WO2024065171A1

WO2024065171A1 - Relay ue selection and admission

Info

Publication number: WO2024065171A1
Application number: PCT/CN2022/121703
Authority: WO
Inventors: Nathan Edward Tenny; Xuelong Wang; Ming-Yuan Cheng
Original assignee: Mediatek Inc.
Priority date: 2022-09-27
Filing date: 2022-09-27
Publication date: 2024-04-04

Abstract

This disclosure describes methods of selecting and admitting to connected-mode operation a relay UE served by a network node. The described methods comprise transmitting, by a relay UE during a discovery procedure, information regarding the operation of the relay UE on an air interface with a network node, such as a Uu interface with a serving gNB. The described methods further comprise transmitting, by a remote UE subsequent to a discovery procedure, a measurement report comprising information regarding the operation of at least one relay UE on an air interface with a network node. The described methods further comprise selecting, by a network node, a target relay UE after receiving information regarding the operation of the target relay UE on an air interface with a network node.

Description

RELAY UE SELECTION AND ADMISSION

FIELD

This disclosure relates to wireless communications, and specifically to methods of selecting and admitting to connected-mode operation a relay UE in a serving cell when a remote UE switches a communication path to use the relay UE.

BACKGROUND

In certain wireless systems, such as 3GPP 5G New Radio (NR) from Rel-17 onward, a first user equipment (UE) may function in a relaying relationship with a second UE. For example, the first UE may be out of direct cellular coverage or in poor coverage, while the second UE is in good coverage, and the second UE may deliver communications between the first UE and the serving cellular network. In this scenario, the first UE may be referred to as a remote UE and the second UE may be referred to as a relay UE. The remote UE may be referred to as being in “indirect service” or having an “indirect path” to the network, while the relay UE may be referred to as being in “direct service” or having a “direct path” to the network. The relay and remote UEs may communicate via a sidelink interface, also called a PC5 interface, in which radio resources are used for direct communication between UEs without an intervening network node. Other interfaces between the relay and remote UEs may be contemplated, such as wired or wireless technologies (for example, WiFi communication) , proprietary connections, and so on.

When a remote UE performs a so-called path switch operation towards a target relay UE, the target relay UE may be in one of several radio resource control (RRC) protocol states. For a target relay UE in an RRC_IDLE state or an RRC_INACTIVE state, the network node (for example, a gNB) that serves the target relay UE may hold little or no information about the target relay UE prior to the path switch operation. Thus, it may be difficult for the gNB to perform certain operations such as selecting one of several candidate target relay UEs, determining whether to admit a target relay UE to an RRC_CONNECTED mode of operation, or predicting the performance of an indirect path through the target relay UE.

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method of discovery is provided, operable at a first UE and comprising transmitting, to a second UE, a discovery message comprising information regarding an interface between the first UE and a network node.

In another aspect of the disclosure, a method of measurement reporting is provided, operable at a first UE and comprising transmitting, to a first network node, a measurement report message comprising a measurement of at least one second UE and information regarding an interface between the at least one second UE and a second network node.

In another aspect of the disclosure, a method of relay selection is provided, operable at a first network node and comprising: receiving, from a first UE or a second network node, information regarding operation of a plurality of second UEs on an interface; and selecting, from the plurality of second UEs, a third UE to operate as a relay UE.

In another aspect of the disclosure, a method of handover admission is provided, operable at a first network node and comprising: receiving, from a second network node, a handover preparation message requesting handover of a first UE and comprising information regarding operation of at least one second UE on an interface between the second UE and the first network node; determining to admit the first UE in handover; and sending, to the second network node, a handover accept message.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of relay and remote UE operation.

FIG. 2 is a diagram illustrating an example of a direct-to-indirect path switch operation by a remote UE towards a target relay UE.

FIG. 3 is a diagram illustrating an example of an indirect-to-indirect path switch operation by a remote UE towards a target relay UE.

FIG. 4 illustrates an example of a message flow for a path switch procedure in which the target relay UE is in an RRC_CONNECTED protocol state.

