Method and user equipment for setting initial PDCP state variables for multicast

Abstract

The present invention provides a method and user equipment for setting initial PDCP state variables for multicast, wherein the method comprises: configuring MRB for one or more MBSs in a wireless network by a user equipment, wherein the MRB configuration enables feedback for one or more MBSs; initiating a joining process to join an MBS session, wherein the MBS session is in an active state; receiving one or more configuration values ​​of PDCP state variables from the wireless network, wherein the PDCP state variables control PDCP transceiving for the MBS session; and configuring the PDCP state variables based on the received one or more configuration values. By utilizing the present invention, the PDCP state variables of a multicast service can be initialized.

Description

Technical Field

[0001] The present invention relates to wireless communications, and more particularly to a method and apparatus for setting initial packet data convergence protocol (PDCP) state variables for multicast. Background Art

[0002] With the exponential growth of wireless data services, content delivery to large mobile user groups has developed rapidly. Various cellular systems, including 4G / long term evolution (LTE) systems and 5G / new radio (NR) systems, can provide multicast capabilities, allowing user equipment (UE) in the system to receive multicast services transmitted by the cellular system. Various applications may rely on multicast transmission communications, such as live streaming, video distribution, vehicle-to-everything (V2X) communications, public safety communications, file downloads, etc. When the UE establishes a multicast radio bearer (MRB), the hyper frame number (HFN) needs to be synchronized between the wireless network and the UE. The initial value of the PDCP receive window also needs to be set. In existing systems, since data transmission / reception starts after the UE is in the RRC connected state, the initial values ​​of the transmit and receive operation variables of the PDCP layer are determined and usually start from zero. In NR multicast, a UE can join a multicast and broadcast service (MBS) session after the MBS session is activated, which means that PDCP packet transmission on the air interface has been ongoing for some time. Therefore, the UE cannot initialize PDCP variables for the MBS session as usual.

[0003] Improvements and enhancements are needed to initialize PDCP state variables for multicast services. Summary of the invention

[0004] An embodiment of the present invention provides a method for setting initial PDCP state variables for multicast, comprising: configuring an MRB for one or more MBSs in a wireless network by a user equipment, wherein the MRB configuration enables feedback for one or more MBSs; initiating a joining process to join an MBS session, wherein the MBS session is in an active state; receiving one or more configuration values ​​of a PDCP state variable from the wireless network, wherein the PDCP state variable controls PDCP transmission and reception for the MBS session; and configuring the PDCP state variable based on the one or more received configuration values.

[0005] Another embodiment of the present invention provides a method for setting initial PDCP state variables for multicast, comprising: a base station in a wireless network receives a join request from a user equipment to join an active MBS session, wherein the MBS session provides services through an MRB, and wherein the base station and the user equipment have a unicast connection for feedback; the base station sends one or more configuration values ​​of a PDCP state variable to the user equipment, wherein the PDCP state variable controls PDCP transmission and reception for the MBS session; and receives feedback from the user equipment about reception information of the MBS session.

[0006] Another embodiment of the present invention provides a user equipment, comprising: a transceiver, used to send and receive radio frequency signals in a wireless network; a configuration module, used to configure MRB for one or more MBSs in the wireless network, wherein the MRB configuration enables feedback for one or more MBSs; a joining module, used to initiate a joining process to join an MBS session, wherein the MBS session is in an active state; a receiving module, used to receive one or more configuration values ​​of a packet data convergence protocol PDCP state variable from the wireless network, wherein the PDCP state variable controls PDCP transceiver for the MBS session; and a state variable module, used to configure the PDCP state variable based on the one or more configuration values ​​received.

[0007] Another embodiment of the present invention provides a storage medium storing a program, wherein when the program is executed, the user equipment executes the steps of the method for setting initial PDCP state variables for multicast of the present invention.

[0008] By utilizing the present invention, the PDCP state variables of the multicast service can be initialized. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings illustrate embodiments of the present invention, wherein like numerals indicate like components.

[0010] Figure 1 4 is a system diagram of an exemplary wireless communication network for initializing PDCP state variables for multicast based on a configuration UE received from a wireless network according to an embodiment of the present invention.

