In C-LTM, the gNB200 includes information indicating the conditions for performing LTM cell switching (e.g., radio quality conditions) for each LTM candidate cell in the RRC Reconfiguration message, for example in step S4 of Figure 6.

[0073] Instead of receiving the LTM cell switching command MAC CE from the gNB200, the UE100 performs LTM cell switching for LTM candidate cells that meet the set execution conditions (wireless quality conditions). This eliminates the need to send and receive L1 measurement reports and cell switching commands MAC CE, enabling faster LTM cell switching. The execution conditions for LTM cell switching may also be called trigger conditions.

[0074] The execution conditions (trigger conditions) set from gNB200 to UE100 include L1 measurement-based execution conditions (also called "L1 trigger conditions") and L3 measurement-based execution conditions (also called "L3 trigger conditions"). The trigger conditions are associated with the LTM candidate cell settings. In other words, in C-LTM, a trigger condition is set for each LTM candidate cell.

[0075] For LTM candidate cells with set L1 trigger conditions, UE100 evaluates whether the L1 trigger condition has been met (also referred to as "L1 event evaluation") based on the L1 measurement result, which is the measurement result of L1. When the L1 trigger condition is met, it is also referred to as "an L1 event has occurred". The L1 event evaluation is performed by the MAC layer of UE100. For example, the L1 trigger conditions set in UE100 are any of the following, and the L1 event evaluation is performed based on the beam intrinsic quality of the serving cell and the LTM candidate cell: - The serving cell's beam deteriorates below an absolute threshold; - The LTM candidate cell's beam is better than the serving cell's beam by an offset amount; - The LTM candidate cell's beam is better than an absolute threshold; - The serving cell's beam deteriorates below absolute threshold 1, and the LTM candidate cell's beam is better than another absolute threshold 2.

[0076] On the other hand, for LTM candidate cells with L3 trigger conditions set, UE100 evaluates whether the L3 trigger conditions have been met (also referred to as "L3 event evaluation") based on the L3 measurement results, which are the measurement results of L3. The meeting of the L3 trigger conditions is also referred to as "an L3 event has occurred." The L3 event evaluation is performed by the RRC layer of UE100. For example, the L3 trigger conditions set in UE100 are existing CondEventA3 or CondEventA5, and the L3 event evaluation is performed based on the cell-specific quality of the serving cell and the LTM candidate cell, respectively.

[0077] Furthermore, C-LTM is considering introducing a new MAC CE to notify UE100 of the TA value. The first cell (source cell, serving cell) sends a new MAC CE containing the TA value of each LTM candidate cell to UE100. UE100 applies the TA value when switching to an LTM candidate cell in C-LTM. UE100 maintains the TA value of the LTM candidate cell using a newly introduced timer. UE100 may discard the TA value when the timer expires.

[0078] Furthermore, C-LTM is not limited to intraCUs, but may also be applicable to interCUs.

[0079] (3) First Embodiment Based on the above-described configuration and operation, the first embodiment will be described.

[0080] As described above, a C-LTM can be set in UE100 by gNB200. When a UE100 with a C-LTM is set, it is common for it to spontaneously perform an LTM cell switch to the LTM candidate cell that satisfies the set execution conditions (trigger conditions) when those conditions are met.

[0081] On the other hand, it is also conceivable that gNB200 can send the LTM cell switching command MAC CE to UE100, which has C-LTM configured. This would make it possible for gNB200 to force UE100 to perform an LTM cell switch, even after C-LTM has been configured on UE100.

[0082] However, in the current technical specifications, the LTM cell switching command MAC CE targets LTM candidate cell settings within the LTM settings, but not LTM candidate cell settings within the C-LTM settings. Here, "LTM settings" refers to the settings information for a regular LTM (not C-LTM), and "C-LTM settings" refers to the settings information for C-LTM.

[0083] Therefore, there is a problem in that it is not possible to trigger LTM cell switching using the LTM cell switching command MAC CE for UE100 units that have C-LTM configured.

[0084] For example, consider a case where the LTM candidate cell setting specified in the LTM cell switching command MAC CE is "LTM Candidate ID = 1". In this case, UE100 can apply the LTM candidate cell setting "LTM Candidate ID = 1" within its own LTM settings, but currently it cannot apply the LTM candidate cell setting "LTM Candidate ID = 1" within its own C-LTM settings.

[0085] Therefore, there is room for improvement in effectively utilizing the C-LTM settings configured in UE100. For example, consider a case where the LTM settings of UE100 include LTM candidate cell settings for three LTM candidate cells, and the C-LTM settings of UE100 include LTM candidate cell settings for five LTM candidate cells. In this case, gNB200 can specify any of the three LTM candidate cells with the LTM cell switching command MAC CE, but it cannot specify any of the five LTM candidate cells with the LTM cell switching command MAC CE.

[0086] In this embodiment, we will describe an operation that solves these problems.

[0087] (3.1) UE Operation Diagram 8 shows the operation of UE 100 according to the first embodiment.

[0088] In step S101, UE100, which has setting information (C-LTM setting) for C-LTM cell switching from gNB200's cells (source cell, serving cell) to LTM candidate cells, receives an LTM cell switching command MAC CE from gNB200 instructing it to execute LTM cell switching to the LTM candidate cells. Here, gNB200 instructs UE100 to execute LTM on the LTM candidate cells that have the C-LTM setting enabled, using the LTM cell switching command MAC CE.

[0089] In step S102, upon receiving the LTM cell switching command MAC CE, UE100 applies the LTM candidate cell settings included in the C-LTM cell switching setting information (C-LTM settings) and performs LTM cell switching to the LTM candidate cell.

[0090] Thus, in this embodiment, the LTM cell switching command MAC CE can trigger an LTM cell switching operation targeting the LTM candidate cell settings within the C-LTM settings. Therefore, even after C-LTM has been set to UE100, it becomes possible to force UE100 to perform an LTM cell switching operation under the guidance of gNB200.

[0091] In other words, the LTM cell switching command MAC CE can apply LTM candidate cells (specifically, LTM candidate cell settings) within the C-LTM settings. Therefore, the gNB200 can select an LTM candidate cell from among the LTM candidate cells of LTM and the LTM candidate cells of C-LTM, thus increasing the number of options. Furthermore, if the gNB200 sets C-LTM to UE100, it will be able to execute both C-LTM and LTM.

[0092] In this embodiment, the C-LTM setting includes information indicating execution conditions (trigger conditions) related to the radio state that must be satisfied in order to perform a C-LTM cell switch to an LTM candidate cell. That is, the UE 100 is set with a C-LTM setting that includes information indicating the execution conditions (trigger conditions). Even if the set execution conditions (trigger conditions) are not satisfied, the UE 100 applies the LTM candidate cell setting in the C-LTM setting and performs an LTM cell switch to an LTM candidate cell in response to the reception of the LTM cell switch command MAC CE.

[0093] This allows the UE100 to perform an LTM cell switch using the LTM candidate cell settings within the C-LTM settings, even if the execution conditions (trigger conditions) for C-LTM are not met, via the LTM cell switch command MAC CE.

[0094] (3.2) Examples of the First Embodiment A specific example of the signaling according to this embodiment (specifically, the signaling of the downlink) will be described.

[0095] (3.2.1) Example 1 of the First Embodiment Figure 9 shows Example 1 of the First Embodiment. The basic operation is the same as in Figure 6, and here we will explain focusing on steps S4 and S10 in Figure 6.

[0096] In step S4, gNB200 sends an RRC Reconfiguration message containing the LTM configuration to UE100. UE100 receives the RRC Reconfiguration message and stores the LTM configuration.

[0097] In this embodiment, each LTM candidate cell setting (LTM Candidate) in the LTM setting and each LTM candidate cell setting (LTM Candidate) in the C-LTM setting are merged into a single list (LTM Candidate ToAddModList), and this list is included in the LTM setting (LTM Config).

