Considering that the target relay UE is in RRC_IDLE or RRC_INACTIVE state, the serving cell of the relay UE should be the cell the relay UE is camping on. The camping cell ID (assuming cell #A) of the relay UE will be included in relay discovery message and will be discovered and reported by the remote UE to the gNB as part of the candidate relay UE's information in the measurement report. So, the target gNB of the relay UE's camping cell (cell #A) will provide RRC reconfiguration parameters for the remote UE's path switching. When the remote UE receives the RRC reconfiguration message from the serving or source gNB (i.e., step 3 in FIG. 1 or FIG. 2), the remote UE needs to send RRC reconfiguration complete message to the target gNB via the relay UE, which triggers the relay UE to establish its own RRC connection with the target gNB corresponding to its current camping cell (i.e., step 6 in FIG. 2).

The problem arises if the relay UE in RRC_IDLE/INACTIVE state has made the cell reselection to another cell (assuming cell #B) during the path switching preparation phase of the remote UE (i.e., the time period between measurement report from the remote UE to the serving gNB in step 1 of FIG. 2 and PC5 connection establishment completed in step 4 of FIG. 2). This is because the relay UE will establish RRC connection with cell #B instead of cell #A. Thus, the RRC reconfiguration complete message of the remote UE will be relayed to the wrong cell (i.e., cell #B instead of cell #A), causing failure of the indirect path switching of the remote UE.

In case of inter-gNB direct-to-indirect or indirect-to-indirect path switching, if the source gNB is responsible for selecting the target relay UE that is served by the target gNB, the relay UE in RRC_CONNECTED state may make HO during path switching phase, which will cause the same path switching failure as described above for the case considering the relay UE in RRC_IDLE/INACTIVE state. Note that it is open whether the source gNB or the target gNB is responsible for selecting the target relay UE.

Example embodiments of the invention are targeted to the failure scenario described above and focus on remote UE's behaviour to identify the failure and make faster failure recovery.

Before describing the example embodiments of the invention in detail, reference is made to FIG. 5 for illustrating a simplified block diagram of various electronic devices that are suitable for use in practicing the example embodiments of this invention.

FIG. 5 shows a block diagram of one possible and non-limiting system in which the example embodiments of the invention may be practiced. In FIG. 5, a user equipment (UE) 10 is in wireless communication with a wireless network 1. A UE is a wireless, typically mobile device that can access a wireless network. The UE 10 includes one or more processors DP 10A, one or more memories MEM 10B, and one or more transceivers TRANS 10D interconnected through one or more buses. Each of the one or more transceivers TRANS 10D includes a receiver and a transmitter. The one or more buses may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, and the like. The one or more transceivers TRANS 10D are connected to one or more antennas for communication 11 and 18 to gNB 12 and NN 13, respectively. The one or more memories MEM 10B include computer program code PROG 10C. The UE 10 communicates with gNB 12 and/or NN 13 via a wireless link 111.

The gNB 12 (NR/5G Node B or possibly an evolved NB) is a base station such as a master or secondary node base station (e.g., for NR or LTE long term evolution) that communicates with devices such as NN 13 and UE 10 of FIG. 5. The gNB 12 provides access to wireless devices such as the UE 10 to the wireless network 1. The gNB 12 includes one or more processors DP 12A, one or more memories MEM 12C, and one or more transceivers TRANS 12D interconnected through one or more buses. In accordance with the example embodiments these TRANS 12D can include X2 and/or Xn interfaces for use to perform the example embodiments of the invention. Each of the one or more transceivers TRANS 12D includes a receiver and a transmitter. The one or more transceivers TRANS 12D are connected to one or more antennas for communication over at least link 11 with the UE 10. The one or more memories MEM 12B and the computer program code PROG 12C are configured to cause, with the one or more processors DP 12A, the gNB 12 to perform one or more of the operations as described herein. The gNB 12 may communicate with another gNB or eNB, or a device such as the NN 13. Further, the link 11 and or any other link may be wired or wireless or both and may implement, e.g., an X2 or Xn interface. Further the link 11 may be through other network devices such as, but not limited to an NCE/MME/SGW device such as the NCE/MME/SGW 14 of FIG. 5.

