Patent Publication Number: US-2023134356-A1

Title: Methods and apparatus to set initial pdcp state variables for multicast

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is filed under 35 U.S.C. § 111(a) and is based on and hereby claims priority under 35 U.S.C. § 120 and § 365(c) from International Application No. PCT/CN/2021/123856, titled “Methods and apparatus to set Initial PDCP State Variables for Multicast,” with an international filing date of Oct. 14, 2021. This application claims priority under 35 U.S.C. § 119 from Chinese Application Number CN 202211132164.0 titled “Methods and apparatus to set Initial PDCP State Variables for Multicast,” filed on Sep. 16, 2022. The disclosure of each of the foregoing documents is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosed embodiments relate generally to wireless communication, and, more particularly, to set initial packet data convergence protocol (PDCP) state variables for multicast. 
     BACKGROUND 
     With the exponential growth of wireless data services, the content delivery to large mobile user groups has grown rapidly. Various cellular systems, including both 4G/long term evolve (LTE) system and 5G/new radio (NR) systems, may provide a multicast functionality, which allows user equipments (UEs) in the system to receive multicast services transported by the cellular system. A variety of applications may rely on communication over multicast transmission, such as live stream, video distribution, vehicle-to-everything (V 2 X) communication, public safety (PS) communication, file download, and so on. When UE establishes multicast radio bearer (MRB), hyper frame number (HFN) needs to be synchronized between the wireless network and the UE. It is also necessary to set initial value of packet data convergence protocol (PDCP) receiving window. In the legacy system, the initial values of the variables for transmit and receive operation at the PDCP layer are deterministic and usually starts from zero because data transmission/reception starts after UE is in the RRC CONNECTED state. In the NR multicast, the UE may join the multicast and broadcast service (MBS) session after the MBS session activation, which implies that the PDCP packets transmission over the air interface has been on-going for a while. Therefore, the UE cannot initialize the PDCP variables as usual for the MBS session. 
     Improvements and enhancements are required to initialize PDCP state variables for multicast services. 
     SUMMARY 
     Apparatus and methods are provided for setting initial PDCP state variables for multicast services. In one novel aspect, the UE sets initial PDCP state variables for the MBS session based on configuration values received from the network. In one embodiment, the UE receives dedicated RRC signaling from the network, which contains initial HFN value and the SN of the next PDCP PDU to be transmitted. In one embodiment, the one or more configuration values are provided in RRC Reconfiguration message. In one embodiment, the one or more configuration values are provided in RRCResume, or RRCSetup message, according to different RRC states of UE. In one embodiment, the UE initializes the RX_DELIV value based on the configuration value of HFN and SN received from the wireless network. When receiving the one or more configuration values of initial PDCP state variables, UE sets HFN to initial HFN value and sets RX DELIV to the COUNT value of next PDCP PDU to be transmitted by network. In another embodiment, the UE stores one or more PDCP packet data units (PDUs) in a reception buffer when the one or more PDCP PDUs are received before receiving one or more configuration values for PDCP state variables from the wireless network. 
     In another embodiment, the gNB receives a join request from a UE to join an active MBS session, wherein the MBS session is served with an MRB, and wherein the gNB and the UE has a unicast connection for feedback; sends one or more configuration values for PDCP state variables to the UE, wherein the PDCP state variables control PDCP transceiving for the MBS session; and receives feedback from the UE regarding reception information of the MBS session. 
     This summary does not purport to define the invention. The invention is defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
         FIG.  1    is a schematic system diagram illustrating an exemplary wireless communication network where the UE initializes the PDCP state variables for multicast based on configurations received from the wireless network. 
         FIG.  2    illustrates an exemplary NR wireless system with centralized upper layers of the NR radio interface stacks. 
         FIG.  3    illustrates exemplary MRB configuration in accordance with embodiments of the current invention. 
         FIG.  4    illustrates an exemplary protocol stack for a MRB configuration with PDCP-based retransmission. 
         FIG.  5    illustrates an exemplary flow diagram of conditions for UE RRC states when MBS sessions are active in accordance with embodiments of the current invention. 
         FIG.  6    illustrates an exemplary flow diagram of conditions for setting the PDCP state variables based on network information for multicast services in accordance with embodiments of the current invention. 