[0098] Furthermore, the LTM setting includes a list (cltm-ServingCellExecutionConditions) that shows the execution conditions (trigger conditions) for each of the one or more LTM candidate cell settings (LTM Candidates). The list includes as entries a set of LTM Candidate ID and execution condition, where the execution condition is an L1 trigger condition (L1-Conditions) and / or an L3 trigger condition (L3-Conditions).

[0099] In this embodiment, UE100 identifies LTM candidate cells having an LTM Candidate ID in the list of execution conditions (cltm-ServingCellExecutionConditions) as C-LTM candidate cells. The execution conditions (cltm-ExecutionConditions) in the LTM candidate cell settings (LTM Candidate) are used by UE100 to perform subsequent LTM cell switching after switching to the corresponding LTM candidate cell.

[0100] In this RRC signaling configuration, each LTM candidate cell setting (LTM Candidate) in the LTM Candidate ToAddModList is assigned a unique setting ID (LTM Candidate ID) that does not overlap with others, for example, as a sequential number. Therefore, the setting IDs (LTM Candidate IDs) do not overlap between each LTM candidate cell setting (LTM Candidate) in the LTM setting and each LTM candidate cell setting (LTM Candidate) in the C-LTM setting.

[0101] In step S9, gNB200 sends an LTM cell switching command MAC CE to UE100, which includes the setting ID (LTM Candidate ID) corresponding to the target cell it has determined. In this embodiment, each LTM candidate cell setting (LTM Candidate) is assigned a unique setting ID, so UE100 can uniquely identify the LTM candidate cell setting (LTM Candidate) specified in the LTM cell switching command MAC CE.

[0102] Upon receiving the LTM cell switching command MAC CE, UE100 identifies the LTM candidate cell configuration (LTM Candidate) corresponding to the configuration ID (LTM Candidate ID) in the LTM cell switching command MAC CE, and applies the information within the identified LTM candidate cell configuration, such as the RRC Reconfiguration in the LTM Candidate Config, to perform the LTM cell switching.

[0103] (3.2.2) Example 2 of the First Embodiment Figure 10 shows Example 2 of the First Embodiment. The basic operation is the same as in Figure 6, and here we will explain focusing on steps S4 and S10 in Figure 6.

[0104] In step S4, gNB200 sends an RRC Reconfiguration message containing the LTM configuration to UE100. UE100 receives the RRC Reconfiguration message and stores the LTM configuration.

[0105] In this embodiment, the LTM configuration and the C-LTM configuration are defined as separate information elements (IEs). In the illustrated example, the RRC Reconfiguration message includes the LTM configuration and the C-LTM configuration as separate IEs.

[0106] Here, the LTM Config includes a list of LTM Candidates for each LTM candidate cell configuration (LTM Candidate ToAddModList) for a typical LTM. In this list, each configuration is assigned a unique, non-overlapping configuration ID (LTM Candidate ID), for example, as a sequential number.

[0107] Furthermore, the C-LTM configuration (C-LTM Config) includes a list of LTM candidate cell configurations (LTM Candidate ToAddModList) for C-LTM. In this list, each configuration is assigned a unique, non-overlapping configuration ID (LTM Candidate ID), for example, as a sequential number.

[0108] However, in this embodiment, duplication of configuration IDs (LTM Candidate IDs) may occur between the list for regular LTMs (LTM Candidate ToAddModList) and the list for C-LTMs (LTM Candidate ToAddModList).

[0109] In step S9, gNB200 sends an LTM cell switching command MAC CE to UE100, which includes a setting ID (LTM Candidate ID) corresponding to the target cell it has determined. In this embodiment, since duplicate setting IDs (LTM Candidate IDs) may occur, there is a problem that UE100 cannot identify whether the LTM candidate cell setting specified in the LTM cell switching command MAC CE is for a normal LTM or for a C-LTM.

[0110] However, if UE100 has a C-LTM setting (C-LTM Config) but does not have an LTM setting (LTM Config), then no duplication of setting IDs (LTM Candidate IDs) occurs. In this case, UE100 applies the C-LTM setting. That is, if LTM cell switching setting information is not set in UE100 as an IE separate from the C-LTM setting, UE100 will apply the LTM candidate cell setting included in the C-LTM setting in response to the reception of the LTM cell switching command MAC CE and perform the LTM cell switching to the LTM candidate cell. For example, if the LTM cell switching command MAC CE is "LTM Candidate ID = 1", UE100 will apply the LTM candidate cell setting (LTM Candidate) with "LTM Candidate ID = 1" in the C-LTM setting it has stored.

[0111] In this embodiment, the form of the LTM cell switching command MAC CE may differ depending on whether the target is an LTM setting or a C-LTM setting. This allows UE 100 to identify whether the LTM cell switching command MAC CE targets an LTM setting or a C-LTM setting based on the form of the LTM cell switching command MAC CE.

[0112] As a first example of how the LTM cell switching command MAC CE may be modified, the LTM cell switching command MAC CE may include an indicator that the C-LTM setting should be applied. In response to the received LTM cell switching command MAC CE containing the indicator, UE 100 applies the LTM candidate cell setting included in the C-LTM setting and performs an LTM cell switch to the LTM candidate cell.

[0113] For example, if gNB200 wants to specify an LTM candidate cell setting within the C-LTM settings, it sets the Reserved bit in the LTM cell switching command MAC CE to "1" and sends it to UE100. Here, Reserved bit = "1" corresponds to an indicator that the C-LTM settings should be applied. Upon receiving the LTM cell switching command MAC CE containing Reserved bit = "1", UE100 determines that the setting ID (LTM Candidate ID) in the LTM cell switching command MAC CE indicates an LTM candidate cell setting within the C-LTM settings.

[0114] On the other hand, if gNB200 wants to specify an LTM candidate cell setting within the LTM settings, it sends the LTM cell switching command MAC CE to UE100 without including the reserved bit = "1". Upon receiving the LTM cell switching command MAC CE without the reserved bit = "1", UE100 determines that the setting ID (LTM Candidate ID) within the LTM cell switching command MAC CE indicates an LTM candidate cell setting within the LTM settings.

[0115] Alternatively, as a second example of how the LTM cell switching command MAC CE may differ in its form, the LTM cell switching command MAC CE includes a specific logical channel identifier (LCID) indicating that a C-LTM setting is to be applied. In response to the inclusion of this specific LCID in the LTM cell switching command MAC CE, UE 100 applies the LTM candidate cell setting included in the C-LTM setting and performs an LTM cell switch to the LTM candidate cell. The MAC CE is accompanied by a subheader, which has a field where the LCID is stored. The type of MAC CE can be identified by the LCID in this field. Therefore, a dedicated LCID is assigned to the LTM cell switching command MAC CE that targets the C-LTM setting.

[0116] For example, if gNB200 wants to specify an LTM candidate cell setting within the C-LTM settings, it assigns a specific LCID, different from the conventional LCID, to the LTM cell switching command MAC CE and sends it to UE100. Upon receiving the LTM cell switching command MAC CE with the specific LCID, UE100 determines that the setting ID (LTM Candidate ID) within the LTM cell switching command MAC CE indicates an LTM candidate cell setting within the C-LTM settings.

[0117] On the other hand, if gNB200 wants to specify an LTM candidate cell setting within the LTM settings, it sends an LTM cell switching command MAC CE with a conventional LCID to UE100. Upon receiving the LTM cell switching command MAC CE with a conventional LCID, UE100 determines that the setting ID (LTM Candidate ID) within the LTM cell switching command MAC CE indicates an LTM candidate cell setting within the LTM settings.

[0118] (4) Second Embodiment The second embodiment will primarily be described as differing from the first embodiment described above. The second embodiment may be implemented in combination with the first embodiment described above. The second embodiment may be implemented independently of the first embodiment described above.

