WO2021143869A1

WO2021143869A1 - Uplink feedback and retransmission for new radio (nr) multicast services

Info

Publication number: WO2021143869A1
Application number: PCT/CN2021/072230
Authority: WO
Inventors: Xuelong Wang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2020-01-16
Filing date: 2021-01-15
Publication date: 2021-07-22
Also published as: WO2021142702A1

Abstract

Apparatus and methods are provided for uplink feedback and retransmission for NR multicast services. In one novel aspect, an enhanced RLC UM mode mimicking an RLC AM mode is use for multicast feedback and retransmission. The enhanced RLC UM mode supports buffering the transmitted RLC packets for retransmission in the unicast manner and discarding packets to slide the transmission window. The enhanced RLC UM mode supports to move one or more transmitted packets from the transmission buffer to the associated unicast RLC AM entity for retransmission. In one embodiment, the UE is configured to establish an associated unicast RLC channel corresponding to one or more MRBs to provide uplink feedback with RLC Status Report PDU. The associated unicast RLC channel is configured for retransmission of non-acknowledged RLC packets for the multicast service in unicast manner.

Description

UPLINK FEEDBACK AND RETRANSMISSION FOR NEW RADIO (NR) MULTICAST SERVICES

CROSS REFERENCE TO RELATED APPLICATIONS

This application is filed under 35 U.S.C. §111 (a) and is based on and hereby claims priority under 35 U.S.C. §120 and §365 (c) from International Application No. PCT/CN2020/072426, titled “Methods and Apparatus Uplink Feedback and Retransmission for NR Multicast Services, ” with an international filing date of January 16, 2020. The disclosure of each of the foregoing documents is incorporated herein by reference.

FIELD OF THE INVENTION

The disclosed embodiments relate generally to wireless communication, and, more particularly, to uplink feedback and retransmission for new radio (NR) multicast services.

BACKGROUND OF THE INVENTION

With the exponential growth of wireless data services, content delivery to large mobile user groups has grown rapidly. Initial wireless multicast/broadcast services include streaming services such as mobile TV and IPTV. With the growing demand for large group content delivery, recent application development for 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 LTE standard defines enhanced multimedia broadcast multicast services eMBMS. The single-cell point to multipoint (SC-PTM) services and multicast-broadcast single-frequency network (MBSFN) are defined. The early multicast/broadcast services, such as mobile TV services, do not require ACK/NACK-based feedback for the multicast data packets. With the increasingly demand for multicast services for critical communication services such as involving disaster situations and public safety services, the necessity of a reliable multicast data delivery requires improvement of the existing mobile multicast/broadcast services. Traditionally, the MBMS service is supported via RLC unacknowledged mode (UM) for RRC-connected UE at higher layer of the Uu interface. The high layer-based feedback is not possible for MBMS. High layer-based retransmission is not possible for MBMS. For RLC UM mode, when indicated from, such as the PDCP layer, to discard a particular RLC SDU, the transmitting UM RLC entity shall discard the indicated RLC SDU, if neither the RLC SDU nor a segment thereof has been submitted to the lower layers. For RLC UM mode, the RLC UM entity submits UMD PDU to lower layer. The UMD PDU may contain a segment or RLC SDU or a whole RLC SDU. It is assumed that RLC UM entity remove the data from its buffer when he delivers RLC SDU, or RLC SDU segment to the lower layer, since no acknowledgement from the peer RLC entity is expected. The existing multicast services without feedback and without retransmission does not meet the requirements for the new multicast services that requires high reliability.

Improvements and enhancements are required to achieve reliable transmission of the NR multicast services via uplink (UL) feedback and retransmission at higher layer of the Uu interface.

