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] The communication control method according to the 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, wherein the base station receives a specified PDCP (Packet Data Convergence Protocol) sequence number designated to be applied to an MBS packet from a core network or another base station, the base station associates the MBS packet with the specified PDCP sequence number, and the base station transmits the MBS packet associated with the specified PDCP sequence number to the user equipment.

[0005] A communication control method according to a second embodiment is a communication control method used in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user device, comprising: the base station receiving a paging message from the core network requesting paging for the user device which is in an RRC (Radio Resource Control) idle state or an RRC inactive state; and the base station performing the paging in response to the receipt of the paging message, wherein the paging message includes an identifier relating to the MBS session received by the user device.

[0006] A third aspect of the communication control method is a communication control method used in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user device, comprising: the base station transmitting MBS data received from the core network to the user device via PTM (Point To Multipoint); the base station sending a notification to the user device if it determines that it cannot continue PTM transmission of the MBS data from the base station to the user device; and the user device establishing a unicast session with the core network to receive the MBS data via unicast in response to receiving the notification.

[0007] A fourth aspect of the communication control method is a communication control method used in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user device, comprising: the user device receiving from a cell MBS control information to be used for receiving MBS data and a control area identifier indicating an MBS control area range which is an area range to which at least a part of the MBS control information can be applied; and the user device re-receiving the MBS control information when it determines that predetermined conditions relating to the MBS control area range have been met. [Brief explanation of the drawing]

[0008] [Figure 1]This figure shows the configuration of a mobile communication system according to one embodiment. [Figure 2] This diagram shows the configuration of a UE (User Equipment) according to one embodiment. [Figure 3] This diagram shows the configuration of a gNB (base station) according to one embodiment. [Figure 4] This diagram shows the protocol stack configuration of the user plane wireless interface that handles data. [Figure 5] This diagram shows the protocol stack configuration of the wireless interface of the control plane that handles signaling (control signals). [Figure 6] This figure shows the correspondence between the logical channel and the transport channel of a downlink according to one embodiment. [Figure 7] This figure shows a method for distributing MBS data according to one embodiment. [Figure 8] This figure shows the operating environment according to one embodiment. [Figure 9] This figure shows the operating environment according to one embodiment. [Figure 10] This figure shows an example of sequence number synchronization operation 1 according to one embodiment. [Figure 11] This figure shows an example of sequence number synchronization operation 2 according to one embodiment. [Figure 12] This figure shows an example of paging operation according to one embodiment. [Figure 13] This figure shows an example of the operation of switching to unicast according to one embodiment. [Figure 14] This diagram shows the operation of a mobile communication system according to one embodiment. [Figure 15] This figure shows the operation when UE100 moves from cell C1 to cell C2 according to one embodiment. [Figure 16] This figure shows the operation when UE100 moves from cell C1 to cell C2 according to one embodiment. [Figure 17]FIG. is a diagram showing an operation example 1 related to re - reception of MBS control information according to an embodiment. [Figure 18] FIG. is a diagram showing an operation example 2 related to re - reception of MBS control information according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0009] It is being considered to introduce multicast and broadcast services into the 5G system (NR). It is desired that the multicast and broadcast service of NR provides a service improved over the multicast and broadcast service of LTE.

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

[0011] A mobile communication system according to an embodiment will be described while referring 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. In the following, 5GS will be taken as an example for description, but the LTE (Long Term Evolution) system may be at least partially applied to the mobile communication system, or the 6th generation (6G) system may be at least partially applied.

[0013] <000009​

[0014] UE100 is a mobile wireless communication device. UE100 can be any device used by a user. For example, UE100 can be a mobile phone terminal (including smartphones), a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or a device provided for a sensor, a vehicle or a device provided for a vehicle (Vehicle UE), an aircraft or a device provided for an 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] The 5GC20 includes the AMF (Access and Mobility Management Function) and the UPF (User Plane Function) 300. The AMF performs various mobility controls for the UE100. The AMF manages the mobility of the UE100 by communicating with it using NAS (Non-Access Stratum) signaling. The UPF controls data transfer. The AMF and UPF are connected to the gNB200 via the NG interface, which is the base station-core network interface.

[0018] Figure 2 shows the configuration of UE100 (user device) according to one embodiment.

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

[0020] 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.

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

[0022] The control unit 130 performs various controls on 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 processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processing.

[0023] Figure 3 shows the configuration of a gNB200 (base station) according to one embodiment.

[0024] As shown in Figure 3, the gNB200 comprises a transmitting unit 210, a receiving unit 220, a control unit 230, and a backhaul communication unit 240.

