WO2024016364A1

WO2024016364A1 - Methods, devices, and medium for communication

Info

Publication number: WO2024016364A1
Application number: PCT/CN2022/107538
Authority: WO
Inventors: You Li; Gang Wang
Original assignee: Nec Corporation
Priority date: 2022-07-22
Filing date: 2022-07-22
Publication date: 2024-01-25

Abstract

Example embodiments of the present disclosure relate to methods, devices, and computer storage medium for communication. A first terminal device receives, from a network device, a path switch command indicating to switch from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device, the path switch command comprising an ID of the second terminal device; initiate a connection establishment with the second terminal device based on the path switch command; and in accordance with a determination that the connection establishment is failed, perform a path switch failure procedure. As such, the path switch failure procedure may be defined and the path switch may be handled, and thus the communication efficiency may be improved.

Description

METHODS, DEVICES, AND MEDIUM FOR COMMUNICATION

FIELD

Example embodiments of the present disclosure generally relate to the field of communication techniques and in particular, to methods, devices, and a computer readable medium for communication.

BACKGROUND

A network device and a terminal device may communicate with each other. In some cases, when the terminal device moves, it may be switch into a UE-to-Network Relay (U2N Relay) scenario to maintain the communication performance.

It is proposed to perform a path switch process, and the communication can be implemented between the network device and the terminal device via another terminal device, i.e., a relay. However, the specific implementation is still needed to be discussed.

SUMMARY

In general, example embodiments of the present disclosure provide methods, devices and a computer storage medium for communication. Embodiments that do not fall under the scope of the claims, if any, are to be interpreted as examples useful for understanding various embodiments of the disclosure.

In a first aspect, there is provided a method of communication. The method comprises: receiving, at a first terminal device from a network device, a path switch command indicating to switch from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device, the path switch command comprising an identifier (ID) of the second terminal device; initiating a connection establishment with the second terminal device based on the path switch command; and in accordance with a determination that the connection establishment is failed, performing a path switch failure procedure.

In a second aspect, there is provided a method of communication. The method comprises: transmitting, at a network device to a first terminal device, a path switch command indicating to switch from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device, the path switch command comprising an identifier (ID) of the second terminal device; and receiving, from the first terminal device, failure information related to a failure of a connection between the first terminal device and the second terminal device, the connection being initiated by the first terminal device based on the path switch command.

In a third aspect, there is provided a method of communication. The method comprises: receiving, at a first terminal device from a second terminal device during a path switch procedure, a notification comprising an indication of a failure of an RRC connection between the second terminal device and the network device, the path switch procedure comprising switching from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device; and performing, based on the notification, at least one of: reverting back to a configuration associated with the network device; or performing a radio resource control (RRC) re-establishment procedure.

In a fourth aspect, there is provided a method of communication. The method comprises: initiating, at a second terminal device, a connection establishment with a first terminal device during a path switch procedure of the first terminal device, the path switch procedure comprising switching from a first path to a second path, the first path being a direct path between the first terminal device and a network device, the second path being an indirect path between the first terminal device and the network device via the second terminal device; and in accordance with a determination that the connection establishment is failed, transmitting, to the network device, a failure report indicating a failure of the connection establishment.

In a fifth aspect, there is provided a first terminal device. The first terminal device comprises a processor and a memory. The memory is coupled to the processor and stores instructions thereon. The instructions, when executed by the processor, cause the first terminal device to perform the method according to the first or the third aspect above.

In a sixth aspect, there is provided a second terminal device. The second terminal device comprises a processor and a memory. The memory is coupled to the processor and stores instructions thereon. The instructions, when executed by the processor, cause the second terminal device to perform the method according to the fourth aspect above.

In a seventh aspect, there is provided a network device. The network device comprises a processor and a memory. The memory is coupled to the processor and stores instructions thereon. The instructions, when executed by the processor, cause the network device to perform the method according to the second aspect above.

In an eighth aspect, there is provided a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to carry out the method according to the first aspect, the second aspect, the third aspect or the fourth aspect above.

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

Through the more detailed description of some example embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein:

FIG. 1 illustrates a schematic diagram of an example communication network in which some embodiments of the present disclosure can be implemented;

FIGS. 2A-2C illustrate schematic diagrams of example communication networks in which some embodiments of the present disclosure can be implemented;

FIGS. 3A-3C illustrate signalling charts illustrating switch processes in which some embodiments of the present disclosure can be implemented;

FIG. 4 illustrates a signalling chart illustrating configuring process in accordance with some embodiments of the present disclosure;

FIG. 5 illustrates an example process of the inter-layer signalling within the first terminal device according to some example embodiments of the present disclosure;

FIG. 6 illustrates a signalling chart illustrating configuring process in accordance with some embodiments of the present disclosure;

FIG. 7 illustrates a signalling chart illustrating configuring process in accordance with some embodiments of the present disclosure;

FIG. 8 illustrates an example process of the inter-layer signalling within the second terminal device according to some example embodiments of the present disclosure;

FIG. 9 illustrates a signalling chart illustrating configuring process according to some example embodiments of the present disclosure;

FIG. 10 illustrates a signalling chart illustrating configuring process according to some example embodiments of the present disclosure;

FIG. 11A illustrates a signalling chart illustrating configuring process according to some example embodiments of the present disclosure;

FIG. 11B illustrates a signalling chart illustrating configuring process according to some example embodiments of the present disclosure;

FIG. 12 illustrates a signalling chart illustrating configuring process according to some example embodiments of the present disclosure;

FIG. 13 illustrates a flowchart of an example method in accordance with some embodiments of the present disclosure;

FIG. 14 illustrates a flowchart of an example method in accordance with some embodiments of the present disclosure;

FIG. 15 illustrates a flowchart of an example method in accordance with some embodiments of the present disclosure;

FIG. 16 illustrates a flowchart of an example method in accordance with some embodiments of the present disclosure; and

FIG. 17 illustrates a simplified block diagram of a device that is suitable for implementing 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. Embodiments 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.

In some examples, values, procedures, or apparatus are referred to as “best, ” “lowest, ” “highest, ” “minimum, ” “maximum, ” or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, higher, or otherwise preferable to other selections.

As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR) , 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 first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) , 5.5G, 5G-Advanced networks, or the sixth generation (6G) 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 “terminal device” refers to any device having wireless or wired communication capabilities. Examples of terminal device include, but not limited to, user equipment (UE) , personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs) , portable computers, tablets, wearable devices, internet of things (IoT) devices, Ultra-reliable and Low Latency Communications (URLLC) devices, Internet of Everything (IoE) devices, machine type communication (MTC) devices, device on vehicle for V2X communication where X means pedestrian, vehicle, or infrastructure/network, devices for Integrated Access and Backhaul (IAB) , Space borne vehicles or Air borne vehicles in Non-terrestrial networks (NTN) including Satellites and High Altitude Platforms (HAPs) encompassing Unmanned Aircraft Systems (UAS) , eXtended Reality (XR) devices including different types of realities such as Augmented Reality (AR) , Mixed Reality (MR) and Virtual Reality (VR) , the unmanned aerial vehicle (UAV) commonly known as a drone which is an aircraft without any human pilot, devices on high speed train (HST) , or image capture devices such as digital cameras, sensors, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. The ‘terminal device’ can further has ‘multicast/broadcast’ feature, to support public safety and mission critical, V2X applications, transparent IPv4/IPv6 multicast delivery, IPTV, smart TV, radio services, software delivery over wireless, group communications and IoT applications. It may also be incorporated one or multiple Subscriber Identity Module (SIM) as known as Multi-SIM. The term “terminal device” can be used interchangeably with a UE, a mobile station, a subscriber station, a mobile terminal, a user terminal or a wireless device.

As used herein, the term “network device” refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a satellite, a unmanned aerial systems (UAS) platform, a Node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a next generation NodeB (gNB) , a transmission reception point (TRP) , a remote radio unit (RRU) , a radio head (RH) , a remote radio head (RRH) , an IAB node, a low power node such as a femto node, a pico node, a reconfigurable intelligent surface (RIS) , and the like.

In one embodiment, the terminal device may be connected with a first network device and a second network device. One of the first network device and the second network device may be a master node and the other one may be a secondary node. The first network device and the second network device may use different radio access technologies (RATs) . In one embodiment, the first network device may be a first RAT device and the second network device may be a second RAT device. In one embodiment, the first RAT device is eNB and the second RAT device is gNB. Information related with different RATs may be transmitted to the terminal device from at least one of the first network device and the second network device. In one embodiment, first information may be transmitted to the terminal device from the first network device and second information may be transmitted to the terminal device from the second network device directly or via the first network device. In one embodiment, information related with configuration for the terminal device configured by the second network device may be transmitted from the second network device via the first network device. Information related with reconfiguration for the terminal device configured by the second network device may be transmitted to the terminal device from the second network device directly or via the first network device.

Communications discussed herein may conform to any suitable standards including, but not limited to, New Radio Access (NR) , Long Term Evolution (LTE) , LTE-Evolution, LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , Code Division Multiple Access (CDMA) , cdma2000, and Global System for Mobile Communications (GSM) and the like. Furthermore, the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.85G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) , and the sixth (6G) communication protocols. The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. The embodiments of the present disclosure may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) communication protocols, 5.5G, 5G-Advanced networks, or the sixth generation (6G) networks.

The terminal device or the network device may have Artificial intelligence (AI) or machine learning capability. It generally includes a model which has been trained from numerous collected data for a specific function, and can be used to predict some information.

The terminal device or the network device may work on several frequency ranges, e.g. FR1 (410 MHz –7125 MHz) , FR2 (24.25GHz to 71GHz) , frequency band larger than 100GHz as well as Tera Hertz (THz) . It can further work on licensed/unlicensed/shared spectrum. The terminal device may have more than one connection with the network device under Multi-Radio Dual Connectivity (MR-DC) application scenario. The terminal device or the network device can work on full duplex, flexible duplex and cross division duplex modes.

The embodiments of the present disclosure may be performed in test equipment, e.g., signal generator, signal analyzer, spectrum analyzer, network analyzer, test terminal device, test network device, or channel emulator.

The embodiments of the present disclosure may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) communication protocols, 5.5G, 5G-Advanced networks, or the sixth generation (6G) networks.

The term “circuitry” used herein may refer to hardware circuits and/or combinations of hardware circuits and software. For example, the circuitry may be a combination of analog and/or digital hardware circuits with software/firmware. As a further example, the circuitry may be any portions of hardware processors with software including digital signal processor (s) , software, and memory (ies) that work together to cause an apparatus, such as a terminal device or a network device, to perform various functions. In a still further example, the circuitry may be hardware circuits and or processors, such as a microprocessor or a portion of a microprocessor, that requires software/firmware for operation, but the software may not be present when it is not needed for operation. As used herein, the term circuitry also covers an implementation of merely a hardware circuit or processor (s) or a portion of a hardware circuit or processor (s) and its (or their) accompanying software and/or firmware.

