Communication methods, user devices, and network nodes, mobile communication systems, user device chipsets and programs

Abstract

This communication method, executed by user equipment in a mobile communication system that provides a multicast / broadcast service (MBS), comprises: a step of performing unicast communication with a serving cell in a radio resource control (RRC) connected state and receiving a broadcast session from a non-serving cell; and a step of transmitting, to a network node managing the serving cell, information indicating a desire to stop the unicast communication in order to receive the broadcast session.

Description

COMMUNICATION METHOD, USER EQUIPMENT, AND NETWORK NODE

[0001] The present disclosure relates to a communication method, a user equipment, and a network node for use in a mobile communication system.

[0002] The 3rd Generation Partnership Project (3GPP) (registered trademark; the same applies hereinafter) defines the technical specifications for NR (New Radio), a fifth-generation (5G) wireless access technology. Compared to LTE (Long Term Evolution), a fourth-generation (4G) wireless access technology, NR has features such as high speed, large capacity, high reliability, and low latency. 3GPP also defines the technical specifications for 5G / NR multicast / broadcast services (MBS).

[0003] 3GPP Technical Specification: TS 38.300 V17.4.0

[0004] A communication method according to a first aspect is a communication method executed by a user equipment in a mobile communication system that provides a multicast / broadcast service (MBS), and includes the steps of: performing unicast communication with a serving cell and receiving a broadcast session from a non-serving cell in a Radio Resource Control (RRC) Connected state; and transmitting information indicating a desire to stop the unicast communication in order to receive the broadcast session to a network node that manages the serving cell.

[0005] A user equipment according to a second aspect is a user equipment used in a mobile communication system that provides a multicast / broadcast service (MBS), and has a receiving unit that, in a radio resource control (RRC) connected state, performs unicast communication with a serving cell and receives a broadcast session from a non-serving cell, and a transmitting unit that transmits information indicating a desire to stop the unicast communication in order to receive the broadcast session to a network node that manages the serving cell.

[0006] A network node according to a third aspect is a network node used in a mobile communication system that provides a multicast / broadcast service (MBS), and includes: a control unit that performs unicast communication with a user equipment in a radio resource control (RRC) connected state in a serving cell managed by the network node; and a receiving unit that receives, from the user equipment that receives a broadcast session from a non-serving cell, information indicating a desire to stop the unicast communication in order to receive the broadcast session.

[0007] 1 is a diagram showing an example of the configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram showing an example of the configuration of a UE (user equipment) according to an embodiment. FIG. 3 is a diagram showing an example of the configuration of a gNB (network node) according to an embodiment. FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). FIG. 6 is a diagram for explaining an operation scenario of a mobile communication system according to an embodiment. FIG. 7 is a diagram showing a communication method executed by a UE according to an embodiment. FIG. 8 is a diagram showing an example of a first operation pattern of a mobile communication system according to an embodiment. FIG. 9 is a diagram showing an example of a second operation pattern of a mobile communication system according to an embodiment.

[0008] A user equipment (UE) in a Radio Resource Control (RRC) Connected state that is in unicast communication with a serving cell may receive a broadcast session from a non-serving cell while in unicast communication with the serving cell. However, such broadcast reception may be difficult due to limited reception resources (e.g., receivers) available to the UE.

[0009] Therefore, an object of the present disclosure is to enable a user equipment to receive MBS from a non-serving cell.

[0010] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0011] (1) System Configuration Example Fig. 1 is a diagram showing a configuration example of a mobile communication system 1 according to an embodiment. The mobile communication system 1 conforms to the 3GPP standard 5th Generation System (5GS). Although 5GS will be described below as an example, the mobile communication system may be at least partially based on an LTE (Long Term Evolution) system. The mobile communication system may be at least partially based on a 6th Generation (6G) system.

[0012] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN: Next Generation Radio Access Network) 10, and a 5G core network (5GC: 5G Core Network) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10. Furthermore, the 5GC 20 may be simply referred to as the core network (CN) 20. The RAN 10 and the CN 20 constitute the network of the mobile communication system 1.

