WO2021138756A1

WO2021138756A1 - Methods and apparatus of traffic forwarding for sidelink relay

Info

Publication number: WO2021138756A1
Application number: PCT/CN2020/070414
Authority: WO
Inventors: Xuelong Wang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2020-01-06
Filing date: 2020-01-06
Publication date: 2021-07-15
Also published as: WO2021139675A1

Abstract

Apparatus and methods are provided to support traffic forwarding at the MAC layer of NR Sidelink Relay UE for the purpose of NR Sidelink Relay operation. In one novel aspect, the Relay UE performs the traffic forwarding operation according to the Remote UE ID and Uu Bearer ID encoded in the MAC PDU over Sidelink for UE to network relaying. In another novel aspect, the Relay UE performs the traffic forwarding operation according to the specific information in the subheader of the specific DL MAC subPDU received from the Uu interface for.

Description

METHODS AND APPARATUS OF TRAFFIC FORWARDING FOR SIDELINK RELAY

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless communication, and, more particularly, to enable traffic forwarding for purpose of NR Sidelink Relay operation.

BACKGROUND

3GPP Rel-13 specified the support for ProSe UE-to-Network Relay. For ProSe UE-to-Network Relay, the traffic between the Remote UE and the Base Station is forwarded at the IP layer by the Relay UE, as the Relay UE works as a Layer-3 Relay.

In 3GPP Rel-14, there was a study for evolved ProSe UE-to-Network Relay, with the aim to support Layer-2 Relay operation by the Relay UE. The evolved ProSe UE-to-Network Relay UE is expected to forward the traffic between the Remote UE and the Base Station at an adaptation layer between RLC and PDCP. Meanwhile, the focus of the study in 3GPP Rel-14 evolved ProSe UE-to-Network Relay is one hop, for example, the transmission from the Base Station to Remote UE (i.e. the wearables) via one smart mobile phone. The Remote UE is identified in the adapter layer header on Uu by a local identifier (i.e. an index) , which is known to at least the eNB and the Relay UE. The details of the local identifier are not discussed at that time. For PC5 no additional UE ID needs to be provided by the adaptation layer. This means the traffic routing between the Base Station to the wearables is not strongly motivated, since the evolved UE-to-Network Relay UE knows the destination of the traffic according to the local index indicating the pair relation between the eRelay UE and eRemote UE.

3GPP Rel-16 specified the support of Integrated Access Backhaul (i.e. IAB) for NR to support Layer-2 based relaying operation between the UE and the Donor Base Station. A BAP protocol layer is specified over the Uu interface (s) on top of RLC over the relaying path. Specific to the relaying, the IAB node constructs a BAP Data PDU header by setting the DESTINATION field to the selected BAP address (10-bit) and setting the PATH field to the selected BAP path identity (10-bit) . In addition, the header of A BAP Data PDU also includes a D/C bit and three Reserved bits. In total, it is 24-bit for the BAP Data PDU header. The BAP protocol is used to do packet routing. There is no SN number allocated for BAP Data PDU. The BAP Control PDU is used to deliver RLF failure information and/or flow control information in hop-by-hop manner.

3GPP Rel-16 specified the support of V2X for NR. The MAC PDU is transmitted over Sidelink between TX UE and RX UE. The MAC PDU includes one SL-SCH subheader and one or more MAC SDU with its specific subheader. The octet aligned SL-SCH subheader of the MAC PDU over Sidelink consists of the following fields:

-V: The MAC PDU format version number field indicates which version of the SL-SCH subheader is used. The V field size is 4 bits;

-SRC: The SRC field size is 16 MSB bits of Source Layer-2 ID as defined in TS 23.287;

-DST: The DST field size is 8 MSB bits of Destination Layer-2 ID as defined in TS 23.287. If the V field is set to "1" , this identifier is a unicast identifier. If the V field is set to "2" , this identifier is a groupcast identifier. If the V field is set to "3" , this identifier is a broadcast identifier.