[0119] As mentioned above, the UE100 can be configured with both LTM and C-LTM settings. Therefore, it is necessary to consider the conflict between LTM cell switching using the LTM setting and LTM cell switching using the C-LTM setting.

[0120] For example, UE100 may receive the LTM cell switching command MAC CE and the execution conditions (trigger conditions) in the C-LTM settings may be met. In this embodiment, the behavior when cell switching by LTM and cell switching by C-LTM are triggered at the same time will be described. Here, "at the same time" means simultaneously or within a certain time range.

[0121] In this embodiment, when cell switching by LTM and cell switching by C-LTM are triggered at the same time, UE100 operates to prioritize cell switching by LTM over cell switching by C-LTM. For example, when UE100 receives the LTM cell switching command MAC CE, it applies the LTM candidate cell setting of the corresponding LTM Candidate ID in the LTM setting.

[0122] Cell switching via LTM is triggered by the LTM cell switching command MAC CE from the gNB200, and therefore reflects the latest network conditions. For this reason, it is desirable to prioritize cell switching via LTM over cell switching via C-LTM. Specifically, the C-LTM setting includes information indicating the execution conditions regarding the radio state that must be met in order to perform C-LTM cell switching to an LTM candidate cell. When the execution conditions are met and the LTM cell switching command MAC CE is received, the UE100 prioritizes the LTM cell switching command MAC CE and performs LTM cell switching according to the LTM cell switching command MAC CE.

[0123] (4.1) Example 1 of the second embodiment Figure 11 shows Example 1 of the second embodiment. In this embodiment, we assume that UE100, which has both LTM setting and C-LTM setting, receives the LTM cell switching command MAC CE from gNB200 (first cell).

[0124] In this embodiment, the MAC layer of UE100, upon receiving the LTM cell switching command MAC CE (step S201), notifies the RRC layer of UE100 that it has received the LTM cell switching command MAC CE (step S203). For example, when UE100 receives the LTM cell switching command MAC CE, the MAC layer may notify the RRC layer that it has received the LTM cell switching command MAC CE. This notification may include information about the target cell, i.e., which LTM candidate cell to execute the LTM on.

[0125] The C-LTM setting configured in UE100 may include information indicating L1 trigger conditions as execution conditions for the radio state that must be satisfied in order to perform a C-LTM cell switch to an LTM candidate cell. In this case, the MAC layer of UE100, which performs L1 event evaluation based on L1 measurement results, may stop the L1 event evaluation based on L1 measurement results in response to the reception of the LTM cell switch command MAC CE (step S202). That is, when UE100 receives the LTM cell switch command MAC CE, it stops the L1 event evaluation at the MAC layer. By stopping the L1 event evaluation at the MAC layer, it prevents L1 events from occurring after the reception of the LTM cell switch command MAC CE.

[0126] The C-LTM setting configured on UE100 may include information indicating L3 trigger conditions as execution conditions for the radio state that must be satisfied in order to perform a C-LTM cell switch to an LTM candidate cell. In this case, the RRC layer of UE100 may stop evaluating L3 events based on L3 measurement results in response to a reception notification from the MAC layer (step S203) (step S204). That is, when the RRC layer of UE100 receives a reception notification for the LTM cell switch command MAC CE from MAC, it stops evaluating events at the RRC layer. By stopping the L3 event evaluation at the RRC layer, it prevents L3 events from occurring after the reception of the LTM cell switch command MAC CE.

[0127] The RRC layer of UE100 may instruct the MAC layer to stop evaluating L1 events at the MAC layer (step S205). In this case, the MAC layer of UE100 may stop evaluating L1 events at the MAC layer in response to the instruction (step S206).

[0128] Then, the RRC layer of UE100, in response to a notification received from the MAC layer (step S203), controls the MAC layer to perform LTM cell switching based on the LTM cell switching command MAC CE (step S207). As a result, LTM cell switching based on the LTM cell switching command MAC CE is executed.

[0129] (4.2) Example 2 of the Second Embodiment Figure 12 shows Example 2 of the Second Embodiment. In this embodiment, we assume that an L1 event occurs in C-LTM in UE100 which has both LTM setting and C-LTM setting. The differences from Example 1 of the Second Embodiment will be mainly explained.

[0130] When an L1 event occurs (step S301), UE100 notifies the RRC layer from the MAC layer (step S302). This notification may include information about the target cell, i.e., which LTM candidate cell to execute LTM on.

[0131] The RRC layer of UE100 may stop evaluating L3 events in response to the notification from the MAC layer in step S302 (step S303).

[0132] If the MAC layer of UE100 receives the LTM cell switching command MAC CE (step S304), it may notify the RRC layer of UE100 of this (step S305).

[0133] The RRC layer of UE100 checks whether or not it has received the LTM cell switching command MAC CE (step S306). For example, the RRC layer of UE100 checks whether or not it has received a notification from the MAC layer (step S305).

[0134] If the LTM cell switching command MAC CE is received (step S306: YES), the RRC layer of UE100 controls the MAC layer to perform an LTM cell switch based on the LTM cell switching command MAC CE (step S307). As a result, an LTM cell switch based on the LTM cell switching command MAC CE is performed. For example, if the LTM cell switching command MAC CE indicates LTM candidate cell "A" and the beam of LTM candidate cell "B" satisfies an L1 event, priority may be given to switching to LTM candidate cell "A" and access to LTM candidate cell "B" may be canceled.

[0135] On the other hand, if the LTM cell switching command MAC CE is not received (step S306: NO), the RRC layer of UE100 controls the MAC layer to perform C-LTM cell switching based on the L1 event (step S308). As a result, C-LTM cell switching based on the L1 event is performed.

[0136] Furthermore, if UE100 receives the LTM cell switching command MAC CE after checking for its reception status (step S306), it may ignore the received LTM cell switching command MAC CE.

[0137] (4.3) Example 3 of the Second Embodiment Figure 13 shows Example 3 of the Second Embodiment. In this embodiment, we assume that an L3 event occurs in C-LTM in a UE100 which has both LTM settings and C-LTM settings. The differences from Examples 1 and 2 of the Second Embodiment will be explained in detail.

[0138] When an L3 event occurs (step S401), UE100 notifies the MAC layer from the RRC layer of this fact (step S402).

[0139] The MAC layer of UE100 may stop evaluating L1 events in response to the notification from the RRC layer in step S402 (step S403).

[0140] If the MAC layer of UE100 receives the LTM cell switching command MAC CE (step S404), it may notify the RRC layer of UE100 of this (step S405).

[0141] The RRC layer of UE100 checks whether or not it has received the LTM cell switching command MAC CE (step S406). For example, the RRC layer of UE100 checks whether or not it has received a notification from the MAC layer (step S405).

[0142] If the LTM cell switching command MAC CE is received (step S306: YES), the RRC layer of UE100 controls the MAC layer to perform an LTM cell switch based on the LTM cell switching command MAC CE (step S407). As a result, an LTM cell switch based on the LTM cell switching command MAC CE is performed. For example, if the LTM cell switching command MAC CE indicates LTM candidate cell "A" and an L3 event is met by LTM candidate cell "B", priority may be given to switching to LTM candidate cell "A", and access to LTM candidate cell "B" may be canceled.

[0143] On the other hand, if the LTM cell switching command MAC CE is not received (step S406: NO), the RRC layer of UE100 controls the MAC layer to perform C-LTM cell switching based on L3 events (step S408). As a result, C-LTM cell switching based on L3 events is performed.

[0144] Furthermore, if UE100 receives the LTM cell switching command MAC CE after checking for its reception status (step S406), it may ignore the received LTM cell switching command MAC CE.

[0145] (5) Third Embodiment The third embodiment will primarily be described in terms of the differences between it and the first and second embodiments described above. The third embodiment may be implemented in combination with the first and / or second embodiments described above. The third embodiment may be implemented independently of the first and second embodiments described above.

