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

Abstract

To provide a communication control method, a user device, and a processor that realize an improved multicast / broadcast service.SOLUTION: In a communication control method used in a mobile communication system that provides a multicast / broadcast service (MBS) from a base station to a user device, a base station gNB transmits a message to a user device UE that configures a Radio Link Control (RLC) entity of the user device, the message includes an information element that specifies an operation mode of the RLC entity for an MBS traffic channel that transmits MBS data.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a communication control method, a user device, and a processor 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 device, and includes transmitting, from the base station to the user device, a message for setting a Radio Link Control (RLC) entity of the user device, where the message includes an information element specifying an operation mode of the RLC entity for an MBS traffic channel that transmits MBS data.

[0005] A second 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 MBS data from the base station; and the RLC (Radio Link Control) entity of the user device setting the sequence number of the MBS data first received from the base station as the initial value of a variable used for a predetermined RLC operation.

[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 user device receiving MBS data from the base station; and the PDCP (Packet Data Convergence Protocol) entity of the user device performing MBS reception processing on the MBS data, wherein the MBS reception processing includes the PDCP entity performing at least one of duplicate packet discarding processing and packet sorting processing without performing at least one of decryption processing and header decompression processing.

[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 MBS data from a first cell; the user device performing a handover from the first cell to a second cell; and, if the PDCP (Packet Data Convergence Protocol) entity of the user device fails to receive the MBS data during the handover, transmitting a sequence number indicating the MBS data that failed to be received to the second cell. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram shows the configuration of a mobile communication system according to an embodiment. [Figure 2] This diagram shows the configuration of the UE (User Equipment) according to the embodiment. [Figure 3] This diagram shows the configuration of the gNB (base station) according to the 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 the downlink according to the embodiment. [Figure 7] This figure shows an example of operation according to the first embodiment. [Figure 8] This figure shows a specific example of operation according to the first embodiment. [Figure 9] This figure shows the RLC operation according to the first embodiment. [Figure 10] This figure shows the RLC operation of the AM according to the first embodiment. [Figure 11] This figure shows the RLC operation of the UM according to the first embodiment. [Figure 12] This is a diagram illustrating the PDCP operating mode according to the second embodiment. [Figure 13] This is a diagram illustrating the PDCP operating mode according to the second embodiment. [Figure 14] This figure shows an example of PDCP operation according to the second embodiment. [Figure 15] This figure shows the handover operation according to the second embodiment. [Figure 16] This figure shows another example of the handover operation according to the second embodiment. [Modes for carrying out the invention]

[0009] The introduction of multicast and broadcast services into a 5G system (NR) is under consideration. It is desired that the multicast and broadcast services of NR provide a service improved over the multicast and broadcast services of LTE.

[0010] Therefore, the present disclosure aims 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 the mobile communication system according to the 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 the LTE (Long Term Evolution) system may be at least partially applied to the mobile communication system.

[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 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 a 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. gNB200s are interconnected via the Xn interface which is an interface between base stations. gNB200 manages one or more cells. gNB200 performs wireless communication with UE100 that has established a connection with its cell. gNB200 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 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 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 an 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 the gNB200 (base station) according to this 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 wireless 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 AMF300'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 the 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) for 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 the downlink according to the 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 Control 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, in the following, 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.

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

[0048] (First Embodiment) Next, a first embodiment will be described based on the mobile communication system and MBS described above. The first embodiment is an embodiment relating to RLC operation for MBS.

[0049] (1) RLC configuration operation for MBS There are three operating modes for the RLC layer: AM (Acknowledged Mode), UM (Unacknowledged Mode), and TM (Transparent Mode). Of these modes, only AM supports retransmission functionality via Automatic Repeat Request (ARQ). AM is a mode in which retransmission control is performed by sending ACK feedback from the receiving RLC entity to the transmitting RLC entity.

[0050] In LTE multicast services, the operating mode of RLC entities is set to UM. However, if a mechanism could be implemented to apply AM to NR multicast services, it is believed that the reliability and flexibility of multicast communication could be improved.

[0051] Figure 7 shows an example of operation according to the first embodiment.

[0052] As shown in Figure 7, cell C, managed by gNB200, contains UE100a in an RRC connected state and UE100b in an RRC idle state. UE100a and UE100b are both interested in receiving MBS data belonging to the same MBS service (same MBS session).

