Communication control method, user device, chipset, program, and mobile communication system

Abstract

To provide a communication control method, user device, chipset, program, and mobile communication system for implementing improved multicast broadcast service.SOLUTION: A mobile communication system causes: a user device to receive, from a cell, multicast broadcast service (MBS) control information to be used for receiving MBS data; the user device in a radio resource control (RRC) inactive state to perform cell reselection to another cell; and the user device in the RRC inactive state to, when it is determined that the MBS control information received from the cell is not available in another cell, transition to an RRC connected state in the other cell.SELECTED DRAWING: Figure 17

Description

Technical Field

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

Background Art

[0002] In recent years, the fifth-generation (5G) mobile communication system has attracted attention. NR (New Radio), which is a radio access technology (RAT) of the 5G system, has characteristics such as high speed, large capacity, high reliability, and low latency compared to LTE (Long Term Evolution), which is a fourth-generation radio access technology.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

[0004] A communication control method according to a first aspect is a communication control method used in a mobile communication system that provides a multicast / broadcast service (MBS) from a base station to a user equipment, the base station receiving, from a core network or another base station, a specified PDCP (Packet Data Convergence Protocol) sequence number designated to be applied to an MBS packet, the base station associating the MBS packet with the specified PDCP sequence number, and the base station transmitting the MBS packet associated with the specified PDCP sequence number to the user equipment.

[0005] The communication control method according to the second aspect is a communication control method used in a mobile communication system that provides a multicast / broadcast service (MBS) from a base station to a user equipment, wherein the base station receives a paging message for requesting paging for the user equipment in the RRC (Radio Resource Control) idle state or the RRC inactive state from a core network, and the base station performs the paging in response to the reception of the paging message, and the paging message includes an identifier related to an MBS session received by the user equipment.

[0006] The communication control method according to the third aspect is a communication control method used in a mobile communication system that provides a multicast / broadcast service (MBS) from a base station to a user equipment, wherein the base station transmits MBS data received from a core network to the user equipment by PTM (Point To Multipoint), and when the base station determines that the PTM transmission of the MBS data from the base station to the user equipment cannot be continued, the base station transmits a notification to the user equipment, and the user equipment establishes a unicast session for receiving the MBS data by unicast with the core network in response to the reception of the notification.

[0007] The communication control method according to the fourth aspect is a communication control method used in a mobile communication system that provides a multicast / broadcast service (MBS) from a base station to a user equipment, wherein the user equipment receives from a cell MBS control information used for receiving MBS data and a control area identifier indicating an MBS control area range which is an area range in which at least a part of the MBS control information is applicable, and when the user equipment determines that a predetermined condition related to the MBS control area range is satisfied, the user equipment re-receives the MBS control information.

Brief Description of the Drawings

[0008]

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[0009] It is considered to introduce a multicast / broadcast service into a 5G system (NR). The multicast / broadcast service of NR is desired to provide a service improved from the multicast / broadcast service of LTE.

[0010] Therefore, an object of the present invention is to realize an improved multicast / broadcast service.

[0011] 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.

[0012] (Configuration of Mobile Communication System) First, the configuration of the mobile communication system according to the embodiment will be described. FIG. 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. This mobile communication system complies with the 5th generation system (5GS) of the 3GPP standard. Hereinafter, 5GS will be described as an example, but an LTE (Long Term Evolution) system may be at least partially applied to the mobile communication system, or a 6th generation (6G) system may be at least partially applied.

[0013] As shown in FIG. 1, the mobile communication system includes a user equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20.

[0014] UE100 is a movable wireless communication device. UE100 can be any device used by a user. For example, UE100 can be a mobile phone terminal (including smartphones), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided for the sensor, a vehicle or a device provided for the vehicle (Vehicle UE), an aircraft or a device provided for the aircraft (Aerial UE).

[0015] NG-RAN10 includes base stations (referred to as "gNB" in the 5G system) 200. The gNBs 200 are interconnected via the 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 UE100 that has established a connection with its cell. The gNB 200 has functions such as 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 the UE100. One cell belongs to one carrier frequency.

[0016] Note that the gNB can also be connected to the EPC (Evolved Packet Core) which is the core network of LTE. The base station of LTE can also be connected to the 5GC. The base station of LTE and the gNB can also be connected via an interface between base stations.

[0017] 5GC20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls and the like for the UE100. The AMF manages the mobility of the UE100 by communicating with the UE100 using NAS (Non-Access Stratum) signaling. The UPF performs data transfer control. The AMF and the UPF are connected to the gNB200 via the NG interface, which is an interface between the base station and the core network.

[0018] FIG. 2 is a diagram showing the configuration of a UE100 (user equipment) according to an embodiment.

[0019] As shown in FIG. 2, the UE100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130.

[0020] The receiving unit 110 performs various receptions 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.

[0021] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmitted signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0022] The control unit 130 performs various controls in the UE100. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for 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 the baseband signal. The CPU executes the programs stored in the memory to perform various processes.

[0023] FIG. 3 is a diagram showing the configuration of the gNB 200 (base station) according to an embodiment.

[0024] As shown in FIG. 3, the gNB 200 includes a transmission unit 210, a reception unit 220, a control unit 230, and a backhaul communication unit 240.

[0025] The transmission unit 210 performs various transmissions under the control of the control unit 230. The transmission 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.

[0026] The reception unit 220 performs various receptions under the control of the control unit 230. The reception unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (reception signal) and outputs it to the control unit 230.

[0027] The control unit 230 performs various controls in the gNB 200. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for 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 the baseband signal, etc. The CPU executes the programs stored in the memory to perform various processes.

[0028] The backhaul communication unit 240 is connected to an adjacent base station via a base station interface. The backhaul communication unit 240 is connected to the AMF / UPF 300 via a base station-core network interface. Note that the gNB is composed of a CU (Central Unit) and a DU (Distributed Unit) (that is, functionally split), and the two units may be connected by an F1 interface.