SUMMARY OF THE INVENTION

Apparatus and methods are provided for uplink feedback and retransmission for NR multicast services. In one novel aspect, an enhanced RLC UM mode mimicking an RLC AM mode is use for multicast feedback and retransmission. The enhanced RLC UM mode supports buffering the transmitted RLC packets for retransmission in the unicast manner and discarding packets to slide the transmission window. The enhanced RLC UM mode supports to move one or more transmitted packets (i.e. RLC SDU, and/or RLC SDU segments) from the transmission buffer to the associated unicast RLC AM entity for retransmission. In one embodiment, the UE is configured to establish an associated unicast RLC channel corresponding to one or more MRBs to provide uplink feedback with RLC Status Report PDU. Polling Request sent over the associated unicast RLC channel by the network to pull the RLC Status Report PDU. The associated unicast RLC channel is configured for retransmission of non-acknowledged RLC packets for the multicast service in unicast manner.

In one embodiment, the UE establishes a MRB to receive multicast data packets for a multicast service from a serving gNB in the NR network, establishes an associated unicast radio link control (RLC) channel for the MRB, performs an uplink feedback the multicast data packets received on the MRB over the associated RLC channel, and receives retransmitted multicast data packets for the multicast service from the gNB through the associated unicast RLC channel. In one embodiment, the associated unicast RLC channel is established with the MRB based on a radio resource control (RRC) configuration message from the serving gNB. In another embodiment, the associated unicast RLC channel is associated with a plurality of multicast services received by the UE. In yet another embodiment, the associated unicast RLC channel is an acknowledged mode (AM) RLC with a corresponding unicast AM RLC entity at the serving gNB. In one embodiment, the UL feedback for the multicast data packets are transmitted over the associate unicast RLC channel, and wherein the UL feedback includes an RLC status report packet data unit (PDU) . In another embodiment, the RLC status report PDU is identified by a bearer ID for the MRB or a logic channel ID for the MRB. In one embodiment, the RLC status report PDU is triggered by a Polling Request from the serving gNB received over the associated unicast RLC channel. In another embodiment, the Polling Request is identified by a bearer ID for the MRB or a logic channel ID for the MRB. In one embodiment, one or more retransmitted non-acknowledged RLC packets received from the serving gNB over the associated unicast RLC channel is identified by a bearer ID for the MRB or a logic channel ID for the MRB. In another embodiment, a RLC entity for the MRB is an enhanced unacknowledged mode (eUM) RLC.

This summary does not purport to define the invention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.

Figure 1 is a schematic system diagram illustrating an exemplary NR wireless network that supports uplink feedback and retransmission for NR multicast services in accordance with embodiments of the current invention.

Figure 2 illustrates an exemplary NR wireless system with centralized higher layers of the NR radio interface stacks and UE stack with multicast protocol and unicast protocol in accordance with embodiments of the current invention.

Figure 3 illustrates exemplary diagrams for NR multicast radio bearer model with one multicast service in accordance with embodiments of the current invention.

Figure 4 illustrates exemplary diagrams for NR multicast radio bearer model with two multicast services in accordance with embodiments of the current invention.

Figure 5 illustrates an exemplary flow diagram of performing feedback and retransmission for NR multicast service in accordance with embodiments of the current invention.

Figure 6 illustrates an exemplary flow chart of the UE performing feedback and retransmission for NR multicast service in accordance with embodiments of the current invention.

DETAILED DESCRIPTION

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

3GPP specified the basic eMBMS with the focus on multicast-broadcast single-frequency network (MBSFN) . Both MBSFN and SC-PTM transmission are supported based on the dedicated MBMS system architecture, where a multi-call/multicast coordination entity (MCE) is located between radio access network (RAN) and core network (CN) . MCE is responsible for the determination of the transmission mode of MBSFN or SC-PTM. Both the MBSFN and SC-PTM rely on the specific MBMS radio bearer. In LTE SC-PTM is characterized by that MBMS is transmitted in the coverage of a single cell. One SC-multicast control channel (MCCH) and one or more SC-multicast traffic channels (MTCHs) are mapped on downlink shared channel (DL-SCH) . The scheduling is done by the base station. The SC-MCCH and SC-MTCH transmissions are each indicated by a logical channel specific radio network temporary identifier (RNTI) on physical downlink control channel (PDCCH) A one-to-one mapping is configured between temporary mobile group identity (TMGI) and group RNTI (G-RNTI) used for the reception of the DL-SCH to which a SC-MTCH is mapped. A single transmission is used for DL-SCH on which SC-MCCH or SC-MTCH is mapped. Neither blind HARQ repetitions nor RLC quick repeat is configured for mapped DL-SCH. With the rapid growth of the multicast services in the NR network, uplink feedback and retransmission for the NR multicast services are needed.