The octet aligned MAC SDU subheader of the MAC PDU over Sidelink consists of the following fields:

-LCID: The Logical Channel ID field identifies the logical channel instance within the scope of one Source Layer-2 ID and Destination Layer-2 ID pair of the corresponding MAC SDU or padding. The LCID field size is 6 bits;

-L: The Length field indicates the length of the corresponding MAC SDU in bytes. The size of the L field is indicated by the F field;

-F: The Format field indicates the size of the Length field. The size of the F field is 1 bit. The value 0 indicates 8 bits of the Length field. The value 1 indicates 16 bits of the Length field;

-R: Reserved bit, set to 0.

In Dec 2019, 3GPP approved an NR study item for Sidelink Relay for Rel-17.In order to support NR Sidelink Relay operation, the traffic forwarding function over Sidelink is to be defined at 3GPP RAN2 to support Layer-2 based relaying operation. Currently, since there is already address information for both source and destination for a particular MAC PDU over Sidelink, there is a possibility to define the traffic forwarding function at the MAC layer.

In this invention, it is sought to achieve traffic forwarding at the MAC layer of NR Sidelink Relay UE to support NR Sidelink Relay operation.

SUMMARY

Methods and apparatus are provided to support traffic forwarding at the MAC layer of NR Sidelink Relay UE for the purpose of NR Sidelink Relay operation. In one novel aspect, the Relay UE performs the traffic forwarding operation according to the Remote UE ID and Uu Bearer ID encoded in the MAC PDU over Sidelink for UE to network relaying.

In another novel aspect, the Relay UE performs the traffic forwarding operation according to the specific information in the subheader of the specific DL MAC subPDU received from the Uu interface.

During the relaying operation, different traffic type including unicast, groupcast and broadcast are distinguished to allow the Relay UE to handle in a different manner.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 (a) is a schematic system diagram illustrating an exemplary Base Station (i.e. BS) in accordance with embodiments of the current invention.

Figure 1 (b) is a schematic system diagram illustrating an exemplary UE in accordance with embodiments of the current invention.

Figure 2 illustrates an exemplary NR wireless system in accordance with embodiments of the current invention.

Figure 3 illustrates an exemplary NR UE-to-Network Relay network with an integration of two UEs in accordance with embodiments of the current invention.

Figure 4 illustrates an exemplary user plane protocol stack for the communication path between the Base Station and a particular Remote UE for Figure 3 in accordance with embodiments of the current invention.

Figure 5 illustrates an exemplary control plane protocol stack for the communication path between the Base Station and a particular Remote UE for Figure 3 in accordance with embodiments of the current invention.

Figure 6 illustrates an exemplary structure of subheader of DL MAC subPDU over Uu for relaying traffic in accordance with embodiments of the current invention.

Figure 7 illustrates an exemplary structure of MAC PDU over Sidelink for communication between the two UE (s) in accordance with embodiments of the current invention.

Figure 8 illustrates an exemplary structure of SL-SCH subheader of MAC PDU over Sidelink for communication of one-hop Sidelink Relay and the last hop of multi-hop Sidelink Relay in accordance with embodiments of the current invention.

Figure 9 illustrates an exemplary structure of SL-SCH subheader of MAC PDU over Sidelink for communication of intermediate hop of multi-hop Sidelink Relay 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.

Figure 1 (a) is a schematic system diagram illustrating an exemplary Base Station (i.e. BS) in accordance with embodiments of the current invention. The BS 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. The Base Station 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 functions. Memory stores program instructions and data to control the operations of Base Station.

Figure 1 (b) is a schematic system diagram illustrating an exemplary UE in accordance with embodiments of the current invention. The UE may also be referred to as a mobile station, a mobile terminal, a mobile phone, smart phone, wearable, an IoT device, a table let, a laptop, or other terminology used in the art. 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. 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.