[0146] The above-described embodiment described a scenario in which a normal LTM and a C-LTM compete. In contrast, this embodiment assumes a scenario in which a C-LTM and a conditional handover (CHO) are set in UE100, and C-LTM events and CHO events compete. Furthermore, this embodiment also assumes a scenario in which multiple event conditions in the C-LTM are set in UE100, and multiple C-LTM events compete. The occurrence of multiple events at the same time is also referred to as "event competition." Here, "at the same time" means simultaneously or within a certain time range.

[0147] CHO is a technology introduced in 3GPP Release 16. Unlike conventional handovers where the gNB200 issues a handover instruction to the UE100, in CHO, the UE100 autonomously hands over to a candidate cell that satisfies the trigger conditions set by the gNB200. In the following, candidate cells in CHO will also be referred to as "CHO ​​candidate cells," and when LTM candidate cells and CHO candidate cells are not distinguished, they will simply be referred to as "candidate cells." Also, trigger conditions in C-LTM will be referred to as "C-LTM trigger conditions," and trigger conditions in CHO will be referred to as "CHO ​​trigger conditions."

[0148] Figure 14 shows the operation of UE100 according to the third embodiment.

[0149] In step S501, UE100, which has multiple execution conditions (multiple trigger conditions) associated with multiple candidate cells, performs an evaluation (event evaluation) to determine whether any of the multiple execution conditions are met. Here, each of the multiple execution conditions indicates a condition for executing a switch from the current serving cell. These multiple execution conditions may include C-LTM trigger conditions and CHO trigger conditions. Furthermore, these multiple execution conditions may include multiple C-LTM trigger conditions.

[0150] In step S502, UE100 selects candidate cells corresponding to the one execution condition and one of the other execution conditions based on a predetermined priority order or a setting from gNB200, in response to the fact that one of the multiple execution conditions is met and another execution condition is met (i.e., multiple events are in conflict).

[0151] In step S503, UE100 switches from the current serving cell to the candidate cell selected in step S502. Here, the switch to the candidate cell differs depending on the selected execution condition (candidate cell), but it is either an LTM cell switch (C-LTM) or a handover (CHO).

[0152] Thus, in this embodiment, when one of the multiple trigger conditions is met and another of the multiple trigger conditions is met, the UE 100 selects a candidate cell corresponding to the one trigger condition and the other trigger condition based on a predetermined priority or setting from the gNB 200. In other words, when multiple events occur simultaneously, the UE 100 selects a candidate cell corresponding to one of the multiple events based on a predetermined priority or setting from the gNB 200. According to this embodiment, it becomes possible to appropriately handle situations where multiple events conflict.

[0153] (5.1) Scenario 1: Scenario in which C-LTM and CHO events conflict In this scenario, the multiple trigger conditions set in UE100 include a first trigger condition (C-LTM trigger condition) for switching a C-LTM cell to a first candidate cell (LTM candidate cell) and a second trigger condition (CHO trigger condition) for CHO to a second candidate cell (CHO candidate cell). When the C-LTM trigger condition is met and the CHO trigger condition is met, UE100 determines whether either the C-LTM cell switch or the CHO is an intraCU and prioritizes selecting the candidate cell corresponding to the intraCU. That is, when both the C-LTM and CHO trigger conditions are met (i.e., when the C-LTM event and the CHO event conflict), UE100 prioritizes the intraCU.

[0154] Comparing the intraCU and interCU, the intraCU's cell switching does not require processing such as PDCP re-establishment, and is expected to have a shorter interruption time compared to the interCU. Therefore, when both the C-LTM and CHO trigger conditions are met, the UE100 prioritizes the intraCU, thereby reducing the interruption time associated with cell switching.

[0155] In this scenario, UE100 may receive from gNB200 a first identifier relating to the CU associated with the current serving cell and a second identifier relating to the CU associated with the LTM candidate cell. UE100 may determine that the C-LTM cell switchover is an intra-CU depending on whether the first and second identifiers are the same.

[0156] Such identifiers may also be the Rel-19 ID (a per-CU ID) newly introduced for interCU LTMs in 3GPP Release 19. The identifier may be referred to as "ltm-NoSecurityChangeID-r19". The identifier may be notified to the UE100 from the gNB200 in an RRC Reconfiguration message. The UE100 determines that a serving cell and an LTM candidate cell are intraCUs if their Rel-19 IDs are the same. Conversely, the UE100 determines that a serving cell and an LTM candidate cell are interCUs if their Rel-19 IDs are different.

[0157] In this scenario, UE100 may receive CHO configuration information (also referred to as "CHO ​​configuration") for a candidate CHO cell from gNB200. UE100 may determine that the CHO is an intraCU depending on whether the CHO configuration includes information indicating PDCP re-establishment. For example, UE100 may determine that it is an intraCU if the information element "re-establishablePDCP" in the CHO configuration is "false". Conversely, UE100 may determine that it is an interCU if the information element "re-establishablePDCP" in the CHO configuration is "true".

[0158] In this scenario, UE100 may prioritize selecting the candidate cell corresponding to CHO if both the C-LTM trigger condition and the CHO trigger condition are met, and both the C-LTM cell switching and CHO are intraCU or interCU events. That is, UE100 prioritizes CHO if both a CHO event and a C-LTM event occur, and both are intraCU or interCU events. Generally, L1 measurement results are highly variable, so CHO (L3 event) is considered to have higher reliability and / or stability in event evaluation. Therefore, if a CHO event and a C-LTM event compete, CHO may be prioritized.

[0159] Alternatively, if the C-LTM trigger condition is met and the CHO trigger condition is met, and both the C-LTM cell switching and CHO are intraCU or interCU, UE100 may prioritize selecting the LTM candidate cell corresponding to the C-LTM cell switching. That is, if both the CHO event and the C-LTM event occur and both are intraCU or interCU, UE100 prioritizes C-LTM. C-LTM may be able to switch cells faster than CHO because it obtains the TA value with early TA. Therefore, if the CHO event and the C-LTM event conflict, C-LTM may be prioritized. In other words, UE100 may prioritize access to a cell that has a valid TA value, or access to a cell that allows RACH-less access.

[0160] In this scenario, when both C-LTM cell switching and CHO are set in UE100, UE100 may receive priority information from gNB200 indicating the priority of each candidate cell. Here, when gNB200 sets both C-LTM and CHO in UE100, it assigns a priority to each candidate cell and notifies UE100 of the priority information. This priority information may be notified from gNB200 to UE100 in an RRC Reconfiguration message. When the C-LTM trigger condition and the CHO trigger condition are met, UE100 selects an LTM candidate cell corresponding to C-LTM cell switching or a CHO candidate cell corresponding to CHO based on the priority information from gNB200. This allows gNB200 to specify which candidate cell UE100 should prioritize in the event of a conflict between CHO events and C-LTM events.

[0161] Figure 15 shows an example of priority information related to this scenario.

[0162] Priority information may include a list consisting of multiple entries (also referred to as a "priority list"). In the illustrated example, the priority list (ExecutionPriorityList) has ExecutionPriority as an entry. Each of the multiple entries includes information indicating priority (ExecutionPriority) and one of the following: an LTM candidate identifier indicating an LTM candidate cell (e.g., LTM candidate ID) and a configuration identifier indicating a CHO candidate cell (e.g., CondReconfigID). For example, gNB200 associates Priority with either an LTM candidate ID or a CondReconfigID in the priority list. With such priority information, UE100 can determine the priority of each candidate cell in the event of an event conflict.