Figure 1 is a schematic system diagram illustrating an exemplary NR wireless network that supports uplink feedback and retransmission for NR multicast services in accordance with embodiments of the current invention. NR wireless system 100 includes one or more fixed base infrastructure units forming a network distributed over a geographical region. The base unit may also be referred to as an access point, an access terminal, a base station, a Node-B, an eNode-B (eNB) , a gNB, or by other terminology used in the art. The network can be a homogeneous network or heterogeneous network, which can be deployed with the same frequency or different frequency. gNB 101 and gNB 102 are base stations in the NR network, the serving area of which may or may not overlap with each other. The backhaul connection, such as 136, connects the non-co-located receiving base units, such as gNB 101 and gNB 102. These backhaul connections can be either ideal or non-ideal. gNB 101 connects with gNB 102 via Xnr interface.

NR wireless network 100 also includes multiple communication devices or mobile stations, such user equipments (UEs) such as

UEs

111, 112, 113, 114, 116, 117, 121, and 122. The exemplary mobile devices in wireless network 100 have sidelink capabilities. The mobile devices can establish one or more unicast connections with one or more base stations. For example, UE 111 has unicast connection 131 with gNB 101.

UEs

114 and 115 connect with gNB 101 with

unicast connections

133 and 134, respectively. Similarly, UEs 121 connects with gNB 102 with unicast connection 132.

In one novel aspect, UL feedback and retransmission are supported for NR multicast services. A multicast service-1 is provided by gNB 101 and gNB 102.

UEs

111, 112 and 113 receive multicast services from gNB 101.

UEs

121 and 122 receive multicast services from gNB 102. Multicast service-2 is provided by gNB 101 to the UE group of

UEs

116, 117, and 118. Multicast service-1 and multicast service-2 are delivered in multicast mode with a multicast radio bearer (MRB) configured by the NR wireless network. The receiving UEs receive data packets of the multicast service through corresponding MRB configured.

Figure 1 further illustrates simplified block diagrams of a base station and a mobile device/UE for adaptation handling for L2-based sidelink relay. gNB 102 has an antenna 156, which transmits and receives radio signals. An RF transceiver circuit 153, coupled with the antenna, receives RF signals from antenna 156, converts them to baseband signals, and sends them to processor 152. RF transceiver 153 also converts received baseband signals from processor 152, converts them to RF signals, and sends out to antenna 156. Processor 152 processes the received baseband signals and invokes different functional modules to perform features in gNB 102. Memory 151 stores program instructions and data 154 to control the operations of gNB 102. gNB 102 also includes a set of control modules 155 that carry out functional tasks to communicate with mobile stations.

Figure 1 also includes simplified block diagrams of a relay UE, such as UE 111. The UE has an antenna 165, which transmits and receives radio signals. An RF transceiver circuit 163, coupled with the antenna, receives RF signals from antenna 165, converts them to baseband signals, and sends them to processor 162. In one embodiment, the RF transceiver may comprise two RF modules (not shown) . A first RF module is used for HF transmitting and receiving, and the other RF module is used for different frequency bands transmitting and receiving which is different from the HF transceiver. RF transceiver 163 also converts received baseband signals from processor 162, converts them to RF signals, and sends out to antenna 165. Processor 162 processes the received baseband signals and invokes different functional modules to perform features in the UE 111. Memory 161 stores program instructions and data 164 to control the operations of the UE 111. Antenna 165 sends uplink transmission and receives downlink transmissions to/from antenna 156 of gNB 102.

