Communication control method, base station, user equipment and processor

Abstract

A communication control method is used in a mobile communication system providing a multicast broadcast service (MBS) from a base station to a user equipment, and includes transmitting, by the base station to the user equipment, a message for performing a configuration related to a radio link control (RLC) entity of the user equipment. The message includes an information element that specifies an operation mode of the RLC entity for an MBS traffic channel that transmits MBS data.

Description

[0001] This application is a divisional application of Chinese invention patent application No. 202180067981.X, entitled "Communication Control Method, Base Station, User Equipment and Processor", filed on August 2, 2021. Technical Field

[0002] This disclosure relates to a communication control method used in a mobile communication system. Background Technology

[0003] In recent years, fifth-generation (5G) mobile communication systems have attracted attention. Compared with Long Term Evolution (LTE), which is the fourth-generation radio access technology (RAT), New Radio (NR), the radio access technology for 5G systems, has features such as high speed, large capacity, high reliability, and low latency.

[0004] Reference List

[0005] Non-patent literature

[0006] Non-patent document 1: 3GPP technical specification "3GPP TS 38.300 V16.2.0 (2020-07)" Summary of the Invention

[0007] A first aspect provides a communication control method for use in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user equipment, the communication control method comprising: sending a message from the base station to the user equipment for performing configuration related to a radio link control (RLC) entity of the user equipment, wherein the message includes an information element specifying an operating mode of the RLC entity for transmitting MBS service channels for MBS data.

[0008] The second aspect provides a communication control method for use in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user equipment, the communication control method comprising: receiving MBS data from the base station by the user equipment; and configuring the initial value of a variable used for predetermined RLC operation by a radio link control (RLC) entity of the user equipment to the sequence number of the MBS data first received from the base station.

[0009] A third aspect provides a communication control method for use in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user equipment, the communication control method comprising: receiving MBS data from a base station by the user equipment; and performing MBS reception processing on the MBS data by a Packet Data Convergence Protocol (PDCP) entity of the user equipment, wherein performing MBS reception processing includes the PDCP entity performing duplicate packet discarding and / or packet reordering without performing decryption and / or header decompression.

[0010] A fourth aspect provides a communication control method for use in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user equipment, the communication control method comprising: receiving MBS data from a first cell by the user equipment; performing a handover from the first cell to a second cell by the user equipment; and when a Packet Data Convergence Protocol (PDCP) entity of the user equipment fails to receive MBS data during the handover, the PDCP entity sends a sequence number to the second cell indicating the unreceived MBS data. Attached Figure Description

[0011] Figure 1 This is a diagram illustrating the structure of a mobile communication system according to an embodiment.

[0012] Figure 2 This is a diagram illustrating the structure of a user equipment (UE) according to an embodiment.

[0013] Figure 3 This is a diagram illustrating the structure of a base station (gNB) according to an embodiment.

[0014] Figure 4 This is a diagram illustrating the structure of the protocol stack of the radio interface for the user plane that processes data.

[0015] Figure 5 This is a diagram showing the structure of the protocol stack of the radio interface of the control plane that processes signaling (control signals).

[0016] Figure 6 This is a diagram illustrating the correspondence between downlink logical channels and downlink transport channels according to an embodiment.

[0017] Figure 7 This is a diagram illustrating an example of operation according to the first embodiment.

[0018] Figure 8 This is a diagram illustrating a specific example of operation according to the first embodiment.

[0019] Figure 9 This is a diagram illustrating RLC operation according to the first embodiment.

[0020] Figure 10 This is a diagram illustrating RLC operation under AM according to the first embodiment.

[0021] Figure 11 This is a diagram illustrating RLC operation under UM according to the first embodiment.

[0022] Figure 12 This is a diagram used to illustrate the PDCP operation mode according to the second embodiment.

[0023] Figure 13 This is a diagram used to illustrate the PDCP operation mode according to the second embodiment.

[0024] Figure 14 This is a diagram illustrating an example of PDCP operation according to the second embodiment.

[0025] Figure 15 This is a diagram illustrating the switching operation according to the second embodiment.

