WO2025028595A1 - Communication method, user equipment, and network node - Google Patents

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

This disclosure relates to a communication method, user equipment, and network node for use in a mobile communication system.

3GPP (3rd Generation Partnership Project) (registered trademark; the same applies below) 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 defines the technical specifications for 5G/NR multicast/broadcast service (MBS).

3GPP Technical Specification: TS 38.300 V17.4.0

The communication method according to the first aspect is a communication method executed by a user device 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.

The user equipment according to the second aspect is a user equipment used in a mobile communication system that provides a multicast/broadcast service (MBS), and has a receiver that performs unicast communication with a serving cell in a radio resource control (RRC) connected state and receives a broadcast session from a non-serving cell, and a transmitter 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.

The network node according to the 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 device in a radio resource control (RRC) connected state in a serving cell managed by the network node, and a receiving unit that receives information indicating a desire to stop the unicast communication in order to receive the broadcast session from the user device that receives a broadcast session from a non-serving cell.

FIG. 1 is a diagram illustrating a configuration example of a mobile communication system according to an embodiment. FIG. 2 is a diagram illustrating a configuration example of a UE (user equipment) according to an embodiment. A diagram showing an example configuration of a gNB (network node) according to an embodiment. A diagram showing the configuration of a protocol stack of a wireless interface of a user plane that handles data. A diagram showing the configuration of a protocol stack of the wireless interface of the control plane that handles signaling (control signals). FIG. 2 is a diagram for explaining an operation scenario of the mobile communication system according to the embodiment. FIG. 2 is a diagram showing a communication method performed by a UE according to an embodiment. FIG. 2 is a diagram showing an example of a first operation pattern of the mobile communication system according to the embodiment. FIG. 11 is a diagram showing an example of a second operation pattern of the mobile communication system according to the embodiment.

A user equipment performing unicast communication with a serving cell in a Radio Resource Control (RRC) connected state may receive a broadcast session from a non-serving cell during unicast communication with the serving cell. However, since the receiving resources (e.g., receivers) available to the user equipment are limited, it may be difficult to perform such broadcast reception.

Therefore, the present disclosure aims to enable user equipment to receive MBS from a non-serving cell.

The mobile communication system according to the embodiment will be described with reference to the drawings. In the drawings, the same or similar parts are denoted by the same or similar reference numerals.

(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 complies with the 3GPP standard 5th generation system (5GS: 5th Generation System). In the following, 5GS will be described as an example, but the LTE (Long Term Evolution) system may be applied at least in part to the mobile communication system. The sixth generation (6G) system may be applied at least in part to the mobile communication system.

The mobile communication system 1 has 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. In the following, the NG-RAN 10 may be simply referred to as the RAN 10. Also, 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.

UE100 is a mobile wireless communication device. UE100 may be any device that is used by a user. For example, UE100 is a mobile phone terminal (including a smartphone) and/or a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

NG-RAN10 includes base station 200 (referred to as "gNB" in the 5G system), which is a type of network node. gNB200 is connected to each other via an Xn interface, which is an interface between base stations. gNB200 manages one or more cells. gNB200 performs wireless communication with UE100 that has established a connection with its own cell. gNB200 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. "Cell" is used as a term indicating the smallest unit of a wireless communication area. "Cell" is also used as a term indicating a function or resource for performing wireless communication with UE100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

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 a base station-to-base station interface.

5GC20 includes AMF (Access and Mobility Management Function) and UPF (User Plane Function) 300. AMF performs various mobility controls for UE100. AMF manages the mobility of UE100 by communicating with UE100 using NAS (Non-Access Stratum) signaling. UPF controls data forwarding. AMF and UPF are connected to gNB200 via the NG interface, which is an interface between a base station and a core network.

FIG. 2 is a diagram showing an example of the configuration of a UE 100 (user equipment) according to an embodiment. The UE 100 has a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit that performs wireless communication with the gNB 200.

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

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 the baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

The control unit 130 performs various controls and processes in the UE 100. Such processes include the 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.

FIG. 3 is a diagram showing an example of the configuration of a gNB 200 (network node) according to an embodiment. The gNB 200 has a transmitting unit 210, a receiving unit 220, a control unit 230, and a backhaul communication unit 240. The transmitting unit 210 and the receiving unit 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 performs communication with the CN 20.