[0025] The transmitting unit 210 performs various types of transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0026] 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.

[0027] The control unit 230 performs various controls in the gNB200. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processing.

[0028] The backhaul communication unit 240 is connected to an adjacent base station via an inter-base station interface. The backhaul communication unit 240 is connected to the AMF / UPF300 via a base station-core network interface. The gNB may consist of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally separated), and the two units may be connected via an F1 interface.

[0029] Figure 4 shows the configuration of the protocol stack for the user plane's wireless interface that handles data.

[0030] As shown in Figure 4, the user plane radio interface protocol 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. Data and control information are transmitted between the UE100's PHY layer and the gNB200's PHY layer via a physical channel.

[0032] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), and random access procedures. Data and control information are transmitted between the MAC layer of the UE100 and the MAC layer of the gNB200 via the transport channel. The MAC layer of the gNB200 includes a scheduler. The scheduler determines the transport format for the up and down links (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to the UE100.

[0033] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the UE100's RLC layer and the gNB200's RLC layer via a logical channel.

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

[0035] The SDAP layer maps IP flows, which are the units under which the core network performs QoS control, to wireless bearers, which are the units under which the AS (Access Stratum) performs QoS control. Note that if the RAN is connected to the EPC, SDAP may not be necessary.

[0036] Figure 5 shows the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals).

[0037] As shown in Figure 5, the protocol stack of the control plane's wireless interface has an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer instead of the SDAP layer shown in Figure 4.

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

[0039] The NAS layer, located above the RRC layer, handles session management and mobility management, among other things. NAS signaling is transmitted between the UE100's NAS layer and the AMF300B's NAS layer.

[0040] In addition to the wireless interface protocol, the UE100 also has an application layer and other components.

[0041] (MBS) Next, an MBS according to one embodiment will be described. MBS is a service that transmits data from NG-RAN10 to UE100 via broadcast or multicast, i.e., one-to-many (PTM: Point To Multipoint). MBS may also be called MBMS (Multimedia Broadcast and Multicast Service). Use cases (service types) of MBS include public security communications, mission-critical communications, V2X (Vehicle to Everything) communications, IPv4 or IPv6 multicast distribution, IPTV, group communications, and software distribution.

[0042] There are two types of MBS transmission methods in LTE: MBSFN (Multicast Broadcast Single Frequency Network) transmission and SC-PTM (Single Cell Point To Multipoint) transmission. Figure 6 shows the correspondence between the logical channel and the transport channel of a downlink according to one embodiment.

[0043] As shown in Figure 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 primarily designed for multi-cell transmission, and in an MBSFN area consisting of multiple cells, each cell synchronously transmits the same signal (same data) using 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 primarily designed for single-cell transmission, performing broadcast or multicast data transmission 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), enabling dynamic resource allocation.

[0045] The following primarily describes an example of MBS being provided using the SC-PTM transmission method, but MBS may also be provided using the MBSFN transmission method. Furthermore, the description will primarily describe an example of MBS being provided via multicast. Therefore, MBS may be interpreted as multicast. However, MBS may also be provided via broadcast.

[0046] Furthermore, MBS data refers to 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 treated in packet units will be referred to as MBS packets.

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

[0048] Figure 7 shows a method for distributing MBS data according to one embodiment.

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

[0050] From the perspective of 5GC20, two delivery methods are possible: Shared MBS Traffic delivery and Individual MBS Traffic delivery.

[0051] In shared MBS data distribution, a connection is established between NG-RAN10, a 5G wireless access network (5G RAN), and 5GC20, and MBS data is distributed from 5GC20 to NG-RAN10. Hereafter, this connection (tunnel) will be referred to as the "MBS connection".

[0052] The MBS connection may also be called a Shared MBS Traffic Delivery connection or a shared transport. The MBS connection terminates at NG-RAN10 (i.e., gNB200). The MBS connection may have a one-to-one correspondence with an MBS session. The gNB200 decides whether to use PTP (Point-to-Point: unicast) or PTM (Point-to-Multipoint: multicast or broadcast) and sends the MBS data to the UE100 using the selected method.

[0053] On the other hand, in individual MBS data distribution, a unicast session is established between NG-RAN10 and UE100, and MBS data is individually distributed from 5GC20 to UE100. Such a unicast may also be called a PDU session. The unicast (PDU session) terminates at UE100.

[0054] (Sequence number synchronization) Next, a sequence number synchronization according to one embodiment will be described. Figures 8 and 9 show the operating environment according to one embodiment.