[0011] Figure 2 is a schematic diagram of an exemplary NR wireless system with a centralized upper layer of an NR radio interface stack according to an embodiment of the present invention.

[0012] Figure 3 is a schematic diagram of an exemplary MRB configuration according to an embodiment of the present invention.

[0013] Figure 4is a schematic diagram of a protocol stack for MRB configuration with PDCP retransmission according to an embodiment of the present invention.

[0014] Figure 5 is an exemplary flow chart of UE RRC state conditions when an MBS session is in an active state according to an embodiment of the present invention.

[0015] Figure 6 is an exemplary flow chart of conditions for setting PDCP state variables based on network information of a multicast service according to an embodiment of the present invention.

[0016] Figure 7 is an exemplary message diagram for setting PDCP state variables based on received network information for a multicast service according to an embodiment of the present invention.

[0017] Figure 8 is an exemplary schematic diagram for setting UE PDCP state variables indicated by the network according to an embodiment of the present invention.

[0018] Fig. 9 The present invention is an exemplary flow chart of a UE receiving one or more configuration values ​​of a UE PDCP state variable of an MBS session from a network and setting the PDCP state variable according to an embodiment of the present invention.

[0019] Fig.10 is an exemplary flow chart of a base station sending one or more configuration values ​​of a UE PDCP state variable for an MBS session according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] Reference will now be made in detail to some embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0021] The present application provides methods, devices, processing systems, and computer-readable media for NR (new radio access technology or 5G technology) or other radio access technologies. NR can support various wireless communication services, such as enhanced mobile broadband for wide bandwidth, millimeter wave for high carrier frequency, large MTC for non-backward compatible machine type communication (MTC) technology, and / or for mission-critical ultra-reliable low-latency communication. These services may have delay and reliability requirements. These services may also have different transmission time intervals (TTI) to meet their respective quality of service (QoS) requirements. In addition, these services can coexist in the same subframe. Several aspects of the telecommunications system will now be introduced with reference to various devices and methods, which will be described in the detailed description below and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc., collectively referred to as "elements". These elements can be implemented using electronic hardware, computer software, or any combination thereof. Whether these elements are implemented as hardware or software depends on the specific application and the design constraints on the entire system.

[0022] Figure 11 is a system diagram of an exemplary wireless communication network for multicasting based on a configuration UE received from a wireless network according to an embodiment of the present invention. The wireless communication network 100 includes one or more fixed infrastructure units that form a network distributed over a geographical area. These basic units may also be referred to as access points, access terminals, base stations, node Bs, evolved node Bs (eNode-Bs), next generation node Bs (gNBs), or other terms used in the art. For example, a base station may provide services for multiple mobile stations within a service area (e.g., a cell or a cell sector). In some systems, one or more base stations are coupled to a controller to form an access network, and the access network is coupled to one or more core networks. gNB 106, gNB 107, and gNB 108 are base stations in a wireless network, and their service areas may or may not overlap with each other. In one example, UE 101 or mobile station 101 is in a service area covered by gNB 106 and gNB 107. In one example, UE 101 or mobile station 101 is only in the service area of ​​gNB 106 and connected to gNB 106, and UE 102 or mobile station 102 is only in the service area of ​​gNB 107 and connected to gNB 107. gNB 106 is connected to gNB 107 via Xn interface 121. gNB 106 is connected to gNB 108 via Xn interface 122. 5G network entity 109 is connected to gNBs 106, 107, and 108 via NG connections 131, 132, and 133, respectively. In one embodiment, gNB 106 and gNB 107 provide the same MBMS service. When UE 101 moves from gNB 106 to gNB 107, and vice versa, service continuity during handover is guaranteed. The area covered by gNBs 106 and 107 with the same MBMS service is a multicast service area of ​​the MBMS service.

[0023] Figure 1 A simplified block diagram of a base station and a mobile device / UE for multicast transmission is further shown. The gNB 106 has an antenna 156 that sends and receives radio signals. An RF transceiver circuit 153 coupled to the antenna receives an RF signal from the antenna 156, converts the RF signal to a baseband signal, and sends the baseband signal to the processor 152. The RF transceiver 153 also converts the baseband signal received from the processor 152 to an RF signal and sends it to the antenna 156. The processor 152 processes the received baseband signal and calls different functional modules to perform functional features in the gNB 106. The memory 151 stores program instructions and data 154 to control the operation of the gNB 106. The gNB 106 also includes a set of control modules 155 for performing functional tasks to communicate with the mobile station. These control modules can be implemented by circuits, software, firmware, or a combination of the above.