FIG. 5 illustrates an example of a path switch procedure in which the target relay UE is in an RRC_IDLE or RRC_INACTIVE protocol state.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

Figure 1 shows an example of relay and remote UE operation. A base station of a communication system, such as the gNB in the figure, serves a first (relay) UE over a first direct interface, such as the Uu interface shown in the figure. In turn, the first UE serves a second (remote) UE over a second direct interface, such as the PC5 interface shown in the figure. The PC5 interface may also be referred to as a sidelink interface. In the figure, the remote UE is shown as being out of coverage of a cell operated by the gNB, but it should be appreciated that a relaying relationship may also exist for a remote UE in coverage. (For example, the remote UE may be in poor coverage at the edge of a cell, allowing it to receive better service through the combination of a good PC5 link to the relay UE and the relay UE’s good Uu link to the base station than it could receive through its own poor Uu link directly to the base station. As another example, the remote UE may have limited radio capabilities, such as a restricted transmission power, and rely on a more capable relay UE to close a high-throughput link with the base station. ) Communications to and/or from the remote UE may be carried through the relay UE from and/or to the base station, allowing the remote UE to be served by the communication system.

Figure 2 shows an example of a first path switch operation in which a remote UE transfers its communication path to a target relay UE. In the example, the remote UE is initially served by gNB A on the direct path, and it transfers its service to the indirect path with gNB B through the target relay UE. This operation may be referred to as a direct-to-indirect path switch procedure. It should be appreciated that gNB A and gNB B in this example can be one and the same, in which case the path switch may be referred to as an intra-gNB operation. If gNB A and gNB B are different, the path switch may be referred to as an inter-gNB operation.

Figure 3 shows an example of a second path switch operation in which a remote UE transfers its communication path to a target relay UE. In the example, the remote UE is initially served by gNB A on the indirect path through a source relay UE, and it transfers its service to the indirect path with gNB B through the target relay UE. This operation may be referred to as an indirect-to-indirect path switch procedure. It should be appreciated that gNB A and gNB B in this example can be one and the same, so that the path switch may be referred to as an intra-gNB operation. If gNB A and gNB B are different, the path switch may be referred to as an inter-gNB operation.

Figure 4 shows an exemplary message flow of an inter-gNB path switch operation, assuming that the target relay UE is initially in an RRC_CONNECTED protocol state. The diagram shows a direct-to-indirect procedure, in which the remote UE initially communicates directly with a source gNB; however, it should be understood that a substantially similar flow can describe an indirect-to-indirect procedure, with the change that

steps

1 and 4 are relayed through a source relay UE (not shown in the figure) . In step 1 of figure 4, the remote UE transmits to the source gNB a measurement report indicating that it has measured signals from the target relay UE. (It is noted that a discovery procedure between the remote UE and the target relay UE may precede step 1, allowing the remote UE to be aware that the target relay UE is offering relay service; this procedure is not shown in the figure. ) In step 2, the source gNB takes the decision to trigger a handover or mobility procedure to induce the remote UE to switch its communication path; this handover decision may be in accordance with any criteria selected by the source gNB according to its implementation. For example, the handover decision may be informed by measurements of the target relay UE reported to the source gNB by the remote UE. In step 3, the source gNB and the target gNB perform a handover preparation procedure, which may, for example, comprise an exchange of signalling messages on an Xn interface. The handover preparation procedure may include determining, by the target gNB, if the remote UE can be admitted to service with the target gNB. In step 4, the source gNB sends to the remote UE a reconfiguration message (for instance, an RRCReconfiguration message of an RRC protocol) , containing instructions to add (i.e., establish a connection with) the target relay UE and release (i.e., release a connection with) the source (the source gNB in the direct-to-indirect case, or the source relay UE in the indirect-to- indirect case) . The reconfiguration message of step 4 may comprise a handover command received from the target gNB as part of the signalling in step 3. In step 5, the remote UE and the target relay UE perform a procedure for link establishment; for example, in case the remote UE and the target relay UE communicate on a PC5 interface, this procedure may comprise a PC5 unicast link establishment procedure and/or a PC5-RRC connection establishment procedure. In step 6, the remote UE sends to the target gNB, via the target relay UE, a handover completion message (for example, an RRCReconfigurationComplete message of an RRC protocol) . The handover completion message indicates to the target gNB that the remote UE has performed its mobility procedure, allowing communication to proceed between the target gNB and the remote UE (via the target relay UE) .

Figure 5 shows an example of a path switch procedure in which the target relay UE is initially in an RRC_IDLE or RRC_INACTIVE protocol state, in accordance with one novel aspect. The distinguishing characteristic of these protocol states is that the target relay UE, while served by the target gNB, does not have an active RRC connection with the target gNB and may not have a context stored at the target gNB. (The sole exceptional case is when the target relay UE is in RRC_INACTIVE and the target gNB happens to be the anchor gNB for the target relay UE. In such a case, the target gNB holds a partial context for the target relay UE, but the target relay UE has no RRC connection with any gNB, has no radio resources assigned for its use, and has no active communication with the target gNB. ) In case the target relay UE is in RRC_IDLE or RRC_INACTIVE, the target gNB is not aware of radio conditions of the target relay UE, and the target gNB may not know that it serves the target relay UE at all. Because of the lack of an RRC connection between the target relay UE and the target gNB, the target relay UE must perform a state transition to an RRC_CONNECTED state before it can exchange relayed communications with the target gNB (for example, to forward signalling and/or traffic originating from the remote UE) .

