The disclosed embodiments relate generally to wireless network communications, and, more particularly, to enable end-to-end MAC CE transmission between remote UE and gNB over layer 2 UE-to-Network relay in 5G new radio (NR) wireless communications systems.
New technologies in 5G new radio (NR) allow cellular devices to connect directly to one another using a technique called sidelink (SL) communications. Sidelink is the new communication paradigm in which cellular devices are able to communicate without relaying their data via the network. The sidelink interface may also be referred to as a PC5 interface. A variety of applications may rely on communication over the sidelink interface, such as vehicle-to-everything (V2X) communication, public safety (PS) communication, direct file transfer between user devices, and so on. To support sidelink relay, there are two kinds of UE-to-Network Relay architecture, i.e., Layer 2 relay (L2 relay) and Layer 3 relay (L3 relay).
In case of L3 based Sidelink Relay, a Relay UE forwards data packet flow of a Remote UE as IP traffic as a general Router in data communication network. The IP traffic-based forwarding is conducted in a best-efforts way. For L3 UE-to-Network Relay, there exist both sidelink radio bearers (SLRBs) over PC5 and Uu Radio Bearers to carry the QoS flows established between Remote UE and 5GC. L3 UE-to-Network Relay can support flow-based mapping at SDAP layer when converting PC5 flow to Uu Flow, or vice versa, during traffic forwarding. Note that since L3 based Sidelink Relay UE works like an IP router, Remote UE is transparent to gNB, i.e., the gNB cannot know whether the traffic transmitted by a relay UE originates from this relay UE itself, or originates from a remote UE but is forwarded by this relay UE.
In contrast, in case of L2 based SL Relay, relaying is performed above RLC sublayer via Relay UE for both control plane (CP) and user plane (UP) between Remote UE and network. Uu SDAP/PDCP and RRC are terminated between Remote UE and gNB, while RLC, MAC and PHY are terminated in each link (i.e., the link between Remote UE and UE-to-Network Relay UE and the link between UE-to-Network Relay UE and the gNB). An adaptation layer over RLC layer is supported in Uu to perform bearer mapping and it can be also placed over PC5 to perform bearer mapping at sidelink. The adaptation layer between the Relay UE and the gNB is able to differentiate between bearers (SRBs, DRBs) of a particular Remote UE. Within a Uu DRB, different Remote UEs and different bearers of the Remote UE can be indicated by additional information included in adaptation layer header. Unlike in L3 relay, the gNB is aware of each remote UE, and thus before the relay UE starts to forward normal data traffic, the end-to-end connection between a remote UE and the gNB should be established first. After establishing the RRC connection via SL relay, the remote UE can then forward data traffic based on the established bearers and the forwarding/router information carried in adaptation layer.
In NR, to enhance MMTEL (multimedia telephony) IMS (IP multimedia subsystem) voice and video, RAN-assisted codec adaptation is introduced. RAN-assisted codec adaptation provides a means for the gNB to send codec adaptation indication with recommended bit rate to assist the UE to select or adapt to a codec rate for MMTEL voice or MMTEL video. The RAN-assisted codec adaptation mechanism supports the uplink/downlink bit rate increase or decrease. For a bearer associated with configuration of MBR greater than GBR, the recommended uplink/downlink bit rate is within boundaries set by the MBR and GBR of the concerned bearer.
For uplink or downlink bit rate adaptation, gNB may send a recommended bit rate to the UE to inform the UE on the currently recommended transport bit rate on the local uplink or downlink, which the UE may use in combination with other information to adapt the bit rate, e.g. the UE may send a bit rate request to the peer UE via application layer messages, which the peer UE may use in combination with other information to adapt the codec bit rate. The recommended bit rate is in kbps at the physical layer at the time when the decision is made.
The recommended bit rate for UL and DL is conveyed as a MAC Control Element (CE) from the gNB to the UE. Based on the recommended bit rate from the gNB, a UE may initiate an end-to-end bit rate adaptation with its peer (UE or MGW). The UE may also send a query message to its local gNB to check if a bit rate recommended by its peer can be provided by the gNB. The UE is not expected to go beyond the recommended bit rate from the gNB. The recommended bit rate query message is conveyed as a MAC CE from the UE to the gNB.
