CN114698018A

CN114698018A - Method and user equipment for initiating PDCP status report process

Info

Publication number: CN114698018A
Application number: CN202111561936.8A
Authority: CN
Inventors: 张园园; 王学龙
Original assignee: MediaTek Singapore Pte Ltd
Current assignee: MediaTek Singapore Pte Ltd
Priority date: 2020-12-30
Filing date: 2021-12-20
Publication date: 2022-07-01
Anticipated expiration: 2041-12-20
Also published as: WO2022141196A1; CN114698018B

Abstract

The invention provides a method for initiating a PDCP status report process, user equipment and a storage medium. Wherein the method comprises the following steps: the user equipment receives the PDCP PDU from the lower layer through the PDCP entity; storing PDCP SDUs corresponding to the received PDCP PDUs in a PDCP reception buffer; triggering a user equipment-initiated status reporting process upon detecting an initial sequence number gap based on one or more stored PDCP SDUs, wherein the user equipment-initiated status reporting process performs sequence number gap monitoring to compile a PDCP status report; and upon detecting one or more predefined trigger events, sending a PDCP status report to the wireless network, wherein the PDCP status report includes the generated updated SN gap information. By utilizing the invention, the PDCP status report initiated by the UE can be supported.

Description

Method and user equipment for initiating PDCP status report process

Technical Field

The present invention relates to wireless communications, and more particularly, to a Packet Data Convergence Protocol (PDCP) status reporting procedure.

Background

As the exponential growth of wireless data services, content delivery to large groups of mobile users has grown rapidly. Initial wireless multicast/broadcast services included streaming media services such as mobile television and IPTV. With the ever-increasing demand for large group content delivery, recent application development of mobile multicast services requires highly robust and critical communication services, such as group communication in disaster situations, and the necessity of public safety network related multicast services. The early 3GPP defined enhanced multimedia broadcast multicast service (eMBMS) in LTE standard, single-cell point-to-multipoint (SC-PTM) service and multicast-broadcast single-frequency network (MBSFN) in LTE standard. The 5G Multicast and Broadcast Service (MBS) is defined based on a unicast 5G core (5G core, 5GC) architecture. Various applications may rely on communication of multicast transmissions, such as live streaming, video distribution, vehicle-to-all (V2X) communication, Public Safety (PS) communication, file downloads, and the like. In some cases, the cellular system may need to enable reliable multicast transmission to guarantee reception quality on the UE side. Reliable transmission of some multicast traffic in NR systems requires feedback on the reception of the multicast transmission, which helps the network to make the necessary content retransmissions to the UE. A specific Radio Bearer (RB) should be introduced to provide the multicast service to the UE.

Improvements and enhancements are needed to support PDCP status reporting procedures.

Disclosure of Invention

An embodiment of the present invention provides a method for initiating a PDCP status report process, including: the user equipment receives the PDCP PDU from the lower layer through the PDCP entity; storing PDCP SDUs corresponding to the received PDCP PDUs in a PDCP reception buffer; triggering a user equipment-initiated status reporting process upon detecting an initial sequence number gap based on one or more stored PDCP SDUs, wherein the user equipment-initiated status reporting process performs sequence number gap monitoring to compile a PDCP status report; and upon detecting one or more predefined trigger events, sending a PDCP status report to the wireless network, wherein the PDCP status report includes the generated updated SN gap information.

Another embodiment of the present invention provides a user equipment, including: a transceiver to transmit and receive radio frequency signals in a wireless network; a PDCP entity for receiving a PDCP PDU from a lower layer; a PDCP control module for storing a PDCP SDU corresponding to the received PDCP PDU in a PDCP reception buffer; a PDCP status report control module to trigger a user equipment-initiated status report process when an initial sequence number gap is detected based on one or more stored PDCP SDUs, wherein the user equipment-initiated status report process performs sequence number gap monitoring to compile a PDCP status report; and a PDCP status report transmitter to transmit a PDCP status report to the wireless network upon detection of one or more predefined triggering events, wherein the PDCP status report includes the generated updated SN gap information.

Another embodiment of the present invention provides a storage medium storing a program, which when executed, causes a user equipment to perform the steps of the method for initiating a PDCP status reporting procedure proposed by the present invention.