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. The term “includes” and its variants are to be read as open terms that mean “includes, but is not limited to. ” The term “based on” is to be read as “based at least in part on. ” The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ” The terms “first, ” “second, ” and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below.

In the context of the present disclosure, the term “proximity communication 5 (PC5) connection” may be used interchangeably with PC5 RRC connection, PC5 RRC unicast link, PC5 unicast link, PC5 link, layer-2 link or layer-2 unicast link, device-to-device (D2D) connection, D2D link, or sidelink (SL) . The term “relay UE” may be used interchangeably with UE-to-network (U2N) relay UE, UE-to-network relay, UE-to-UE (U2U) relay UE, U2U relay, candidate relay UE, target relay UE, candidate UE, target UE, layer 2 (L2) relay UE, layer 3 (L3) relay UE, or relay device.

In the context of the present disclosure, the term “upper layer” may be used interchangeably with proximity-services (ProSe) layer, vehicle-to-everything (V2X) layer, non-access stratum (NAS) layer or PC5-signalling (PC5-S) layer. The term “lower layer” may be used interchangeably with access stratum (AS) layer, radio resource control (RRC) layer, packet data convergence protocol (PDCP) layer, radio link control (RLC) layer, medium access control (MAC) layer, layer-2 or layer 2. The term “ProSe” may be used interchangeably with proximity based services or proximity services.

The term “Layer2 ID of Remote UE” may be a source L2 ID of Remote UE, which may has integer times of 8 bits, such as 24 bits, 32 bits or the like. The term “Layer2 ID of Relay UE” may be used interchangeably with SL-SourceIdentity, SL-SourceIdentityRelayUE, or source L2 ID of Relay UE, which may has integer times of 8 bits, such as 24 bits, 32 bits or the like. The term “ID of a terminal device” may be used interchangeably with UE ID, path ID, link ID, or the like.

For U2N relay, Rel-17 WI on sidelink relay has captured the procedures for connection setup via Relay UE and intra-gNB path switch. Also, some basic failure and abnormal cases have been found and corresponding procedures to handle them have been defined.

In some examples, after receiving notification from Relay UE about its change of serving cell or Uu radio link failure (RLF) , Remote UE in RRC_CONNECTED may perform RRC re-establishment procedure as defined in “5.8.9.10 Notification Message” . In some examples, after determining reconfiguration failure during path switch, Remote UE performs path switch failure procedure and initiates RRC re-establishment procedure as defined in “5.3.5.8.3 T304 expiry (Reconfiguration with sync Failure) or T420 expiry (Path switch failure) ” . However, the detailed path switch failure procedure needed to be further studied.

Embodiments of the present disclosure provide a solution of communication. In the solution, a first terminal device may initiate a connection establishment with a target relay based on a path switch command from the network device, and may further perform a path switch failure procedure in case the connection establishment is failed. As such, the path switch failure procedure may be defined and the path switch may be handled, and thus the communication efficiency may be improved.

FIG. 1 illustrates a schematic diagram of an example communication network 100 in which some embodiments of the present disclosure can be implemented. As shown in FIG. 1, the communication network 100 may include a first terminal device 110, a second terminal device 120 and a network device 130. In the example of FIG. 1, the first terminal device 110 may communicate with the network device 130. In some examples, the network device 130 may be a serving gNB of the first terminal device 110.

In some embodiments, there may be a direct network connection between the first terminal device 110 and the network device 130. In some embodiments, the network device 130 may communicate with the first terminal device 110 via a Uu link.

In some embodiments, there may be an indirect network connection between the first terminal device 110 and the network device 130. For example, the second terminal device 120 may serve as a relay UE between the first terminal device 110 and the network device 130, and the first terminal device 110 may serve as a remote UE. In some embodiments, the network device 130 may communicate with the second terminal device 120 via a Uu link, and the first terminal device 110 may communicate with the second terminal device 120 via a sidelik (SL) . For example, the first terminal device 110 may be connected with the second terminal device 120 via a sidelink interface (such as PC5) .

In some embodiments, the first terminal device 110 and the second terminal device 120 may communicate with each other via a sidelink channel, such as a physical sidelink shared channel (PSSCH) , a physical sidelink control channel (PSCCH) , a physical sidelink feedback channel (PSFCH) , a physical sidelink broadcast channel (PSBCH) or the like. For example, a PC5 link or PC5 RRC connection may be established between the first terminal device 110 and the second terminal device 120.

It is to be understood that the number of network devices in FIG. 1 is given for the purpose of illustration without suggesting any limitations to the present disclosure.

In some embodiments, the second terminal device 120 may locate within the coverage of the network device 130. In some embodiments, the first terminal device 110 may move to outside of the coverage of the network device 130. The present disclosure does not limit this aspect.

The communications in the communication network 100 may conform to any suitable standards including, but not limited to, Global System for Mobile Communications (GSM) , Long Term Evolution (LTE) , LTE-Evolution, LTE-Advanced (LTE-A) , New Radio (NR) , Wideband Code Division Multiple Access (WCDMA) , Code Division Multiple Access (CDMA) , GSM EDGE Radio Access Network (GERAN) , Machine Type Communication (MTC) and the like. Furthermore, the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. The embodiments of the present disclosure may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) communication protocols, 5.5G, 5G-Advanced networks, or the sixth generation (6G) networks.

It is to be understood that the number of terminal devices in FIG. 1 is given for the purpose of illustration without suggesting any limitations to the present disclosure. In some embodiments, the communication network 100 may include any suitable number of second terminal devices, so that multiple hops are needed for the communication from the first terminal device 110 to the network device 130. The present disclosure does not limit this aspect.

FIG. 2A illustrates a schematic diagram of an example communication network 210 in which some embodiments of the present disclosure can be implemented. As shown in FIG. 2A, a UE 211 may communicate with a network device via a relay UE. The network device may be a gNB 212 or a NG-eNB 213, the relay UE may be a UE 214 or a UE 215. In some embodiments, the sidelink transmission and reception over the PC5 interface are supported when the UE 211 is inside Next Generation Radio Access Network (NG-RAN) coverage, irrespective of which RRC state the UE is in, and also supported and when the UE 211 is outside NG-RAN coverage. In some embodiments, the UE 211 may be the first terminal device 110 as shown in FIG. 1, the UE 214 or the UE 215 may be the second terminal device 120 as shown in FIG. 1, and the gNB 212 or the NG-eNB 213 may be the network device 130 as shown in FIG. 1.

FIG. 2B illustrates a schematic diagram of an example communication network 220 in which some embodiments of the present disclosure can be implemented. As shown in FIG. 2B, a remote UE 221 may communicate with a gNB 223 via a U2N relay 222. It is understood that the communication with a core network, such as a 5G core (5GC) 224 and/or a domain network (DN) 225 may be implemented. In some embodiments, the remote UE 221 may be the first terminal device 110 as shown in FIG. 1, the U2N relay 222 may be the second terminal device 120 as shown in FIG. 1, and the gNB 223 may be the network device 130 as shown in FIG. 1.

FIG. 2C illustrates a schematic diagram of an example communication network 230 in which some embodiments of the present disclosure can be implemented. As shown in FIG. 2C, a remote UE 231 may communicate with a gNB 235 (such as an intra-gNB or an inter gNB) directly or indirectly via a relay UE 233. A remote UE 232 may communicate with the gNB 235 (such as an intra-gNB or an inter gNB) indirectly via a relay UE 233 or via a relay UE 234. In some embodiments, the transmission path may be switched. For example, the path may be switched between direct and indirect paths for the remote UE 231. For example, the path may be switched between two relay paths for the remote UE 232.

In some embodiments, the direct network connection may be regarded as one mode of network connection, where there is no relay UE between a UE and the 5G network. In some embodiments, the indirect network connection may be regarded as one mode of network connection, where there is a relay UE between a UE and the 5G network.

The present disclosure relates to switching from a direct path to an indirect path, which may be referred to as an intra-gNB direct-to-indirect (D2I) path switch. In some embodiments, the remote UE 231 may be the first terminal device 110 as shown in FIG. 1, the relay UE 233 may be the second terminal device 120 as shown in FIG. 1, and the gNB 235 may be the network device 130 as shown in FIG. 1.

FIG. 3A illustrates a signalling chart illustrating switch process 310 in which some embodiments of the present disclosure can be implemented. The process 310 involves a remote UE 231, a relay UE 233 and a gNB 235. In some examples, the remote UE 231 may also be called as an L2 U2N remote UE, and the relay UE 233 may also be called as an L2 U2N relay UE.

At step 0, it is assumed that there is an UL/DL data transmission between the remote UE 231 and the gNB 235. At step 1, the remote UE 231 reports one or multiple candidate L2 U2N Relay UE (s) and Uu measurements, after it measures/discovers the candidate L2 U2N Relay UE (s) . At step 2, the gNB 235 decides to switch the remote UE 231 (L2 U2N Remote UE) to the relay UE 233 (a target L2 U2N Relay UE) . Then the gNB 235 sends an RRCReconfiguration message to the relay UE 233, which includes at least L2 U2N Remote UE's local ID and L2 ID, Uu and PC5 Relay RLC channel configuration for relaying, and bearer mapping configuration. For example, the relay UE 233 may be chosen from the one or multiple candidate L2 U2N Relay UE (s) .

At step 3, the gNB 235 sends the RRCReconfiguration message to the remote UE 231. The RRCReconfiguration message includes at least L2 U2N Relay UE ID, Remote UE's local ID, PC5 Relay RLC channel configuration for relay traffic and the associated end-to-end radio bearer (s) . The remote UE 231 stops UL/DL transmission over Uu after reception of RRCReconfiguration message from the gNB 235.

At step 4, the remote UE 231 establishes PC5 RRC connection with the relay UE 233. At step 5, the remote UE 231 completes the path switch procedure by sending the RRCReconfigurationComplete message to the gNB 235 via the relay UE 233. At step 6, the data path is switched from direct path to indirect path between the remote UE 231 and the gNB 235. It is understood that the further DL/UL transmission may be performed through the indirect path.

In some embodiments, the selected target L2 U2N relay UE, i.e., the relay UE 233, is in an RRC connected state (RRC_CONNECTED) . In case the selected L2 U2N Relay UE (i.e., the relay UE 233) for direct to indirect path switch is in an RRC idle state (RRC_IDLE) or an RRC inactive state (RRC_INACTIVE) , the connection between the relay UE 233 and the gNB 235 needs to be established.

FIG. 3B illustrates a signalling chart illustrating switch process 320 in which some embodiments of the present disclosure can be implemented. The process 320 involves a remote UE 231, a relay UE 233 and a gNB 235. In some examples, the remote UE 231 may also be called as an L2 U2N remote UE, and the relay UE 233 may also be called as an L2 U2N relay UE. It is assumed that the relay UE 233 is in the RRC idle state.

At step 301, the remote UE 231 reports one or multiple candidate L2 U2N Relay UE (s) and Uu measurements, after it measures/discovers the candidate L2 U2N Relay UE (s) . At step 302, the gNB 235 decides to switch the remote UE 231 (L2 U2N Remote UE) to the relay UE 233 (a target L2 U2N Relay UE) .