[0026] Figure 16 This is a diagram illustrating another example of the switching operation according to the second embodiment. Detailed Implementation

[0027] The introduction of multicast service into 5G systems (NR) is under investigation. Compared to LTE multicast service, NR multicast service is expected to provide enhanced services.

[0028] This disclosure provides enhanced multicast broadcast services.

[0029] A mobile communication system according to an embodiment will be described with reference to the accompanying drawings. In the description of the drawings, the same or similar parts are indicated by the same or similar reference numerals.

[0030] Structure of mobile communication systems

[0031] First, the structure of the mobile communication system according to an embodiment will be described. Figure 1 This is a diagram illustrating the structure of a mobile communication system according to an embodiment. The mobile communication system conforms to the 5th generation (5GS) system of the 3GPP standard. The following description uses 5GS as an example, but the Long Term Evolution (LTE) system can be applied at least partially to the mobile communication system.

[0032] like Figure 1 As shown, the mobile communication system includes user equipment (UE) 100, 5G radio access network (Next Generation Radio Access Network (NG-RAN)) 10 and 5G core network (5GC) 20.

[0033] UE 100 is a mobile wireless communication device. UE 100 can be any device as long as it is used by a user. Examples of UE 100 include mobile phone terminals (including smartphones), tablet terminals, laptop PCs, communication modules (including communication cards or chipsets), sensors or devices mounted on sensors, vehicles or devices mounted on vehicles (vehicle UEs) and / or flying objects or devices mounted on flying objects (aviation UEs).

[0034] NG-RAN 10 includes base stations (referred to as "gNBs" in 5G systems) 200. gNBs 200 are interconnected via the Xn interface, which serves as an inter-base station interface. Each gNB 200 manages one or more cells. gNBs 200 perform wireless communication with UE 100, which has established a connection to a cell of the gNB 200. gNBs 200 have radio resource management (RRM) functions, functions for routing user data (hereinafter referred to as "data"), measurement and control functions for mobility control and scheduling, etc. "Cell" is used as a term to represent the smallest unit of wireless communication area. "Cell" is also used as a term to represent the functions or resources used to perform wireless communication with UE 100. A cell belongs to one carrier frequency.

[0035] Note that a gNB can connect to the Evolved Packet Core (EPC) corresponding to the LTE core network. LTE base stations can also connect to the 5GC. LTE base stations and gNBs can connect via an inter-base station interface.

[0036] The 5GC 20 includes Access and Mobility Management Functions (AMF) and User Plane Functions (UPF) 300. The AMF performs various types of mobility control for the UE 100. The AMF manages the mobility of the UE 100 by communicating with it using Non-Access Stratum (NAS) signaling. The UPF controls data transmission. The AMF and UPF are connected to the gNB 200 via the NG interface, which serves as the interface between the base station and the core network.

[0037] Figure 2 This is a diagram illustrating the structure of a UE 100 (user equipment) according to an embodiment.

[0038] like Figure 2 As shown, UE 100 includes receiver 110, transmitter 120 and controller 130.

[0039] Receiver 110 performs various types of reception under the control of controller 130. Receiver 110 includes an antenna and receiving equipment. The receiving equipment converts the radio signals received through the antenna into baseband signals (received signals) and outputs the obtained signals to controller 130.

[0040] Transmitter 120 performs various types of transmissions under the control of controller 130. Transmitter 120 includes an antenna and a transmitting device. The transmitting device converts the baseband signal (transmit signal) output by controller 130 into a radio signal and transmits the obtained signal through the antenna.

[0041] Controller 130 performs various types of control within UE 100. Controller 130 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be used for the processing performed by the processor. The processor may include a baseband processor and a central processing unit (CPU). The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0042] Figure 3 This is a diagram showing the structure of a gNB 200 (base station) according to an embodiment.

[0043] like Figure 3 As shown, the gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communicator 240.

[0044] Transmitter 210 performs various types of transmissions under the control of controller 230. Transmitter 210 includes an antenna and a transmitting device. The transmitting device converts the baseband signal (transmit signal) output by controller 230 into a radio signal and transmits the obtained signal through the antenna.

