Method and device for group switching in communication system

Abstract

The present invention discloses a method and apparatus for group handover in a communication system. The method for operating a head terminal includes the following steps: sending a configuration information message including a first indicator indicating a measurement report target to a member terminal participating in sidelink multicast communication; if the measurement report target indicated by the first indicator is a head terminal, receiving a measurement report message from the member terminal including the results of a measurement operation performed on at least one neighboring base station; and sending a configuration report message including the results of the measurement operation to a serving base station accessed by the head terminal. Consequently, the performance of the communication system can be improved.

Description

Technical Field

[0001] The present disclosure relates to a sidelink communication technology, and more particularly, to a group switching technology in a sidelink communication performed in a multicast scheme. Background Art

[0002] Fifth-generation (5G) communication systems (e.g., New Radio (NR) communication systems) using higher frequency bands than fourth-generation (4G) communication systems (e.g., Long Term Evolution (LTE) communication systems or LTE-Advanced (LTE-A) communication systems) have been considered for wireless data processing, along with frequency bands of 4G communication systems. 5G communication systems can support enhanced mobile broadband (eMBB) communication, ultra-reliable low-latency communication (URLLC), massive machine-type communication (mMTC), and the like.

[0003] 4G and 5G communication systems can support vehicle-to-everything (V2X) communications. V2X communications supported in cellular communication systems (such as 4G and 5G systems) can be referred to as cellular-V2X (C-V2X) communications. V2X communications (e.g., C-V2X communications) can include vehicle-to-vehicle (V2V) communications, vehicle-to-infrastructure (V2I) communications, vehicle-to-pedestrian (V2P) communications, and vehicle-to-network (V2N) communications.

[0004] In a cellular communication system, V2X communication (e.g., C-V2X communication) can be performed based on a sidelink communication technology (e.g., Proximity Services (ProSe) communication technology, Device-to-Device (D2D) communication technology, etc.). For example, a sidelink channel can be established for vehicles participating in V2V communication, and the sidelink channel can be used for communication between vehicles.

[0005] At the same time, vehicles participating in the formation (e.g., communication nodes located in the vehicles) can communicate with a base station (e.g., a roadside unit (RSU)). In addition, side link communication can be performed between vehicles participating in the formation. One of the vehicles participating in the formation can be referred to as a team leader (PL), and PL can refer to a terminal located in the corresponding vehicle (e.g., a head terminal). Among the vehicles participating in the formation, the remaining vehicles except the PL can be referred to as team members (PM), and each PM can refer to a terminal located in the corresponding vehicle (e.g., a member terminal).

[0006] Vehicles participating in the formation can perform side link communication (hereinafter referred to as "side link multicast communication") in a multicast manner. Vehicles participating in the side link multicast communication (for example, terminals located in vehicles) can belong to a multicast group. Each of the terminals belonging to the multicast group can perform a switching operation. In this case, the base stations (for example, serving base stations) to which the terminals belonging to the same multicast group are connected can be different from each other. For example, when member terminals #1 and #2 belong to the same multicast group, member terminal #1 can be connected to base station #1, and member terminal #2 can be connected to base station #2. The side link resources allocated by base station #1 to member terminal #1 may overlap with the side link resources allocated by base station #2 to member terminal #2. In this case, because the performance of the side link communication (for example, side link multicast communication) deteriorates, a method for solving such problems is needed. Summary of the Invention

[0007] The purpose of the present invention to solve the above problems is to provide a group switching method and device for sidelink multicast communication.

[0008] According to the first exemplary embodiment of the present disclosure, the operating method of the head terminal for achieving this purpose may include: sending a configuration information message including a first indicator indicating the target of the measurement report to the member terminals participating in the side link multicast communication; when the target of the measurement report indicated by the first indicator is the head terminal, receiving a measurement report message including the results of the measurement operation on one or more adjacent base stations from the member terminal; and sending a configuration report message including the results of the measurement operation to the service base station connected to the head terminal.

[0009] Each of the measurement report messages may include at least one of an identifier of the member terminal that transmits the measurement report message, reception quality information, an identifier of a neighboring base station related to the reception quality information, and a combination thereof.

[0010] The measurement report message may be received when a handover event occurs in the member terminal, and whether the handover event occurs may be determined based on an offset or a threshold, and the offset or the threshold may be included in the configuration information message.

[0011] The configuration report message may also include information indicating the number of member terminals and an identifier of each of the member terminals.

[0012] The operation method may also include: receiving a first connection reconfiguration message of the target base station configuration information determined based on the result of the measurement operation from the serving base station; sending a second connection reconfiguration message including the configuration information of the target base station to the member terminal; and executing an access process with the target base station based on the configuration information of the target base station.

[0013] The configuration information of the target base station may include an identifier of the target base station and resource pool information of the target base station.

[0014] The second connection reconfiguration message may further include a second indicator indicating application of the configuration information of the serving base station and the configuration information of the target base station.

[0015] The operation method may further include: sending a connection completion message indicating release of the connection with the serving base station to the member terminal when the access procedure between the head terminal and the target base station is completed.

[0016] According to a second exemplary embodiment of the present invention for achieving this purpose, the operation method of the head terminal may include: sending a configuration information message including a first indicator indicating the target of the measurement report to the member terminals participating in the side link multicast communication; when the target of the measurement report indicated by the first indicator is the serving base station, receiving a first connection reconfiguration message from the serving base station, which includes configuration information of the target base station determined based on the result of the measurement operation performed in the member terminal, sending a second connection reconfiguration message including the configuration information of the target base station to the member terminal; and executing an access process with the target base station based on the configuration information of the target base station.

[0017] The operation method may further include, before receiving the first connection reconfiguration message, receiving a mobility notification message from the serving base station, which indicates that a handover operation is performed to a target base station based on a result of a measurement operation performed in the member terminal.

[0018] The mobility notification message may include an identifier of each of the member terminals that has transmitted the result of the measurement operation to the serving base station.

[0019] The configuration information of the target base station may include an identifier of the target base station and resource pool information of the target base station, and the second connection reconfiguration message may further include a second indicator indicating application of the configuration information of the serving base station and the configuration information of the target base station.

[0020] The operation method may further include, when the access procedure between the head terminal and the target base station is completed, sending a connection completion message indicating release of the connection with the serving base station to the member terminal.

[0021] According to a third exemplary embodiment of the present disclosure for achieving this goal, an operating method of a member terminal may include: receiving a configuration information message including a first indicator indicating a target for a measurement report from a head terminal that manages side link multicast communications; performing measurement operations on a service base station and one or more adjacent base stations to which the head terminal is connected; when the object of the measurement report indicated by the first indicator is the head terminal, sending a measurement report message including a result of the measurement operation to the head terminal; and receiving a connection reconfiguration message from the head terminal including configuration information of a target base station determined by the service base station.

[0022] The measurement report message may be sent when a handover event occurs, and whether the handover event occurs may be determined based on an offset or a threshold, and the offset or the threshold may be included in the configuration information message.

[0023] The operating method may also include receiving system information including the first indicator from the serving base station.

[0024] The operating method may further include receiving a connection completion message from the head terminal indicating release of connection with the serving base station when the access procedure between the head terminal and the target base station is completed.