The NN 13 can comprise a mobility function device such as an AMF or SMF, further the NN 13 may comprise a NR/5G Node B or possibly an evolved NB a base station such as a master or secondary node base station (e.g., for NR or LTE long term evolution) that communicates with devices such as the gNB 12 and/or UE 10 and/or the wireless network 1. The NN 13 includes one or more processors DP 13A, one or more memories MEM 13B, one or more network interfaces, and one or more transceivers TRANS 12D interconnected through one or more buses. In accordance with the example embodiments these network interfaces of NN 13 can include X2 and/or Xn interfaces for use to perform the example embodiments of the invention. Each of the one or more transceivers TRANS 13D includes a receiver and a transmitter connected to one or more antennas. The one or more memories MEM 13B include computer program code PROG 13C. For instance, the one or more memories MEM 13B and the computer program code PROG 13C are configured to cause, with the one or more processors DP 13A, the NN 13 to perform one or more of the operations as described herein. The NN 13 may communicate with another mobility function device and/or eNB such as the gNB 12 and the UE 10 or any other device using, e.g., link 11 or another link. These links maybe wired or wireless or both and may implement, e.g., an X2 or Xn interface. Further, as stated above the link 11 may be through other network devices such as, but not limited to an NCE/MME/SGW device such as the NCE/MME/SGW 14 of FIG. 5. The NCE/MME/SGW 14 including MME (Mobility Management Entity)/SGW (Serving Gateway) functionality, such as User Plane Functionalities, and/or an Access Management functionality for LTE and similar functionality for 5G.

The one or more buses of the device of FIG. 5 may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, wireless channels, and the like. For example, the one or more transceivers TRANS 12D, TRANS 13D and/or TRANS 10D may be implemented as a remote radio head (RRH), with the other elements of the gNB 12 being physically in a different location from the RRH, and the one or more buses 157 could be implemented in part as fiber optic cable to connect the other elements of the gNB 12 to a RRH.

It is noted that although FIG. 5 shows a network node or base station such as the gNB 12 as in FIG. 5 and mobility management device such as the NN 13 as in FIG. 5, these devices can incorporate or be incorporated into an eNodeB or eNB or gNB such as for LTE and NR, and would still be configurable to perform example embodiments of the invention as described in this application.

Also, it is noted that description herein indicates that “cells” perform functions, but it should be clear that the gNB that forms the cell and/or a user equipment and/or mobility management function device that will perform the functions. In addition, the cell makes up part of a gNB, and there can be multiple cells per gNB.

The wireless network 1 may include a network control element (NCE/MME/SGW) 14 that may include NCE (Network Control Element), MME (Mobility Management Entity)/SGW (Serving Gateway) functionality, and which provides connectivity with a further network, such as a telephone network and/or a data communications network (e.g., the Internet). The gNB 12 and the NN 13 are coupled via a link 13 and/or link 14 to the NCE/MME/SGW 14. In addition, it is noted that the operations in accordance with example embodiments of the invention, as performed by the NN 13, may also be performed at the NCE/MME/SGW 14.

The NCE/MME/SGW 14 includes one or more processors DP 14A, one or more memories MEM 14B, and one or more network interfaces (N/W I/F(s)), interconnected through one or more buses coupled with the link 13 and/or 14. In accordance with the example embodiments these network interfaces can include X2 and/or Xn interfaces for use to perform the example embodiments of the invention. The one or more memories MEM 14B include computer program code PROG 14C. The one or more memories MEM14B and the computer program code PROG 14C are configured to, with the one or more processors DP 14A, cause the NCE/MME/SGW 14 to perform one or more operations which may be needed to support the operations in accordance with the example embodiments of the invention.

The wireless Network 1 may implement network virtualization, which is the process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Network virtualization involves platform virtualization, often combined with resource virtualization. Network virtualization is categorized as either external, combining many networks, or parts of networks, into a virtual unit, or internal, providing network-like functionality to software containers on a single system. Note that the virtualized entities that result from the network virtualization are still implemented, at some level, using hardware such as processors DP10A, DP12A, DP13A, and/or DP14A and memories MEM 10B, MEM 12B, MEM 13B, and/or MEM 14B, and also such virtualized entities create technical effects.

The computer readable memories MEM 10B, MEM 12B, MEM 13B, and MEM 14B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The computer readable memories MEM 10B, MEM 12B, MEM 13B, and MEM 14B may be means for performing storage functions. The processors DP10A, DP12A, DP13A, and DP14A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples. The processors DP10A, DP12A, DP13A, and DP14A may be means for performing functions, such as controlling the UE 10, gNB 12, NN 13, NCE/MME/SGW 14 and other functions as described herein.