[0045] Receiver 220 performs various types of reception under the control of controller 230. Receiver 220 includes an antenna and receiving equipment. The receiving equipment converts the radio signals received through the antenna into baseband signals (received signals) and outputs the obtained signals to controller 230.

[0046] The controller 230 performs various types of control over the gNB 200. The controller 230 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be used for the processing performed by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0047] The backhaul communicator 240 is connected to the adjacent base station via the inter-base station interface. The backhaul communicator 240 is also connected to the AMF / UPF 300 via the interface between the base station and the core network. Note that the gNB may include a central unit (CU) and a distributed unit (DU) (i.e., functions are divided), and the two units may be connected via the F1 interface.

[0048] Figure 4 This is a diagram illustrating the structure of the protocol stack of the radio interface for the user plane that processes data.

[0049] like Figure 4As shown, the user plane radio interface protocol includes the physical (PHY) layer, media access control (MAC) layer, radio link control (RLC) layer, packet data convergence protocol (PDCP) layer, and service data adaptation protocol (SDAP) layer.

[0050] The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. It transmits data and control information between the PHY layer of UE 100 and the PHY layer of gNB 200 via physical channels.

[0051] 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 UE 100 and the MAC layer of gNB 200 via the transport channel. The MAC layer of gNB 200 includes a scheduler. The scheduler determines the transmission format (transmission block size, modulation and coding scheme (MCS)) in the uplink and downlink, as well as the resource blocks to be allocated to UE 100.

[0052] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of UE 100 and the RLC layer of gNB 200 via logical channels.

[0053] The PDCP layer performs header compression and decompression, as well as encryption and decryption.

[0054] The SDAP layer performs the mapping between IP flows, which are the unit of QoS control performed by the core network, and radio bearers, which are the unit of QoS control performed by the access layer (AS). Note that SDAP may not be provided when the RAN is connected to the EPC.

[0055] Figure 5 This is a diagram showing the structure of the protocol stack of the radio interface of the control plane that processes signaling (control signals).

[0056] like Figure 5 As shown, the protocol stack of the control plane's radio interface includes a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer, instead of... Figure 4 The SDAP layer is shown.

[0057] RRC signaling for various configurations is transmitted between the RRC layer of UE 100 and the RRC layer of gNB 200. The RRC layer controls logical channels, transport channels, and physical channels based on the establishment, re-establishment, and release of radio bearers. UE 100 is in an RRC connected state when a connection (RRC connection) exists between the RRC layers of UE 100 and gNB 200. UE 100 is in an RRC idle state when a connection (RRC connection) does not exist. UE 100 is in an RRC inactive state when the connection between the RRC layers of UE 100 and gNB 200 is suspended.

[0058] The NAS layer, which is above the RRC layer, performs session management, mobility management, etc. NAS signaling is sent between the NAS layer of UE 100 and the NAS layer of AMF 300.

[0059] Note that in addition to the radio interface protocol, UE 100 also includes the application layer.

[0060] MBS

[0061] MBS will be described according to an embodiment. MBS is a service that provides broadcast or multicast (i.e., point-to-multipoint (PTM)) data transmission from NG-RAN 10 to UE 100. MBS may be referred to as Multimedia Broadcast and Multicast Service (MBMS). Note that use cases (service types) for MBS include public communications, mission-critical communications, V2X (vehicle-to-anything) communications, IPv4 or IPv6 multicast delivery, IPTV, group communications, and software delivery.

[0062] MBS transmission in LTE includes two schemes: Multicast-Broadcast Single Frequency Network (MBSFN) transmission and Single Cell Point-to-Multipoint (SC-PTM) transmission. Figure 6 This is a diagram illustrating the correspondence between downlink logical channels and downlink transport channels according to an embodiment.

[0063] like Figure 6 As shown, the logical channels used for MBSFN transmission are the Multicast Service Channel (MTCH) and the Multicast Control Channel (MCCH), and the transport channel used for MBSFN transmission is the Multicast Control Channel (MCH). MBSFN transmission is mainly designed for multi-cell transmission, and in an MBSFN area that includes multiple cells, each cell synchronously transmits the same signal (the same data) in the same MBSFN subframe.