[0025] According to a fourth example embodiment for achieving this purpose, the operating method of a member terminal may include receiving a configuration information message including a first indicator indicating a target of a measurement report from a head terminal that manages side link multicast communication; performing measurement operations on a service base station and one or more adjacent base stations to which the head terminal is connected; when the target of the measurement report indicated by the first indicator is the service base station, sending a measurement report message including a result of the measurement operation to the service base station; and receiving a connection reconfiguration message including configuration information of a target base station determined by the service base station from the head terminal.

[0026] The configuration information of the target base station may include an identifier of the target base station and resource pool information of the target base station, and the connection reconfiguration message may further include a second indicator indicating application of the configuration information of the serving base station and the configuration information of the target base station.

[0027] The operating method may further include receiving a connection completion message from the head terminal indicating release of connection with the serving base station when the access procedure between the head terminal and the target base station is completed.

[0028] Beneficial effects

[0029] According to the present disclosure, the head terminal that manages / controls the side link multicast communication can send information indicating the target (e.g., the head terminal or the serving base station) for reporting the measurement operation results to the member terminal. The member terminal can send the results of the measurement operation to the target indicated by the head terminal. When the object of the report is the head terminal, the head terminal can notify the serving base station of the results of the measurement operation received from the member terminal. The serving base station can determine a target base station based on the results of the measurement operation. The configuration information of the target base station can be sent to the head terminal and the member terminal. In this case, the head terminal and the member terminal can perform a switching operation to the same target base station. Therefore, the resource conflict problem that occurs when the terminals participating in the side link multicast communication (e.g., the head terminal and the member terminal) perform switching operations to different target base stations can be solved. Therefore, the performance of the communication system can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1This is a conceptual diagram illustrating a V2X communication scenario.

[0031] Figure 2 is a conceptual diagram illustrating an exemplary embodiment of a cellular communication system.

[0032] Figure 3 is a conceptual diagram illustrating an exemplary embodiment of a communication node constituting a cellular communication system.

[0033] Figure 4 is a block diagram illustrating an exemplary embodiment of a user plane protocol stack of a UE performing sidelink communication.

[0034] Figure 5 is a block diagram illustrating a first exemplary embodiment of a control plane protocol stack of a UE performing sidelink communication.

[0035] Figure 6 is a block diagram illustrating a second exemplary embodiment of a control plane protocol stack of a UE performing sidelink communication.

[0036] Figure 7 This is a conceptual diagram illustrating a formation scheme in a communication system.

[0037] Figure 8a is a sequence diagram illustrating a first exemplary embodiment of a measurement reporting method in a group handover procedure.

[0038] Figure 8b is a sequence diagram illustrating a first exemplary embodiment of a method of accessing a target base station in a group handover procedure. DETAILED DESCRIPTION

[0039] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and described in detail. However, it should be understood that the description is not intended to limit the present disclosure to the specific embodiments, but on the contrary, the present disclosure covers all modifications, equivalents, and alternative forms that fall within the spirit and scope of the present disclosure.

[0040] Although the terms "first," "second," etc., may be used herein to refer to various elements, such elements should not be construed as being limited by these terms. These terms are merely used to distinguish one element from another. For example, a first element may be referred to as a second element, and a second element may be referred to as a first element, without departing from the scope of this disclosure. The term "and / or" includes any and all combinations of one or more of the related listed items.

[0041] It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or intervening elements may exist. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements.

[0042] The terms used herein are only used for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are also intended to include the plural forms. It will be further understood that the terms "comprise" and / or "include" when used herein specify the features, integers, steps, operations, elements, parts and / or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or combinations thereof.

[0043] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. It will also be understood that, unless expressly defined as such herein, terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and not interpreted in an idealized or overly formal sense.

[0044] Hereinafter, preferred exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In describing the present disclosure, in order to facilitate overall understanding, throughout the description of the drawings, the same reference numerals refer to the same elements and their repeated description will be omitted.

[0045] Figure 1 This is a conceptual diagram illustrating a V2X communication scenario.

[0046] like Figure 1 As shown, V2X communication may include vehicle-to-vehicle (V2V) communication, vehicle-to-infrastructure (V2I) communication, vehicle-to-pedestrian (V2P) communication, vehicle-to-network (V2N) communication, etc. V2X communication may be supported by a cellular communication system (e.g., cellular communication system 140), and V2X communication supported by cellular communication system 140 may be referred to as "cellular-V2X (C-V2X) communication." Here, cellular communication system 140 may include a 4G communication system (e.g., an LTE communication system or an LTE-A communication system), a 5G communication system (e.g., an NR communication system), etc.

[0047] V2V communication may include communication between a first vehicle 100 (e.g., a communication node located in vehicle 100) and a second vehicle 110 (e.g., a communication node located in vehicle 110). Various driving information such as speed, heading, time, location, etc. may be exchanged between vehicles 100 and 110 through V2V communication. For example, autonomous driving (e.g., platooning) may be supported based on the driving information exchanged through V2V communication. The V2V communication supported in the cellular communication system 140 may be performed based on a "sidelink" communication technology (e.g., ProSe and D2D communication technology, etc.). In this case, the communication between vehicles 100 and 110 may be performed using at least one sidelink channel established between vehicles 100 and 110.

[0048] V2I communication may include communication between the first vehicle 100 (e.g., a communication node located in the vehicle 100) and infrastructure (e.g., a roadside unit (RSU)) 120 located on the roadside. The infrastructure 120 may also include traffic lights or streetlights located on the roadside. For example, when V2I communication is performed, communication may be performed between the communication node located in the first vehicle 100 and the communication node located in the traffic light. Through V2I communication, traffic information, driving information, etc. may be exchanged between the first vehicle 100 and the infrastructure 120. The V2I communication supported in the cellular communication system 140 may also be performed based on a sidelink communication technology (e.g., ProSe and D2D communication technology, etc.). In this case, communication between the vehicle 100 and the infrastructure 120 may be performed using at least one sidelink channel established between the vehicle 100 and the infrastructure 120.

[0049] V2P communication may include communication between the first vehicle 100 (e.g., a communication node located in the vehicle 100) and the person 130 (e.g., a communication node carried by the person 130). Driving information of the first vehicle 100 and movement information of the person 130 (such as speed, direction, time, location, etc.) may be exchanged between the vehicle 100 and the person 130 through V2P communication. The communication node located in the vehicle 100 or the communication node carried by the person 130 may generate an alert indicating danger by determining a dangerous situation based on the obtained driving information and movement information. The V2P communication supported in the cellular communication system 140 may be performed based on a sidelink communication technology (e.g., ProSe and D2D communication technology, etc.). In this case, communication between the communication node located in the vehicle 100 and the communication node carried by the person 130 may be performed using at least one sidelink channel established between the communication nodes.

[0050] V2N communication may be communication between the first vehicle 100 (e.g., a communication node located in the vehicle 100) and a server connected via the cellular communication system 140. V2N communication may be performed based on 4G communication technology (e.g., LTE or LTE-A) or 5G communication technology (e.g., NR). In addition, V2N communication may be performed based on Wireless Access in Vehicular Environments (WAVE) communication technology, wireless local area network (WLAN) communication technology defined in Institute of Electrical and Electronics Engineers (IEEE) 802.11, or wireless personal area network (WPAN) communication technology defined in IEEE 802.15.