At step 303, the gNB 235 sends an RRCReconfiguration message to the remote UE 231. The RRCReconfiguration message may also be called as a path switch command or a handover command. At step 304, the remote UE 231 establishes a PC5 link with the relay UE 233 after receiving the path switch command, and sends an RRCReconfigurationComplete message via the relay UE 233 at step 305, which triggers the relay UE 233 to enter RRC_CONNECTED state. The relay UE 233 may enter to the RRC connected state through steps 321-323, during which the relay UE 233 transmits an RRC setup request to the gNB 235 at step 321, the gNB 235 transmits an RRC setup command to the relay UE 233 at step 322 and the relay UE 233 transmits an RRC setup complete to the gNB 235 at step 323. As such, the RCReconfigurationComplete message may be transmitted from the remote UE 231 to the gNB 235 via the relay UE 233 at step 305.

At step 306, the gNB 235 transmits an RRCReconfiguration message for the remote UE 231 to the relay UE 233. At step 307, the relay UE 233 transmits an RRCReconfiguration complete message to gNB 235. Accordingly, further data transmission between the remote UE 231 and the gNB 235 may be performed, which may refer to step 6 in FIG. 3A.

FIG. 3C illustrates a signalling chart illustrating switch process 330 in which some embodiments of the present disclosure can be implemented. The process 330 involves a remote UE 231, a relay UE 233 and a gNB 235. In some examples, the remote UE 231 may also be called as an L2 U2N remote UE, and the relay UE 233 may also be called as an L2 U2N relay UE. It is assumed that the relay UE 233 is in the RRC inactive state.

It is noted that the steps 301-307 shown in FIG. 3C may refer to those described with reference to FIG. 3B, and will not be repeated herein.

In FIG. 3C, the relay UE 233 sends an RRCReconfigurationComplete message via the relay UE 233 at step 305, which triggers the relay UE 233 to enter RRC_CONNECTED state. The relay UE 233 may enter to the RRC connected state through steps 331-333, during which the relay UE 233 transmits an RRC resume request to the gNB 235 at step 331, the gNB 235 transmits an RRC resume command to the relay UE 233 at step 332 and the relay UE 233 transmits an RRC resume complete to the gNB 235 at step 333.

Based on the description with reference to FIGS. 3B-3C, in case the selected L2 U2N Relay UE (relay UE 233) for direct to indirect path switch is in RRC_IDLE or RRC_INACTIVE, after receiving the path switch command, the remote UE 231 establishes a PC5 link with the relay UE 233 and sends the RRCReconfigurationComplete message via the relay UE 233, which triggers the relay UE 233 to enter RRC_CONNECTED state. The procedure for remote UE 231 switching to indirect path in FIG. 3A can be also applied for the case that the selected relay UE 233 for direct to indirect path switch is in RRC_IDLE or RRC_INACTIVE with the exception the RRCReconfiguration message for the remote UE 231 is sent from the gNB 235 to the relay UE 233 after the relay UE 233 enters RRC_CONNECTED state.

As such, the path switch may be performed successfully and the data transmission between the remote UE 231 and the gNB 235 may be continued. However, in some other cases, the connection between the remote UE 231 and the relay UE 233 may be failed, and it is needed to be further studied how to handle this failure.

It should be understood that the above illustrated issues are only for the purpose of illustration without suggesting any limitations. Principles and implementations of the present disclosure will be described in detail below with reference to the figures.

Reference is first made to FIG. 4, which illustrates a signalling chart illustrating configuring process 400 according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 400 will be described with reference to FIG. 1. The process 400 may involve the first terminal device 110, the second terminal device 120 and the network device 130 in FIG. 1. It is to be understood that the first terminal device 110 may be a remote UE, and the second terminal device 120 may be a relay UE, as discussed above. In some embodiments, the second terminal device 120 may be in an RRC connected state. In some other embodiments, the second terminal device 120 may be in an RRC idle or inactive state.

The network device 130 transmits 410 a path switch command 412 to the first terminal device 110. In some embodiments, the path switch command 412 may indicate the first terminal 110 to switch from a first path to a second path. The first path may be a direct path between the first terminal device 110 and the network device 130, and the second path may be an indirect path between the first terminal device 110 and the network device 130 via a second terminal device 120. In some embodiments, the path switch command 412 may include an ID of the second terminal device 120.

On the other side of communication, the first terminal device 110 receives 414 the path switch command 412 which include the ID the second terminal device 120. For example, the ID of the second terminal device 120 may be carried in an information element (IE) or a field “targetRealyUEIdentity” of path switch command 412. The first terminal device 110 initiates 420 a connection establishment with the second terminal device 120 based on the path switch command 412. In some embodiments, the connection between the first terminal device 110 and the second terminal device 120 may be a RC5 RRC unicast link, and may also be called any of other links as stated above.

In some embodiments, the first terminal 110 may start a timer for a path switch procedure, upon receiving the path switch command 412 or upon the initiation of the connection establishment. In some examples, the timer may be a T420 or another timer, the present disclosure does not limit this aspect. In some examples, the timer may be set with a time period, and it is understood that the timer is running within the time period.

Specifically, an RRC/AS layer of the first terminal device 110 may indicate the upper layer of the first terminal device 110 with the ID of the second terminal device 120, to trigger or request the PC5 RRC unicast link establishment. The upper layer may send PC5-S signalling to establish the unicast link with the second terminal device 120. In some embodiments, the upper layer may indicate a failure of the PC5 connection establishment, or unsuccessful operation of PC5 unicast link establishment to the RRC/AS layer. The inter-layer signalling may refer to FIG. 5 described below.

In some embodiments, the first terminal device 110 may determine that the connection is failed based on one or more of: an indication from an upper layer on the connection being not successfully established; the connection being not successfully established within a time period, the time period being for a path switch procedure associated with the path switch command; or a maximum number of retries being reached.

The first terminal device 110 performs 430 a path switch failure procedure. In some embodiments, the first terminal device 110 may perform the path switch failure procedure (may also be referred to as path switch failure handling procedure) by one or more of: performing a reconfiguration failure procedure; performing an RRC re-establishment procedure; reverting back to a configuration associated with the network device 130; performing a cell reselection procedure; or performing a relay reselection procedure. The reconfiguration failure procedure may also be referred to as RRC reconfiguration failure procedure or RRC connection reconfiguration failure procedure, including reverting back to a configuration associated with the network device 130 and performing an RRC re-establishment procedure.

In some embodiments, the first terminal device 110 may perform a reconfiguration failure procedure then trigger (or initiate) an RRC re-establishment procedure. In some examples, a legacy trigger event for RRC re-establishment procedure may be reused, for example, the trigger event may be: upon re-configuration with sync failure of the main cell group. In some examples, a new trigger event for path switch configuration failure may be considered, for example, the trigger event may be: upon a failure of PC5 unicast link establishment. In some other examples, a new trigger event for path switch configuration failure may be considered, for example, the trigger event may be: upon a failure of PC5 unicast link establishment while the timer associated with the path switch command (such as T420) is still running.

In some embodiments, the RRC re-establishment procedure is triggered based on the indication from the upper layer. In some examples, a new trigger event for RRC re-establishment procedure may be considered, for example, the trigger event may be: upon a failure of PC5 unicast link establishment indicated by the upper layer of the first terminal device 110, where the first terminal device 110 (i.e., the remote UE) is in an RRC connected state. In some examples, further actions may be performed by the first terminal device 110, such as a cell reselection, and/or a relay reselection.

As such, the first terminal device 110 is enabled to handle the unsuccessful operation of path switch due to the failure of PC5 link establishment. In some embodiments, the problem associated with the path switch may be solved before the expiry of the timer (such as T420) .

In some embodiments, upon receiving an indication of failure from the upper layer, the RRC/AS layer of the first terminal device 110 may resend the ID of the second terminal device 120 to the upper layer, to initiate a PC5 re-establishment procedure. In some examples, if the timer (such as T420) is still running (not expired) , the RRC/AS layer may resend the ID of the second terminal device 120 to the upper layer. And the RRC/AS layer may repeat this procedure if it encounter a succession of failures of PC5 connection establishment. In some other examples, if the maximum number of retries, which may or may not include the first attempt, is not reached, the RRC/AS layer may resend the ID of the second terminal device 120 to the upper layer. In some other examples, if the timer is still running (not expired) , and the maximum number of retries is not reached, the RRC/AS layer may resend the ID of the second terminal device 120 to the upper layer. In some examples, if the timer is timeout (expired) , then a legacy procedure may be performed, and will not be described herein.

In some embodiments, the maximum number of retries may be configured by the network device 130. For example, the network device 130 may transmit an indication of the maximum number of retries to the first terminal device 110, and accordingly the first terminal device 110 may receive the indication of the maximum number of retries. In some examples, the indication of the maximum number of retries may be carried in an RRC message or system information.

In some embodiments, the maximum number of retries may be determined by the first terminal device 110. In some examples, the first terminal device 110 may determine the maximum number of retries based on an implementation of the first terminal device 110. As such, the maximum number of retries is up to UE implementation.

In some embodiments, there may be a counter at the first terminal device 110 for counting the number. In some examples, the counter is added 1 after the RRC/AS layer sending (or re-sending) the ID of the second terminal device 120 to the upper layer. In some examples, if the counter reaches the maximum number of retries, the first terminal device 110 may determine that the connection is failed and a path switch failure procedure may be further performed, as discussed above.

In some embodiments, both the timer and the maximum number of retries are configured, and the first terminal device 110 may determine that the connection is failed if the timer is expired, or if the maximum number of retries is reached while the timer is still running.

As such, the first terminal device 110 is enabled to handle the unsuccessful operation of path switch due to the failure of PC5 link establishment. It is understood that, if the signal interruption or channel quality degradation is caused by sudden occlusion or block when perform PC5 connection establishment, the problem may be solved by retrying.

The above various embodiments of the present disclosure may have partial impact to the current specification. For example, the current specification in TS 38.331 may be updated (underlined) as follows in view of the above embodiments of the present disclosure.

The UE shall:

1> if T304 of the MCG expires, or

1> if T420 expires, or,

1> if the target L2 U2N Relay UE (i.e., the UE indicated by targetRelayUE-Identity in the received RRCReconfiguration message containing reconfigurationWithSync indicating path switch as specified in 5.3.5.5.2) changes its serving PCell before path switch , or

1> if the PC5 connection to the target L2 U2N Relay UE (i.e., the UE indicated by targetRelayUE-Identity in the received RRCReconfiguration message containing reconfigurationWithSync indicating path switch as specified in 5.3.5.5.2) is not successfully established:

2> release dedicated preambles provided in rach-ConfigDedicated if configured;

2> release dedicated msgA PUSCH resources provided in rach-ConfigDedicated if configured;

2> else:

3> revert back to the UE configuration used in the source PCell;

3> if the associated T304 was not initiated upon cell selection performed while timer T311 was running, as defined in clause 5.3.7.3:

4> store the handover failure information in VarRLF-Report as described in the clause 5.3.10.5;

3> initiate the connection re-establishment procedure as specified in clause 5.3.7.

