WO2024036573A1

WO2024036573A1 - Method of path addition and removal to support multipath configuration

Info

Publication number: WO2024036573A1
Application number: PCT/CN2022/113385
Authority: WO
Inventors: Guan-Yu Lin; Xuelong Wang; Nathan Edward Tenny
Original assignee: MediaTek Inc
Current assignee: MediaTek Inc
Priority date: 2022-08-18
Filing date: 2022-08-18
Publication date: 2024-02-22
Anticipated expiration: 2025-02-18

Abstract

Apparatus and methods are provided to establish the second path towards the network for a UE support multipath configuration. In one aspect, the remote UE performs measurement for candidate serving cells and/or candidate relay UE, when first path is already established and works normally and the remote UE is multipath enabled. In one aspect, a remote UE perform measurement report when measurement events specific to multipath occur, wherein 3 new measurement events are disclosed in the invention. In one aspect, based on measurement report, the gNB transmit RRC message via existing path to reconfigure the second path (for path addition) or to release the configuration (for path removal).

Description

METHOD OF PATH ADDITION AND REMOVAL TO SUPPORT MULTIPATH CONFIGURATION

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless communication, and, more particularly, to introduce detailed signaling for second path additional and second path removal for a remote UE supporting multipath feature.

BACKGROUND

L2 Relay and L3 relay

To extend network coverage, diverse relay technologies are developed. A relay node can be used to forward the packet/signal between the network node (e.g. the based station, the transmission and reception point (TRP) ) and the use equipment (UE) .

The relay node can be network vendor deployed infrastructure, such as LTE Relay node, or NR IAB (integrated access backhaul) node specified since 3GPP Rel-16. This kind of relay nodes are controlled by the network and probably be transparent to the UE.

Another kind of relay node could be a user deployed relay, e.g., using a user equipment as relay (UE relay) . This kind of relay node, compared to IAB, has a much more limited transmission/reception capability in forwarding traffic. However, its advantage is to support low-cost and dynamic/flexible deployment. Using a UE relay to extend network coverage is known as UE-to-NW relay.

In 3GPP context, a relay UE uses sidelink (SL, different from uplink and downlink) resource to communicate with a remote UE (or source UE, who is the source of traffic to be forwarded) . Therefore, in 3GPP, UE-to-NW relay is also known as SL relay.

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) .

L3 based Sidelink Relay UE forwards data packet flow of the 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 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 the base station, i.e., the base station 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 CP and 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. Unlike in L3 relay, in L2 relay the base station 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 base station 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.

Relay selection

In 3GPP R17, sidelink relay is supported to enable network coverage extension. To extend network coverage, there are RSRP (received signal strength xxx) criteria to determine whether a UE can serve as a relay UE or a remote UE.

To be specific, in 3GPP R17 spec for SL relay, it is specified that a remote UE should have the measured Uu RSRP below a RSRP threshold (threshHighRemote) . This means a UE can request for help traffic forwarding only when the UE has a very bad Uu RSRP. Besides, a UE can serve as a relay UE only when its Uu RSRP is above a RSRP threshold (threshLowRelay) . This means a UE can help other UE to forward traffic only when the UE has good Uu link quality. In addition, a UE can be a relay UE only when its Uu RSRP is below another RSRP threshold (known as threshHighRelay) , which is used to prevent cell-center UE from being a relay. Otherwise, if a relay UE is in very cell center, and a remote UE is in cell edge, the remote UE would transmit with a very large power to communicate with the cell center UE and thus cause much interference to its neighboring UE. Finally, there is a sidelink RSRP threshold (sl-RSRP-Thresh) used to measure the sidleink quality between the remote UE and the relay UE. If the SL RSRP is below the threshold, the sidelink towards the relay is considered too bad to support satisfactory relay performance.

When a UE satisfies the remote UE criteria (Uu RSRP below threshHighRemote) , it is up to UE implementation to perform cell reselection or relay selection.

Single path relay and multipath relay

Note that in 3GPP R17, only single path UE-to-NW relay is supported. That is, a UE can select one of direct path (i.e. directly connect to a gNB via Uu link) or indirect path (i.e. connect to the gNB via traffic forwarding of a relay UE) , but not both. Besides, 3GPP R17 only support single-hop UE-to-NW relay. Support of multi-hop UE-to-NW relay is left to future releases.

