Indirect path failure procedure in multipath

Abstract

Exemplary embodiments of the present disclosure relate to a first UE, a second UE, a base station, methods, devices, and a computer-readable medium for an indirect path failure procedure in a multipath scenario. The first UE receives a indication from the second UE that the connection between the second UE and a third device has failed. The first UE also transmits the failure information to the third device or ignores the indication from the second UE. Thus, an indirect path failure procedure is discussed, and thus UE behavior is defined, and communication between the first UE and the third device is ensured.

Description

Technology Field

[0001] The present disclosure relates to wireless communication, and more specifically, to network units, methods, apparatuses, and computer-readable media for an indirect path failure procedure in multipath communication. Background Technology

[0002] A wireless communication system may include one or more network communication devices, such as base stations, which may be otherwise known by other appropriate terms, such as eNodeBs (eNBs), next-generation NodeBs (gNBs), or other appropriate terms. Each network communication device, such as a base station, may support wireless communication with one or more user communication devices, such as user equipment (UEs) or other appropriate terms. A wireless communication system may support wireless communication with one or more user communication devices by utilizing the resources of the wireless communication system (e.g., time resources (e.g., symbols, slots, subframes, frames, etc.) or frequency resources (e.g., subcarriers, carriers)). Additionally, a wireless communication system may support wireless communication through various radio access technologies, including 3G (third generation) radio access technology, 4G (fourth generation) radio access technology, and 5G (fifth generation) radio access technology, among other appropriate radio access technologies beyond 5G (e.g., 6th generation (6G)).

[0003] The scenario for UE-to-network (U2N) relay was discussed at the 3rd Generation Partner Project (3GPP). An indirect path is a type of U2N transmission path where data is forwarded through a U2N relay UE between a remote U2N UE and a network.

[0004] Currently, intra-gNB-based multipath is being discussed, where, for example, UEs can communicate with the gNB via direct and indirect paths, respectively. However, some related issues, including indirect and direct path failures, need to be further investigated.

[0005] The present disclosure relates to a first UE, a second UE, a base station, methods, devices, and a computer-readable medium for an indirect path failure procedure in a multipath scenario. According to the proposed solution, an indirect path in multipath can be released based on indication from the second UE (relay UE).

[0006] In some implementations, a first UE is provided. The first UE comprises at least one memory; and at least one processor coupled to the at least one memory, and the at least one processor is configured to cause the first UE to receive a signal from the second UE indicating that a connection between the second UE and a third device has failed—the first UE is configured with a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE—; and to transmit failure information of the indirect path to the third device based on the signal, or to ignore the signal from the second UE.

[0007] In some implementations, a first UE is provided. The first UE comprises at least one memory; and at least one processor coupled to the at least one memory, and the at least one processor is configured to cause the first UE to transmit to the second UE a indication indicating one of the serving cell of the first UE being different from an additional serving cell of the second UE, or that an unsolicited system information block 1 (SIB1) forwarding is not expected; and to ignore the unsolicited SIB1 forwarding from the second UE—the first UE is configured with a direct path between the first UE and the base station (BS) and an indirect path between the first UE and the BS through the second UE.

[0008] In some implementations, a first UE is provided. The first UE comprises at least one memory; and at least one processor coupled to the at least one memory, and the at least one processor is configured to cause the first UE to receive a reconstruction message from a BS that includes an identifier of a candidate relay UE, and - the first UE is configured with a direct path between the first UE and the BS and an indirect path between the first UE and the BS through a second UE -; and to initiate a procedure for releasing the direct path upon determining that the candidate relay UE is identical to the second UE.

[0009] In some implementations, a second UE is provided. The second UE comprises at least one memory; and at least one processor coupled to the at least one memory, and the at least one processor is configured to cause the second UE to transmit to the first UE an indication that the connection between the second UE and the third device has failed in response to the failure of the connection between the second UE and the third device - the first UE is configured with a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE.

[0010] In some implementations, a BS is provided. The BS comprises at least one memory; and at least one processor coupled to the at least one memory, and the at least one processor is configured to cause the BS to receive failure information of an indirect path from a first UE, which consists of a direct path between the first UE and the BS and an indirect path between the first UE and the BS through a second UE; to transmit a path switch message to the first UE that includes an identifier of a candidate relay UE; and, upon a determination that a complete message is received from the first UE, to perform a switch from the indirect path to an additional indirect path—the additional indirect path is for a connection between the first UE and the BS through a candidate relay UE.

[0011] In some implementations, a second UE is provided. The second UE comprises at least one memory; and at least one processor coupled to the at least one memory, and the at least one processor is configured to cause the second UE to receive a indication from the first UE or BS indicating one of the serving cell of the first UE being different from an additional serving cell of the second UE, or that unsolicited SIB1 forwarding is not expected; and based on the indication, to stop unsolicited SIB1 forwarding from BS to the first UE—the first UE is configured with a direct path between the first UE and BS and an indirect path between the first UE and BS through the second UE.

[0012] In some implementations, a method performed by a first UE is provided. The method includes receiving from a second UE an indication that a connection between the second UE and a third device has failed—the first UE is composed of a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE—; and transmitting information of failure of the indirect path to the third device based on the indication, or ignoring the indication from the second UE.