For example,

5.3.7 RRC connection re-establishment

5.3.7.2 Initiation

The UE initiates the procedure when one of the following conditions is met:

1> upon detecting sidelink radio link failure by L2 U2N Remote UE in RRC_CONNECTED, in accordance with clause 5.8.9.3; or

1> upon reception of NotificationMessageSidelink including indicationType by L2 U2N Remote UE in RRC_CONNECTED, in accordance with clause 5.8.9.10; or

1> upon PC5 unicast link release indicated by upper layer at L2 U2N Remote UE in RRC_CONNECTED ; or

1> upon failure of PC5 unicast link establishment indicated by upper layer at L2 U2N Remote UE in RRC_CONNECTED.

1> if the UE is acting as L2 U2N Remote UE:

2> if the PC5 RRC connection with the U2N Relay UE is determined to be released:

3> perform the PC5 RRC connection release as specified in 5.8.9.5;

3> perform either cell selection in accordance with the cell selection process as specified in TS 38.304 [20] , or relay selection as specified in clause 5.8.15.3, or both;

2> else if the PC5 RRC connection with the target U2N Relay UE is failed to be established:

2> else:

3> maintain the PC5 RRC connection and stop T311 if running;

Now further referring to FIG. 4, alternatively or in addition, the first terminal device 110 may further transmit 440 failure information 442 to the network device 130. The failure information 442 may be related to a failure of a connection between the first terminal device 110 and the second terminal device 120. On the other side of communication, the network device 130 receives 444 the failure information 442.

In some embodiments, the failure information 442 may be carried in a UE information response, which will be described in detail with reference to FIG. 12.

FIG. 5 illustrates an example process 500 of the inter-layer signalling within the first terminal device 110 according to some example embodiments of the present disclosure. The process 500 may involve an RRC/AS layer 510 and an upper layer 520. The RRC/AS layer 510 may indicate an ID of the second terminal device 120 to the upper layer 520, and the upper layer 520 may indicate a failure of the PC5 RRC connection with the second terminal device 120. In some embodiments, the signalling transferred between the RRC/AS layer 510 and the upper layer 520 may be a PC5-S.

FIG. 6 illustrates a signalling chart illustrating configuring process 600 according to some example embodiments of the present disclosure. The process 600 involves the first terminal device 110, the second terminal device 120 and the network device 130 in FIG. 1.

At step 610, the first terminal device 110 reports one or multiple candidate relay UEs and Uu measurements. For example, the first terminal device 110 may measures or discovers the candidate relay UEs, which are also called as L2 U2N Relay UEs. It is understood that the step 610 may refer to the step 1 as shown in FIG. 3A, and thus will not be described in detail.

At step 620, the network device 130 determines to switch. For example, the network device 130 may make a decision of switching, and a target relay UE (such as the second terminal device 120) may be selected from the one or multiple candidate relay UEs. At step 630, the network device 130 transmits an RRC reconfiguration message to the second terminal device 120, and the RRC reconfiguration is for the first terminal device 110. In some examples, the RRC reconfiguration message in step 630 may include an ID of the first terminal device 110. At step 640, the second terminal device 120 transmits an RRC reconfiguration complete to the network device 130. It is understood that the steps 620-640 may refer to the step 2 as shown in FIG. 3A, and thus will not be described in detail.

At step 650, the network device 130 transmits an RRC reconfiguration message to the first terminal device 110. The RRC reconfiguration in step 650 may be called as a path switch command. In some embodiments, the path switch command includes an ID of the second terminal device. It is understood that the step 650 may refer to the step 3 as shown in FIG. 3A, and thus will not be described in detail.

At step 660, the first terminal device 110 initiates a PC5 connection establishment with the second terminal device 120, but the connection is failed. It is understood that the step 660 may refer to the operation 420 as shown in FIG. 4, and thus will not be described in detail.

At step 670, the first terminal device 110 performs an RRC re-establishment with the network device 130. In some embodiments, the first terminal device 110 may perform a reconfiguration failure procedure and then initiate or trigger the RRC re-establishment procedure. It is understood that the step 670 may refer to the operation 430 as shown in FIG. 4, and thus will not be described in detail.

It should be appreciated that further operations may be included in the example process 600 in FIG. 6, those skilled in the art would understand that the description in FIG. 6 is given for the purpose of illustration without suggesting any limitations.

Reference is now made to FIG. 7, which illustrates a signalling chart illustrating configuring process 700 according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 700 will be described with reference to FIG. 1. The process 700 may involve the first terminal device 110, the second terminal device 120 and the network device 130 in FIG. 1. It is to be understood that the first terminal device 110 may be a remote UE, and the second terminal device 120 may be a relay UE, as discussed above. In some embodiments, the second terminal device 120 may be in an RRC connected state.

The second terminal device 120 initiates 710 a connection establishment with the first terminal device 110 during a path switch procedure of the first terminal device 110. In some embodiments, the path switch procedure includes switching from a first path to a second path. The first path may be a direct path between the first terminal device 110 and the network device 130, and the second path may be an indirect path between the first terminal device 110 and the network device 130 via a second terminal device 120.

In some embodiments, the path switch procedure may be a D2I path switch. In some embodiments, the connection between the first terminal device 110 and the second terminal device 120 may be a PC5 RRC unicast link, and may also be called any of other links as stated above.

In some embodiments, the second terminal device 120 may receive the ID of the first terminal device 110 from the network device 130 prior of the operation 710. For example, the ID of the first terminal device 110 may be carried in an information element (IE) “targetRealyUEIdentity” . In some examples, the ID of the first terminal device 110 may be carried in an RRC reconfiguration message from the network device 130.

Specifically, an RRC/AS layer of the second terminal device 120 may indicate the upper layer of the second terminal device 120 with the ID of the first terminal device 110, to trigger the PC5 RRC unicast link establishment. The upper layer may send PC5-Ssignalling to establish the unicast link with the first terminal device 110. In some embodiments, the upper layer may indicate a failure of the PC5 connection establishment, or unsuccessful operation of PC5 unicast link establishment to the RRC/AS layer. The inter-layer signalling may refer to FIG. 8 described below.

In some embodiments, the second terminal device 120 may determine that the connection is failed based on one or more of: an indication from an upper layer on the connection being not successfully established; or a maximum number of retries being reached.

The second terminal device 120 transmits 720 a failure report 722 to the network device 130. In some embodiments, the failure report may indicate that the failure of the connection establishment between the first terminal device 110 and the second terminal device 120. In some embodiments, the network device 130 is a serving gNB of the second terminal device 120.

In some embodiments, the failure report 722 may be implemented as or be carried in an RRC signalling, such as a Uu RRC signalling. For example, the IE for carrying the failure report 722 may be UEAssistanceInformation (UAI) , SidelinkUeInformation (SUI) , or the like. In some embodiments, the failure report 722 may be implemented as or be carried in an MAC Control Element (CE) or Uplink Control Information (UCI) or other layer 2 signalling.

In some embodiments, the failure report 722 may indicate that a failure occurs during the path switch procedure of the first terminal device 110. For example, the failure report 722 may indicate a failure type or failure cause of a failure of PC5 unicast link establishment corresponding to path switch. In some embodiments, the failure report 722 may include the ID of the first terminal device 110.

In some embodiments, upon receiving an indication of failure from the upper layer, the RRC/AS layer of the second terminal device 120 may resend the ID of the first terminal device 110 to the upper layer, to initiate a PC5 re-establishment procedure. In some examples, if a maximum number of retries is not reached, the RRC/AS layer of the second terminal device 120 may resend the ID of the first terminal device 110 to the upper layer of the second terminal device 120.

In some embodiments, the maximum number of retries (or be called as a maximum number of attempt times) may be configured by the network device 130. For example, the network device 130 may transmit an indication of the maximum number of retries to the second terminal device 120, and accordingly the second terminal device 120 may receive the indication of the maximum number of retries. In some examples, the indication of the maximum number of retries may be carried in an RRC message or system information.

In some embodiments, the maximum number of retries may be determined by the second terminal device 120. In some examples, the second terminal device 120 may determine the maximum number of retries based on an implementation of the second terminal device 120. As such, the maximum number of retries is up to UE implementation.

In some embodiments, there may be a counter at the second terminal device 120 for counting the number. In some examples, the counter is added 1 after the RRC/AS layer of the second terminal device 120sending (or re-sending) the ID of the first terminal device 110 to the upper layer of the second terminal device 120. In some examples, if the counter reaches the maximum number of retries, the second terminal device 120 may determine that the connection is failed and a failure report 722 may be further transmitted, as discussed above.

As such, the second terminal device 120 is enabled to handle the unsuccessful operation of path switch due to the failure of PC5 link establishment. It is understood that, if the signal interruption or channel quality degradation is caused by sudden occlusion or block when perform PC5 connection establishment, the problem may be solved by retrying.

On the other side of communication, the network device 130 receives 724 the failure report 722. In some embodiments, the network device 130 may send another message to the first terminal device 110 to perform path switch.

FIG. 8 illustrates an example process 800 of the inter-layer signalling within the second terminal device 120 according to some example embodiments of the present disclosure. The process 800 may involve an RRC/AS layer 810 and an upper layer 820. The RRC/AS layer 810 may indicate an ID of the first terminal device 110 to the upper layer 820, and the upper layer 820 may indicate a failure of the PC5 RRC connection with the first terminal device 110. In some embodiments, the signalling transferred between the RRC/AS layer 810 and the upper layer 820 may be a PC5-S.

FIG. 9 illustrates a signalling chart illustrating configuring process 900 according to some example embodiments of the present disclosure. The process 900 involves the first terminal device 110, the second terminal device 120 and the network device 130 in FIG. 1.

At step 910, the first terminal device 110 reports one or multiple candidate relay UEs and Uu measurements. For example, the first terminal device 110 may measures or discovers the candidate relay UEs, which are also called as L2 U2N Relay UEs. It is understood that the step 910 may refer to the step 1 as shown in FIG. 3A, and thus will not be described in detail.

At step 920, the network device 130 determines to switch. For example, the network device 130 may make a decision of switching, and a target relay UE (such as the second terminal device 120) may be selected from the one or multiple candidate relay UEs. At step 930, the network device 130 transmits an RRC reconfiguration message to the second terminal device 120, and the RRC reconfiguration is for the first terminal device 110. In some examples, the RRC reconfiguration message in step 930 may include an ID of the first terminal device 110. At step 940, the second terminal device 120 transmits an RRC reconfiguration complete to the network device 130. It is understood that the steps 920-940 may refer to the step 2 as shown in FIG. 3A, and thus will not be described in detail.

At step 950, the network device 130 transmits an RRC reconfiguration message to the first terminal device 110. The RRC reconfiguration in step 950 may be called as a path switch command. In some embodiments, the path switch command includes an ID of the second terminal device. It is understood that the step 950 may refer to the step 3 as shown in FIG. 3A, and thus will not be described in detail.