To further extend the UE-to-NW relay, we can consider multi-hop and multi-path aspects. Multi-hop relay, obviously, can help to eliminate deep coverage hole. In contrast, multipath relay allows multiple traffic forwarding paths from the source to destination, which definitely increase the transmission reliability and may be also beneficial to remote UE throughput.

SUMMARY

Methods are provided to establish the second path towards the network for a UE support multipath configuration.

In one aspect, the remote UE performs measurement for candidate serving cells and/or candidate relay UE, when first path is already established and works normally and the remote UE is multipath enabled.

In one aspect, a remote UE perform measurement report when measurement events specific to multipath occur.

In one aspect, a new event to trigger measurement report for multipath, is when PCell becomes better than threshold1 and candidate L2 U2N Relay UE becomes better than threshold2.

In one embodiment, a new event to trigger measurement report for multipath, is when serving L2 U2N Relay UE becomes better than threshold1, and NR Cell becomes better than threshold2.

In one embodiment, a new event to trigger measurement report for multipath, is when serving L2 U2N Relay UE becomes better than threshold1, and a candidate L2 U2N Relay UE becomes better than threshold2.

In one aspect, based on measurement report, the gNB transmit RRC message via existing path to reconfigure the second path (for path addition) or to release the configuration (for path removal) .

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 and Figure 2 show exemplary signaling for a remote UE who has an indirect path to be configured with a new direct path as the second path.

Figure 1 is the intra-gNB case, i.e. relay UE and remote UE select the serving cells of the same gNB.

Figure 2 is the inter-gNB case, i.e. relay UE and remote UE select serving cells of different gNB.

Figure 3 (a) , 3 (b) , 3 (c) , and 4 are exemplary signaling for a remote UE who has a direct path to be configured with a new indirect path as the second path.

Figure 3 (a) , 3 (b) , and 3 (c) are for the intra-gNB case, while Figure 4 is for the inter-gNB case.

Figure 3 (a) is the exemplary signaling for a remote UE to add an indirect path, wherein the remote UE provide measurement report and it is up to the network to configure the second path for a remote UE.

Figure 3 (b) is the exemplary signaling for a remote UE to add an indirect path, wherein the remote UE transmit RRC message to request for setting up the indirect path.

Figure 3 (c) is the exemplary signaling for a remote UE to add an indirect path, wherein the remote UE autonomously select a suitable relay, and transmit RRC message to report the establishment of the second (indirect) path.

Figure 4 is the exemplary signaling for a remote UE to add an indirect path wherein the relay UE is served by a different gNB.

DETAILED DESCRIPTION

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

In the following description, we use dual-path as examples to explain our inventions. But notice that our ideas are not limited to dual path but can be generalized to multipath scenarios wherein the number of paths between remote UE and gNB are equal to or more than 2.

Model for the second path

When remote UE has already a first path (with RRC connection established) , there are several approaches to model the second path addition for the remote UE.

When remote UE has built a direct path, there are several models for the remote UE to add the second path (an indirect path) using a relay.

In one embodiment, if remote UE and the relay are connected to the same base station (or TRP) , we consider the addition of the second path as SCell addition, regardless of whether the first path of the remote UE is a direct or an indirect path. That is, the definition of SCell addition is extended/generalized to cover “adding an indirect path via relay” .

In one embodiment, if remote UE and the relay are connected to the same base station (or TRP) , we consider addition of the second path as relay addition (regardless of whether the first path is a direct or an indirect path. The procedure of “relay addition” here is a bit different from legacy relay selection procedure. Relay selection means remote UE adds a relay without an existing RRC connection between remote UE and gNB, while relay addition means remote UE adds a relay given an existing RRC connection.

In one embodiment, if remote UE and the relay are connected to the same base station (or TRP) , we consider addition of the second path as relay addition if the first path is an indirect path as well; otherwise, we consider it as relay selection. In this embodiment, we define relay selection as the procedure for a remote to select its first relay, and define relay addition as the procedure for a remote to select the second or more relay.

In one embodiment, if remote UE and the relay are connected to the same base station (or TRP) , we reuse relay selection procedure whenever adding a relay as a new indirect path.