MAC CE does not support SL relay forwarding. Most MAC CE are used to manage link between UE and gNB. However, a few MAC CEs are not used for link management, including (1) bit rate query and recommendation MAC CE and (2) UL BSR. The current SL relay design does not support MAC CE forwarding, and thus remote UE cannot tell gNB its preferred bit rate and its data in buffer.
A solution is sought.
A method is provided to support remote UE transmitting recommended bit rate query to the base station via the processing of relay UE. In one novel aspect, a new sidelink MAC CE is introduced to indicate the desired bit rate for a specific sidelink logical channel or for a specific Uu/SL radio bearer. In one novel aspect, after receiving the recommended bit rate query MAC CE, the relay UE forwards the MAC CE of this remote UE to the base station over Uu interface after adding information related to remote UE identity. In one novel aspect, the recommended bit rate query MAC CE, when received by the relay UE, is mapped to a specific uplink logical channel priority value or a specific uplink logical channel priority level, which can be used to compare priority with other UL data or UL MAC CE.
A method is also provided for a base station to transmit recommended bit rate to a remote UE. In one novel aspect, the recommended bit rate MAC CE for a remote UE is transmitted along with the identity of the remote UE from the base station to the relay UE. In one novel aspect, after relay UE receives the recommended bit rate MAC CE, the relay UE forwards the MAC CE to the targeted remote UE according to the associated identity of remote UE. In one novel aspect, the recommended bit rate MAC CE has a fixed or configured sidelink logical channel priority value, and/or a related priority value comparable with other SL data and SL MAC CE.
Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims.
Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings.
To support sidelink relay, there are two kinds of UE-to-Network Relay architecture, i.e., Layer 2 relay (L2 relay) and Layer 3 relay (L3 relay). However, MAC Control Element (CE) does not support sidelink relay forwarding. Although most MAC CEs are used to manage links between UE and gNB, a few MAC CEs are not used for link management, including (1) bit rate query and recommendation MAC CE and (2) UL buffer status report (BSR). For example, the recommended bit rate for uplink and downlink is conveyed as a MAC CE from the gNB to the UE, and the recommended bit rate query message is conveyed as a MAC CE from the UE to the gNB. The current SL relay design, however, does not support such MAC CE forwarding.
In accordance with one novel aspect, a method is proposed to allow uplink and downlink MAC CE forwarding through sidelink relay. As illustrated in
Similarly, for wireless device 211 (e.g., a remote UE), antennae 217 and 218 transmit and receive RF signals. RF transceiver module 216, coupled with the antennae, receives RF signals from the antennae, converts them to baseband signals and sends them to processor 213. The RF transceiver 216 also converts received baseband signals from the processor, converts them to RF signals, and sends out to antennae 217 and 218. Processor 213 processes the received baseband signals and invokes different functional modules and circuits to perform features in wireless device 211. Memory 212 stores program instructions and data 220 to control the operations of the device 211.
The wireless devices 201 and 211 also include several functional modules and circuits that can be implemented and configured to perform embodiments of the present invention. In the example of
In case of L2 based SL Relay, relaying is performed above RLC sublayer via Relay UE for both control plane (CP) and user plane (UP) between Remote UE and network. Uu SDAP/PDCP and RRC are terminated between Remote UE and gNB, while RLC, MAC and PHY are terminated in each link (i.e., the link between Remote UE and UE-to-Network Relay UE and the link between UE-to-Network Relay UE and the gNB). An adaptation layer over RLC layer is supported in Uu to perform bearer mapping and it can be also placed over PC5 to perform bearer mapping at sidelink. The adaptation layer between the Relay UE and gNB is able to differentiate between bearers (SRBs, DRBs) of a particular Remote UE. Within a Uu DRB, different Remote UEs and different bearers of the Remote UE can be indicated by additional information included in adaptation layer header. In one example, a remote UE can transmit a recommended bit rate query MAC CE to a base station via the processing of a relay UE. In another example, the remote UE can receive a recommended bit rate MAC CE from the base station via the processing of the relay UE.