[0064] The logical channels used for SC-PTM transmission are the Single Cell Multicast Service Channel (SC-MTCH) and the Single Cell Multicast Control Channel (SC-MCCH), and the transport channel used for SC-PTM transmission is the Downlink Shared Channel (DL-SCH). SC-PTM transmission is primarily designed for single-cell transmission and corresponds to cell-by-cell broadcast or multicast data transmission. The physical channels used for SC-PTM transmission are the Physical Downlink Control Channel (PDCCH) and the Physical Downlink Control Channel (PDSCH), and dynamic resource allocation is possible.

[0065] Although the following will primarily describe examples of providing MBS using the SC-PTM transport scheme, MBS can also be provided using the MBSFN transport scheme. The examples of providing MBS using multicast will be described primarily. Therefore, MBS can be interpreted as multicast. Note that broadcast can also be used to provide MBS.

[0066] In the following text, MBS data refers to data transmitted via MBS. The MBS control channel refers to MCCH or SC-MCCH, and the MBS traffic channel refers to MTCH or SC-MTCH.

[0067] The network can provide different MBS services for each MBS session. MBS services are identified by a Temporary Mobile Group Identifier (TMGI) and / or a session identifier, and at least one of these identifiers is called an MBS service identifier. This MBS service identifier can be referred to as an MBS session identifier or a multicast group identifier.

[0068] First Embodiment

[0069] Next, given the aforementioned mobile communication system and MBS, a first embodiment will be described. This first embodiment relates to RLC operation for the MBS.

[0070] (1) RLC configuration operation for MBS

[0071] The RLC layer has three operating modes: AM (Acknowledged Mode), UM (Unacknowledged Mode), and TM (Transparent Mode). Of these modes, only AM supports retransmission functionality based on Automatic Repeat reQuest (ARQ). AM is a mode in which retransmission control is performed by the receiving RLC entity providing ACK feedback to the sending RLC entity.

[0072] In LTE multicast services, the operating mode of the RLC entity is configured as UM. However, it is worth considering implementing a mechanism to enable AM ​​to be applied to NR multicast services, thereby improving the reliability and flexibility of multicast communication.

[0073] Figure 7This is a diagram illustrating an example of operation according to the first embodiment.

[0074] like Figure 7 As shown, UE 100a, which is in RRC connected state, and UE 100b, which is in RRC idle state, exist in cell C managed by gNB 200. Assume that UE 100a and UE 100b are interested in receiving MBS data belonging to the same MBS service (same MBS session).

[0075] The gNB 200 sends a message (hereinafter referred to as the "configuration message") to perform configuration related to the RLC entity of the UE 100. The configuration message contains information elements (hereinafter referred to as "RLC configuration information") that specify the operating mode of the RLC entity for the MBS traffic channel used to transmit MBS data.

[0076] The RLC configuration information specifies one of two operating modes for the RLC entity: a first mode (i.e., AM) that performs automatic repeater control and a second mode that does not perform automatic repeater control. The second mode is either UM or TM, and the following description focuses on an example where the second mode is UM.

[0077] For example, gNB 200 broadcasts a configuration message. Each of UE 100a in RRC connected state and UE 100b in RRC idle state receives the configuration message. Broadcasting the configuration message also enables UE 100b in RRC idle state to receive the configuration message.

[0078] For example, configuration messages can be MBS system information sent via the Broadcast Control Channel (BCCH). Configuration messages can also be MBS control information sent via the MBS Control Channel.

[0079] Configuration messages can be UE-specific signaling. For example, a configuration message can be an RRC reconfiguration message, which is a type of RRC message. This UE-specific signaling and broadcast signaling can be used in combination.

[0080] In this scenario, the configuration content broadcast in the MBS system information or MBS control channel may differ from the configuration content in the dedicated signaling. However, the UE 100 receiving the dedicated signaling (specifically, UE 100a in RRC connected state) preferentially applies the dedicated signaling instead of the broadcast signaling. This enables a configuration that allows a specific UE 100 to provide feedback (AM) while disallowing other UEs 100 to provide feedback (UM).