When remote UE has an indirect path, and it wants to add a direct path, there are also several ways to model the second path addition.

In one embodiment, when a remote UE wants to add a direct path as the second (or third …) path, we model it as SCell addition. For example, gNB can configure the remote UE to add a NR Cells via RRCReconfiguration, and may use MAC CE to activate or deactivate the configured serving cell.

In one embodiment, when a remote UE wants to add a direct path as the second (or third …) path, the path addition is considered as SCell addition, if there is already existing direct link for a serving cell of same gNB. Otherwise (if there is no direct link for a serving cell of the same gNB) , the path addition is considered as cell selection.

To determine whether to perform procedure for second path addition, the remote UE needs to perform measurement report in case a candidate cell or candidate relay becomes available. Note that in addition to second path addition, measurement report is required for second path removal as well.

The procedure for second path addition can be generalized as follows:

1. Remote UE can perform the measurement (for Uu or PC5) according to the measurement configuration (including configured measurement events)

2. Remote UE performs the measurement report according to its measurement to gNB

3. gNB decides the addition of the secondary path and sends the corresponding RRC messages to Remote UE (and candidate Relay UE)

4. Establish the secondary path

Signaling for second path establishment/removal

Figure 1 shows the exemplary signaling for remote UE, who already has an indirect path established to add a second path (direct path) , and wherein the candidate cell is exactly the same as the cell of the serving relay. In step 0, the remote UE perform measurement for NR cells including the serving cell of the serving relay UE. When measurement event happens, e.g. remote UE receives gNB with RSRP/SINR above threshold, the remote UE sends a measurement report to gNB via relay forwarding. That is, even when UE selects a serving relay, UE can still be configured with measurement report for NR cell measurement. In step 2, the network could transmit message (e.g. reuse existing message such as RRCReconfiguration or apply a specific message triggering second path addition) to the remote UE, trigger the remote UE to establish the second path. After receiving the triggering message, in STEP 3, the remote UE perform RACH procedure. The intention is to acquired UL sync with the gNB in Uu link, and perform UL/DL beam alignment. After remote UE completes RACH procedure, gNB then can transmit RRC Reconfiguration message to further configure UE’s Uu link. Note that if step 2 is a RRC Reconfiguration message, UE may transmit RRC Reconfiguration complete message to the gNB as the response to the RRC reconfiguration message in step 2. Finally, note that

step

1 and 2 can be saved if remote UE is configured to perform autonomous second path addition. That is, once remote UE consider the NR cell with good Uu link quality, the remote UE can trigger RACH to establish the Uu link as long as the criteria of Uu link quality configured by the network is satisfied.

Figure 2 shows another example of second path addition, wherein remote UE selects a relay, and would like to add a direct path to the candidate gNB which is different for the gNB of the selected relay. The procedure could reuse the procedure for NR DC SCG addition, and the only difference is that remote and its MCG gNB communicates via SL relay.

Figure 3 (a) and 3 (b) shows the exemplary signaling for a remote UE with direct link established to add a second path (indirect path via a candidate relay) .

Figure 3 (a) shows the example when second path addition procedure is initiated by the network. In step 0, remote UE is configured to measure for candidate relay UE (e.g. for its SL-RSRP or SD-RSRP) when remote UE already has a serving cell. When (NW-configured) measurement event occurs, e.g. a candidate relay has SL-RSRP above a SL threshold, and optionally the serving cell (or PCell) has Uu-RSRP above a Uu threshold, the remote UE send measurement report to the gNB. The identity of qualified candidate relay can be indicated in one of the measurement report, SidelinkUEInformation, or UEAssistanceInformation. After receiving the indication, as step 2, the gNB can transmit RRC reconfiguration message to configure the Uu and SL RLC channel configuration for the indirect path. The signaling in step 2 can be transmitted via direct link or indirect link.

Figure 3 (b) shows the example that the remote UE initiate second path addition procedure by sending request message. To be specific, when a remote UE is configured with multipath enabled, and when the remote UE consider the candidate relay qualified (as configured by the network) , the remote UE can transmit a request message for second path addition via relay forwarding to the gNB. This request message may extend existing RRCSetupRequest message or create a new RRC message to indicate the request for the second path. Besides, the request message may contain one or a list of suitable relay UEs who meet the AS criteria, wherein the AS criteria may apply the legacy criteria for R17 SL relay (e.g. a SL RSRP threshold) , the serving cell of the suitable relay UE (s) , or other criteria related to relay UE capability or relay Uu link condition. As a response, the gNB may reply with a message (e.g. agree or reject) , wherein the response message may extend the existing RRCSetup/RRCReject message or apply a new RRC message. If a list of multiple relay UEs are provided to the network, the network can select one for the remote UE.

