WO2022141196A1

WO2022141196A1 - Methods and apparatus to deliver reliable multicast services via pdcp retransmission

Info

Publication number: WO2022141196A1
Application number: PCT/CN2020/141399
Authority: WO
Inventors: Yuanyuan Zhang; Xuelong Wang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2020-12-30
Filing date: 2020-12-30
Publication date: 2022-07-07
Also published as: CN114698018A; CN114698018B

Abstract

This disclosure describes methods and apparatus to deliver multicast services via MRB. A particular radio bearer called MRB is introduced, which is associated to a multicast logical channel and a unicast logical channel to enhance the reliability. The procedures to perform PDCP-based retransmission through PDCP status report are required.

Description

METHODS AND APPARATUS TO DELIVER RELIABLE MULTICAST SERVICES VIA PDCP RETRANSMISSION

FIELD

The present disclosure relates generally to communication systems, and more particularly, themethod to supportreliable multicast service deliveryvia PDCP Retransmissionfrom the wireless network to the UEs.

BACKGROUND

Various cellular systems, including both 4G/LTE and 5G/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 (V2X) communication, public safety (PS) communication, file download, and so on. In some cases, there may be a need for the cellular system to enable reliable multicast transmission in order to ensure the reception quality at the UE side. In these cases, it may be beneficial for the receiving UE to provide the feedback on its reception of the multicast transmission, which helps the network to perform necessary retransmission of the content to the UE. A particular radio bearer (RB) should be introduced to deliver the multicast services to UE.

In this invention, apparatus and mechanisms are sought to perform PDCP-based retransmission, so as toenhance the reliable delivery for the multicast services.

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. In MRB establishment procedure, UE establishes a PDCP entity for the MRB. UE establishes one or two RLC entities and configures two logical channel MTCH and DTCH for the MRB. For PDCP-based retransmission, in one novel aspect, when each PDCP PDU is received, UE takes a series of actions to determine whether to store the resulting PDCP SDU in the reception buffer. When the PDCP SDU is stored in the reception buffer, PDCP re-ordering and status report triggering is performed. In one embodiment, when t-Reordering expires, UE triggers PDCP status report.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a schematic system diagram illustrating an exemplary wireless network in accordance with embodiments of the current invention.

Figure 2 illustrates an exemplary NR wireless system with centralization of the upper layers of the NR radio stacks in accordance with embodiments of the current invention.

Figure 3 illustrates an exemplary Multicast radio bearer (MRB) in accordance with embodiments of the current invention.

Figure 4 illustrates an exemplary protocol stack for a MRB with PDCP-based retransmission in accordance with embodiments of the current invention.

Figure 5 illustrates an exemplary flowchart of conditions for starting and stopping t-Reordering as well as triggering PDCP status report in PDCP retransmission in accordance with embodiments of the current invention.

Figure 6 illustrates an exemplary flowchart for compiling a PDCPstatus report if triggered by t-Reordering expiry in accordance with embodiments of the current invention.

Figure 7 illustrates an exemplary process to update the state variables and trigger a PDCP status report under the control of t-Reordering in accordance with embodiments of the current invention.

Figure 8 illustrates an exemplary flowchart to control t-Reordering and PDCP status report through a process after PDCPPDUis received in accordance with embodiments of the current invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

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.

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 technology. NR may support various wireless communication services. These services may have differentquality of service (QoS) requirements e.g. latency and reliability requirements.

Figure 1 illustrates a schematic system diagram illustrating an exemplary wireless network in accordance with embodiments of the current invention. Wireless system 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, 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 1 and gNB 2 are base stations in NR, the serving area of which may or may not overlap with each other. As an example, UE1 or mobile station is only in the service area of gNB 1 and connected with gNB1. UE1 is connected with gNB1 only, gNB1 is connected with gNB 102 via Xn interface. UE2 is in the overlapping service area of gNB1 and gNB2. In one embodiment, both gNB1 and gNB2 provide the same MBMS services, service continuity during handover is guaranteed when UE 2 moves from gNB1 to gNB2 and vice versa.

Figure 1 further illustrates simplified block diagrams for UE2 and gNB2, respectively. UE has an antenna, which transmits and receives radio signals. A RF transceiver, coupled with the antenna, receives RF signals from antenna, converts them to baseband signal, and sends them to processor. In one embodiment, the RF transceiver may comprise two RF modules (not shown) . A first RF module is used for transmitting and receiving on one frequency band, and the other RF module is used for different frequency bands transmitting and receiving which is different from the first transmitting and receiving. RF transceiver also converts received baseband signals from processor, converts them to RF signals, and sends out to antenna. Processor processes the received baseband signals and invokes different functional modules to perform features in UE. Memory stores program instructions and data to control the operations of mobile station. UE also includes multiple function modules that carry out different tasks in accordance with embodiments of the current invention.

A RRC State controller, which controls UE RRC state according to network’s command and UE conditions. RRC supports the following states, RRC_IDLE, RRC_CONNECTED and RRC_INACTIVE. In one embodiment, UE can receive the 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.