In step 1 of figure 5, the target relay UE provides information to the remote UE as part of a discovery procedure. This step is shown in isolation, as a communication from the target relay UE to the remote UE, but it should be understood as part of a bidirectional discovery procedure whose other components are not shown in the figure. Various models of such a bidirectional discovery procedure can be employed. For example, the target relay UE may initiate discovery by advertising its availability as a relay UE (in accordance with step 1 of the figure) , whereupon the remote UE may respond to the advertisement to indicate its interest in relay service. Alternatively, the remote UE may initiate discovery by soliciting a relay service, whereupon the target relay UE may respond to the solicitation by indicating its availability as a relay UE (in accordance with step 1 of the figure) . For purposes of this discussion, either model of discovery may apply, but the information of interest for the path switch procedure is delivered in the discovery message from the target relay UE to the remote UE in step 1. This discovery message may, for example, contain an indication of the observed or expected link quality of a Uu interface between the target relay UE and the target gNB, or between the target relay UE and one cell hosted by the target gNB. The indication may comprise a measure of radio quality, such as a reference signal received power (RSRP) or reference signal received quality (RSRQ) measurement. The indication may comprise a threshold of radio quality; for example, a measured RSRP and/or RSRQ value, or a filtered set of RSRP and/or RSRQ values, may be compared against a set of one or more thresholds to determine a level of radio quality that is less precise but potentially more stable than an individual “raw” RSRP or RSRQ value. The indication may comprise an anticipated level of performance or throughput available through the Uu interface, such as a nominal throughput level based on assumptions about the performance of the link as measured by the target relay UE. The indication may be controlled by a specific defined measurement event, where some or all of a configured threshold, an offset, a hysteresis parameter, and/or a time-to-trigger parameter may apply. For example, when the reference signal received power (RSRP) measured by the relay UE on the Uu interface is higher (or higher by an offset) than a configured threshold for an amount of time (e.g., a time to trigger) , then the indication can be set up by the relay UE within the discovery message. Alternatively or additionally, the discovery message may comprise an indication of one or more communication capabilities of the target relay UE, such as an indication or level of support for carrier aggregation (CA) , multiple input/multiple output (MIMO) operation, and so on. Such an indication of communication capabilities may allow the source or target gNB to infer an expected performance of the target relay UE; for example, a target relay UE supporting a higher MIMO rank may be preferred to one supporting a lower MIMO rank, since the higher MIMO rank may allow greater throughput on the Uu interface. Alternatively or additionally, the discovery message may comprise an indication of an RRC state of the target relay UE, allowing the source and/or target gNBs in subsequent steps to know if the target relay UE is in a particular RRC state.

In some embodiments, the target gNB may have the ability to configure maximum and/or minimum radio thresholds for operation as a relay UE. As a result, the target relay UE may be allowed to perform discovery only if, for instance, it measures the Uu interface above a minimum RSRP and below a maximum RSRP. The intention of a link quality indication in the discovery signalling is to provide a finer-grained measure of the anticipated performance of the Uu link, so that, for instance, the source or target gNB can compare a plurality of candidate relay UEs (all of which may meet the radio criteria for operation as a relay UE) and select as the target relay UE one of the plurality of candidate relay UEs based at least in part on the link quality.

In step 2 of figure 5, the remote UE transmits, to the source gNB, a measurement report indicating a measured quantity of the target relay UE. As one example, if the remote UE and the target relay UE communicate on a PC5 interface, the measurement report may indicate a PC5-RSRP value of signals received by the remote UE from the target relay UE. The measurement report may also include any additional information acquired by the remote UE during discovery, such as a serving cell ID of the target relay UE, an identifier such as a layer 2 identifier (L2ID) of the target relay UE, an indication of Uu link performance as described above, an indication of communication capabilities as described above, an indication of an RRC state of the target relay UE as described above, and so on.