The UE also includes a set of control modules that carry out functional tasks. These control modules can be implemented by circuits, software, firmware, or a combination of them. A multicast radio bearer (MRB) handler 191 establishes an MRB to receive multicast data packets for a multicast service from a serving gNB in the NR network. A unicast channel handler 192 establishes an associated unicast radio link control (RLC) channel for the MRB. A feedback handler 193 performs an uplink (UL) feedback for the multicast data packets received on the MRB over the associated RLC channel. A retransmission handler 194 receives retransmitted multicast data packets for the multicast service from the gNB through the associated unicast RLC channel.

Figure 2 illustrates an exemplary NR wireless system with centralized higher layers of the NR radio interface stacks and UE stack with multicast protocol and unicast protocol in accordance with embodiments of the current invention. Different protocol split options between central unit (CU) and distributed unit (DU) of gNB nodes may be possible. The functional split between the CU and DU of gNB nodes may depend on the transport layer. Low performance transport between the CU and DU of gNB nodes can enable the higher protocol layers of the NR radio stacks to be supported in the CU, since the higher protocol layers have lower performance requirements on the transport layer in terms of bandwidth, delay, synchronization and jitter. In one embodiment, SDAP and PDCP layer are located in the CU, while RLC, MAC and PHY layers are located in the DU. A core unit 201 is connected with one central unit 211 with gNB higher layer 252. In one embodiment 250, gNB higher layer 252 includes the PDCP layer and optionally the SDAP layer. Central unit 211 connects with distributed

units

221, 222, and 221. Distributed

units

221, 222, and 223 each corresponds to a

cell

231, 232, and 233, respectively. The DUs, such as 221, 222 and 223 includes gNB lower layers 251. In one embodiment, gNB lower layers 251 include the PHY, MAC and the RLC layers. In another embodiment 260, each gNB has the protocol stacks 261 including SDAP, PDCP, RLC, MAC and PHY layers.

Similarly, a UE 202 has a protocol stack 281 including the PHY, MAC, RLC, PDCP, and optional SDAP layers. For RRC_CONNECTED mode UE, the multicast radio bearer (MRB) 282 is added through RRC reconfiguration for a multicast service when the UE initiates the joining procedure at the higher layers. The base station is notified by the CN the start of the corresponding session. When the multicast PDU session starts, a QoS flow is created by the gNB, and a SDAP entity is also created to map the flow to a specific MRB. To establish a corresponding MRB, a PDCP entity is created with specific security configuration. An RLC entity is also created. The MAC configuration is configured with a specific multicast logical channel MTCH. A new LCID is allocated for this new MTCH. In one embodiment, a portion of the LCID field is reserved for the MTCH at MAC layer. The configuration of SDAP/PDCP/RLC/MAC is sent to UE during RRC Reconfiguration procedure for this MRB. The UE establishes the MRB and sends the RRC Reconfiguration Complete message to the gNB. The security configuration of MRB can be enforced by PDCP. Alternatively, there is no security configuration for MRB. The security is enforced at higher layer or service application layer. When the security configurations, such as the ciphering and/or integrity protection of MRB is enforced by PDCP entity, the security configuration of PDCP entity is common for all the UEs receiving the multicast services. The same robust header compression (ROHC) configuration and selected ROHC mode are applicable to all the UEs receiving the multicast service. A unicast stack 283 is established for simultaneous unicast services. In one embodiment, an associated RLC protocol stack 284 is established for feedback and retransmission functions.

Figure 3 illustrates exemplary diagrams for NR multicast radio bearer model with one multicast service in accordance with embodiments of the current invention. A UE with a radio bearer configuration 310 is connected with a gNB with a radio bearer configuration 350. The UE is configured with a unicast bearer 318 and a multicast radio bearer 319. The gNB is configured with a unicast bearer 358 and a multicast bearer 359. Unicast bearer 318 of the UE has a MAC entity 311, an RLC UM unicast entity 341, a PDCP unicast entity 342 and an SDAP unicast entity 343. Similarly, unicast bearer 358 of the gNB has a MAC entity 351, an RLC UM unicast entity 381, a PDCP unicast entity 382 and an SDAP unicast entity 383.

