WO2024026818A1

WO2024026818A1 - Mobility support in u2n relay

Info

Publication number: WO2024026818A1
Application number: PCT/CN2022/110486
Authority: WO
Inventors: Ling Yu; Vinh Van Phan; Xiang Xu; Mohamed Amin Nassar; Faranaz SABOURI-SICHANI; György Tamás Wolfner; Stepan Kucera; Ravi Prasad R K
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2022-08-05
Filing date: 2022-08-05
Publication date: 2024-02-08

Abstract

Embodiments of the present disclosure relate to mobility support in User Equipment (UE) -to-Network Relay (U2N Relay). In example embodiments, a network device determines to hand over a relay terminal device from the network device to a target network device. Then, the network device determines a reconfiguration of a remote terminal device associated with the relay terminal device, the reconfiguration being caused by the handover. Moreover, the network device transmits a first radio resource control message to the relay terminal device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.

Description

MOBILITY SUPPORT IN U2N RELAY

FIELD

Various example embodiments relate to the field of telecommunication and in particular, to methods, devices, apparatuses, and computer readable storage media for mobility support in User Equipment (UE) -to-Network Relay (U2N Relay) .

BACKGROUND

Sidelink (SL) relay is introduced to support the U2N Relay function to provide connectivity to the network for a U2N Remote UE. The user plane (UP) and control plane (CP) protocol stacks of Layer 2 (L2) U2N relay are introduced respectively. For a remote UE, the higher layer protocols, such as Uu service data adaptation protocol (SDAP) , packet data convergence protocol (PDCP) , and radio resource control (RRC) protocols, are terminated end-to-end between the remote UE and a New Radio (NR) NodeB (gNB) . The lower layer protocols, such as radio link control (RLC) , medium access control (MAC) , and physical layer (PHY) protocols are terminated in each hop between the remote UE and the relay UE or between the relay UE and the gNB. There are also further protocols, such as Uu Sidelink Relay Application Protocol (SRAP) between the relay UE and the gNB and Proximity Services (ProSe) Communication 5 (PC5) SRAP between the remote UE and the relay UE, introduced in each hop to handle the traffic mapping of different bearers and remote UEs.

In addition, with the development of communications technologies, there is a new network architecture developed to split functions of a base station in a radio access network for improving flexibility of deployment. Some functions of the base station are deployed on a central unit (CU) , and other functions are deployed on a distributed unit (DU) . For example, the CU may be responsible for some higher-level protocol stack functions and the DU may be responsible for the lower-level protocol stack functions.

SUMMARY

In general, example embodiments of the present disclosure provide a solution for mobility support in U2N relay.

In a first aspect, there is provided a network device. The network device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the network device at least to: determine to hand over a relay terminal device from the network device to a target network device; determine a reconfiguration of a remote terminal device associated with the relay terminal device, the reconfiguration being caused by the handover; and transmit a first radio resource control message to the relay terminal device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.

In a second aspect, there is provided a relay terminal device. The relay terminal device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the relay terminal device at least to: receive, from a network device, a first radio resource control message to hand over from the network device to a target network device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for a remote terminal device associated with the relay terminal device is received from the network device or delivered to the remote terminal device; and based on determining that the last message received from the network device or is delivered to the remote terminal device, detach from the network device.

In a third aspect, there is provided a remote terminal device. The remote terminal device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the remote terminal device at least to: receive, from a network device via a relay terminal device associated with the remote terminal device, a second radio resource control message for a reconfiguration of the remote terminal device, the second radio resource control message indicating the remote terminal device to transmit an indication of last message delivery to the relay terminal device upon receiving the second radio resource control message; and transmit, to the relay terminal device, an indication that the last message is delivered to the remote terminal device.

In a fourth aspect, there is provided a method implemented at a network device. The method comprises determining to hand over a relay terminal device from the network device to a target network device; determining a reconfiguration of a remote terminal device associated with the relay terminal device, the reconfiguration being caused by the handover; and transmitting a first radio resource control message to the relay terminal device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.

In a fifth aspect, there is provided a method implemented at a relay terminal device. The method comprises receiving, from a network device, a first radio resource control message to hand over from the network device to a target network device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for a remote terminal device associated with the relay terminal device is received from the network device or delivered to the remote terminal device; and based on determining that the last message is received from the network device or delivered to the remote terminal device, detaching from the network device.

In a sixth aspect, there is provided a method implemented at a remote terminal device. The method comprises receiving, receive, from a network device via a relay terminal device associated with the remote terminal device, a second radio resource control message for a reconfiguration of the remote terminal device, the second radio resource control message indicating the remote terminal device to transmit an indication of last message delivery to the relay terminal device upon receiving the second radio resource control message; and transmitting, to the relay terminal device, an indication that the last message is delivered to the remote terminal device.

In a seventh aspect, there is provided an apparatus. The apparatus comprises means for determining, at a network device, to hand over a relay terminal device from the network device to a target network device; means for determining a reconfiguration of a remote terminal device associated with the relay terminal device, the reconfiguration being caused by the handover; and means for transmitting a first radio resource control message to the relay terminal device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.

In an eighth aspect, there is provided an apparatus. The apparatus comprises means for receiving, at a relay terminal device, from a network device, a first radio resource control message to hand over from the network device to a target network device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for a remote terminal device associated with the relay terminal device is received from the network device or delivered to the remote terminal device; and means for, based on determining that the last message is received from the network device or delivered to the remote terminal device, detaching from the network device.

In a ninth aspect, there is provided an apparatus. The apparatus comprises means for receiving, at a remote terminal device, receive, from a network device via a relay terminal device associated with the remote terminal device, a second radio resource control message for a reconfiguration of the remote terminal device, the second radio resource control message indicating the remote terminal device to transmit an indication of last message delivery to the relay terminal device upon receiving the second radio resource control message; and means for transmitting, to the relay terminal device, an indication that the last message is delivered to the remote terminal device.

In a tenth aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method according to any one of the above fourth to sixth aspects.

In an eleventh aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to perform at least the method according to any one of the above fourth to sixth aspects.

In a twelfth aspect, there is provided a network device. The network device comprises: determining circuitry configured to determine, at a network device, to hand over a relay terminal device from the network device to a target network device; determining circuitry configured to determine a reconfiguration of a remote terminal device associated with the relay terminal device, the reconfiguration being caused by the handover; and transmitting circuitry configured to transmit a first radio resource control message to the relay terminal device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.

In a thirteenth aspect, there is provided a relay terminal device. The relay terminal device comprises: receiving circuitry configured to receive, at a relay terminal device, from a network device, a first radio resource control message to hand over from the network device to a target network device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for a remote terminal device associated with the relay terminal device is received from the network device or delivered to the remote terminal device; and detaching circuitry configured to, based on determining that the last message is received from the network device or delivered to the remote terminal device, detach from the network device.

In an fourteenth aspect, there is provided a remote terminal device. The remote terminal device comprises: receiving circuitry configured to receive, at a remote terminal device, receive, from a network device via a relay terminal device associated with the remote terminal device, a second radio resource control message for a reconfiguration of the remote terminal device, the second radio resource control message indicating the remote terminal device to transmit an indication of last message delivery to the relay terminal device upon receiving the second radio resource control message; and transmitting circuitry configured to transmit, to the relay terminal device, an indication that the last message is delivered to the remote terminal device.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described with reference to the accompanying drawings, where:

FIG. 1A illustrates an example of a network environment in which some example embodiments of the present disclosure may be implemented;

FIG. 1B illustrates an example scenario in which some example embodiments of the present disclosure may be implemented;

FIG. 1C illustrates a user plane protocol stack for L2 UE-to-Network Relay according to some example embodiments of the present disclosure;

FIG. 1D illustrates a control plane protocol stack for L2 UE-to-Network Relay according to some example embodiments of the present disclosure;

FIG. 2 illustrates a signaling flow between devices according to some example embodiments of the present disclosure;

FIG. 3 illustrates an example of the indication using a header of sidelink relay adaptation protocol (SRAP) protocol data unit (PDU) according to some example embodiments of the present disclosure;

FIG. 4 illustrates an example of the indication using an SRAP control PDU (C-PDU) according to some example embodiments of the present disclosure;

FIG. 5 illustrates a signaling flow between devices according to some other example embodiments of the present disclosure;

FIG. 6 illustrates an example process for mobility support in U2N relay with one remote UE according to some example embodiments of the present disclosure;

FIG. 7 illustrates another example process for mobility support in U2N relay with one remote UE according to some other example embodiments of the present disclosure;

FIG. 8 illustrates an example process for mobility support in U2N relay with multiple remote UEs according to some example embodiments of the present disclosure;

FIG. 9 illustrates another example process for mobility support in U2N relay with multiple remote UEs according to some other example embodiments of the present disclosure;

FIG. 10 illustrates a flowchart of a method implemented at a network device according to some embodiments of the present disclosure;

FIG. 11 illustrates a flowchart of a method implemented at a relay terminal device according to some other embodiments of the present disclosure;

FIG. 12 illustrates a flowchart of a method implemented at a remote terminal device according to some other embodiments of the present disclosure;

FIG. 13 illustrates a simplified block diagram of a device that is suitable for implementing some example embodiments of the present disclosure; and

FIG. 14 illustrates a block diagram of an example of a computer readable medium in accordance with some example embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an embodiment, ” “an example embodiment, ” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof. As used herein, “at least one of the following: <a list of two or more elements>” and “at least one of <a list of two or more elements>” and similar wording, where the list of two or more elements are joined by “and” or “or” , mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) :

(i) a combination of analog and/or digital hardware circuit (s) with software/firmware and

(ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

As used herein, the term “communication network” refers to a network following any suitable communication standards, such as Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the third generation (3G) , the fourth generation (4G) , 4.5G, the future fifth generation (5G) communication protocols, and/or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP) , for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a NR NB (also referred to as a gNB) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , a relay, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology.