[0013] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone) and / or a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0014] The NG-RAN 10 includes a base station (referred to as "gNB" in the 5G system) 200, which is a type of network node. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, etc. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource that performs wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0015] In addition, gNBs can also be connected to the Evolved Packet Core (EPC), which is the core network of LTE. LTE base stations can also be connected to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0016] The 5GC20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and the UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0017] 2 is a diagram illustrating an example configuration of a UE 100 (user equipment) according to an embodiment. The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 configure a wireless communication unit that performs wireless communication with the gNB 200.

[0018] The receiving unit 110 performs various reception operations under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0019] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0020] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer described below. The operations of the UE 100 described above and below may be operations under the control of the control unit 230. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0021] 3 is a diagram showing an example configuration of a gNB 200 (network node) according to an embodiment. The gNB 200 has a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN 20.

[0022] The transmitting unit 210 performs various transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0023] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0024] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes for each layer described below. The operations of the gNB 200 described above and below may be operations under the control of the control unit 230. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0025] The backhaul communication unit 240 is connected to adjacent base stations via an Xn interface, which is an interface between base stations. The backhaul communication unit 240 is connected to the AMF / UPF 300 via an NG interface, which is an interface between a base station and a core network. Note that the gNB 200 is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and the two units may be connected by an F1 interface, which is a fronthaul interface.

[0026] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0027] The user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0028] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has a CRC (Cyclic Redundancy Code) parity bit scrambled by the RNTI added.

[0029] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of the UE 100 and the MAC layer of the gNB 200 via a transport channel. The MAC layer of the gNB 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to the UE 100.

[0030] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via a logical channel.

[0031] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0032] The SDAP layer maps IP flows, which are units for Quality of Service (QoS) control by the core network, to radio bearers, which are units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP may not be required.

[0033] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0034] The protocol stack of the radio interface of the control plane has an RRC (Radio Resource Control) layer and an NAS (Non-Access Stratum) layer instead of the SDAP layer shown in FIG.

[0035] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0036] The NAS layer (also simply referred to as "NAS") positioned above the RRC layer performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300A. Note that the UE 100 has an application layer and the like in addition to the radio interface protocol. Also, a layer lower than the NAS layer is referred to as the AS layer (also simply referred to as "AS").

[0037] (2) Overview of MBS The mobile communication system 1 can perform resource-efficient distribution using multicast / broadcast services (MBS).

[0038] (2.1) MBS Broadcast In the case of a broadcast communication service (also referred to as "MBS Broadcast"), the same service and the same specific content data are simultaneously provided to all UEs 100 in a geographical area. That is, all UEs 100 within the broadcast service area are permitted to receive the data. The broadcast communication service is delivered to the UEs 100 using a broadcast session, which is a type of MBS session. The UEs 100 can receive the broadcast session in any of the RRC idle state, RRC inactive state, and RRC connected state. Note that the MBS session can be identified by an MBS session ID, for example, a Temporary Mobile Group Identity (TMGI).

[0039] Point-to-Multipoint (PTM) delivery is applied to broadcast communication services. In the case of PTM transmission, the gNB 200 delivers a single copy of an MBS packet to a set (group) of multiple UEs 100. For example, the gNB 200 schedules a group-common PDSCH scrambled by a G-RNTI (Group RNTI), which is a group-common RNTI, using a group-common PDCCH having a CRC scrambled by the G-RNTI.

[0040] In the case of a broadcast communication service, the UE 100 receives a broadcast session in the following procedure. First, the UE 100 receives a system information block type 20 (SIB20) from the gNB 200. The SIB20 includes a configuration of a multicast control channel (MCCH), which is a type of logical channel. Second, the UE 100 receives the MCCH from the gNB 200 based on the SIB20. The MCCH includes a PTM configuration. The PTM configuration transmits a configuration for a multicast traffic channel (MTCH), which is a type of logical channel, and a configuration of a broadcast MRB, which is a multicast radio bearer (MRB) for the broadcast session. The information transmitted by the MCCH is sometimes referred to as MBS broadcast control information. Third, the UE 100 receives the MTCH based on the MCCH. The MTCH transmits the broadcast session (specifically, MBS data belonging to the broadcast session).

[0041] The MCCH is a PTM downlink channel for transmitting MBS broadcast control information associated with one or more MTCHs from the network 10 to the UE 100. The MTCH is a PTM downlink channel for transmitting MBS data of either a multicast session or a broadcast session from the network 10 to the UE 100.