[0081] Configuration messages may include identifiers associated with RLC configuration information. These identifiers are used to identify MBS service channels and are, for example, MBS service identifiers and / or Group Radio Network Temporary Identifiers (RNTIs). This allows specifying the operating mode of the RLC entity for each MBS service channel. The following will primarily describe examples of MBS service identifiers (e.g., TMGI) used as the aforementioned identifiers.

[0082] Configuration messages can include multiple sets of RLC configuration information and MBS service identifiers. For example, in a configuration message, MBS service identifier #1 can be associated with the RLC configuration information of a specified AM, and MBS service identifier #2 can be associated with the RLC configuration information of a specified UM.

[0083] In the first embodiment, when UE 100 is in RRC connected state, UE 100 can configure the operating mode of the RLC entity according to the RLC configuration information included in the configuration message. When in RRC idle state or RRC inactive state, UE 100 can configure the operating mode to the second mode (UM), regardless of the RLC configuration information included in the configuration message. UE 100 in RRC idle state or RRC inactive state cannot send ACK / NACK feedback (STATUSPDU) to gNB 200, therefore the operation is in the second mode (UM).

[0084] However, in the gNB 200, the RLC entity associated with the MBS traffic channel operates in AM mode. Therefore, a UE 100b with an RLC entity of UM needs to be able to process AM packets (AMD PDUs) from the gNB 200. Thus, the gNB 200 can restrict the sequence number length used in AM to a configuration suitable for the sequence number length present in UM. For example, the sequence number length used in AM can be set to 12 bits, corresponding to the maximum sequence number length present in UM. Alternatively, the sequence number length of UM packets (UMDPDUs) can be extended to 18 bits.

[0085] After configuring the operating mode of the RLC entity for each UE 100 according to the configuration message, the gNB 200 transmits MBS data via the MBS service channel. Each UE 100 receives the MBS data.

[0086] Figure 8 This is a diagram illustrating a specific example of operation according to the first embodiment.

[0087] like Figure 8 As shown, in step S101, gNB 200 sends a configuration message. Here, it is assumed that the configuration message is sent on the broadcast control channel or the MBS control channel. UE 100 receives the configuration message.

[0088] When UE 100, which has received the configuration message, is in the RRC connection state (step S102: Yes) and specifies AM in the configuration message (step S103: Yes), in step S104, UE 100 configures the RLC entity to be in AM for the MBS service channel (AM RLC entity).

[0089] On the other hand, when the UE 100 that has received the configuration message is not in the RRC connection state (step S102: No), or specifies UM in the configuration message (step S103: No), in step S106, the UE 100 configures the RLC entity to be in UM (UM RLC entity) for the MBS service channel.

[0090] In step S106, gNB 200 transmits MBS data via the MBS service channel. UE 100 receives the MBS data. Here, the RLC entity of UE 100 processes the packets (AMD PDUs) corresponding to the MBS data.

[0091] Note that in the example above, the second mode that does not perform automatic repeater control is UM, but the second mode can be a newly defined RLC operating mode. In this RLC operating mode, AMD PDUs can be received, but feedback-related operations (e.g., polling and status reporting for ARQ) are not performed. When AM is specified by broadcast signaling, the RLC entity of UE 100 in RRC idle or RRC inactive state can operate in this new RLC operating mode.

[0092] (2) RLC operation for MBS

[0093] The RLC operation for MBS according to the first embodiment will be described. The receive RLC entity performs receive processing by using a sliding window that moves in response to the reception of RLC packets. This sliding window is controlled by variables of the RLC entity.

[0094] The variables used for this sliding window control are initialized when the RLC entity is established or re-established. The sequence number corresponding to the initial value is essentially "0", which serves as a reference for determining the initial position of the sliding window. In unicast communication, UE100 can first receive the RLC packet with sequence number "0" from gNB 200, and therefore can handle the variables as described above without any problems.

[0095] However, for MBS, UE 100 can join an MBS session in the middle of the session, and the sequence number received first by UE 100 is variable. Therefore, the first packet received may be a packet not within the sliding window. In this case, RLC reception processing cannot be performed until subsequent packets within the sliding window are received. Therefore, burst errors may occur at the start of MBS reception.