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 the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

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

The control unit 230 performs various controls and processes in the gNB 200. Such processes include the processes of 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.

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 may be composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and the two units may be connected via an F1 interface, which is a fronthaul interface.

Figure 4 shows the protocol stack configuration of the wireless interface of the user plane that handles data.

The user plane radio interface protocol has 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.

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 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 CRC (Cyclic Redundancy Code) parity bits scrambled by the RNTI added.

The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), and random access procedures. Data and control information are transmitted between the MAC layer of UE100 and the MAC layer of gNB200 via a transport channel. The MAC layer of gNB200 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 assigned to UE100.

The RLC layer uses the functions of the MAC layer and PHY layer to transmit data to the RLC layer on the receiving side. Data and control information are transmitted between the RLC layer of UE100 and the RLC layer of gNB200 via logical channels.

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

The SDAP layer maps IP flows, which are the units for which the core network controls QoS (Quality of Service), to radio bearers, which are the units for which the AS (Access Stratum) controls QoS. Note that if the RAN is connected to the EPC, SDAP is not necessary.

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

The protocol stack of the radio interface of the control plane has an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer instead of the SDAP layer shown in Figure 4.

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 in response 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.

The NAS layer (also simply referred to as "NAS"), which is positioned above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of UE100 and the NAS layer of AMF300A. In addition to the radio interface protocol, UE100 also has an application layer, etc. Also, the layer below the NAS layer is called the AS layer (also simply referred to as "AS").

(2) Overview of MBS The mobile communication system 1 can perform resource-efficient distribution by using a multicast/broadcast service (MBS).

(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 provided simultaneously to all UEs 100 in a geographical area. That is, all UEs 100 in a broadcast service area are allowed 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 following states: 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, TMGI (Temporary Mobile Group Identity).

Point-to-Multipoint (PTM) delivery is applied to the broadcast communication service. 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 the G-RNTI (Group RNTI), which is a group-common RNTI, using a group-common PDCCH having a CRC scrambled by the G-RNTI.

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 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, the MBS data belonging to the broadcast session).

Note that 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.

(2.2) MBS Multicast In the case of a multicast communication service (also called "MBS multicast"), the same service and the same specific content data are provided simultaneously to a specific set of UEs, i.e. not all UEs 100 within a multicast service area are allowed 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.

UE 100 can receive a multicast session only after joining the multicast session. Joining a multicast session may mean being registered in network 5 (CN 20) as UE 100 capable of receiving the multicast session.

In the case of multicast communication services, in 3GPP Release 17, only UEs 100 in an RRC connected state can receive multicast sessions. On the other hand, in 3GPP Release 18, this is expected to be expanded so that UEs 100 in an RRC inactive state can also receive multicast sessions.

(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 FIG. 6 to FIG.

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

UE100, which exists 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 (adjacent cell) of UE100. Cell a is operated at frequency (carrier frequency) a, and cell b may be operated 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.

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

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 the broadcast session from cell b, which is a non-serving cell (hereinafter also 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.

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

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

For example, due to the load of unicast communication on UE100, it may be possible to receive MTCH from a non-serving cell but not be able to receive MCCH from the non-serving cell. Also, as a result of UE100 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 MTCH in the non-serving cell. Furthermore, the frequency on which MBS broadcast is provided in the non-serving cell may be changed.

(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. Fig. 7 is a diagram showing a communication method performed by the UE 100 according to the embodiment. The UE 100 is assumed to be in an RRC connected state in a serving cell (cell a).

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

In step S2, UE100 transmits information indicating a desire to stop unicast communication to receive the broadcast session to gNB200 (gNB200a) that manages the serving cell (cell a). In an embodiment, UE100 may transmit an MBS Interest Indication message including the information to gNB200 (gNB200a). Alternatively, UE100 may transmit a UE Assistance Information message including the information to gNB200 (gNB200a). Note that the MBS Interest Indication message (hereinafter also referred to as the "MII message") and the UE Assistance Information message (hereinafter also referred to as the "UAI message") are both RRC layer messages (i.e., RRC messages).

The UE 100 that performs such operations has a receiver 110 that performs unicast communication with a serving cell (cell a) in an RRC connected state 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 FIG. 2).

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 the RRC connected state in the serving cell (cell a), and a receiving unit 220 that receives information indicating a desire to stop unicast communication in order to receive the broadcast session from UE100 that receives a broadcast session from a non-serving cell (cell b) (see Figure 3).