Figure 2 illustrates an exemplary NR wireless system in accordance with embodiments of the current invention. Different protocol split options between Central Unit and Distributed Unit of gNB nodes may be possible. 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 NR UE-to-Network Relay network with an integration of two UEs in accordance with embodiments of the current invention. In NR, The Base Station is a gNB in NR system. The Relay UE in Figure 3 relays the traffic between the Base Station and the Remote UE. The Relay UE can operate as Layer 2 Relay. There is an NR Uu air interface between the Base Station and Relay UE. The NR Uu air interface includes both Downlink and Uplink. Optionally there is also an NR air interface between the Base Station and Remote UE. There is PC5 interface (i.e. Sidelink) between the Remote UE and the Relay UE.

Figure 4 illustrates an exemplary NR UE-to-UE Relay network with an integration of three UEs in accordance with embodiments of the current invention. The Relay UE in Figure 4 relays the traffic between the Remote UEs. The Relay UE can operate as Layer 2 Relay. There is PC5 interface (i.e. Sidelink) between the Remote UE and the Relay UE.

Figure 5 illustrates an exemplary user plane protocol stack for the communication path between the Base Station and a particular Remote UE for Figure 3 in accordance with embodiments of the current invention. Figure 6 illustrates an exemplary control plane protocol stack for the communication path between the Base Station and a particular Remote UE for Figure 3 in accordance with embodiments of the current invention. For both user plane and control plane protocol stacks as illustrated in Figure 5 and Figure 6, an adaptation layer is introduced over Uu interface. There is no adaptation layer over the PC5 interface between the Remote UE and the Relay UE. Alternatively, there is no adaptation layer introduced over Uu interface.

In the Layer-2 relaying operation, the Remote UE establishes the Uu radio bearers with the Base Station separately. The Base Station maintain a radio bearer list for each Remote UE as well as for each Relay UE following the legacy behavior. The Base Station and the Relay UE can create one relaying Uu radio bearer per Remote UE Uu radio bearer. Alternatively, the Base Station and the Relay UE support multiplexing between relaying Uu radio bearers and Remote UE Uu radio bearers depending on the QoS requirement of Remote UE Uu radio bearers. The reason is that the number of Uu radio bearers between the Base Station and the Relay UE is limited.

The Remote UE needs to establish the connection with the Relay UE in order to communicate with the Base Station in relaying manner. The Remote UE and the Relay UE can create one SLRB over PC5 per Uu radio bearer, or one SLRB over PC5 for all Uu radio bearer. In any case, the Remote UE and the Relay UE maintains the mapping between the SLRB over PC5 and the Uu radio bearer for a particular Remote UE-Relay UE association. In case of multi-hop Sidelink Relay, the two adjacent Relay UEs in the Sidelink Relay communication path support multiplexing between ingress SLRBs and egress SLRBs depending on the QoS requirement of Remote UE Uu radio bearers. The reason is that the number of SLRBs over PC5 between the two adjacent Relay UEs is limited. The two adjacent Relay UEs maintain the multiplexing information (i.e. the bearer mapping information) .

For Sidelink Relay, the Remote UE ID and the Relay UE ID can be the Source Layer-2 ID (as specified by 3GPP TS23.287) , part of Source Layer-2 ID, Destination Layer-2 ID (as specified by 3GPP TS23.287) , part of Destination Layer-2 ID, or the local ID assigned locally by the Base Station for an Sidelink Relay communication path. The Bearer ID follows 3GPP legacy definition.

The Remote UE ID and the Uu Bearer ID in combination identifies the Uu radio bearer of the Remote UE. The Relay UE ID and the Uu Bearer ID in combination identifies the Uu radio bearer of the Relay UE. The PC5 Bearer ID identifies the PC5 radio bearer (i.e. SLRB) for a pair of Relay UE-Remote UE. In case of multiple Remote UEs served by the Relay UE, the Remote UE ID and the PC5 Bearer ID in combination identifies the PC5 radio bearer (i.e. SLRB) for a pair of Relay UE-Remote UE.