[0042] (2.2) MBS Multicast In the case of a multicast communication service (also referred to as "MBS multicast"), the same service and the same specific content data are simultaneously provided to a specific set of UEs. That is, not all UEs 100 within a multicast service area are permitted to receive the data. The multicast communication service is delivered to the UEs 100 using a multicast session, which is a type of MBS session.

[0043] The UE 100 can receive the multicast session only after joining the multicast session (session join). Joining the multicast session may mean being registered in the network 5 (CN 20) as the UE 100 that can receive the multicast session.

[0044] In the case of a multicast communication service, only UEs 100 in an RRC connected state can receive a multicast session in 3GPP Release 17. On the other hand, in 3GPP Release 18, this will be extended so that UEs 100 in an RRC inactive state can also receive a multicast session.

[0045] (3) Operation of the Mobile Communication System The operation of the mobile communication system 1 according to the embodiment will be described with reference to FIGS.

[0046] (3.1) Operation Scenario FIG. 6 is a diagram for explaining an operation scenario of the mobile communication system 1 according to the embodiment.

[0047] UE100 existing in the overlapping area of ​​cell a and cell b is in an RRC connected state with cell a and performs unicast communication with cell a. That is, cell a is the serving cell of UE100, and cell b is a non-serving cell (neighboring cell) of UE100. Cell a operates at frequency (carrier frequency) a, and cell b may operate at frequency b different from frequency a. In the illustrated example, cell a is managed by gNB200a, and cell b is managed by gNB200b different from gNB200a. However, cell a and cell b may be managed by the same gNB200.

[0048] In cell a, UE100 in an RRC connected state performs unicast communication (specifically, data communication) with cell a (gNB200a). For example, UE100 is assigned a C-RNTI from gNB200a as an RRC connection identifier. gNB200a assigns radio resources (specifically, uplink communication resources and downlink communication resources) to UE100 by scheduling for UE100.

[0049] Cell b (gNB200b) transmits MBS data belonging to the broadcast session in PTM, i.e., broadcasts it by MBS broadcast. UE100 performs unicast communication with cell a, which is the serving cell, and receives a broadcast session from cell b, which is a non-serving cell (hereinafter simply referred to as "broadcast reception" or "MBS broadcast reception"). Here, UE100 performs broadcast reception by receiving MTCH from the non-serving cell based on MCCH from the non-serving cell.

[0050] For example, the UE 100 has at least two receivers (RX), specifically, RX #1 and RX #2. The RX #1 and RX #2 may constitute a receiving unit 110. The UE 100 uses one RX (e.g., RX #1) for unicast communication and the other RX (e.g., RX #2) for MBS broadcast reception.

[0051] Thus, in the embodiment, the UE 100 performing unicast communication with the serving cell (cell a) in the RRC connected state can receive a broadcast session from a non-serving cell (cell b) during the unicast communication with the serving cell. However, since the reception resources (e.g., RX) available to the UE 100 are limited, it may be difficult to perform such broadcast reception.

[0052] For example, due to the load of unicast communication of UE 100, it may be possible to receive the MTCH from a non-serving cell but not receive the MCCH from the non-serving cell. Also, as a result of UE 100 receiving an MCCH change notification from a non-serving cell, it may be necessary to reduce the load of unicast communication in order to continue receiving the MTCH in the non-serving cell. Furthermore, it may be possible that the frequency providing the MBS broadcast in the non-serving cell is changed.

[0053] (3.2) Overview of Operation of Mobile Communication System In the embodiment, the UE 100 is facilitated to receive MBS broadcast from a non-serving cell. Figure 7 is a diagram showing a communication method executed by the UE 100 according to the embodiment. It is assumed that the UE 100 is in an RRC connected state in the serving cell (cell a).

[0054] In step S1, the UE 100 performs unicast communication with a serving cell (cell a) and receives a broadcast session from a non-serving cell (cell b).

[0055] In step S2, the UE 100 transmits information indicating a desire to stop unicast communication in order to receive the broadcast session to the gNB 200 (gNB 200a) that manages the serving cell (cell a). In an embodiment, the UE 100 may transmit an MBS Interest Indication message including the information to the gNB 200 (gNB 200a). Alternatively, the UE 100 may transmit a UE Assistance Information message including the information to the gNB 200 (gNB 200a). Note that the MBS Interest Indication message (hereinafter also referred to as an "MII message") and the UE Assistance Information message (hereinafter also referred to as a "UAI message") are both RRC layer messages (i.e., RRC messages).