[0163] (5.2) Scenario 2: Scenario where multiple C-LTM events conflict In this scenario, the multiple C-LTM trigger conditions set in UE100 include a first C-LTM trigger condition for switching the first C-LTM cell to the first LTM candidate cell, and a second C-LTM trigger condition for switching the second C-LTM cell to the second LTM candidate cell. When the first C-LTM trigger condition is met and the second C-LTM trigger condition is met, UE100 may determine whether either the first C-LTM cell switching or the second C-LTM cell switching is an intraCU, and may prioritize selecting the LTM candidate cell corresponding to the intraCU. In this way, when multiple C-LTM events conflict, UE100 can reduce the interruption time associated with cell switching by prioritizing the intraCU. The method by which UE100 determines whether or not C-LTM is an intra-CU is the same as in the scenario described above.

[0164] In this scenario, if the first C-LTM trigger condition is met and the second C-LTM trigger condition is met, and both the first C-LTM cell switchover and the second C-LTM cell switchover are intraCU or interCU, UE100 may prioritize selecting the LTM candidate cell from the first LTM candidate cell and the second LTM candidate cell that has a valid timing advance value. That is, if multiple C-LTM events are in conflict and all are intraCU or interCU, UE100 may prioritize the LTM candidate cell that has a valid TA value. Here, the valid TA value may be one that gNB200 has notified UE100 via MAC CE (and is the TA value before the timer expires). The valid TA value may also be one that UE100 has derived itself.

[0165] In this scenario, one of the first C-LTM trigger condition and the second C-LTM trigger condition may be an L1 trigger condition, and the other of the first and second trigger conditions may be an L3 trigger condition. When the first trigger condition is met and the second trigger condition is met, and both the first C-LTM cell switching and the second C-LTM cell switching are intraCU or interCU, UE100 may prioritize selecting the LTM candidate cell corresponding to the L3 trigger condition from among the first LTM candidate cell and the second LTM candidate cell. That is, when the L1 and L3 events of C-LTM conflict and both are intraCU or interCU, UE100 may prioritize the LTM candidate cell corresponding to the L3 event.

[0166] In this scenario, if the first C-LTM trigger condition is met and the second C-LTM trigger condition is met, and both the first C-LTM cell switching and the second C-LTM cell switching are intraCUs or interCUs, UE100 may prioritize selecting the LTM candidate cell with the highest wireless quality among the first and second LTM candidate cells. Wireless quality may be RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality), or SINR (Signal to Interference plus Noise Ratio). In other words, if multiple C-LTM events are competing and all are intraCUs or interCUs, UE100 may prioritize the LTM candidate cell with the highest wireless quality.

[0167] (5.3) Figure 16 of the third embodiment is a diagram showing an example of the third embodiment.

[0168] In step S601, gNB200 sends an RRC Reconfiguration message to UE100 containing multiple execution conditions (multiple trigger conditions) associated with multiple candidate cells. UE100 receives the RRC Reconfiguration message and stores the multiple trigger conditions. Each trigger condition is associated with the configuration information of the candidate cell. Here, gNB200 may also include the priority information mentioned above in the RRC Reconfiguration message and send it to UE100.

[0169] In step S602, UE100 performs a trigger evaluation for each set trigger condition.

[0170] In step S603, UE100 detects a conflict between multiple events.

[0171] In step S604, UE100 performs the operations described in Scenario 1 and / or Scenario 2 above.

[0172] For example, UE100 may prioritize intraCUs among multiple competing events and select and apply the settings for candidate cells. For C-LTM, UE100 may determine it is an intraCU if the Rel-19 ID is the same for both the serving cell and the candidate cell. For CHO, UE100 may determine it is an intraCU if restablePDCP included in drb-ToAddModList in RadioBearerConfig is false.

[0173] UE100 may prioritize the candidate cell for CHO or the candidate cell for C-LTM if C-LTM and CHO events are in conflict and both candidate cells are intraCU or interCU.

[0174] If multiple C-LTM events conflict, UE100 may perform the following actions 1) to 3).

[0175] 1) In the event of a conflict between L1 events, UE100 may prioritize LTM candidate cells that have a valid TA value. UE100 may prioritize LTM candidate cells that have a valid TA value because a random access procedure would be required during cell switching for LTM candidate cells that do not have a valid TA value.

[0176] 2) In the event of a conflict between an L1 event and an L3 event, UE100 may prioritize the LTM candidate cell corresponding to the L3 event among these LTM candidate cells. This is because, generally, L1 measurement results are highly variable, and L3 events are considered to have higher reliability and / or stability in their evaluation.

[0177] 3) In the event of a conflict between L3 events, UE100 may prioritize the LTM candidate cell that has a valid TA value among these LTM candidate cells.

[0178] However, as an example of a modification to operation 1) to 3), if multiple C-LTM events conflict, UE100 may prioritize the LTM candidate cell with the highest wireless quality among these LTM candidate cells.

[0179] In step S605, UE100 detaches from the source cell and sets the selected candidate cell as the target cell.

[0180] In step S606, if UE100 does not have a TA value for the target cell, it performs a random access procedure to the target cell.

[0181] In step S607, UE100 completes the cell switchover by sending an RRC Reconfiguration Complete message to target gNB200.

[0182] (6) Other Embodiments Each of the above-described operation flows can be implemented not only separately and independently, but also in combination of two or more operation flows. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow. It is not necessary to execute all steps in each flow, and only some steps may be executed. In addition, the order of steps in each flow may be changed as appropriate.

[0183] In the embodiments and examples described above, an example was given in which the base station is an NR base station (gNB), but the base station may also be an LTE base station (eNB) or a 6G base station. Furthermore, 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 an IAB node. Additionally, UE100 may be an MT (Mobile Termination) of an IAB node. That is, UE100 may be a terminal function unit (a type of communication module) for the base station to control a repeater that performs signal relay. Such a terminal function unit is referred to as an MT. Examples of MTs other than IAB-MT include, for example, NCR (Network Controlled Repeater)-MT and RIS (Reconfigurable Intelligent Surface)-MT.

[0184] Furthermore, 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). Additionally, a network node may consist of a combination of at least a part of the core network device and at least a part of a base station.

[0185] A program may be provided that causes a computer to execute each process performed by the UE100 or gNB200. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may be a recording medium such as a CD-ROM and / or DVD-ROM. Alternatively, the circuits that execute each process performed by the UE100 or gNB200 may be integrated, and at least a part of the UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC: System on a chip).

[0186] The functions realized by UE100 or gNB200 may be implemented in a circuit or processing circuit, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (Central Processing Units), conventional circuits, and / or combinations thereof, programmed to realize the described functions. A processor, including transistors and / or other circuits, is considered a circuit or processing circuit. A processor may be a programmed processor that executes a program stored in memory. In this specification, circuit, unit, and means are hardware programmed to realize or perform the described functions. Such hardware may be any hardware disclosed herein, or any hardware known to be programmed to realize or perform the described functions. If the hardware is a processor that is considered to be of the type of circuit, then the circuit, means, or unit is a combination of hardware and software used to constitute the hardware and / or processor.

[0187] The phrases “based on” and “depending on / in response to” used in this disclosure do not mean “based solely on” or “depending solely on” unless otherwise specified. The phrase “based on” means both “based solely on” and “at least partially on.” Similarly, the phrase “depending on” means both “at least partially on” and “at least partially on.” The terms “include,” “comprise,” and variations thereof do not mean that only the listed items are included, but that they may include only the listed items or that they may include additional items in addition to the listed items. Furthermore, the term “or” used in this disclosure is not intended to mean exclusive OR. In addition, any reference to elements using designations such as “first,” “second,” etc., used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient way to distinguish between two or more elements. Thus, references to first and second elements do not mean that only two elements may be employed therein, or that the first element must precede the second element in any way. In this disclosure, if articles are added by translation, such as a, an, and the in English, these articles shall be considered plural unless it is clearly indicated otherwise by the context.

[0188] Although the embodiments have been described in detail above with reference to the drawings, the specific configuration is not limited to those described above, and various design changes can be made without departing from the gist of the invention.