[0053] The gNB200 sends a message (hereinafter referred to as the "configuration message") to configure the RLC entity of the UE100. The configuration message includes information elements (hereinafter referred to as the "RLC configuration information") that specify the operating mode of the RLC entity for the MBS traffic channel that transmits MBS data.

[0054] The RLC configuration information specifies either a first mode (i.e., AM) that performs automatic retransmission control or a second mode that does not perform automatic retransmission control as the operating mode of the RLC entity. The second mode can be UM or TM, but the following explanation will mainly focus on an example where the second mode is UM.

[0055] For example, the gNB200 broadcasts a configuration message. Both the UE100a, which is in the RRC connected state, and the UE100b, which is in the RRC idle state, receive the configuration message. By broadcasting the configuration message, the UE100b, which is in the RRC idle state, can also receive the configuration message.

[0056] For example, a configuration message may be MBS system information transmitted via the Broadcast Control Channel (BCCH). A configuration message may also be MBS control information transmitted via the MBS control channel.

[0057] Alternatively, the configuration message may be a UE-specific signaling message. For example, the configuration message may be an RRC Reconfiguration message, which is a type of RRC message. Such UE-specific signaling and broadcast signaling may be used in combination.

[0058] In this case, the settings broadcast in the MBS system information or MBS control channel may differ from the settings in the individual signaling. However, a UE100 that receives the individual signaling (specifically, a UE100a in the RRC connected state) will prioritize the individual signaling over the broadcast signaling. This makes it possible to set certain UE100s to allow feedback (AM) and other UE100s to not allow feedback (UM).

[0059] Configuration messages may include identifiers associated with RLC configuration information. These identifiers are used to identify MBS traffic channels and are, for example, MBS service identifiers and / or group RNTIs (Radio Network Temporary Identifiers). This allows specifying the operating mode of the RLC entity for each MBS traffic channel. The following primarily describes an example where an MBS service identifier (e.g., TMGI) is used as such an identifier.

[0060] A configuration message may contain multiple sets of RLC configuration information and MBS service identifiers. For example, in a configuration message, MBS service identifier #1 may be associated with RLC configuration information specifying AM, and MBS service identifier #2 may be associated with RLC configuration information specifying UM.

[0061] In the first embodiment, if UE100 is in the RRC connected state, UE100 may set the operating mode of the RLC entity according to the RLC configuration information included in the configuration message. If UE100 is in the RRC idle state or RRC inactive state, it may set the second mode (UM) regardless of the RLC configuration information included in the configuration message. UE100 in the RRC idle state or RRC inactive state cannot send ACK / NACK feedback (STATUS PDU) to gNB200, and is therefore configured to operate in the second mode (UM).

[0062] However, in the gNB200, RLC entities associated with MBS traffic channels operate in AM mode. Therefore, a UE100b with UM RLC entities needs to be able to process AM packets (AMD PDUs) from the gNB200. Thus, the gNB200 may limit the sequence number length used in AM to a setting that matches the sequence number length existing in UM. For example, the sequence number length used in AM could be set to 12 bits, which is the maximum sequence number length existing in UM. Alternatively, the sequence number length of UM packets (UMD PDUs) could be extended to 18 bits.

[0063] After the operating mode of each UE100's RLC entity is set by a configuration message, the gNB200 sends MBS data via the MBS traffic channel. Each UE100 receives this MBS data.

[0064] Figure 8 shows a specific example of the operation according to the first embodiment.

[0065] As shown in Figure 8, in step S101, the gNB200 sends a configuration message. Here, it is assumed that the configuration message is sent on the broadcast control channel or the MBS control channel. The UE100 receives the configuration message.

[0066] If UE100 receives a configuration message and is in an RRC connected state (step S102: YES), and AM is specified in the configuration message (step S103: YES), then in step S104, it configures an AM RLC entity (AM RLC entity) for the MBS traffic channel.

[0067] On the other hand, if UE100 receives a configuration message and is not in an RRC connected state (step S102: NO), or if UM is specified in the configuration message (step S103: NO), then in step S106, it configures the UM's RLC entity (UM RLC entity) for the MBS traffic channel.

[0068] In step S106, gNB200 transmits MBS data via the MBS traffic channel. UE100 receives the MBS data. Here, the RLC entity of UE100 processes the packet (AMD PDU) corresponding to the MBS data.