[0056] A UE 100 that performs such operations has, in an RRC connected state, a receiver 110 that performs unicast communication with a serving cell (cell a) and receives a broadcast session from a non-serving cell (cell b), and a transmitter 120 that transmits information indicating a desire to stop unicast communication in order to receive the broadcast session to a gNB 200 (gNB 200a) that manages the serving cell (cell a) (see Figure 2).

[0057] On the other hand, gNB200 (gNB200a) that manages the serving cell (cell a) has a control unit 230 that performs unicast communication with UE100 in an RRC connected state in the serving cell (cell a), and a receiving unit 220 that receives information from UE100 that receives a broadcast session from a non-serving cell (cell b) indicating a desire to stop unicast communication in order to receive the broadcast session (see Figure 3).

[0058] In a first operation pattern of the embodiment, in step S2, the UE 100 transmits to the gNB 200 (gNB 200a) stop request information indicating a desire to temporarily stop unicast communication. The UE 100 may transmit to the gNB 200 (gNB 200a) stop request information including information indicating a period during which the unicast communication is temporarily stopped. During the period during which the unicast communication is temporarily stopped, the UE 100 may change the reception resources (e.g., RX) used for receiving the unicast communication to be used for receiving a broadcast session. The UE 100 may change the reception resources to be used for unicast communication according to the end of the period during which the unicast communication is temporarily stopped.

[0059] In a second operation pattern of the embodiment, in step S2, the UE 100 transmits change request information indicating a desire to change the serving cell (cell a) to the gNB 200 (gNB 200a). The UE 100 may transmit change request information including information indicating the frequency of the serving cell to be changed to the gNB 200 (gNB 200a). The UE 100 may receive an RRC reconfiguration message from the gNB 200 instructing the change of the serving cell. Then, in response to the change of the serving cell, the UE 100 may change the reception resources (e.g., RX) used for receiving unicast communications to be used for receiving broadcast sessions.

[0060] In the following description of the embodiment, the term "reception resource" is a term that mainly refers to the receiver (RX) of the UE 100. However, the term "reception resource" may be a term that refers to the processing capacity of the UE 100 (for example, the processing capacity (processing capacity) of a processor) that is used for reception, in addition to or instead of the RX of the UE 100.

[0061] (4) Specific Examples of Operation Examples of the first and second operation patterns of the mobile communication system 1 according to the embodiment will be described.

[0062] (4.1) Example of First Operation Pattern Figure 8 is a diagram showing an example of a first operation pattern of the mobile communication system 1 according to the embodiment. In the first operation pattern, the UE 100 transmits, to the gNB 200 (gNB 200a), request information for stopping unicast scheduling for a certain period of time.

[0063] In step S100, UE 100 is in an RRC connected state in a serving cell (cell a).

[0064] In step S101, the UE 100 performs unicast communication with a serving cell (cell a).

[0065] In step S102, UE 100 performs unicast communication with a serving cell (cell a) and receives an MBS broadcast from a non-serving cell (cell b). For example, UE 100 uses RX #1 for unicast communication and RX #2 for MBS broadcast reception.

[0066] In step S103, the UE 100 may receive an MCCH from a non-serving cell (cell b). The UE 100 may determine, based on the MCCH, that the MBS broadcast frequency is to be changed.

[0067] In step S104, UE100 determines to temporarily allocate a receiving resource (e.g., RX#1) used in unicast communication to MBS broadcast. Note that, if there are multiple RXs used in unicast communication, UE100 may determine to temporarily allocate the multiple RXs used in unicast communication to MBS broadcast. Alternatively, UE100 may determine to temporarily allocate the receiving capability (receiving processing amount) used in unicast communication to MBS broadcast.

[0068] For example, when the UE 100 detects that the MBS broadcast frequency is changed, the UE 100 may determine to temporarily allocate the reception resources used in the unicast communication to the MBS broadcast. Under the premise of performing a search (full scan) to find the changed MBS broadcast frequency, the UE 100 temporarily allocates the RX used in the unicast communication to the MBS broadcast and performs the search, so that the search can be completed faster by using two RXs than one RX.