[0055] As shown in Figure 8, gNB200A manages cell C1, and gNB200B manages cell C2. UE100A resides in cell C1, and UE100B resides in cell C2. UE100A can move from cell C1 to cell C2. Similarly, UE100B can move from cell C2 to cell C1.

[0056] Note that while the diagram illustrates an example where cells C1 and C2 have equivalent sizes, their sizes may differ. The geographical regions of cells C1 and C2 overlap at least partially. Such relationships between cells are sometimes referred to as adjacent cells. UE100A and UE100B may reside in the overlapping region of these cells.

[0057] gNB200A and gNB200B can communicate with each other via the Xn interface (Xn connection), which is the inter-base station interface. However, communication between gNB200A and gNB200B is not limited to the Xn interface; it may also occur via the NG interface, which is the inter-base station core network interface, and the core network equipment. Below, we will mainly describe an example in which communication between gNB200A and gNB200B is performed via the Xn interface.

[0058] Cells C1 and C2 may belong to the same MBS area. An MBS area is an area consisting of multiple cells that provide the same MBS session. Multiple cells belonging to the same MBS area may provide MBS sessions at the same frequency and constitute an SFN (Single Frequency Network).

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

[0060] In this environment, gNB200B has an MBS connection with UPF300A. gNB200B receives MBS packets from UPF300A via the MBS connection and transmits the received MBS packets via PTM in cell C2. Here, the PDCP entity of gNB200B transmits the MBS packets with a PDCP header containing a PDCP sequence number (PDCP SN) attached. The PDCP SN is counted up (incremented) for each MBS packet transmitted.

[0061] On the other hand, the gNB200A does not have an MBS connection with the UPF300A. Assuming a scenario where cells C1 and C2 constitute an SFN, as shown in Figure 9, the gNB200A needs to establish an MBS connection with the UPF300A. Furthermore, it is desirable that the PDCP SNs of the MBS packets transmitted by the gNB200A and gNB200B are synchronized. In other words, for MBS packets transmitted via MBS Shared Delivery, it is desirable that the air interface side transmits PTM using synchronized PDCP SNs across multiple gNB200s (gNB200A and gNB200B).

[0062] However, gNB200B has already started PTM transmission for the target MBS session, and the PDCP SN value has increased. Therefore, if gNB200A counts up the PDCP SN from its initial value (e.g., zero), it will not be possible to perform PTM transmission with synchronized PDCP SNs across multiple gNB200s (gNB200A and gNB200B).

[0063] Therefore, in one embodiment, the core network specifies the value of the PDCP SN of the MBS packet transmitted by gNB200A. Here, it is assumed that 5GC20 (core network) is aware of the current PDCP SN of gNB200B. 5GC20 specifies the value of the PDCP SN of the MBS packet transmitted by gNB200A so that the MBS packet and its PDCP SN transmitted by gNB200A match the MBS packet and its PDCP SN transmitted by gNB200B.

[0064] To obtain the current PDCP SN of gNB200B, 5GC20 may query gNB200B for current PDCP SN information. This query may include MBS session information. gNB200B may report the current PDCP SN information to 5GC20. This report may include MBS session information. This report may be made in response to receiving the query.

[0065] In one embodiment, gNB200A receives an MBS packet and a designated PDCP SN specified to apply to the MBS packet from 5GC20, 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 via PTM.

[0066] Figure 10 shows an example of sequence number synchronization operation 1 according to one embodiment.

[0067] As shown in Figure 10, in step S101, 5GC20 (for example, UPF300A or AMF300B) sends configuration information for establishing an MBS connection (hereinafter referred to as "MBS connection configuration information") to gNB200A. 5GC20 may also send MBS connection configuration information to gNB200A upon request from gNB200A.

[0068] The MBS connection configuration information includes the configuration parameters for the MBS connection and the specified PDCP SN information for the specified PDCP SN. The MBS connection configuration information may also include MBS session information associated with the specified PDCP SN information. The MBS session information includes identifiers for the MBS session. Such identifiers may be session identifiers (e.g., TMGI), QoS flow identifiers, and / or G-RNTI in PTM transmissions. Based on the MBS session information, the gNB200A can determine the MBS session corresponding to the MBS connection to be established.

[0069] The designated PDCP SN information includes the designated PDCP SN specified to be applied to the first MBS packet received by the gNB200 via the MBS connection from the 5GC20. In other words, the 5GC20 specifies the initial value of the PDCP SN that the gNB200A should set in the MBS packet. Figure 10 shows an example where the designated PDCP SN is "10". Note that if the 5GC20 sends MBS connection configuration information and MBS packets to the gNB200A simultaneously, the designated PDCP SN information may also be the designated PDCP SN specified to be applied to the current corresponding MBS packet.