In one novel aspect, an associated unicast RLC channel in RLC AM mode is configured to assist the NR multicast radio bearer in RLC UM mode. The associated (unicast) RLC channel can be named by other term but with the same functionality as described in this invention. The associated unicast RLC channel operates based on the establishment of a specific associated unicast RLC AM entities, such as an associated unicast RLC AM entity 321 of the UE and an associated unicast RLC AM entity 361 of the gNB. The associated unicast RLC channel is configured for each UE during NR multicast radio bearer establishment via RRC message to RRC connected mode UE. The associated RLC channel for the UE includes the associated unicast RLC AM entity 321, the PDCP multicast entity 332, and the SDAP multicast entity 333. The associated RLC channel for the gNB includes the associated unicast RLC AM entity 361, the PDCP multicast entity 372, and the SDAP multicast entity 373. The MRB 319 for the UE includes the RLC eUM multicast entity 331, the PDCP multicast entity 332, and the SDAP multicast entity 333. The MRB 359 for the gNB includes the RLC eUM multicast entity 371, the PDCP multicast entity 372, and the SDAP multicast entity 373. The unicast DRB 393 is formed with the UE unicast bearer 318 and the gNB unicast bearer 358. The multicast bearer 392 is formed with the UE multicast bearer 319 and the gNB multicast bearer 359. The associated unicast RLC channel 391 is formed with the UE associated RLC channel and the gNB associated RLC channel.

In one embodiment, the RLC is enhanced UM (eUM) RLC, such as an RLC eUM multicast entity 331 for the UE and an RLC eUM multicast entity 371 for the gNB. For Downlink, the gNB sends the Polling request to the UE through the associated unicast RLC channel. For Uplink, the UE sends the RLC Status Report PDU response to the gNB through the associated unicast RLC channel. The associated unicast RLC channel serves as the Uplink feedback channel to the NR multicast radio bearer (i.e. MRB) . The intention of establishing this association between unicast RLC channel and MRB is to mimic the RLC AM mode operation for NR MRB.

In one embodiment, the associated unicast RLC channel is also used as the backup downlink (DL) transmission channel for the configured NR multicast radio bearer for a particular UE. When one or more RLC service data units (SDUs) , and/or one or more RLC SDU segments, cannot be successfully received by the UE, the gNB performs retransmission of these packets via the unicast. The packets are sent over the associated unicast RLC channel in AM mode.

The RLC UM mode configured for multicast radio bearer is not a traditional RLC UM mode, and it is an enhanced RLC UM mode. Correspondingly, the RLC UM entities for MRB at the UE and the gNB are enhanced RLC UM entities. The enhanced RLC UM mode requires the transmitter, the gNB, to buffer the transmitted packets, such as RLC SDU and RLC SDU segment, in the buffer for a period after transmission. In a first embodiment, the transmitted packets is cleared from the buffer in case the packets are acknowledged by all of the UEs receiving the multicast service, through the RLC Status Report via associated RLC channels. The transmission window is sliding forward when the packets are acknowledged by all UEs. In a second embodiment, the transmission window is sliding forward under the control of a configured timer. A discard timer is configured per transmitted packet at the RLC layer. In a third embodiment, the transmission window is sliding forward under the counting of the number of packets transmitted. When a predefined number M of packets (e.g. N, N+1, N+2, …, N+M) was transmitted, the previous packets (e.g. N-M, N-M-1, etc. ) are discarded. The value M of the number of packets transmitted is configurable. The enhanced RLC UM entity, such as RLC eUM multicast entity 331 for the UE and RLC eUM multicast entity 371 for the gNB, moves one or more transmitted packets (i.e. RLC SDU, and/or RLC SDU segments) from its buffer during packet discarding to the associated unicast RLC AM entity, such as associated unicast RLC AM entity 321 for the UE and associated unicast RLC AM entity 361 for the gNB, for retransmission. The uplink feedback at RLC layer for MRB enables the gNB to retransmit non-acknowledged RLC packets to one or more UEs when multicast transmission from the gNB to the one or more UEs are not successfully received at the one or more UEs. The one or more UEs continue to receive the new RLC packets from MRB RLC UM multicast entity, and/or other multicast radio bearer (s) . The associated unicast RLC AM entity 321 needs to deliver the received RLC packets to MRB RLC UM multicast entity 331 for packet assembly and/or in-order delivery to the PDCP layer. Packet assembly occurs at MRB RLC UM multicast entity 331 when some of the RLC SDU segments are already received previously by MRB RLC UM entity and then additional RLC SDU segments received from the associated unicast RLC AM entity is delivered to MRB RLC UM entity for assembly. Non-segmented RLC SDUs are delivered to PDCP layer directly by the associated unicast RLC AM entity if no requirement for in-order delivery to PDCP layer at the UE. The associated unicast RLC channel transmits the data in AM mode. The RLC Polling Request PDU of unicast data and the RLC Status Report PDU of unicast data are also transmitted over the associated unicast RLC channel. The transmitted data and control PDU(s) over this associated RLC channel include the RLC Polling Request of MRB data, the RLC Status Report PDU of MRB data, the RLC Polling Request of unicast data, the RLC Status Report PDU of unicast data, and the unicast data for both retransmission and new transmission.