         FIG.  7    illustrates an exemplary message diagram of setting the PDCP state variables based on the received network information for multicast services in accordance with embodiments of the current invention. 
         FIG.  8    illustrates an exemplary diagram for setting the UE PDCP state variables indicated by the network in accordance with embodiments of the current invention. 
         FIG.  9    illustrates an exemplary flow chart for the UE receiving one or more configuration values for UE PDCP state variables for an MBS session from the network and setting the PDCP state variables in accordance with embodiments of the current invention. 
         FIG.  10    illustrates an exemplary flow chart for the base station sending one or more configuration values for UE PDCP state variables for an MBS session in accordance with embodiments of the current invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
     Aspects of the present disclosure provide methods, apparatus, processing systems, and computer readable mediums for NR (new radio access technology, or 5G technology) or other radio access technologies. NR may support various wireless communication services, such as enhanced mobile broadband targeting wide bandwidth, millimeter wave targeting high carrier frequency, massive machine type communications targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications. These services may include latency and reliability requirements. These services may also have different transmission. time intervals (TTI) to meet respective quality of service (QoS) requirements. In addition, these services may co-exist in the same subframe. Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc., collectively referred to as “elements”. These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. 
       FIG.  1    is a schematic system diagram illustrating an exemplary wireless communication network where the UE initializes the PDCP state variables for multicast based on configurations received from the wireless network. Wireless communication network  100  includes one or more fixed base infrastructure units forming a network distributed over a geographical region. The base unit may also be referred to as an access point, an access terminal, a base station, a Node-B, an eNode-B (eNB), a gNB, or by other terminology used in the art. As an example, base stations serve a number of mobile stations within a serving area, for example, a cell, or within a cell sector. In some systems, one or more base stations are coupled to a controller forming an access network that is coupled to one or more core networks. gNB  106 , gNB  107  and gNB  108  are base stations in the wireless network, the serving area of which may or may not overlap with each other. As an example, user equipment (UE)  101  or mobile station  101  is in the serving area covered by gNB  106  and gNB  107 . As an example, UE  101  or mobile station  101  is only in the service area of gNB  106  and connected with gNB  106 . UE  102  or mobile station  102  is only in the service area of gNB  107  and connected with gNB  107 . gNB  106  is connected with gNB  107  via Xn interface  121 . gNB  106  is connected with gNB  108  via Xn interface  122 . A  5 G network entity  109  connects with gNB  106 ,  107 , and  108  via NG connection  131 ,  132 , and  133 , respectively. In one embodiment, gNB  106  and gNB  107  provide the same MBMS services. The service continuity during handover is guaranteed when UE  101  moves from gNB  106  to gNB  107  and vice versa. The area covered by gNB  106  and  107  with the same MBMS services is a multi-cast service area for the MBMS services. 
       FIG.  1    further illustrates simplified block diagrams of a base station and a mobile device/UE for multicast transmission. gNB  106  has an antenna  156 , which transmits and receives radio signals. An RF transceiver circuit  153 , coupled with the antenna  156 , receives RF signals from antenna  156 , converts them to baseband signals, and sends them to processor  152 . RF transceiver  153  also converts received baseband signals from processor  152 , converts them to RF signals, and sends out to antenna  156 . Processor  152  processes the received baseband signals and invokes different functional modules to perform features in gNB  106 . Memory  151  stores program instructions and data  154  to control the operations of gNB  106 . gNB  106  also includes a set of control modules  155  that carry out functional tasks to communicate with mobile stations. These control modules can be implemented by circuits, software, firmware, or a combination of them. 
       FIG.  1    also includes simplified block diagrams of a UE, such as UE  101 . The UE has an antenna  165 , which transmits and receives radio signals. An RF transceiver circuit  163 , coupled with the antenna, receives RF signals from antenna  165 , converts them to baseband signals, and sends them to processor  162 . In one embodiment, the RF transceiver  163  may comprise two RF modules (not shown) which are used for different frequency bands transmitting and receiving. RF transceiver  163  also converts received baseband signals from processor  162 , converts them to RF signals, and sends out to antenna  165 . Processor  162  processes the received baseband signals and invokes different functional modules to perform features in UE  101 . Memory  161  stores program instructions and data  164  to control the operations of UE  101 . Antenna  165  sends uplink transmission and receives downlink transmissions to/from antenna  156  of gNB  106 . 