[0051] Meanwhile, the cellular communication system 140 supporting V2X communication may be configured as follows.

[0052] Figure 2 is a conceptual diagram illustrating an exemplary embodiment of a cellular communication system.

[0053] like Figure 2 As shown, the cellular communication system may include an access network, a core network, etc. The access network may include a base station 210, a relay 220, user equipments (UEs) 231 to 236, etc. The UEs 231 to 236 may include Figure 1 The communication nodes in vehicles 100 and 110 are located Figure 1 The communication nodes in the infrastructure 120 are composed of Figure 1 When the cellular communication system supports 4G communication technology, the core network may include a serving gateway (S-GW) 250, a packet data network (PDN) gateway (P-GW) 260, a mobility management entity (MME) 270, and the like.

[0054] When the cellular communication system supports 5G communication technology, the core network may include a user plane function (UPF) 250, a session management function (SMF) 260, an access and mobility management function (AMF) 270, etc. Alternatively, when the cellular communication system operates in a non-standalone networking (NSA) mode, the core network composed of the S-GW 250, the P-GW 260, and the MME 270 may support 5G communication technology and 4G communication technology, and the core network composed of the UPF 250, the SMF 260, and the AMF 270 may support 4G communication technology and 5G communication technology.

[0055] In addition, when the cellular communication system supports network slicing technology, the core network can be divided into multiple logical network slices. For example, network slices supporting V2X communication (such as V2V network slices, V2I network slices, V2P network slices, V2N network slices, etc.) can be configured, and V2X communication is supported through the V2X network slices configured in the core network.

[0056] Communication can be performed by using at least one communication technology among code division multiple access (CDMA) technology, time division multiple access (TDMA) technology, frequency division multiple access (FDMA) technology, orthogonal frequency division multiplexing (OFDM) technology, filtered OFDM technology, orthogonal frequency division multiple access (OFDMA) technology, single carrier FDMA (SC-FDMA) technology, non-orthogonal multiple access (NOMA) technology, generalized frequency division multiplexing (GFDM) technology, filter bank multi-carrier (FBMC) technology, universal filtered multi-carrier (UFMC) technology and space division multiple access (SDMA) technology, including communication nodes of a cellular communication system (for example, base stations, repeaters, UE, S-GW, P-GW, MME, UPF, SMF, AMF, etc.).

[0057] The communication nodes (e.g., base stations, relays, UEs, S-GWs, P-GWs, MMEs, UPFs, SMFs, AMFs, etc.) comprising a cellular communication system may be configured as follows.

[0058] Figure 3 is a conceptual diagram illustrating an exemplary embodiment of a communication node constituting a cellular communication system.

[0059] like Figure 3 As shown, the communication node 300 may include at least one processor 310 connected to a network to perform communication, a memory 320, and a transceiver 330. In addition, the communication node 300 may further include an input interface device 340, an output interface device 350, a storage device 360, etc. Each component included in the communication node 300 can communicate with each other when connected through a bus 370.

[0060] However, each of the components included in the communication node 300 may be connected to the processor 310 via a separate interface or a separate bus instead of the common bus 370. For example, the processor 310 may be connected to at least one of the memory 320, the transceiver 330, the input interface device 340, the output interface device 350, and the storage device 360 via a dedicated interface.

[0061] The processor 310 may execute at least one instruction stored in at least one of the memory 320 and the storage device 360. The processor 310 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which the method according to an embodiment of the present disclosure is executed. Each of the memory 320 and the storage device 360 may include at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 320 may include at least one of a read-only memory (ROM) and a random access memory (RAM).

[0062] Reference again Figure 2In the communication system, base station 210 may form a macro cell or a small cell and may be connected to a core network via an ideal backhaul or a non-ideal backhaul. Base station 210 may transmit signals received from the core network to UEs 231 to 236 and relay 220, and may transmit signals received from UEs 231 to 236 and relay 220 to the core network. UEs 231, 232, 234, 235, and 236 may belong to the cell coverage of base station 210. UEs 231, 232, 234, 235, and 236 may connect to base station 210 by performing a connection establishment procedure with base station 210. After connecting to base station 210, UEs 231, 232, 234, 235, and 236 may communicate with base station 210.

[0063] Relay 220 may be connected to base station 210 and may relay communications between base station 210 and UEs 233 and 234. That is, relay 220 may transmit signals received from base station 210 to UEs 233 and 234, and may transmit signals received from UEs 233 and 234 to base station 210. UE 234 may be within the cell coverage of base station 210 and the cell coverage of relay 220, and UE 233 may be within the cell coverage of relay 220. That is, UE 233 may be outside the cell coverage of base station 210. UEs 233 and 234 may connect to relay 220 by performing a connection establishment procedure with relay 220. After connecting to relay 220, UEs 233 and 234 may communicate with relay 220.

[0064] The base station 210 and the relay 220 may support multiple-input multiple-output (MIMO) technology (e.g., single-user (SU)-MIMO, multi-user (MU)-MIMO, massive MIMO, etc.), coordinated multi-point (CoMP) communication technology, carrier aggregation (CA) communication technology, unlicensed band communication technology (e.g., licensed assisted access (LAA), enhanced LAA (eLAA)), sidelink communication technology (e.g., ProSe communication technology, D2D communication technology), etc. UEs 231, 232, 235, and 236 may perform operations corresponding to the base station 210 and operations supported by the base station 210. UEs 233 and 234 may perform operations corresponding to the relay 220 and operations supported by the relay 220.

[0065] Here, the base station 210 may be referred to as a Node B (NB), an evolved Node B (eNB), a base transceiver station (BTS), a radio remote head (RRH), a transmission reception point (TRP), a radio unit (RU), a roadside unit (RSU), a radio transceiver, an access point, an access node, etc. The relay 220 may be referred to as a small base station, a relay node, etc. Each of the UEs 231 to 236 may be referred to as a terminal, an access terminal, a mobile terminal, a station, a subscriber station, a mobile station, a portable subscriber station, a node, a device, an onboard unit (OBU), etc.

[0066] Meanwhile, the communication between UE 235 and 236 may be performed based on the sidelink communication technology. The sidelink communication may be performed based on a one-to-one scheme or a one-to-many scheme. When performing V2V communication using the sidelink communication technology, UE 235 may be located at Figure 1 The communication node in the first vehicle 100 and the UE 236 may be located Figure 1 When V2I communication is performed using the sidelink communication technology, the UE 235 may be a communication node located in the second vehicle 110. Figure 1 The communication node in the first vehicle 100 and the UE 236 may be located Figure 1 When performing V2P communication using the sidelink communication technology, the UE 235 may be a communication node located in the infrastructure 120. Figure 1 The communication node in the first vehicle 100 and the UE 236 may be composed of Figure 1 The person 130 carries the communication node.

[0067] The scenarios in which side link communication is applied can be classified according to the locations of the UEs (eg, UEs 235 and 236) participating in the side link communication as shown in Table 1 below. For example, Figure 2 The scenario of sidelink communication between UEs 235 and 236 shown may be sidelink communication scenario C.