As similarly stated above, this invention is targeted to the failure scenario described above and focus on remote UE's behaviour to identify the failure and make faster failure recovery.

The Notification message procedure in sidelink was specified in 3GPP standards for relay UE to send NotificationMessageSidelink to the connected remote UE in the following scenario:

- upon Uu RLF happens to relay UE
- upon HO is configured to relay UE
- upon cell reselection from relay UE
- upon RRC connection establish/resume failure.

The NotificationMessageSidelink from relay UE will trigger the remote UE in RRC_CONNECTED state (this is the case for remote UE performing path switching) to initiate RRC connection re-establishment procedure.

The specified Notification message procedure in sidelink can only be applied between relay UE and connected remote UE. In the scenario that the problem is identified above, relay UE and remote UE may not have PC5 connection established yet when relay UE makes cell change either due to cell reselection or handover (HO). Therefore, the Notification message procedure cannot solve the problem in order to avoid path switching failure if relay UE makes a cell change during path switching preparation phase and there is no PC5 connection established between relay UE and remote UE.

Example embodiments of this invention proposes remote UE's behaviour after detecting a change of serving/camping cell of the relay UE that has been reported by the remote UE to the serving gNB (source gNB) as the candidate relay UE or has been configured by the serving gNB or by the target gNB via the serving gNB as the target relay UE for indirect path switching of the remote UE. The change of serving/camping cell of the relay UE may be identified or detected by the remote UE, e.g., either upon receiving the upcoming relay discovery (RD) message from the relay UE after the remote UE reported the relay UE as candidate relay UE, or upon receiving the transferred System Information (SI) from the relay UE after the remote UE establishes the PC5 connection with the target relay UE configured from the gNB. The received RD message or SI from the relay UE indicates a new serving/camping cell ID of the relay UE different from that indicated before by the relay UE and reported to the serving gNB by the remote UE. When the remote UE detected the relay UE has changed the serving/camping cell, the remote UE may be configured or triggered to perform the following actions:

- The remote UE may be configured to trigger another measurement report when it receives relay discovery message from the relay UE that is included in the candidate relay list reported to the gNB and the relay discovery message indicates the relay UE's serving/camping cell ID is different from the one reported to the gNB in the candidate relay list. This means a new trigger for measurement report from the remote UE needs to be specified and/or configured from the gNB;
- In addition to or instead of triggering another measurement report, the remote UE may be triggered to initiate RRC connection re-establishment procedure instead of responding with RRC reconfiguration complete message via the relay UE if the remote UE identifies the latest serving/camping cell of the target relay UE is different from the target cell ID that the remote UE is configured to connect to. This means a new condition of initiating RRC connection re-establishment procedure needs to be specified.

Example embodiments of the invention are given in FIG. 3 and FIG. 4. It is assumed therein that the relay UE is in RRC_IDLE/INACTIVE state and camping in cell #A when the remote UE has discovered the relay UE and reported the relay UE as one of the candidate relay UE(s) to the gNB in measurement report in step 1 of FIG. 3 and FIG. 4.

It may happen that, not long after the remote UE sent the measurement report to the gNB, the relay UE in RRC_IDLE/INACTIVE state may perform cell reselection and camp to another cell, e.g., cell #B. If the relay UE sends a new relay discovery message after the cell reselection to cell #B indicating ID of cell #B, the remote UE may identify the cell ID of cell #B included in the newly received relay discovery message from the relay UE is different from the cell ID of cell #A that the remote UE has reported to the gNB in the candidate relay UE list and associated with the relay UE in question. Upon identifying the change of the serving/camping cell from the relay UE, the remote UE may be triggered to send another measurement report to indicate the candidate relay UE list with the updated cell ID associated with the relay UE in question. The measurement report may be triggered only if the remote UE has not yet received the RRC reconfiguration message from the gNB to configure the remote UE for path switching via the relay UE. This means the gNB may not make the path switching decision yet or at least may not issue the RRC reconfiguration message to the remote UE yet for path switching configuration. The new measurement report with the new cell ID of the relay UE can trigger the gNB to either make or renew the path switching decision to the correct cell. To facilitate the remote UE to detect the cell change of the relay UE for triggering another measurement report as early as possible, the relay UE may be configured to send one or more additional relay discovery message(s) after every cell change within a configured time interval starting from the time instance of the cell reselection decision at the relay UE. This may be implemented in access stratum layer to allow the relay UE to send additional relay discovery messages with the new cell ID. Or it can be implemented by upper layer with cross layer interaction upon receiving the change or update of cell ID from access stratum layer at the relay UE. It means when the relay UE selects a new cell or is handed over to a new cell, the access stratum layer of the UE indicates to the upper layer (e.g., non-access stratum layer or application layer) cell ID of the new cell (the change of the cell ID). This triggers the upper layer that is responsible for controlling/managing relay discovery message transmission to send one or more additional relay discovery message(s).