[0029] FIG. 4 is a diagram showing the configuration of the protocol stack of the radio interface of the user plane that handles data.

[0030] As shown in FIG. 4, the radio interface protocol of the user plane has a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0031] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Between the PHY layer of UE100 and the PHY layer of gNB200, data and control information are transmitted via a physical channel.

[0032] The MAC layer performs priority control of data, retransmission processing by hybrid ARQ (HARQ), and random access procedures, etc. Between the MAC layer of UE100 and the MAC layer of gNB200, data and control information are transmitted via a transport channel. The MAC layer of gNB200 includes a scheduler. The scheduler determines the uplink and downlink transport formats (transport block size, modulation and coding scheme (MCS)) and the resource blocks allocated to UE100.

[0033] The RLC layer uses the functions of the MAC layer and the PHY layer to transmit data to the RLC layer on the receiving side. Between the RLC layer of UE100 and the RLC layer of gNB200, data and control information are transmitted via a logical channel.

[0034] The PDCP layer performs header compression / decompression and encryption / decryption.

[0035] The SDAP layer performs the mapping between the IP flow, which is the unit for the core network to perform QoS control, and the radio bearer, which is the unit for the AS (Access Stratum) to perform QoS control. Note that when the RAN is connected to the EPC, the SDAP may not be necessary.

[0036] Figure 5 is a diagram showing the configuration of the protocol stack of the radio interface of the control plane that handles signaling (control signals).

[0037] As shown in Figure 5, 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 Figure 4.

[0038] Between the RRC layer of UE100 and the RRC layer of gNB200, RRC signaling for various settings is transmitted. The RRC layer controls the logical channel, transport channel, and physical channel in response to the establishment, re-establishment, and release of the radio bearer. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in the RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in the RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in the RRC inactive state.

[0039] The NAS layer located 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 AMF300B.

[0040] Note that UE100 has an application layer, etc. in addition to the protocol of the radio interface.

[0041] (MBS) Next, the MBS according to an embodiment will be described. MBS is a service that performs broadcast or multicast, that is, one-to-many (PTM: Point To Multipoint) data transmission from the NG-RAN 10 to the UE 100. MBS may be called MBMS (Multimedia Broadcast and Multicast Service). Note that the use cases (service types) of MBS include public security communication, mission-critical communication, V2X (Vehicle to Everything) communication, IPv4 or IPv6 multicast distribution, IPTV, group communication, and software distribution, etc.

[0042] In LTE, there are two types of MBS transmission methods, namely MBSFN (Multicast Broadcast Single Frequency Network) transmission and SC-PTM (Single Cell Point To Multipoint) transmission. FIG. 6 is a diagram showing the correspondence between the downlink logical channel and the transport channel according to an embodiment.

[0043] As shown in FIG. 6, the logical channels used for MBSFN transmission are MTCH (Multicast Traffic Channel) and MCCH (Multicast Control Channel), and the transport channel used for MBSFN transmission is MCH (Multicast Channel). MBSFN transmission is mainly designed for multicell transmission, and in an MBSFN area composed of multiple cells, each cell synchronously transmits the same signal (the same data) in the same MBSFN subframe.

[0044] The logical channels used for SC-PTM transmission are SC-MTCH (Single Cell Multicast Traffic Channel) and SC-MCCH (Single Cell Multicast Control Channel), and the transport channel used for SC-PTM transmission is DL-SCH (Downlink Shared Channel). SC-PTM transmission is mainly designed for single cell transmission, and performs data transmission in a broadcast or multicast manner on a cell-by-cell basis. The physical channels used for SC-PTM transmission are PDCCH (Physical Downlink Control Channel) and PDSCH (Physical Downlink Shared Channel), and dynamic resource allocation is enabled.

[0045] In the following, an example of providing MBS using the SC-PTM transmission method will be mainly described, but MBS may also be provided using the MBSFN transmission method. Also, an example of providing MBS by multicast will be mainly described. For this reason, MBS may be read as multicast. However, MBS may also be provided by broadcast.

[0046] Also, MBS data refers to the data transmitted by MBS, the MBS control channel refers to MCCH or SC-MCCH, and the MBS traffic channel refers to MTCH or SC-MTCH. However, MBS data may also be transmitted by unicast. MBS data may also be called MBS traffic. In the following, MBS data when handled in packet units is called an MBS packet.

[0047] The network can provide different MBS services for each MBS session. An MBS session is identified by at least one of a TMGI (Temporary Mobile Group Identity) and a session identifier, and at least one of these identifiers is called an MBS session identifier. Such an MBS session identifier may also be called an MBS service identifier or a multicast group identifier.

[0048] FIG. 7 is a diagram showing a method for delivering MBS data according to an embodiment.

[0049] As shown in FIG. 7, MBS data (MBS Traffic) is delivered from a single data source (application service provider) to a plurality of UEs. The 5G CN (5GC) 20, which is a 5G core network, receives MBS data from the application service provider, creates (Replication) copies of the MBS data, and distributes them.

[0050] From the perspective of the 5GC 20, two delivery methods are possible: shared MBS data delivery and individual MBS data delivery.

[0051] In shared MBS data delivery, a connection is established between the NG-RAN 10, which is a 5G radio access network, and the 5GC 20, and the 5GC 20 distributes MBS data to the NG-RAN 10. Hereinafter, such a connection (tunnel) is called an "MBS connection".

[0052] The MBS connection may also be referred to as a Shared MBS Traffic delivery connection or a shared transport. The MBS connection terminates at the NG-RAN 10 (i.e., gNB 200). The MBS connection may correspond one-to-one with an MBS session. The gNB 200 selects either PTP (Point-to-Point: unicast) or PTM (Point-to-Multipoint: multicast or broadcast) at its own discretion and transmits MBS data to the UE 100 in the selected manner.