By utilizing the invention, the PDCP status report initiated by the UE can be supported.

Drawings

Various embodiments of the present invention, which are set forth by way of example, will be described in detail with reference to the following drawings, wherein like reference numerals refer to like elements, and wherein:

figure 1 is a schematic system diagram of a wireless communication network supporting a PDCP status reporting procedure according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of an exemplary NR wireless system with a centralized upper layer of the NR radio interface stack in accordance with an embodiment of the present invention.

Fig. 3 is a flow chart of top layer PDCP status report for supporting reliable MBS and an exemplary diagram of MRB configuration according to an embodiment of the present invention.

Figure 4 is a diagram of an exemplary protocol stack for MRB configuration with PDCP based retransmission, according to an embodiment of the present invention.

Fig. 5 is an exemplary diagram of conditions and procedures for UE-initiated PDCP status reporting according to an embodiment of the present invention.

Fig. 6 is an exemplary diagram of conditions for PDCP status report according to an embodiment of the present invention.

Fig. 7 is an exemplary diagram of a process of updating a state variable and triggering a PDCP status report under control of a t-Reordering timer according to an embodiment of the present invention.

Fig. 8 is an exemplary flowchart of a UE initiating a PDCP status reporting procedure according to an embodiment of the present 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.

The present invention provides methods, apparatus, processing systems, and computer readable media for a New Radio (NR) access technology or 5G technology or other radio access technologies. NRs, etc. may support various wireless communication services such as enhanced mobile broadband for wide bandwidths, millimeter waves for high carrier frequencies, massive MTC for non-backward compatible Machine Type Communication (MTC) technologies, and/or mission critical for ultra-reliable low latency communication. These services may have delay and reliability requirements. These services may also have different Transmission Time Intervals (TTIs) to meet respective quality of service (QoS) requirements. Furthermore, these services may coexist in the same subframe.

Figure 1 is a schematic system diagram of a wireless communication network supporting a PDCP status reporting procedure according to an embodiment of the present invention. The wireless communication network 100 includes one or more fixed infrastructure elements that form a network distributed over a geographic area. The infrastructure elements 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 terminology used in the art. A base station may serve multiple mobile stations within a service area (e.g., a cell or a sector of a cell), such as within a cell or a sector of a cell. In some systems, one or more base stations are coupled to a controller, forming an access network coupled to one or more core networks, the access network being coupled to the one or more core networks. gNB 106, gNB107, and gNB 108 are base stations in a wireless network, and their service areas may or may not overlap with each other. In an embodiment, User Equipment (UE) or mobile station 101 is located in the service areas covered by gNB 106 and gNB 107. As an example, UE or mobile station 101 is located only in the service area of gNB 106 and is connected to gNB 106. UE or mobile station 102 is located only in the service area of gNB107 and is connected to gNB 107. The gNB 106 is connected to the gNB107 through an Xn interface 121. The gNB 106 is connected to the gNB 108 through an Xn interface 122. The 5G network entity 109 is connected to the gnbs 106, 107 and 108 via

NG connections

131, 132 and 133, respectively. In an embodiment, gNB 106 and gNB107 provide the same MBMS service. Service continuity during handover is guaranteed when UE 101 moves from gNB 106 to gNB107 and vice versa. The area covered by the gnbs 106 and 107 having the same MBMS service is a multicast service area for the MBMS service.

Fig. 1 further shows a simplified block schematic diagram of a base station and a mobile device/UE for multicast transmission. The gNB 106 has an antenna 156 that transmits and receives radio signals. RF transceiver circuitry 153 coupled to the antenna receives RF signals from antenna 156, converts the RF signals to baseband signals, and sends the baseband signals to processor 152. The RF transceiver 153 also converts a baseband signal received from the processor 152 into an RF signal and transmits to the antenna 156. Processor 152 processes the received baseband signals and invokes different functional blocks to perform functional features in the gNB 106. Memory 151 stores program instructions and data 154 to control the operation of gNB 106. The gNB 106 also includes a set of control modules 155 for performing functional tasks for communicating with mobile stations. These control modules may be implemented in circuitry, software, firmware, or a combination thereof.