[0069] Alternatively, the UE 100 may measure the reception quality of the MTCH and / or MCCH in a non-serving cell (cell b), and when it detects that the reception quality has deteriorated below a threshold, it may determine to temporarily allocate the reception resources used in unicast communication to the MBS broadcast. The reception quality may be at least one of the reference signal received power (RSRP), the reference signal received quality (RSRP), the signal-to-interference-and-noise ratio (SINR), the bit error rate (BER), the block error rate (BLER), and the packet error rate (PER). The threshold may be set to the UE 100 by the gNB 200 (gNB 200a). For example, the UE 100 can improve the reception sensitivity (reception quality) of the MBS broadcast reception by allocating the RX used for unicast to the MBS broadcast reception and performing diversity reception with 2RX.

[0070] Alternatively, UE 100 may measure the reception processing amount (processing load) in a non-serving cell (cell b), and when it detects that the reception processing amount is greater than a threshold, it may determine to temporarily allocate the reception resources used in unicast communication to MBS broadcast. For example, if the subcarrier spacing (SCS: Sub-Carrier Spacing) of MBS broadcast becomes wider, that is, if the symbol length becomes shorter, the processing load of digital signal processing increases, making it impossible to process MBS broadcast reception, and packet errors may occur. In such a case, the reception quality of MBS broadcast reception can be improved by allocating the processing capacity used for unicast communication to MBS broadcast reception.

[0071] In step S105, the UE 100 transmits an MII message (or a UAI message) including stop request information indicating a desire (request) to temporarily suspend unicast communication to the serving cell, cell a (gNB 200a). The gNB 200a receives the message.

[0072] The stop request information may include time information indicating a period during which the unicast communication is to be stopped. The time information may include at least one of information indicating a start timing of the period during which the unicast communication is to be stopped and information indicating a length of time (duration) during which the unicast communication is to be stopped. The time information may include information indicating an end timing of the period during which the unicast communication is to be stopped.

[0073] The stop request information may include cause information indicating the reason for temporarily stopping the unicast communication, which may be information indicating that the reason is reception of an MBS broadcast.

[0074] In step S106, if gNB200a accepts the request of step S105, it may send a notification or configuration indicating such acceptance to UE100.

[0075] The setting may be a suspend setting for temporarily transitioning the UE 100 to an RRC inactive state.

[0076] The notification or setting may include time information indicating a period during which unicast communication is stopped. The time information may include at least one of information indicating a start timing of the period during which unicast communication is stopped and information indicating a length of time (duration) during which unicast communication is stopped. The information indicating the length of time may be a timer value set in a timer described below. The time information may include information indicating an end timing of the period during which unicast communication is stopped.

[0077] In step S107, the UE 100 stops the unicast communication when the stop request information is transmitted in step S105 or when the notification or setting is received in step S106. The UE 100 may start a timer that specifies a time for stopping the unicast communication.

[0078] In step S108, that is, during the period in which the unicast communication is temporarily stopped, the UE 100 changes the reception resources (e.g., RX and / or processing capacity) used in the unicast communication to be used for MBS broadcast reception. That is, the UE 100 attempts to receive the MBS broadcast using the reception resources used in the unicast communication.

[0079] For example, UE 100 may temporarily allocate the RX used for unicast communication to MBS broadcast and perform a search under the assumption that the MBS broadcast frequency is changed. Alternatively, UE 100 may allocate the RX used for unicast communication to MBS broadcast reception and perform diversity reception with 2RX under the assumption that the reception quality of the MTCH and / or MCCH in a non-serving cell (cell b) has deteriorated below a threshold. Alternatively, UE 100 may allocate the processing capacity used for unicast communication to MBS broadcast reception under the assumption that the reception processing amount (processing load) in a non-serving cell (cell b) has increased above a threshold.

[0080] In step S109, i.e., at the end of the period during which unicast communication is temporarily stopped (e.g., when the timer expires), UE100 changes the receiving resources allocated for MBS broadcast reception to be used for unicast communication, and returns to (resumes) the original unicast communication state.

[0081] In this operation example, if the problem is not resolved even after temporarily allocating the reception resource to the MBS broadcast reception in step S108, the UE 100 may perform the following operation.

[0082] For example, when the UE 100 prioritizes MBS broadcast reception, the UE 100 may transmit to the gNB 200a Release Assistance Information (RAI) indicating that it desires to transition from the RRC connected state to the RRC idle state or the RRC inactive state. Here, the UE 100 may transmit cause information indicating that the MBS broadcast reception is prioritized together with the RAI.