As used herein, the term “network element” refers to a device that can implement some of the functions of the network device, such as a CU or a DU. For example, the CU may be responsible for some high-level protocol stack functions and the DU may be responsible for the lower-level functions.

The term “terminal device” refers to any end-user device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE) , a Subscriber Station (SS) , a Portable Subscriber Station, a Mobile Station (MS) , or an Access Terminal (AT) . The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA) , portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) , an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD) , a vehicle, a drone, a medical device and applications (e.g., remote surgery) , an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts) , a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. In the following description, the terms “terminal device” , “communication device” , “terminal” , “user equipment” and “UE” may be used interchangeably.

As stated above, SL relay is introduced to support the U2N Relay function to provide connectivity to the network for a U2N Remote UE. The following traffic mapping rules are specified in L2 U2N relay:

- Over Uu interface, the traffic of the remote UE and traffic of the relay UE cannot be mapped to the same Uu-RLC channel.

- Over Uu interface, the user plane traffic or control plane traffic of the same or different remote UEs can be mapped/multiplexed into the same Uu-RLC channel of the relay UE.

- Over Uu interface and PC5 interface, the UP traffic (corresponding to the remote UE’s Data Radio Bearer (DRB) traffic) and CP traffic of the remote UE (corresponding to the remote UE’s Signaling Radio Bearer (SRB) traffic) cannot be mapped/multiplexed into the same RLC channel.

In the third generation partnership project (3GPP) release 18 (Rel-18) , NR SL Relay enhancement has been discussed. The objectives of a Work Item (WI) is to enhance service continuity for single-hop L2 UE-to-NW relay for the following scenarios:

a) Inter-gNB indirect-to-direct path switching (i.e., “remote UE <-> first relay UE <-> Source gNB (S-gNB) ” to “remote UE <-> Target gNB (T-gNB) ” )

b) Inter-gNB direct-to-indirect path switching (i.e., “remote UE <-> S-gNB” to “remote UE <-> first relay UE <-> T-gNB” )

c) Intra-gNB indirect-to-indirect path switching (i.e., “remote UE <-> first relay UE <-> S-gNB” to “remote UE <-> second relay UE <-> S-gNB” )

d) Inter-gNB indirect-to-indirect path switching (i.e., “remote UE<-> first relay UE <-> S-gNB” to “remote UE <-> second relay UE <-> T-gNB” )

The above scenario d) is to be supported by reusing solutions for the other scenarios without specific optimizations.

When the remote UE has already established a U2N relay connection via the relay UE with the source gNB, the remote UE’s UP and CP traffic transmissions with the source gNB are forwarded via the relay UE. When the relay UE is configured by the source gNB to hand over to a target gNB, the remote UE needs to be reconfigured to perform either handover to the same target gNB, or path switching to the direct path of the source gNB or another gNB or path switching to another indirect path via a re-selected relay UE, etc. This will trigger the source gNB to initiate an RRC reconfiguration procedure to the remote UE for handover or path switching while at the same time initiating an RRC reconfiguration procedure to the relay UE for handover to the target gNB.

In the L2 U2N relay, the RRC reconfiguration procedure of the remote UE is terminated between the remote UE and the source gNB. The relay UE only provides the relaying functions in the lower radio L2 protocol under PDCP. So the relay UE is not aware of which RRC procedure message has been initiated by the source gNB towards the remote UE. When the relay UE receives an RRCReconfiguration message (i.e. handover command message in handover case) of its own from the source gNB to configure the relay UE to perform handover, the relay UE may perform handover by detaching from the serving cell before it successfully receives the RRCReconfiguration message of the remote UE over Uu interface from the source gNB. When this happens, the remote UE will fail to get the RRCReconfiguration message from the source gNB for handover or path switching while the relay UE hands over to the target gNB. Thus, the remote UE’s RRC connection to the source gNB will be interrupted and the service continuity of ongoing traffic of the remote UE will be impacted until the remote UE re-establishes the RRC connection.

The gNB implementation may solve the above problem by triggering the remote UE’s RRC reconfiguration procedure for handover or path switching always earlier than the relay UE’s RRC reconfiguration for handover. However, there are some constraints to make the gNB implementation solution impractical.

For example, it may be too late to initiate the RRC reconfiguration procedure to the relay UE for handover if the gNB needs to wait for the completion of the remote UE’s RRC reconfiguration procedure. This may impact the robustness of the handover of the relay UE, especially in a high mobility scenario which is a typical scenario for many Vehicle to anything (V2X) use cases.

In addition, in the normal handover procedure, the RRC reconfiguration completion message from the UE is not sent to the source gNB but to the target gNB. In this case, with regards to the handover of the remote UE, the source gNB is not able to ensure the RRCReconfiguration message has been delivered to the remote UE before it initiates the RRC reconfiguration procedure to the relay UE for handover, as there is no end-to-end RLC or MAC protocol between the gNB and the remote UE to allow gNB to be aware of the delivery of RRCReconfiguration message by Automatic Repeat Request (ARQ) or Hybrid Automatic Repeat Request (HARQ) feedback.

Moreover, if the source gNB doesn’ t need to wait for completion confirmation from the remote UE, but just initiates and delivers the RRCReconfiguration message of the remote UE to the lower layer before delivering the RRCReconfiguration message of the relay UE to the lower layer, it cannot make sure that the remote UE’s RRCReconfiguration message can be transmitted to the relay UE always earlier than the relay UE’s own RRCReconfiguration message by the lower layer protocol. The reason is that the relay UE’s SRB and the remote UE’s SRB cannot be multiplexed into the same Uu-RLC channel, but different remote UEs’S RBs may be multiplexed into the same Uu-RLC channel. For example, if multiple remote UEs are connected to the same relay UE, the transmission of the remote UEs’ RRC messages multiplexed into the same Uu-RLC channel may experience a longer delay in the lower layer protocol (for example, in the MAC layer for multiplexing and logical channel priority) than the relay UE’s RRC message mapped to the different Uu-RLC channel and logical channel.

Besides, it is specified in Release 17 that the relay UE sends a SL notification to the connected remote UE, when one of the following conditions is met:

- upon Uu Radio Link Failure (RLF) ;

- upon reception of an RRCReconfiguration message including the reconfigurationWithSync (i.e. handover command) ;

- upon cell reselection;

- upon the relay UE's RRC connection failure including RRC connection reject, Timer T300 expiry, and RRC resume failure.

When the remote UE receives the SL notification from the relay UE, it initiates an RRC re-establishment procedure or releases the PC5 connection with the relay UE depending on the RRC state of the remote UE. 3GPP Release 17 specifies the SL notification and that the remote UE initiates the RRC re-establishment procedure upon receiving the SL notification because it was agreed that no optimization feature will be pursued in Release 17 due to the time limitation on finalizing the WI in Release 17.

However, the service continuity of the remote UE will be impacted during the relay UE’s handover or the failure cases if the remote UE can only be triggered to initiate the RRC re-establishment procedure. Therefore, there is a service continuity enhancement objective in Release 18 SL relay WI. According to the Release 17 specification, there is no need to initiate the RRC reconfiguration procedure for the remote UE when the relay UE is reconfigured for handover. Therefore, the problem described above was not discussed during the 3GPP Release 17 timeframe. By now, there is no effective way to address the above issues to further improve the communication performance of the user.

According to embodiments of the present disclosure, there is providing a scheme for mobility support in U2N relay. With this scheme, a network device determines to hand over a relay terminal device from the network device to a target network device; Then, the network device determines a reconfiguration of a remote terminal device associated with the relay terminal device. The reconfiguration is caused by the handover. Moreover, the network device transmits a first radio resource control (RRC) message to the relay terminal device. The first RRC message requests the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.

Then, the relay terminal device detaches from the network device based on determining that the last message for the remote terminal device is delivered to the remote terminal device. This scheme improves user experience by avoiding the service interruption caused by the failed delivery of the remote UE’s RRCReconfiguration message. As such, it is possible to improve communication efficiency.