Figure 4 illustrates exemplary diagrams for NR multicast radio bearer model with two multicast services in accordance with embodiments of the current invention. When the UE is configured with multiple multicast radio bearers to receive multiple multicast services, a single associated unicast RLC channel is established to provide the uplink feedback. The UE maintains the one-to-many mapping between associated unicast RLC channel and MRBs. A UE with a radio bearer configuration 410 is connected with a gNB with a radio bearer configuration 450. The UE is configured with a multicast radio bearer 418 and a multicast radio bearer 419. The gNB is configured with a multicast radio bearer 458 and a multicast radio bearer 459. Multicast bearer 418 of the UE has a MAC entity 411, an RLC eUM unicast entity 441, a PDCP unicast entity 442 and an SDAP unicast entity 443. Multicast bearer 419 of the UE has a MAC entity 411, an RLC eUM unicast entity 431, a PDCP unicast entity 432 and an SDAP unicast entity 433. Similarly, multicast bearer 459 of the gNB has a MAC entity 451, an RLC UM unicast entity 471, a PDCP unicast entity 472 and an SDAP unicast entity 473.

In one novel aspect, an associated unicast RLC channel in RLC AM mode is configured to assist the NR multicast radio bearer in RLC UM mode. The associated unicast RLC channel operates based on the establishment of a specific associated unicast RLC AM entities, such as an associated unicast RLC AM entity 421 of the UE and an associated unicast RLC AM entity 461 of the gNB. The associated unicast RLC channel is configured for each UE during NR multicast radio bearer establishment via RRC message to RRC connected mode UE. The associated RLC channels of the two

multicast radio bearers

418 and 419 for the UE include the associated unicast RLC AM entity 421, the PDCP multicast entity 432, and the SDAP multicast entity 433 for the first associated RLC channel for MRB 418, and the associated unicast RLC AM entity 421, the PDCP multicast entity 442, and the SDAP multicast entity 443 for the second associated RLC channel for MRB 419. The associated RLC channels of the two

multicast radio bearers

458 and 459 for the gNB include the associated unicast RLC AM entity 461, the PDCP multicast entity 482, and the SDAP multicast entity 483 for the first associated RLC channel for MRB 458, and the associated unicast RLC AM entity 461, the PDCP multicast entity 472, and the SDAP multicast entity 473 for the second associated RLC channel for MRB 459. The associated unicast RLC channel 491 is formed with the UE associated RLC channel and the gNB associated RLC channel. The multicast RB 492 is formed with

multicast RB

419 and 459. The multicast RB 492 is formed with

multicast RB

418 and 458. When multiple MRB shares one associated unicast RLC channel, the ID of MRB, and/or the LCID of MRB are indicated within the RLC Polling Request of MRB data, RLC Status Report PDU of MRB data, RLC Polling Request of unicast data, RLC Status Report PDU of unicast data, and/or unicast data. The MRB ID and/or the LCID ID are used by the associated unicast RLC AM entity at the receiving side to determine where to deliver the received RLC Polling Request, RLC Status Report PDU, and/or unicast retransmitted RLC packets. For example, the associated unicast RLC AM 421 at UE side determines whether a polling request is forwarded to RLC eUM multicast entity 441 of MRB 418 or RLC eUM multicast entity 431 of MRB 419 based on the MRB ID and/or the LCID in the received packets.