Specific to multi-hop Sidelink Relay, the next hop Relay UE ID and the PC5 Bearer ID in combination identifies the egress PC5 radio bearer (i.e. SLRB) for a pair of Relay UE-Relay UE. The previous hop Relay UE ID and the PC5 Bearer ID in combination identifies the ingress PC5 radio bearer (i.e. SLRB) for a pair of Relay UE-Relay UE.

In DL, the Base Station puts the Remote UE ID and Bearer ID into the header of the adaptation layer to indicate the exact bearer information and the final destination of the data to the Relay UE. Alternatively, the Base Station puts the Remote UE ID and Bearer ID as adaptation information into the subheader of DL MAC subPDU specific to relaying transmission to indicate the exact bearer information the final destination of the data to the Relay UE. In this alternative way, the Bearer Mapping and traffic forwarding is done at MAC layer in Uu interface based on the information within the subheader of MAC subPDU.

Figure 6 illustrates an exemplary structure of subheader of DL MAC subPDU over Uu for relaying traffic in accordance with embodiments of the current invention. As depicted in Figure 6, the following fields are included in this MAC subPDU subheader:

-R: Reserved bit;

-Uu LCID: The Uu Logical Channel ID field identifies the logical channel instance. The LCID field size is 6 bits;

-V: The version number field. The V field size is 4 bits;

-Uu Bearer ID: The Bearer ID field. The Uu Bearer ID field size is 4 bits;

-Remote UE ID: This field is 24 bits in the example.

The Reserved bit (following the F bit) can be used to indicate this specific MAC subPDU subheader for relaying purpose. Alternatively, other bit (s) in the traditional DL subPDU header is used to indicate the specific MAC subPDU subheader for relaying purpose.

The V field is used to notify the Relay UE the type of MAC PDU for relaying operation: Unicast, Groupcast, or Broadcast.

The Remote UE ID field is used to express the address of the Remote UE. In case of one-hop Sidelink Relay, the Relay UE looks up a routing table to find the entry of the Remote UE according to the Remote UE ID field from traffic forwarding perspective, and then decides the egress port. In case of multi-hop Sidelink Relay, the Relay UE looks up a routing table to find the entry of the next intermediate Relay UE and then decides the egress port. In case of the last hop of multi-hop Sidelink Relay, the Relay UE looks up a routing table to find the entry of the Remote UE and then decides the egress port.

As shown in the following, the Remote UE ID and Relay UE ID is used for both bearer mapping and destination identification for purpose of traffic forwarding at Relay UE.

In case of one-hop Sidelink Relay, the Relay UE translates the Remote UE ID and Uu Bearer ID into the Sidelink Radio Bearer (i.e. SLRB) he established with the right Remote UE (identified by Remote UE ID plus SLRB ID) . The Uu Bearer ID as adaptation information forwarded during the succeeding transmission from the Relay UE to the Remote UE and the Remote UE ID is discarded. The Remote UE uses the Uu Bearer ID to find the correct RLC entity and PDCP entity at high layer to handle the data of the SLRB. The Uu Bearer ID can be put into the SL-SCH subheader of the Sidelink MAC PDU. Alternatively, the Uu Bearer ID can be put into the RLC header, PDCP header or any adaptation layer over PC5.

Figure 7 illustrates an exemplary structure of MAC PDU over Sidelink for communication between the two UE (s) in accordance with embodiments of the current invention. There is a SL-SCH subheader and multiple MAC SDUs concatenated with its own subheader (i.e. R/F/LCID/L subheader) .