[0068] [Table 1]

[0069] Sidelink communication scenario Location of UE 235 Location of UE 236 A Outside the coverage of base station 210 Outside the coverage of base station 210 B Within the coverage area of base station 210 Outside the coverage of base station 210 C Within the coverage area of base station 210 Within the coverage area of base station 210 D Within the coverage area of base station 210 Within the coverage area of other base stations

[0070] Meanwhile, a user plane protocol stack of a UE (eg, UEs 235 and 236 ) performing sidelink communication may be configured as follows.

[0071] Figure 4 is a block diagram illustrating an exemplary embodiment of a user plane protocol stack of a UE performing sidelink communication.

[0072] like Figure 4 As shown, the left UE can be Figure 2 The UE 235 shown in FIG and the right UE may be Figure 2UE 236 is shown. The scenario of the sidelink communication between UEs 235 and 236 can be one of the sidelink communication scenarios A to D in Table 1. The user plane protocol stack of each of UEs 235 and 236 may include a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, and a packet data convergence protocol (PDCP) layer.

[0073] Sidelink communication between UEs 235 and 236 may be performed using a PC5 interface (e.g., a PC5-U interface). A layer-2 identifier (ID) (e.g., source layer-2 ID, destination layer-2 ID) may be used for sidelink communication, and the layer-2 ID may be an ID configured for V2X communication (e.g., V2X service). Furthermore, in sidelink communication, hybrid automatic repeat request (HARQ) feedback operation may be supported, and RLC acknowledged mode (RLC AM) or RLC unacknowledged mode (RLC UM) may be supported.

[0074] Meanwhile, a control plane protocol stack of a UE (eg, UEs 235 and 236 ) performing sidelink communication may be configured as follows.

[0075] Figure 5 is a block diagram illustrating a first exemplary embodiment of a control plane protocol stack of a UE performing sidelink communication, and Figure 6 is a block diagram illustrating a second exemplary embodiment of a control plane protocol stack of a UE performing sidelink communication.

[0076] like Figure 5 and 6 As shown, the left UE can be Figure 2 The UE 235 shown and the right UE may be Figure 2 The scenario for sidelink communication between UEs 235 and 236 may be one of the sidelink communication scenarios A to D of Table 1. Figure 5 The control plane protocol stack shown in may be a control plane protocol stack for transmitting and receiving broadcast information (eg, a physical sidelink broadcast channel (PSBCH)).

[0077] Figure 5 The control plane protocol stack shown may include a PHY layer, a MAC layer, an RLC layer, and a radio resource control (RRC) layer.Sidelink communications between UEs 235 and 236 may be performed using a PC5 interface (eg, a PC5-C interface). Figure 6 The control plane protocol stack shown may be a control plane protocol stack for one-to-one side link communication. Figure 6 The control plane protocol stack shown may include a PHY layer, a MAC layer, an RLC layer, a PDCP layer, and a PC5 signaling protocol layer.

[0078] Meanwhile, channels used in sidelink communication between UEs 235 and 236 may include a physical sidelink shared channel (PSSCH), a physical sidelink control channel (PSCCH), a physical sidelink discovery channel (PSDCH), and a physical sidelink broadcast channel (PSBCH). The PSSCH may be used to transmit and receive sidelink data and may be configured in a UE (e.g., UE 235 or 236) through higher layer signaling. The PSCCH may be used to transmit and receive sidelink control information (SCI) and may also be configured in a UE (e.g., UE 235 or 236) through higher layer signaling.

[0079] The PSDCH can be used for discovery procedures. For example, discovery signals can be sent via the PSDCH. The PSBCH can be used to send and receive broadcast information (e.g., system information). In addition, demodulation reference signals (DM-RS), synchronization signals, etc. can be used in sidelink communications between UEs 235 and 236. Synchronization signals can include a primary sidelink synchronization signal (PSSS) and a secondary sidelink synchronization signal (SSSS).

[0080] Meanwhile, sidelink transmission modes (TMs) may be classified into sidelink TMs 1 to 4 as shown in Table 2 below.

[0081] [Table 2]

[0082] SidelinkTM describe 1 Transmission using resources scheduled by the base station 2 UE autonomous transmission without base station scheduling 3 Transmission using resources scheduled by the base station in V2X communications 4 UE autonomous transmission in V2X communication without base station scheduling

[0083] When sidelink TM 3 or 4 is supported, each of the UEs 235 and 236 may perform sidelink communication using a resource pool configured by the base station 210. A resource pool may be configured for each of sidelink control information and sidelink data.

[0084] The resource pool for sidelink control information can be configured based on an RRC signaling process (e.g., a dedicated RRC signaling process, a broadcast RRC signaling process). The resource pool for receiving sidelink control information can be configured by a broadcast RRC signaling process. When sidelink TM 3 is supported, the resource pool for transmitting sidelink control information can be configured by a dedicated RRC signaling process. In this case, the sidelink control information can be sent by resources scheduled by the base station 210 within the resource pool configured by the dedicated RRC signaling process. When sidelink TM 4 is supported, the resource pool for transmitting sidelink control information can be configured by a dedicated RRC signaling process or a broadcast RRC signaling process. In this case, the sidelink control information can be sent by resources autonomously selected by the UE (e.g., UE 235 or 236) within the resource pool configured by the dedicated RRC signaling process or the broadcast RRC signaling process.

[0085] When sidelink TM 3 is supported, a resource pool for transmitting and receiving sidelink data may not be configured. In this case, sidelink data can be transmitted and received using resources scheduled by base station 210. When sidelink TM 4 is supported, a resource pool for transmitting and receiving sidelink data can be configured using a dedicated RRC signaling procedure or a broadcast RRC signaling procedure. In this case, sidelink data can be transmitted and received using resources autonomously selected by a UE (e.g., UE 235 or 236) within a resource pool configured using a dedicated RRC signaling procedure or a broadcast RRC signaling procedure.

[0086] Hereinafter, the side link multicast communication method will be described. Even when describing a method to be performed at a first communication node among communication nodes (e.g., transmission or reception of a signal), the corresponding second communication node may also perform a method corresponding to the method performed at the first communication node (e.g., reception or transmission of a signal). That is, when describing the operation of UE#1 (e.g., vehicle #1), the UE#2 corresponding thereto (e.g., vehicle #2) may perform an operation corresponding to the operation of UE#1. In contrast, when describing the operation of UE#2, the corresponding UE#1 may perform an operation corresponding to the operation of UE#2. In the exemplary embodiment described below, the operation of the vehicle may be the operation of a communication node located in the vehicle.

[0087] Sidelink signals may be synchronization signals and reference signals used for sidelink communications. For example, synchronization signals may be synchronization signal / physical broadcast channel (SS / PBCH) blocks, sidelink synchronization signals (SLSS), primary sidelink synchronization signals (PSSS), secondary sidelink synchronization signals (SSSS), etc. Reference signals may be channel state information reference signals (CSI-RS), DM-RS, phase tracking reference signals (PT-RS), cell-specific reference signals (CRS), sounding reference signals (SRS), discovery reference signals (DRS), etc.