FIG. 1 also includes a simplified block diagram of a UE, such as UE 101. The UE has an antenna 165 for transmitting and receiving radio signals. The RF transceiver circuit 163, which is coupled to the antenna, receives RF signals from the antenna 165, converts the RF signals to baseband signals, and sends the baseband signals to the processor 162. In one embodiment, the RF transceiver 163 may include two RF modules (not shown) for transmitting and receiving of different frequency bands. The RF transceiver 163 also converts a baseband signal received from the processor 162 into an RF signal and transmits to the antenna 165. The processor 162 processes the received baseband signals and invokes 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. Antenna 165 sends uplink transmissions to antenna 156 of gNB 106 and receives downlink transmissions from antenna 156 of gNB 106.

The UE 101 also includes a set of control modules for performing functional tasks. These control modules may be implemented in circuitry, software, firmware, or a combination thereof. In an embodiment, the UE also has a Radio Resource Control (RRC) state controller 197, an MBS controller 198, and a protocol stack controller 199. The RRC state controller 197 controls the UE RRC state according to a command from the network and a UE status. RRC supports the following states: RRC IDLE (RRC _ IDLE), RRC CONNECTED (RRC _ CONNECTED), and RRC INACTIVE (RRC _ INACTIVE). In an embodiment, the UE may receive multicast and broadcast services in an RRC idle/inactive state. The UE applies a Multicast Radio Bearer (MRB) setup procedure to start a session to receive the service it is interested in. The UE stops receiving the session using the MRB release procedure. MBS controller 198 controls the establishment/addition, reconfiguration/modification, and release/removal of MRBs based on different sets of conditions for MRB establishment, reconfiguration, and release. The protocol stack controller 199 is used to add, modify or remove protocol stacks for the MRB.

The protocol stack includes a Packet Data Convergence Protocol (PDCP) layer 182, a Radio Link Control (RLC) layer 183, a Medium Access Control (MAC) layer 184, and a Physical (PHY) layer (not shown). The PDCP layer (PDCP entity) 182 receives PDCP Packet Data Units (PDUs) from a lower layer (lower layer). In an embodiment, the PDCP layer supports reordering (reordering) functions 1821 of data transport, maintenance of PDCP SNs, header compression and decompression using robust header compression (ROHC) protocol, ciphering and deciphering, integrity protection and integrity verification, timer-based SDU discard, routing to separate bearers, repetition, reordering and in-order delivery, out-of-order delivery, and repeat discard. In an embodiment, a receiving PDCP entity supporting the PDCP status reporting function 1822 sends a PDCP status report upon expiration of a Reordering timer (t-Reordering). In an embodiment, the PDCP status report triggers PDCP retransmission by the network side peer-to-peer transmission PDCP entity. The PDCP control module 192 stores a PDCP Service Data Unit (SDU) of the received PDCP PDU, which has a Sequence Number (SN) and a Hyper Frame Number (HFN), in a PDCP reception buffer. The COUNT value RCVD _ COUNT of the latest received PDCP SDU [ RCVD _ HFN, RCVD _ SN ]. The PDCP status report control module 193 triggers a UE-initiated status reporting process upon detecting an initial SN gap based on one or more stored SDUs, wherein the UE-initiated status reporting process performs SN gap monitoring to compile a PDCP status report. The PDCP status report transmitter 194 transmits a PDCP status report to the wireless network upon detection of one or more predefined trigger events, wherein the PDCP status report includes information of the generated updated SN gap.

In an embodiment, a Service Data Adaptation Protocol (SDAP) layer 181 is an optional configuration. In one embodiment, the RLC layer 183 supports error correction by automatic repeat request (ARQ), segmentation and reassembly, re-segmentation, repetition detection, re-establishment, and other functions. In an embodiment, a new procedure for RLC reconfiguration is performed, which may reconfigure the RLC entity association to one or two logical channels. In another embodiment, MAC layer 184 supports mapping, multiplexing, demultiplexing, hybrid automatic repeat request (HARQ), radio resource selection, etc., between logical channels and transport channels.