A MRB controller, which 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, which manage to add, modify or remove the protocol stack for the MRB. The protocol Stack includes RLC, MAC and PHY layers. In one embodiment, the SDAP layer is optionally configured.

In one embodiment, the PDCP layer supports the functions of transfer of data, maintenance of PDCP SN, header compression and decompression using the ROHC protocol, ciphering and deciphering, integrity protection and integrity verification, timer based SDU discard, routing for split bearer, duplication, re-ordering and in-order delivery; out of order delivery and duplication discarding. 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 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 one embodiment, the MAC layer supports the following functions: mapping between logical channels and transport channels, multiplexing/demultiplexing, HARQ, radio resource selection, etc.

Similarly, gNB2 has an antenna, which transmits and receives radio signals. A RF transceiver, coupled with the antenna, receives RF signals from antenna, converts them to baseband signals, and sends them to processor. RF transceiver also converts received baseband signals from processor, converts them to RF signals, and sends out to antenna. Processor processes the received baseband signals and invokes different functional modules to perform features in gNB2. Memory stores program instructions and data to control the operations of gNB2. gNB2 also includes multiple function modules that carry out different tasks in accordance with embodiments of the current invention.

A RRC State controller, which performs access control for the UE.

A MRB controller, which 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, which manage to add, modify or remove the protocol stack for the MRB. The protocol Stack includes RLC, MAC and PHY layers. In one embodiment, the transmitting PDCP entity buffers the PDCP PDUs and performs retransmission based on the received PDCP status reports from the UEs. In one embodiment, the SDAP layer is optionally configured.

Figure 2 illustrates an exemplary NR wireless system with centralization of the upper layers of the NR radio stacks in accordance with embodiments of the current invention. Different protocol split options between Central Unit and lower layers of gNB nodes may be possible. The functional split between the Central Unit and lower layers of gNB nodes may depend on the transport layer. Low performance transport between the Central Unit and lower layers of gNB nodes can enable the higher protocol layers of the NR radio stacks to be supported in the Central Unit, 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 central unit, while RLC, MAC and PHY layers are located in the distributed unit.

Figure 3 illustrates an exemplary Multicast radio bearer (MRB) in accordance with embodiments of the current invention. Multicast radio bearer provides multicast services, which is carried by MTCH, DTCH or both of MTCH and DTCH. In one embodiment, the MRB is configured to be associated to a MTCH. In one embodiment, the MRB is configured to be associated to a DTCH. In one embodiment, the MRB is configured to be associated to a MTCH and a DTCH. In one embodiment, the MRB is configured in PTM&PTP transmission mode. One or multiple multicast Radio Bearers (MRB) 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 Point-to-Multiple Point (i.e. PTM) , Point-to -Point (i.e. PTP) transmission or combination of PTM and PTP transmission within a cell. In one embodiment, the MRB is configured in PTP transmission mode. In one embodiment, the MRB is configured in PTM mode. In one embodiment, the MRB is configured in PTM&PTP transmission mode.

The described invention operates in the context of multicast transmission in a cellular system. 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 multicastand broadcast transmission is modelled in an independent way from unicast transmission. Because of the unidirectional transmission for legacy MBMS/eMBMS service, RLC UM node is used for the transmission of multicast/broadcast 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.

There is a clear requirement on the reliable transmission for NR multicast services. But the characteristics of multicast transmission does not allow the network to ensure all the UEs to make successful reception for the services. Otherwise, the network should apply very conservative link adaptation, which may impact the radio resource utilization efficiency.

In order 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 L2 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 L2 retransmission (e.g. RLC retransmission and/or PDCP retransmission) . In addition, the feedback channel may be used for HARQ retransmission.

Figure 4 illustrates an exemplary protocol stack for a MRB with PDCP-based retransmission in accordance with embodiments of the current invention. There is one PDCP entity 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. From UE aspect, the PDCP status report to trigger PDCP retransmission is delivered to the RLC entity corresponding to DTCH. From network aspect, the PDCP PDUs subject to retransmission is delivered through DTCH. In one embodiment, the MAC entity maps the logical channel MTCH to the transport channel MCH and maps the logical channel DTCH to the transport channel DL-SCH. In one embodiment, the MAC entity maps both the logical channel MTCH and the logical channel DTCH to the transport channel DL-SCH. UE monitors the unicast and multicast transmission via different RNTIs. The ROHC function and security function is optional for multicast transmission.

Figure 5 illustrates an exemplary flowchart of conditions for starting and stoppingt-Reordering as well as triggering PDCP status report in PDCP retransmission in accordance with embodiments of the current invention. When each PDCP PDU is received, UE takes a series of actions to determine whether to store the resulting PDCP SDU in the reception buffer. If PDCP SDU is stored in the reception buffer, PDCP re-ordering and status report triggering is performed. If SN_gap is closed, i.e. t-Reordering is running and RX_DELIV ＞=RX_REORD, it means that all SDUs that are received out of order have been successfully received, UE stops and resets t-Reordering. If a new SN_gap occurs, i.e. t-Reordering is not running and RX_DELIV＜RX_NEXT, , UE updates RX_REORD to RX_NEXT and startst-Reordering. If the existing SN gap is not closed i.e. t-Reordering expires, it indicates thatSTATUS report needs to be sent. UE triggers STATUS report, updates RX_REORD to RX_NEXT and starts t_Reordering. In one embodiment, when t-Reordering expires, UE delivers the PDCP SDUs when RCVD_COUNT=RX_DELIV. UE deliver to upper layers in ascending order of the associated COUNT value after performing header decompression if not decompressed before; all stored PDCP SDU (s) with consecutively associated COUNT value (s) starting from COUNT=RE_DELIV. UE updates RX_DELIV to the COUNT value of the first PDCP SDU which has not been delivered to upper layers with COUNT value＞RX DELIV.