Depending on the time instance when the relay UE performs the cell reselection and/or when additional discovery message is sent by the relay UE, the remote UE may not have enough time to identify the change of camping cell of the relay UE and, based on that, send another or updated measurement report to the serving gNB before the gNB makes decision of indirect path switching and sends RRC reconfiguration message to the remote UE. In this case, the remote UE may request PC5 connection establishment with the relay UE, as expected. Upon PC5 connection establishment between the remote UE and the relay UE, the relay UE may forward the SIs (e.g., System Information Block #1 (SIB1), as there are a number of indexed SIB #specified in standards at the time of this application, that contains cell ID of the current serving/camping cell of the relay UE) to the remote UE, which may be used by the remote UE to identify the cell change of the relay UE. According to the current 3GPP standards, it's up to the relay UE's implementation to forward SIB1 to the remote UE based on the remote UE's request or use unsolicited forwarding of SIB1. Herein to facilitate the remote UE to identify the change of serving/camping cell from the relay UE, the relay UE may be configured to forward at least SIB1 upon establishment of PC5 connection with the remote UE, which may be also conditioned to perform the unsolicited forwarding of SIB1 within a configured time interval starting from the time instance of the cell reselection decision at the relay UE. Or the remote UE may receive another relay discovery message from the relay UE after receiving RRC reconfiguration message. If the cell ID in the newly received relay discovery message or identified from forwarded SI is not the same as the target cell ID that is indicated in the received RRC reconfiguration message, the remote UE can also identify the change of the camping cell from the relay UE. Thus, the remote UE is triggered to initiate RRC connection re-establishment procedure with either the source cell or the target cell instead of responding with RRC reconfiguration complete message as in baseline procedure.

The above implementation examples assume the relay UE in RRC_IDLE/INACTIVE state makes cell reselection during the remote UE's path switching either before or after the serving or source gNB makes path switching decision. The same problem of paths switching failure will happen in the case when the relay UE in RRC_CONNECTED state makes HO after the gNB sent RRC Reconfiguration message to the remote UE in step 4 of FIG. 4. The proposed solution as illustrated in FIG. 4 can be applied for this case, too.

FIG. 3 and FIG. 4 each show an illustration of some example embodiments of the invention.

Example embodiments of the invention as shown in FIG. 3 include operations of a Remote UE, a Relay UE, and a Source gNB. As shown in FIG. 3 the Relay UE is camping on cell #A. As shown in step 1 of FIG. 3 the Remote UE sends a measurement configuration and reporting message to the source gNB. As shown in step 1a of FIG. 3 the Relay UE is performing cell reselection to cell #B. As shown in step 1b of FIG. 3 the Relay UE is triggered to increase frequency of a relay discovery message. As shown in step 2 of FIG. 3 the Relay UE sends to the Remote UE a relay discovery message. As shown in step 3 of FIG. 3 the Remote UE identifies a change of camping cell of the relay UE and triggers another measurement report. As shown in step 4 of FIG. 3 the Remote UE sends to the source gNb measurement configuration and reporting messaging. Then as shown in step 5 of FIG. 3 the Source gNB makes a decision of switching to a relay UE.

Example embodiments of the invention as shown in FIG. 4 include operations of a Remote UE, a Relay UE, Source gNB, and Target gNB. As shown in FIG. 4 the Relay UE is camping on cell #A served by the target gNB. As shown in step 1 of FIG. 4 the Remote UE sends a measurement configuration and reporting message to the source gNB. As shown in step 1a of FIG. 4 the Relay UE is performing cell reselection to cell #B. As shown in step 2 of FIG. 4 the Source gNB makes a decision of switching to a relay UE. As shown in step 3 of FIG. 4 there is a path switching operation between the Source gNB and the Target gNB. As shown in step 4 of FIG. 4 the Source gNB sends to the Remote UE an RRC reconfiguration message (path switching command) As shown in step 4a of FIG. 4 the Relay UE is triggered to increase frequency of a relay discovery message. As shown in step 5 of FIG. 4 there is PC5 connection establishment between the Remote UE and the Relay UE. As shown in step 6 of FIG. 4 the Relay UE sends to the Remote UE a relay discovery message. As shown in step 7 of FIG. 4 the Remote UE is identifying the change of camping cell of target relay UE and triggering RRC connection re-establishment. Then as shown in step 8 of FIG. 4 the Remote UE sends towards the Source gNB an RRC connection re-establishment message.