[0189] This application claims priority to U.S. Provisional Application No. 63 / 754103 (filed February 5, 2025), the entirety of which is incorporated into the specification of this application.

[0190] (7) Appendix 1 The features of the above-described embodiment are described below.

[0191] - Appendix 1 A communication method for use in a mobile communication system that supports LTM (L1 / L2-Triggered Mobility), comprising: a user device having setting information for conditional LTM cell switching from a network node cell to a candidate cell receiving an LTM cell switching command MAC (Medium Access Control) CE (Control Element) from the network node instructing the execution of LTM cell switching to the candidate cell; and the user device, in response to receiving the LTM cell switching command MAC CE, applying the candidate cell setting included in the setting information for conditional LTM cell switching and executing the LTM cell switching to the candidate cell.

[0192] - Appendix 2 The setting information for the conditional LTM cell switching includes information indicating execution conditions relating to the wireless state that must be satisfied in order to perform the conditional LTM cell switching to the candidate cell, and the communication method described in Appendix 1, wherein the user device applies the candidate cell setting and performs the LTM cell switching to the candidate cell in response to the receipt of the LTM cell switching command MAC CE, even if the execution conditions are not satisfied.

[0193] - Appendix 3: If LTM cell switching setting information is not set in the user device as an information element separate from the setting information for the conditional LTM cell switching, the communication method according to Appendix 1 or 2, in which the user device, upon receiving the LTM cell switching command MAC CE, applies the candidate cell setting included in the setting information for the conditional LTM cell switching and performs the LTM cell switching to the candidate cell.

[0194] - Appendix 4 In cases where LTM cell switching setting information is defined as an information element separate from the setting information for the conditional LTM cell switching, the LTM cell switching command MAC CE includes an indicator indicating that the setting information for the conditional LTM cell switching should be applied, and the user device, in response to the LTM cell switching command MAC CE including the indicator, applies the candidate cell setting included in the setting information for the conditional LTM cell switching and performs the LTM cell switching to the candidate cell, according to any one of the communications methods described in Appendix 1 to 3.

[0195] - Appendix 5 In cases where LTM cell switching setting information is defined as an information element separate from the setting information for the conditional LTM cell switching, the LTM cell switching command MAC CE includes a specific logical channel identifier indicating that the setting information for the conditional LTM cell switching is to be applied, and the user device, in response to the LTM cell switching command MAC CE including the specific logical channel identifier, applies the candidate cell setting included in the setting information for the conditional LTM cell switching and performs the LTM cell switching to the candidate cell, according to any one of the communications methods described in Appendix 1 to 3.

[0196] - Appendix 6 The communication method according to any one of Appendix 1 to 5, wherein the MAC layer of the user device that has received the LTM cell switching command MAC CE notifies the RRC layer of the user device that it has received the LTM cell switching command MAC CE.

[0197] - Appendix 7 The setting information for the conditional LTM cell switching includes information indicating a Layer 1 (L1) trigger condition as an execution condition relating to the wireless state that should be satisfied in order to perform the conditional LTM cell switching to the candidate cell, and the MAC layer of the user device that performs L1 event evaluation based on the L1 measurement result stops the L1 event evaluation in response to the reception of the LTM cell switching command MAC CE, as described in Appendix 6.

[0198] - Appendix 8 The setting information for the conditional LTM cell switching includes information indicating a Layer 1 (L1) trigger condition as an execution condition relating to the wireless state that should be satisfied in order to perform the conditional LTM cell switching to the candidate cell, and the MAC layer of the user device that evaluates the L1 trigger condition based on the L1 measurement result stops the L1 event evaluation in response to an instruction from the RRC layer, according to the communication method described in Appendix 6 or 7.

[0199] - Appendix 9 The setting information for the conditional LTM cell switching includes information indicating a Layer 3 (L3) trigger condition as an execution condition relating to the wireless state that should be satisfied in order to perform the conditional LTM cell switching to the candidate cell, and the RRC layer of the user device that evaluates the L3 trigger condition based on the L3 measurement result stops the L3 event evaluation in response to the notification from the MAC layer, according to any one of the communication methods described in Appendix 6 to 8.

[0200] - Appendix 10 The setting information for the conditional LTM cell switching includes information indicating execution conditions relating to the wireless state that should be satisfied in order to perform the conditional LTM cell switching to the candidate cell, and the RRC layer of the user device checks whether the LTM cell switching command MAC CE has been received when the execution conditions are met, and the communication method according to any one of the appendices 1 to 9 executes the conditional LTM cell switching in response to the confirmation that the LTM cell switching command MAC CE has not been received.

[0201] - Appendix 11 The setting information for the conditional LTM cell switching includes information indicating execution conditions relating to the wireless state that should be satisfied in order to perform the conditional LTM cell switching to the candidate cell, and the communication method according to any one of the appendices 1 to 10 wherein the user device, when the execution conditions are satisfied and the LTM cell switching command MAC CE is received, prioritizes the LTM cell switching command MAC CE and performs LTM cell switching in accordance with the LTM cell switching command MAC CE.

[0202] - Appendix 12 A communication method for use in a mobile communication system that supports LTM (L1 / L2-Triggered Mobility), comprising: a user device having set a plurality of execution conditions associated with a plurality of candidate cells, evaluating whether any of the plurality of execution conditions are met, wherein each of the plurality of execution conditions indicates a condition for performing a switch from the current serving cell; selecting a candidate cell corresponding to one of the execution conditions and the other execution condition based on a predetermined priority order or a setting from the network node, in response to the fulfillment of one of the plurality of execution conditions and another execution condition; and switching from the current serving cell to the selected candidate cell.

[0203] - Appendix 13 The communication method according to Appendix 12, wherein the plurality of execution conditions include a first execution condition for conditional LTM cell switching to a first candidate cell and a second execution condition for conditional handover to a second candidate cell, and when the first execution condition and the second execution condition are met, the user device determines whether either the conditional LTM cell switching or the conditional handover is an intraCU (Central Unit), and selects a candidate cell corresponding to the intraCU with priority.

[0204] - Appendix 14 The communication method according to Appendix 13, wherein the user device further receives from a network node a first identifier relating to a CU associated with the current serving cell and a second identifier relating to a CU associated with the first candidate cell, and the user device determines that the conditional LTM cell switching is an intra CU depending on whether the first identifier and the second identifier are the same.

[0205] - Appendix 15 The communication method according to Appendix 13, wherein the user device further receives the conditional handover setting information to the second candidate cell from a network node, and the user device determines that the conditional handover is an intraCU in response to the conditional handover setting information including information indicating PDCP (Packet Data Convergence Protocol) re-establishment.

[0206] - Appendix 16 The communication method according to any one of Appendix 13 to 15, wherein when the first execution condition and the second execution condition are met, and both the conditional LTM cell switching and the conditional handover are intraCUs (Central Units) or interCUs, the user device preferentially selects a candidate cell corresponding to the conditional handover.

[0207] - Appendix 17 The communication method according to any one of Appendix 13 to 16, wherein when the first execution condition and the second execution condition are met, and both the conditional LTM cell switching and the conditional handover are intraCUs (Central Units) or interCUs, the user device preferentially selects the first candidate cell corresponding to the conditional LTM cell switching.

[0208] - Appendix 18 The communication method according to any one of Appendix 13 to 17, wherein when both the conditional LTM cell switching and the conditional handover are set on the user device, the user device receives priority information indicating the priority of each candidate cell from the network node, and when the first execution condition and the second execution condition are met, the user device selects the first candidate cell corresponding to the conditional LTM cell switching or the second candidate cell corresponding to the conditional handover based on the priority information.

[0209] - Appendix 19 The communication method described in Appendix 18, wherein the priority information includes a list consisting of multiple entries, and each of the multiple entries includes information indicating the priority and one of the LTM candidate identifier indicating the first candidate cell and the setting identifier indicating the second candidate cell.