     The UE also includes a set of control modules that carry out functional tasks. These control modules can be implemented by circuits, software, firmware, or a combination of them. A configuration module  191  configures an MRB for one or more multicast and broadcast services (MBSs) in a wireless network, wherein an MRB configuration enables feedback for the one or more MBSs. A joining module  192  initiates a join procedure to join an MBS session, wherein the MBS session is active. A reception module  193  receives one or more configuration values for packet data convergence protocol (PDCP) state variables from the wireless network, wherein the PDCP state variables control PDCP transceiving for the MBS session. A state variable module  194  configures PDCP state variables based on the received one or more configuration values. A PDCP processing module  195  stores one or more PDCP packet data units (PDUs) in a reception buffer when the one or more PDCP PDUs are received before receiving one or more configuration values for PDCP state variables from the wireless network. 
     In one embodiment, the UE further has an RRC state controller, an MBS controller, and a protocol stack controller. RRC state controller controls UE RRC state according to commands from the network and UE conditions. RRC supports the following states, RRC_IDLE, RRC_CONNECTED and RRC_INACTIVE. In one embodiment, UE can receive the multicast and broadcast services in RRC IDLE/INACTIVE state. The UE applies the MRB establishment procedure to start receiving a session of a service it has an interest in. The UE applies the MRB release procedure to stop receiving a session. MBS controller controls to establish/add, reconfigure/modify and release/remove a MRB based on different sets of conditions for MRB establishment, reconfiguration, and release. A protocol stack controller manages to add, modify, or remove the protocol stack for the MRB. The protocol Stack includes the packet data convergence protocol (PDCP) layer  182 , the radio link control (RLC)  183 , the MAC layer  184  and the PHY layer  185 . In one embodiment, the service data adaptation protocol (SDAP) layer  181  is optionally configured. 
     In one embodiment, the PDCP layer supports the functions of transfer of data, maintenance of PDCP sequence number (SN), header compression and decompression using the robust header compression (ROHC) protocol, ciphering and deciphering, integrity protection and integrity verification, timer based SDU discard, routing for split bearer, duplication, re-ordering, in-order delivery, out of order delivery and duplication discarding. The PDCP entity includes a reordering buffer  188  and a status reporter  189 . In one embodiment, the receiving PDCP entity sends PDCP status report upon t-Reordering expiry. In one embodiment, the PDCP status reports triggers PDCP retransmission at the peer transmitting PDCP entity at the network side. 
     In one embodiment, the RLC layer  183  supports the functions of error correction through ARQ, segmentation and reassembly, re-segmentation, duplication detection, re- establishment, etc. In one embodiment, a new procedure for RLC reconfiguration is performed, which can reconfigure the RLC entity to associated to one or two logical channels. In another embodiment, the MAC layer  184  supports mapping between logical channels and transport channels, multiplexing, demultiplexing, HARQ, radio resource selection, and etc. 
       FIG.  2    illustrates an exemplary NR wireless system with centralized upper layers of the NR radio interface stacks. Different protocol split options between central unit (CU) and distributed unit (DU) of gNB nodes may be possible. The functional split between the CU and DU of gNB nodes may depend on the transport layer. Low performance transport between the CU and DU of gNB nodes can enable the higher protocol layers of the NR radio stacks to be supported in the CU, since the higher protocol layers have lower performance requirements on the transport layer in terms of bandwidth, delay, synchronization, and jitter. In one embodiment, SDAP and PDCP layer are located in the CU, while RLC, MAC and PHY layers are located in the DU. A core unit  201  is connected with one central unit  211  with gNB upper layer  252 . In one embodiment  250 , gNB upper layer  252  includes the PDCP layer and optionally the SDAP layer. Central unit  211  connects with distributed units  221 ,  222 , and  221 . Distributed units  221 ,  222 , and  223  each corresponds to a cell  231 ,  232 , and  233 , respectively. The DUs, such as  221 ,  222  and  223  includes gNB lower layers  251 . In one embodiment, gNB lower layers  251  include the PHY, MAC and the RLC layers. In another embodiment  260 , each gNB has the protocol stacks  261  including SDAP, PDCP, RLC, MAC and PHY layers. 