Figure 8 illustrates an exemplary structure of SL-SCH subheader of MAC PDU over Sidelink for communication of one-hop Sidelink Relay and the last hop of multi-hop Sidelink Relay in accordance with embodiments of the current invention. As depicted in Figure 8, the octet aligned SL-SCH subheader of the MAC PDU over Sidelink consists of the following fields:

-Uu Bearer ID: The Bearer ID field. The Uu Bearer ID field size is 4 bits;

-SRC: The SRC field size is 16 MSB bits of Source Layer-2 ID;

-DST: The DST field size is 8 MSB bits of Destination Layer-2 ID;

In SL-SCH subheader of the MAC PDU over Sidelink, the reserved bits (4bits) in Rel-16 can be reused to express the Uu Bearer ID. The V field is used to notify the Relay UE the type of MAC PDU for relaying operation: Unicast, Groupcast, or Broadcast.

In case of multi-hop Sidelink Relay, at the first hop, the Relay UE translates the Remote UE ID and Uu Bearer ID into the Sidelink Radio Bearer (i.e. SLRB) ID and the intermediate Relay UE ID according to the SLRB (s) he established with the intermediate Relay UE. At the intermediate hop, the intermediate Relay UE translates the previous intermediate Relay UE ID and SLRB ID into next intermediate Relay UE ID and Sidelink Radio Bearer (i.e. SLRB) ID he established with the next intermediate Relay UE. At the last hop, the intermediate Relay UE translate the intermediate Relay UE ID and Sidelink Radio Bearer (i.e. SLRB) ID into the Sidelink Radio Bearer (i.e. SLRB) he established with the right Remote UE (identified by Remote UE ID plus SLRB ID) . The Remote UE ID as adaptation information forwarded during the succeeding transmission from the Relay UE to the Remote UE until the last hop (as shown at Figure 9) . The Uu Bearer ID as adaptation information is forwarded during the succeeding transmission from the Relay UE to the Remote UE from the first hop to the last hop. The Remote UE uses the Uu Bearer ID to find the correct RLC entity and PDCP entity at high layer to handle the data in the SLRB. The Uu Bearer ID can be put into the SL-SCH subheader of the Sidelink MAC PDU. Alternatively, the Uu Bearer ID can be put into the RLC header, PDCP header or any adaptation layer over PC5.

Figure 9 illustrates an exemplary structure of SL-SCH subheader of MAC PDU over Sidelink for communication of intermediate hop of multi-hop Sidelink Relay in accordance with embodiments of the current invention. As depicted in Figure 9, the octet aligned SL-SCH subheader of the MAC PDU over Sidelink consists of the following fields:

-Uu Bearer ID: The Bearer ID field. The Uu Bearer ID field size is 4 bits;

-SRC: The SRC field size is 16 MSB bits of Source Layer-2 ID;

-DST: The DST field size is 8 MSB bits of Destination Layer-2 ID;

-Remote UE ID: The Remote UE ID field size is 24 bits in the example.

The intention of adding Remote UE ID into the subheader of MAC data PDU is to enable the traffic forwarding (i.e. packet routing) at MAC layer. In this manner, there are three different type of address information within the MAC data PDU subheader. The SRC field expresses the Source Layer-2 ID or other type of address ID of the sender (i.e. the Relay TX UE) . The DST field expresses the Destination Layer-2 ID of the receiver. The Remote UE ID field represents the Destination Layer-2 ID or other type of address ID of the final receiver.

In one embodiment, the Remote UE ID field is corresponding to the routing address or a specific local index appliable to the Sidelink Relay operation. If there are multiple path between the Relay UE and the destined Remote UE, a path ID may be optionally included in the Remote UE ID field. The routing address, a specific local index, path ID can be configured by the control plane signalling.

As described above, there exists two types of SL-SCH subheader of the MAC PDU over Sidelink for Sidelink Relay operation, one SL-SCH subheader with Remote UE ID field, the other without Remote UE ID field. One code point of the V field can be used to express this omission. This specific code point shows that the specific SL-SCH subheader with or without Remote UE ID field is used. This specific code point shows that the next hop is the final hop transmission.

When the receiving Relay UE correctly receives the MAC PDU, he always use his own address to replace the address in the SRC field of the SL-SCH subheader of the received MAC PDU for succeeding transmission.