Figure 3 (c) shows the example that the remote UE adds the indirect path autonomously by sending a RRC message as notification through relay. When receiving the message, the gNB knows that the remote UE wants to apply the candidate relay to build the second path. The gNB then reconfigure per-hop UL/SL RLC channel and end-to-end bearer for the indirect path.

Figure 4 illustrate the exemplary signaling for a remote UE with direct path to add the second (indirect) path. The signaling flow could be similar to NR DC for secondary node addition.

Relay UE and remote UE may select different serving cells. However, in some cases, the serving cell/gNB/TRP may only support multipath configuration wherein remote UE and relay UE are linked to the same gNB or serving cell.

In one embodiment, if a remote UE has a direct path, and its PCell does not support inter-gNB multipath, the remote UE excludes those candidate relay UEs connected to different gNB.

In one embodiment, if a remote UE has an indirect path, and the PCell of the relay UE does not support inter-gNB multipath, then the remote UE does not consider NR Cell different from that of relay UE as candidate cell.

In one embodiment, remote UE may need to change its relay UE if its relay UE changes serving cell when PCell of the remote UE does not support inter-gNB multipath. For example, if relay UE performs handover and thus link to different gNB from the remote UE, then the remote UE may need to change its serving cell (e.g. handover to keep the indirect path) or change its relay (e.g. drop the indirect path and perform relay reselection, searching for a candidate relay linked to same gNB as the relay UE) .

Multipath: remove the second path

For inter-gNB multipath, i.e. one path is on MCG and one path is one SCG, we can apply existing 3GPP R17 mechanism to release the indirect path, since the two paths belong to different RRC connection and can be handled separately.

For intra-gNB multipath, two paths share the same RRC connection. The UE can then use the existing (first) path to report the status of the second (removed) path, if needed.

In one embodiment, the indirect path or the selected relay UE of the remote UE may become unavailable (e.g. SL radio link failure occurs, SL-RSRP below a threshold, upper layers indicate not to use the currently selected relay, or upper layers request the release of the PC5-RRC connection or when AS layer releases the the PC5-RRC connection with the currently selected U2N Relay UE) . In this case, the remote UE reports via Uu link to gNB. For example, SidelinkUEInformation may be used to carry information when SL is not applicable. Remote UE reports the reason/cause to release the indirect path. After receiving the notification, gNB would reconfigure the remote UE, e.g. release SL configuration for the indirect path towards the unused relay, and the procedures for PDCP reestablishment or PDCP recovery may be triggered. Un-received PDCP packets may be retransmitted for both UL and DL directions via the direct path. A remote UE configured with multipath feature, after an indirect path is tear down, need not perform RRC reestablishment procedure (since the direct link still work normally) , but can trigger relay (re) selection procedure to search for suitable relay UE for second path addition.

In one embodiment, gNB can trigger UE to release a path. For example, in case UE has infrequent traffic to transmit, gNB may want UE to maintain a single indirect path to save power. To trigger second path removal, gNB can send a RRC message to the remote UE (via either direct or indirect path) to indicate which path to be removed, and instruct the remote UE to reconfigure/release the corresponding AS configuration. For example, to release an indirect path, remote UE may be configured to release the SL RLC configuration towards indirect path. For example, to release a direct path, the remote UE may be instructed to flush all PUCCH/SRS configuration for the released serving cell, and reset the Uu MAC entity. If the two (direct and indirect) paths are considered as different RRC connections, RRC release message can be reused. Otherwise, the network may extend existing RRC message (e.g. RRC Release or RRC reconfiguration) to remove a path without changing RRC state or triggering RRC reestablishment procedure.