Fig. 2 is a schematic diagram of an exemplary NR wireless system with a centralized upper layer of the NR radio interface stack in accordance with an embodiment of the present invention. Different protocol partitioning options are possible between the upper layer of the Central Unit (CU)/gNB node and the lower layer of the Distributed Unit (DU)/gNB node. The functional division between the central unit and the lower layers of the gbb may depend on the transport layer. Since higher protocol layers have lower performance requirements on the transport layer in terms of bandwidth, delay, synchronization and jitter, low performance transmission between the central unit and the lower layers of the gNB may enable the high protocol layers of the NR radio stack to be supported in the central unit. In one embodiment, the SDAP and PDCP layers are located in a central unit, while the RLC, MAC layers, and physical layers are located in a distributed unit. A core unit (core unit)201 is connected to a central unit 211 having a gNB upper layer 252. In an embodiment 250, the gbb upper layers 252 include a PDCP layer and an optional SDAP layer. Central unit 211 is connected to distributed

units

221, 222, and 223, where distributed

units

221, 222, and 223 correspond to

cells

231, 232, and 233, respectively. Distributed

units

221, 222, and 223 include a gbb lower layer 251. In an embodiment, the gbb lower layer 251 includes PHY, MAC, and RLC layers. In another embodiment 260, each gNB has a protocol stack 261 that includes SDAP, PDCP, RLC, MAC, and PHY layers.

Fig. 3 is a top layer PDCP status reporting flow diagram 300 for supporting a reliable MBS and an exemplary diagram of an MRB configuration according to an embodiment of the present invention. In an embodiment, the UE monitors the SNs of the PDCP SDUs and triggers a UE-initiated PDCP status report. In step 301, the UE receives PDCP PDUs from a lower layer. In step 302, the UE stores the PDCP SDU in the reception buffer. In step 303, the UE checks the SN gap according to the received data packet, and updates the state variable. In one embodiment, when a SN gap is detected, a reorder timer is started to monitor whether the SN gap is closed (closed). In step 304, the UE triggers UE-initiated PDCP status report upon detection of one or more predefined trigger events.

In an embodiment, UE-initiated PDCP status reports are used for MBS. In some systems, such as NR, NR multicast/broadcast is transmitted within the cell coverage. In an embodiment, a Multicast Control Channel (MCCH) provides information of a list of NR multicast/broadcast services having ongoing sessions transmitted on a Multicast Traffic Channel (MTCH). In the physical layer, the MTCH is scheduled by the gNB in a search space of a Physical Downlink Control Channel (PDCCH), which is scrambled by a group radio network temporary identity (G-RNTI). The UE decodes MTCH data of the multicast session in a multicast Physical Downlink Shared Channel (PDSCH). The multicast radio bearer provides multicast services, which are carried only by MTCH with the UE protocol stack, only by Dedicated Traffic Channel (DTCH) with the UE protocol stack, or both MTCH and DTCH with the UE protocol stack 301. In an embodiment 310, the MRB 311 is configured to be associated with MTCH and DTCH. To support over-the-air multicast transmission of the downlink, one or more multicast MRBs may be established to correspond to multicast streams for a particular multicast session. The MRB may perform point-to-multipoint (PTM) transmissions, point-to-point (PTP) transmissions, and a combination of PTM and PTP transmissions within a cell. Different configurations may be described as different transmission modes/channels/MRB types. In the embodiment 310 with a split (split) MRB configuration, the MRB is configured with a PTM 312 branch and a PTP 313 branch.

In legacy systems that support MBMS/eMBMS, the radio bearer structure for multicast and broadcast transmissions is modeled independently of unicast transmissions. Due to the unidirectional transmission of the conventional MBMS/eMBMS service, the transmission of the multicast/broadcast session employs an RLC Unacknowledged Mode (UM). In this case, no interaction between multicast and unicast is required for a particular UE in RRC connected state. For NR networks, providing new services over MBS requires reliable transmission. Conventional multicast transmission does not guarantee successful reception for all UEs unless very conservative link adaptation is performed, which greatly reduces resource efficiency. In order to support reliable multicast transmission of MBS, each UE receiving the service needs a feedback channel in the uplink. The receiving UE may use the feedback channel to feed back its reception status regarding the service to the network, and the network may perform necessary retransmission according to the feedback to improve the reliability of the transmission. From an uplink feedback perspective, the feedback channel may be used for layer 2 (L2) feedback, such as RLC status reports and/or PDCP status reports. In addition, a feedback channel may be used for HARQ feedback. Furthermore, the feedback should be a bi-directional channel between the UE and the network, and it is assumed that the network can use this channel to perform the required packet retransmissions. The packet retransmission is an L2 retransmission (e.g., RLC retransmission and/or PDCP retransmission). Furthermore, the feedback channel may be used for HARQ retransmissions. In an embodiment, the MRB is associated with a multicast channel that receives MBS data packets and a unicast channel that sends feedback (e.g., PDCP status reports) and receives data retransmissions.