At step 960, the second terminal device 120 initiates a PC5 connection establishment with the first terminal device 110, but the connection is failed. It is understood that the step 960 may refer to the operation 710 as shown in FIG. 7, and thus will not be described in detail.

At step 970, the second terminal device 120 transmits a failure report to the network device 130. It is understood that the step 970 may refer to the operation 720 as shown in FIG. 7, and thus will not be described in detail.

It should be appreciated that further operations may be included in the example process 900 in FIG. 9, those skilled in the art would understand that the description in FIG. 9 is given for the purpose of illustration without suggesting any limitations.

Reference is now made to FIG. 10, which illustrates a signalling chart illustrating configuring process 1000 according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 1000 will be described with reference to FIG. 1. The process 1000 may involve the first terminal device 110, the second terminal device 120 and the network device 130 in FIG. 1. It is to be understood that the first terminal device 110 may be a remote UE, and the second terminal device 120 may be a relay UE, as discussed above. In some embodiments, the second terminal device 120 may be in an RRC inactive state or an idle state.

The second terminal device 120 transmits 1010 a notification 1012 to the first terminal device 110, during a path switch procedure of the first terminal device 110. In some embodiments, the notification 1012 comprises an indication of a failure of a connection between the second terminal device 120 and the network device 130. In some embodiments, the path switch procedure includes switching from a first path to a second path. In some embodiments, the first path is a direct path between the first terminal device 110 and the network device 130, and the second path is an indirect path between the first terminal device 110 and the network device 130 via the second terminal device 120.

In some example embodiments, the network device 130 may transmit a path switch command to the first terminal device 110, and it may expect that the execution of the path switch will be completed successfully within a predefined time period. In other words, the first terminal device 110 may start a timer upon/while receiving the path switch command, and stop this timer upon the execution of the path switch command is completed successfully. In some example embodiments, the network device 130 may transmit a path switch command to the first terminal device 110, the first terminal device 110 may record a first time point while receiving the path switch command, the first terminal device 110 may record a second time point while receiving the notification, and may determine whether the path switch command is received within a predefined time period by a time length between the first time point and a second time point. In other words, the first terminal device 110 may start another timer upon/while receiving the path switch command and may determine whether another timer is still running (not expired) while receiving the notification. In some embodiments, the path switch command may indicate the first terminal device 110 to switch from the first path to the second path.

In some embodiments, the predefined time period may be configured or indicated by the network device 130. In some examples, the network device 130 may transmit an indication of the predefined time period to the first terminal device 110, and accordingly the first terminal device 110 may receive the indication of the predefined time period. In some examples, the indication of the predefined time period may be carried in an RRC message or in system information, and the present disclosure does not limit this aspect.

In some example embodiments, the second terminal device 120 may be in an RRC inactive state or in an idle state. In some embodiments, the notification may indicate a failure of Uu connection of the second terminal device 120, for example, the second terminal device 120 fails to enter into an RRC connected state.

On the other side of communication, the first terminal device 110 receives 1014 the notification 1012. The first terminal device 110 further performs 1020 path switch failure handling procedure, such as reverting back to a configuration associated with the network device 130 and/or performing an RRC re-establishment procedure.

In some example embodiments, the first terminal device 110 may start a timer for path switch procedure, the time may be T420, and the time length of the timer may be configured by the network device 130 or be pre-defined. Some detailed embodiments while considering the timer will be further discussed with reference to FIGS. 11A-11B.

FIG. 11A illustrates a signalling chart illustrating configuring process 1110 according to some example embodiments of the present disclosure. The process 1110 involves involve the first terminal device 110, the second terminal device 120 and the network device 130 in FIG. 1.

At step 1101, the first terminal device 110 reports one or multiple candidate relay UEs and Uu measurements. For example, the first terminal device 110 may measures or discovers the candidate relay UEs, which are also called as L2 U2N Relay UEs. It is understood that the step 1101 may refer to the step 1 as shown in FIG. 3A, and thus will not be described in detail.

At step 1103, the network device 130 transmits an RRC reconfiguration message to the first terminal device 110. The RRC reconfiguration in step 1103 may be called as a path switch command. In some embodiments, the path switch command includes an ID of the second terminal device. It is understood that the step 1103 may refer to the step 3 as shown in FIG. 3A, and thus will not be described in detail.

At step 1104, the first terminal device 110 initiates a PC5 connection establishment with the second terminal device 120. In some example embodiments, the first terminal device 110 may start a timer upon the initiation of the PC5 connection establishment, at 11035 as shown in FIG. 11A. In some other example embodiments, the first terminal device 110 may start a timer upon the receiving the RRC reconfiguration message at step 1103, or upon the executing of the RRC reconfiguration, at 11035 as shown in FIG. 11A. In some examples, the timer may be T420.

At step 1105, the first terminal device 110 tries to transmit an RRC Reconfiguration complete message to the network device 130 via the second terminal device 120.

At step 1106, the second terminal device 120 transmits an RRC setup request or an RRC resume request to the network device 130. In some embodiments, if the second terminal device 120 is in the RRC idle state, the RRC setup request may be transmitted. In some embodiments, if the second terminal device 120 is in the RRC inactive state, the RRC resume request may be transmitted.

At step 1107, the RRC connection is rejected or other cases occur. In some example embodiments, the network device 130 may transmit an RRC rejection to the second terminal device 120. In some example embodiments, the connection is failed due to a movement of the second terminal device 120. In some example embodiments, the connection is rejected due to other reasons, and will not be listed herein.

At step 1111, the second terminal device 120 transmits a PC5 RLC ACK to the first terminal device 110. In some example embodiments, the first terminal device 110 may determine that the RRC Reconfiguration complete message at step 1105 is successfully transmitted and stop the timer (such as T420) upon the receipt of the PC5 RLC ACK, at 11115 as shown in FIG. 11A.

At step 1112, the second terminal device 120 transmits a notification to the first terminal device 110. In some embodiments, the notification may indicate that a failure of a connection between the second terminal device 120 and the network device 130. For example, the notification may indicate that the failure type is relayUE-Uu-RRC-Failure, which may be carried in an IE “indicationType” . In some examples, the notification may be carried in a message “NotificationMessageSidelink” .

The above various embodiments of the present disclosure may have partial impact to the current specification. For example, the second terminal device 120 serving as a U2N Relay UE may initiate the procedure of transmitting a notification.

The U2N Relay UE may initiate the procedure when one of the following conditions is met:

1> upon Uu RLF as specified in 5.3.10;

1> upon reception of an RRCReconfiguration including the reconfigurationWithSync;

1> upon cell reselection;

1> upon L2 U2N Relay UE's RRC connection failure including RRC connection reject as specified in 5.3.3.5 and 5.3.13.10, and T300 expiry as specified in 5.3.3.7, and RRC resume failure as specified in 5.3.13.5;

At step 1113, the first terminal device 110 performs path switch failure handling. In some examples, the first terminal device 110 may initiate an RRC re-establishment at step 1114.

In some example embodiments, if the timer has been stopped (expired) , and if the indicate type in the notification is relayUE-Uu-RRC-Failure, then the first terminal device 110 may revert back to a previous configuration, such as used in a latest serving cell, such as a latest primary cell. In some example embodiments, if the timer has been stopped (expired) , and if the indicate type in the notification is relayUE-Uu-RRC-Failure, then the first terminal device 110 may initiate an RRC connection re-establishment procedure. In some example embodiments, if the indicate type in the notification is relayUE-Uu-RRC-Failure, and if it is the first notification after receiving the path switch command at step 1103 or after executing the path switch command or after sending/transmitting the RRC Reconfiguration complete message at step1105 or after executing the path switch command successfully or after transmitting the RRC Reconfiguration complete message successfully, then the first terminal device 110 may revert back to a previous configuration, such as used in a latest serving cell, such as a latest primary cell.

The above various embodiments of the present disclosure may have partial impact to the current specification. The first terminal device 110 serving as a U2N remote UE may initiate the path switch failure handling procedure. For example, the current specification in TS 38.331 may be updated (underlined) as follows in view of the above embodiments of the present disclosure.

Upon receiving the NotificationMessageSidelink, the U2N Remote UE shall:

1> if the indicationType is included:

2> if the indicationType is relayUE-Uu-RRC-Failure:

3> revert back to the UE configuration used in the source Pcell/last/latest Pcell served it;

3> initiate the RRC connection re-establishment procedure as specified in 5.3.7;

2> else if the UE is L2 U2N Remote UE in RRC_CONNECTED:

2> else (the UE is L3 U2N Remote UE, or L2 U2N Remote UE in RRC_IDLE or RRC_INACTIVE) :

3> if the PC5 RRC connection with the U2N Relay UE is determined to be released:

4> perform the PC5 RRC connection release as specified in 5.8.9.5.

3> else:

4> maintain the PC5 RRC connection;

4> if the UE is L2 U2N Remote UE and the indicationType is relayUE-HO or relayUE-CellReselection:

5> consider cell re-selection occurs; …

In some example embodiments, if the timer (such as T420) has been stopped (expired) , if the indicate type in the notification is relayUE-Uu-RRC-Failure, and if a path switch command is received during a predefined time period, then the first terminal device 110 may revert back to a previous configuration, such as used in a latest serving cell, a latest primary cell. In some example embodiments, if the timer has been stopped (expired) , if the indicate type in the notification is relayUE-Uu-RRC-Failure, and if a path switch command is received during a predefined time period, then the first terminal device 110 may initiate an RRC connection re-establishment procedure. For example, the timer has been stopped refers to that the time period of the timer is expired. For ease of understanding, the timer with the time period may be called as a first timer (such as T420) .

In some embodiments, there may be another timer, also be called as a second timer here, (such as T490, a newly defined timer for this procedure) started upon receiving the path switch command from the network device 130, and the time length of the second timer may be set as a predefined time period. For example, the predefined time period (such as the maximum value) of the second timer (such as T490) may be bigger than that of T420. In some examples, the predefined time period may be configured by the network device 130. For example, the network device 130 may transmit an RRC message (such as an RRC reconfiguration message) or system information which includes the predefined time period. In some examples, the predefined time period may be configured if the second terminal device 120 is in the RRC idle state or the RRC inactive state.

As such, for the first terminal device serving as the U2N Remote UE, the following specification may be followed:

1> if sl-PathSwitchConfig is included:

2> start timer T420 for the corresponding target L2 U2N Relay UE with the timer value set to T420, as included in the sl-PathSwitchConfig;

2> start timer T490 for the corresponding target L2 U2N Relay UE with the timer value set to T490, as/if included in the sl-PathSwitchConfig; …

Upon receiving the NotificationMessageSidelink, the U2N Remote UE shall:

1> if the indicationType is included:

2> if the UE is L2 U2N Remote UE and the indicationType is relayUE-Uu- RRC-Failure and if it received (D2I, I2I) path switch command during a predefined time period (e.g. if T490 is still running) :

2> else if the UE is L2 U2N Remote UE in RRC_CONNECTED:

4> perform the PC5 RRC connection release as specified in 5.8.9.5.