[0024] Figure 1 A simplified block diagram of a UE (such as UE 101) is also shown. The UE has an antenna 165 for sending and receiving radio signals. An RF transceiver circuit 163 coupled to the antenna receives an RF signal from the antenna 165, converts the RF signal into a baseband signal, and sends the baseband signal to the processor 162. In one embodiment, the RF transceiver may include two RF modules (not shown) for transmission and reception in different frequency bands. The RF transceiver 163 also converts the baseband signal received from the processor 162 into an RF signal and sends it to the antenna 165. The processor 162 processes the received baseband signal and calls different functional modules to perform functional features in the UE 101. The memory 161 stores program instructions and data 164 to control the operation of the UE 101. The antenna 165 performs uplink transmission and downlink reception with the antenna 156 of the gNB 106.

[0025] The UE also includes a set of control modules for performing functional tasks. These functional modules can be implemented by circuits, software, firmware, or a combination of the above. The configuration module 191 configures MRBs for one or more multicast broadcast services (MBS) in the wireless network, wherein the MRB configuration enables feedback for one or more MBSs. The joining module 192 initiates a joining process to join an MBS session, wherein the MBS session is in an active state (active). The receiving module 193 receives one or more configuration values ​​of PDCP state variables from the wireless network, wherein the PDCP state variables control the PDCP transceiver of the MBS session. The state variable module 194 configures the PDCP state variables based on the received one or more configuration values. When the PDCP processing module 195 receives one or more PDCP packet data units (PDUs) before receiving one or more configuration values ​​of the PDCP state variables from the wireless network, it stores one or more PDCP PDUs in the receiving buffer.

[0026] In one embodiment, the UE further includes a radio resource control (RRC) state controller, an MBS controller, and a protocol stack controller. The RRC state controller controls the UE RRC state according to commands from the network and UE conditions. RRC supports the following states: RRC idle state, RRC connected state, and RRC inactive state. In one embodiment, the UE can receive MBS in the RRC idle / inactive state. The UE can apply the MRB establishment process to start receiving a session of services it is interested in. The UE can apply the MRB release process to stop receiving a session. The MBS controller controls the establishment / addition, reconfiguration / modification, and release / deletion of MRBs based on different condition sets for MRB establishment, reconfiguration, and release. The protocol stack controller can add, modify, or delete a protocol stack for an MRB. The protocol stack includes a PDCP layer 182, a radio link control (RLC) layer 183, a media access control (MAC) layer 184, and a physical (PHY) layer 185. In one embodiment, the service data adaptation protocol (SDAP) layer 181 is an optional configuration.

[0027] In one embodiment, the PDCP layer supports data transmission, PDCP sequence number (SN) maintenance, header compression and decompression using the robust header compression (ROHC) protocol, encryption and decryption, integrity protection and integrity verification functions, timer-based service data unit (SDU) discard, split bearer routing, duplication, reordering, in-sequence delivery, out-of-sequence delivery, and duplicate discard. The PDCP entity includes a reordering buffer 188 and a status reporter 189. In one embodiment, the receiving PDCP entity sends a PDCP status report when the reordering timer (t-reordering) expires. In one embodiment, the PDCP status report triggers a PDCP retransmission at the peer sending PDCP entity on the network side.

[0028] In one embodiment, the RLC layer 183 supports functions such as error correction, segmentation and reassembly, re-segmentation, duplicate detection, and reconstruction through ARQ. In one embodiment, a new process of RLC reconfiguration is performed, which can reconfigure the RLC entity to be associated with one or two logical channels. In another embodiment, the MAC layer 184 supports mapping, multiplexing, demultiplexing, HARQ, radio resource selection, etc. between logical channels and transport channels.