Figure 4 is a diagram of an exemplary protocol stack for MRB configuration with PDCP based retransmission, according to an embodiment of the present invention. In PDCP based retransmission 490, there is one PDCP entity 491 per MRB. Two logical channels (i.e., MTCH and DTCH) are associated with the PDCP entity, one RLC entity for each logical channel. The RLC entity 492 corresponds to MTCH4971 and the RLC entity 493 corresponds to DTCH 4972. From the UE perspective, the PDCP status report that triggers the PDCP retransmission is delivered to the RLC entity 493 corresponding to the DTCH. From the network perspective, the PDCP protocol data unit PDUs for retransmission are delivered via DTCH. The MAC entity 494 maps the logical channels MTCH and DTCH to two transport channels, transport channel-14981 such as Multicast Channel (MCH) and downlink shared channel (DL-SCH), transport channel-24982 such as MCH and DL-SCH, respectively. The UE monitors two independent transport channels through different Radio Network Temporary Identities (RNTIs). The ROHC function and the security function are optional for multicast transmission. The RLC layer includes only segmentation and the ARQ function of the RLC layer moves to the PDCP layer. RLC 492 and RLC 493 are mapped to MAC entity 494 and used to send data packets to PHY 495.

A network entity, such as a base station/gNB, transmits MBS data packets to the N UEs on the PTM link and retransmits the MBS data packets on the PTP link associated with the PDCP protocol stack based on the feedback. And correspondingly configuring the UE based on the PDCP protocol stack to receive the MBS data packet from the base station on the PTM RB and send feedback to the base station. The scheduling of the multicast is independent of the 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. SDAP layer 401 handles QoS flows 481, including QoS flow handling 411 for UE-1 and QoS flow handling 412 for UE-N at the base station, and QoS flow handling 413 for UE at the UE. The PDCP layer 402 includes an ROHC function and a security function. The ROHC function and the security function are optional for multicast transmission. The PDCP layer 402 includes the 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 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 capabilities at the base station, including 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; and segmentation and ARQ functions at the UE, including segmentation and ARQ 435 for unicast channels and segmentation and ARQ 436 for multicast channels. RLC channel 483 is processed in RLC layer 403. The MAC layer 404 includes the functionality of scheduling and prioritization 441 at the base station, multiplexing 443 and HARQ 446 for UE-1, multiplexing 444 and HARQ 447 for UE-N at the base station; and scheduling and prioritization 442 for the UE, multiplexing 445 and HARQ 448 for the UE at the UE. The MAC layer 404 handles logical channels 484 and transport channels 485.

According to an embodiment, a PDCP status report is initiated by the UE when a SN gap is detected in a PDCP SDU receive buffer for a period of time. PDCP status reporting is not triggered by network commands or network configuration. The UE initiates a PDCP status reporting procedure based on the UE local conditions. In an embodiment, the time period is controlled by a reordering timer at the UE. The UE monitors SN of the received PDCP SDU. When a SN gap is detected in the receive buffer, the UE performs a UE-initiated PDCP status reporting procedure. The UE-initiated PDCP status report is generated upon detection of one or more predefined conditions. The UE compiles and sends a PDCP status report to the radio network. Subsequent figures illustrate the conditions and operations for the UE to initiate the PDCP status reporting procedure.