Principles and embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Reference is first made to FIG. 1A, which illustrates an example environment 100 in which example embodiments of the present disclosure can be implemented.

The environment 100, which may be a part of a communication network, comprises a network device 105. In some example embodiments, the network device 105 may comprises two

network elements

110 and 120 communicating with each other or with other devices via each other. For example, the network element 120 may be under the control of the network element 110. In some example embodiments, a CU of a network device (e.g. a gNB-CU) will be taken as an example of the network element 110, and a DU of the network device (e.g. a gNB-DU) will be taken as an example of the network element 120. In some example embodiments, the network element110 and the network element 120 can be implemented as one network device 105 such as one base station, or next generation Node B (i.e. gNB) etc.

The environment 100 further comprises two

terminal devices

130 and 140 communicating with each other or with other devices via each other. The terminal device 140 may communicate with the network device 105 via the terminal device 130. For the purpose of discussion, the

terminal devices

130 and 140 will be referred to as relay terminal device 130 and remote terminal device 140 respectively. For example, the relay terminal device 130 may connect with the first network element 110 via the network element 120. The terminal device 140 may connect with the network element110 via the network element 120 and the relay terminal device 130.

It is to be understood that the devices are shown in the environment 100 only for the purpose of illustration, without suggesting any limitation to the scope of the present disclosure. In some example embodiments, the environment 100 may comprise a further device to communicate information with one or more of the above devices.

The communications in the environment 100 may follow any suitable communication standards or protocols, which are already in existence or to be developed in the future, such as Universal Mobile Telecommunications System (UMTS) , long term evolution (LTE) , LTE-Advanced (LTE-A) , the fifth generation (5G) New Radio (NR) , Wireless Fidelity (Wi-Fi) and Worldwide Interoperability for Microwave Access (WiMAX) standards, and employs any suitable communication technologies, including, for example, Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Division Multiplexing (OFDM) , time division multiplexing (TDM) , frequency division multiplexing (FDM) , code division multiplexing (CDM) , Bluetooth, ZigBee, and machine type communication (MTC) , enhanced mobile broadband (eMBB) , massive machine type communication (mMTC) , ultra-reliable low latency communication (URLLC) , Carrier Aggregation (CA) , Dual Connection (DC) , and New Radio Unlicensed (NR-U) technologies.

Reference is now made to FIG. 1B, which illustrates an example scenario in which some example embodiments of the present disclosure may be implemented. For the purpose of discussion, FIG. 1B will be described with reference to FIG. 1A. As shown in FIG. 1B, the remote terminal device 140 has an indirect path via the relay terminal device 130 to the source network device 105. As the relay terminal device 130 is configured to hand over to the target network device 160, the remote terminal device 140 is configured to hand over to the target network device 160 simultaneously. In this case, the remote terminal device 140 connects to the target network device 160 directly.

FIGS. 1C and 1D illustrate the user plane and control plane protocol stacks of L2 U2N relay respectively according to some example embodiments of the present disclosure. For a remote UE, the higher layer protocols, such as Uu SDAP, PDCP, and RRC protocols, are terminated end-to-end between the remote UE and a New Radio (NR) NodeB (gNB) . The lower layer protocols, such as RLC, MAC and PHY protocols, are terminated in each hop between the remote UE and the relay UE or between the relay UE and the gNB. Besides, there are also some protocols, such as Uu SRAP and PC5 SRAP protocols, supproted in each hop to handle the traffic mapping of different bearers and remote UEs.

FIG. 2 illustrates a signaling flow 200 between devices according to some example embodiments of the present disclosure. For the purpose of discussion, the signaling flow 200 will be described with reference to FIG. 1A. As shown in FIG. 2, the network device 105 determines (205) to hand over the relay terminal device 130 from the network device 105 to a target network device. Then, the network device 105 determines (210) a reconfiguration of the remote terminal device 140 associated with the relay terminal device 130. The reconfiguration is caused by the handover. Further, the network device 105 transmits (215) a first RRC message 216 to the relay terminal device 130. Accordingly, the relay terminal device 130 receives (220) the first RRC message 216 from the network device 105. The first RRC message 216 requests the relay terminal device 130 to detach from the network device 105 based on determining that a last message for the remote terminal device 140 is received from the network device 105.

Then, the network device 105 transmits (225) , to the relay terminal device 130, a second RRC message 226 for the remote terminal device 140 and an indication 227 that the second RRC message 226 is the last message to be delivered to the remote terminal device 140 via the relay terminal device 130. On the other side of the transmission, the relay terminal device 130 receives (230) the second RRC message 226 and the indication 227 from the network device 105. The relay terminal device 130 then transmits (235) , to the remote terminal device 140, the second RRC message 226. Accordingly, the remote terminal device 140 receives (240) the second RRC message 226 from the relay terminal device 130.

The relay terminal device 130 may determine that the last message for the remote terminal device 140 is received from the network device 105, and then detaches (245) , from the network device 105. For example, the relay terminal device 130 may detach from the network device 105 after receiving the indication 227 from the network device 105. In some example embodiments, the network device 105 may comprise the network element 110, such as a CU of the network device 105, and the network element 120, such as a DU of the network device 105. In this case, since the relay terminal device 130 connects with the network element 110 via the network element 120, the detaching from the network device 105 also means the relay terminal device 130 detaches from the network element 110 and/or the network element 120.

In some example embodiments, the network device 105 may determine, based on Quality of Service (QoS) or characteristics of the remote terminal device 140’s traffic relayed by the relay terminal device 130, whether there is a need for the relay terminal device 130 to determine that the last message for the remote terminal device 140 is received from the network device 105 before detaching from the network device 105. For example, if the remote terminal device 140’s traffic requires strict service continuity, the network device 105 may configure the relay terminal device 130 to wait for the indication that the last message for the remote terminal device 140 is received from the network device 105, before detaching from the network device 105.

In some example embodiments, the first RRC message 216 may comprise a configuration for a timer. The timer may define a maximum duration for the relay terminal device 130 to determine that the last message is received from the network device 105 before it may detach from the network device 105. In this case, the first RRC message 216 may further indicate to the relay terminal device 130 to detach from the network device 105 based on an expiration of the timer. In an alternative, the timer may be configured to the relay terminal device 130 in advance using, for example, common or dedicated RRC signalling by the network device 105 and the indication for the relay terminal device 130 to use the timer along with the first RRC message 216 may become implicit. Accordingly, upon the expiration of the timer, the relay terminal device 130 may detach from the network device 105 even if it fails to determine that the last message for the remote terminal device 140 is received from the network device 105.

For example, the second RRC message 226 for the remote terminal device 140 may be a reconfiguration message to configure the remote terminal device 140 to hand over to the target network device and connect with the target network device via the relay terminal device 130. As another example, the second RRC message 226 for the remote terminal device 140 may be a reconfiguration message to configure the remote terminal device 140 to hand over to the target network device or another target network device/element, and connect with the target network device or another target network via another relay terminal device. As a further example, the second RRC message 226 for the remote terminal device 140 may be a reconfiguration message to configure the remote terminal device 140 to connect to the network device 105, the target network device, or another target network device directly. Alternatively or in addition, the second RRC message 226 for the remote terminal device 140 may be a reconfiguration message to configure the remote terminal device 140 to perform path switching to connect to the network device 105 via another relay terminal device.

In some example embodiments, the network device 105 may transmit, to the relay terminal device 130, the indication 227 that the second RRC message 226 is the last message to be delivered to the remote terminal device 140 via the relay terminal device 130 in a plurality of ways. For example, the indication 227 may be transmitted using enhanced SRAP protocol when the second RRC message 226 of the remote terminal device 140 is transmitted to the relay terminal device 130 over the Uu interface. As the second RRC message 226 of the remote terminal device 140 is terminated end-to-end between the remote terminal device 140 and the network device 105, the relay terminal device 130 may not identify that the second RRC message 226 of the remote terminal device 140 is transmitted from the network device 105. In this case, as an example, the network device 105 may transmit, to the relay terminal device 130, the indication 227 in a header of an SRAP PDU. As another example, the network device 105 may transmit, to the relay terminal device 130, the indication 227 in an SRAP C-PDU. It is to be understood that other signaling or message may be used to transmit the indication 227, and the scope of the present disclosure will not be limited in this regard.

FIGS. 3-4 illustrate examples of the indication 227 using the SRAP PDU and the SRAP C-PDU respectively according to some example embodiments of the present disclosure. For instance, when the network device 105 initiates the transmission of the second RRC message 226 of the remote terminal device 140 via the relay terminal device 130, the RRC layer entity of the network device may indicate to the Uu SRAP layer entity that the second RRC message 226 is the last message for the remote terminal device 140. When the Uu SRAP entity forms the SRAP PDU of the last message of the remote terminal device 140, it may set the “I” bit in the SRAP PDU header to provide the indication 227 as shown in FIG. 3, or use the SRAP C-PDU as shown in FIG. 4 to carry the last message for an implicit option of the indication 227 or to provide the indication 227 explicitly along with a SRAP PDU carrying the last message. Then, the Uu SRAP entity at the network device 105 may transmit the last message and the indication 227 to the relay terminal device 130 via the same Uu-RLC channel. In FIGS. 3-4, the “D” bit refers to a data PDU, the “C” bit refers to a control PDU, and the R” bit is a reserved bit. In this case, for example, as shown in FIG. 3, the “I” bit may be used as a one-bit indication in the SRAP PDU header to indicate whether the transmitted SRAP PDU contains the last RRC message of the remote terminal device 140 or not.