[0088] The sidelink channel may be a PSSCH, PSCCH, PSDCH, PSBCH, physical sidelink feedback channel (PSFCH), etc. In addition, a sidelink channel may refer to a sidelink channel including a sidelink signal mapped to specific resources in the corresponding sidelink channel. Sidelink communication may support broadcast services, multicast services, groupcast services, and unicast services.

[0089] Figure 7 This is a conceptual diagram illustrating a formation scheme in a communication system.

[0090] like Figure 7As shown, multiple vehicles 711 to 714 can participate in a platoon. One of the multiple vehicles 711 to 714 participating in the platoon (e.g., a terminal located in the vehicle) can be referred to as a team leader (PL). For example, vehicle 711 at the head of the multiple vehicles 711 to 714 participating in the platoon (e.g., UE#1 located in vehicle 711) can be referred to as a PL or head terminal. PL 711 can lead the platoon and can control the other vehicles 712 to 714.

[0091] Among the plurality of vehicles 711 to 714 participating in the platoon, the remaining vehicles 712 to 714 (e.g., terminals belonging to the vehicle) other than vehicle 711 may be referred to as a platoon member (PM) or a member terminal. Alternatively, the last vehicle 714 among the plurality of vehicles 711 to 714 participating in the platoon may be referred to as a platoon tail (PT). PMs 712 to 714 may operate under the control of PL 711.

[0092] Multiple vehicles 711 to 714 participating in a platoon can perform sidelink multicast communications. In this case, PL 711 can be referred to as a sidelink multicast head (SGH), and PMs 712 to 714 can be referred to as sidelink multicast members (SGMs). That is, in the following exemplary embodiments, PL can refer to SGH, and SGH can represent PL. Furthermore, PM can refer to SGM, and SGM can refer to PM.

[0093] When PL711 is Figure 2 When the UE 235 is shown, each of the PMs 712 to 714 may be Figure 2 UE 236 shown in FIG. Each of PL 711, PM 712, PM 713 and PM 714 can be connected to Figure 3 The communication nodes 300 shown are configured identically or similarly. For example, each of PL 711, PM 712, PM 713, and PM 714 may include an antenna array including a plurality of antenna elements. Each of PL 711, PM 712, PM 713, and PM 714 may support Figures 4 to 6 The protocol stack shown.

[0094] Each of the PL 711, PM 712, PM 713, and PM 714 participating in the formation can be connected to the base station 700 (e.g., an RSU) and can communicate with the base station 700 using a beamforming scheme. In this case, a pair of transmit and receive beams can be configured between the base station 700 and each of the PL 711, PM 712, PM 713, and PM 714, and beamforming-based communication can be performed using the pair of transmit and receive beams. Here, the receive beam can represent a reception direction.

[0095] Furthermore, sidelink communication can be performed between PL 711, PM 712, PM 713, and PM 714 participating in the formation, and can be performed using a beamforming scheme. In this case, a pair of transmit and receive beams can be configured for each pair of PM 712, PM 713, PM 714, and PL 711, and beamforming-based communication can be performed using this pair of transmit and receive beams. This pair of transmit and receive beams can be configured through a beam management process (e.g., a beam configuration process).

[0096] Meanwhile, a transmission mode (TM) for V2X communication may be defined as shown in Table 3 below.

[0097] [Table 3]

[0098]

[0099] The V2X™ protocol defined in Table 3 can be used for sidelink communication between vehicles participating in a platoon. The sidelink resources required by V2X™ can vary. Therefore, the base station can allocate the sidelink resources required by V2X™ to the PL (e.g., the SGH), and the PL can perform sidelink communication according to V2X™ using the sidelink resources allocated by the base station. The following exemplary embodiments will describe a sidelink communication method according to V2X™.

[0100] Figure 8a is a sequence diagram illustrating a first exemplary embodiment of a measurement reporting method in a group handover procedure, and Figure 8b is a sequence diagram illustrating a first exemplary embodiment of a method of accessing a target base station in a group handover procedure. Figure 8b The operations shown can be Figure 8a The operations shown are then performed.

[0101] like Figure 8a and 8b As shown, the communication system may include a serving base station, a head terminal, a member terminal #1, a member terminal #2, etc. The serving base station, the head terminal, the member terminal #1 and the member terminal #2 may be Figure 7 The base station 700, PL 711, PM 712 and PM 713 are shown. Each of the serving base station, head terminal, member terminal #1 and member terminal #2 can be connected to Figure 3 The communication nodes 300 shown are configured identically or similarly. Each of the member terminal #1 and the member terminal #2 can support Figures 4 to 6 The protocol stack shown.

[0102] The head terminal, member terminal #1 and member terminal #2 may belong to the same multicast group and may perform side link multicast communication. The head terminal may manage / control side link multicast communication. The head terminal, member terminal #1 and member terminal #2 may access the same serving base station. The head terminal may operate in an RRC connected state. Each of member terminals #1 and #2 may operate in an RRC connected state, an RRC inactive state or an RRC idle state. In the multicast group configuration step, the head terminal may generate a multicast configuration information message (e.g., a GroupcastConfiguration message) and may send the multicast configuration information message to member terminals #1 and #2 (S800). The multicast configuration information message may be an RRC message and may include multicast configuration information. The multicast configuration information message may include the information elements listed in Table 4 below. In addition, the multicast configuration information message may also include other information elements as well as the information elements listed in Table 4 below.

[0103] [Table 4]

[0104]

[0105] The multicast configuration information message may include an identifier of the multicast group (e.g., group-RNTI in Table 4), a multicast identifier (e.g., groupcastIdentity in Table 4), information of the SS / PBCH block used for sidelink communication (e.g., sl-SSB in Table 4), etc. In addition, the multicast configuration information message may also include information indicating the target for reporting the measurement results (e.g., HOAssistIndication in Table 4). In an exemplary embodiment, the information indicating the target for reporting the measurement results may be referred to as a "measurement report indicator". The measurement result may be the result of a measurement operation performed by a member terminal on one or more base stations (e.g., a serving base station and / or one or more neighboring base stations). A measurement report indicator set to a first value may indicate that the measurement information is reported to the group head. A measurement report indicator set to a second value may indicate that the measurement information is reported to the serving base station.

[0106] In addition, the multicast configuration information message may also include an offset and / or threshold value for determining whether a handover event (e.g., a group handover event) occurs. The offset may be classified into a Type 1 offset used when the speed of a terminal (e.g., a head terminal, a member terminal) is greater than or equal to a speed threshold, and a Type 2 offset used when the speed of a terminal (e.g., a head terminal, a member terminal) is less than a speed threshold. In addition, the threshold may be classified into a Type 1 threshold used when the speed of a terminal (e.g., a head terminal, a member terminal) is equal to or greater than a speed threshold, and a Type 2 threshold used when the speed of a terminal (e.g., a head terminal, a member terminal) is less than a speed threshold. Here, the speed threshold may be included in the multicast configuration information message.

[0107] At the same time, the serving base station may send system information (e.g., system information block (SIB) 26) including a measurement report indicator to the terminals belonging to the multicast group (e.g., the head terminal, member terminal #1, member terminal #2). That is, the measurement report indicator may be sent through system information instead of a multicast configuration information message. Alternatively, the measurement report indicator may be sent through both the multicast configuration information message and the system information. When the measurement report indicator is sent through system information, a terminal that is not operating in an RRC connected state (e.g., a member terminal operating in an RRC inactive state or an RRC idle state) may also obtain the measurement report indicator. The system information may include the information elements listed in the following Table 5. In Table 5, HOAssitIndication may be a measurement report indicator. In addition, the system information may further include a speed threshold, an offset (e.g., type 1-offset, type 2-offset) and / or a threshold (e.g., type 1-threshold, type 2-threshold).