[0096] Therefore, the RLC entity of UE 100 changes the variables as described above based on the sequence number of the first received RLC packet. Figure 9 This is a diagram illustrating RLC operation according to the first embodiment.

[0097] like Figure 9 As shown, in step S201, the RLC entity of UE 100 receives MBS data (RLC packets) from gNB 200.

[0098] In step S202, the RLC entity of UE 100 configures the initial value of the variable used for the scheduled RLC operation (e.g., sliding window control) to the sequence number of the MBS data (RLC packet) first received from gNB 200.

[0099] This ensures that the sequence number of the first received packet is within the sliding window, allowing for successful RLC receive processing. Therefore, the likelihood of sudden errors occurring at the start of MBS receive can be reduced.

[0100] Figure 10 This is a diagram illustrating RLC operation under AM according to the first embodiment. (See diagram below.) Figure 10 As shown, the UE 100's AM RLC entity manages the receive window, which is a sliding window. The UE 100's AM RLC entity temporarily stores and reassembles packets received within the receive window in the receive buffer and passes the received packets to the upper layer. The UE 100's AMRLC entity discards packets with sequence numbers (SNs) that are not within the receive window. The size of the receive window is determined based on the sequence number length (SN length). The variable defining the start point of this receive window is called "RX_Next". The UE 100's AM RLC entity initializes the variable "RX_Next" with the sequence number of the first MBS data (RLC packet) received from gNB 200.

[0101] Figure 11 This is a diagram illustrating RLC operation under UM according to the first embodiment. (See diagram below.) Figure 11As shown, the UE 100's UMRLC entity manages a reassembly window as a sliding window and a window for discarding packets (here referred to as the discard window). The UE 100's UM RLC entity reassembles packets with sequence numbers that are within the reassembly window but not within the discard window in the receive buffer and passes the obtained packets to the upper layer. Packets with other sequence numbers are discarded. The variable defining the endpoint of the reassembly window is called "RX_Next_Highest". The UE 100's UM RLC entity initializes the variable "RX_Next_Highest" with the sequence number of the first MBS data (RLC packet) received from the gNB 200.

[0102] Second Embodiment

[0103] The second embodiment will now be described primarily regarding its differences from the first embodiment. The second embodiment relates to PDCP operation for MBS.

[0104] (1) PDCP operation for MBS

[0105] LTE multicast services do not use the PDCP entity. However, it is assumed that NR MBS supports handover and expects the PDCP entity to compensate for packet loss during handover. The PDCP entity is required when the MBS performs PDCP replication, in which the PDCP entity double-transmits the same PDCP packets through two paths.

[0106] Here, in multicast, for example, when a UE 100 that has already joined communication in the middle of an MBS session performs a subsequent PDCP receive operation, it may fail to process packets.

[0107] - Header decompression

[0108] PDCP header compression (IP header compression, etc.) is achieved through the following operations: the receiving PDCP entity saves the header (IP header, etc.) of the first received packet; the sending PDCP entity removes the header from the second packet and sends the resulting second packet; and the receiving PDCP entity combines the saved header with the second packet and passes the resulting second packet to the upper-layer entity. Therefore, UE 100, which has already joined an MBS session in the middle of the session, did not receive the first packet and therefore cannot decompress the header (i.e., reproduce the packet).

[0109] - Decrypt (Decrypt)

[0110] Once PDCP packets are encrypted, decryption cannot be performed if information such as keys or serial numbers derived from the UE identifier is unavailable. For example, a UE 100 that has already had an MBS session inserted in the middle of a session does not have the information required for decryption, and therefore decryption fails.

[0111] On the other hand, when multiple bearers (i.e. multiple data paths) are terminated by a single PDCP entity, as is the case with PDCP replication, the following PDCP receive operation may be required.

[0112] - Duplicate grouping and discarding (duplicate discarding)

[0113] When duplicate PDCP packets (i.e., multiple PDCP packets with the same sequence number) are received via multiple bearers, packet discarding is required to avoid duplication. Specifically, the receiving PDCP entity passes one of the multiple PDCP packets with the same sequence number to the upper layer and discards the remaining PDCP packets.