In some example embodiments, the network device 105 may determine a plurality of reconfigurations of a plurality of remote terminal devices associated with the relay terminal device 130. The remote terminal device 140 is one of the plurality of remote terminal devices. In this case, the first RRC message 216 from the network device 105 may request the relay terminal device 130 to detach from the network device 105 based on determining that a respective last message for each of the plurality of remote terminal devices is received from the network device 105.

Accordingly, the relay terminal device 130 may determine, based on a respective indication that a respective second radio resource control message is the last message to be delivered to a respective remote terminal device via the relay terminal device 130 from the network device 105, that the last message for the respective remote terminal device is received from the network device 105, and then detaches from the network device 105. In this way, it is enabled to improve user experience by avoiding the service interruption caused by the failed delivery of the remote terminal device’s reconfiguration message. As such, it is possible to improve communication efficiency.

FIG. 5 illustrates a signaling flow 500 between devices according to some other example embodiments of the present disclosure. For the purpose of discussion, the signaling flow 500 will be described with reference to FIG. 1A. As shown in FIG. 5, the network device 105 determines (505) to hand over the relay terminal device 130 from the network device 105 to a target network device. Then, the network device 105 determines (510) a reconfiguration of the remote terminal device 140 associated with the relay terminal device 130. The reconfiguration is caused by the handover. Further, the network device 105 transmits (515) a first RRC message 516 to the relay terminal device 130. Accordingly, the relay terminal device 130 receives (517) the first RRC message 516 from the network device 105. The first RRC message 516 requests the relay terminal device 130 to detach from the network device 105 based on determining that a last message for the remote terminal device 140 is delivered to the remote terminal device 140.

Then, the network device 105 transmits (520) , to the relay terminal device 130, a second RRC message 521 for the remote terminal device 140. The second RRC message 521 comprises an indication that remote terminal device 140 transmits an indication of last message delivery to the relay terminal 130 upon receiving the second RRC message 521. For example, the indication 521 may be implicit or explicit. On the other side of the transmission, the relay terminal device 130 receives (525) the second RRC message 521 from the network device 105. The relay terminal device 130 then transmits (530) , to the remote terminal device 140, the second RRC message 521. Accordingly, the remote terminal device 140 receives (535) the second RRC message 521 from the relay terminal device 130.

Further, after receiving, from the network device 105 via the relay terminal device 130, the second RRC message 521 indicating the remote terminal device 140 to transmit, to the relay terminal device 130, an indication of last message delivery to the relay terminal 130 upon receiving the second RRC message 521, the remote terminal device 140 transmits (540) an indication 546 that the last message is delivered to the remote terminal device 140 to the relay terminal device 130. On the receiving side, the relay terminal device 130 receives (545) the indication 546 from the remote terminal device 140. The relay terminal device 130 may determine, based on the indication 546, that the last message for the remote terminal device 140 is delivered to the remote terminal device 140, and then detaches (550) from the network device 105. For example, the relay terminal device 130 may detaches from the network device 105 after receiving the indication 546 from the remote terminal device 140.

In some example embodiments, the network device 105 may determine, based on QoS or characteristics of the remote terminal device 140’s traffic relayed by the relay terminal device 130, whether there is a need for the relay terminal device 130 to determine that the last message for the remote terminal device 140 is delivered to the remote terminal device 140 before detaching from the network device 105. For example, if the remote terminal device 140’s traffic requires strict service continuity, the network device 105 may configure the relay terminal device 130 to wait for the indication that the last message for the remote terminal device 140 is delivered to the remote terminal device 140, before detaching from the network device 105.

In some example embodiments, the first RRC message 516 may comprise a configuration for a timer. The timer may define a maximum duration for the relay terminal device 130 to determine that the last message is delivered to the remote terminal device 140. In this case, the first RRC message 516 may further indicate to the relay terminal device 130 to detach from the network device 105 based on an expiration of the timer. In an alternative, the timer may be configured to the relay terminal device in advance using, for example, common or dedicated RRC signalling by the network device 105 and the indication for the relay terminal device to use the timer along with the first RRC message 516 may become implicit. Accordingly, upon the expiration of the timer, the relay terminal device 130 may detach from the network device 105 even if it fails to determine that the last message is delivered to the remote terminal device 140.

For example, the second RRC message 521 for the remote terminal device 140 may be a reconfiguration message to configure the remote terminal device 140 to hand over to the target network device and connect with the target network device via the relay terminal device 130. As another example, the second RRC message 521 for the remote terminal device 140 may be a reconfiguration message to configure the remote terminal device 140 to hand over to the target network device or another target network device/element, and connect with the target network device or another target network via another relay terminal device. As a further example, the second RRC message 521 for the remote terminal device 140 may be a reconfiguration message to configure the remote terminal device 140 to connect to the network device 105, the target network device, or another target network device directly. Alternatively or in addition, the second RRC message 521 for the remote terminal device 140 may be a reconfiguration message to configure the remote terminal device 140 to perform path switching to connect to the network device 105 via another relay terminal device.

In some example embodiments, upon receiving the second RRC message 521 via the relay terminal device 130, the remote terminal device 140 may be triggered to transmit, to the relay terminal device 130 over the PC5 interface, the indication of receiving the last RRC message, that is, the indication 546 that the last message is delivered to the remote terminal device 140. To trigger the remote terminal device 140 transmitting the indication 546, the network device 105 may mark the last RRC message of the remote terminal device 140, that is the second RRC message 521, for example when the network device 105 initiates the handover procedure of the relay terminal device 130 and the RRC reconfiguration procedure of the remote terminal device 140 at the same time. The marking bit (s) may be introduced into the second RRC message 521 to indicate whether the remote terminal device 140 needs to transmit the indication 546 to the relay terminal device 140 after receiving the second RRC message 521, i.e., the last message. Alternatively or in addition, the relay terminal device 130 may request the remote terminal device 140 to transmit the indication 546 upon receiving the first RRC message 516 for the handover of the relay terminal device 130.

In some example embodiments, the remote terminal device 140 may transmit, to the relay terminal device 130, the indication 546 that the last message is delivered to the remote terminal device 140 in a plurality of ways. For example, the remote network device 240 may transmit, to the relay terminal device 130, the indication 546 in a sidelink RRC signaling. As another example, the remote network device 240 may transmit, to the relay terminal device 130, the indication 546 in a sidelink media access control (MAC) control element (CE) . As a further example, the remote network device 240 may transmit, to the relay terminal device 130, the indication 546 in a header of an SRAP PDU. Alternatively or in addition, the remote network device 240 may transmit, to the relay terminal device 130, the indication 546 in an SRAP C-PDU. It is to be understood that other signaling or carrier may be used to transmit the indication 546, and the scope of the present disclosure will not be limited in this regard.

In some example embodiments, the network device 105 may determine a plurality of reconfigurations of a plurality of remote terminal devices associated with the relay terminal device 130. The remote terminal device 140 is one of the plurality of remote terminal devices. In this case, the first RRC message 516 from the network device 105 may request the relay terminal device 130 to detach from the network device 105 based on determining that a respective last message for each of the plurality of remote terminal devices is delivered to the respective remote terminal device. Accordingly, the relay terminal device 130 may detach from the network device 105 after receiving, from each of the plurality of remote terminal devices, a respective indication 546 that the last message for a respective remote terminal device is delivered to the respective remote terminal device. In this way, it is enabled to improve user experience by avoiding the service interruption caused by the failed delivery of the remote terminal device’s reconfiguration message. As such, it is possible to improve communication efficiency.

FIG. 6 illustrates an example process for mobility support in U2N relay with one remote UE according to some example embodiments of the present disclosure. For the purpose of discussion, the process 600 will be described with reference to FIG. 1A. In this case, the remote terminal device 140 is implemented by a remote UE 601, and the relay terminal device 130 is implemented by a relay UE 603, and the network device 105 is implemented by a gNB 605. In this case, the relay UE 603 is connected to the gNB 605, and the remote UE 601 has established an indirect path with the serving gNB 605 via the relay UE 603. In this example, the network element 110 and the network element 120 are implemented in the same network device, i.e. the gNB 605.