[0053] On the other hand, in individual MBS data delivery, a unicast session is established between the NG-RAN 10 and the UE 100, and MBS data is delivered to the UE 100 individually from the 5GC 20. Such a unicast may also be referred to as a PDU Session. The unicast (PDU Session) terminates at the UE 100.

[0054] (Sequence number synchronization) Next, sequence number synchronization according to an embodiment will be described. FIGS. 8 and 9 are diagrams showing an operating environment according to an embodiment.

[0055] As shown in FIG. 8, the gNB 200A manages the cell C1, and the gNB 200B manages the cell C2. The UE 100A exists in the cell C1, and the UE 100B exists in the cell C2. The UE 100A can move from the cell C1 to the cell C2. Similarly, the UE 100B can move from the cell C2 to the cell C1.

[0056] Although an example in which the cell sizes of the cell C1 and the cell C2 are equal is illustrated, the cell sizes of the cell C1 and the cell C2 may be different from each other. The geographical areas of the cell C1 and the cell C2 at least partially overlap. Such a relationship between cells is sometimes referred to as an adjacent cell. The UE 100A and the UE 100B may exist in the overlapping area of these cells.

[0057] gNB200A and gNB200B can communicate with each other via the Xn interface (Xn connection), which is an interface between base stations. However, the communication between gNB200A and gNB200B is not limited to being performed via the Xn interface. The communication between gNB200A and gNB200B may also be performed via the NG interface, which is an interface between the base station and the core network, and a core network device. In the following, an example in which the communication between gNB200A and gNB200B is performed via the Xn interface will be mainly described.

[0058] Cell C1 and Cell C2 may belong to the same MBS area. The MBS area refers to an area composed of a plurality of cells that provide the same MBS session. A plurality of cells belonging to the same MBS area may provide an MBS session at the same frequency and may form an SFN (Single Frequency Network).

[0059] Note that the establishment and release of the MBS connection are controlled by AMF300B. AMF300B is another example of a core network device. However, instead of AMF300B, an SMF (Session Management Function) may control the establishment and release of the MBS connection. The SMF is another example of a core network device.

[0060] In such an environment, gNB200B has an MBS connection with UPF300A. gNB200B receives MBS packets from UPF300A via the MBS connection and transmits the received MBS packets in PTM in Cell C2. Here, the PDCP entity of gNB200B attaches a PDCP header having a PDCP sequence number (PDCP SN) to the MBS packet and transmits it. The PDCP SN is incremented for each MBS packet to be transmitted.

[0061] On the other hand, gNB200A does not have an MBS connection with UPF300A. Here, assuming a case where SFN is configured by cells C1 and C2, as shown in FIG. 9, gNB200A needs to establish an MBS connection with UPF300A. Also, it is desirable that the PDCP SNs of the MBS packets transmitted by gNB200A and gNB200B are synchronized. In other words, for the MBS packets transmitted by MBS Shared Delivery, on the air interface side, it is desirable to perform PTM transmission with PDCP SNs synchronized among multiple gNB200s (gNB200A and gNB200B).

[0062] However, gNB200B has already started PTM transmission for the target MBS session, and the value of the PDCP SN is increasing. Therefore, if gNB200A counts up the PDCP SN from the initial value (for example, zero), PTM transmission cannot be performed with PDCP SNs synchronized among multiple gNB200s (gNB200A and gNB200B).

[0063] Thus, in one embodiment, the core network designates the value of the PDCP SN of the MBS packets transmitted by gNB200A. Here, it is assumed that 5GC20 (core network) knows the current PDCP SN of gNB200B. 5GC20 designates the value of the PDCP SN of the MBS packets transmitted by gNB200A so that the MBS packets transmitted by gNB200A and their PDCP SNs match the MBS packets transmitted by gNB200B and their PDCP SNs.

[0064] In order for 5GC20 to know the current PDCP SN of gNB200B, 5GC20 may query gNB200B for the current PDCP SN information. The query may include MBS session information. gNB200B may report the current PDCP SN information to 5GC20. The report may include MBS session information. The report may be performed in response to receiving the query.

[0065] In one embodiment, gNB200A receives, from 5GC20, an MBS packet and a designated PDCP SN designated to be applied to the MBS packet, and associates the MBS packet with the designated PDCP SN. gNB200A transmits the MBS packet associated with the designated PDCP SN to UE100. For example, gNB200A sets the designated PDCP SN in the PDCP header of the MBS packet, and transmits the MBS packet with the designated PDCP SN set in the PDCP header by PTM.

[0066] FIG. 10 is a diagram showing an operation example 1 of sequence number synchronization according to one embodiment.

[0067] As shown in FIG. 10, in step S101, 5GC20 (for example, UPF300A or AMF300B) transmits setting information (hereinafter referred to as "MBS connection setting information") for establishing an MBS connection to gNB200A. 5GC20 may transmit the MBS connection setting information to gNB200A in response to a request from gNB200A.

[0068] The MBS connection setting information includes setting parameters for the MBS connection and designated PDCP SN information regarding the designated PDCP SN. The MBS connection setting information may include MBS session information associated with the designated PDCP SN information. The MBS session information includes an identifier regarding the MBS session. Such an identifier may be a session identifier (for example, TMGI), a QoS flow identifier, and / or a G-RNTI in PTM transmission. gNB200A can grasp the MBS session corresponding to the MBS connection to be established based on the MBS session information.

[0069] The specified PDCP SN information includes the specified PDCP SN designated to be applied to the first MBS packet received by gNB200 from 5GC20 via the MBS connection. That is, 5GC20 designates the initial value of the PDCP SN that gNB200A should set for the MBS packet. In FIG. 10, an example where the specified PDCP SN is "10" is shown. Note that when 5GC20 simultaneously transmits the MBS connection setup information and the MBS packet to gNB200A, the specified PDCP SN information may be the specified PDCP SN designated to be applied to the current corresponding MBS packet.