In some embodiments, the remote UE may discover and measure a plurality of candidate relay UEs. In this case, the measurement report may comprise measurements and associated information for a plurality of candidate relay UEs. Alternatively, step 2 may be expanded to comprise a plurality of measurement reports associated with different candidate relay UEs. In some embodiments, the source gNB may select a target relay UE from among the plurality of candidate relay UEs; in other embodiments, the source gNB may pass to the target gNB information on some or all of the plurality of candidate relay UEs, and the target gNB may select a target relay UE. Diverse criteria may be applied (e.g., by the source or target gNB) to select a target relay UE; for example, the source or target gNB may prefer a target relay UE that is already in RRC_CONNECTED, a target relay UE with high communication capabilities, a target relay UE with a high-quality Uu link with the target gNB, and so on.

In step 3 of figure 5, the source gNB, having taken the decision to trigger a path switch procedure, sends a handover preparation message to the target gNB. In case the source gNB has selected a target relay UE, the handover preparation message may comprise information specific to the selected target relay UE. On the other hand, in case the target gNB is responsible for selecting a target relay UE, the handover preparation message may comprise information related to a plurality of candidate relay UEs. In either case, the information related to the relay UE (s) may include information on the quality or anticipated performance of the Uu link, information on one or more communication capabilities, information on the RRC state (s) of the relay UE (s) , identifiers such as L2IDs of the relay UEs, and so on. The handover preparation message may also comprise information related to the configuration and context of the remote UE, allowing the target gNB to take an informed decision on whether it should admit the remote UE into service with the target gNB.

In step 4 of figure 5, the target gNB selects a target relay UE if necessary and determines to admit the remote UE and the target relay UE into service on the target gNB. Alternatively, target relay selection may be performed by the source gNB (not shown in the figure) , in which case the target gNB only needs to perform handover admission for the remote UE and the target relay UE. The selection of a target relay UE may be based on implementation-dependent criteria, which may take into account any of the information provided in the measurement report (step 2) and/or the handover preparation message (step 3) . The decision to admit the UEs as part of the handover procedure may be based on system load at the target gNB, on information received by the target gNB in step 3 (for example, regarding the status of the target relay UE) , or on any other information available to the target gNB implementation.

In step 5 of figure 5, the target gNB sends, to the source gNB, a handover accept message. The handover accept message indicates that the target gNB has concluded that it can admit the remote UE and the target relay UE to service as part of the path switch procedure. If the target gNB selected a target relay UE in step 4, the handover accept message may include an identifier (for instance, a L2ID) of the selected target relay UE. The handover accept message may comprise a handover command formulated by the target gNB and including a configuration to be delivered to the remote UE, in accordance with a handover procedure.

In step 6 of figure 5, the source gNB forwards the handover command to the remote UE, for example, as part of an RRCReconfiguration message of an RRC protocol. The message containing the handover command may further contain one or more configuration instructions for the remote UE;for example, the message containing the handover command may be an RRCReconfiguration message instructing the remote UE to establish a connection on a PC5 interface with the target relay UE, to release an existing connection on a PC5 interface with a source relay UE (not shown in the figure) , and so on.

In step 7 of figure 5, the remote UE triggers a connection establishment procedure with the target relay UE. In case the remote UE and the target relay UE communicate on a PC5 interface, the connection establishment procedure may comprise a PC5 unicast link establishment procedure, which may also result in the establishment of a PC5-RRC connection. In case the remote UE and the target relay UE communicate via a different interface, such as a WiFi link or a proprietary technology, the connection establishment procedure may comprise any signalling necessary to establish a connection in the underlying technology. In some technologies, there may be no explicit connection establishment procedure, such as, for instance, technologies in which the remote UE and the target relay UE are preconfigured to operate together with prior knowledge of one another’s identities, and in such a case step 7 of the figure may not occur.

In step 8 of figure 5, the remote UE delivers a handover complete message (for instance, an RRCReconfigurationComplete message of an RRC protocol) to the target relay UE, with the expectation that the handover complete message will be forwarded to the target gNB to conclude the handover procedure. The handover complete message may be transmitted by the remote UE on radio resources configured as part of the connection establishment procedure in step 7, and/or on radio resources configured by a subsequent link reconfiguration procedure (not shown in the picture-this subsequent link reconfiguration procedure may, for instance, be triggered by an RRCReconfigurationSidelink message of a PC5-RRC protocol) .

If the target relay UE were in an RRC_CONNECTED state, it would be expected to deliver the handover complete message to the target gNB directly. However, recalling that for this figure the target relay UE is initially in an RRC_IDLE or RRC_INACTIVE state, the target relay UE needs to establish or resume an RRC connection with the target gNB so that the target relay UE can deliver the handover complete message to the target gNB. Accordingly, in step 9 of figure 5, the target relay UE triggers a random access channel (RACH) procedure to induce the target gNB to bring the target relay UE to an RRC_CONNECTED state. Various forms of the RACH procedure may be invoked in this step, triggered, for example, by the transmission of an initial “Msg1” or “MsgA” signal from the target relay UE to the target gNB.