As shown in FIG. 6, at 610, the relay UE 603 transmits a measurement report to the gNB 605. At 612, the remote UE 601 transmits a measurement report to the gNB 605 via the relay UE 603. At 614, based on measurement reports from the relay UE 603 and the remote UE 601, the gNB 605 makes the handover (HO) decision for the relay UE 603 and initiates an RRC reconfiguration procedure for the remote UE 601 due to the relay UE 603’s HO. The RRC reconfiguration procedure for the remote UE 601 may configure the remote UE 601 to either perform handover together with the relay UE 603, or make path switching to a direct path to the serving gNB 605 or a neighboring gNB, or switch to another reselected relay UE to continue the indirect path with the same serving gNB 605 or another neighboring gNB.

At 616, when the gNB 605 sends a RRCReconfiguration message (i.e. handover command) to the relay UE 603, the gNB 605 requests the relay UE 603 to wait for the indication of the last RRC message for the connected remote UE 601, for example, an RRCReconfiguration message from the gNB 605, before detaching from the serving gNB 605. In other words, the gNB 605 requests the relay UE 603 to detach from the gNB 605 based on determining that the last RRC message for the remote UE 601 is received from the gNB 605. At 618, the gNB 605 logically transmits, to the remote UE 601, the last RRCReconfiguration message for the remote UE 601 via the relay UE 603 that can be realized physically as follows. At 619, the gNB 605 makes an inter-layer indication of the last RRC message of the remote UE 601 along with passing down the last RRC message. In this case, the RRC layer entity of the gNB 605 may indicate to the Uu SRAP layer entity that the RRC message is the last message of the remote UE 601. When Uu SRAP layer entity at the gNB 605 forms the SRAP PDU of the last RRC message of the remote UE 601 to be delivered to the relay UE 603, it may indicate, in the SRAP PDU header or the SRAP C-PDU, that this is the last RRC message of the connected remote UE 601 to be delivered to the remote UE 601.

Then, at 620, the Uu SRAP layer entity at the gNB 605 transmits the SRAP PDU (and/or the SRAP C-PDU) carrying the last RRC message and the indication of the last RRC message to the relay UE 603. The PC5 SRAP at the relay UE 603 then forwards the last RRC message to the remote UE 601. At 622, the relay UE 603 identifies the reception of the last RRC message of the remote UE 601 based on the indication from the SRAP PDU header or the SRAP C-PDU. Then, at 624, the relay UE 603 detaches from the gNB 605 based on determining that the last RRC message for the remote UE 601 is received from the gNB 605. All operations and features as described above with reference to FIGS. 2-4 are likewise applicable to the process 600 and have similar effects. For the purpose of simplification, the details will be omitted.

FIG. 7 illustrates another example process for mobility support in U2N relay with one remote UE according to some other example embodiments of the present disclosure. For the purpose of discussion, the process 700 will be described with reference to FIG. 1A. In this case, the remote terminal device 140 is implemented by a remote UE 701, and the relay terminal device 130 is implemented by a relay UE 703, and the network device 105 is implemented by a gNB 605. In this case, the relay UE 703 is connected to the gNB 705, and the remote UE 701 has established an indirect path with the serving gNB 705 via the relay UE 703.

As shown in FIG. 7, at 710, the relay UE 703 transmits a measurement report to the gNB 705. At 712, the remote UE 701 transmits a measurement report to the gNB 705 via the relay UE 703. At 714, based on measurement reports from the relay UE 703 and the remote UE 701, the gNB 705 makes the handover (HO) decision for the relay UE 703 and initiates an RRC reconfiguration procedure for the remote UE 701 due to the relay UE 703’s HO. The RRC reconfiguration procedure for the remote UE 701 may configure the remote UE 701 to either perform handover together with the relay UE 703, make path switching to a direct path to the serving gNB 705 or a neighboring gNB, or switch to another reselected relay UE to continue the indirect path with the same serving gNB 705 or a nieghboring gNB.

At 716, when the gNB 705 sends a RRCReconfiguration message (i.e. handover command) to the relay UE 703, the gNB 705 requests the relay UE 703 to wait from the remoter UE 701 for the indication of the delivery of the last RRC message for the connected remote UE 701, for example, an RRCReconfiguration message, before detaching from the serving gNB 705. In other words, the gNB 705 requests the relay UE 603 to detach from the gNB 705 based on determining that the last RRC message for the remote UE 701 is delivered to the remote UE 701. At 718, the gNB 705 transmits, to the remote UE 701, RRCReconfiguration message for the remote UE 701 via the relay UE 703.

At 720, the remote UE 701 transmits, to the relay UE 703, an indication that the last RRC message is delivered to the remote UE 701. At 722, the relay UE 703 identifies the reception of the last RRC message of the remote UE 701 based on the indication from the remote UE 701. Then, at 724, the relay UE 703 detaches from the gNB 705. All operations and features as described above with reference to FIG. 5 are likewise applicable to the process 700 and have similar effects. For the purpose of simplification, the details will be omitted.

FIG. 8 illustrates an example process for mobility support in U2N relay with multiple remote UEs according to some example embodiments of the present disclosure. For the purpose of discussion, the process 800 will be described with reference to FIG. 1A. In this case, the remote terminal device 140 is implemented by a remote UE 801. The process 800 involves

remote UEs

802 and 803. The relay terminal device 130 is implemented by a relay UE 803. The network element 120 is implemented by a DU of the source gNB (also denoted as Source gNB-DU) 807. The network element 110 is implemented by a CU of the source gNB (also denoted as Source gNB-CU) 809.

As shown in FIG. 8, at 810, remote UEs 801-803 are connected with the relay UE 805, and further connected with the source gNB-CU 809 via the source gNB-DU 807. At 812-816, the remote UEs 801-803 transmit measurement reports towards the source gNB-CU 809. Then, at 818, the source gNB-CU 809 decide to hand over the relay UE 805 and the

remotes

801 and 802 together. For example, the source gNB-CU 809 may make this decision based on QoS or other characteristic requirement of the traffic of the respective remote UE relayed by the relay UE 805. In this case, the QoS or other characteristics of relayed traffic of the

remote UEs

801 and 803 relayed by the relay UE 805 may require low service interruption, and thus the source gNB-CU 809 may configure the relay UE 805 to wait for indications related to the delivery of the last RRC message for each of the

remote UEs

801 and 803 from the gNB. Besides, the QoS or other characteristics of relayed traffic of the remote UE 802 relayed by the relay UE 805 may not require low service interruption, and thus the source gNB-CU 809 may hand over the remote UE 802 to a different target gNB, or to the same target gNB but with possible interruption.

At 820, the source gNB-CU 809 initiates the handover preparation procedure for the relay UE 805 and the

remote UEs

801 and 803. At 822, the source gNB-CU 809 transmits, to the relay UE 805 via the source gNB-DU 807, a RRC message (e.g. RRCReconfiguration message) requesting the relay UE 805 to wait for indications for each of the

remote UEs

801 and 803 from the gNB indicating that a respective last RRC message is the last message to be delivered to the respective remote UE before detaching from the source gNB-CU 809.

At 824, the source gNB-CU 809 transmits, to the source gNB-DU 807, an F1 application protocol (F1AP) message for the remote UE 801 including the RRCReconfiguration message for the remote UE 801 and an indication (also referred ti a first indication) that the RRCReconfiguration message is the last message to be delivered to the remote UE 801 via the relay UE 805. At 826, the source gNB-DU 807 transmits, to the relay UE 805, the RRC message (i.e. RRCReconfiguration message) and another indication (also referred to a second indication) . The second indication indicates to the relay UE 805 that the received RRC message is the last message to be delivered to the remote UE 801 via the relay UE 805. For example, the first indication and second indication may be transmitted in the SRAP PDU header or the SRAP C-PDU. Then at 828, the relay UE 805 transmits the RRCReconfiguration message for the remote UE 801 to the remote UE 801.

Likewise, at 830, the source gNB-CU 809 transmits, to the source gNB-DU 807, an F1AP message for the remote UE 803 including the RRCReconfiguration messag for the remote UE 803 and an indication (also referred to a third indication) that the RRCReconfiguration message is the last message to be delivered to the remote UE 803 via the relay UE 805. At 832, the source gNB-DU 807 transmits, to the relay UE 805, the RRC message (i.e. RRCReconfiguration message) and another indication (also referred to a fourth indication) . The fourth indication indicates to the relay UE 805 that the received RRC message is the last message to be delivered to the remote UE 803 via the relay UE 805. For example, the above third and fourth indications may be transmitted in the SRAP PDU header or the SRAP C-PDU. Then at 834, the relay UE 805 transmits the RRCReconfiguration message for the remote UE 803 to the remote UE 803. At 836, the relay UE 905 knows that the

remote UEs

801 and 803 are ready for their reconfigurations, as the last RRCReconfiguration messages have been delivered to them, and then detaches from the source gNB-CU 809. All operations and features as described above with reference to FIGS. 2-4 are likewise applicable to the process 800 and have similar effects. For the purpose of simplification, the details will be omitted.