Figure 5 illustrates an exemplary flow diagram of performing feedback and retransmission for NR multicast service in accordance with embodiments of the current invention. The NR wireless network includes a UE 501 and a gNB 502. At step 511, one or more MRBs are configured with enhanced RLC UM mode for the multicast service. The associated unicast RLC entity is configured in AM mode. At step 521, UE 501 in connected mode receives the two multicast radio bearers, MRB-1 and MRB2. In one embodiment, one or more unicast DRBs are also configured for the UE with unicast data packets. At step 531, gNB 502 sends the Polling Request to UE 501. In a first embodiment, the Polling Request is carried by the RLC data PDU over MRB-1. In a second embodiment, the Polling Request is carried in a RLC control PDU over associated unicast RLC channel. A new type of RLC control PDU is introduced. The bearer ID of MRB-1 is included in the Polling Request. In a third embodiment, a specific MAC CE is used to indicate the Polling Request over the associated unicast RLC channel. The bearer ID of MRB-1 or the LCID of MRB-1 is included in the subheader of the MAC CE on top of the legacy structure of the subheader of the MAC CE. At step 541, after receiving the multicast related Polling Request on MRB-1 from gNB 502, UE 501 sends the RLC Status Report to gNB 502 for MRB-1. An additional field is added in the RLC Status Report to indicate the ID of radio bearer of MRB-1 or the LCID of MRB-1. At step 551, according to the reception status of the MRB-1 at UE 501, the RLC UM entity of MRB-1 at gNB 502 initiates a retransmission over MRB-1 for one or more RLC packets. gNB 502 uses the unicast channel to retransmit the RLC packets when gNB 502 slides the transmission window forward without receiving the acknowledgement from UE 501 for one or more transmitted RLC packets (i.e. RLC SDU or RLC SDU segment) for MRB-1. The RLC UM entity of gNB 501 for MRB-1 delivers the corresponding RLC SDU (s) or RLC SDU segment (s) to the associated unicast RLC AM entity for the UE before discarding the packets. At step 561, the associated unicast RLC AM entity at gNB 502 sends the RLC packets to the UE via unicast mode. The data is identified at the MAC layer via the logic channel ID of the associated unicast RLC channel. To distinguish the data for different MRB (s) , the LCID or Bearer ID is included within the data PDU. In a first embodiment, the bearer ID of MRB is included within the RLC header of the RLC data PDU, or within the subheader of the MAC data sub-PDU. In a second embodiment, the LCID of MRB is included within the RLC header of the RLC data PDU, or within the subheader of the MAC data sub-PDU. The receiving side of the associated unicast RLC channel delivers the RLC packets to the corresponding RLC UM entity of MRB following the bearer ID and/or LCID indication. In another embodiment, at step 562, the associated unicast RLC AM entity at gNB 502 sends the Polling request to UE 501 to pull the RLC Status Report from UE. At step 563, UE 501, in response, sends the RLC status PDU for unicast data over the associated unicast RLC channel. The Polling request and RLC Status Report for unicast retransmission data is differed from the Polling request and RLC Status Report for multicast retransmission data via bearer ID and/or LCID indication. At step 571, gNB 502 decides to resume multicast transmission for MRB-1 for the UE 501. At step 581, gNB 502 performs multicast transmission for MRB-1 and MRB-2 for the UE 501. In other embodiments, the feedback and retransmission procedures apply to the UL feedback procedure for NR broadcast services.