New measurement events for multipath

In 3GPP R17 SL relay, there are several measurement events defined for a UE to trigger event-based measurement report. To be specific, event X1, X2, Y1, and Y2 are specified for R17 SL relay. Event X1 means serving L2 U2N Relay UE becomes worse than threshold1 and NR Cell becomes better than threshold2; event X2 means serving L2 U2N Relay UE becomes worse than threshold; event Y1 means PCell becomes worse than threshold1 and candidate L2 U2N Relay UE becomes better than threshold2; and event Y2 means candidate L2 U2N Relay UE becomes better than threshold.

To support multipath configuration, several new measurement events can be specified, so that network have knowledge about cell/relay link quality, which can be used to determine whether to add or remove the second path.

In one embodiment, new event M1/M2/M3/M4 for multipath configuration have same definition as the event X1/X2/Y1/Y2 respectively, and the threshold could be in unit of dB for RSRQ or SINR, or in unit of dBm for RSRP.

In one embodiment, a new event to trigger measurement report for multipath, is when PCell becomes better than threshold1 and candidate L2 U2N Relay UE becomes better than threshold2. The event intends to inform network of the availability to add the second path (an indirect path) .

In one embodiment, a new event to trigger measurement report for multipath, is when serving L2 U2N Relay UE becomes better than threshold1, and NR Cell becomes better than threshold2. The event intends to inform network of the availability to add the second path (a direct path) .

In one embodiment, a new event to trigger measurement report for multipath, is when serving L2 U2N Relay UE becomes better than threshold1, and a candidate L2 U2N Relay UE becomes better than threshold2. The event intends to inform network of the availability to add the second path (an indirect path) .

In one embodiment, a remote UE configured with multipath is not requested to measure for potential candidate serving cell or candidate relay UEs if this remote UE is already configured with the maximum number of configurable paths, and all configured paths works well, e.g. above threshold.

Claims

A method for a remote UE to be configured with the second path towards the network comprising:

(Step 1) Remote UE receives RRC message from the network for second path addition.

(Step 2) Remote UE configure the second path based on the received RRC message.
The method of claim 1, wherein the remote UE is configured with measurement configuration (e.g. object and events) for potential candidate serving cell and/or candidate relay UE, even when the first path works normally (e.g. RRC Reestablishment procedure is not ongoing) .
The method of claim 1, wherein the mentioned second path is a direct path of the remote UE, the first path is an indirect path via a serving relay, and the candidate serving cell and serving cell of the serving relay UE share the same gNB/TRP.
The method of claim 3, wherein the remote UE apply cell (re-) selection procedure to evaluate a candidate serving cell for second path addition. The candidate serving cell may be set as the PCell after the completion of second path addition.
The method of claim 3, wherein SCell addition procedure is applied to add the new serving cell as the second path for the remote UE.
The method of claim 3, the remote UE would transmit measurement report via indirect path when configured measurement events for candidate serving cells occur.
The method of claim 1, wherein the mentioned second path is an indirect path, the first path is a direct path of the remote UE, and the serving cell of the remote UE and serving cell of the candidate relay UE share the same gNB/TRP.
The method of claim 7, wherein the remote UE apply the relay selection procedure to evaluate the candidate relay UE for second path addition.
The method of claim 7, wherein the remote UE apply a relay addition procedure to add the second path.
The method of claim 9, wherein in the mentioned relay addition procedure, the remote UE reports to the gNB when there is update for the list of candidate relay UEs who meet the criteria for second path addition. The report can be transmitted via UEAssistanceInformation or SidelinkUEInformation.
The method of claim 10, wherein the mentioned criteria for candidate relay UE in relay addition procedure is different from the criteria in legacy relay selection procedure, e.g. different metrics or different configured values.
The method of claim 10, wherein the gNB transmit RRC message (e.g. RRC Reconfiguration message) to configure the indirect path, after making decision based on remote UE’s report.
The method of claim 2, wherein a new event to trigger event-based measurement report for multipath, is when PCell becomes better than threshold1 and candidate L2 U2N Relay UE becomes better than threshold2.
The method of claim 2, wherein a new event to trigger event-based measurement report for multipath, is when serving L2 U2N Relay UE becomes better than threshold1, and NR Cell becomes better than threshold2.
The method of claim 2, wherein a new event to trigger event-based measurement report for multipath, is when serving L2 U2N Relay UE becomes better than threshold1, and a candidate L2 U2N Relay UE becomes better than threshold2.