Fig. 5 is an exemplary diagram of conditions and procedures for UE-initiated PDCP status reporting according to an embodiment of the present invention. In an embodiment, the UE initiates a PDCP status report procedure and sends a PDCP status report to the network. In an embodiment, the UE uses a t-Reordering timer 502 to determine whether to trigger a PDCP status report. In another embodiment, the UE also monitors a set of SN parameters 501. In an embodiment, the UE sets the count value RX _ DELIV to the count value of the first PDCP SDU that has not been delivered to the upper layer. The COUNT value RCVD _ COUNT of the latest received PDCP SDU [ RCVD _ HFN, RCVD _ SN ]. Upon receiving each PDCP PDU, the UE takes a series of actions to determine whether to store PDCP SDUs in a receive buffer. The count value RX _ NEXT is the count value of the NEXT PDCP SDU expected to be received. The UE updates RX _ NEXT to RCVD _ COUNT + 1. When RX _ NEXT is greater than RX _ DELIV, a SN gap is detected. The reordering count value RX _ REORD is set to RX _ NEXT when it detects a SN gap and is updated when more data packets are received. The UE performs PDCP status reporting according to the count values (including RX _ DELIV, RX _ NEXT and RX _ REORD). If the PDCP SDUs are stored in the reception buffer, a PDCP reordering and status report triggering is performed. In another embodiment, the reordering count value RX _ REORD is set to RX _ NEXT when the PDCP status report is transmitted.

For conditional 511, the UE determines whether an SN gap is closed, e.g., RX _ DELIV > -RX _ REORD, and a t-Reordering timer is running. When the t-Reordering timer is still running, the SN gap is not closed, which indicates that all SDUs received out of order have been successfully received. If the condition 511 is true, the UE stops and resets the t-Reordering timer in step 512. For conditional 521, the UE determines whether a new SN gap occurs, i.e., RX _ DELIV < RX _ NEXT, and the t-Reordering timer is not running. If condition 521 is true, the UE updates RX _ REORD to RX _ NEXT in step 522 and starts a t-Reordering timer in step 523. For conditional 531, the UE determines whether the existing SN gap is not closed and the t-Reordering timer expires. If conditional 531 is true, it indicates that a UE-initiated PDCP status report needs to be sent. In step 532, the UE triggers a status report, updates RX _ REORD to RX _ NEXT in step 533, and starts a t-Reordering timer in step 534. In an embodiment, the UE delivers PDCP SDUs to an upper layer when the t-Reordering timer expires. If not, the UE transmits to the upper layer in ascending order of the associated count value after performing header decompression. Starting from the COUNT value RX _ DELIV, all stored PDCP SDUs with consecutive associated RCVD _ COUNT values are delivered to the upper layer. The UE updates RX _ DELIV to a count value of the first PDCP SDU that has not been transferred to the upper layer, wherein the count value > RX _ DELIV.

Fig. 6 is an exemplary diagram of conditions for PDCP status report according to an embodiment of the present invention. In an embodiment, the UE initiates PDCP status reporting based on one or more predefined trigger events. The PDCP status report triggers PDCP-based retransmission. In step 601, the UE monitors one or more predefined trigger events. The triggering event is one or more predefined/preconfigured events including expiration 611 of a t-Reordering timer, detection 612 of a SN gap, and enabling 613 of the UE's ability to initiate PDCP status reporting. If one or more predefined trigger events trigger the PDCP status report, the UE compiles the PDCP status report in step 621. The PDCP status report is sent to the network to trigger PDCP retransmission.

Fig. 7 is an exemplary diagram of a process of updating a state variable and triggering a PDCP status report under the control of a t-Reordering timer according to an embodiment of the present invention. In the initial state T0701, SDUs are not received, and the PDCP SDU buffer is empty. The initial values for RX _ NEXT and RX _ DELIV are: RX _ NEXT ═ 0 and RX _ DELIV ═ 0. In the T1 state 702, when SDUs with a count value of 0 are received, RX _ NEXT and RX _ DELIV are updated to RX _ NEXT 1 and RX _ DELIV 1. In states 701 and 702, the timer t-Reordering is not triggered, and RX _ REORD is not initialized because no PDCP SDUs are lost. In another embodiment, RX _ REORD is set to a non-initialized value. In the T2 state 703, an SDU with a count value of 0, 1, 2 has been received, and then an SDU with a count value of 17 has been received. Since SDUs must be delivered to an upper layer in order, the first count value, which is not delivered to SDUs, is '3'. The UE updates RX _ DELIV to 3 and RX _ NEXT to 18. At T2703, the UE detects the initial SN gap 736 when RX _ DELIV < RX _ NEXT. RX _ REORD is updated to a count value after the count value associated with the current PDCP SDU, i.e., RX _ NEXT ═ 18. The UE detects a trigger event condition where there is an SN gap and no t-Reordering timer is running. At step 737, a t-Reordering timer is started. Between the T2703 and T3704 states, a T-Reordering timer is running and SDUs with a count value of 3, 4, 10, 18, 19 are received. During this time, the UE sequentially transfers PDCP SDUs only in ascending order of the associated count value, and updates RX _ DELIV to 5. RX _ REORD is updated to RX _ NEXT ═ 20. At state 704 of T3, the T-Reordering timer expires. Since RX _ DELIV-5 and RX _ REORD-20, the updated SN gap 746 is not closed, PDCP status report is triggered at step 748, according to condition 531 of fig. 5. At step 749, the t-Reordering timer is restarted. The exemplary example in the figure does not show that before the t-Reordering timer expires, if the SN gap is closed, i.e. RX _ DELIV equals RX _ REORD, the t-Reordering timer stops.