For DL, the general aspects of unicast relay operation applies also to groupcast. The difference is that the Remote UE ID Field in the subheader of MAC subPDU is replaced by a Group ID field. The Group ID represents a Group Address. One code point of the V field can be used to express the relaying groupcast traffic. Specific to the relaying groupcast traffic, when the Relay UE correctly receives the MAC PDU, he needs to deliver the MAC PDU to the upper layer for message resolution and at the same time generate the relay transmission via groupcast manner over Sidelink.

For DL, the general aspects of unicast relay operation applies also to broadcast. The difference is that the Remote UE ID Field in the subheader of MAC subPDU is replaced by a broadcast service ID field. Service ID represents a broadcast service. One code point of the V field can be used to express the relaying broadcast service. Specific to the relaying broadcast service, when the Relay UE correctly receives the MAC PDU, he needs to deliver the MAC PDU to the upper layer for message resolution and at the same time generate the relay transmission via broadcast manner over Sidelink.

For UL transmission (i.e. the Remote UE to the Base Station) , when the Remote UE sends the data over Sidelink to the Relay UE, the Remote UE puts the Uu Bearer ID into the SL-SCH Subheader of MAC PDU over Sidelink. In case of one-hop Sidelink Relay, no additional adaptation information is needed. Specific to a pair of Remote UE-Relay UE. The exemplary structure of SL-SCH subheader of MAC subPDU over Sidelink as depicted at Figure 8 for DL is also applicable to UL relaying traffic for one-hop Sidelink Relay. The difference is the mean of V field. For UL, a codepoint of the V field is used to notify the Relay UE that the type of MAC PDU is for relaying to the Base Station.

For UL transmission, in case of multi-hop Sidelink Relay, for both first hop and intermediate hop, both Uu Bearer ID and Remote UE ID are included in the SL-SCH subheader of MAC subPDU destined to the Base Station. The exemplary structure of SL-SCH subheader of MAC subPDU over Sidelink for DL as depicted at Figure 9 applies also to UL. The difference is the mean of V field. For UL, a codepoint of the V field is used to notify the Relay UE that the type of MAC PDU is for relaying to the Base Station.

For UL, when the Relay UE transmits the relaying traffic to the Base Station over Uu interface, a specific MAC subPDU subheader is used to indicate the relaying information in this last hop transmission. The exemplary structure of subheader of DL MAC subPDU over Uu for relaying traffic as depicted in Figure 6 is also applicable to UL. The difference is the mean of V field. For UL, a codepoint of the V field is used to notify the Base Station that the type of MAC PDU is for relaying to the Base Station.

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 comprising:

Performing the DL traffic forwarding and UL traffic forwarding by the Relay UE at MAC layer for purpose of UE to Network Relay.
The method of claim 1, wherein the traffic forwarding by the Relay UE is based on the Remote UE ID field and Uu Bearer ID encoded in the MAC PDU over Sidelink.
The method of claim 1, wherein the traffic forwarding by the Relay UE is based on the Uu Bearer ID field encoded in the MAC PDU over Sidelink.
The method of claim 1, wherein the DL traffic forwarding by the Relay UE is performed via groupcast manner based on the Group ID field and/or V field encoded in the MAC PDU over Sidelink.
The method of claim 1, wherein the DL traffic forwarding by the Relay UE is performed via broadcast manner based on the Service ID field and/or V field encoded in the MAC PDU over Sidelink.
The method of claim 1, wherein the Relay UE omits Relay Destination field during the traffic forwarding for the final hop and use one code point of the V field encoded in the MAC PDU over Sidelink to express this omission.
The method of claim 1, wherein UL traffic forwarding is identified based on the codepoint of the V field notifying the Relay UE that the type of MAC PDU is for relaying to the Base Station.
The method of claim 1, wherein the traffic forwarding is based on two different MAC PDU message format as indicated in V field.