In the embodiment of
Similarly, the base station may send recommended bit rate to a remote UE to suggest the suitable bit rate. In L2 relay, since gNB is aware of the existence of each remote UE, the information of recommended bit rate from gNB should be received by the remote UE. In one embodiment, as illustrated in
After a relay UE receives the recommended bit rate query, there are several ways to handle the query. In one embodiment, if the recommended bit rate query is carried in a format of SL MAC CE without associated RLC header or adaptation layer header, the relay UE may consider the SL MAC CE as a RLC SDU. That means the relay UE adds adaptation layer header and RLC header in front of the SL MAC CE payload to form a RLC PDU, and then transmit to gNB by applying legacy Uu LCP procedure. When the RLC PDU is multiplexed into an UL MAC PDU, the MAC subheader associated with the RLC PDU for recommend bit rate query may include an UL LCID value corresponding for “recommend bit rate query MAC CE from remote UE”. For multi-hop scenario, the relay UE 403 may package the SL MAC CE to be a SL RLC PDU, and then transmit it to the upstream relay UE 402 by applying legacy sidelink LCP procedure. Similarly, the MAC subheader for the SL RLC SDU has a LCID to identify the content of RLC SDU as a recommended bit rate query MAC CE. In one example, the added adaptation layer header includes identity of the remote UE who initiates the query.
In one embodiment, if the recommended bit rate query is carried in a format of SL MAC CE with associated RLC header or adaptation layer header, a relay UE updates the RLC header and adaptation layer header, and then forwards the updated RLC PDU to the next hop (i.e., gNB or the upstreaming relay UE). If the relay UE 402 forwards the RLC PDU to gNB 401 (step 413), the MAC subheader of the RLC PDU indicates the LCID value corresponding to recommended bit rate query MAC CE from remote UE. In contrast, if the relay UE 403 forwards the RLC PDU to the upstream relay UE 402 (step 412), the SL MAC subheader of the RLC PDU indicates the LCID value corresponding to recommended bit rate query SL MAC CE.
In one example, to send recommended bit rate for a remote UE, the gNB put the information of the targeted remote UE (e.g., target remote UE ID) in the adaptation layer header, while other information mentioned above is included in the payload of a MAC CE. For example, the gNB may treat the MAC CE payload as a RLC SDU, and thus sequentially adds adaptation layer header, optionally RLC header, and MAC subheader for it to form a MAC subPDU. After relay UE receives a DL MAC PDU including the MAC subPDU, the relay UE knows that this MAC subPDU carries a recommended bit rate MAC CE towards a remote UE by checking the LCID value indicated in LCID and/or eLCID field in the MAC subheader. The relay UE then updates the RLC header (if exist and needed) and adaptation layer header (if needed), and forwards the SL RLC SDU to the remote UE (step 513) or the downstream relay UE (step 512). When multiplexing the SL RLC SDU to a SL MAC PDU, the SL MAC subheader associated with the SL RLC SDU includes an LCID value corresponding to recommended bit rate MAC CE over sidelink. Note that similar to recommended bit rate query MAC CE over sidelink, the recommended bit rate MAC CE over sidelink has its unique LCID value.
There are two ways for a relay UE to forward the recommended bit rate MAC CE to the remote UE. In one embodiment, the MAC CE payload, along with the adaptation layer header, optionally the RLC header, and the MAC subheader forms a SL MAC subPDU and is sent by relay UE to the remote UE. From the LCID for the MAC subheader of the MAC subPDU, remote UE knows that this is a recommended bit rate MAC CE, and removes RLC header and adaptation layer header to read the MAC CE payload. In one embodiment, only the MAC CE payload and the MAC subheader forms a MAC subPDU. Upon receiving the MAC subPDU, from the LCID for the MAC subheader of the MAC subPDU, remote UE knows that this is a recommended bit rate MAC CE.
For SL MAC CE forwarding, since both the source and the target of a SL MAC CE are UEs, the adaptation layer header needs to include both the source UE ID and the target UE ID, so that the target UE can know who initiates the SL MAC CE by the source UE ID. In the example of
The SL-SCH MAC subheader comprises a SRC field and a DST field, used to indicate who send the SL MAC PDU (SRC) and who should receive the SL MAC PDU (DST). For example, if an SL MAC PDU is sent from remote UE, to relay UE2, to relay UE1, and to gNB, then when remote UE send the SL MAC PDU over SL, the DST field is relay UE2, and when relay UE2 forwards the SL MAC PDU, the SRC field is relay UE2, and the DST field is relay UE1.