FIG. 9 illustrates another example process for mobility support in U2N relay with multiple remote UEs according to some other example embodiments of the present disclosure. For the purpose of discussion, the process 900 will be described with reference to FIG. 1A. In this case, the remote terminal device 140 is implemented by a remote UE 901. The process 900 involves

remote UEs

902 and 903. The relay terminal device 130 is implemented by a relay UE 903. The network element 120 is implemented by a DU of the source gNB (also denoted as Source gNB-DU) 907. The network element 110 is implemented by a CU of the source gNB (also denoted as Source gNB-CU) 909.

As shown in FIG. 9, at 910, remote UEs 901-903 are connected with the relay UE 905, and further connected with the source gNB-CU 909 via the source gNB-DU 907. At 912-916, the remote UEs 901-903 transmit measurement reports towards the source gNB-CU 909. Then, at 918, the source gNB-CU 909 decide to hand over the relay UE 905 and the

remotes

901 and 902 together. For example, the source gNB-CU 909 may make this decision based on QoS or other characteristic requirement of the traffic of the respective remote UE relayed by the relay UE 905. In this case, the QoS or other characteristics of relayed traffic of the

remote UEs

901 and 903 relayed by the relay UE 905 may require low service interruption, and thus the source gNB-CU 909 may configure the relay UE 905 to wait for indications related to the delivery of the last RRC message for each of the

remote UEs

901 and 903 from the gNB. Besides, the QoS or other characteristics of relayed traffic of the

remote UEs

901 and 903 relayed by the relay UE 905 may not require low service interruption, and thus the source gNB-CU 909 may hand over the remote UE 902 to a different target gNB, or the same target gNB but with possible interruption.

At 920, the source gNB-CU 909 initiates the handover preparation procedure for the relay UE 905 and the

remote UEs

901 and 903. At 922, the source gNB-CU 909 transmits, to the relay UE 905 via the source gNB-DU 907, a RRC message (e.g. RRCReconfiguration message) requesting the relay UE 905 to wait for indications for each of the

remote UEs

901 and 903 from the gNB indicating that a respective last RRC message is received or delivered to the respective remote UE before detaching from the source gNB-CU 909.

At 924, the source gNB-CU 909 transmits, to the source gNB-DU 907, an F1 application protocol (F1AP) message for the remote UE 901 comprising the RRCReconfiguration message for the remote UE 901. The RRCReconfiguration message comprises an indication that the remote UE 901 transmits an indication of last message delivery to the relay UE 905 upon receiving the RRCReconfiguration message, which causes the remote UE 901 to transmit another indication (e.g. ready indication) to the relay UE 905. At 926, the source gNB-DU 907 transmits, to the relay UE 905, the RRCReconfiguration message for the remote UE 901. Then at 928, the relay UE 905 transmits the RRCReconfiguration message for the remote UE 901 to the remote UE 901. At 930, remote UE 901 transmits, to the relay UE 905, another indication (e.g. ready indication) indicating that the last message is delivered to the remote UE 901.

Likewise, at 932, the source gNB-CU 909 transmits, to the source gNB-DU 907, an F1 application protocol (F1AP) message for the remote UE 903 comprising the RRCReconfiguration message for the remote UE 903. The RRCReconfiguration message comprises an indication that the remote UE 903 transmits an indication of last message delivery to the relay UE 905 upon receiving the RRCReconfiguration message, which causes the remote UE 903 to transmit another indication (e.g. ready indication) to the relay UE 905. At 934, the source gNB-DU 907 transmits, to the relay UE 905, the RRCReconfiguration message for the remote UE 903. Then at 936, the relay UE 905 transmits the RRCReconfiguration message for the remote UE 903 to the remote UE 903. At 938, remote UE 903 transmits, to the relay UE 905, another indication (e.g. ready indication) indicating that the last message is delivered to the remote UE 903. At 940, the relay UE 905 knows that

remote UEs

901 and 903 have received the respective RRCReconfiguration message (e.g. are ready for their reconfigurations) , and then detaches from the source gNB-CU 909. All operations and features as described above with reference to FIG. 5 are likewise applicable to the process 900 and have similar effects. For the purpose of simplification, the details will be omitted.

FIG. 10 illustrates a flowchart 1000 of a method implemented at a network device 105 according to some embodiments of the present disclosure. For the purpose of discussion, the method 1000 will be described from the perspective of the network device 105 with reference to FIG. 1A.

At block 1010, the network device 105 determines to hand over a relay terminal device 130 from the network device 105 to a target network device. At block 1020, the network device 105 determines a reconfiguration of a remote terminal device 140 associated with the relay terminal device 130, the reconfiguration being caused by the handover. At block 1030, the network device 105 transmits a first radio resource control message to the relay terminal device 130, the first radio resource control message requesting the relay terminal device 130 to detach from the network device 105 based on determining that a last message for the remote terminal device 140 is received from the network device 105 or delivered to the remote terminal device 140.

In some example embodiments, the network device 105 transmits, to the relay terminal device 130, a second radio resource control message for the reconfiguration of the remote terminal device 140 and an indication that the second radio resource control message is the last message to be delivered to the remote terminal device 140 via the relay terminal device 130.

In some example embodiments, the network device 105 transmits, to the relay terminal device, the indication in a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU, or in an SRAP control PDU, C-PDU.

In some example embodiments, the network device 105 transmits, to the remote terminal device 140 via the relay terminal device 130, a second radio resource control message for the reconfiguration of the remote terminal device 140, the second radio resource control message comprising an indication that the remote terminal device 140 transmits an indication of last message delivery to the relay terminal device 130 upon receiving the second radio resource control message.

In some example embodiments, the first radio resource control message comprises a configuration for a timer defining a maximum duration for the relay terminal device 130 to determine that the last message is received from the network device 105 or delivered to the remote terminal device 140, and wherein the first radio resource control message further indicates to the relay terminal device 130 to detach from the network device 105 based on an expiration of the timer.

In some example embodiments, the second radio resource control message for the remote terminal device 140 is a reconfiguration message comprising at least one of the following: configuring the remote terminal device 140 to hand over to the target network device and connect with the target network device via the relay terminal device 130; configuring the remote terminal device 140 to hand over to the target network device or another target network device, and connect with the target network device or another target network via another relay terminal device 130; configuring the remote terminal device 140 to connect to the network device 105, or the target network device, or another target network device directly; and configuring the remote terminal device 140 to perform path switching to connect to the network device 105 via another relay terminal device 130.

In some example embodiments, the network device 105 determines a plurality of reconfigurations of a plurality of remote terminal devices associated with the relay terminal device 130, the remote terminal device 140 being one of the plurality of remote terminal devices.

In some example embodiments, the first radio resource control message requests the relay terminal device 130 to detach from the network device 105 based on determining that a respective last message for each of the plurality of remote terminal devices is received from the network device 105 or delivered to the respective remote terminal device.

FIG. 11 illustrates a flowchart of a method implemented at a relay terminal device 130 according to some other embodiments of the present disclosure. For the purpose of discussion, the method 1100 will be described from the perspective of the relay terminal device 130 with reference to FIG. 1A.

At block 1110, the relay terminal device 130 receives, from a network device 105, a first radio resource control message to hand over from the network device 105 to a target network device, the first radio resource control message requesting the relay terminal device 130 to detach from the network device 105 based on determining that a last message for a remote terminal device 140 associated with the relay terminal device 130 is received from the network device 105 or delivered to the remote terminal device 140. At block 1120, the relay terminal device 130, based on determining that the last message is received from the network device 105 or delivered to the remote terminal device 140, detaches from the network device 105.

In some example embodiments, the relay terminal device 130 receives, from the network device 105, a second radio resource control message for the remote terminal device 140, and an indication that the second radio resource control message is the last message to be delivered to the remote terminal device 140 via the relay terminal device 130; and transmit, to the remote terminal device 140, the second radio resource control message. Further, the relay terminal device 130 detaches from the network device 105 after receiving the indication from the network device 105.

In some example embodiments, the relay terminal device 130 receives the indication from the in a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU, or in an SRAP control PDU, C-PDU.

In some example embodiments, the relay terminal device 130 receives, from the remote terminal device 140, an indication that the last message is delivered to the remote terminal device 140, and the relay terminal device 130 detaches from the network device 105 after receiving the indication from the remote terminal device 140.

In some example embodiments, the relay terminal device 130 receives, from the remote terminal device 140, the indication over a sidelink connection between the relay terminal device 130 and the remote terminal device 140 in one of the following: a sidelink radio resource control, RRC, signaling; a sidelink media access control, MAC, control element, CE; a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU; or an SRAP control PDU, C-PDU.

In some example embodiments, the first radio resource control message requests the relay terminal device 130 to detach from the network device 105 based on determining that a respective last message for each of a plurality of remote terminal devices is received from the network device or delivered to the respective remote terminal device, the remote terminal device 140 being one of the plurality of remote terminal devices.

In some example embodiments, the relay terminal device 130 detaches from the network device 105 based on determining that the respective last message for each of the plurality of remote terminal devices is received from the network device or delivered to the respective remote terminal device.

