WO2023060512A1

WO2023060512A1 - Methods and apparatus to set initial pdcp state variables for multicast services

Info

Publication number: WO2023060512A1
Application number: PCT/CN2021/123856
Authority: WO
Inventors: Xiaonan Zhang; Yuanyuan Zhang; Xuelong Wang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2021-10-14
Filing date: 2021-10-14
Publication date: 2023-04-20
Also published as: CN115988427A

Abstract

This disclosure describes methods and apparatus to set initial value of PDCP state variables during MRB establishment. A particular procedure is introduced to initialize PDCP state variables according to the indicator from network. According to one embodiment, a UE receives one or more values for the state variables controlling PDCP transmit/receive operation from the network. The UE sets the state variables for PDCP transmit/reception operation according to the one or more values.

Description

METHODS AND APPARATUS TO SET INITIAL PDCP STATE VARIABLES FOR MULTICAST SERVICES

TECHNICAL FIELD

The present disclosure relates generally to communication systems, and more particularly, the method to set proper initial value of PDCP state variables for multicast services during MRB establishment.

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. When UE establishes MRB, HFN needs to be synchronized between network and UE. It is also necessary to set initial value of PDCP receiving window. In legacy system, the initial values of the variables for Transmit and Receive operation at PDCP layer are deterministic and usually starts from 0 because data transmission/reception starts after UE is in RRC CONNECTED state. In NR multicast, UE may join the multicast session after session activate, which implies that the PDCP packets transmission over the air interface has been on-going for a while. So UE can’t initialize the variables as usual for MBS and a different approach to set PDCP state variables is required.

In this invention, apparatus and mechanisms are sought to perform PDCP state variables initialization by UE according to network indication.

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 receives dedicated RRC signaling indicated by network, which contains initial HFN value and the SN of the next PDCP PDU to be transmitted. In one embodiment, the indicator is provided in RRC Reconfiguration message. In one embodiment, the indicator is provided in RRC Setup/Resume signal, according to different RRC states of UE. In one embodiment, the indicator is provided by PDCP Control PDU. When receiving indicator of initial PDCP state variables, UE sets HFN to initial HFN value and sets RX_NEXT, RX_DELIV to the COUNT value of next PDCP PDU to be transmitted by network.

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 illustrate an exemplary flowchart of conditions for RRC states of UE when multicast session activates in accordance with embodiments of the current invention.

Figure 6 illustrate an exemplary flowchart of conditions for setting initial values of PDCP states variables by RRC signaling indicated by network in accordance with embodiments of the current invention.

Figure 7 illustrates an exemplary process to set the initial values of PDCP states variables after UE is in RRC CONNECTED state in accordance with embodiments of the current invention.

Figure 8 illustrates an exemplary process to set the initial values of PDCP states variables indicated by network and the behavior of UE in case of potential packet loss in accordance with embodiments of the current invention.

Figure 9 illustrates an exemplary flowchart to receive values for PDCP state variables from network and set initial PDCP state variables through a process when multicast session activates 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 different quality 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 1and 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 MBS 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 multicast and 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. The PDCP PDUs subject to retransmission is delivered through DTCH. 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 illustrate an exemplary flowchart of conditions for RRC states of UE when multicast session activates in accordance with embodiments of the current invention. After UE joined multicast session, it can transit to RRC idle/inactive states for power saving or stay in CONNECTED state for other receptions. The multicast session may not be activated at this time. In one embodiment, UE transits to idle/inactive states. When multicast session activates, UE receives session activation notification and will transit to RRC CONNECTED state. In one embodiment, UE stays in CONNECTED state. After that, UE in CONNECTED receives RRC signaling to set initial PDCP state variables.