[0083] The gNB 200a transitions the UE 100 from the RRC connected state to the RRC idle state or the RRC inactive state according to the RAI. As a result, the reception resources used for unicast communication are released, and the reception resources become available for receiving MBS broadcasts.

[0084] On the other hand, if the problem is not resolved even after temporarily allocating receiving resources to MBS broadcast reception in step S108 and unicast communication is prioritized, UE100 may stop MBS broadcast reception and discard the broadcast MRB.

[0085] (4.2) Example of second operation pattern Figure 9 is a diagram showing an example of a second operation pattern of the mobile communication system 1 according to the embodiment. In the second operation pattern, the UE 100 transmits information indicating a desire to change the serving cell to the gNB 200a.

[0086] In this operation example, it is assumed that UE 100 has two RXs, RX #1 and RX #2, with RX #1 corresponding to frequencies F1 and F3, and RX #2 corresponding to frequency F2. Under this assumption, UE 100 receives unicast at F1 (RX #1) and MBS broadcast at F2 (RX #2). If the MBS broadcast is subsequently changed from F2 to F3, it may be necessary for UE 100 to allocate RX #1 to the MBS broadcast.

[0087] In step S200, the UE 100 is in an RRC connected state in a serving cell (cell a) operated at frequency F1.

[0088] In step S201, the UE 100 performs unicast communication with a serving cell (cell a) that operates at frequency F1.

[0089] In step S202, UE 100 performs unicast communication with a serving cell (cell a) operating at frequency F1, and also performs MBS broadcast reception from a non-serving cell (cell b) operating at frequency F2. For example, UE 100 uses RX #1 for unicast communication with the serving cell (cell a), and uses RX #2 for MBS broadcast reception from the non-serving cell (cell b).

[0090] In step S203, the UE 100 may receive an MCCH from a non-serving cell (cell b). The UE 100 may determine, based on the MCCH, that the MBS broadcast frequency is changed from frequency F2 to frequency F3.

[0091] In step S204, UE100 determines that RX#1, which is used for unicast communication with the serving cell (cell a), will be continuously allocated to MBS broadcast. In this operation example, UE100 has two RXs, RX#1 and RX#2, where RX#1 supports frequencies F1 and F3, and RX#2 supports frequency F2. When the MBS broadcast frequency is changed from frequency F2 to frequency F3, UE100 determines that the use of RX#1 corresponding to frequency F3 will be changed from unicast communication to MBS broadcast reception in order to receive the MBS broadcast. UE100 also determines that the use of RX#2 corresponding to frequency F2 will be changed from MBS broadcast reception to unicast communication.

[0092] In step S205, gNB200b changes the MBS broadcast frequency providing the broadcast session from frequency F2 to frequency F3.

[0093] In step S206, UE100 transmits an MII message (or UAI message) including change request information indicating a desire (request) to change the serving cell to cell a (gNB200a), which is the serving cell. gNB200a receives the message. The change request information includes frequency information indicating the frequency of the handover destination cell, and may be a request for handover to a cell of that frequency (handover request). The change request information may include cause information indicating the reason for changing the serving cell. The cause information may be information indicating that the reason is MBS broadcast reception.

[0094] In step S207, if the gNB200a accepts the request of step S206, it transmits an RRC Reconfiguration message equivalent to a handover command to the UE100 to change the serving cell. The RRC Reconfiguration message includes information specifying cell c operated in frequency F2 as the handover target. Cell c may be the cell of gNB200c.

[0095] In step S207, in response to the reception of the handover command (RRC Reconfiguration message) in step S207, the UE 100 accesses the cell c operating at the frequency F2 and changes the serving cell from the cell a to the cell c. Here, the UE 100 changes to use RX #2 for unicast communication with the cell c.

[0096] In step S209, UE100 attempts to receive the MBS broadcast provided at frequency F3 using RX#1 that was used for unicast communication, and receives the MBS broadcast from the non-serving cell (cell b) using RX#1.

[0097] In step S210, UE100 performs unicast communication with cell c (gNB200c), which is a new serving cell, using RX#2.