[0069] While we have described an example where the second mode, which does not perform automatic retransmission control, is UM, the second mode may also be a newly defined RLC operating mode. Such an RLC operating mode is one in which AMD PDUs can be received but feedback-related operations (e.g., polling for ARQ or Status Reporting) are not performed. If AM is specified by broadcast signaling, RLC entities of UE100 that are in an RRC idle or RRC inactive state may operate in such a new RLC operating mode.

[0070] (2) RLC operation for MBS Next, the RLC operation for MBS according to the first embodiment will be described. The receiving RLC entity performs reception processing using a sliding window that moves in response to the reception of RLC packets. This sliding window is controlled by various variables of the RLC entity.

[0071] Each variable used for this sliding window control is initialized when an RLC entity is established or re-established. The sequence number corresponding to the initial value is basically "0", and the initial position of the sliding window is determined based on this. In the case of unicast communication, the UE100 can receive the first RLC packet with sequence number "0" from the gNB200, so this handling of variables is not a problem.

[0072] However, in the case of MBS, UE100 can join an MBS session midway through, and it is uncertain which sequence number UE100 will receive first. Therefore, the first packet received may be outside the sliding window. In this case, RLC reception processing cannot be performed until subsequent packets enter the sliding window. Thus, a burst error may occur at the beginning of MBS reception.

[0073] Therefore, the RLC entity of UE100 changes the variables described above to match the sequence number of the first RLC packet received. Figure 9 shows the RLC operation according to the first embodiment.

[0074] As shown in Figure 9, in step S201, the RLC entity of UE100 receives MBS data (RLC packets) from gNB200.

[0075] In step S202, the RLC entity of UE100 sets the sequence number of the first MBS data (RLC packet) received from gNB200 as the initial value of a variable used for a predetermined RLC operation (e.g., sliding window control).

[0076] This ensures that the first packet received enters the sliding window, allowing the RLC receive process to function correctly. Therefore, the possibility of a burst error occurring at the beginning of MBS reception can be reduced.

[0077] Figure 10 shows the RLC operation of the AM according to the first embodiment. As shown in Figure 10, the AM RLC entity of UE100 manages a receiving window, which is a type of sliding window. The AM RLC entity of UE100 temporarily stores packets received within the receiving window in a reception buffer, reassembles them, and then passes them to the upper layer. The AM RLC entity of UE100 discards packets with sequence numbers (SN) outside the receiving window. The size of the receiving window is determined by the sequence number length (SN length). The variable that defines the starting point of such a receiving window is called "RX_Next". The AM RLC entity of UE100 sets the sequence number of the first MBS data (RLC packet) received from gNB200 as the initial value of the variable "RX_Next".

[0078] Figure 11 shows the RLC operation of the UM according to the first embodiment. As shown in Figure 11, the UM RLC entity of UE100 manages a reassembly window, which is a type of sliding window, and a window used for discarding packets (here called the discard window). The UM RLC entity of UE100 reassembles packets with sequence numbers that are within the reassembly window but outside the discard window in the reception buffer and passes them to the upper layer. Packets with other sequence numbers are discarded. The variable that defines the endpoint of such a reassembly window is called "RX_Next_Highest". The UM RLC entity of UE100 sets the sequence number of the first MBS data (RLC packet) received from gNB200 as the initial value of the variable "RX_Next_Highest".

[0079] (Second Embodiment) Next, the second embodiment will be described, primarily focusing on the differences from the first embodiment. The second embodiment is an embodiment relating to PDCP operation for MBS.

[0080] (1) PDCP operation for MBS PDCP entities are not used in LTE multicast / broadcast services. However, handover is expected to be supported in NR MBS, and it is desirable that PDCP entities can compensate for packet loss during handover. Furthermore, PDCP entities are necessary when applying PDCP duplication, where a PDCP entity sends the same PDCP packet twice on two paths, to an MBS.

[0081] In the case of multicast, for example, if UE100 joins the communication midway through an MBS session and then performs the next PDCP receive operation, there is a risk that it may not be able to process the packets correctly.

[0082] • Header decompression process PDCP header compression works by first saving the upper-layer header (such as the IP header) of the packet received by the receiving PDCP entity, then the transmitting PDCP entity removes the header from the second packet and sends it, and finally combines the header saved by the receiving PDCP entity and passes it to the upper-layer entity to achieve header compression (such as IP header compression). Therefore, UE100, which joined the MBS session midway, did not receive the first packet and cannot decompress the header (i.e., reconstruct the packet).