[0114] - Grouping and reordering

[0115] When the receiving PDCP entity receives PDCP packets out of sequence number order, it needs to reorder the PDCP packets according to their sequence numbers before passing them to the upper layer. However, for UM bearers, packet reordering is not required.

[0116] Therefore, in the second embodiment, a receive PDCP entity that receives PDCP packets via multiple bearers, including a bearer for MBS service, performs a PDCP receive operation for MBS reception. Specifically, in the PDCP receive operation for MBS reception, the receive PDCP entity performs duplicate packet discarding and / or packet reordering without performing decryption and / or header decompression. The receive PDCP entity may also remove the PDCP header.

[0117] Figure 12 and Figure 13 This is a diagram illustrating the PDCP operation modes according to the second embodiment. In the second embodiment, the PDCP entity operates in one of three operation modes.

[0118] like Figure 12 As shown, Mode A is applied to bearers of user data other than MBS data (e.g., unicast data). In Mode A, the sending PDCP entity performs sequence number allocation, header compression, encryption, PDCP header appending, and routing / copying on packets from the upper layer. The receiving PDCP entity performs PDCP header removal, decryption, packet reordering, duplicate packet discarding, and header decompression on packets from the sending PDCP entity.

[0119] Mode B is used for carrying control data such as RRC messages. In Mode B, the sending PDCP entity performs sequence number allocation, header compression, PDCP header appending, and routing / copying on packets from the upper layer. The receiving PDCP entity performs PDCP header removal and header decompression on packets from the sending PDCP entity.

[0120] like Figure 13 As shown, Mode C is applied to the bearer for MBS data (MBS bearer). In Mode C, the sending PDCP entity performs sequence number allocation, PDCP header addition, and routing / copying on packets from the upper layer. The receiving PDCP entity performs PDCP header removal, packet reordering, and deduplication on packets from the sending PDCP entity.

[0121] For MBS, gNB 200 performs configuration for UE 100 to allow UE 100's PDCP entity to operate in Mode C. For example, gNB 200 sends RRC messages (e.g., RRC reconfiguration messages) to UE 100 to configure the bearer.

[0122] Here, the gNB 200 includes informational elements in its configuration information that indicate that the bearer is for MBS (MBS bearer). For example, each bearer configuration in an RRC message includes additional informational elements such as "multicast-bearer ENUM(true)optional".

[0123] When this RRC message is received from gNB 200, UE 100 generates a PDCP entity for MBS operating in Mode C. The PDCP entity for MBS performs MBS receive processing on the MBS data belonging to the MBS bearer.

[0124] Figure 14 This is a diagram illustrating an example of PDCP operation according to the second embodiment.

[0125] like Figure 14 As shown, in step S301, the PDCP entity of UE 100 receives MBS data (PDCP packets) from gNB 200. Here, it is assumed that the PDCP entity of gNB 200 does not perform header compression and encryption on PDCP packets belonging to MBS service (MBS session).

[0126] In step S302, after performing PDCP header removal on the received PDCP packets, the PDCP entity of UE 100 performs duplicate packet discarding and / or packet reordering using the receive buffer. However, the PDCP entity of UE 100 does not perform header decompression and decryption on the received PDCP packets.

[0127] (2) PDCP operation during handover during MBS reception

[0128] The PDCP operation performed during handover according to the second embodiment will now be described. UE100 may perform handover during MBS reception. Handover refers to a cell handover operation of UE100 in RRC connected state. The following description primarily assumes that each cell (in other words, the source cell and the target cell) provides the same MBS service (the same MBS session) before and after handover.

[0129] When UE 100 performs a handover during MBS reception, MBS data packets may be lost due to operations such as connecting to the target cell. The PDCP layer includes a retransmission function for PDCP packets based on feedback (status reports) from UE 100 to gNB 200. The second embodiment allows the target cell to compensate for packet loss that occurs during handover during MBS reception by using the retransmission function of the PDCP layer.

[0130] Figure 15 This is a diagram illustrating the switching operation according to the second embodiment. Figure 15 An example of a gNB 200 managing source cell C1 and target cell C2 is shown.