[0070] Alternatively, the specified PDCP SN information may include information associating the identifier assigned to the MBS packet received by gNB200 from 5GC20 via the MBS connection with the specified PDCP SN. The identifier assigned to the MBS packet may be the GTP SN included in the GTP header used in the GTP tunnel constituting the MBS connection and / or the SN included in the IP header of the MBS packet (IP packet). In the example of FIG. 10, the specified PDCP SN information may include a set of the identifier (e.g., "A") assigned to MBS packet A and the PDCP SN "10", and a set of the identifier (e.g., "B") assigned to MBS packet B and the PDCP SN "11".

[0071] Note that the specified PDCP SN information may include the SN length (bit length) of the PDCP SN. These SN lengths are, for example, 12 bits or 18 bits. By specifying the SN length, it is possible to synchronize the timing (wrap around) at which the SN returns to zero.

[0072] In step S102, gNB200A establishes an MBS connection with 5GC20 based on the MBS connection setup information from 5GC20.

[0073] In step S103, 5GC20 transmits MBS packet A to gNB200A via the MBS connection. gNB200A receives MBS packet A.

[0074] In step S104, the PDCP entity of gNB200A sets the specified PDCP SN designated by 5GC20 in the PDCP header of MBS packet A based on the specified PDCP SN information from 5GC20.

[0075] In step S105, gNB200A transmits MBS packet A with the specified PDCP SN set in the PDCP header to UE100A in PTM.

[0076] After that, gNB200A updates so as to count up the PDCP SN for each MBS packet transmitted by gNB200A.

[0077] For example, in step S106, 5GC20 transmits MBS packet B to gNB200A via the MBS connection. gNB200A receives MBS packet B.

[0078] In step S107, the PDCP entity of gNB200A sets the updated PDCP SN (here, SN = 11) in the PDCP header of MBS packet B.

[0079] In step S108, gNB200A transmits MBS packet B with the updated PDCP SN set in the PDCP header to UE100A in PTM.

[0080] Note that in operation example 1, an example in which each gNB200 transmits an MBS packet in PTP has been described, but each gNB200 may transmit an MBS packet in PTM.

[0081] Next, operation example 2 of sequence number synchronization according to an embodiment will be described. Operation example 2 is an example in which PDCP SNs are synchronized before and after the handover when UE100 performs a handover. Here, an example in which UE100 in the RRC connected state performs a handover from gNB200A to gNB200B will be described.

[0082] In operation example 2, gNB200B, which is the target gNB, receives the specified PDCP SN designated to be applied to the MBS packet from gNB200A, which is the source gNB, and associates the MBS packet with the specified PDCP SN. gNB200A transmits the MBS packet associated with the specified PDCP SN to UE100.

[0083] In operation example 2, gNB200B receives the PDCP SN of the MBS packet that UE100 failed to receive at gNB200A from UE100 that has performed a handover from gNB200A to gNB200B. gNB200B transmits (retransmits) the MBS packet associated with the PDCP SN received from UE100 to UE100.

[0084] FIG. 11 is a diagram showing operation example 2 of sequence number synchronization according to an embodiment. In FIG. 11, each of gNB200A and gNB200B has an MBS connection with UPF300A and is assumed to receive the same MBS packet from UPF300A. However, it is assumed that the MBS packets transmitted by gNB200A and gNB200B have asynchronous PDCP SNs.

[0085] As shown in FIG. 11, in steps S201 to S203, gNB200A transmits MBS packets A to C to UE100 by PTM. The PDCP SNs of MBS packets A to C are "11" to "13". Here, it is assumed that UE100 fails to receive MBS packet C (for example, detects a decoding error).

[0086] In step S204, gNB200A determines a handover of UE100 to gNB200B.

[0087] In step S205, gNB200A transmits a handover request message for requesting a handover of UE100 to gNB200B.

[0088] The handover request message includes specified PDCP SN information. The specified PDCP SN information may include information associating an identifier assigned to an MBS packet received by gNB200A from 5GC20 via an MBS connection with the specified PDCP SN. The identifier assigned to the MBS packet may be the GTP SN included in the GTP header used in the GTP tunnel constituting the MBS connection and / or the SN included in the IP header of the MBS packet (IP packet). In the example of FIG. 11, the specified PDCP SN information may include a set of an identifier (e.g., "A") assigned to MBS packet A and PDCP SN "11", a set of an identifier (e.g., "B") assigned to MBS packet B and PDCP SN "12", and a set of an identifier (e.g., "C") assigned to MBS packet C and PDCP SN "13".

[0089] Here, an example in which the handover request message includes specified PDCP SN information has been described, but gNB200B may obtain the specified PDCP SN information from gNB200A by querying gNB200A. gNB200B may obtain the specified PDCP SN information from 5GC20. In this case, gNB200B may obtain the specified PDCP SN information from 5GC20 by querying 5GC20.

[0090] In step S206, gNB200B associates each MBS packet received by gNB200B from 5GC20 (UPF300A) with the specified PDCP SN based on the specified PDCP SN information.

[0091] In step S207, gNB200B transmits a handover response message to gNB200A.

[0092] In step S208, gNB200A transmits a handover command message to UE100.

[0093] In step S209, UE100 performs a handover from gNB200A to gNB200B.

[0094] In step S210, UE100 sends a retransmission request including the PDCP SN "13" of the MBS packet C that failed to be received in step S203 to gNB200B. This retransmission request may be a PDCP Status PDU.

[0095] Note that in the handover request of step S205, gNB200A (source gNB) may notify the information of the SN that is considered to have been missed by UE100 (that is, network-initiated retransmission request). In this case, step S210 is not essential.

[0096] In step S211, gNB200B sends the MBS packet C corresponding to the PDCP SN "13" for which retransmission is requested from UE100 to UE100 based on the association in step S206.

[0097] Thus, according to operation example 2, even when UE100 performs a handover between gNBs with non-synchronized PDCP SNs, UE100 can correctly transmit (retransmit) the MBS packets that it could not receive from the source gNB from the target gNB.