       FIG.  3    illustrates exemplary MRB configuration in accordance with embodiments of the current invention. Multicast radio bearer  305  provides multicast service, which is carried by multicast traffic channel (MTCH) of a point to multipoint (PTM)  306 , a dedicated traffic channel (DTCH) of a point to point(PTP)  307 , or both MTCH  306  and DTCH  307  with a UE protocol stack  301 . In one embodiment  320 , the MRB is configured to be associated to a MTCH. In another embodiment  330 , the MRB is configured to be associated to a DTCH. In yet another embodiment  310 , the MRB is configured to be associated to a MTCH and a DTCH. In embodiment  310 , the MRB is configured in PTM&amp;PTP transmission mode. One or multiple MRBs are established corresponding to the multicast flows of a particular multicast session in order to support the multicast transmission in the downlink over the air. The multicast Radio Bearer (i.e., RB) can be subject to PTM and/or PTP transmission within a cell. In embodiment  320 , the MRB is configured in PTM transmission mode. In embodiment  330 , the MRB is configured in PTM mode. In embodiment  310 , the MRB is configured in PTM&amp;PTP transmission mode. 
     In certain systems, such as NR systems, NR multicast/broadcast is transmitted in the coverage of a cell. In one embodiment, MCCH provides the information of a list of NR multicast/broadcast services with ongoing sessions transmitted on MTCH(s). At physical layer, MTCH is scheduled by gNB in the search space of PDCCH with G-RNTI scrambled. UE decodes the MTCH data for a multicast session in the multicast PDSCH. In legacy system supporting MBMS/eMBMS, the radio bearer structure for multicast and broadcast transmission is modelled in an independent way from unicast transmission. Because of the unidirectional transmission for legacy MBMS/eMBMS service, RLC unacknowledged mode (UM) node is used for the transmission of MBS session. In this case there is no need to make the interaction between multicast and unicast for a particular UE which is in RRC CONNECTED state. For the NR network, with new services provided through MBS, reliable transmission is required. The traditional multicast transmission does not ensure successful reception for all UEs, unless very conservative link adaptations are implemented, which greatly degrades the resource efficiency. To support the reliable transmission for NR multicast service, a feedback channel in the uplink is needed for each UE receiving the service, which can be used by the receiving UE to feedback its reception status about the service to the network. Based on the feedback, the network may perform necessary retransmission to improve the transmission reliability. From uplink feedback perspective, the feedback channel may be used for L 2  feedback (e.g., RLC Status Report and/or PDCP Status Report). In addition, the feedback channel may be used for HARQ feedback. Furthermore, the feedback should be a bidirectional channel between the UE and the network, with the assumption that the network may take that channel to perform needed packet retransmission. The said packet retransmission is L 2  retransmission (e.g., RLC retransmission and/or PDCP retransmission). In addition, the feedback channel may be used for HARQ retransmission. 
       FIG.  4    illustrates an exemplary protocol stack for a MRB configuration with PDCP-based retransmission. In the PDCP-based retransmission  490 , there is one PDCP entity  491  per MRB. Two logical channels, i.e., MTCH and DTCH are associated to the PDCP entity. Each logical channel is corresponding to a RLC entity, RLC  492  corresponding to the MTCH and RLC  493  corresponding to the DTCH. From UE aspect, the PDCP status report to trigger PDCP retransmission is delivered to the RLC entity  493  corresponding to DTCH. From network aspect, the PDCP protocol data units (PDUs) subject to retransmission are delivered through DTCH. The MAC entity maps the logical channel MTCH to the transport channel  1  (e.g., MCH, DL-SCH) and maps the logical channel DTCH to the transport channel  2  (e.g., MCH, DL-SCH). UE monitors two independent transport channels via different radio network temporary identifiers (RNTIs). The ROHC function and security function are optional for multicast transmission. The RLC layer includes only segmentation and the ARQ function of RLC layer is moved to PDCP layer. RLC  492  and RLC  493  maps to MAC  494  and send the data packets to PHY  495 . 