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

[0071] The specified PDCP SN information may also include the SN length (bit length) of the PDCP SN. These SN lengths are, for example, 12 bits or 18 bits. Specifying the SN length allows for synchronization of the timing (wrap-around) when the SN returns to zero.

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

[0073] In step S103, 5GC20 sends 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 designated PDCP SN specified by 5GC20 in the PDCP header of MBS packet A, based on the designated PDCP SN information from 5GC20.

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

[0076] Subsequently, the gNB200A updates the PDCP SN count to increment for each MBS packet it transmits.

[0077] For example, in step S106, 5GC20 sends 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 (in this case, SN=11) in the PDCP header of MBS packet B.

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

[0080] In Operation Example 1, we described an example where each gNB200 sends MBS packets using PTP, but each gNB200 may also send MBS packets using PTM.

[0081] Next, an example of sequence number synchronization operation 2 according to one embodiment will be described. Operation example 2 is an embodiment in which the PDCP SN is synchronized before and after a 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, the target gNB, gNB200B, receives a designated PDCP SN from the source gNB, gNB200A, which is specified to be applied to the MBS packet, and associates the MBS packet with the designated PDCP SN. gNB200A then sends the MBS packet, which is associated with the designated PDCP SN, to UE100.

[0083] In Operation Example 2, gNB200B receives the PDCP SN of the MBS packet that UE100 failed to receive on gNB200A from UE100, which performed a handover from gNB200A to gNB200B. gNB200B then sends (resends) the MBS packet associated with the PDCP SN received from UE100 back to UE100.

[0084] Figure 11 shows an example of sequence number synchronization operation 2 according to one embodiment. In Figure 11, gNB200A and gNB200B each have an MBS connection with UPF300A and receive the same MBS packets from UPF300A. However, the MBS packets transmitted by gNB200A and gNB200B are assumed to have asynchronous PDCP SN.

[0085] As shown in Figure 11, in steps S201 to S203, gNB200A transmits MBS packets A to C to UE100 via PTM. The PDCP SNs of MBS packets A to C are "11" to "13". Now, let's assume that UE100 failed to receive MBS packet C (for example, detected a decoding error).

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

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

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

[0089] Here, an example of a handover request message containing specified PDCP SN information has been described. However, gNB200B may obtain the specified PDCP SN information from gNB200A by querying gNB200A. gNB200B may also 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 designated PDCP SN based on the designated PDCP SN information.

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

[0092] In step S208, gNB200A sends 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 to gNB200B containing the PDCP SN "13" of the MBS packet C that failed to be received in step S203. This retransmission request may also be a PDCP Status PDU.

[0095] In addition, during the handover request in step S205, gNB200A (source gNB) may notify UE100 of the SN information that it believes it failed to receive (i.e., a network-initiated retransmission request). In this case, step S210 is not required.

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

[0097] Thus, according to Operation Example 2, even when the UE100 performs a handover between gNBs whose PDCP SNs are not synchronized, the UE100 can correctly send (retransmit) MBS packets that it could not receive from the source gNB from the target gNB.

[0098] (paging) Next, we will describe paging according to one embodiment.

[0099] When UE100, which is in the RRC idle or RRC connected state, performs MBS reception, gNB200 may receive a paging message addressed to UE100 from 5GC20 (AMF300B). If gNB200 pages UE100 without considering the timing of UE100's MBS reception, there is a concern that the MBS reception timing and the paging reception timing will conflict in UE100, potentially causing a reception error.

[0100] The following describes an operation to resolve such problems. In one embodiment, gNB200 receives a paging message from 5GC20 (AMF300B) requesting paging for UE100 which is in an RRC idle or RRC inactive state. This paging message includes an identifier (e.g., TMGI) relating to the MBS session received by UE100.

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

[0102] The gNB200 performs paging on the UE100 in response to receiving a paging message from the AMF300B. Specifically, the gNB200 sends an RRC paging message addressed to the UE100.

[0103] Here, the gNB200 performs paging at a different timing than the transmission timing of the MBS session received by the UE100, based on the session identifier included in the paging message from the AMF300B (by sending an RRC paging message). This avoids a conflict between the MBS reception timing and the paging reception timing at the UE100.

[0104] Figure 12 shows an example of paging operation according to one embodiment. In Figure 12, UE100 is assumed to be in the RRC idle state or the RRC connected state.