Figure 6 illustrate an exemplary flowchart of conditions for setting initial values of PDCP states variables by RRC signaling indicated by network in accordance with embodiments of the current invention. When UE is in CONNECTED state and session activates, UE receives RRC reconfiguration message from network for detailed RRC configuration. Network may 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, the indicator is provided by RRC Reconfiguration message. In one embodiment, the indicator is provided by RRC Setup/Resume signal according to RRC states of UE (not shown) . In one embodiment, the indicator is provided by PDCP control PDU (not shown) . The UE set HFN to the value of the HFN indicated by the network (i.e. initial-HFN) , and set SN part of RX_DELIV and RX_NEXT to the SN of the first PDU will be transmitted by the network (i.e. Next-Sn) . After UE applies the RRC configurations, UE transmits RRCReconfigurationComplete message

Figure 7 illustrates an exemplary process to set the initial values of PDCP states variables after UE is in RRC CONNECTED state in accordance with embodiments of the current invention. There may be different about the RRC states of UE before session activation. In one embodiment, UE is in RRC CONNECTED before session activate, which may because UE receives unicast services simultaneously. In this case, network will transmit RRC reconfiguration message without additional session activation notification. In one embodiment, UE is in Idle/Inactive state before session activate and needs to monitor session activation notification. After network notify session activation, UE transits to RRC CONNECTED states to receive multicast service. In any case, when session activates and UE is in RRC CONNECTED, UE may receive RRC signaling for detailed RRC configuration. 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. UE sets HFN to initial_HFN and sets SN parts of RX_NEXT, RX_DELIV to Next_Sn. After finishing RRC reconfiguration including PDCP state variables initialization, UE submits RRCReconfigurationComplete message to the network.

In one embodiment, modification can be made at clause 5.1.1 in TS 38.323

In one embodiment, modification can be made at clause 7.1

Figure 8 illustrates an exemplary process to set the initial values of PDCP states variables indicated by network and the behavior of UE in case of potential packet loss in accordance with embodiments of the current invention. When UE establish an MRB, initial value of PDCP state variables will be transmitted in RRC signaling. 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. In one embodiment, UE have to receive data PDUs after receiving RRC signaling. UE set HFN=X, SN parts of RX DELIV=RX_NEXT=N. In one embodiment, UE may receive subsequent data PDUs earlier than RRC signaling (not shown) . Since RRC configuration message is not received, the received PDUs may be stored in the reception buffer until RRC signaling, and SN part of RX_NEXT will be updated according to the SN of received PDUs.

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. 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 (i.e., N+2+1=N+3) . Since RX_DELIV<RX_NEXT, t-reordering will be triggered and PDUs will be stored in the reception buffer until missing PDUs is received or timer expires. In one embodiment, when t-reordering expires, PDUs stored in the reception buffer will be delivered to upper layer. In one embodiment, when t-reordering expires, PDCP status report is automatically triggered.

Figure 9 illustrates an exemplary flowchart to receive values for PDCP state variables from network and set initial PDCP state variables through a process when multicast session activates in accordance with embodiments of the current invention. If UE joined the multicast session and session is activated. UE receives values for PDCP state variables from network and set PDCP state variables for PDCP transmit/reception operation.

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 method to control a UE to set the initial value of PDCP state variables during MRB establishment, comprising the steps of:

receiving one or more values for the state variables controlling PDCP transmit/receive operation from the network; and

setting the state variables for PDCP transmit/reception operation according to the one or more values.
The method of claim 1, wherein the one or more values for PDCP transmit/receive operation is provided by RRCReconfiguration.
The method of claim 1, wherein the one or more values for PDCP transmit/receive operation is provided by RRCResume.
The method of claim 1, wherein the one or more values for PDCP transmit/receive operation is received by RRCSetup.
The method of claim 1, wherein the one or more values for PDCP transmit/receive operation is received by PDCP Control PDU.
The method of claim 1, wherein the values for PDCP transmit/receive operation include HFN and SN value of the first/next PDCP PDU to be transmitted from the network to the UE.
The method of claim 1, wherein the value for PDCP transmit/receive operation include COUNT value of the first/next PDCP PDU to be transmitted from the network to the UE.
The method of claim 1, further comprising setting HFN to HFN value received from the network.
The method of claim 1, further comprising setting/initialization the state variables RX_DELIV and RX_NEXT to the COUNT value of the first/next PDCP PDU to be transmitted from the network to the UE.
The method of claim 1, further comprising triggering PDCP status report when t-reordering timer expires.
The method of claim 1, further comprising storing the PDCP PDUs in the reception buffer if those PDCP PDUs arrives before the values for the state variables controlling PDCP transmit/receive operation is received or applied.
The method of claim 11, further comprising processing the stored PDCP PDUs when the values for the state variables controlling PDCP transmit/receive operation is received or applied.