[0029] Figure 2 2 is a schematic diagram of an exemplary NR wireless system with a centralized upper layer of an NR radio interface stack according to an embodiment of the present invention. There may be different protocol partitioning options between the central unit (CU) and the distributed unit (DU) of the gNB node. The functional division between the CU and the DU of the gNB node may depend on the transport layer. Since the higher protocol layers have lower performance requirements on the transport layer in terms of bandwidth, delay, synchronization and jitter, low-performance transmission between the CU and the DU of the gNB node can enable the high protocol layers of the NR radio stack to be supported in the CU. In one embodiment, the SDAP and PDCP layers are located in the CU, while the RLC, MAC and PHY layers are located in the DU. The core unit 201 is connected to the central unit 211 with the gNB upper layer 252. In one embodiment 250, the gNB upper layer 252 includes a PDCP layer and an optional SDAP layer. The CU 211 is connected to the DUs 221, 222 and 223, where the DUs 221, 222 and 223 correspond to the cells 231, 232 and 233, respectively. DUs such as 221, 222, and 223 include gNB lower layers 251. In one embodiment, the gNB lower layers 251 include PHY, MAC, and RLC layers. In another embodiment 260, each gNB has a protocol stack 261 including SDAP, PDCP, RLC, MAC, and PHY layers.

[0030] Figure 3305 is a schematic diagram of an exemplary MRB configuration according to an embodiment of the present invention. MRB 305 provides multicast services, which are carried by a multicast traffic channel (multicast traffic channel, MTCH) of point to multipoint (PTM) 306, a dedicated traffic channel (dedicated traffic channel, DTCH) 307 of point to point (PTP) 307, or both MTCH 306 and DTCH 307 through UE protocol stack 301. In one embodiment 320, the MRB is configured to be associated with the MTCH. In another embodiment 330, the MRB is configured to be associated with the DTCH. In yet another embodiment 310, the MRB is configured to be associated with the MTCH and the DTCH. In embodiment 310, the MRB is configured as a PTM&PTP transmission mode. One or more MRBs corresponding to a multicast stream of a specific multicast session can be established to support multicast transmission in the air downlink. MRBs can be used for multiple PTM and / or PTP transmissions within a cell. In embodiment 320, the MRB is configured for PTM transmission mode. In embodiment 330, the MRB is configured for PTP mode. In embodiment 310, the MRB is configured for PTM & PTP transmission mode.

[0031] In certain systems such as NR systems, NR multicast / broadcast is transmitted within the coverage of a cell. In one embodiment, MCCH provides information of the NR MBS list of ongoing sessions transmitted on MTCH. At the physical layer, MTCH is scheduled by gNB in ​​the search space of the physical downlink control channel (PDCCH) scrambled by the group radio network temporary identifier (G-RNTI). The UE decodes the MTCH data for multicast sessions in the physical downlink shared channel (PDSCH). In existing systems supporting MBMS / eMBMS, the radio bearer structure for multicast and broadcast transmissions is modeled in a manner independent of unicast transmissions. Since traditional MBMS / eMBMS services are unidirectional transmissions, RLC unacknowledged mode (UM) nodes can be used to transmit MBS sessions. In this case, for a specific UE in the RRC connected state, no interaction between multicast and unicast is required. In NR networks that provide new services through MBS, reliable transmission is required. Unless very conservative link adaptation is implemented, traditional multicast transmission cannot guarantee successful reception for all UEs, which greatly reduces resource efficiency. In order to support reliable transmission of NR multicast services, each UE receiving the service requires a feedback channel in the uplink, through which the receiving UE can feedback the reception status of its service to the network. Based on the feedback, the network can perform necessary retransmissions to improve transmission reliability. From the perspective of uplink feedback, the feedback channel can be used for layer 2 (L2) feedback (such as RLC status report and / or PDCP status report). The feedback channel can also be used for HARQ feedback. In addition, the feedback should be a bidirectional channel between the UE and the network, and it is assumed that the network can use this channel to perform the required packet retransmission. Packet retransmission is L2 retransmission (such as RLC retransmission and / or PDCP retransmission). In addition, the feedback channel can be used for HARQ retransmission.