[0105] As shown in Figure 12, in step S301, UPF300A transmits MBS data to gNB200 via the MBS connection. In step S302, gNB200 transmits the MBS data received from UPF300A to UE100 via PTM. Here, it is assumed that the timing for gNB200 to transmit MBS data via PTM is predetermined. For example, gNB200 notifies UE100 in advance of the timing of an MBS transmission opportunity (which may also be the MBS transmission cycle), and UE100 performs MBS reception at the notified MBS transmission timing.

[0106] In step S303, the AMF300B sends a paging message to the gNB200 addressed to the UE100. The paging message includes a set of identifiers for the UE100 and identifiers for the MBS sessions that the UE100 will receive (MBS session information).

[0107] In step S304, gNB200 determines the paging timing for UE100 based on the information contained in the paging message from AMF300B. For example, gNB200 identifies the MBS transmission timing for this MBS session based on the MBS session information contained in the paging message from AMF300B. gNB200 also identifies the paging opportunity (paging timing) for this UE100 based on the UE identifier contained in the paging message from AMF300B. Then, gNB200 determines paging timings that do not coincide with the identified MBS transmission timing, while avoiding paging timings that coincide with the identified MBS transmission timing.

[0108] In step S305, UPF300A transmits MBS data to gNB200 via the MBS connection. In step S306, gNB200 transmits the MBS data received from UPF300A to UE100 via PTM. Note that if UE100 determines that a paging opportunity and an MBS reception opportunity conflict, it may prioritize MBS reception.

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

[0110] This example assumes that UE100 cannot perform MBS reception and paging reception simultaneously. However, it is also possible that UE100 has the capability to perform MBS reception and paging reception simultaneously. For this reason, AMF300B may further include information in the paging message indicating whether or not UE100 has the capability to perform MBS reception and paging reception simultaneously (capability information). Based on this capability information, gNB200 may simultaneously send MBS data and an RRC paging message to UE100 that has this capability.

[0111] (Switching to unicast) Next, we will describe the switch to unicast according to one embodiment.

[0112] For example, when handing over a UE100 that is receiving MBS data transmitted via PTM, if the target gNB200 does not support PTM transmission (or MBS service), the UE100 will not be able to continue receiving MBS data. Similarly, if the gNB200 stops PTM transmission (or MBS service), the UE100 will not be able to continue receiving MBS data.

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

[0114] In one embodiment, gNB200 transmits the MBS data received from 5GC20 to UE100 via PTM. If gNB200 determines that it cannot continue PTM transmission of MBS data from gNB200 to UE100, it sends a notification to UE100. Upon receiving this notification, UE100 establishes a unicast session with 5GC20 to receive MBS data via unicast. In this way, the notification from gNB200 prompts UE100 to establish a unicast session, enabling UE100 to establish a unicast session and continue receiving MBS data.

[0115] Figure 13 shows an example of the operation of switching to unicast according to one embodiment.

[0116] As shown in Figure 13, in step S401, 5GC20 (UPF300A) transmits MBS data to gNB200 via the MBS connection.

[0117] In step S402, gNB200 transmits the MBS data received from 5GC20 to UE100 via PTM.

[0118] In step S403, gNB200 determines that it cannot continue providing the MBS service while UE100 is receiving PTM. For example, gNB200 determines that it cannot continue providing the MBS service because it needs to hand over UE100, or because gNB200 stops PTM transmission. However, the MBS service itself continues.

[0119] In step S404, gNB200 notifies UE100 to make a service request for MBS reception via unicast.

[0120] The notification may include the identifier of the MBS service (MBS session) in question, for example, TMGI. The notification may also be a notification that PTM will no longer be able to continue providing MBS services.

[0121] Assuming that UE100 is in an RRC connected state, dedicated signaling can be used for such notification. If UE100 is in an RRC idle or RRC inactive state, a broadcasted MBS control channel or paging (RRC paging message) can be used.

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

[0123] In step S406, UE100 continues to receive MBS services via unicast. UE100 may notify gNB200 that a unicast session has been established. This notification may follow step S405. This notification allows gNB200 to perform a handover or stop PTM transmission at the appropriate time.

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

[0125] The UE100, which receives MBS data, can move across cells. For such a UE100 to continue receiving MBS data, it must receive the MBS control channel (MBS control information) at the destination cell at least when switching cells. This increases the load and power consumption of the UE100, and makes it difficult to quickly receive MBS data from the destination cell. The MBS control information includes configuration information (MBS settings) for receiving the MBS traffic channel.