[0131] like Figure 15 As shown, UE 100, in RRC connection state, performs a handover from source cell C1 to target cell C2 while receiving MBS data from source cell C1. Here, if UE 100 fails to receive MBS data during the handover, after the handover, UE 100's PDCP entity sends the sequence number (specifically, the PDCP sequence number) of the unreceived MBS data (PDCP packet) to target cell C2.

[0132] When the source cell C1 configures a handover command (when the RRC layer requests PDCP re-establishment), the PDCP entity of UE 100 sends the sequence number of the lost packets to the target cell C2 after completing the PDCP re-establishment process. UE 100 can also send the MBS service identifier associated with the sequence number of the lost packets to the target cell C2. The PDCP entity of UE 100 can include the sequence number indicating the unreceived MBS data (i.e., the lost PDCP packets) in the PDCP layer status report message and send the status report message to the target cell C2.

[0133] When gNB 200 receives the sequence number of a lost packet from UE 100 via target cell C2, it retransmits the lost packet to UE 100 via target cell C2 based on that sequence number. This allows the target cell to compensate for packet loss that occurs during handover during MBS reception by using the retransmission function of the PDCP layer. Therefore, the reliability of MBS reception can be improved.

[0134] Figure 16 This is a diagram illustrating another example of the switching operation according to the second embodiment. Figure 16 Examples of different gNB 200s (gNB 200A and gNB 200B) managing source cell C1 and target cell C2 are shown.

[0135] exist Figure 16 In the operating environment shown, 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.

[0136] In this scenario, even if gNB 200B, managing target cell C2, receives the sequence number of the lost packet from UE 100, gNB 200B does not retain the lost packet. Instead, gNB 200B notifies gNB 200A, managing source cell C1, of the lost sequence number (and MBS service identifier). Based on the notification from gNB 200B, gNB 200A forwards the lost packet (PDCP packet) (data forwarding) to gNB 200B. gNB 200B then sends the PDCP packet sent from gNB 200A to UE 100.

[0137] Other embodiments

[0138] The above embodiments can be implemented individually and independently, or they can be implemented as a combination of two or more embodiments.

[0139] A program may be provided that enables the computer to execute each procedure performed by the UE 100 or gNB 200. This program may be recorded on a computer-readable medium. The use of a computer-readable medium allows the program to be installed on the computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. There are no particular limitations on the non-transitory recording medium, and it may be, for example, a recording medium such as a CD-ROM or DVD-ROM.

[0140] Circuitry for performing the process to be performed by UE 100 or gNB 200 can be integrated, and at least a portion of UE 100 or gNB 200 can be configured as a semiconductor integrated circuit (chipset or SoC).

[0141] The embodiments have been described in detail above with reference to the accompanying drawings, but the specific configurations are not limited to those described above, and various design modifications can be made without departing from the spirit of this disclosure.

[0142] This patent application claims priority to Japanese Patent Application No. 2020-132044, filed on August 3, 2020, the entire contents of which are incorporated herein by reference.

Claims

1. A communication control method used in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user equipment, the communication control method comprising: The user equipment receives MBS data from the base station; as well as The user equipment configures the initial values ​​of variables used for pre-defined Radio Link Control (RLC) operations to the sequence number of the MBS data first received from the base station.

2. A user equipment, comprising: The receiving unit is configured to receive Multicast Broadcast Service (MBS) data from the base station; as well as The control unit is configured to set the initial value of a variable used for predetermined Radio Link Control (RLC) operation to the sequence number of MBS data first received from the base station.

3. A control unit configured to control user equipment, comprising: The processor performs the following processes: Receive Multicast Broadcast Service (MBS) data from the base station; as well as The initial values ​​of the variables used for the pre-defined Radio Link Control (RLC) operation are configured to the sequence number of the MBS data first received from the base station.

4. A mobile communication system that provides multicast broadcast service (MBS) from a base station to a user equipment, wherein, The user equipment receives MBS data from the base station; as well as The user equipment configures the initial value of the variable used for the scheduled radio link control (RLC) operation to the sequence number of the MBS data first received from the base station.

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