[0032] Figure 44 is a schematic diagram of a protocol stack for MRB configuration with PDCP retransmission according to an embodiment of the present invention. In PDCP-based retransmission 490, there is a PDCP entity 491 for each MRB. Two logical channels (MTCH and DTCH) are associated with the PDCP entity. Each logical channel corresponds to an RLC entity, RLC 492 corresponds to MTCH, and RLC 493 corresponds to DTCH. From the perspective of the UE, the PDCP status report that triggers PDCP retransmission is passed to the RLC entity 493 corresponding to the DTCH. From the perspective of the network, the retransmitted PDCP protocol data unit (PDU) is delivered via the DTCH. The MAC entity maps the logical channel MTCH to transport channel 1 (such as multicast channel (MCH), downlink shared channel (DL-SCH), and maps the logical channel DTCH to transport channel 2 (such as MCH, DL-SCH). The UE monitors two independent transport channels through different radio network temporary identification (RNTI). ROHC function and security function are optional for multicast transmission. The RLC layer only includes segmentation, and the ARQ function of the RLC layer is moved to the PDCP layer. RLC 492 and RLC 493 are mapped to MAC494 and send data packets to PHY 495.

[0033] A network entity such as a base station / gNB transmits an MBS data packet to N UEs on a PTM link and retransmits the MBS data packet on a PTP link associated with a PDCP protocol stack based on feedback. A UE configured with a PDCP-based protocol stack receives an MBS data packet from the base station on a PTM RB and sends feedback to the base station. The scheduling of multicast is independent of PTP transmission. The protocol stack of the base station and the UE includes an SDAP layer 401, a PDCP layer 402, an RLC layer 403, and a MAC layer 404. The SDAP layer 401 processes QoS flows 481, including QoS flow processing 411 for UE-1 and QoS flow processing 412 for UE-N at the base station, and QoS flow processing 413 for UE at the UE. The PDCP layer 402 includes a ROHC function and a security function. The ROHC function and the security function are optional for multicast transmission. The PDCP layer 402 includes functions of ROHC 421 and security 424 for UE-1 multicast, ROHC 4212 and security 4242 for UE-1 unicast, ROHC 422 and security 425 for UE-N multicast, ROHC 4222 and security 4252 for UE-N unicast at the base station, and ROHC 423 and security 426 at the UE. RB 482 is processed in the PDCP layer 402. The RLC layer 403 includes segmentation and ARQ 431 for UE-1 multicast at the base station, segmentation and ARQ 432 for UE-1 unicast at the base station, segmentation and ARQ 433 for UE-N multicast at the base station, segmentation and ARQ 434 for UE-N unicast at the base station; and segmentation and ARQ 435 for unicast channels at the UE, and segmentation and ARQ 436 for multicast channels at the UE. RLC channels 483 are processed in the RLC layer 403. The MAC layer 404 includes scheduling and priority processing 441 at the base station, multiplexing 443 and HARQ 446 for UE-1 at the base station, multiplexing 444 and HARQ 447 for UE-N at the base station; and scheduling and priority processing 442 for UE at the UE, multiplexing 445 and HARQ 448 for UE at the UE. Logical channels 484 and transport channels 485 are processed at the MAC layer 404.

[0034] Figure 5is an exemplary flow chart of UE RRC state conditions when an MBS session is in an active state according to an embodiment of the present invention. The UE is configured with one or more MBS services. In step 501, the UE joins a multicast / MBS session. In one embodiment, the UE sends a request to join the MBS session. After the UE joins the multicast session, in one embodiment, the UE joins the active MBS session, that is, when the UE joins, the MBS session is in an active state in step 502. In other scenarios, the MBS session is not activated, and when the MBS session is activated, the UE will receive a session activation notification. In some scenarios, when the MBS session is not activated, the UE will transition to an RRC idle / inactive state to save power. In other scenarios, when the MBS session is not activated, the UE may stay in an RRC connected state for other reception. If the MBS session is not activated, the RRC connected state UE may stay in the RRC connected state or transition to the RRC idle / inactive state. When the multicast session is activated, the UE receives a session activation notification in step 502 and detects that the MBS session is in an active state. If it is detected that the MBS session is in an active state, the UE determines whether the UE is in an RRC connected state at step 510. If the result of the determination at step 510 is no, the UE switches to the RRC connected state at step 512. If the result of the determination at step 510 is yes, at step 511, the UE in the RRC connected state receives RRC signaling to set an initial PDCP state variable.