3> else:

4> maintain the PC5 RRC connection;

5> consider cell re-selection occurs; …

FIG. 11B illustrates illustrates a signalling chart illustrating configuring process 1120 according to some example embodiments of the present disclosure. The process 1120 involves involve the first terminal device 110, the second terminal device 120 and the network device 130 in FIG. 1.

It is to be understood that the steps 1101-1107 in FIG. 11B may refer to those described with reference to FIG. 11A, and thus will not be repeated herein.

Similarly, the first terminal device 110 may start a timer upon receiving or executing the RRC reconfiguration message at step 1103, at 11035 as shown in FIG. 11B. In some examples, the timer may be T420.

At step 1121, the second terminal device 120 transmits a notification to the first terminal device 110. In some embodiments, the notification may indicate that a failure of a connection between the second terminal device 120 and the network device 130. For example, the notification may indicate that the failure type is relayUE-Uu-RRC-Failure, which may be carried in an IE “indicationType” . In some examples, the notification may be carried in a message “NotificationMessageSidelink” .

At step 1122, the first terminal device 110 performs path switch failure handling. In some examples, the first terminal device 110 may initiate an RRC re-establishment at step 1123.

In some example embodiments, if the timer is still running (not expired) , and if the indicate type in the notification is relayUE-Uu-RRC-Failure, then the first terminal device 110 may revert back to a previous configuration, such as used in a latest serving cell, a latest primary cell.

The (Remote) UE shall:

1> if T304 of the MCG expires, or

1> if T420 expires, or,

1> if the target L2 U2N Relay UE (i.e., the UE indicated by targetRelayUE-Identity in the received RRCReconfiguration message containing reconfigurationWithSync indicating path switch as specified in 5.3.5.5.2) changes its serving PCell before path switch, or,

1> if T420 is running and upon receiving the NotificationMessageSidelink with the indicationType set as relayUE-Uu-RRC-Failure:

2> if any DAPS bearer is configured, and radio link failure is not detected in the source PCell, according to clause 5.3.10.3:

2> else:

3> revert back to the UE configuration used in the source PCell; --interpretation: Remote UE is not connected to the target gNB, so the configuration corresponding to the target gNB should not be used.

It should be appreciated that further operations may be included in the example embodiments in FIG. 11A or 11B, those skilled in the art would understand that the description in FIG. 11A or 11B is given for the purpose of illustration without suggesting any limitations.

Reference is now made to FIG. 12, which illustrates a signalling chart illustrating configuring process 1200 according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 1200 will be described with reference to FIG. 1. The process 1200 may involve the first terminal device 110 and the network device 130 in FIG. 1. It is to be understood that the first terminal device 110 may be a remote UE, as discussed above.

In some embodiments, the process 1200 may be performed before or during a path switch procedure of the first terminal device 110, for example switching from a first path to a second path. In some other embodiments, the process 1200 may be performed after finishing a path switch procedure of the first terminal device 110, for example switching from a first path to a second path. The first path may be a direct path between the first terminal device 110 and the network device 130, and the second path may be an indirect path between the first terminal device 110 and the network device 130 via a second terminal device 120.

The network device 130 transmits 1210 UE information request 1212 to the first terminal device 110, and accordingly the first terminal device 110 receives 1214 the UE information request 1212.

The first terminal device 110 transmits 1220 UE information response 1222 to the network device 130, and accordingly the network device 130 receives 1224 the UE information response 1222. In some embodiments, the UE information response 1222 may indicate sidelink relay related failure information. For example, the UE information response 1222 may indicate the failure information 442 as discussed in FIG. 4.

In some example embodiments, the first terminal device 110 may record the failure information upon: receiving, from the second terminal device 120, a notification comprising a type of the failure, or determining a reconfiguration failure for a path switch procedure, determining that the connection establishment between the first terminal device 110 and the second terminal device 120 is failed, or a PC5 RLF is detected.

In some examples, the failure information may be recorded in VarRLFReport or VarSidelinkRelayRLFReport other VarXX, and the present disclosure does not limit this aspect. In some examples, the notification from the second terminal device 120 may be implemented as NotificationMessageSidelink. In some examples, the reconfiguration failure for a path switch procedure may be based a cell reselection or change, an expiry of T420, or other event.

In some example embodiments, the UE information response 1222 may include one of more of: an ID of the second terminal device 120, a list of serving cell IDs of the second terminal device 120, a type of the failure, or cause information of the failure.

In some embodiments, the ID of the second terminal device 120 may be an L2 ID or an L2 source ID, such as with 24 bits or 32 bits. In some embodiments, the ID of the second terminal device 120 may be a Uu ID, such as a cell-Radio Network Temporary Identity (C-RNTI) or inactive-Radio Network Temporary Identity (I-RNTI) .

In some embodiments, the list of serving cell IDs of the second terminal device 120 may include an ID of the latest serving cell (a latest serving cell ID) of the second terminal device 120, for example a Pcell ID of the second terminal device 120.

In some embodiments, the list of serving cell IDs of the second terminal device 120 may include multiple serving cell IDs, where the ID of the latest serving cell (the latest serving cell ID) may be at a predefined position in the list of serving cell IDs. For example, the ID of the latest serving cell may be the first ID in the list of serving cell IDs.

In some embodiments, the type of the failure may indicate the failure being occurred during a path switch procedure, or the failure being related to a sidelink (such as data transmission via the sidelink) . In some examples, the type of the failure may be called as a connection failure type, and the present disclosure does not limit this aspect.

In some embodiments, the type of the failure may be carried in a new defined IE, such as SidelinkRelay-RLF-Report. In some embodiments, the type of the failure may be carried in an IE of RLF-Report for new release, such as RLF-Report-r18/19 or nr-RLF –Report--r18/19.

In some example embodiments, all sidelink relay related failure cases are indicated with the same connection failure type. In some examples, a specific IE may be designed to report the sidelink relay relate information, and if only one type is defined, there may be no need to indicate the connection failure type explicitly; for example, the specific IE does not include the connection failure type. In some examples, an IE “relayf/slrelayf” may be used to indicate that the failure is related to sidelink relay procedures, for example,

connectionFailureType ENUMERATED {

slrelayf/slrf} .

In some embodiments, the cause information may indicate the reason (s) of the failure. In some embodiments, the cause information may indicate one or more of: an RLF of a link between the second terminal device 120 and the network device 130, a handover performed by the second terminal device 120, an RLF of a PC5 interface of the first terminal device 110, an expiry of a timer for a path switch procedure, an RRC connection of the second terminal device 120 (such as Relay UE) is failed corresponding to the path switch procedure, a change of serving cells of the second terminal device 120 prior the path switch procedure, or a failure of the connection establishment between the first terminal device 110 and the second terminal device 120.

In some examples, the following causes may be introduced to indicate the corresponding failures:

● relayUE-Uu-RLF, to indicate Uu RLF detected by Relay UE;

● relayUE-HO, to indicate reception of RRCReconfiguration including the reconfigurationWithSync by Relay UE, or relay UE performs handover;

● PC5-RLF or remoteUE-PC5-RLF, to indicate the RLF is detected on PC5 interface (by Remote UE) ;

● t420-Expiry, to indicate T420 expiry;

● relayUE-Uu-RRC-Failure, to indicate Relay UE’s RRC connection failure including RRC connection reject and T300 expiry, and RRC resume failure. Additionally, the RRC connection or RRC resume is triggered corresponding to (during/for/as result of) path switch;

● targetRelayUE-CellChange, to indicate the target Relay UE changes its serving PCell before path switch;

● PC5-EstablishFailure or remoteUE-PC5-EstablishFailure, to indicate the failure of PC5 connection establishment failure between Remote UE and the target Relay UE.

In some embodiments, the cause information may be carried in a new defined IE or field. In some examples, the new IE or filed may be slRelayFailure-Cause or slRelayRlf-Cause or rlf-Cause-r18/r19, ENUMERATED {relayUE-Uu-RLF, relayUE-HO, PC5-RLF (or remoteUE-PC5-RLF) , t420-Expiry, relayUE-Uu-RRC-Failure, targetRelayUE-CellChange, PC5-EstablishFailure (or remoteUE-PC5-EstablishFailure) } , …

In some embodiments, the cause information may be carried in an IE which is reused for the cause information. In some examples, the reused IE may be rlf-Cause. For example,

rlf-Cause-r16 ENUMERATED {t310-Expiry, randomAccessProblem, rlc-MaxNumRetx, beamFailureRecoveryFailure, lbtFailure-r16, bh-rlfRecoveryFailure, t312-expiry-r17, t420-Expiry, …} .

In some embodiments, the failure causes such as relayUE-Uu-RLF, relayUE-HO, PC5-RLF t420-Expiry, relayUE-Uu-RRC-Failure, targetRelayUE-CellChange, PC5-EstablishFailure can be used only when the connection failure type is indicated as “slrf” . The present disclosure does not limit this aspect.

In some example embodiments, all sidelink relay related failure cases are indicated with at least two separate connection failure types. In some examples, the two separate connection failure types may include a failure type related to sidelink , and a failure type related to path switch.

In some embodiments, one of the two separate connection failure types may indicate a connection status of sidelink relay, for example the failure or abnormal cases are detected during data transmission.

In some examples, the failure type related to sidelink (such as sidelink data transmission) may be represented by “slrelayf” or “slrf” (sidelink realy failure) . In some examples, some causes may be introduced associated with the failure type related to sidelink, such as: relayUE-Uu-RLF, relayUE-HO, and PC5-RLF or remoteUE-PC5-RLF, which may be refer to those described above. In some examples, the cause information associated with the failure type related to sidelink may be carried in a new defined IE or field for “slrf” , such as:

slRelayFailure-Cause ENUMERATED {relayUE-Uu-RLF, relayUE-HO, remoteUE-PC5-RLF} .

In some embodiments, the other one of the two separate connection failure types may indicate that a connection failure or abnormal cases are detected during path switch or related to path switch. In some examples, the failure type related to path switch may be represented by “slrpsf” (sidelink realy path switch failure) , such as:

connectionFailureType ENUMERATED {rlf, hof, slrf, slrpsf} ; Or

connectionFailureType ENUMERATED {slrf, slrpsf} .

In some examples, some causes may be introduced associated with the failure type related to path switch, such as: t420-Expiry, relayUE-Uu-RRC-Failure, targetRelayUE-CellChange, or PC5-EstablishFailure/remoteUE-PC5-EstablishFailure, which may be refer to those described above.

In some examples, the cause information associated with the failure type related to path switch may be carried in a new defined IE or field for “slrpsf” , such as:

slRelayPSFailure-Cause ENUMERATED {t420-Expiry, relayUE-Uu-RRC-Failure, targetRelayUE-CellChange, remoteUE-PC5-EstablishFailure} .

In some examples, the cause information associated with the failure type related to path switch may be carried in a reused IE or field. For example, the reused IE or filed may be used only for “slrpsf” . For example, the reused IE or filed may be used for both “slrf” and “slrpsf” . For example, the reused IE or filed may indicate slRelayFailure-Cause or slRelayRlf-Cause. In some embodiments, the causes are chosen according to their corresponding connection failure type, and the detailed causes may refer to those described above.