[0098] (Paging) Next, paging according to an embodiment will be described.

[0099] When UE100 in the RRC idle state or the RRC connected state performs MBS reception, gNB200 can receive a paging message addressed to this UE100 from 5GC20 (AMF300B). If gNB200 pages UE100 without considering the timing at which UE100 performs MBS reception, there is a concern that the MBS reception timing and the paging reception timing may conflict in UE100, resulting in reception errors.

[0100] The operations for solving such problems will be described. In one embodiment, gNB200 receives a paging message from 5GC20 (AMF300B) that requests paging for UE100 in the RRC idle state or the RRC inactive state. This paging message includes an identifier (e.g., TMGI) related to the MBS session received by UE100.

[0101] Specifically, AMF300B knows the MBS session received by UE100 in the RRC idle state or the RRC inactive state, and when sending a paging message addressed to this UE100 to gNB200, it notifies gNB200 of the identifier of the MBS session.

[0102] In response to receiving the paging message from AMF300B, gNB200 performs paging for UE100. Specifically, gNB200 sends an RRC paging message addressed to UE100.

[0103] Here, gNB200 performs paging (sends an RRC paging message) at a timing different from the transmission timing of the MBS session received by UE100 based on the session identifier included in the paging message from AMF300B. Thereby, it is possible to avoid the competition between the MBS reception timing and the paging reception timing at UE100.

[0104] FIG. 12 is a diagram showing an operation example of paging according to one embodiment. In FIG. 12, assume that UE100 is in the RRC idle state or the RRC connected state.

[0105] As shown in FIG. 12, in step S301, the UPF 300A transmits MBS data to the gNB 200 via the MBS connection. In step S302, the gNB 200 transmits the MBS data received from the UPF 300A to the UE 100 by PTM. Here, it is assumed that the timing at which the gNB 200 transmits the MBS data by PTM is determined. For example, the gNB 200 notifies the UE 100 in advance of the timing of the MBS transmission opportunity (which may be the MBS transmission period), and the UE 100 performs MBS reception at the notified MBS transmission timing.

[0106] In step S303, the AMF 300B transmits a paging message addressed to the UE 100 to the gNB 200. The paging message includes a set of the identifier of the UE 100 and the identifier of the MBS session (MBS session information) received by this UE 100.

[0107] In step S304, the gNB 200 determines the paging timing of the UE 100 based on the information included in the paging message from the AMF 300B. For example, the gNB 200 identifies the MBS transmission timing of this MBS session based on the MBS session information included in the paging message from the AMF 300B. Also, the gNB 200 identifies the paging opportunity (paging timing) of this UE 100 based on the UE identifier included in the paging message from the AMF 300B. Then, the gNB 200 determines a paging timing that does not match the identified MBS transmission timing while avoiding the paging timing that matches the identified MBS transmission timing.

[0108] In step S305, the UPF 300A transmits MBS data to the gNB 200 via the MBS connection. In step S306, the gNB 200 transmits the MBS data received from the UPF 300A to the UE 100 by PTM. Note that if the UE 100 determines that the paging opportunity and the MBS reception opportunity collide, the UE 100 may prioritize MBS reception.

[0109] In step S307, gNB200 transmits an RRC paging message to UE100 at the paging timing determined in step S304.

[0110] In this operation example, it is assumed that UE100 cannot perform MBS reception and paging reception simultaneously. However, it is also conceivable that UE100 has the ability to perform MBS reception and paging reception simultaneously. Therefore, AMF300B may further include information (capability information) indicating whether UE100 has the ability to perform MBS reception and paging reception simultaneously in the paging message. Based on the capability information, gNB200 may transmit MBS data and an RRC paging message to UE100 having such capability simultaneously.

[0111] (Switching to Unicast) Next, switching to unicast according to an embodiment will be described.

[0112] For example, when performing a handover of UE100 while receiving MBS data transmitted by PTM, if the target gNB200 does not support PTM transmission (or MBS service), UE100 can no longer continue to receive MBS data. Also, when gNB200 stops PTM transmission (or MBS service), UE100 can no longer continue to receive MBS data.

[0113] In such a case, since the core network (5GC20) is in a state where it can continue to provide the MBS service, by establishing a unicast session (PDU session) as shown in FIG. 7 and switching to individual MBS data delivery, UE100 can continue to receive MBS data. However, in order to establish a unicast session, it is necessary for UE100 to send an establishment request to 5GC20.

[0114] In one embodiment, the gNB 200 transmits the MBS data received from the 5GC 20 to the UE 100 by PTM. If the gNB 200 determines that it cannot continue the PTM transmission of the MBS data from the gNB 200 to the UE 100, the gNB 200 transmits a notification to the UE 100. In response to receiving the notification, the UE 100 establishes a unicast session with the 5GC 20 for receiving the MBS data by unicast. In this way, the notification from the gNB 200 prompts the UE 100 to establish a unicast session, enabling the UE 100 to establish a unicast session and continue receiving the MBS data.

[0115] FIG. 13 is a diagram showing an operation example of switching to unicast according to one embodiment.

[0116] As shown in FIG. 13, in step S401, the 5GC 20 (UPF 300A) transmits MBS data to the gNB 200 via the MBS connection.

[0117] In step S402, the gNB 200 transmits the MBS data received from the 5GC 20 to the UE 100 by PTM.

[0118] In step S403, the gNB 200 determines that the UE 100 cannot continue to provide the MBS service during PTM reception. For example, the gNB 200 determines that it is necessary to hand over the UE 100 or that the gNB 200 stops PTM transmission, etc., and thus determines that the provision of the MBS service cannot continue. However, the MBS service itself continues.

[0119] In step S404, the gNB 200 notifies the UE 100 to make a service request for receiving MBS by unicast.

[0120] The notification may include an identifier of the target MBS service (MBS session), for example, TMGI. The notification may be a notification indicating that the continuation of the MBS service by PTM is no longer possible.