FIG. 6A and FIG. 6B each show a method in accordance with example embodiments of the invention which may be performed by an apparatus.

FIG. 6A illustrates operations which may be performed by a device such as, but not limited to, a remote user device (e.g., the UE 10 as in FIG. 5). As shown in step 605 of FIG. 6A there is sending, by a remote user equipment of a source cell, towards a network node of the source cell a measurement report comprising a candidate relay list. As shown in step 610 of FIG. 6A wherein the candidate relay list comprises at least one of a serving cell identification or camping cell identification for at least one candidate relay user equipment for an indirect path switching from the source cell to a target cell associated with a candidate relay user equipment. As shown in step 615 of FIG. 6A there is detecting a change of a serving cell or camping cell of the candidate relay user equipment from the target cell to another cell based on receiving from the candidate relay user equipment at least one message that indicates at least one of serving cell identification or camping cell identification for the candidate relay user equipment is different than as reported to the network node in the measurement report. Then as shown in step 620 of FIG. 6A there is, based on the detecting, performing one of sending an updated measurement report towards the network node triggering renewing a path switch decision or initiating a radio resource control connection re-establishment procedure with the source cell or the target cell.

In accordance with the example embodiments as described in the paragraph above, wherein the at least one message comprises a discovery message that indicates the at least one of serving cell identification or camping cell identification for the candidate relay user equipment is different than as reported to the network node in the measurement report.

In accordance with the example embodiments as described in the paragraphs above, wherein the at least one non-transitory memory including computer program code storing instructions is executed by the at least one processor to cause the apparatus at least to perform: identifying a path switch decision to use the candidate relay user equipment of the candidate relay list being configured from the network node for the path switch, wherein the identifying is based on receiving a radio resource control reconfiguration message from the network node to configure the remote user equipment for path switching via the candidate relay user equipment.

In accordance with the example embodiments as described in the paragraphs above, wherein the at least one non-transitory memory including computer program code storing instructions is executed by the at least one processor to cause the apparatus at least to perform: initiating a radio resource control connection re-establishment procedure with the source cell or the target cell, wherein the initiating is based on that the change of the serving cell or camping cell of the candidate relay user equipment detected one of after identifying the path switch decision or after receiving the radio resource control reconfiguration message from the network node to configure the remote user equipment for path switching via the candidate relay user equipment.

In accordance with the example embodiments as described in the paragraphs above, wherein the at least one non-transitory memory including computer program code storing instructions is executed by the at least one processor to cause the apparatus at least to perform: establishing a direct connection with the candidate relay user equipment being configured from the network node.

In accordance with the example embodiments as described in the paragraphs above, wherein the at least one non-transitory memory including computer program code storing instructions is executed by the at least one processor to cause the apparatus at least to perform: during or after the direct connection establishment, receiving from the candidate relay user equipment system information comprising a cell identification of a current serving cell or camping cell of the candidate relay user equipment used to identify a cell change of the candidate relay user equipment.

In accordance with the example embodiments as described in the paragraphs above, wherein the at least one message comprises the system information from the candidate relay user equipment received during or after the remote user equipment establishes the direct connection with the candidate relay user equipment.

In accordance with the example embodiments as described in the paragraphs above, wherein the candidate relay user equipment is in an idle or inactive state, and wherein the candidate relay user equipment in the idle or inactive state has performed cell reselection from the target cell to another cell causing the cell change of the candidate relay user equipment with a different at least one of serving cell identification or camping cell identification for the candidate relay user equipment.

In accordance with the example embodiments as described in the paragraphs above, wherein the updated measurement report comprises an updated candidate relay list indicating the different at least one of a serving cell identification or camping cell identification for the candidate relay user equipment.

In accordance with the example embodiments as described in the paragraphs above, wherein the updated measurement report is triggered based on the remote user equipment not yet receiving a radio resource control reconfiguration message from the network node to configure the remote user equipment for path switching via the candidate relay user equipment.

A non-transitory computer-readable medium (MEM