[0035] Figure 66 is an exemplary flow chart of the conditions for setting PDCP state variables based on network information of a multicast service according to an embodiment of the present invention. In step 601, the UE is in an RRC connected state. In one embodiment, an MBS session is activated. In step 602, the UE receives a message for detailed RRC configuration from the network. In one embodiment, the network message is an RRC message. According to some embodiments, the RRC message may be an RRC reconfiguration (RRCReconfiguration) message, an RRC recovery (RRCResume) message, or an RRC establishment (RRCSetup) message, etc. The wireless network indicates the SN (such as next-SN) and the corresponding HFN value (such as initial_HFN) of the first PDU to be sent to the UE. In one embodiment 621, the above indication is provided by an RRC reconfiguration message, wherein the initial_HFN and next_SN information are added to the RRC message. In one embodiment, the above indication is provided by an RRC establishment / recovery signal according to the RRC state of the UE (not shown). In step 603, the UE sets the HFN to the value of the HFN indicated by the network, i.e., initial_HFN in the RRC message; and sets the SN of RX_DELIV and / or RX_NEXT to the SN of the first PDU to be transmitted by the network, i.e., next_SN in the RRC message. After the UE applies the RRC configuration, in step 604, the UE sends an RRC message to the wireless network, such as an RRCReconfigurationComplete message.

[0036] Figure 7is an exemplary message diagram for setting PDCP state variables based on received network information for a multicast service according to an embodiment of the present invention. UE 701 is configured with one or more MBSs in a wireless network with gNB 702. Before the UE receives data packets from the configured MBSs, different scenarios should be considered. In one scenario 711, UE 701 is in an RRC idle / inactive state. In another scenario, the MBS session is not activated. In step 721, the network notifies to activate the MBS session. In one embodiment, gNB 702 sends an MBS session activation notification to one or more UEs (including UE 701). In one embodiment, the MBS session activation notification is broadcast. In one embodiment, the MBS session activation notification may be unicast to each UE. In some scenarios, the MBS session is activated when UE 701 is in an RRC idle / inactive state, while in other scenarios, UE 701 is in an RRC connected state. The MBS session is activated before or after UE 701 determines to join the session. In one embodiment, UE 701 is in an RRC connected state before the session is activated. UE 701 receives unicast services at the same time. In this case, the network will send an RRC reconfiguration message without an additional session activation notification. In one embodiment, the UE is in an RRC idle / inactive state before the session is activated. The UE needs to listen to the session activation notification. After the network notifies the session activation, the UE transitions to the RRC connected state to receive the multicast service. In one scenario, at step 712, UE 712 enters the RRC connected state. At step 722, the MBS session is activated.

[0037] When the MBS session is activated and the UE 701 is in the RRC connected state, the UE receives the HFN and SN values ​​of the UE PDCP state variables for the active MBS session from the network. In one embodiment, at step 731, the UE 701 receives RRC signaling for detailed RRC configuration. The RRC signaling from the network includes one or more configuration values ​​of the UE PDCP state variables for the MBS session, including a HFN value (such as initial_HFN) and a SN value (such as next_SN). In one embodiment, the network uses an RRC reconfiguration message to indicate the HFN and the SN of the next PDCP PDU to be sent. At step 713, the UE 701 sets the HFN to the initial_HFN included in the RRC message from the network. At step 718, the UE 701 sets the HFN to initial_HFN. At step 719, the UE 701 sets the SN part of RX_DELIV to next_SN. Optionally, the UE 701 sets the SN part of RX_NEXT to next_SN. After completing the RRC reconfiguration including the initialization of the PDCP state variables, at step 732, UE 701 sends an RRC reconfiguration complete message to the network.