In some example embodiments, the first radio resource control message comprises a configuration for a timer defining a maximum duration for the relay terminal device 130 to determine that the last message for the reconfiguration is received from the network device or delivered to the remote terminal device 140, and the relay terminal device 130 detaches from the network device 105 based on an expiration of the timer.

FIG. 12 illustrates a flowchart of a method implemented at a remote terminal device 140 according to some other embodiments of the present disclosure. For the purpose of discussion, the method 1200 will be described from the perspective of the remote terminal device 140 with reference to FIG. 1A.

At block 1210, the remote terminal device 140 receives, from a network device 105 via a relay terminal device 130 associated with the remote terminal device 140, a second radio resource control message for a reconfiguration of the remote terminal device 140, the second radio resource control message indicating the remote terminal device 140 to transmit an indication of last message delivery to the relay terminal device 130 upon receiving the second radio resource control message. At block 1220, the remote terminal device 140 transmits, to the relay terminal device 130, an indication that the last message is delivered to the remote terminal device 140.

In some example embodiments, the remote terminal device 140 transmits the indication to the relay terminal device 130 over a sidelink connection between the relay terminal device 130 and the remote terminal device 140 in one of the following: a sidelink radio resource control, RRC, signaling; a sidelink media access control, MAC, control element, CE; a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU; or an SRAP control PDU, C-PDU.

In some example embodiments, the reconfiguration of the remote terminal device 140 comprises at least one of the following: configuring the remote terminal device 140 to hand over to a target network device and connect with the target network device via the relay terminal device 130; configuring the remote terminal device 140 to hand over to a target network device and connect with the target network device via another relay terminal device 130; configuring the remote terminal device 140 to connect to the network device 105 or a target network device directly; and configuring the remote terminal device 140 to perform path switching to connect to the network device 105 via another relay terminal device 130.

In some example embodiments, an apparatus capable of performing the method 1000 (for example, the network device 105) may comprise means for performing the respective steps of the method 1000. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for determining, at the network device, to hand over a relay terminal device from the network device to a target network device; means for determining a reconfiguration of a remote terminal device associated with the relay terminal device, the reconfiguration being caused by the handover; and means for transmitting a first radio resource control message to the relay terminal device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.

In some example embodiments, the apparatus further comprises means for transmitting, to the relay terminal device, a second radio resource control message for the reconfiguration of the remote terminal device and an indication that the second radio resource control message is the last message to be delivered to the remote terminal device via the relay terminal device.

In some example embodiments, the apparatus further comprises means for transmitting, to the relay terminal device, the indication in a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU, or in an SRAP control PDU, C-PDU.

In some example embodiments, the apparatus further comprises means for transmitting, to the remote terminal device via the relay terminal device, a second radio resource control message for the reconfiguration of the remote terminal device, the second radio resource control message comprising an indication that the remote terminal device transmits an indication of last message delivery to the relay terminal device upon receiving the second radio resource control message.

In some example embodiments, the first radio resource control message comprises a configuration for a timer defining a maximum duration for the relay terminal device to determine that the last message is received from the network device or delivered to the remote terminal device, and wherein the first radio resource control message further indicates to the relay terminal device to detach from the network device based on an expiration of the timer.

In some example embodiments, the second radio resource control message for the remote terminal device is a reconfiguration message comprising at least one of the following: configuring the remote terminal device to hand over to the target network device and connect with the target network device via the relay terminal device; configuring the remote terminal device to hand over to the target network device or another target network device, and connect with the target network device or another target network device via another relay terminal device; configuring the remote terminal device to connect to the network device, or the target network device, or another target network device directly; and configuring the remote terminal device to perform path switching to connect to the network device via another relay terminal device.

In some example embodiments, the means for determining the reconfiguration of the remote terminal device associated with the relay terminal device comprises means for determining a plurality of reconfigurations of a plurality of remote terminal devices associated with the relay terminal device, the remote terminal device being one of the plurality of remote terminal devices.

In some example embodiments, the first radio resource control message requests the relay terminal device to detach from the network device based on determining that a respective last message for each of the plurality of remote terminal devices is received from the network device or delivered to the respective remote terminal device.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 1000. In some embodiments, the means comprises at least one processor and at least one memory including computer program code. The at least one memory and computer program code are configured to, with the at least one processor, cause the performance of the apparatus.

In some example embodiments, an apparatus capable of performing the method 1100 (for example, the relay terminal device 130) may comprise means for performing the respective steps of the method 1100. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for receiving, at a relay terminal device, from a network device, a first radio resource control message to hand over from the network device to a target network device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for a remote terminal device associated with the relay terminal device is received from the network device or delivered to the remote terminal device; and means for, based on determining that the last message is received from the network device or delivered to the remote terminal device, detaches from the network device.

In some example embodiments, the apparatus further comprises means for receiving, from a second network device, a second radio resource control message for the remote terminal device, and an indication that the second radio resource control message is the last message to be delivered to the remote terminal device via the relay terminal device; and means for transmit, to the remote terminal device, the second radio resource control message. The means for detaching from the network device comprises: means for detaching from the network device after receiving the indication from the network device.

In some example embodiments, the means for receiving the indication comprises: means for receiving the indication from the network device in a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU, or in an SRAP control PDU, C-PDU.

In some example embodiments, the apparatus comprises means for receiving, from the remote terminal device, an indication that the last message is delivered to the remote terminal device. The means for detaching from the network device comprises: means for detaching from the network device after receiving the third indication from the remote terminal device .

In some example embodiments, the means for receiving the indication comprises means for receiving, from the remote terminal device, the indication over a sidelink connection between the relay terminal device and the remote terminal device in one of the following: a sidelink radio resource control, RRC, signaling; a sidelink media access control, MAC, control element, CE; a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU; or an SRAP control PDU, C-PDU.

In some example embodiments, the first radio resource control message requests the relay terminal device to detach from the network device based on determining that a respective last message for each of a plurality of remote terminal devices is received from the network device or delivered to the respective remote terminal device, the remote terminal device being one of the plurality of remote terminal devices.

In some example embodiments, the means for detaching from the network device comprises means for detaching from the network device based on determining that the respective last message for each of the plurality of remote terminal devices is received from the network device or delivered to the respective remote terminal device.

In some example embodiments, the first radio resource control message comprises a configuration for a timer defining a maximum duration for the relay terminal device to determine that the last message for the reconfiguration is received from the network device or delivered to the remote terminal device, and the apparatus further comprises means for detaching from the network device based on an expiration of the timer.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 1100. In some embodiments, the means comprises at least one processor and at least one memory including computer program code. The at least one memory and computer program code are configured to, with the at least one processor, cause the performance of the apparatus.

In some example embodiments, an apparatus capable of performing the method 1200 (for example, the remote terminal device 140) may comprise means for performing the respective steps of the method 1200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for receiving, at a remote terminal device, from a network device via a relay terminal device associated with the remote terminal device, a second radio resource control message for a reconfiguration of the remote terminal device, the second radio resource control message indicating the remote terminal device to transmit an indication of last message delivery to the relay terminal device upon receiving the second radio resource control message; and means for transmitting, to the relay terminal device, the indication that the last message is delivered to the remote terminal device.

In some example embodiments, the means for transmitting the indication comprises means for transmitting the indication to the relay terminal device over a sidelink connection between the relay terminal device and the remote terminal device in one of the following: a sidelink radio resource control, RRC, signaling; a sidelink media access control, MAC, control element, CE; a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU; or an SRAP control PDU, C-PDU.

In some example embodiments, the reconfiguration of the remote terminal device comprises at least one of the following: configuring the remote terminal device to hand over to a target network device and connect with the target network device via the relay terminal device; configuring the remote terminal device to hand over to a target network device and connect with the target network device via another relay terminal device; configuring the remote terminal device to connect to the network device or a target network device directly; and configuring the remote terminal device to perform path switching to connect to the network device via another relay terminal device.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 1200. In some embodiments, the means comprises at least one processor and at least one memory including computer program code. The at least one memory and computer program code are configured to, with the at least one processor, cause the performance of the apparatus.

FIG. 13 illustrates a simplified block diagram of a device 1300 that is suitable for implementing some example embodiments of the present disclosure. The device 1300 may be provided to implement the communication device, for example, the network device 105, the relay terminal device 130, or the remote terminal device 140 as shown in FIG. 1A. As shown, the device 1300 includes one or more processors 1310, one or more memories 1320 coupled to the processor 1310, and one or more communication modules 1340 coupled to the processor 1310.

The communication module 1340 is for bidirectional communications. The communication module 1340 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network elements.

The processor 1310 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1300 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 1320 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 1324, an electrically programmable read only memory (EPROM) , a flash memory, a hard disk, a compact disc (CD) , a digital video disk (DVD) , and other magnetic storage and/or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 1322 and other volatile memories that will not last in the power-down duration.

A computer program 1330 includes computer executable instructions that are executed by the associated processor 1310. The program 1330 may be stored in the ROM 1324. The processor 1310 may perform any suitable actions and processing by loading the program 1330 into the RAM 1322.