     A network entity, such as a base station/gNB, transmits MBS data packets with PTM link to a number N of UEs and retransmits MBS data packets based on feedbacks through associated PTP link with the PDCP-based protocol stack. An exemplary UE, correspondingly configured with PDCP-based protocol stack receives MBS data packets on the PTM RB from the bases station and sends feedback to the base station. The multicast is scheduled independently from PTP transmission. The protocol stack for both the base station and the UE includes SDAP layer  401 , PDCP layer  402 , RLC layer  403 , and MAC layer  404 . SDAP layer  401  handles QoS flows  481 , including functions at the base station of QoS flow handling  411  for UE- 1  and QoS flow handling  412  for UE-N, and functions at the UE of QoS flow handling  413  for the UE. The PDCP layer  402  includes ROHC functions and security functions. The ROHC function and security function are optional for multicast transmission. PDCP layer  402  includes base station 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, and functions at the UE of ROHC  423  and security  426 . RBs  482  are handled in PDCP layer  402 . The RLC layer  403  includes both segmentation and ARQ function at base Station of segmentation and ARQ  431  for UE- 1  multicast, segmentation and ARQ  432  for UE- 1  unicast, segmentation and ARQ  433  for UE-N multicast, segmentation and ARQ  434  for UE-N unicast, as well as UE functions of segmentation and ARQ  435  for the unicast channel of the UE, and segmentation and ARQ  436  for the multicast channel. RLC channels  483  are handled in RLC layer  403 . MAC layer  404  includes functions of scheduling and priority handling  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 functions for the UE of scheduling and priority handling  442  of the UE, multiplexing  445  of the UE and HARQ  448  of the UE. Logic channels  484  and transport channels  485  are handled at MAC layer  404 . 
       FIG.  5    illustrates an exemplary flow diagram of conditions for UE RRC states when MBS sessions are active in accordance with embodiments of the current invention. The UE is configured with one or more MBS services. At step  501 , the UE joins a multicast/MBS session. In one embodiment, a request is sent from the UE to join the MBS session. After UE joined multicast session, in one embodiment, the UE joins an active MBS session, i.e., the MBS session is active at step  502  when the UE joins. In other scenarios, the MBS session is not active and when the MBS session activates, the UE will receive a session activation notification. In some scenarios, the UE transit to RRC IDLE/INACTIVE states for power saving when the MBS session was not active. In other scenarios, the UE may stay in RRC CONNECTED state for other receptions when the MBS session was not active. The RRC CONNECTED state UE may stay in the RRC CONNECTED state or transits to RRC IDLE/INACTIVE state if the MBS session is not active. When multicast session activates, UE receives session activation notification and detected that the MBS session is active at step  502 . Upon detecting the MBS session is active, at step  510 , the UE determines if the UE is in the RRC CONNECTED state. If step  510  determines no, the UE transits to RRC CONNECTED state at step  512 . If step  510  determines yes, at step  511 , the UE in the RRC CONNECTED state receives RRC signaling to set initial PDCP state variables. 
       FIG.  6    illustrates an exemplary flow diagram of conditions for setting the PDCP state variables based on network information for multicast services in accordance with embodiments of the current invention. At step  601 , the UE is in the RRC CONNECTED state. In one embodiment, the MBS session is activated. At step  602 , the UE receives message from network for detailed RRC configuration. In one embodiment, the network message is an RRC message. According to some embodiments, the RRC message is a RRCReconfiguration message, a RRCResume message, or a RRCSetup message. The wireless network indicates the SN of the first PDU will be transmitted to UE (e.g., next_SN) and corresponding HFN value (e.g., initial_HFN). In one embodiment  621 , the indicator is provided by RRC Reconfiguration message, with the initial_HFN and next_SN information added to the RRC message. In one embodiment, the indicator is provided by RRC Setup/Resume signal according to RRC states of UE (not shown). At step  603 , the UE sets HFN to the value of the HFN indicated by the network, which is the initial_HFN in the RRC message; and set SN of RX_DELIV and/or RX_NEXT to the SN of the first PDU will be transmitted by the network, which is the next_SN in the RRC message. After the UE applies the RRC configurations, at step  604 , the UE transmits a RRC message, such as RRCReconfigurationComplete message to the wireless network. 