[0121] Assuming that the UE100 is in the RRC connected state, dedicated signaling can be used as the notification. Assuming that the UE100 is in the RRC idle state or the RRC inactive state, the broadcast MBS control channel or paging (RRC paging message) can be used.

[0122] In step S405, based on the notification from the gNB200, the NAS layer of the UE100 sends a session establishment request for the unicast session of the receiving service (TMGI) to the 5GC20.

[0123] In step S406, the UE100 continues to receive the MBS service unicast. The UE100 may notify the gNB200 that the unicast session has been established. The notification of the establishment of the unicast session may be performed following step S405. With this notification, the gNB200 can perform handover execution and PTM transmission stop at an appropriate timing.

[0124] (MBS control area range) Next, the MBS control area range according to an embodiment will be described.

[0125] The UE100 that performs MBS reception can move across cells. In order for such a UE100 to continue MBS reception, it is necessary to receive the MBS control channel (MBS control information) in the target cell at least when switching cells. For this reason, there are problems that the load and power consumption of the UE100 increase, and it is difficult to quickly receive MBS data from the target cell. Note that the MBS control information includes setting information (MBS setting) for receiving the MBS traffic channel.

[0126] In one embodiment, a function (hereinafter referred to as a "control area function") that can be shared within an area range composed of a plurality of cells (hereinafter referred to as an "MBS control area range") of MBS control information is introduced. As a result, since the MBS control information can be reused across cells within the MBS control area range, the above-described problem can be solved.

[0127] That is, the gNB 200 according to one embodiment transmits, via the MBS control channel of its own cell, the MBS control information used for receiving MBS data to the UE 100. The gNB 200 transmits a control area identifier indicating an MBS control area range, which is an area range in which at least a part of the MBS control information is applicable, to the UE 100. Thereby, the UE 100 can grasp the MBS control area range in which the MBS control information of the current cell can be reused.

[0128] The UE 100 stores the MBS control information and the control area identifier from the gNB 200. Then, the UE 100 receives MBS data based on the stored MBS control information within the MBS control area range indicated by the stored control area identifier. In this way, since the MBS control information can be reused across cells within the stored area range to receive MBS data, the load and power consumption of the UE 100 can be suppressed, and it becomes easier to receive MBS data quickly from the target cell.

[0129] FIG. 14 is a diagram showing the operation of a mobile communication system according to one embodiment.

[0130] As shown in FIG. 14, in step S501, the gNB 200 that manages cell C1 transmits MBS system information to the UE 100 via the broadcast control channel (BCCH: Broadcast Control Channel) of cell C1. The transmission of the MBS system information is performed by broadcast using a predetermined RNTI. The UE 100 receives the MBS system information. Note that the system information may be referred to as an SIB (System Information Block).

[0131] The MBS system information includes the scheduling information necessary for receiving the MBS control channel. For example, the MBS system information includes at least one of information indicating the period in which the content (MBS control information) of the MBS control channel can be changed, information indicating the time interval of MBS control channel transmission in terms of the number of radio frames, information indicating the offset of the radio frame in which the MBS control channel is scheduled, and information indicating the subframe in which the MBS control channel is scheduled.

[0132] In one embodiment, the MBS system information further includes MBS control area setting. The MBS control area setting includes an information element (hereinafter referred to as "applicability flag") indicating whether the cell C1 can apply the control area function. When the cell C1 can apply the control area function, the MBS system information includes a control area identifier. However, when the MBS system information exists, it is implicitly considered that the control area function is applicable, and the applicability flag may not exist.

[0133] The MBS control area setting may include expiration information (for example, valid until a certain radio frame, valid until a certain time, valid within a certain time) indicating the period during which this MBS control area setting is valid. After the expiration of this expiration date, the adjacent cells constituting the MBS control area range may change their own MBS control information. Such a change may be implemented by the operator's device and / or the core network. Also, such a change may be implemented by signaling between gNBs 200.

[0134] Note that there may be a limitation that the control area function can be enabled only when a plurality of cells including the cell C1 constitute an SFN (Single Frequency Network). An SFN refers to a network in which a plurality of cells operating at the same frequency transmit the same signal simultaneously. The UE 100 receives the signals (combined signals) from the plurality of cells without identifying from which cell they are transmitted. The control area function may be enabled for the MBS control channel for constituting the SFN.

[0135] Further, the control area identifier may be shared with the system information area identifier indicating the system information area range. The system information area range refers to the area range in which the MBS system information can be reused. When the control area identifier is shared with the system information area identifier, the MBS system information may include information indicating that the MBS control information conforms to the setting of the area range of the MBS system information. That is, this information is information indicating that the system information area identifier is treated as the control area identifier.

[0136] There may be a plurality of MBS control channels in cell C1. For example, MBS control channels are provided for each MBS service or for each MBS service category. In this case, the MBS system information may include MBS control area settings for each MBS control channel. The MBS system information may include an MBS service identifier and / or an MBS control channel identifier, and an MBS control area setting associated with this identifier. Instead of or in addition to the MBS control area setting, a network slice identifier associated with the MBS control channel may be included in the MBS system information.

[0137] Based on the MBS system information received from gNB200 in step S501, UE100 grasps the scheduling of the MBS control channel. Also, UE100 stores the MBS control area setting included in this MBS system information.

[0138] In step S502, gNB200 transmits MBS control information via the MBS control channel by scheduling according to the MBS system information transmitted in step S501. The transmission of the MBS control information is performed by broadcast (or multicast) using a predetermined RNTI. The transmission of the MBS control information may be performed by unicast using C-RNTI (i.e., UE individual setting).

[0139] The MBS control information includes a list of scheduling information for MBS traffic channels. The MBS traffic channels are provided for each MBS service. The scheduling information for the MBS traffic channels includes, for example, an MBS service identifier (e.g., TMGI) corresponding to the MBS traffic channel and a group RNTI, and scheduling information (DRX (Discontinuous Reception) information) for the MBS traffic channel. The group RNTI is mapped one-to-one with the MBS service identifier.