In an embodiment, the PDCP status report includes information of the generated updated SN gap. In an embodiment 750, the updated SN gap information includes a First Missing Count (FMC) and a bitmap (bitmap). For example, the FMC for T3 status 704 is "5". The bit length allocated by the bitmap is equal to the count from the first missing PDCP SDU to the last out-of-sequence PDCP SDU (excluding the first missing PDCP SDU but including the last out-of-sequence PDCP SDU), rounded up (round up) to a multiple of "8"; or at most one PDCP SDU with a PDCP control PDU size equal to 9000 bytes, whichever comes first. The UE sets all PDCP SDUs not yet received and, optionally, PDCP SDUs that failed decompression to "0" in the bitmap field. For all received PDCP SDUs, the UE is set to "1" in the bitmap field. For example, when FMC is 5, the first bit of the bitmap starts with a count value of 6. The SDU with a count value of 6, 7, 8, 9, 11, 12, 13, 14, 15, 16 is missing and the corresponding bit in the bitmap is set to "0". The SDU count is 10, 17, 18, 19 received correctly and the corresponding bit in the bitmap is set to "1". Padding (padding) may be inserted when it is desired to round the bitmap to a multiple of "8".

Fig. 8 is an exemplary flowchart of a UE initiating a PDCP status reporting procedure according to an embodiment of the present invention. In step 801, the UE receives PDCP PDUs from a lower layer through a PDCP entity. In step 802, the UE stores PDCP SDUs corresponding to the received PDCP PDUs in a PDCP reception buffer. In step 803, the UE triggers a UE-initiated status reporting process when an initial SN gap is detected based on one or more stored SDUs, wherein the UE-initiated status reporting process performs SN gap monitoring to compile a PDCP status report. In step 804, the UE sends a PDCP status report to the wireless network after detecting one or more predefined trigger events, wherein the PDCP status report includes the generated updated SN gap information.

In one embodiment, a storage medium (e.g., a computer-readable storage medium) stores a program that, when executed, causes a UE to perform various embodiments of the present invention.

Although the present invention has been described in connection with the specified embodiments for the purpose of illustration, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of the various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.

Claims

1. A method of initiating a packet data convergence protocol status reporting process, comprising:

the user equipment receives a PDCP packet data unit PDU from a lower layer through a packet data convergence protocol PDCP entity;

storing a PDCP service data unit SDU corresponding to the received PDCP PDU in a PDCP receive buffer;

triggering a user equipment-initiated status reporting process upon detecting an initial sequence number gap based on one or more stored PDCP SDUs, wherein the user equipment-initiated status reporting process performs sequence number gap monitoring to compile a PDCP status report; and

upon detecting one or more predefined triggering events, a PDCP status report is sent to the wireless network, wherein the PDCP status report includes the generated updated SN gap information.

2. The method of initiating a packet data convergence protocol status report process of claim 1, wherein the received PDCP PDUs are multicast data packets for a multicast broadcast service received from a multicast radio bearer.

3. The method of initiating a packet data convergence protocol status reporting process according to claim 2 wherein the multicast broadcast service is associated with a multicast channel for receiving multicast broadcast service data packets and a unicast channel for sending feedback and receiving data retransmissions, and wherein the PDCP status report is sent to the wireless network over the associated unicast channel.