It should be appreciated that further operations may be included in the example embodiments in FIG. 12, those skilled in the art would understand that the description in FIG. 12 is given for the purpose of illustration without suggesting any limitations.

According to the embodiments described with reference to FIG. 4 to FIG. 12, the remote UE and/or the relay UE may handle the failure during a path switch procedure of the remote UE, the remote UE may be connected to the network device by further path switch failure procedure, so that the efficiency can be improved.

FIG. 13 illustrates a flowchart of an example method 1300 implemented at a first terminal device in accordance with some embodiments of the present disclosure. For the purpose of discussion, the method 1300 will be described from the perspective of the first terminal device 110 with reference to FIG. 1.

At block 1310, the first terminal device 110 receives, from a network device 130, a path switch command indicating to switch from a first path to a second path, the first path is a direct path between the first terminal device 110 and the network device 130, the second path is an indirect path between the first terminal device 110 and the network device 130 via a second terminal device 120, the path switch command includes an ID of the second terminal device 120. At block 1320, the first terminal device 110 initiates a connection establishment with the second terminal device based on the path switch command. At block 1330, the first terminal device 110 performs a path switch failure procedure if the connection establishment is failed.

In some example embodiments, the first terminal device 110 performs the path switch failure procedure comprises at least one of: performing a reconfiguration failure procedure; performing a radio resource control (RRC) re-establishment procedure; performing a cell reselection procedure; or performing a relay reselection procedure.

In some example embodiments, the first terminal device 110 determines that the connection establishment is failed based on at least one of: an indication from an upper layer on the connection being not successfully established; the connection being not successfully established within a time period, the time period being for a path switch procedure associated with the path switch command; or a maximum number of retries being reached.

In some example embodiments, the first terminal device 110 receives, from the network device 130, an indication of the maximum number of retries, the indication is carried in an RRC message or system information.

In some example embodiments, the first terminal device 110 determines the maximum number of retries based on an implementation of the first terminal device 110.

In some example embodiments, the first terminal device 110 transmits, to the network device 130, failure information related to a failure of the connection establishment.

In some example embodiments, the failure information indicates at least one of: the ID of the second terminal device, a list of serving cell IDs of the second terminal device, a type of the failure, or cause information of the failure.

In some example embodiments, the list of serving cell IDs comprises an ID of a latest serving cell of the second terminal device, and the ID of the latest serving cell is at a predefined position in the list of serving cell IDs.

In some example embodiments, the type indicates at least one of: the failure being occurred during a path switch procedure, or the failure being related to a sidelink.

In some example embodiments, the cause information indicates at least one of: a radio link failure (RLF) of a link between the second terminal device and the network device, a handover performed by the second terminal device, an RLF of a PC5 interface of the first terminal device, an expiry of a timer for a path switch procedure, an RRC connection of the second terminal device 120 is failed corresponding to the path switch procedure, a change of serving cells of the second terminal device prior the path switch procedure, or a failure of the connection establishment.

In some example embodiments, the first terminal device 110 records the failure information upon: receiving, from the second terminal device, a notification comprising a type of the failure, determining a reconfiguration failure for a path switch procedure, or determining that the connection establishment is failed.

In some example embodiments, a connection between the first terminal device and the second terminal device comprises a PC5 RRC unicast link. In some example embodiments, the second terminal device is in an RRC connected state.

FIG. 14 illustrates a flowchart of an example method 1400 implemented at a network device in accordance with some embodiments of the present disclosure. For the purpose of discussion, the method 1400 will be described from the perspective of the network device 130 with reference to FIG. 1.

At block 1410, the network device 130 transmits, to a first terminal device 110, a path switch command indicating to switch from a first path to a second path, the first path is a direct path between the first terminal device 110 and the network device 130, the second path is an indirect path between the first terminal device 110 and the network device 130 via a second terminal device 120, the path switch command includes an ID of the second terminal device 120. At block 1420, the network device 130 receives, from the first terminal device 110, failure information related to a failure of a connection between the first terminal device 110 and the second terminal device 120, the connection is initiated by the first terminal device 110 based on the path switch command.

In some example embodiments, the cause information indicates at least one of: a radio link failure (RLF) of a link between the second terminal device and the network device, a handover performed by the second terminal device, an RLF of a PC5 interface of the first terminal device, an expiry of a timer for a path switch procedure, an RRC reconnection is failed corresponding to the path switch procedure, a change of serving cells of the second terminal device prior the path switch procedure, or a failure of the connection establishment.

In some example embodiments, the network device 130 transmits, to the first device 110, an indication of a maximum number of retries, the retries is performed at the first terminal device 110 for the connection, the indication is carried in an RRC message or system information.

FIG. 15 illustrates a flowchart of an example method 1500 implemented at a first terminal device in accordance with some embodiments of the present disclosure. For the purpose of discussion, the method 1500 will be described from the perspective of the first terminal device 110 with reference to FIG. 1.

At block 1510, the first terminal device 110 receives, from a second terminal device 120 during a path switch procedure, a notification includes an indication of a failure of an RRC connection between the second terminal device 120 and the network device 130, the path switch procedure includes switching from a first path to a second path, the first path is a direct path between the first terminal device 110 and the network device 130, the second path is an indirect path between the first terminal device 110 and the network device 130 via the second terminal device 120. At block 1520, the first terminal device110 performs, based on the notification, at least one of: reverting back to a configuration associated with the network device; or performing a radio resource control (RRC) re-establishment procedure.

In some example embodiments, the first terminal device 110 receives, from the network device 130 prior the performing, a path switch command within a predefined time period, the path switch command indicates the switching.

In some example embodiments, the first terminal device 110 receives, from the network device 130, an indication of the predefined time period, the indication is carried in an RRC message or system information.

In some example embodiments, the second terminal device is in an idle state or an inactive state.

FIG. 16 illustrates a flowchart of an example method 1600 implemented at a second terminal device in accordance with some embodiments of the present disclosure. For the purpose of discussion, the method 1600 will be described from the perspective of the second terminal device 120 with reference to FIG. 1.

At block 1610, the second terminal device 120 initiates a connection establishment with a first terminal device 110 during a path switch procedure of the first terminal device 110, the path switch procedure includes switching from a first path to a second path, the first path is a direct path between the first terminal device 110 and a network device 130, the second path is an indirect path between the first terminal device 110 and the network device 130 via the second terminal device 120. At block 1620, the second terminal device 120 transmits, to the network device 130, a failure report indicating a failure of the connection establishment if the connection establishment is failed.

In some example embodiments, the second terminal device 120 determines that the connection establishment is failed based on at least one of: a maximum number of retries being reached, the retries being performed for the connection establishment, or an indication from an upper layer on the connection being not successfully established.

In some example embodiments, the second terminal device 120 receives, from the network device 130, an indication of the maximum number of retries, the indication is carried in a radio resource control (RRC) message or system information.

In some example embodiments, the second terminal device 120 determines the maximum number of retries based on an implementation of the second terminal device.

In some example embodiments, the failure report indicates at least one of: the failure occurring during the path switch procedure, or an identifier of the first terminal device.

In some example embodiments, the failure report is transmitted via an RRC message. In some example embodiments, the second terminal device is in an RRC connected state.

Details of some embodiments according to the present disclosure have been described with reference to FIGS. 1-16. Now an example implementation of the first terminal device, the second terminal device, and the network device will be discussed below.

In some example embodiments, a first terminal device comprises circuitry configured to: receive, from a network device, a path switch command indicating to switch from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device, the path switch command comprising an identifier (ID) of the second terminal device; initiate a connection establishment with the second terminal device based on the path switch command; and in accordance with a determination that the connection establishment is failed, perform a path switch failure procedure.

In some example embodiments, the first terminal device comprises circuitry configured to: perform the path switch failure procedure by at least one of: performing a reconfiguration failure procedure; performing a radio resource control (RRC) re-establishment procedure; performing a cell reselection procedure; or performing a relay reselection procedure.

In some example embodiments, the first terminal device comprises circuitry configured to: determine that the connection establishment is failed based on at least one of: an indication from an upper layer on the connection being not successfully established; the connection being not successfully established within a time period, the time period being for a path switch procedure associated with the path switch command; or a maximum number of retries being reached.

In some example embodiments, the first terminal device comprises circuitry configured to: receive, from the network device, an indication of the maximum number of retries, the indication being carried in an RRC message or system information.

In some example embodiments, the first terminal device comprises circuitry configured to: determine the maximum number of retries based on an implementation of the first terminal device.

In some example embodiments, the first terminal device comprises circuitry configured to: transmit, to the network device, failure information related to a failure of the connection establishment.

In some example embodiments, the cause information indicates at least one of: a handover performed by the second terminal device, an RLF of a PC5 interface of the first terminal device, an expiry of a timer for a path switch procedure, an RRC connection of the second terminal device is failed corresponding to the path switch procedure, a change of serving cells of the second terminal device prior the path switch procedure, or a failure of the connection establishment.

In some example embodiments, the first terminal device comprises circuitry configured to: record the failure information upon: receiving, from the second terminal device, a notification comprising a type of the failure, or determining a reconfiguration failure for a path switch procedure, or determining that the connection establishment is failed.

In some example embodiments, a connection between the first terminal device and the second terminal device comprises a PC5 RRC unicast link.

In some example embodiments, the second terminal device is in an RRC connected state.

In some example embodiments, a network device comprises circuitry configured to: transmit, to a first terminal device, a path switch command indicating to switch from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device, the path switch command comprising an identifier (ID) of the second terminal device; and receive, from the first terminal device, failure information related to a failure of a connection between the first terminal device and the second terminal device, the connection being initiated by the first terminal device based on the path switch command.

In some example embodiments, the network device comprises circuitry configured to:transmit, to the first device, an indication of a maximum number of retries, the retries being performed at the first terminal device for the connection, the indication being carried in a radio resource control (RRC) message or system information.

In some example embodiments, a first terminal device comprises circuitry configured to: receive, from a second terminal device during a path switch procedure, a notification comprising an indication of a failure of an RRC connection between the second terminal device and the network device, the path switch procedure comprising switching from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via the second terminal device; and perform, based on the notification, at least one of: reverting back to a configuration associated with the network device; or performing a radio resource control (RRC) re-establishment procedure.

In some example embodiments, the first terminal device comprises circuitry configured to: receive, from the network device prior the performing, a path switch command within a predefined time period, the path switch command indicating the switching.

In some example embodiments, the first terminal device comprises circuitry configured to: receive, from the network device, an indication of the predefined time period, the indication being carried in an RRC message or system information.

In some example embodiments, a second terminal device comprises circuitry configured to: initiate a connection establishment with a first terminal device during a path switch procedure of the first terminal device, the path switch procedure comprising switching from a first path to a second path, the first path being a direct path between the first terminal device and a network device, the second path being an indirect path between the first terminal device and the network device via the second terminal device; and in accordance with a determination that the connection establishment is failed, transmit, to the network device, a failure report indicating a failure of the connection establishment.