[0038] Figure 8 is an exemplary schematic diagram for setting UE PDCP state variables indicated by the network according to an embodiment of the present invention. UE 802 is configured with one or more MBSs in a wireless network with gNB 801. When UE 802 establishes an MRB, the initial value of the PDCP state variable will be transmitted in the RRC signaling. In step 811, gNB 801 sends an RRC message / signaling with the configuration value of the PDCP state variable, including the HFN value and the SN value. In step 821, UE 802 sets the PDCP state variable based on the configuration value received from the RRC message. Assuming that the value of the initial HFN indicated by the network is X, the SN of the next PDCP PDU to be transmitted is N, and the network sends a data packet 810 with SN of N, N+1, N+2, N+3, etc.

[0039] In one embodiment, the UE may receive subsequent data PDUs earlier than the RRC signaling (not shown). The UE receives the MBS data packet 820 and processes the received packet based on the network configuration value of the UE PDCP state variable. In one embodiment, the UE must receive the MBS data PDU after receiving the RRC signaling. When one or more PDCP PDUs are received before one or more configuration values ​​of the PDCP state variable are received from the wireless network, the UE stores the one or more PDCP PDUs in a receive buffer. Subsequently, when one or more configuration values ​​from the wireless network are received and applied, the UE processes the stored PDCP PDUs. Upon receiving the RRC signaling with the configuration value of the UE PDCP state variable, the UE sets HFN=X and the SN part of RX_DELIV=N. As shown in the figure, the SN part of RX_NEXT will be updated according to the SN of the received PDU. In step 831, if some PDUs are lost (assuming that [X,N] and [X,N+1] are lost), the UE will update RX_NEXT to the SN+1 of the next received PDU. In step 832, RX_NEXT is updated to N+3. In step 833, when it is determined that RX_NEXT is not equal to RX_DELIV, the UE starts reordering when processing the stored PDCP PDU. In step 834, RX_NEXT is updated to N+4. In subsequent reception, if a PDCP PDU with COUNT[X,N] is successfully received, the SN part of RX_NEXT and RX DELIV will be updated to N+1.

[0040] Fig. 9 The present invention is an exemplary flowchart for a UE to receive one or more configuration values ​​of a UE PDCP state variable for an MBS session from a network and set the PDCP state variable according to an embodiment of the present invention. In step 901, the UE configures an MRB for one or more MBSs in a wireless network, wherein the MRB configuration enables feedback for the one or more MBSs. In step 902, the UE initiates a join process to join an MBS session, wherein the MBS session is in an active state. In step 903, the UE receives one or more configuration values ​​of a PDCP state variable from a wireless network, wherein the PDCP state variable controls PDCP transceiving for the MBS session. In step 904, the UE configures the PDCP state variable based on the received one or more configuration values.

[0041] Fig.10is an exemplary flow chart of a base station sending one or more configuration values ​​of a UE PDCP state variable for an MBS session according to an embodiment of the present invention. In step 1001, the base station / gNB receives a join request from a UE to join an active MBS session, wherein the MBS session is served via an MRB, and wherein the base station / gNB and the UE have a unicast connection for feedback. In step 1002, the base station / gNB sends one or more configuration values ​​of a PDCP state variable to the UE, wherein the PDCP state variable controls PDCP transceiving for the MBS session. In step 1003, the base station / gNB receives feedback from the UE regarding reception information of the MBS session.

[0042] In one embodiment, a storage medium (such as a computer-readable storage medium) stores a program, and when the program is executed, the UE executes various embodiments of the present invention.

[0043] Although the present invention has been described in conjunction with specific embodiments for illustrative purposes, the present invention is not limited thereto. Therefore, various modifications, adaptations and combinations of the various features of the described embodiments may be implemented without departing from the scope of the present invention as described in the claims.

Claims

1. A method for setting initial PDCP state variables for multicast, comprising: configuring, by a user equipment, a multicast radio bearer (MRB) for one or more multicast broadcast services (MBSs) in a wireless network, wherein the MRB configuration enables feedback for the one or more MBSs; Initiating a joining procedure to join the MBS session, wherein the MBS session is in an active state; receiving one or more configuration values ​​of Packet Data Convergence Protocol (PDCP) state variables from the wireless network, wherein the PDCP state variables control PDCP transmissions and receptions for the MBS session; and The PDCP state variables are configured based on the received one or more configuration values, wherein the one or more configuration values ​​include a superframe number and a sequence number.