4. The method of initiating a packet data convergence protocol status report procedure according to claim 1, wherein the stored PDCP SDUs having consecutive sequence numbers are transferred to an upper layer, a transfer count value RX DELIV is set to a count value of a first PDCP SDU which has not been transferred to the upper layer, and wherein the initial sequence number gap is detected when RX _ NEXT is greater than RX DELIV.

5. The method of initiating a packet data convergence protocol status reporting process according to claim 4, wherein a reordering count value, RX _ REORD, is set to RX _ NEXT upon detection of the initial sequence number gap.

6. The method for initiating a packet data convergence protocol status reporting process according to claim 4, wherein a reordering count value, RX _ REORD, is set to RX _ NEXT when sending the PDCP status report.

7. The method of initiating a packet data convergence protocol status report procedure according to claim 4, characterized in that when RX _ DELIV is detected to be equal to RX _ NEXT, the UE detects that the sequence number slot is closed and resets the reordering count value RX _ REORD.

8. The method of initiating a packet data convergence protocol status report process according to claim 1, characterized in that the user equipment initiated status report process starts a reordering timer when the initial sequence number gap is detected and the reordering timer is not running.

9. The method of initiating a packet data convergence protocol status report process according to claim 8, characterized in that the one or more predefined triggering events comprise an expiration of the reordering timer.

10. The method of initiating a packet data convergence protocol status report process according to claim 8, wherein the user equipment detects sequence number gap closure and stops the reordering timer.

11. The method of initiating a packet data convergence protocol status report process according to claim 8, wherein the updated sequence number gap is based on a count value of a first PDCP SDU that has not been transferred to an upper layer and RX _ NEXT, and wherein the PDCP status report further comprises a bitmap of a reception status of PDCP SDUs between a most recently transferred consecutive PDCP SDU and RX _ NEXT.

12. A user equipment, comprising:

a transceiver to transmit and receive radio frequency signals in a wireless network;

a Packet Data Convergence Protocol (PDCP) entity for receiving a PDCP Packet Data Unit (PDU) from a lower layer;

a PDCP control module for storing a PDCP service data unit SDU corresponding to the received PDCP PDU in a PDCP reception buffer;

a PDCP status report control module to trigger a user equipment-initiated status reporting procedure when an initial sequence number gap is detected based on one or more stored PDCP SDUs, wherein the user equipment-initiated status reporting procedure performs sequence number gap monitoring to compile a PDCP status report; and

a PDCP status report transmitter to transmit a PDCP status report to the wireless network upon detection of one or more predefined trigger events, wherein the PDCP status report includes the generated updated SN gap information.

13. The user equipment as claimed in claim 12, wherein the stored PDCP SDUs having consecutive sequence numbers are transferred to an upper layer, a transfer count value RX _ DELIV is set to a count value of a first PDCP SDU which has not been transferred to the upper layer, and wherein the initial sequence number gap is detected when RX _ NEXT is detected to be greater than RX _ DELIV.

14. The UE of claim 13, wherein a reordering count value RX _ REORD is set to RX _ NEXT when the initial sequence number gap is detected.

15. The user equipment of claim 13, wherein a reordering count value RX _ REORD is set to RX _ NEXT when transmitting the PDCP status report.

16. The UE of claim 13, wherein the UE detects that a sequence number slot is closed and resets a reordering count value RX REORD when RX _ DELIV is detected to be equal to RX _ NEXT.

17. The UE of claim 12, wherein the UE-initiated status reporting procedure starts a reordering timer when the initial sequence number gap is detected and the reordering timer is not running.

18. The UE of claim 17, wherein the one or more predefined trigger events comprise an expiration of the reordering timer.

19. The UE of claim 17, wherein the UE detects that a sequence number gap is closed and stops the reordering timer.

20. The UE of claim 17, wherein the updated sequence number gap is based on a count value of a first PDCP SDU that has not been transmitted to an upper layer and a count value RX _ NEXT of a NEXT PDCP SDU expected to be received, and wherein the PDCP status report further comprises a bitmap of a reception status of PDCP SDUs between a most recently transmitted consecutive PDCP SDU and RX _ NEXT.

21. A storage medium storing a program which, when executed, causes a user equipment to perform the steps of the method of initiating a packet data convergence protocol status report procedure of any one of claims 1-11.