[0126] In one embodiment, a function (hereinafter referred to as the "control area function") is introduced that allows MBS control information to be shared within an area range consisting of multiple cells (hereinafter referred to as the "MBS control area range"). This makes it possible to reuse MBS control information even when crossing cells within the MBS control area range, thus solving the above-mentioned problem.

[0127] In other words, according to one embodiment, the gNB200 transmits MBS control information used for receiving MBS data to the UE100 via its own cell's MBS control channel. The gNB200 transmits to the UE100 a control area identifier indicating the MBS control area range, which is the area range to which at least a portion of the MBS control information can be applied. This allows the UE100 to understand the MBS control area range to which the current cell's MBS control information can be reused.

[0128] The UE100 stores MBS control information and control area identifiers from the gNB200. Then, within the MBS control area range indicated by the stored control area identifier, the UE100 receives MBS data based on the stored MBS control information. In this way, because the MBS control information can be reused to receive MBS data even across cells within the stored area range, the load and power consumption of the UE100 can be reduced, and it becomes easier to quickly receive MBS data from the target cell.

[0129] Figure 14 shows the operation of a mobile communication system according to one embodiment.

[0130] As shown in Figure 14, in step S501, the gNB200, which manages cell C1, transmits MBS system information to the UE100 via the Broadcast Control Channel (BCCH) of cell C1. The transmission of MBS system information is performed by broadcast using a predetermined RNTI. The UE100 receives the MBS system information. This system information is sometimes referred to as a System Information Block (SIB).

[0131] The MBS system information includes scheduling information necessary for receiving the MBS control channel. For example, the MBS system information includes at least one of the following: information indicating the period during which the contents of the MBS control channel (MBS control information) may be changed; information indicating the time interval for 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 an MBS control area setting. The MBS control area setting includes an information element (hereinafter referred to as the "applicability flag") indicating whether or not cell C1 is eligible for the control area function. If cell C1 is eligible for the control area function, the MBS system information includes a control area identifier. However, if the MBS system information is present, it is implicitly assumed that the control area function is eligible, and the applicability flag may not be present.

[0133] The MBS control area setting may include expiration information indicating the period during which the MBS control area setting is valid (e.g., valid until a certain radio frame, valid until a certain time, valid within a certain time). After this expiration date, neighboring cells constituting the MBS control area range may change their own MBS control information. Such changes may be made by the operator's equipment and / or the core network. Alternatively, such changes may be made through gNB200 signaling.

[0134] Furthermore, the control area function may be restricted to being enabled only when multiple cells, including cell C1, constitute an SFN (Single Frequency Network). An SFN is a network in which multiple cells operating on the same frequency simultaneously transmit the same signal. The UE100 receives the signals (composite signals) from these multiple cells without identifying which cell transmitted them. The control area function may be enabled for the MBS control channel used to configure the SFN.

[0135] Furthermore, the control area identifier may be shared with the system information area identifier that indicates the system information area range. The system information area range refers to the area range in which 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 area range setting of the MBS system information. In other words, this information indicates that the system information area identifier will be treated as a control area identifier.

[0136] Multiple MBS control channels may exist in cell C1. For example, an MBS control channel may be provided for each MBS service or each MBS service category. In this case, the MBS system information may include an MBS control area setting 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 determines the scheduling of the MBS control channels. UE100 also stores the MBS control area settings included in this MBS system information.

[0138] In step S502, the gNB200 transmits MBS control information via the MBS control channel according to the scheduling based on 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 also be performed by unicast using a C-RNTI (i.e., UE-specific configuration).

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

[0140] In step S503, UE100 stores the MBS control information received from gNB200 in step S502, associating it with the MBS control area settings (at least the control area identifier) ​​included in the MBS control information received from gNB200 in step S501. Furthermore, UE100 understands the scheduling of MBS traffic channels based on the MBS control information received from gNB200 in step S502. For example, UE100 understands the scheduling of MBS traffic channels corresponding to MBS services of interest and attempts to receive these MBS traffic channels.

[0141] In step S504, the gNB200 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 MBS data is performed by multicast (or broadcast) using group RNTI. The UE100 receives MBS data on the MBS traffic channel corresponding to the MBS service of interest to it.

[0142] Next, we will describe the case where UE100 moves from cell C1 to another cell (an adjacent cell), which is cell C2, after the above-described operation. Figure 15 is a diagram showing the operation when UE100 moves from cell C1 to cell C2 according to one embodiment. In Figure 15, an example is shown in which cell C1 is managed by gNB200A and cell C2 is managed by gNB200B.

[0143] As shown in Figure 15, UE100 performs a handover or cell reselection when moving from cell C1 to cell C2. Handover refers to the cell switching operation of UE100 when it is in the RRC connected state. Cell reselection refers to the cell switching operation of UE100 when it is in the RRC idle state or RRC inactive state.