LCID for SL-LCH is used to indicate the content of the payload in an SL MAC subPDU. For example, if the value of LCID is <20, then the payload is MAC SDU, and if the value of LCID is equal to 62, then the payload is a MAC CE for SL CSI reporting. In current MAC specification, there are two tables define the values of LCID for DL-LCH and UL-SCH. For example, the recommended bit rate DL message has LCID==47, and the recommended bit query UL message has LCID==53. In accordance with one novel aspect, two SL LCID values are added in LCID table for SL-SCH. First, “SL recommendation bit rate query MAC CE” for UE-to-gNB (uplink direction) with LCID==61 is added as a counterpart to “UL recommendation bit rate query MAC CE”. Second, “SL recommendation bit rate” for gNB-to-UE (downlink direction) with LCID==60 is added as a counterpart to “DL recommendation bit rate MAC CE”.
To distinguish the recommended bit rate query MAC CE for relay UE and for remote UE, the recommended bit rate query MAC CE for remote UE with a distinct SL LCID, e.g., SL LCID set as 61. Here, the UL MAC CE is referred to as “relay-specific recommended bit rate query” since it is used only in the SL relay scenario. When relay UE 802 checks SL MAC subheader and finds the SL LCID value is 61, relay UE 802 knows that this MAC payload includes MAC CE for “recommended bit rate query”, and thus in UL transmission (from relay 802 to gNB 801) relay UE 802 selects the UL LCID value for “recommended bit rate query”, i.e., 53 as specified in UL LCID table.
In this invention, method on how to deliver a UL MAC CE (recommended bit rate query MAC CE) from a remote UE to the base station is proposed. The main concept is that when forwarding a MAC CE, this MAC CE needs to add adaptation layer header for routing. With the addition of adaption layer header, additional LCID is needed. For example, to forward a UL MAC CE, a new UL LCID specific for relay is needed, so that when base station receives the UL MAC CE, the base station knows that this UL MAC CE comes from a remote UE, and knows the existence of adaptation layer header included in the MAC SDU.
To avoid the ambiguity, the recommended bit rate MAC CE for remote UE is assigned with a distinct SL LCID, e.g., SL LCID set as 60. Here, the DL MAC CE is referred to as “relay-specific recommended bit rate” since it is used only in the SL relay scenario. When relay UE 902 checks DL MAC subheader and find the DL LCID value is 47, relay UE 902 knows that this MAC payload includes MAC CE for “recommended bit rate”, and thus in SL transmission (from relay UE 902 to relay UE 903) relay UE 902 selects the SL LCID value for “recommended bit rate”, i.e., 60 as specified in SL LCID table.
In this invention, method on how to deliver a DL MAC CE (recommended bit rate MAC CE) from the base station to a remote UE is proposed. The main concept is that when forwarding a MAC CE, this MAC CE needs to add adaptation layer header for routing. With the addition of adaption layer header, additional LCID is needed. For example, to forward a DL MAC CE, a new DL LCID specific for relay is needed so that when relay UE receives the DL MAC subPDU, the relay UE knows the existence of adaptation layer header, and thus can route it correctly.
The above illustrated framework can be used to carry other UL MAC CE or DL MAC CE. For example, it would be quite useful if a remote UE can send UL BSR (buffer status report) via the forwarding of the relay UE to inform gNB of its amount of uplink data available in uplink buffer. Based on the feedback from remote UE, the base station can provide sufficient resource or higher priority along the path to forward traffic of the remote UE, if remote UE has a lot of data to transmit.
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.
Number | Date | Country | Kind |
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202210855683.3 | Jul 2022 | CN | national |
§ 111(a) and is based on and hereby claims priority under 35 U.S.C. § 120 and § 365(c) from International Application No. PCT/CN2021/110298, entitled “METHOD AND APPARATUS TO TRANSMIT MESSAGES FOR BIT RATE QUERY AND RECOMMENDATION OVER UE-TO-NETWORK RELAY,” filed on Aug. 3, 2021. This application claims priority under 35 U.S.C. § 119 from Chinese Application Number CN202210855683.3, filed on Jul. 20, 2022. The disclosure of each of the foregoing documents is incorporated herein by reference.
Number | Date | Country | |
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Parent | PCT/CN2021/110298 | Aug 2021 | US |
Child | 17877307 | US |