In the first operation pattern of the embodiment, in step S2, UE100 transmits stop request information to gNB200 (gNB200a) indicating a desire to temporarily stop unicast communication. UE100 may transmit stop request information to gNB200 (gNB200a) including information indicating a period during which unicast communication is temporarily stopped. UE100 may change the reception resource (e.g., RX) used for receiving unicast communication during the period during which unicast communication is temporarily stopped to be used for receiving a broadcast session. UE100 may change the reception resource to be used for unicast communication according to the end of the period during which unicast communication is temporarily stopped.

In the second operation pattern of the embodiment, in step S2, UE100 transmits change request information indicating a desire to change the serving cell (cell a) to gNB200 (gNB200a). UE100 may transmit change request information including information indicating the frequency of the serving cell to be changed to gNB200 (gNB200a). UE100 may receive an RRC reconfiguration message from gNB200 instructing the change of the serving cell. Then, in response to the change of the serving cell, UE100 may change the receiving resource (e.g., RX) used for receiving unicast communication to be used for receiving a broadcast session.

In the following description of the embodiment, the term "reception resource" refers primarily to the receiver (RX) of UE100. However, the term "reception resource" may also refer to the processing capacity of UE100 (e.g., the processing capacity (processing capacity) of a processor) used for reception in addition to or instead of the RX of UE100.

(4) Specific Example of Operation An example of the first and second operation patterns of the mobile communication system 1 according to the embodiment will be described.

(4.1) Example of the first operation pattern Fig. 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.

In step S100, UE100 is in an RRC connected state in the serving cell (cell a).

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

In step S102, UE 100 performs unicast communication with the 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 receiving an MBS broadcast.

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

In step S104, UE 100 determines that the receiving resource (e.g., RX #1) used in unicast communication is to be temporarily assigned to the MBS broadcast. Note that, if there are multiple RXs used in unicast communication, UE 100 may determine that the multiple RXs used in unicast communication are to be temporarily assigned to the MBS broadcast. Alternatively, UE 100 may determine that the receiving capability (receiving processing capacity) used in unicast communication is to be temporarily assigned to the MBS broadcast.

For example, when UE100 detects that the MBS broadcast frequency is changed, it may determine that the reception resources used in unicast communication are temporarily assigned to the MBS broadcast. Under the premise of performing a search (full scan) to find the changed MBS broadcast frequency, UE100 temporarily assigns the RX used in unicast communication to the MBS broadcast and performs the search, so that the search can be completed more quickly by using 2RX than 1RX.

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 the unicast communication to the MBS broadcast. The reception quality may be at least one of the reference signal reception power (RSRP), the reference signal reception quality (RSRP), the signal-to-interference-plus-noise ratio (SINR), the bit error rate (BER), the block error rate (BLER), and the packet error rate (PER). The threshold may be set in 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.

Alternatively, UE100 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, i.e., the symbol length becomes shorter, it is assumed that 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.

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.

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

The stop request information may include cause information indicating the reason for temporarily stopping unicast communication. The cause information may be information indicating that the reason is MBS broadcast reception.

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

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

The notification or setting may include time information indicating the period during which unicast communication is stopped. The time information may include at least one of information indicating the start timing of the period during which unicast communication is stopped and information indicating the 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, which will be described later. The time information may include information indicating the end timing of the period during which unicast communication is stopped.

In step S107, UE 100 stops unicast communication when it transmits the stop request information in step S105 or when it receives the notification or setting in step S106. UE 100 may start a timer that specifies the time for stopping unicast communication.

In step S108, i.e., during the period in which the unicast communication is temporarily stopped, the UE 100 changes the reception resources (e.g., RX and/or processing power) used for the unicast communication to be used for receiving the MBS broadcast. In other words, the UE 100 attempts to receive the MBS broadcast using the reception resources used for the unicast communication.

For example, UE100 may temporarily assign the RX used for unicast communication to MBS broadcast and perform a search under the assumption that the MBS broadcast frequency is changed. Alternatively, UE100 may assign the RX used for unicast communication to MBS broadcast reception and perform diversity reception with 2RX under the assumption that the reception quality of MTCH and/or MCCH in a non-serving cell (cell b) becomes worse than a threshold. Alternatively, UE100 may assign 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) becomes greater than a threshold.