In some example embodiments, the second terminal device comprises circuitry configured to: determine that the PC5 connection establishment is failed based on at least one of: a maximum number of retries being reached, the retries being performed for the connection establishment, or an indication from an upper layer on the connection being not successfully established.

In some example embodiments, the second terminal device comprises circuitry configured to: receive, from the network device, an indication of the maximum number of retries, the indication being carried in a radio resource control (RRC) message or system information.

In some example embodiments, the second terminal device comprises circuitry configured to: determine the maximum number of retries based on an implementation of the second terminal device.

FIG. 17 illustrates a simplified block diagram of a device 1700 that is suitable for implementing embodiments of the present disclosure. The device 1700 can be considered as a further example implementation of the first terminal device 110, the second terminal device 120 and/or the network device 130 as shown in FIG. 1. Accordingly, the device 1700 can be implemented at or as at least a part of the first terminal device 110, the second terminal device 120, or the network device 130.

As shown, the device 1700 includes a processor 1710, a memory 1720 coupled to the processor 1710, a suitable transmitter (TX) and receiver (RX) 1740 coupled to the processor 1710, and a communication interface coupled to the TX/RX 1740. The memory 1710 stores at least a part of a program 1730. The TX/RX 1740 is for bidirectional communications. The TX/RX 1740 has at least one antenna to facilitate communication, though in practice an Access Node mentioned in this disclosure may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2 interface for bidirectional communications between eNBs, S1 interface for communication between a Mobility Management Entity (MME) /Serving Gateway (S-GW) and the eNB, Un interface for communication between the eNB and a relay node (RN) , or Uu interface for communication between the eNB and a terminal device.

The program 1730 is assumed to include program instructions that, when executed by the associated processor 1710, enable the device 1700 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to FIGS. 4-16. The embodiments herein may be implemented by computer software executable by the processor 1710 of the device 1700, or by hardware, or by a combination of software and hardware. The processor 1710 may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 1710 and memory 1720 may form processing means 1750 adapted to implement various embodiments of the present disclosure.

The memory 1720 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 1720 is shown in the device 1700, there may be several physically distinct memory modules in the device 1700. The processor 1710 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1700 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.

In summary, embodiments of the present disclosure may provide the following solutions.

The present disclosure provides a method of communication, comprises: receiving, at a first terminal device from a network device, a path switch command indicating to switch from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device, the path switch command comprising an identifier (ID) of the second terminal device; initiating a connection establishment with the second terminal device based on the path switch command; and in accordance with a determination that the connection establishment is failed, performing a path switch failure procedure.

In one embodiment, the method as above, performing the path switch failure procedure comprises at least one of: performing a reconfiguration failure procedure; performing a radio resource control (RRC) re-establishment procedure; performing a cell reselection procedure; or performing a relay reselection procedure.

In one embodiment, the method as above, further comprising: determining that the connection establishment is failed based on at least one of: an indication from an upper layer on the connection being not successfully established; the connection being not successfully established within a time period, the time period being for a path switch procedure associated with the path switch command; or a maximum number of retries being reached.

In one embodiment, the method as above, further comprising: receiving, from the network device, an indication of the maximum number of retries, the indication being carried in an RRC message or system information.

In one embodiment, the method as above, further comprising: determining the maximum number of retries based on an implementation of the first terminal device.

In one embodiment, the method as above, further comprising: transmitting, to the network device, failure information related to a failure of the connection establishment.

In one embodiment, the method as above, the failure information indicates at least one of: the ID of the second terminal device, a list of serving cell IDs of the second terminal device, a type of the failure, or cause information of the failure.

In one embodiment, the method as above, the list of serving cell IDs comprises an ID of a latest serving cell of the second terminal device, and the ID of the latest serving cell is at a predefined position in the list of serving cell IDs.

In one embodiment, the method as above, the type indicates at least one of: the failure being occurred during a path switch procedure, or the failure being related to a sidelink.

In one embodiment, the method as above, the cause information indicates at least one of: a handover performed by the second terminal device, an RLF of a PC5 interface of the first terminal device, an expiry of a timer for a path switch procedure, an RRC connection of the second terminal device is failed corresponding to the path switch procedure, a change of serving cells of the second terminal device prior the path switch procedure, or a failure of the connection establishment.

In one embodiment, the method as above, further comprising: recording the failure information upon: receiving, from the second terminal device, a notification comprising a type of the failure, or determining a reconfiguration failure for a path switch procedure, or determining that the connection establishment is failed.

In one embodiment, the method as above, a connection between the first terminal device and the second terminal device comprises a PC5 RRC unicast link.

In one embodiment, the method as above, the second terminal device is in an RRC connected state.

The present disclosure provides a method of communication, comprises: transmitting, at a network device to a first terminal device, a path switch command indicating to switch from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device, the path switch command comprising an identifier (ID) of the second terminal device; and receiving, from the first terminal device, failure information related to a failure of a connection between the first terminal device and the second terminal device, the connection being initiated by the first terminal device based on the path switch command.

In one embodiment, the method as above, further comprising: transmitting, to the first device, an indication of a maximum number of retries, the retries being performed at the first terminal device for the connection, the indication being carried in a radio resource control (RRC) message or system information.

The present disclosure provides a method of communication, comprises: receiving, at a first terminal device from a second terminal device during a path switch procedure, a notification comprising an indication of a failure of an RRC connection between the second terminal device and the network device, the path switch procedure comprising switching from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via the second terminal device; and performing, based on the notification, at least one of: reverting back to a configuration associated with the network device; or performing a radio resource control (RRC) re-establishment procedure.

In one embodiment, the method as above, further comprising: receiving, from the network device prior the performing, a path switch command within a predefined time period, the path switch command indicating the switching.

In one embodiment, the method as above, further comprising: receiving, from the network device, an indication of the predefined time period, the indication being carried in an RRC message or system information.

In one embodiment, the method as above, the second terminal device is in an idle state or an inactive state.

The present disclosure provides a method of communication, comprises: initiating, at a second terminal device, a connection establishment with a first terminal device during a path switch procedure of the first terminal device, the path switch procedure comprising switching from a first path to a second path, the first path being a direct path between the first terminal device and a network device, the second path being an indirect path between the first terminal device and the network device via the second terminal device; and in accordance with a determination that the connection establishment is failed, transmitting, to the network device, a failure report indicating a failure of the connection establishment.

In one embodiment, the method as above, further comprising: determining that the connection establishment is failed based on at least one of: a maximum number of retries being reached, the retries being performed for the connection establishment, or an indication from an upper layer on the connection being not successfully established.

In one embodiment, the method as above, further comprising: receiving, from the network device, an indication of the maximum number of retries, the indication being carried in a radio resource control (RRC) message or system information.

In one embodiment, the method as above, further comprising: determining the maximum number of retries based on an implementation of the second terminal device.

In one embodiment, the method as above, the failure report indicates at least one of:

the failure occurring during the path switch procedure, or an identifier of the first terminal device.

In one embodiment, the method as above, the failure report is transmitted via an RRC message.

The present disclosure provides a first terminal device, comprising: a processor; and a memory storing computer program codes; the memory and the computer program codes configured to, with the processor, cause the first terminal device to perform the method implemented at the first terminal device discussed above.

The present disclosure provides a second terminal device, comprising: a processor; and a memory storing computer program codes; the memory and the computer program codes configured to, with the processor, cause the second terminal device to perform the method implemented at the second terminal device discussed above.

The present disclosure provides a network device, comprising: a processor; and a memory storing computer program codes; the memory and the computer program codes configured to, with the processor, cause the network device to perform the method implemented at the network device discussed above.

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 representation, it will be appreciated that the blocks, apparatus, systems, techniques or methods 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 process or method as described above with reference to FIGS. 4-16. 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.

The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine 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 machine 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.

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 language 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 method of communication, comprising:

receiving, at a first terminal device from a network device, a path switch command indicating to switch from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device, the path switch command comprising an identifier (ID) of the second terminal device;

initiating a connection establishment with the second terminal device based on the path switch command; and

in accordance with a determination that the connection establishment is failed, performing a path switch failure procedure.
The method of claim 1, wherein performing the path switch failure procedure comprises at least one of:

performing a reconfiguration failure procedure;

performing a radio resource control (RRC) re-establishment procedure;

performing a cell reselection procedure; or

performing a relay reselection procedure.
The method of claim 1, further comprising: determining that the connection establishment is failed based on at least one of:

an indication from an upper layer on the connection being not successfully established;

the connection being not successfully established within a time period, the time period being for a path switch procedure associated with the path switch command; or

a maximum number of retries being reached.
The method of claim 3, further comprising:

receiving, from the network device, an indication of the maximum number of retries, the indication being carried in an RRC message or system information.
The method of claim 1, further comprising:

transmitting, to the network device, failure information related to a failure of the connection establishment.
The method of claim 5, wherein the failure information indicates at least one of:

the ID of the second terminal device,

a list of serving cell IDs of the second terminal device,

a type of the failure, or

cause information of the failure.
The method of claim 6, wherein the type indicates at least one of:

the failure being occurred during a path switch procedure, or

the failure being related to a sidelink.
The method of claim 6, wherein the cause information indicates at least one of:

a handover performed by the second terminal device,

an RLF of a proximity communication 5 (PC5) interface of the first terminal device,

an expiry of a timer for a path switch procedure,

an RRC connection of the second terminal device is failed corresponding to the path switch procedure,

a change of serving cells of the second terminal device prior the path switch procedure, or

a failure of the connection establishment.
The method of claim 5, further comprising: recording the failure information upon:

receiving, from the second terminal device, a notification comprising a type of the failure,

determining a reconfiguration failure for a path switch procedure, or

determining that the connection establishment is failed.
The method of claim 1, wherein a connection between the first terminal device and the second terminal device comprises a PC5 RRC unicast link.
The method of claim 1, wherein the second terminal device is in an RRC connected state.
A method of communication, comprising:

transmitting, at a network device to a first terminal device, a path switch command indicating to switch from a first path to a second path, the first path being a direct path between the first terminal device and the network device, the second path being an indirect path between the first terminal device and the network device via a second terminal device, the path switch command comprising an identifier (ID) of the second terminal device; and

receiving, from the first terminal device, failure information related to a failure of a connection between the first terminal device and the second terminal device, the connection being initiated by the first terminal device based on the path switch command.
The method of claim 12, wherein the failure information indicates at least one of:

the ID of the second terminal device,

a list of serving cell IDs of the second terminal device,

a type of the failure, or

cause information of the failure.
A first terminal device comprising:

a processor; and

a memory storing computer program codes;

the memory and the computer program codes configured to, with the processor, cause the first terminal device to perform the method according to any of claims 1-11.
A network device comprising:

a processor; and

a memory storing computer program codes;

the memory and the computer program codes configured to, with the processor, cause the network device to perform the method according to any of claims 12-13.
A computer readable medium having instructions stored thereon, the instructions, when executed by a processor of an apparatus, causing the apparatus to perform the method according to any of claims 1-13.