[0210] - Appendix 20 The communication method according to any one of the appendices 12 to 19, wherein the plurality of execution conditions include a first execution condition for switching a first conditional LTM cell to a first candidate cell and a second execution condition for switching a second conditional LTM cell to a second candidate cell, and the user device determines whether either the first conditional LTM cell switching or the second conditional LTM cell switching is an intraCU (Central Unit), and selects a candidate cell corresponding to the intraCU as a priority.

[0211] - Appendix 21 The communication method according to Appendix 20, wherein when the first execution condition and the second execution condition are met, and both the first conditional LTM cell switching and the second conditional LTM cell switching are intraCUs (Central Units) or interCUs, the user device preferentially selects a candidate cell from among the first candidate cell and the second candidate cell that has a valid timing advance value.

[0212] - Appendix 22 The communication method according to Appendix 20 or 21, wherein one of the first execution condition and the second execution condition is a Layer 1 (L1) trigger condition, and the other of the first and second execution conditions is a Layer 3 (L3) trigger condition, and when the first execution condition and the second execution condition are both met, and both the first conditional LTM cell switching and the second conditional LTM cell switching are intraCUs (Central Units) or interCUs, the user device selects, in preference to the candidate cell corresponding to the L3 trigger condition from among the first candidate cell and the second candidate cell.

[0213] (8) Appendix 2 Introduction In RAN2#127bis, the following was agreed upon regarding the L1 execution conditions.

[0214] 2. Events similar to LTM3 and LTM5 will be used as conditional LTM execution conditions. The reuse of CHO conditions will be considered in the future.

[0215] The agreements regarding the execution conditions in RAN#128 are as follows:

[0216] Agreements Regarding C-LTM: "2. CondEventA3 and CondEventA5 conditions may serve as the baseline for conditional LTM execution. 3. The L1 execution condition for a candidate cell is associated with only one trigger event. 4. The L3 execution condition may consist of one or two trigger conditions. If there are two trigger conditions associated with the same candidate cell, the UE shall consider the execution condition satisfied only if both trigger conditions are met. Only a single RS type is supported, and up to two different trigger quantities can be set simultaneously for evaluating the execution condition of a single candidate cell. 5. To support initial and subsequent conditional LTMs, the following items may be considered regarding the configuration of execution conditions: - The CLTM configuration for each candidate cell shall include execution conditions for the initial conditional LTM, which are generated by the initial source cell to trigger the candidate cell's CLTM. - The CLTM configuration of each candidate cell may include execution conditions for subsequent conditional LTMs generated by that candidate cell to trigger the CLTMs of other candidate cells when the candidate cell becomes a serving cell. 11. For L1-based conditional LTMs, condition evaluation is performed at the MAC level, and for L3-based conditional LTMs, condition evaluation is performed at the RRC level.

[0217] This appendix describes the various coexistence scenarios identified and discusses approaches to achieving them.

[0218] Discussion: Coexistence of C-LTM and LTM In the revised WID, support for the coexistence of C-LTM and LTM remains unclear. On the other hand, the draft agenda encourages each company to consider whether or not to support the coexistence of C-LTM and LTM, and the impact on any additional specifications. Therefore, whether or not additional impacts are foreseeable at each phase of (C-)LTM will be discussed.

[0219] Regarding the preparation phase, according to the current RRC Running CR, the L1 / L3 conditions for C-LTM are configured as an extension within the existing LTM configuration (LTM Config). Therefore, the coexistence of C-LTM and LTM can be achieved with little to no impact on the specifications. Figure 19 shows an example of the information elements of this LTM configuration.

[0220] Since the same LTM configuration (LTM Config) is reused, the same LTM candidate ID for each LTM candidate is applicable regardless of whether the LTM candidate includes L1 / L3 condition IE or not. Therefore, the network (NW) can specify the LTM candidate ID of a C-LTM candidate cell by the LTM cell switch command MAC CE (LTM CSC MAC CE) without making any changes (including MAC CE format and corresponding UE operation). Thus, even when using the LTM configuration IE (LTM Config IE) of Rel-19, the NW-controlled LTM execution (i.e., the LTM of Rel-18) is triggered by the conventional LTM CSC MAC CE.

[0221] RAN2 should agree that, similar to the current RRC running CR (running CR), the Rel-19 C-LTM configuration and the Rel-18 LTM configuration can coexist within the existing LTM configuration.

[0222] RAN2 should agree that if the NW instructs the UE to execute an LTM candidate with L1 / L3 conditions set for C-LTM, the existing LTM cell switch command MAC CE can be reused as is.

[0223] If Proposal 2 is agreeable, the NW may instruct the UE to access the LTM candidate cell under C-LTM event evaluation for the same candidate cell (Scenario #A) or a different candidate cell (Scenario #B) using LTM CSC MAC CE. In the case of CHO (Conditional Handover), if the UE receives a conventional handover command while evaluating the CHO condition, it discards the CHO evaluation and proceeds with processing according to the most recently received handover setting.

[0224] The LTM cell switch command MAC CE may initiate a Rel-18 LTM execution toward an LTM candidate cell under C-LTM event evaluation.

[0225] In addition to the discussion in Consideration 1, we will further discuss the UE behavior when an LTM CSC MAC CE is received and the C-LTM event condition is simultaneously met. In that case, there are two possible scenarios.

[0226] Scenario #A (Figure 17, top): When the cell that satisfies the execution conditions for C-LTM is the same as the cell indicated by LTM CSC MAC CE, the execution conditions are met for LTM candidate ID = 1, and LTM CSC MAC CE indicates LTM candidate ID = 1.

[0227] Scenario #B (bottom of Figure 17): If the cell where the execution conditions for C-LTM are met is different from the cell indicated by LTM CSC MAC CE, the trigger execution conditions are met. LTM candidate ID = 1. LTM CSC MAC CE indicates LTM candidate ID = 2 (regardless of whether LTM Rel-18 or C-LTM Rel-19 is set by CSC MAC CE).

[0228] In Scenario #A, no problems are observed because the same LTM candidate cell is designated by the LTM CSC MAC CE and the execution conditions are met. In other words, it is sufficient for the UE to simply access the LTM candidate cell. Scenario #A does not need to be considered if the C-LTM LTM candidate cell may not be configured to send measurement reports.

[0229] On the other hand, in Scenario #B, the LTM candidate cell indicated by the LTM CSC MAC CE is different from the LTM candidate cell that satisfies the execution conditions. Therefore, the UE may not be sure which LTM candidate cell to execute LTM on. If the selection of the LTM candidate cell is left to the UE implementation, it may lead to a "handover to the wrong cell". Since the network generally has more knowledge about movement control, this can potentially be avoided if the UE follows the CSC MAC CE indicated by the network. Therefore, the UE should access the LTM candidate cell indicated by the LTM CSC MAC CE from the network.

[0230] RAN2 should agree that LTM executions triggered by the LTM cell switch command MAC CE take precedence over those triggered by the C-LTM execution conditions.

[0231] If Proposal 3 is agreeable, further consideration should be given to UE behavior to prioritize LTM CSC MAC CE. For example, in C-LTM, two types of execution conditions are agreed upon: L1 execution conditions and L3 execution conditions. Therefore, there are two scenarios to consider. Scenario #B-1: When the L1 execution condition is met simultaneously with the reception of LTM CSC MAC CE. Scenario #B-2: When the L3 execution condition is met simultaneously with the reception of LTM CSC MAC CE. In Scenario #B-1, the evaluation of the L1 execution condition is performed at the MAC layer, so LTM CSC MAC CE can be prioritized. However, in Scenario #B-2, the evaluation of the L3 execution condition is performed at the RRC layer, which is different from the layer that receives LTM CSC MAC CE. Therefore, coordination between layers is necessary.

[0232] If Proposal 3 is agreeable, RAN2 should further discuss how the RRC layer should handle the situation when the MAC sublayer simultaneously receives the LTM cell switch command MAC CE and the L3 execution condition is met.