[0108] [Table 5]

[0109]

[0110] When the measurement report indicator is transmitted via system information, the head terminal may obtain the measurement report indicator by receiving the system information from the serving base station. In this case, the head terminal may generate a multicast configuration information message including a measurement report indicator having the same value (e.g., the first value or the second value) as the measurement report indicator included in the system information. The head terminal may send the multicast configuration information message including the measurement report indicator to member terminals #1 and #2.

[0111] Member terminals #1 and #2 can receive system information (e.g., the system information listed in Table 5) from the serving base station. In addition, member terminals #1 and #2 can receive a multicast configuration information message (e.g., the multicast configuration information message shown in Table 4) from the head terminal. Each of member terminals #1 and #2 can obtain a measurement report indicator from the system information and / or the multicast configuration information message. When the measurement report indicator is set to a first value, member terminals #1 and #2 can determine that the results of the measurement operation on one or more base stations (e.g., the serving base station and / or one or more neighboring base stations) will be reported to the group head. When the measurement report indicator is set to a second value, member terminals #1 and #2 can determine that the results of the measurement operation on one or more base stations (e.g., the serving base station and / or one or more neighboring base stations) will be reported to the serving base station.

[0112] Member terminals #1 and #2 may perform measurement operations on one or more base stations (e.g., a serving base station and / or one or more neighboring base stations) (S801). For example, member terminals #1 and #2 may receive reference signals from a serving base station and / or one or more neighboring base stations, and may measure the reception quality of the reference signals. Here, the reference signal may be a CSI-RS, a DM-RS, a PT-RS, or the like. Alternatively, in order to measure the reception quality of one or more base stations, an SS / PBCH block may be used instead of a reference signal. The reception quality may be a reference signal received power (RSRP), a reference signal strength indicator (RSSI), a reference signal received quality (RSRQ), a signal-to-noise ratio (SNR), or a signal-to-interference-plus-noise ratio (SINR).

[0113] In the following exemplary embodiments, a case where the measurement report indicator is set to a first value may be defined as "Case 1", and a case where the measurement report indicator is set to a second value may be defined as "Case 2".

[0114] ■Situation 1

[0115] When the measurement report indicator is set to the first value, each of member terminals #1 and #2 can send a measurement report message including the result of the measurement operation (e.g., reception quality information, information of neighboring base stations with good reception quality) to the head terminal (S802-1). The measurement report message may include the identifier of the member terminal sending the measurement report message, the reception quality information, and one or more identifiers of one or more neighboring base stations related to the corresponding reception quality information. Alternatively, another RRC message can be used instead of the measurement report message. Another RRC message may include information elements required for the handover decision of the multicast group (e.g., the identifier of the member terminal, reception quality information, identifiers of one or more base stations related to the corresponding reception quality information, etc.). For example, another RRC message may include one or more information elements included in the measurement report message.

[0116] When a handover event is satisfied, each of the member terminals #1 and 2 may send a measurement report message to the head terminal. When a conditional handover (CHO) operation is performed, the handover event may be a handover preparation event or a handover execution event.

[0117] When the difference between the reception quality of the neighboring base station measured by the member terminal and the reception quality of the serving base station measured by the member terminal is equal to or greater than the Type 1 offset, Type 2 offset, 'existing offset + Type 1 offset', or 'existing offset + Type 2 offset', the member terminal can determine that a handover event has occurred. Here, the member terminal can use the Type 1 offset or Type 2 offset based on the comparison result of its own speed with the speed threshold. Alternatively, when the reception quality of the neighboring base station measured by the member terminal is greater than or equal to the Type 1 threshold, Type 2 threshold, 'existing threshold + Type 1 threshold', or 'existing threshold + Type 2 threshold', the member terminal can determine that a handover event has occurred. Here, the member terminal can use the Type 1 threshold or Type 2 threshold based on the comparison result of its own speed with the speed threshold. Alternatively, regardless of whether the handover event is satisfied, a measurement report message can be sent to the head terminal.

[0118] The head terminal can receive a measurement report message from member terminals #1 and #2, and can identify the information elements included in the measurement report message. The neighboring base station indicated by the measurement report message may be a neighboring base station that the head terminal does not know. That is, the head terminal can obtain information about the neighboring base stations that the head terminal does not know by receiving the measurement report message from member terminals #1 and #2. The head terminal can generate a multicast configuration report message based on the information elements included in the measurement report message, and can send the multicast configuration report message to the serving base station (S803-1). The multicast configuration report message can be used to request resource allocation (for example, allocating resources for sidelink multicast communication) from the serving base station. The multicast configuration report message may include the information elements listed in Table 6 below. In addition, the multicast configuration report message may also include other information elements as well as the information elements listed in Table 6 below.

[0119] [Table 6]

[0120]

[0121] The multicast configuration report message may include the number of member terminals managed / controlled by the head terminal (such as numberofGroupcastMember in Table 6), identifiers of the member terminals (such as GroupcastMember-Identity in Table 6), a list of member terminals (such as GroupcastMember-List in Table 6), etc. The identifier of the member terminal may be a layer 2 (e.g., access stratum (AS) layer) identifier. The layer 2 identifier (i.e., L2 ID) may be mapped one-to-one with a higher layer identifier. The list of member terminals may be a list of member terminals managed / controlled by the head terminal.

[0122] ■Situation 2

[0123] When the measurement report indicator is set to the second value, each of member terminals #1 and #2 may transmit a measurement report message including the result of the measurement operation (e.g., reception quality information) to the serving base station (S802-2). The measurement report message may include the information elements listed in Table 7 below. In addition, the measurement report message may also include one or more information elements included in the existing measurement report message and the information elements shown in Table 7 below.

[0124] [Table 7]

[0125]

[0126] The measurement report message may include an identifier of the head terminal (e.g., GroupcastHeader-Identity in Table 7). In addition, the measurement report message may also include an identifier of the member terminal sending the measurement report message, reception quality information, an identifier of a neighboring base station related to the reception quality information, and the like. When a handover event occurs, each of member terminals #1 and #2 may send a measurement report message to the base station. The neighboring base station indicated by the measurement report message may be the neighboring base station where the handover event occurs. When a CHO operation is performed, the handover event may be a handover preparation event or a handover execution event. Alternatively, the measurement report message may be sent to the serving base station regardless of whether a handover event occurs.

[0127] At the same time, the serving base station may determine the target base station based on the multicast configuration report message received from the head terminal in case 1 or the measurement report messages received from member terminals #1 and #2 in case 2 (S804). For example, in case 1, the serving base station may determine one of the one or more neighboring base stations indicated by the multicast configuration report message as the target base station. In case 2, the serving base station may determine one of the one or more neighboring base stations indicated by the measurement report message as the target base station.