       FIG.  7    illustrates an exemplary message diagram of setting the PDCP state variables based on the received network information for multicast services in accordance with embodiments of the current invention. A UE  701  is configured with one or more MBSs in a wireless network with a gNB  702 . Considering different scenarios before the UE receiving data packets from a configured MBS. In one scenario  711 , UE  701  is in the RRC IDLE/INACTIVE state. In another scenario, the MBS session is not activated. At step  721 , the network notifies to activate 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 broadcasted. In one embodiment, the MBS session activation notification is unicasted to each UE. In some scenarios, the MBS session becomes activated when UE  701  is the RRC IDLE/INACTIVE state, while in other scenarios, UE  701  is in the RRC CONNECTED state. The MBS session becomes activated before or after UE  701  determines to join the session. In one embodiment, UE  701  is in RRC CONNECTED before session activate. UE  701  receives unicast services simultaneously. In this case, network will transmit RRC reconfiguration message without additional session activation notification. In one embodiment, UE is in RRC IDLE/INACTIVE state before session activate. The UE needs to monitor session activation notification. After network notify session activation, UE transits to RRC CONNECTED states to receive multicast service. In one scenario, at step  712 , UE  712  enters RRC CONNECTED state. At step  722 , the MBS session is activated. 
     When the MBS session is activated and UE  701  is in the RRC CONNECTED state, the UE receives from the network the HFN and SN values for the UE PDCP state variables for the active MBS session. In one embodiment, at step  731 , UE  701  receives RRC signaling for detailed RRC configuration. The RRC signaling from the network includes one or more configuration values for the UE PDCP state variables of the MBS session, including an HFN value, such as the initial_HFN, and an SN value, such as the next_SN. In one embodiment, RRC Reconfiguration message is used from network with the indicator of HFN and the SN of the next PDCP PDU to be transmitted. At step  713 , UE  701  sets HFN to initial_HFN included in the RRC message from the network. At step  718 , UE  701  sets HFN to initial_HFN. At step  719 , UE  701  sets SN parts of RX_DELIV to next_SN. Optionally, UE  701  sets SN parts of RX_NEXT to next_SN. After finishing RRC reconfiguration including PDCP state variables initialization, at step  732 , UE  701  submits RRCReconfigurationComplete message to the network. 
       FIG.  8    illustrates an exemplary diagram for setting the UE PDCP state variables indicated by the network in accordance with embodiments of the current invention. A UE  802  is configured with one or more MBSs in a wireless network with a gNB  801 . When UE  802  establish an MRB, initial value of PDCP state variables will be transmitted in RRC signaling. At step  811 , gNB  801  sends an RRC message/signal with configuration values for PDCP state variables, including an HFN value and an SN value. At step  821 , UE  802  sets PDCP state variables based on the configuration values received from the RRC message. Assuming that the value of the initial HFN indicated by the network is X and the SN of the next PDCP PDU to be transmitted is N. The network sends data packets  810  with SN of N, N+1, N+2, N+3, and etc. 
     In one embodiment, UE may receive subsequent data PDUs earlier than RRC signaling (not shown). The UE receives MBS data packets  820  and processes the received packets based on the network configuration values for the UE PDCP state variables. In one embodiment, UE have to receive MBS data PDUs after receiving RRC signaling. The UE stores one or more PDCP PDUs in reception buffer when the one or more PDCP PDUs are received before receiving one or more configuration values for PDCP state variables from the wireless network. Subsequently, the UE processes the stored PDCP PDUs when one or more configuration values from the wireless network are received and applied. Upon receiving the RRC signal with the configuration values for the UE PDCP state variables, the UE sets HFN=X, SN parts of RX_DELIV=N. As illustrated, SN part of RX_NEXT will be updated according to the SN of received PDUs. At step  831 , if some PDUs is lost (assume[X,N] and [X,N+1] is lost), UE will update RX_NEXT to the SN of the next received PDU+1. At step  832 , the RX_NEXT is updated to N+3. At step  833 , upon determining that RX_NEXT is not equal to RX_DELIV, the UE start reordering when processing the stored PDCP PDUs. At step  834 , the RX_NEXT is update to N+4. In subsequent reception, if PDCP PDU with COUNT [X,N] is successfully received, SN parts of RX_NEXT and RX DELIV will be updated to N+1. 
       FIG.  9    illustrates an exemplary flow chart for the UE receiving one or more configuration values for UE PDCP state variables for an MBS session from the network and setting the PDCP state variables in accordance with embodiments of the current invention. At step  901 , the UE configures an MRB for one or more MBSs in a wireless network, wherein an MRB configuration enables feedback for the one or more MBSs. At step  902 , the UE initiates a join procedure to join an MBS session, wherein the MBS session is active. At step  903 , the UE receives one or more configuration values for PDCP state variables from the