[0083] • Deciphering process If a PDCP packet is encrypted, it cannot be decrypted without information such as a key or sequence number derived from the UE identifier. For example, UE100, which joined the MBS session midway through, does not have the information necessary for decryption and therefore cannot decrypt the packet.

[0084] On the other hand, when multiple bearers (i.e., multiple data paths) are terminated by a single PDCP entity, as in PDCP duplication, the following PDCP receive operation may be required.

[0085] • Duplicate packet discarding When duplicate PDCP packets (i.e., multiple PDCP packets with the same sequence number) are received via multiple bearers, packet discarding is necessary to avoid duplication. Specifically, the receiving PDCP entity will keep one of the multiple PDCP packets with the same sequence number, pass it to the upper layer, and discard the others.

[0086] • Packet reordering process If a receiving PDCP entity does not receive PDCP packets in sequence number order, it must sort the PDCP packets in sequence number order before passing them to the upper layer. However, in the case of a UM bearer, packet sorting is not required.

[0087] Therefore, in the second embodiment, a receiving PDCP entity that receives PDCP packets via a plurality of bearers, including a bearer of the MBS service, performs PDCP reception operations for MBS reception. Specifically, in the PDCP reception operations for MBS reception, the receiving PDCP entity performs at least one of duplicate packet discarding and packet sorting, without performing at least one of decryption processing and header decompression processing. The receiving PDCP entity may also remove the PDCP header.

[0088] Figures 12 and 13 are diagrams illustrating the PDCP operating modes according to the second embodiment. In the second embodiment, the PDCP entity operates in one of three operating modes.

[0089] As shown in Figure 12, Mode A is the mode applied to bearers of user data other than MBS data (e.g., unicast data). In Mode A, the transmitting PDCP entity performs sequence numbering, header compression, encryption, PDCP header addition, and routing / duplication processing on packets from the upper layer. The receiving PDCP entity performs PDCP header removal, decryption, packet reordering, duplicate packet discarding, and header decompression processing on packets from the transmitting PDCP entity.

[0090] Mode B is the mode applied to bearers of control data such as RRC messages. In Mode B, the transmitting PDCP entity performs sequence numbering, header compression, PDCP header addition, and routing / duplication processing on packets from higher layers. The receiving PDCP entity performs PDCP header removal and header decompression processing on packets from the transmitting PDCP entity.

[0091] As shown in Figure 13, Mode C is the mode applied to the MBS data bearer (MBS bearer). In Mode C, the transmitting PDCP entity performs sequence number assignment, PDCP header assignment, and routing / duplication processing on packets from the upper layer. The receiving PDCP entity performs PDCP header removal, packet reordering, and duplicate packet discarding processing on packets from the transmitting PDCP entity.

[0092] For MBS, the gNB200 configures the UE100 so that its PDCP entities operate in mode C. For example, the gNB200 sends an RRC message (e.g., an RRC Reconfiguration message) to the UE100 to configure the bearer.

[0093] Here, the gNB200 includes an information element in its configuration to indicate that the bearer is an MBS bearer (MBS bearer). For example, an information element such as "multicast-bearer ENUM(true) optional" is added to each bearer setting in the RRC message.

[0094] When UE100 receives such an RRC message from gNB200, it generates a PDCP entity for MBS operating in mode C. The PDCP entity for MBS performs MBS reception processing on the MBS data belonging to the MBS bearer.

[0095] Figure 14 shows an example of PDCP operation according to the second embodiment.

[0096] As shown in Figure 14, in step S301, the PDCP entity of UE100 receives MBS data (PDCP packets) from gNB200. Here, it is assumed that the PDCP entity of gNB200 does not perform header compression or encryption on PDCP packets belonging to the MBS service (MBS session).

[0097] In step S302, the PDCP entity of UE100 removes the PDCP header from the received PDCP packet, and then uses the receive buffer to discard duplicate packets and / or sort packets. However, the PDCP entity of UE100 does not perform header decompression or decryption on the received PDCP packet.