2. The method for setting initial PDCP state variables for multicast according to claim 1, wherein: The one or more configuration values ​​of the PDCP state variables are received from a Radio Resource Control (RRC) message.

3. The method for setting initial PDCP state variables for multicast according to claim 2, wherein: The RRC message is an RRC reconfiguration message, an RRC recovery message or an RRC establishment message.

4. The method for setting initial PDCP state variables for multicast according to claim 1, wherein: Configuring the PDCP state variables includes initializing an RX_DELIV value based on configured values ​​of a hyperframe number and a sequence number received from the wireless network.

5. The method for setting initial PDCP state variables for multicast according to claim 1, wherein: Configuring the PDCP state variables includes setting an RX_NEXT value based on configured values ​​of a hyperframe number and a sequence number received from a wireless network.

6. The method for setting initial PDCP state variables for multicast according to claim 1, wherein: Further including: When one or more PDCP packet data units are received before the one or more configuration values ​​of the PDCP state variables are received from the wireless network, the one or more PDCP packet data units are stored in a receive buffer.

7. The method for setting initial PDCP state variables for multicast according to claim 6, wherein: Further including: The one or more stored PDCP packet data units are processed when the one or more configuration values ​​from the wireless network are received and applied.

8. A method for setting initial PDCP state variables for multicast, comprising: A base station in a wireless network receives a join request from a user equipment to join an active multicast broadcast service (MBS) session, wherein the MBS session is served by a multicast radio bearer (MRB), and wherein the base station and the user equipment have a unicast connection for feedback; The base station sends one or more configuration values ​​of a Packet Data Convergence Protocol (PDCP) state variable to the user equipment, wherein the PDCP state variable controls PDCP transmission and reception for the MBS session, and the one or more configuration values ​​include a superframe number and a sequence number; and Feedback regarding reception information of the MBS session is received from the user equipment.

9. The method for setting initial PDCP state variables for multicast according to claim 8, wherein: The one or more configuration values ​​of the PDCP state variable are sent via a radio resource control (RRC) message.

10. The method for setting initial PDCP state variables for multicast according to claim 9, wherein: The RRC message is an RRC reconfiguration message, an RRC recovery message or an RRC establishment message.

11. A user equipment, comprising: transceivers, which are used to send and receive radio frequency signals in wireless networks; a configuration module configured to configure a multicast radio bearer (MRB) for one or more multicast broadcast services (MBSs) in the wireless network, wherein the MRB configuration enables feedback for the one or more MBSs; a joining module, configured to initiate a joining process to join an MBS session, wherein the MBS session is in an active state; a receiving module, configured to receive one or more configuration values ​​of a Packet Data Convergence Protocol (PDCP) state variable from the wireless network, wherein the PDCP state variable controls PDCP transmission and reception for the MBS session; as well as A state variable module is configured to configure the PDCP state variable based on the received one or more configuration values, wherein the one or more configuration values ​​include a superframe number and a sequence number.

12. The user equipment according to claim 11, wherein: The one or more configuration values ​​of the PDCP state variables are received from a Radio Resource Control (RRC) message.

13. The user equipment according to claim 12, wherein: The RRC message is an RRC reconfiguration message, an RRC recovery message or an RRC establishment message.

14. The user equipment according to claim 11, wherein Configuring the PDCP state variables includes initializing an RX_DELIV value based on configured values ​​of a hyperframe number and a sequence number received from the wireless network.

15. The user equipment according to claim 11, wherein: Configuring the PDCP state variables includes setting an RX_NEXT value based on configured values ​​of a hyperframe number and a sequence number received from a wireless network.

16. The user equipment according to claim 11, wherein: Further including: The PDCP processing module is configured to store the one or more PDCP packet data units in a receiving buffer when one or more PDCP packet data units are received before the one or more configuration values ​​of the PDCP state variable are received from the wireless network.

17. The user equipment according to claim 16, wherein: The PDCP processing module processes the one or more stored PDCP packet data units upon receiving and applying the one or more configuration values ​​from the wireless network.

18. A storage medium storing a program, wherein when the program is executed, the program causes a user equipment to perform the steps of the method for setting initial PDCP state variables for multicast according to any one of claims 1 to 7.

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