[0233] Coexistence of L1 and L3 events: In RAN2#127bis, it was agreed that L1 execution conditions (i.e., equivalent to Event LTM3 / 5) would be used, while in RAN2#128, it was agreed that L3 execution conditions (i.e., CondEventA3 / 5) could serve as the baseline for C-LTM execution.

[0234] According to the current RRC execution CR, the network cannot simultaneously set L1 and L3 execution conditions for the same LTM candidate ID. However, there is no restriction that L1 execution conditions can be set for one LTM candidate ID and L3 execution conditions for another LTM candidate ID. In other words, L1 / L3 evaluation conditions can coexist within the LTM configuration (LTM Config). Therefore, in the following scenario, the network can set L1 and L3 execution conditions for different LTM candidate IDs for the user audience (UE).

[0235] The L3 execution condition is set for low-frequency C-LTM candidate cells.

[0236] Since the results of the L3 measurement are more reliable and stable than those of the L1 measurement, the L3 execution conditions are set.

[0237] The L1 execution condition is set for the high-frequency C-LTM candidate cell.

[0238] Because the wireless environment fluctuates significantly, making it difficult for L3 measurements to keep up, L1 execution conditions are set.

[0239] RAN2 should agree on the coexistence of L1 / L3 conditions, that is, the simultaneous existence of a candidate cell with an L1 condition and another candidate cell with an L3 condition.

[0240] According to TS 38.331 below, CHO has provisions for cases where multiple execution conditions are triggered simultaneously, and it is left to the UE implementation which candidate cell to hand over to.

[0241] 5.3.5.13.5 Execution of Conditional Reset The UE shall do the following: "1> If there are two or more pairs of triggered PCells and associated triggered PSCells: 2> Select one of the triggered PCells and associated triggered PSCells as the selected cell for the execution of conditional reset. (omitted)"

[0242] Note: If multiple NR cells are triggered during a conditional reset, the choice of which to select is left to the UE implementation (for example, the UE will consider beam and beam quality to select one of the triggered cells for execution).

[0243] Therefore, in C-LTM, multiple execution conditions may be triggered simultaneously. If Proposal 5 is agreeable, there are three possible scenarios (Figure 18): Scenario 1: The L1 execution condition is triggered simultaneously in different C-LTM candidate cells. Scenario 2: The L3 execution condition is triggered simultaneously in different C-LTM candidate cells. Scenario 3: The L1 and L3 execution conditions are triggered simultaneously in different C-LTM candidate cells.

[0244] In scenarios 1 and 2, as with CHO, the execution conditions are triggered at the same layer. Therefore, it is possible to compare the radio quality of both candidate cells from different layers that evaluate the event, and the candidate cell with better radio conditions should be selected. Alternatively, the decision of which C-LTM candidate cell to run LTM on may be left to the UE implementation.

[0245] However, in Scenario 3, the execution conditions are triggered at different layers. Since the triggering of multiple execution conditions at different layers has not been discussed so far, this should be considered as a new scenario.

[0246] In C-LTM, it is necessary to consider the case where the L1 execution condition and the L3 execution condition are simultaneously met for different C-LTM candidate cells.

[0247] In Scenario 3, the following three types of UE behavior are possible: Type 1: The UE accesses a C-LTM candidate cell that triggers the L1 execution condition. Type 2: The UE accesses a C-LTM candidate cell that triggers the L3 execution condition. Type 3: The UE implementation is left to decide which C-LTM candidate cell to select.

[0248] According to TS 38.300 below, after deriving beam quality at the physical layer (i.e., L1 measurement), cell quality is derived from multiple beams at the RRC level (i.e., L3 measurement). Therefore, the L3 execution condition (i.e., type 2), which uses the results of the L3 measurement, is considered to have higher reliability and stability compared to the L1 execution condition (i.e., type 1). Consequently, if the L1 and L3 execution conditions are met simultaneously, the UE should prioritize access to the C-LTM candidate cell (type 2) that satisfies the L3 execution condition over the L1 (type 1). Filtering is performed at two different levels: first to derive beam quality at the physical layer, and then to derive cell quality from multiple beams at the RRC level.

[0249] On the other hand, similar to scenarios 1 and 2, it is also possible to consider a Type 3 that leaves the selection of C-LTM candidate cells to the UE implementation.

[0250] RAN2 should discuss whether the UE should access C-LTM candidate cells that trigger L3 execution conditions, or whether it should select C-LTM candidate cells based on the UE's implementation.

[0251] Coexistence of C-LTM and Conditional Reset (CHO / CPC / CPA) According to the revised WID, C-LTM is not currently supported in DC. Therefore, there is no need to consider the coexistence of C-LTM, CPC, and CPA at this time. However, C-LTM and CHO may be set simultaneously. In this case, as in Section 2.2, multiple execution conditions may be triggered simultaneously, and the following scenarios are considered: Scenario i: In different C-LTM candidate cells, the L1 execution condition of C-LTM and the execution condition of CHO are triggered simultaneously. Scenario ii: In different C-LTM candidate cells, the L3 execution condition of C-LTM and the execution condition of CHO are triggered simultaneously.

[0252] If it is worthwhile to discuss the case of simultaneous triggering of different C-LTM execution conditions (i.e., L1 and L3 execution conditions), then the case of simultaneous triggering of CHO and C-LTM execution conditions should also be discussed.

[0253] 1: Mobile communication system 5: Network 10: RAN 20: CN 100: UE 110: Receiving unit 120: Transmitting unit 130: Control unit 140: Wireless communication unit 200: gNB 201a, 201b: gNB-CU 202a, 202b: gNB-DU 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 for use in a mobile communication system that supports LTM (L1 / L2-Triggered Mobility), comprising: a user device having setting information for conditional LTM cell switching from a network node cell to a candidate cell receiving an LTM cell switching command MAC (Medium Access Control) CE (Control Element) from the network node instructing the execution of LTM cell switching to the candidate cell; and the user device, in response to receiving the LTM cell switching command MAC CE, applying the candidate cell setting included in the setting information for conditional LTM cell switching and executing the LTM cell switching to the candidate cell.

2. The communication method according to claim 1, wherein the setting information for the conditional LTM cell switching includes information indicating execution conditions relating to the wireless state that should be satisfied in order to perform the conditional LTM cell switching to the candidate cell, and the user device applies the candidate cell setting and performs the LTM cell switching to the candidate cell in response to the receipt of the LTM cell switching command MAC CE, even if the execution conditions are not satisfied.

3. The communication method according to claim 1, wherein the setting information for the conditional LTM cell switching is included in the setting information for LTM cell switching, and the user device, in response to receiving the LTM cell switching command MAC CE, applies the candidate cell setting included in the setting information for the conditional LTM cell switching and performs the LTM cell switching to the candidate cell.

4. The communication method according to claim 1, wherein the MAC layer of the user device that has received the LTM cell switching command MAC CE notifies the RRC layer of the user device that it has received the LTM cell switching command MAC CE.

5. The communication method according to claim 4, wherein the setting information for the conditional LTM cell switching includes information indicating a Layer 1 (L1) trigger condition as an execution condition relating to a wireless state that should be satisfied in order to perform the conditional LTM cell switching to the candidate cell, and the MAC layer of the user device that evaluates the L1 trigger condition based on the L1 measurement result stops the L1 event evaluation in response to an instruction from the RRC layer.

6. The communication method according to claim 4, wherein the setting information for the conditional LTM cell switching includes information indicating a Layer 3 (L3) trigger condition as an execution condition relating to a wireless state that should be satisfied in order to perform the conditional LTM cell switching to the candidate cell, and the RRC layer of the user device that evaluates the L3 trigger condition based on the L3 measurement result stops the L3 event evaluation in response to the notification from the MAC layer.

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