[0098] (5) Modification In the above embodiment, the serving cell, cell a (gNB200a), may belong to a first public land mobile network (PLMN), and the non-serving cell, cell b (gNB200b), may belong to a second PLMN different from the first PLMN. Such a PLMN relationship is also referred to as inter-PLMN.

[0099] The UE 100 may have a SIM (Subscriber Identity Module) corresponding to the first PLMN, but may not have a SIM corresponding to the second PLMN. For example, cell b (gNB 200b) may provide a broadcast session in ROM (Receive-Only Mode) and / or FTA (Free-To-Air). Such an MBS broadcast may be a broadcast-only service such as a general television broadcast or radio broadcast. ROM is a mode in which MBS reception is possible even for a UE 100 that does not have a SIM (Subscriber Identity Module) and / or does not have a service contract with an operator (PLMN). FTA is an application (service) that enables free broadcast content broadcast. FTA may be one aspect of ROM. The MBS broadcasts provided in the FTA may be made available to all users who are not mobile subscribers.

[0100] Alternatively, the UE 100 may have both a SIM corresponding to the first PLMN and a SIM corresponding to the second PLMN. Such a UE 100 is also called a Multi-SIM UE or a Multi-USIM (Universal Subscriber Identity Module) UE. The UE 100 receives an MBS broadcast provided by a ROM or FTA from the second PLMN.

[0101] (6) Other Embodiments In the above-described embodiment, a scenario in which UE 100 receives an MBS broadcast from a non-serving cell is assumed, but a scenario in which UE 100 receives an MBS multicast from a non-serving cell may also be assumed. Therefore, the reception scenario of a broadcast (broadcast session) in the operation according to the above-described embodiment may be diverted to a reception scenario of a multicast (multicast session).

[0102] The above-described operational flows are not limited to being implemented independently, but can also be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow. In each flow, it is not necessary to execute all steps, and only some steps may be executed.

[0103] In the above-described embodiments and examples, an example in which the network node is an NR base station (gNB) has been described, but the network node may be an LTE base station (eNB) or a 6G base station. The network node may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The network node may also be a DU of the IAB node. The UE 100 may also be an MT (Mobile Termination) of the IAB node.

[0104] That is, the UE 100 may be a terminal function unit (a type of communication module) for a base station to control a repeater that relays signals. Such a terminal function unit is referred to as an MT. Examples of the MT include, in addition to the IAB-MT, an NCR (Network Controlled Repeater)-MT and a RIS (Reconfigurable Intelligent Surface)-MT.

[0105] The term "network node" primarily refers to a base station, but may also refer to a core network device or a part of a base station (CU, DU, or RU). A network node may also be configured by a combination of at least a part of a core network device and at least a part of a base station.

[0106] A program may be provided that causes a computer to execute each process performed by the UE 100 or the gNB 200. The program may be recorded on a computer-readable medium. Using a computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by the UE 100 or the gNB 200 may be integrated, and at least a portion of the UE 100 or the gNB 200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0107] The functions performed by the UE 100 or the NB 200 (network node) may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a CPU (a Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to perform the described functions. A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. A processor may also be a programmed processor that executes a program stored in memory. In this specification, circuitry, unit, or means refers to hardware that is programmed to perform the described functions or that executes the described functions. The hardware may be any hardware disclosed herein or any hardware known to be programmed or capable of performing the described functions. If the hardware is a processor, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0108] As used in this disclosure, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Additionally, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0109] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0110] This application claims priority from Japanese Patent Application No. 2023-125274 (filed August 1, 2023), the entire contents of which are incorporated herein by reference.

[0111] (7) Supplementary Notes The following are additional notes regarding the features of the above-described embodiment.

[0112] (Supplementary Note 1) A communication method executed by a user equipment in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a step of performing unicast communication with a serving cell and receiving a broadcast session from a non-serving cell in a radio resource control (RRC) connected state; and a step of transmitting information indicating a desire to stop the unicast communication in order to receive the broadcast session to a network node that manages the serving cell.

[0113] (Supplementary Note 2) The communication method according to Supplementary Note 1, wherein the transmitting step includes a step of transmitting stop request information indicating a desire to temporarily stop the unicast communication to the network node.

[0114] (Supplementary Note 3) The communication method according to Supplementary Note 2, wherein the step of transmitting the stoppage desire information includes a step of transmitting the stoppage desire information including information indicating a period for which the unicast communication is temporarily stopped to the network node.