[0144] In cell C1, UE100 stores the MBS control information for cell C1, associating it with the control area identifier (see step S503 in Figure 14). When switching from cell C1 to cell C2, UE100 receives the MBS system information transmitted on the broadcast control channel of cell C2 and obtains the MBS control area setting from this MBS system information.

[0145] If the applicable flag for the acquired MBS control area setting is on (i.e., cell C2 is eligible for the control area function), UE100 determines whether the acquired control area identifier for the MBS control area setting (the control area identifier for cell C2) matches the control area identifier it has stored (the control area identifier for cell C1). If they match, UE100 determines that the MBS control information it has stored (the MBS control information for cell C1) is valid and does not receive (skips) the MBS control channel for cell C2. Then, based on the MBS control information it has stored (the MBS control information for cell C1), UE100 attempts to receive the MBS traffic channel for cell C2 and receives MBS data from cell C2.

[0146] In this way, UE100 reads the system information of cell C2 and, if the MBS control area range is the same, determines that the MBS control information of cell C1 is valid in cell C2. It can then attempt to receive the MBS traffic channel of cell C2 without receiving the MBS control channel of cell C2. This reduces the MBS reception interruption time.

[0147] In the example shown in Figure 15, cells C1 and C2 are managed by separate gNB200s. However, as shown in Figure 16, cells C1 and C2 may be managed by the same gNB200.

[0148] As shown in Figures 15 and 16, when UE100 moves from cell C1 to cell C2, UE100 may perform the operation of receiving MBS from cell C1 while simultaneously acquiring the control area identifier of cell C2 before moving to cell C2. If UE100 has only one receiver, this operation may become difficult. For example, UE100 would need to temporarily interrupt MBS reception from cell C1 to acquire the control area identifier of cell C2.

[0149] Therefore, gNB200 (cell C1) may transmit adjacent cell information to UE100 to determine whether cell C2 (adjacent cell) belongs to the same MBS control area range as cell C1. Based on the adjacent cell information from cell C1, UE100 can determine whether cell C2 (adjacent cell) belongs to the same MBS control area range as cell C1. For example, after receiving and storing the adjacent cell information, UE100 determines whether it must obtain MBS control information from the adjacent cell during cell switching. For example, if cell C2 (adjacent cell) belongs to the same MBS control area range as cell C1, UE100 does not obtain the control area identifier for cell C2 (it skips this step).

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

[0151] Adjacent cell information includes the control area identifier of the adjacent cell (cell C2). Adjacent cell information may also include the cell identifier and / or frequency identifier and / or MBS service identifier of the adjacent cell (cell C2), and the control area identifier associated with this identifier. If cell C2 has multiple MBS control channels, the adjacent cell information may also include the MBS control channel identifier and the control area identifier associated with this identifier. Alternatively, the adjacent cell information may be limited to adjacent cells belonging to the same or different MBS control area range as cell C1, and may include the cell identifier and / or frequency identifier of these adjacent cells. The adjacent cell information may further include a system information area identifier indicating the system information area range of the adjacent cell.

[0152] In one embodiment, UE100 receives MBS control information used for receiving MBS data and a control area identifier indicating an MBS control area range to which at least a portion of the MBS control information can be applied from cell C1. If UE100 determines that predetermined conditions regarding the MBS control area range have been met, it re-receives the MBS control information.

[0153] Figure 17 shows an example of operation 1 related to the re-reception of MBS control information according to one embodiment.

[0154] As shown in Figure 17, in step S601, UE100, which is in an RRC idle or RRC inactive state, re-selects another cell (cell C2) and obtains a control area identifier indicating the MBS control area range to which the other cell (cell C2) belongs.

[0155] In step S602, UE100 determines whether predetermined conditions regarding the MBS control area range are met. In operation example 1, the predetermined condition is that the control area identifier received from cell C1 is different from the control area identifier received from another cell (cell C2), that is, the MBS control area range to which cell C1 belongs is different from the MBS control area range to which the other cell (cell C2) belongs.

[0156] If it is determined that the predetermined conditions are met (step S602: YES), in step S603, UE100 transitions to the RRC connected state in the other cell (cell C2). Specifically, UE100 establishes an RRC connection with the other cell (cell C2) if it wants to continue receiving the MBS service that is currently being received. For example, if UE100 is in the RRC idle state, it sends an RRC Setup Request message to the other cell (cell C2). If 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 its desire to receive MBS control information (MBS settings) for the RRC idle state or RRC inactive state, and of at least one of the MBS services (MBS sessions) of interest. Also in step S603, UE100 may notify the other cell (cell C2) that it would like to transition to the RRC idle state or RRC inactive state after receiving the MBS settings.