In step 10 of figure 5, responsive to the triggering of the RACH procedure, the target gNB transmits, to the target relay UE, a connection setup message (for example, an RRCSetup message if the target relay UE is initially in RRC_IDLE, or an RRCResume message if the target relay UE is initially in RRC_INACTIVE) . The connection setup message may be transmitted, for example, as part of a “Msg3” or “MsgB” transmission of the RACH procedure that was initiated in step 9. The connection setup message may contain a configuration allowing relaying service to start. Alternatively or additionally, the target gNB may transmit, to the target relay UE, a reconfiguration message (not shown in the figure) comprising a configuration allowing relaying service to start.

In step 11 of figure 5, the target relay UE transmits, to the target gNB, a forwarded version of the handover complete message from step 8. This message, when received at the target gNB, concludes the handover procedure and allows communication between the target gNB and the remote UE via the target relay UE.

It is understood that the specific order or hierarchy of blocks in the processes /flowcharts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes /flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

Claims

A method of discovery, operable at a first [target relay] UE and comprising:

transmitting, to a second [remote] UE, a discovery message comprising information regarding an interface between the first UE and a [target] network node.
The method of claim 1, wherein the information comprises an indication of radio quality on the interface.
The method of claim 2, wherein the indication is a measurement of at least one of RSRP and RSRQ.
The method of claim 2, wherein the indication is a threshold of link quality.
The method of claim 2, wherein the indication is a measure of anticipated link performance.
The method of claim 1, wherein the information comprises an indication of at least one supported communication capability on the interface.
The method of claim 6, wherein the capability is a supported CA capability.
The method of claim 6, wherein the capability is a supported MIMO capability.
The method of claim 1, wherein the information comprises an indication of a protocol state in which the first UE operates on the interface.
A method of measurement reporting, operable at a first [remote] UE and comprising:

transmitting, to a first [source] network node, a measurement report message comprising a measurement of at least one second [candidate relay] UE and information regarding an interface between the at least one second UE and a second [target] network node.
The method of claim 10, wherein the information comprises an indication of radio quality on the interface.
The method of claim 11, wherein the indication is a measurement of at least one of RSRP and RSRQ.
The method of claim 11, wherein the indication is a threshold of link quality.
The method of claim 11, wherein the indication is a measure of anticipated link performance.
The method of claim 10, wherein the information comprises an indication of at least one supported communication capability on the interface.
The method of claim 15, wherein the capability is a supported CA capability.
The method of claim 15, wherein the capability is a supported MIMO capability.
The method of claim 10, wherein the information comprises an indication of a protocol state in which the first UE operates on the interface.
A method of relay selection, operable at a first [source or target] network node and comprising:

receiving, from a first [remote] UE or a second [source] network node, information regarding operation of a plurality of second [candidate target relay] UEs on an interface; and

selecting, from the plurality of second UEs, a third [target relay] UE to operate as a relay UE.
The method of claim 19, wherein the information comprises an indication of radio quality on the interface.
The method of claim 20, wherein the indication is a measurement of at least one of RSRP and RSRQ.
The method of claim 20, wherein the indication is a threshold of link quality.
The method of claim 20, wherein the indication is a measure of anticipated link performance.
The method of claim 19, wherein the information comprises an indication of at least one supported communication capability on the interface.
The method of claim 24, wherein the capability is a supported CA capability.
The method of claim 24, wherein the capability is a supported MIMO capability.
The method of claim 19, wherein the information comprises an indication of a protocol state in which the first UE operates on the interface.
A method of handover admission, operable at a first [target] network node and comprising:

receiving, from a second [source] network node, a handover preparation message requesting handover of a first [remote] UE and comprising information regarding the operation of at least one second [target relay] UE on an interface between the second UE and the first network node;

determining to admit the first UE in handover; and

sending, to the second network node, a handover accept message.
The method of claim 28, wherein the information comprises an indication of radio quality on the interface.
The method of claim 29, wherein the indication is a measurement of at least one of RSRP and RSRQ.
The method of claim 29, wherein the indication is a threshold of link quality.
The method of claim 29, wherein the indication is a measure of anticipated link performance.
The method of claim 28, wherein the information comprises an indication of at least one supported communication capability on the interface.
The method of claim 33, wherein the capability is a supported CA capability.
The method of claim 33, wherein the capability is a supported MIMO capability.
The method of claim 28, wherein the information comprises an indication of a protocol state in which the first UE operates on the interface.