[0140] In step S503, the UE 100 associates and stores the MBS control information received from the gNB 200 in step S502 with the MBS control area setting (at least the control area identifier) included in the MBS control information received from the gNB 200 in step S501. Also, the UE 100 grasps the scheduling of the MBS traffic channel based on the MBS control information received from the gNB 200 in step S502. For example, the UE 100 grasps the scheduling of the MBS traffic channel corresponding to the MBS service of its own interest and attempts to receive this MBS traffic channel.

[0141] In step S504, the gNB 200 transmits MBS data via the MBS traffic channel according to the scheduling based on the MBS control information transmitted in step S502. The transmission of the MBS data is performed by multicast (or broadcast) using the group RNTI. The UE 100 receives the MBS data of the MBS traffic channel corresponding to the MBS service of its own interest.

[0142] Next, a case where the UE 100 moves from the cell C1 to another cell (adjacent cell), which is the cell C2, after the above operations will be described. FIG. 15 is a diagram showing the operations when the UE 100 moves from the cell C1 to the cell C2 according to an embodiment. In FIG. 15, an example is shown in which the cell C1 is managed by the gNB 200A and the cell C2 is managed by the gNB 200B.

[0143] As shown in FIG. 15, when the UE 100 moves from cell C1 to cell C2, it performs handover or cell reselection. Handover refers to the cell switching operation of the UE 100 in the RRC connected state. Cell reselection refers to the cell switching operation of the UE 100 in the RRC idle state or RRC inactive state.

[0144] In cell C1, the UE 100 stores the MBS control information of cell C1 in association with the control area identifier (see step S503 in FIG. 14). When the UE 100 switches from cell C1 to cell C2, it receives the MBS system information transmitted on the broadcast control channel of cell C2 and obtains the MBS control area setting in this MBS system information.

[0145] Here, when the applicability flag in the obtained MBS control area setting is on (that is, cell C2 can apply the control area function), the UE 100 determines whether the control area identifier in the obtained MBS control area setting (the control area identifier of cell C2) matches the control area identifier it stores (the control area identifier of cell C1). If they match, the UE 100 determines that the MBS control information it stores (the MBS control information of cell C1) is valid and does not receive (skip) the MBS control channel of cell C2. Then, based on the MBS control information it stores (the MBS control information of cell C1), the UE 100 attempts to receive the MBS traffic channel of cell C2 and receives MBS data from cell C2.

[0146] In this way, if the MBS control area range is the same after the UE 100 reads the system information of cell C2, the UE 100 determines that the MBS control information of cell C1 is valid in cell C2, does not receive the MBS control channel of cell C2, and can attempt to receive the MBS traffic channel of cell C2. Thereby, the MBS reception interruption time is reduced.

[0147] In the example of FIG. 15, an example in which cells C1 and C2 are managed by different gNB200s has been described. However, as shown in FIG. 16, cells C1 and C2 may be managed by the same gNB200.

[0148] As shown in FIGS. 15 and 16, when the UE100 moves from cell C1 to cell C2, the UE100 may perform an operation of acquiring the control area identifier of cell C2 before moving to cell C2 while receiving MBS from cell C1. Assuming that the UE100 has only one receiver, such an operation may become difficult. For example, the UE100 needs to temporarily interrupt the MBS reception from cell C1 to acquire the control area identifier of cell C2.

[0149] Therefore, the gNB200 (cell C1) may transmit adjacent cell information to the UE100 for identifying whether the cell C2 (adjacent cell) belongs to the same MBS control area range as cell C1. The UE100 can grasp whether the cell C2 (adjacent cell) belongs to the same MBS control area range as cell C1 based on the adjacent cell information from cell C1. For example, after receiving and storing the adjacent cell information, the UE100 determines whether it is necessary to acquire MBS control information from the adjacent cell during cell handover. For example, when the cell C2 (adjacent cell) belongs to the same MBS control area range as cell C1, the UE100 does not acquire (skips) the control area identifier of cell C2.

[0150] The gNB200 (cell C1) may transmit the adjacent cell information in the MBS system information via the broadcast control channel of cell C1, or may transmit the adjacent cell information via the MBS control channel of cell C1.

[0151] The neighboring cell information includes a control area identifier of a neighboring cell (cell C2). The neighboring cell information may include a cell identifier and / or a frequency identifier and / or an MBS service identifier of the neighboring cell (cell C2), and a control area identifier associated with this identifier. When there are a plurality of MBS control channels in cell C2, the neighboring cell information may include an MBS control channel identifier and a control area identifier associated with this identifier. Alternatively, the neighboring cell information may be limited to neighboring cells belonging to the same or different MBS control area ranges as cell C1, and may include a cell identifier and / or a frequency identifier of this neighboring cell. The neighboring cell information may further include a system information area identifier indicating a system information area range of the neighboring cell.

[0152] In one embodiment, after receiving, from cell C1, MBS control information used for receiving MBS data and a control area identifier indicating an MBS control area range which is an area range in which at least a part of the MBS control information is applicable, if it is determined that a predetermined condition regarding the MBS control area range is satisfied, the UE100 re-receives the MBS control information.

[0153] FIG. 17 is a diagram showing an operation example 1 regarding re-reception of MBS control information according to one embodiment.

[0154] As shown in FIG. 17, in step S601, the UE100 in the RRC idle state or the RRC inactive state performs cell reselection to another cell (cell C2), and acquires a control area identifier indicating an MBS control area range to which the other cell (cell C2) belongs.

[0155] In step S602, the UE100 determines whether or not a predetermined condition regarding the MBS control area range is satisfied. In operation example 1, the predetermined condition is that the control area identifier received from cell C1 and the control area identifier received from the other cell (cell C2) are different, that is, the condition that the MBS control area range to which cell C1 belongs and the MBS control area range to which the other cell (cell C2) belongs are different.