Figure 6 illustrates an exemplary flowchart of conditions for PDCP status reports in accordance with embodiments of the current invention. For PDCP-based retransmission, if a PDCP status report is triggered by t-Reordering expiry, UE compiles a PDCP status report. UE sets the FMC field to RX_DELIV. If RX DELIV＜RX_NEXT, UE allocates a bitmap field of length in bits equal to the number of COUNTs from and not including the first missing PDCP SDU up to and including the last out-of-sequence PDCP SDUs, rounded up to the next multiple of 8, or up to and including a PDCP SDU for which the resulting PDCP control PDU size is equal to 9000bytes, whichever comes first. UE sets in the bitmap field as ‘0’ for all PDCP SDUs that have not been received, and optionally PDCP SDUs for which decompression have failed and sets in the bitmap field as ‘1’ for all PDCP SDUs that have been received.

Figure 7 illustrates an exemplary process to update the state variables and trigger a PDCP status report under the control of t-Reordering in accordance with embodiments of the current invention.. In the initial state T0, no SDU is received, and the initial values of RX_NEXT and RX_DELIV are 0. In T1 state, when SDU with RCVD_COUNT=0 is received, RX_NEXT and RX_DELIV are updated to 1. In both states, t-Reordering is not triggered because there is no missing PDCP SDU, so RX_REORD is not initialized. In T2 state, SDUs with count = 0, 1, 2 have been received, and then SDUs with count = 17 is received. Since SDUs must be delivered to the upper layer in order, the first COUNT valueof SDU which is not delivered to the upper layers is 3, so RX_DELIV is updated to 3, and RX_NEXT is updated to 18. This state causes RX_DELIV ＜RX_NEXT to be true, so RX_REORD is updated to the COUNT value following the COUNT value associated with the current PDCP Data PDU (that is, RX_NEXT=18) andt-Reordering is started. Between T2 and T3 states, t-Reordering is in progress, and SDU with RCVD_COUNT = 3, 4, 18, 19 is received. During this period, UE only delivers the PDCP SDUs in ascending order of the associated COUNT value consecutively and updates RX_DELIV to 5.. RX_REORD = 18 remains unchanged. In T3 state, t-Reordering expires, and SN_gap has not closed, soaccording to figure 5, a PDCP STATUS report is triggered, RX_REORD is updated to RX_NEXT = 20, and t-Reordering is started. In PDCPSTATUS report, the first missing count (FMC) of T3 state is 5, UE allocates a bitmap field of length in bits equal to the number of COUNTs from and not including the first missing PDCP SDU up to and including the last out-of-sequence PDCP SDUs, rounded up to the next multiple of 8. As can be seen from the bitmap, SDUs with count = 6, 7, 8, 9, 11, 12, 13, 14, 15, 16 are missing (value is 0) , and SDU with count = 10 is correctly received (value is 1) . This shows the PDCP SDU missed in SN_gap in the T3 state.

Figure 8 illustrates an exemplary flowchart to control t-Reordering and PDCP status report through a process after PDCPPDUis received in accordance with embodiments of the current invention. After receiving PDCP PDUs, UE performs a series of steps to determine whether to store the SDUs in the reception buffer. When SDUsare stored in the receptionbuffer, UE performs PDCP reordering, i.e. checks the SN gap, updates the state variables and controls t-Reordering. If t-Reordering expires, the status report will also be sent.

It is understood that the specific order or hierarchy of blocks in the processes /flowcharts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes /flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modifications, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.

Claims

A methodto control a UE toreceive the multicast services with enhanced reliability via multicast radio bearer, wherein the MRB is associated to a unicast channel, a multicast channel or both a unicast channel and a multicast channel and the reliability is enhanced by PDCP-based retransmission through the unicast channel, comprising the steps of:

receiving a PDCP data PDU from lower layer;

storingthe resulting PDCP SDU in the reception buffer;

triggering PDCP status report when t-Reordering expires;

compiling a PDCP status report and sending it to the network.
The method of claim 1, wherein triggering PDCP status report when t-Reordering expires further comprising: updating RX_REORD to RX_NEXT, and starting t-Reordering.
The method of claim 1, wherein triggering PDCP status report when t-Reordering expires further comprising: delivering to upper layers all stored PDCP SDU (s) with consecutively associated COUNT values starting from COUNT=RE_DELIV.
The method of claim 1, wherein compiling the PDCP status report further comprising: setting the FMC field to RX_DELIV and allocating a bitmap field.