[0098] (2) PDCP operation during handover while MBS reception Next, the PDCP operation during handover while receiving MBS according to the second embodiment will be described. The UE100 can perform a handover while receiving MBS. A handover refers to the cell switching operation of the UE100 while it is in the RRC connected state. In the following, we will mainly assume that each cell before and after the handover (i.e., the source cell and the target cell) provides the same MBS service (the same MBS session).

[0099] If UE100 performs a handover while receiving MBS data, packet loss of MBS data may occur due to connection operations to the target cell, etc. The PDCP layer has a function to retransmit PDCP packets based on feedback (status report) from UE100 to gNB200. In the second embodiment, packet loss during handover while receiving MBS data can be compensated for in the target cell by the retransmission function of the PDCP layer.

[0100] Figure 15 shows a handover operation according to the second embodiment. Figure 15 shows an example in which a single gNB200 manages both source cell C1 and target cell C2.

[0101] As shown in Figure 15, UE100, in the RRC connected state, receives MBS data from source cell C1 and performs a handover from source cell C1 to target cell C2. Here, if the PDCP entity of UE100 fails to receive MBS data during the handover, after the handover it sends a sequence number (specifically, a PDCP sequence number) indicating the MBS data (PDCP packet) that failed to be received to target cell C2.

[0102] If a handover command is set from source cell C1 (i.e., the RRC layer requests PDCP re-establishment), the UE100 PDCP entity sends the sequence number of the missing packet to target cell C2 after the PDCP re-establishment process is complete. The UE100 may further send the MBS service identifier associated with the sequence number of the missing packet to target cell C2. The UE100 PDCP entity may send a status report message to target cell C2 that includes the sequence number indicating the MBS data that failed to be received (i.e., the missing PDCP packet) in the PDCP layer's Status Report message.

[0103] When the gNB200 receives the sequence number of a missing packet from the UE100 via target cell C2, it retransmits the missing packet to the UE100 via target cell C2 based on that sequence number. This allows packet loss during handover while MBS reception to be compensated for in target cell C2 by the PDCP layer's retransmission function, thereby improving the reliability of MBS reception.

[0104] Figure 16 shows another example of the handover operation according to the second embodiment. In Figure 15, an example is shown in which source cell C1 and target cell C2 are managed by separate gNB200s (gNB200A and gNB200B).

[0105] In the operating environment shown in Figure 16, it is assumed that source cell C1 and target cell C2 provide MBS services asynchronously. In other words, target cell C2 does not provide the MBS service (MBS session) provided by target cell C1.

[0106] In this case, gNB200B, which manages target cell C2, does not retain the missing packet even if it receives the sequence number of the missing packet from UE100. Therefore, gNB200B notifies gNB200A, which manages source cell C1, of the missing sequence number (and MBS service identifier). Based on the notification from gNB200B, gNB200A forwards the missing packet (PDCP packet) to gNB200B (data forwarding). gNB200B then sends the PDCP packet from gNB200A to UE100.

[0107] (Other embodiments) Each of the embodiments described above can be implemented not only separately and independently, but also in combination of two or more embodiments.

[0108] 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.

[0109] 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).

[0110] 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.

[0111] This application claims priority to Japanese Patent Application No. 2020-132044 (filed on August 3, 2020), and all of its contents are incorporated into the specification of this application.

Claims

1. A communication control method used in a mobile communication system that provides multicast broadcast services (MBS) from a network node to user equipment, The user device receives MBS data and unicast data from the network node, The PDCP (Packet Data Convergence Protocol) entity of the user device performs MBS reception processing for the MBS data and unicast reception processing for the unicast data. , has, The aforementioned PDCP entity is In the aforementioned unicast reception process, decryption processing is performed, In the aforementioned MBS reception process, at least one of the following is performed: duplicate packet discarding and packet reordering, without performing decryption. Communication control method.

2. User device, A receiving unit that receives multicast broadcast service (MBS) data and unicast data from network nodes, The system includes a control unit that includes a PDCP (Packet Data Convergence Protocol) entity that performs MBS reception processing for the MBS data and unicast reception processing for the unicast data, The aforementioned PDCP entity is In the aforementioned unicast reception process, decryption processing is performed, In the aforementioned MBS reception process, at least one of the following is performed: duplicate packet discarding and packet reordering, without performing decryption. User device.

3. Used in a user device, and performing the communication method described in claim 1. Processor.

4. Cause the user device to execute the communication method described in claim 1. program.

5. The user device according to claim 2 and a network node are provided. Mobile communication system.

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