The embodiments of the present disclosure may be implemented by means of the program 1330 so that the device 1300 may perform any process of the disclosure as discussed with reference to FIGS. 2 to 12. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some example embodiments, the program 1330 may be tangibly contained in a computer readable medium which may be included in the device 1300 (such as in the memory 1320) or other storage devices that are accessible by the device 1300. The device 1300 may load the program 1330 from the computer readable medium to the RAM 1322 for execution. The computer readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like.

FIG. 14 illustrates a block diagram of an example of a computer readable medium 1400 in accordance with some example embodiments of the present disclosure. The computer readable medium 1400 has the program 1330 stored thereon. It is noted that although the computer readable medium 1400 is depicted in form of CD or DVD in FIG. 14, the computer readable medium 1400 may be in any other form suitable for carry or hold the program 1330.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the method as described above with reference to any of FIGS. 10-12. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. The term “non-transitory, ” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM) .

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A network device comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the network device at least to:

determine to hand over a relay terminal device from the network device to a target network device;

determine a reconfiguration of a remote terminal device associated with the relay terminal device, the reconfiguration being caused by the handover; and

transmit a first radio resource control message to the relay terminal device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.
The network device of claim 1, wherein the network device is further caused to:

transmit, to the relay terminal device, a second radio resource control message for the reconfiguration of the remote terminal and an indication that the second radio resource control message is the last message to be delivered to the remote terminal device via the relay terminal device.
The network device of claim 2, wherein the network device is caused to transmit the indication by:

transmitting, to the relay terminal device, the indication in a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU, or in an SRAP control PDU, C-PDU.
The network device of claim 1, wherein the network device is further caused to:

transmit, to the remote terminal device via the relay terminal device, a second radio resource control message for the reconfiguration of the remote terminal device, the second radio resource control message comprising an indication that the remote terminal device transmits an indication of last message delivery to the relay terminal device upon receiving the second radio resource control message.
The network device of any of claims 1-4, wherein the first radio resource control message comprises a configuration for a timer defining a maximum duration for the relay terminal device to determine that the last message is received from the network device or delivered to the remote terminal device, and wherein the first radio resource control message further indicates to the relay terminal device to detach from the network device based on an expiration of the timer.
The network device of any of claims 1-5, wherein the second radio resource control message for the remote terminal device is a reconfiguration message comprising at least one of the following:

configuring the remote terminal device to hand over to the target network device and connect with the target network device via the relay terminal device;

configuring the remote terminal device to hand over to the target network device or another target network device, and connect with the target network device or another target network via another relay terminal device;

configuring the remote terminal device to connect to the network device, or the target network device, or another target network device directly; and

configuring the remote terminal device to perform path switching to connect to the network device via another relay terminal device.
The network device of any of claims 1-6, wherein the network device is caused to determine the reconfiguration of the remote terminal device associated with the relay terminal device by:

determining a plurality of reconfigurations of a plurality of remote terminal devices associated with the relay terminal device, the remote terminal device being one of the plurality of remote terminal devices.
The network device of claim 7, wherein the first radio resource control message requests the relay terminal device to detach from the network device based on determining that a respective last message for each of the plurality of remote terminal devices is received from the network device or delivered to the respective remote terminal device.
A relay terminal device comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the relay terminal device at least to:

receive, from a network device, a first radio resource control message to hand over from the network device to a target network device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for a remote terminal device associated with the relay terminal device is received from the network device or delivered to the remote terminal device; and

based on determining that the last message is received from the network device or delivered to the remote terminal device, detach from the network device.
The relay terminal device of claim 9, wherein the relay terminal device is further caused to:

receive, from the network device, a second radio resource control message for the remote terminal device, and an indication that the second radio resource control message is the last message to be delivered to the remote terminal device via the relay terminal device; and

transmit, to the remote terminal device, the second radio resource control message, and

wherein the relay terminal device is caused to detach from the network device by:

detaching from the network device after receiving the indication from the network device.
The relay terminal device of claim 10, wherein the relay terminal device is caused to receive the indication by:

receiving the indication from the network device in a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU, or in an SRAP control PDU, C-PDU.
The relay terminal device of claim 9, wherein the relay terminal device is further caused to:

receive, from the remote terminal device, an indication that the last message is delivered to the remote terminal device, and

wherein the relay terminal device is caused to detach from the network device by:

detaching from the network device after receiving the indication from the remote terminal device.
The relay terminal device of claim 12, wherein the relay terminal device is caused to receive the indication by:

receiving, from the remote terminal device, the indication over a sidelink connection between the relay terminal device and the remote terminal device in one of the following:

a sidelink radio resource control, RRC, signaling;

a sidelink media access control, MAC, control element, CE;

a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU; or

an SRAP control PDU, C-PDU.
The relay terminal device of any of claims 9-13, wherein the first radio resource control message requests the relay terminal device to detach from the network device based on determining that a respective last message for each of a plurality of remote terminal devices is received from the network device or delivered to the respective remote terminal device, the remote terminal device being one of the plurality of remote terminal devices.
The relay terminal device of claim 14, wherein the relay terminal device is caused to detach from the network device by:

detaching from the network device based on determining that the respective last message for each of the plurality of remote terminal devices is received from the network device or delivered to the respective remote terminal device.
The relay terminal device of any of claims 9-15, wherein the first radio resource control message comprises a configuration for a timer defining a maximum duration for the relay terminal device to determine that the last message for the reconfiguration is received from the network device delivered to the remote terminal device, and the relay terminal device is further caused to:

detach from the network device based on an expiration of the timer.
A remote terminal device, comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the remote terminal device at least to:

receive, from a network device via a relay terminal device associated with the remote terminal device, a second radio resource control message for a reconfiguration of the remote terminal device, the second radio resource control message indicating the remote terminal device to transmit an indication of last message delivery to the relay terminal device upon receiving the second radio resource control message; and

transmit, to the relay terminal device, an indication that the last message is delivered to the remote terminal device.
The remote terminal device of claim 17, wherein the remote terminal device is caused to transmit the indication by:

transmitting the indication to the relay terminal device over a sidelink connection between the relay terminal device and the remote terminal device in one of the following:

a sidelink radio resource control, RRC, signaling;

a sidelink media access control, MAC, control element, CE;

a header of a sidelink relay adaptation protocol, SRAP, protocol data unit, PDU; or

an SRAP control PDU, C-PDU.
The remote terminal device of claim 17 or 18, wherein the reconfiguration of the remote terminal device comprises at least one of the following:

configuring the remote terminal device to hand over to a target network device and connect with the target network device via the relay terminal device;

configuring the remote terminal device to hand over to a target network device and connect with the target network device via another relay terminal device;

configuring the remote terminal device to connect to the network device or a target network device directly; and

configuring the remote terminal device to perform path switching to connect to the network device via another relay terminal device.
A method, comprising:

determining, at a network device, to hand over a relay terminal device from the network device to a target network device;

determining a reconfiguration of a remote terminal device associated with the relay terminal device, the reconfiguration being caused by the handover; and

transmitting a first radio resource control message to the relay terminal device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.
A method, comprising:

receiving, at a relay terminal device, from a network device, a first radio resource control message to hand over from the network device to a target network device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for a remote terminal device associated with the relay terminal device is received from the network device or delivered to the remote terminal device; and

based on determining that the last message is received from the network device or delivered to the remote terminal device, detaching from the network device.
A method, comprising:

receiving, at a remote terminal device, from a network device via a relay terminal device associated with the remote terminal device, a last message for a reconfiguration of the remote terminal device, the last message indicating the remote terminal device to transmit, to the relay terminal device, an indication that the last message is delivered to the remote terminal device; and

transmitting, to the relay terminal device, the indication that the last message is delivered to the remote terminal device.
An apparatus, comprising:

means for determining, at a network device, to hand over a relay terminal device from the network device to a target network device;

means for determining a reconfiguration of a remote terminal device associated with the relay terminal device, the reconfiguration being caused by the handover; and

means for transmitting a first radio resource control message to the relay terminal device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for the remote terminal device is received from the network device or delivered to the remote terminal device.
An apparatus, comprising:

means for receiving, at a relay terminal device, from a network device, a first radio resource control message to hand over from the network device to a target network device, the first radio resource control message requesting the relay terminal device to detach from the network device based on determining that a last message for a remote terminal device associated with the relay terminal device is received from the network device or delivered to the remote terminal device; and

means for based on determining that the last message is received from the network device or delivered to the remote terminal device, detaching from the network device.
An apparatus, comprising:

means for receiving, at a remote terminal device, from a network device via a relay terminal device associated with the remote terminal device, a last message for a reconfiguration of the remote terminal device, the last message indicating the remote terminal device to transmit, to the relay terminal device, an indication that the last message is delivered to the remote terminal device; and

means for transmitting, to the relay terminal device, the indication that the last message is delivered to the remote terminal device.
A non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method of any of claims 20-22.