Figure 6 illustrates an exemplary flow chart of the UE performing feedback and retransmission for NR multicast service in accordance with embodiments of the current invention. At step 601, the UE establishes an MRB to receive multicast data packets for a multicast service from a serving gNB by a user equipment in a new radio (NR) network. At step 602, the UE establishes an associated unicast radio link control (RLC) channel for the MRB. At step 603, the UE performs an uplink (UL) feedback for the multicast data packets received on the MRB over the associated RLC channel. At step 604, the UE receives retransmitted multicast data packets for the multicast service from the gNB through the associated unicast RLC channel.

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

Claims

A method comprising:

establishing a multicast radio bearer (MRB) to receive multicast data packets for a multicast service from a serving gNB by a user equipment in a new radio (NR) network;

establishing an associated unicast radio link control (RLC) channel for the MRB;

performing an uplink (UL) feedback for the multicast data packets received on the MRB over the associated RLC channel; and

receiving retransmitted multicast data packets for the multicast service from the gNB through the associated unicast RLC channel.
The method of claim 1, wherein the associated unicast RLC channel is established with the MRB based on a radio resource control (RRC) configuration message from the serving gNB.
The method of claim 1, wherein the associated unicast RLC channel is associated with a plurality of multicast services received by the UE.
The method of claim 1, wherein the associated unicast RLC channel is an acknowledged mode (AM) RLC with a corresponding unicast AM RLC entity at the serving gNB.
The method of claim 1, wherein the UL feedback for the multicast data packets is transmitted over the associate unicast RLC channel, and wherein the UL feedback includes an RLC status report packet data unit (PDU) .
The method of claim 5, wherein the RLC status report PDU is identified by a bearer ID for the MRB or a logic channel ID for the MRB.
The method of claim 5, wherein the RLC status report PDU is triggered by a Polling Request from the serving gNB received over the associated unicast RLC channel.
The method of claim 7, wherein the Polling Request is identified by a bearer ID for the MRB or a logic channel ID for the MRB.
The method of claim 1, wherein one or more retransmitted non-acknowledged RLC packets received from the serving gNB over the associated unicast RLC channel is identified by a bearer ID for the MRB or a logic channel ID for the MRB.
The method of claim 1, wherein a RLC entity for the MRB is an enhanced unacknowledged mode (eUM) RLC.
A user equipment (UE) , comprising:

a transceiver that transmits and receives radio frequency (RF) signal in a new radio (NR) wireless network;

a multicast radio bearer (MRB) handler that establishes an MRB to receive multicast data packets for a multicast service from a serving gNB in the NR network;

a unicast channel handler that establishes an associated unicast radio link control (RLC) channel for the MRB;

a feedback handler that performs an uplink (UL) feedback for the multicast data packets received on the MRB over the associated RLC channel; and

a retransmission handler that receives retransmitted multicast data packets for the multicast service from the gNB through the associated unicast RLC channel.
The UE of claim 11, wherein the associated unicast RLC channel is established with the MRB based on a radio resource control (RRC) configuration message from the serving gNB.
The UE of claim 11, wherein the associated unicast RLC channel is associated with a plurality of multicast services received by the UE.
The UE of claim 11, wherein the associated unicast RLC channel is an acknowledged mode (AM) RLC with a corresponding unicast AM RLC entity at the serving gNB.
The UE of claim 11, wherein the UL feedback for the multicast data packets is transmitted over the associate unicast RLC channel, and wherein the UL feedback includes an RLC status report packet data unit (PDU) .
The UE of claim 15, wherein the RLC status report PDU is identified by a bearer ID for the MRB or a logic channel ID for the MRB.
The UE of claim 15, wherein the RLC status report PDU is triggered by a Polling Request from the serving gNB received over the associated unicast RLC channel.
The UE of claim 17, wherein the Polling Request is identified by a bearer ID for the MRB or a logic channel ID for the MRB.
The UE of claim 11, wherein one or more retransmitted non-acknowledged RLC packets received from the serving gNB over the associated unicast RLC channel is identified by a bearer ID for the MRB or a logic channel ID for the MRB.
The UE of claim 11, wherein a RLC entity for the MRB is an enhanced unacknowledged mode (eUM) RLC.