[0128] In this case, the serving base station may send a message (hereinafter referred to as a "mobility notification message") indicating that a handover to a neighboring base station (e.g., a target base station) detected by member terminals #1 and #2 will be performed to the head terminal (S805). The mobility notification message may include the information elements listed in Table 8 below. The mobility notification message may be a MemberTriggeredMobilityNotification of Table 8 below. In addition, the mobility notification message may also include other information elements as well as the information elements listed in Table 8 below.

[0129] [Table 8]

[0130]

[0131] The mobility notification message may include an identifier of the member terminal that has sent a measurement report message to the serving base station (e.g., MobilityTriggerMember-Identity in Table 8), a list of member terminals (e.g., MobilityTriggerMember-List in Table 8), a physical cell ID (e.g., physCellId in Table 8), a cell global ID (e.g., cellGlobalId in Table 8), a tracking area (TA) code (e.g., trackingAreaCode in Table 8), a public land mobile network (PLMN) identifier list (e.g., plmn-IdentityList listed in Table 8), etc. The identifier of the member terminal may be a layer 2 ID.

[0132] The head terminal may receive a mobility notification message from the serving base station and identify the information elements included in the mobility notification message. The head terminal may determine that a mobility operation (e.g., a handover operation) was triggered by the member terminal indicated in the mobility notification message. In case 1, since the head terminal receives measurement report messages from member terminals #1 and #2, step S805 may not be performed.

[0133] At the same time, the base station may generate a handover request message and may send the handover request message to the target base station. The handover request message may include information of the head terminal and information of one or more member terminals managed by the head terminal. For example, the handover request message may include an identifier of the head terminal, an identifier of the member terminal, a cell radio network temporary identifier (C-RNTI) assigned to the head terminal by the serving base station, a C-RNTI assigned to the member terminal by the serving base station, context information of the head terminal (e.g., UE context information, RRC context information), context information of the member terminal (e.g., UE context information, RRC context information), bearer configuration information of the head terminal, bearer configuration information of the member terminal, information of the AS layer of the header (e.g., security information), information of the AS layer of the member terminal (e.g., security information), etc. The handover request message may include the information elements listed in Table 9 below. In addition, the handover request message may also include information elements included in the existing handover request message and information elements shown in Table 9 below.

[0134] [Table 9]

[0135]

[0136]

[0137] The target base station may receive a handover request message from the serving base station and may identify the information elements included in the handover request message. The target base station may determine whether to approve the handover of the multicast group based on the information elements included in the handover request message. When the handover of the multicast group is approved, the target base station may send a handover request acknowledgement (ACK) message to the serving base station. The handover request ACK message may include the C-RNTI for the head / member terminal (e.g., the C-RNTI allocated by the target base station), context information (e.g., UE context information, RRC context information), bearer configuration information, etc.

[0138] In addition, the target base station can configure a group-RNTI for sidelink multicast communication and can send the group-RNTI to the serving base station. The group-RNTI can be included in the handover request ACK message. For resource allocation within the cell of the target base station, the target base station can map the group-RNTI to the terminals (e.g., head terminals and member terminals) belonging to the multicast group. The handover request ACK message may include the information elements listed in the following Table 10. In addition, the handover request ACK message may also include the information elements included in the existing handover request ACK message and the information elements shown in the following Table 10.

[0139] [Table 10]

[0140]

[0141] The serving base station may receive a handover request ACK message from the target base station and may identify the information elements included in the handover request ACK message. The serving base station may generate an RRC connection reconfiguration message including information about the head terminal and the member terminal, and may send the RRC connection reconfiguration message to the head terminal (S806). The RRC connection reconfiguration message may include an identifier of the target base station, resource configuration information of the target base station (e.g., information about an abnormal resource pool), etc. The RRC connection reconfiguration message may include the information elements listed in Tables 11 to 13 below. In addition, the RRC connection reconfiguration message may include the information elements included in the existing RRC connection reconfiguration message and the information elements shown in Tables 11 to 13 below.

[0142] [Table 11]

[0143]

[0144] [Table 12]

[0145]

[0146] [Table 13]

[0147]

[0148] The RRC connection reconfiguration message may indicate the use of resources configured by the target base station (e.g., an abnormal resource pool) instead of resources configured by the serving base station (e.g., dedicated resources). That is, the RRC connection reconfiguration message may further include transmission information of a handover reconfiguration application indicator (e.g., TxHOReconfigApplyIndication in Table 13). The transmission information of the handover reconfiguration application indicator set to a first value may instruct the head terminal to send the handover reconfiguration application indicator to the member terminal in order to apply the resource pool configuration included in the RRC connection reconfiguration message. The transmission information of the handover reconfiguration application indicator set to a second value may instruct the head terminal not to send the handover reconfiguration application indicator to the member terminal.

[0149] The head terminal may receive an RRC connection reconfiguration message from a serving base station and may identify information elements included in the RRC connection reconfiguration message. When the transmission information of the handover reconfiguration application indicator included in the RRC connection reconfiguration message received from the serving base station is set to a first value, the head terminal may send one or more information elements included in the corresponding RRC connection reconfiguration message to member terminals #1 and #2 (S807). The one or more information elements transmitted from the head terminal to member terminals #1 and #2 may be sent in the form of an RRC connection reconfiguration message. The RRC connection reconfiguration message may be sent from the head terminal to each of member terminals #1 and #2 via a PC5 interface.

[0150] The head terminal can instruct member terminals #1 and #2 to use the resource configuration of the target base station (e.g., an abnormal resource pool) by sending an RRC connection reconfiguration message. The RRC connection reconfiguration message sent from the head terminal to member terminals #1 and #2 may include the information elements shown in Tables 14 to 16 below. In addition, the RRC connection reconfiguration message may include the information elements included in the existing RRC connection reconfiguration message and the information elements shown in Tables 14 and 16 below. The RRC connection reconfiguration message may include a handover reconfiguration application indicator (e.g., HOReconfigApplyIndication described in Table 15). The handover reconfiguration application indicator set to a first value may instruct the member terminal to apply the resource pool configuration included in the RRC connection reconfiguration message. Alternatively, the handover reconfiguration application indicator set to a first value may instruct the member terminal to apply the resource pool configuration included in the RRC connection reconfiguration message and the resource pool configuration of the serving base station. The handover reconfiguration application indicator set to a second value may instruct the member terminal not to apply the resource pool configuration included in the RRC connection reconfiguration message.

[0151] [Table 14]

[0152]

[0153] [Table 15]

[0154]

[0155] [Table 16]

[0156]

[0157] Member terminals #1 and #2 may receive an RRC connection reconfiguration message from the head terminal and may identify an information element included in the RRC connection reconfiguration message. When the handover reconfiguration application indicator included in the RRC connection reconfiguration message is set to a first value, member terminals #1 and #2 may use the resource configuration (e.g., an abnormal resource pool) of the target base station included in the RRC connection reconfiguration message. Alternatively, when the handover reconfiguration application indicator is set to a first value, member terminals #1 and #2 may use the resource configuration of the target base station and the resource configuration of the serving base station.