[0115] (Supplementary Note 4) The communication method according to Supplementary Note 2 or 3, further comprising the step of changing a reception resource used for receiving the unicast communication to be used for receiving the broadcast session during a period in which the unicast communication is temporarily stopped.

[0116] (Supplementary Note 5) The communication method according to Supplementary Note 4, further comprising the step of changing the receiving resources to be used for the unicast communication in response to an end of the period during which the unicast communication is temporarily suspended.

[0117] (Supplementary Note 6) The communication method according to Supplementary Note 1, wherein the transmitting step includes the step of transmitting, to the network node, change desire information indicating a desire to change the serving cell.

[0118] (Supplementary Note 7) The communication method according to Supplementary Note 6, wherein the step of transmitting the change request information includes a step of transmitting the change request information including information indicating a frequency of a serving cell to be changed to the network node.

[0119] (Supplementary Note 8) The communication method according to Supplementary Note 6 or 7, further comprising: receiving an RRC reconfiguration message from the network node instructing a change of the serving cell; and, in response to the change of the serving cell, changing reception resources used for receiving the unicast communication to be used for receiving the broadcast session.

[0120] (Supplementary Note 9) The communication method according to any one of Supplementary Notes 1 to 8, wherein the transmitting step includes the step of transmitting an MBS interest indication message including the information to the network node.

[0121] (Supplementary Note 10) A user equipment used in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a receiving unit that performs unicast communication with a serving cell and receives a broadcast session from a non-serving cell in a radio resource control (RRC) connected state; and a transmitting unit that transmits information indicating a desire to stop the unicast communication in order to receive the broadcast session to a network node that manages the serving cell.

[0122] (Supplementary Note 11) A network node used in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a control unit that performs unicast communication with a user equipment in a radio resource control (RRC) connected state in a serving cell managed by the network node; and a receiving unit that receives, from the user equipment that receives a broadcast session from a non-serving cell, information indicating a desire to stop the unicast communication in order to receive the broadcast session.

[0123] 1: Mobile communication system 5: Network 10: RAN 20: CN 100: UE (user equipment) 110: Receiving unit 120: Transmitting unit 130: Control unit 200: gNB (network node) 210: Transmitting unit 220: Receiving unit 230: Control unit 240: Backhaul communication unit

Claims

1. A communication method performed by a user device that is a Multi-USIM (Universal Subscriber Identity Module) UE in a mobile communication system, To communicate with serving cells belonging to the first network, The user device, while in a Radio Resource Control (RRC) connected state on the first network, transmits a message to the network node managing the serving cell, containing information indicating a desire to change the settings of the serving cell for communication on the second network. Communication method.

2. The message includes frequency information desired by the user device for communication in the second network. The communication method according to claim 1.

3. A user device that is a Multi-USIM (Universal Subscriber Identity Module) UE, A control unit that communicates with a serving cell belonging to the first network, The user device has a transmitting unit that, while the user device is in a Radio Resource Control (RRC) connected state on the first network, transmits a message to the network node managing the serving cell, which includes information indicating a desire to change the settings of the serving cell for communication on the second network. User device.

4. A network node for use in a mobile communication system, In a serving cell managed by the aforementioned network node and belonging to the first network, a control unit communicates with a user device which is a Multi-USIM (Universal Subscriber Identity Module) UE in a Radio Resource Control (RRC) connected state, The system includes a receiving unit that receives a message from the user device, which is in an RRC connected state in the first network, that includes information indicating a desire to change the settings of the serving cell for communication in the second network. Network node.

5. The user device according to claim 3, The network node manages the serving cell and receives the message. Mobile communication system.

6. A chipset for a user device that is a Multi-USIM (Universal Subscriber Identity Module) UE, To communicate with serving cells belonging to the first network, While the user device is in a Radio Resource Control (RRC) connected state on the first network, it sends a message to the network node managing the serving cell, containing information indicating a desire to change the settings of the serving cell for communication on the second network. Chipset.

7. A user device that is a Multi-USIM (Universal Subscriber Identity Module) UE, The process involves communicating with a serving cell belonging to the first network, While the user device is in a Wireless Resource Control (RRC) connected state on the first network, the user device will perform the following process: send a message to the network node managing the serving cell, containing information indicating a desire to change the settings of the serving cell for communication on the second network. program.