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 reception resources allocated to MBS broadcast reception to be used for unicast communication, and returns to the original state of unicast communication (resumes it).

In this operation example, if the problem is not resolved even after temporarily allocating reception resources to MBS broadcast reception in step S108, UE100 may perform the following operation.

For example, when UE100 prioritizes MBS broadcast reception, UE100 may transmit to gNB200a Release Assistance Information (RAI) indicating that UE100 wishes to transition from the RRC connected state to the RRC idle state or the RRC inactive state. Here, UE100 may transmit cause information indicating the reason for prioritizing MBS broadcast reception together with the RAI.

The gNB200a transitions the UE100 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 the MBS broadcast.

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

(4.2) Example of second operation pattern Fig. 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.

In this operation example, it is assumed that UE100 has two RXs, RX#1 and RX#2, the corresponding frequencies of RX#1 are F1 and F3, and the corresponding frequency of RX#2 is F2. Under such assumptions, UE100 receives unicast at F1 (RX#1) and receives MBS broadcast at F2 (RX#2). If the MBS broadcast is subsequently changed from F2 to F3, it may be necessary for UE100 to assign RX#1 to the MBS broadcast.

In step S200, UE100 is in an RRC connected state in a serving cell (cell a) that operates at frequency F1.

In step S201, UE100 performs unicast communication with a serving cell (cell a) that operates at frequency F1.

In step S202, UE100 performs unicast communication with a serving cell (cell a) operating at frequency F1, and receives an MBS broadcast from a non-serving cell (cell b) operating at frequency F2. For example, UE100 uses RX#1 for unicast communication with the serving cell (cell a), and uses RX#2 for receiving an MBS broadcast from a non-serving cell (cell b).

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

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

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

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 reception of an MBS broadcast as the reason.

In step S207, if gNB200a accepts the request in step S206, it sends an RRC Reconfiguration message equivalent to a handover command to UE100 and changes the serving cell. The RRC Reconfiguration message includes information that specifies cell c, which operates at frequency F2, as the handover target. Cell c may be a cell of gNB200c.

In step S207, in response to receiving the handover command (RRC Reconfiguration message) in step S207, UE100 accesses cell c operating at frequency F2 and changes the serving cell from cell a to cell c. Here, UE100 changes to use RX#2 for unicast communication with cell c.

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.

In step S210, UE100 uses RX#2 to perform unicast communication with cell c (gNB200c), which is the new serving cell.

(5) Modification In the above embodiment, the serving cell cell a (gNB 200a) may belong to a first public land mobile network (PLMN), and the non-serving cell cell b (gNB 200b) may belong to a second PLMN different from the first PLMN. Such a PLMN relationship is also referred to as inter-PLMN.

UE100 may have a SIM (Subscriber Identity Module) corresponding to the first PLMN and may not have a SIM corresponding to the second PLMN. For example, cell b (gNB200b) 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 UE100 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. MBS broadcasts provided under the FTA may be made available to all users who are not mobile subscribers.

Alternatively, UE100 may have both a SIM corresponding to the first PLMN and a SIM corresponding to the second PLMN. Such a UE100 is also called a Multi-SIM UE or a Multi-USIM (Universal Subscriber Identity Module) UE. UE100 receives an MBS broadcast provided by ROM or FTA from the second PLMN.

(6) Other embodiments In the above-described embodiment, a scenario in which the UE 100 receives an MBS broadcast from a non-serving cell is assumed, but a scenario in which the UE 100 receives an MBS multicast from a non-serving cell may 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).

Each of the above-mentioned operation flows can be implemented not only separately but also by combining two or more operation flows. For example, some steps of one operation flow can be added to another operation flow, or some steps of one operation flow can be replaced with some steps of another operation flow. In each flow, it is not necessary to execute all steps, and only some of the steps can be executed.

In the above-mentioned embodiment and example, 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 an IAB node. The UE 100 may also be an MT (Mobile Termination) of an IAB node.

In other words, UE100 may be a terminal function unit (a type of communication module) that allows a base station to control a repeater that relays signals. Such a terminal function unit is called an MT. Examples of MT include, in addition to IAB-MT, NCR (Network Controlled Repeater)-MT and RIS (Reconfigurable Intelligent Surface)-MT.