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

[0159] Figure 18 shows an example of operation 2 related to the re-reception of MBS control information according to one embodiment.

[0160] As shown in Figure 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 an expiration period, it becomes easier to change the MBS settings from a network perspective. This is because changing the MBS settings interrupts MBS reception by UE100. Therefore, by defining an expiration period, it is possible to provide the possibility of changing the MBS settings at a certain interval.

[0161] In step S702, UE100 starts a validity period that measures the specified validity period.

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

[0163] If it is determined that the predetermined conditions are met (step S703: YES), in step S704, UE100 receives (re-receives) MBS control information from cells within the control area range to which cell C1 belongs. For example, in the case of a dedicated UE configuration, UE100 establishes an RRC connection in the same way as in operation example 1. In the case of a broadcast configuration, UE100 reacquires the broadcasted MBS control channel.

[0164] (Other embodiments) In the above embodiment, an example was described in which the base station is an NR base station (gNB), but the base station may also be an LTE base station (eNB). Furthermore, the base station may be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU (Distributed Unit) of an IAB node.

[0165] In the embodiments described above, communication between base stations was primarily assumed, but communication within a base station may also be assumed. For example, a base station may be separated into a CU and a DU, and communication may take place between the CU and the DU. In this case, the Xn interface described above may be replaced with the F1 interface, which is the CU-DU interface, and the various messages and information described above may be sent and received via the F1 interface. Also, the gNB200A and gNB200B described above may be replaced with a CU and / or a DU, respectively.

[0166] Furthermore, the CU may be separated into CU-CP and CU-UP, and communication may take place between CU-CP and CU-UP. In this case, the above-mentioned Xn interface may be read as the E1 interface, which is the interface between CU-CP and CU-UP, and the above-mentioned various messages and information may be sent and received via the E1 interface. Also, the above-mentioned gNB200A and gNB200B may be read as CU-CP and / or CU-UP, respectively.

[0167] A program may be provided that causes a computer to perform each of the processes that UE100 or gNB200 performs. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may be a recording medium such as a CD-ROM or DVD-ROM.

[0168] Alternatively, the circuits that perform each process carried out by the UE100 or gNB200 may be integrated, and at least a portion of the UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC).

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

[0170] This application claims priority to U.S. Provisional Application No. 63 / 094437 (filed October 21, 2020), the entirety of which is incorporated into the specification of this application. [Explanation of Symbols]

[0171] 10: NG-RAN (5G RAN) 20:5GC(5G CN) 100 :UE 110: Receiver 120: Transmitter 130: Control Unit 200 :gNB 210: Transmitter 220: Receiving unit 230: Control Unit 240: Backhaul Communications Department

Claims

1. A communication control method, The user device receives MBS control information from the cell to be used for receiving multicast broadcast service (MBS) data, The user device, which is in an RRC inactive state, performs cell reselection to another cell, The user device, which is in the RRC inactive state, determines that the MBS control information received from the cell is unavailable in the other cell, and the other cell transitions to the RRC connected state. Communication control method.

2. User device, A receiving unit that receives MBS control information from a cell for receiving multicast broadcast service (MBS) data, The user device includes a control unit that performs cell reselection to another cell when the RRC is inactive, If the control unit determines that the MBS control information received from the cell is unavailable in the other cell, it transitions the other cell to the RRC connected state. User device.

3. A chipset for a user device, The process of receiving MBS control information from a cell for receiving multicast broadcast service (MBS) data, When the user device is in an RRC inactive state, the process involves re-selecting a cell to another cell, If the MBS control information received from the aforementioned cell is determined to be unavailable in the other cell, the other cell will perform the following process: transition to the RRC connected state. Chipset.

4. On the user device, The process of receiving MBS control information from a cell for receiving multicast broadcast service (MBS) data, When the user device is in an RRC inactive state, the process involves re-selecting a cell to another cell, If the MBS control information received from the aforementioned cell is determined to be unavailable in the other cell, the process of transitioning the other cell to the RRC connected state is executed. program.

5. A mobile communication system having user equipment, The user device receives MBS control information from the cell for receiving multicast broadcast service (MBS) data. The user device, which is in an RRC inactive state, performs cell reselection to another cell, If the user device determines that the MBS control information received from the cell is unavailable in the other cell, it transitions to the RRC connected state in the other cell. Mobile communication system.

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