[0158] After sending the RRC connection reconfiguration message to member terminals #1 and #2, the head terminal may perform an access procedure with the target base station (S808). Alternatively, the access procedure between the head terminal and the target base station may be performed before sending the RRC connection reconfiguration message. In the access procedure between the head terminal and the target base station, a random access procedure and a sending / receiving process of an RRC message (e.g., an RRC connection reconfiguration completion message) may be performed. When the access procedure between the head terminal and the target base station is completed, the head terminal may send a message indicating the completion of the access procedure (hereinafter referred to as a "connection completion message") to member terminals #1 and #2 (S809). The connection completion message may be used to instruct member terminals #1 and #2 to release the connection with the serving base station. The connection completion message may include the AS layer configuration (i.e., ASLayerConfiguration) of Table 17 below. That is, the connection completion message may be an RRC message including the AS layer configuration. Alternatively, the connection completion message may also be an RRC message other than the RRC message including the AS layer configuration.

[0159] [Table 17]

[0160]

[0161] Member terminals #1 and #2 receive a connection completion message from the head terminal. In this case, member terminals #1 and #2 may stop using the resource pool configured by the serving base station and may use the resource pool indicated by the RRC connection reconfiguration message received from the head terminal (e.g., the resource pool configured by the target base station). In addition, member terminals #1 and #2 may disconnect from the serving base station. Here, the resource pool configured by the target base station may be a Mode 1 Tx resource pool or a Mode 2 Tx resource pool.

[0162] When the above operations are completed (i.e., when the group handover operation is completed), the target base station can operate as the serving base station for the head terminal and member terminals #1 and #2. In other words, all terminals participating in sidelink multicast communication (e.g., head terminal and member terminals) can be handed over to the same target base station. Sidelink multicast communication can be performed using the resources configured by the new serving base station.

[0163] The exemplary embodiments of the present disclosure may be implemented as program instructions that can be executed by a variety of computers and recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, or a combination thereof. The program instructions recorded on the computer-readable medium may be specifically designed and configured for the present disclosure, or may be well known and available to those skilled in the art of computer software.

[0164] Examples of computer-readable media may include hardware devices such as ROM, RAM, and flash memory, which are specifically configured to store and execute program instructions. Examples of program instructions include, for example, machine code generated by a compiler and high-level language code executed by a computer using an interpreter. The above-mentioned exemplary hardware devices may be configured to operate as at least one software module to perform embodiments of the present disclosure, and vice versa.

[0165] Although the embodiments of the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the scope of the disclosure.

Claims

1. A method for operating a head terminal in sidelink multicast communication, the method comprising: sending a configuration information message to member terminals participating in the sidelink multicast communication, the configuration information message including a first indicator indicating a target of a measurement report; When the target of the measurement report indicated by the first indicator is the head terminal, receiving a measurement report message including a result of a measurement operation on one or more neighboring base stations from the member terminal; sending a configuration report message including a result of the measurement operation to a serving base station connected to the head terminal; receiving, from the serving base station, a first connection reconfiguration message including configuration information of a target base station determined based on a result of the measurement operation; sending a second connection reconfiguration message including configuration information of the target base station to the member terminal; Executing an access process with the target base station based on the configuration information of the target base station; as well as When the access process between the head terminal and the target base station is completed, a connection completion message is sent to the member terminal, where the connection completion message indicates that the connection with the serving base station is released.

2. The operating method according to claim 1, wherein: Each of the measurement report messages includes at least one of an identifier of a member terminal that transmits the measurement report message, reception quality information, an identifier of a neighboring base station related to the reception quality information, and a combination thereof.

3. The operating method according to claim 1, wherein: The measurement report message is received when a handover event occurs in the member terminal, and whether the handover event occurs is determined based on an offset or a threshold, wherein the offset or the threshold is included in the configuration information message.

4. The operating method according to claim 1, wherein: The configuration report message also includes information indicating the number of the member terminals and an identifier of each of the member terminals.

5. The operating method according to claim 1, wherein: The configuration information of the target base station includes an identifier of the target base station and resource pool information of the target base station.

6. The operating method according to claim 1, wherein: The second connection reconfiguration message further includes a second indicator, where the second indicator indicates application of the configuration information of the serving base station and the configuration information of the target base station.

7. A method for operating a head terminal in sidelink multicast communication, the method comprising: sending a configuration information message to member terminals participating in the sidelink multicast communication, the configuration information message including a first indicator indicating a target of a measurement report; When the target of the measurement report indicated by the first indicator is a serving base station, receiving a first connection reconfiguration message from the serving base station, the first connection reconfiguration message including configuration information of a target base station determined based on a result of the measurement operation performed by the member terminal, sending a second connection reconfiguration message including configuration information of the target base station to the member terminal; Executing an access process with the target base station based on the configuration information of the target base station; When the access process between the head terminal and the target base station is completed, a connection completion message is sent to the member terminal, where the connection completion message indicates that the connection with the serving base station is released.

8. The operating method according to claim 7, further comprising: Before receiving the first connection reconfiguration message, a mobility notification message is received from the serving base station, the mobility notification message indicating that a handover operation to the target base station will be performed based on a result of the measurement operation performed in the member terminal.

9. The operating method according to claim 8, wherein: The mobility notification message includes an identifier of each of the member terminals that has transmitted the result of the measurement operation to the serving base station.

10. The operating method according to claim 8, wherein: The configuration information of the target base station includes an identifier of the target base station and resource pool information of the target base station, and the second connection reconfiguration message also includes a second indicator, which indicates the application of the configuration information of the serving base station and the configuration information of the target base station.

11. A method for operating a member terminal in sidelink multicast communication, the method comprising: receiving a configuration information message from a head terminal managing the sidelink multicast communication, the configuration information message including a first indicator indicating a target of a measurement report; Performing measurement operations on a serving base station and one or more neighboring base stations to which the head terminal is connected; When the target of the measurement report indicated by the first indicator is the head terminal, sending a measurement report message including a result of the measurement operation to the head terminal; receiving a connection reconfiguration message from the head terminal, the connection reconfiguration message including configuration information of a target base station determined by the serving base station; receiving system information including the first indicator from the serving base station; as well as When the access procedure between the head terminal and the target base station is completed, a connection completion message is received from the head terminal, where the connection completion message indicates that the connection with the serving base station is released.

12. The operating method according to claim 11, wherein: The measurement report message is sent when a handover event occurs, and whether the handover event occurs is determined based on an offset or a threshold, and the offset or the threshold is included in the configuration information message.

13. A method for operating a member terminal in sidelink multicast communication, the method comprising: receiving a configuration information message from a head terminal managing the sidelink multicast communication, the configuration information message including a first indicator indicating a target of a measurement report; Performing measurement operations on a serving base station and one or more neighboring base stations to which the head terminal is connected; When the target of the measurement report indicated by the first indicator is the serving base station, sending a measurement report message including a result of the measurement operation to the serving base station; receiving a connection reconfiguration message from the head terminal, the connection reconfiguration message including configuration information of a target base station determined by the serving base station; as well as When the access procedure between the head terminal and the target base station is completed, a connection completion message is received from the head terminal, where the connection completion message indicates that the connection with the serving base station is released.

14. The operating method according to claim 13, wherein: The configuration information of the target base station includes an identifier of the target base station and resource pool information of the target base station, and the connection reconfiguration message also includes a second indicator indicating application of the configuration information of the serving base station and the configuration information of the target base station.

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