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

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

The functions performed by UE100 or NB200 (network node) may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (Central Processing Units), conventional circuits, and/or combinations thereof, programmed to perform the described functions. Processors include transistors and other circuits and are considered to be circuitry or processing circuitry. Processors may be programmed processors that execute programs stored in memory. In this specification, circuitry, units, and means are hardware that is programmed to perform the described functions or hardware that executes them. The hardware may be any hardware disclosed herein or any hardware known to be programmed or capable of performing the described functions. If the hardware is a processor considered to be a type of circuitry, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and/or processor.

As used in this disclosure, the terms "based on" and "depending on/in response to" do not mean "based only on" or "only in response to," unless otherwise specified. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "in response to" means both "only in response to" and "at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the items listed, but may include only the items listed, or may include additional items in addition to the items listed. In addition, 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 is not intended to generally limit the quantity or order of those elements. These designations may be used herein as a convenient way to distinguish between two or more elements. Thus, a reference to a first and 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 manner. In this disclosure, where articles are added by translation, such as, for example, a, an, and the in English, these articles are intended to include the plural unless the context clearly indicates otherwise.

The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to the above, and various design changes can be made without departing from the spirit of the invention.

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.

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

(Appendix 1)
A communication method performed by a user equipment in a mobile communication system providing a multicast/broadcast service (MBS), comprising:
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;
transmitting information indicating a desire to stop the unicast communication in favor of receiving the broadcast session to a network node that manages the serving cell.

(Appendix 2)
The communication method according to claim 1, wherein the transmitting step includes a step of transmitting stop request information indicating a request to temporarily stop the unicast communication to the network node.

(Appendix 3)
The communication method according to claim 2, wherein the step of transmitting the stop request information includes a step of transmitting the stop request information including information indicating a period during which the unicast communication is temporarily stopped to the network node.

(Appendix 4)
The communication method according to claim 2 or 3, further comprising the step of changing a receiving 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.

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

(Appendix 6)
2. The communication method of claim 1, wherein the transmitting step includes the step of transmitting change desire information indicating a desire to change the serving cell to the network node.

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

(Appendix 8)
receiving an RRC reconfiguration message from the network node indicating a change of the serving cell;
The communication method according to claim 6 or 7, further comprising the step of changing a receiving resource used for receiving the unicast communication to be used for receiving the broadcast session in response to the change of the serving cell.

(Appendix 9)
9. The method of claim 1, wherein the transmitting step comprises transmitting an MBS interest indication message including the information to the network node.

(Appendix 10)
A user equipment for use in a mobile communication system providing 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;
A transmitting unit configured to transmit 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.

(Appendix 11)
A network node for use in a mobile communication system providing 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;
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.

1: Mobile communication system 5: Network 10: RAN
20: C.N.
100: UE (user equipment)
110: Receiving unit 120: Transmitting unit 130: Control unit 200: gNB (network node)
210: Transmitter 220: Receiver 230: Controller 240: Backhaul Communication Unit

Claims (11)

A communication method performed by a user equipment in a mobile communication system providing a multicast/broadcast service (MBS), comprising:
In a radio resource control (RRC) connected state, performing unicast communication with a serving cell and receiving a broadcast session from a non-serving cell;
transmitting information indicating a desire to stop the unicast communication in favor of receiving the broadcast session to a network node that manages the serving cell. The communication method according to claim 1 , wherein the transmitting step includes transmitting stop request information indicating a desire to temporarily stop the unicast communication to the network node. The communication method according to claim 2 , wherein transmitting the stoppage desire information includes transmitting, to the network node, the stoppage desire information including information indicating a period during which the unicast communication is to be temporarily stopped. The communication method according to claim 2 or 3, further comprising changing a receiving 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. The communication method according to claim 4 , further comprising 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. The method of claim 1 , wherein the transmitting step includes transmitting change desire information indicating a desire to change the serving cell to the network node. The communication method according to claim 6 , wherein transmitting the change desire information comprises transmitting the change desire information including information indicating a frequency of a serving cell to be changed to the network node. receiving an RRC reconfiguration message from the network node indicating a change of the serving cell;
The communication method according to claim 6 or 7, further comprising changing a reception resource used for receiving the unicast communication to a reception resource used for receiving the broadcast session in response to the change of the serving cell. The method of claim 1 , wherein the transmitting step comprises transmitting an MBS interest indication message including the information to the network node. A user equipment for use in a mobile communication system providing 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;
A transmitting unit configured to transmit 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. A network node for use in a mobile communication system providing 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;
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.

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