[0156] When it is determined that the specified conditions are satisfied (step S602: YES), in step S603, UE100 transitions to the RRC connected state in another cell (cell C2). Specifically, when UE100 wants to continue receiving the MBS service being received, it establishes an RRC connection with the other cell (cell C2). For example, when UE100 is in the RRC idle state, it sends an RRC Setup Request message to the other cell (cell C2). When UE100 is in the RRC inactive state, it sends an RRC Resume Request message to the other cell (cell C2).

[0157] In step S603, UE100 may notify the other cell (cell C2) of at least one of the desire to receive MBS control information (MBS settings) for the RRC idle state or RRC inactive state and the MBS services (MBS sessions) of interest. Also, in step S603, UE100 may notify the other cell (cell C2) that it desires to transition to the RRC idle state or RRC inactive state after receiving the MBS settings.

[0158] In step S604, UE100 in the RRC connected state receives (re - receives) MBS control information from the other cell (cell C2).

[0159] FIG. 18 is a diagram showing an operation example 2 regarding the re - reception of MBS control information according to an embodiment.

[0160] As shown in FIG. 18, in step S701, UE100 receives MBS control information (MBS setting information) and information indicating the validity period of the MBS control information (expiration date information) from cell C1. By defining such a validity period, it becomes easier to change the MBS settings from the network's perspective. This is because changing the MBS settings will interrupt the MBS reception of UE100. Therefore, by defining the validity period, the possibility of changing the MBS settings can be given at a certain regular interval.

[0161] In step S702, UE100 starts a validity period for measuring the specified validity period.

[0162] In step S703, UE100 determines whether a predetermined condition regarding the MBS control area range is satisfied. In operation example 2, the predetermined condition is the condition that the validity period has expired within the control area range to which cell C1 belongs.

[0163] If it is determined that the predetermined condition is satisfied (step S703: YES), in step S704, UE100 receives (re - receives) MBS control information from the cells within the control area range to which cell C1 belongs. For example, in the case of UE individual settings (Dedicated config.), UE100 establishes an RRC connection in the same manner as in operation example 1. In the case of broadcast settings (Broadcast config.), UE100 re - acquires the broadcast MBS control channel.

[0164] (Other embodiments) In the above - described embodiments, an example where the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB). Also, the base station may be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may be the DU (Distributed Unit) of the IAB node.

[0165] In the above - described embodiments, inter - base - station communication has been mainly assumed, but intra - base - station communication may be assumed. For example, if the base station is separated into a CU and a DU, communication may be performed between the CU and the DU. In this case, the above - described Xn interface may be read as the F1 interface, which is the CU - DU interface, and various messages and information described above may be transmitted and received via the F1 interface. Also, each of the above - described gNB200A and gNB200B may be read as a CU and / or a DU.

[0166] Furthermore, the CU is separated into a CU-CP and a CU-UP, and communication may be performed between the CU-CP and the CU-UP. In this case, the above-described Xn interface may be reinterpreted as an E1 interface, which is an interface between the CU-CP and the CU-UP, and the above-described various messages and information may be transmitted and received via the E1 interface. Also, each of the above-described gNB200A and gNB200B may be reinterpreted as a CU-CP and / or a CU-UP.

[0167] A program may be provided that causes a computer to execute each process performed by the UE100 or the gNB200. The program may be recorded on a computer-readable medium. By using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-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.

[0168] Also, a circuit that executes each process performed by the UE100 or the gNB200 may be integrated, and at least a part of the UE100 or the gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0169] As described above, the embodiments have been described in detail with reference to the drawings, but the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the gist.

[0170] This application claims the priority of U.S. Provisional Application No. 63 / 094,437 (filed on October 21, 2020), and all of its contents are incorporated herein by reference.

Description of Reference Numerals

[0171] 10: NG-RAN (5G RAN) 20: 5GC (5G CN) 100: UE 110: Receiver 120: Transmission unit 130: Control unit 200: gNB 210: Transmission unit 220: Reception unit 230: Control unit 240: Backhaul communication unit

Claims

1. A communication control method, comprising: receiving, by a user equipment, multicast and broadcast service (MBS) control information from a cell for use in receiving MBS data; The user equipment in an RRC inactive state performs cell reselection to another cell; When the user equipment in the RRC inactive state determines that the MBS control information received from the cell is unavailable in the other cell, the user equipment transitions to an RRC connected state in the other cell. Communications control method.

2. A user device, a receiving unit for receiving Multicast Broadcast Service (MBS) control information from a cell for use in receiving MBS data; A control unit that performs cell reselection to another cell when the user equipment is in an RRC inactive state, When the control unit determines that the MBS control information received from the cell is unavailable in the other cell, the control unit transitions to an RRC connected state in the other cell. User equipment.

3. A chipset for a user device, comprising: receiving Multicast Broadcast Service (MBS) control information from a cell for use in receiving MBS data; A process of performing cell reselection to another cell when the user equipment is in an RRC inactive state; When it is determined that the MBS control information received from the cell is unavailable in the other cell, a process of transitioning to an RRC connected state in the other cell is executed. Chipset.

4. A user device includes: receiving Multicast Broadcast Service (MBS) control information from a cell for use in receiving MBS data; A process of performing cell reselection to another cell when the user equipment is in an RRC inactive state; and when it is determined that the MBS control information received from the cell is unavailable in the other cell, a process of transitioning to an RRC connected state in the other cell is executed. program.

5. A mobile communication system having a user equipment, The user equipment receives Multicast Broadcast Service (MBS) control information from a cell for use in receiving MBS data; The user equipment in the RRC inactive state performs cell reselection to another cell, When the user equipment determines that the MBS control information received from the cell is unavailable in the other cell, the user equipment transitions to an RRC connected state in the other cell. Mobile communication system.

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