[0013] In some implementations, a method performed by a first UE is provided. The method comprises: transmitting to the second UE a indication indicating that the serving cell of the first UE is different from an additional serving cell of the second UE, or that an unsolicited SIB1 forwarding is not expected; and ignoring an unsolicited SIB1 forwarding from the second UE - wherein the first UE is composed of a direct path between the first UE and the BS and an indirect path between the first UE and the BS through the second UE.

[0014] In some implementations, a method performed by a first UE is provided. The method includes the steps of receiving a reconstruction message from a BS containing an identifier of a candidate relay UE—the first UE is composed of a direct path between the first UE and the BS and an indirect path between the first UE and the BS through a second UE—; and initiating a procedure to release the direct path upon determining that the candidate relay UE is identical to the second UE.

[0015] In some implementations, a method performed by a second UE is provided. The method includes the step of transmitting to a first UE an indication that the connection between the second UE and the third device has failed in response to the failure of the connection between the second UE and the third device—the first UE is composed of a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE.

[0016] In some implementations, a method performed by a BS is provided. The method comprises: receiving failure information of an indirect path from a first UE, which consists of a direct path between the first UE and the BS and an indirect path between the first UE and the BS through a second UE; transmitting a path switching message to the first UE that includes an identifier of a candidate relay UE; and, upon determining that a complete message is received from the first UE, performing a transition from the indirect path to an additional indirect path—the additional indirect path is for a connection between the first UE and the BS through a candidate relay UE.

[0017] In some implementations, a method performed by a second UE is provided. The method comprises: receiving a indication from the first UE or BS indicating one of the following: that the serving cell of the first UE is different from an additional serving cell of the second UE, or that unsolicited SIB1 forwarding is not expected; and, based on the indication, stopping unsolicited SIB1 forwarding from the BS to the first UE—the first UE is composed of a direct path between the first UE and the BS and an indirect path between the first UE and the BS through the second UE.

[0018] In some implementations, a processor for wireless communication is provided. The processor includes at least one controller coupled with at least one memory, and the at least one controller is configured to allow the processor to receive a signal from a second UE indicating that the connection between the second UE and a third device has failed—the first UE is configured with a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE—; and to transmit information of failure of the indirect path to the third device based on the signal, or to ignore the signal from the second UE.

[0019] In some implementations, a processor for wireless communication is provided. The processor includes at least one controller coupled with at least one memory, and the at least one controller is configured to cause the processor to transmit to the second UE a indication indicating one of the serving cell of the first UE being different from an additional serving cell of the second UE, or that an unsolicited SIB1 forwarding is not expected; and to ignore the unsolicited SIB1 forwarding from the second UE—the first UE being configured with a direct path between the first UE and the BS and an indirect path between the first UE and the BS through the second UE.

[0020] In some implementations, a processor for wireless communication is provided. The processor includes at least one controller coupled with at least one memory, and the at least one controller is configured to cause the processor to receive a reconfiguration message from a BS that includes an identifier of a candidate relay UE - the first UE consists of a direct path between the first UE and the BS and an indirect path between the first UE and the BS through a second UE -; and to initiate a procedure for releasing the direct path upon determining that the candidate relay UE is the same as the second UE.

[0021] In some implementations, a processor for wireless communication is provided. The processor includes at least one controller coupled with at least one memory, and the at least one controller is configured to cause the processor to transmit to the first UE an indication that the connection between the second UE and the third device has failed in response to the failure of the connection between the second UE and the third device - the first UE is configured with a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE.

[0022] In some implementations, a processor for wireless communication is provided. The processor includes at least one controller coupled with at least one memory, and the at least one controller is configured to cause the processor to receive failure information of an indirect path from a first UE, which consists of a direct path between a first UE and a BS and an indirect path between a first UE and a BS through a second UE; to transmit a path switching message to the first UE that includes an identifier of a candidate relay UE; and, upon a determination that a complete message is received from the first UE, to perform a switch from an indirect path to an additional indirect path—the additional indirect path is for a connection between a first UE and a BS through a candidate relay UE.

[0023] In some implementations, a processor for wireless communication is provided. The processor includes at least one controller coupled with at least one memory, and the at least one controller is configured to cause the processor to receive a indication from a first UE or a BS indicating one of the serving cell of the first UE being different from an additional serving cell of the second UE, or that unsolicited SIB1 forwarding is not expected; and based on the indication, to stop unsolicited SIB1 forwarding from the BS to the first UE—the first UE being configured with a direct path between the first UE and the BS and an indirect path between the first UE and the BS through the second UE.

[0024] In the methods described herein and some implementations of the first UE, the third device is a BS and receives from the BS a route switching message including an identifier of a candidate relay UE; and based on the route switching message, perform a transition from an indirect path to an additional indirect path—the additional indirect path is for a connection between the first UE and the BS through the candidate relay UE—further comprises.

[0025] In the methods and some implementations of the first UE described in this specification, the third device is BS and further includes ignoring the display based on the determination that the display indicates a handover of the second UE.

[0026] In the methods described herein and in some implementations of the first UE, the indirect path is maintained unchanged; and the PCell (primary cell) change from the first cell associated with the direct path to the second cell associated with the indirect path is further included.

[0027] In the methods described herein and in some implementations of the first UE, it further includes determining to use resources configured in a configured sidelink grant for the second UE based on a determination that a timer for adding or changing a route is running.

[0028] In some implementations of the methods described herein, the first UE, the second UE, and the BS, the third device is the BS, and the indication indicates one of a radio link failure (RLF) of the link between the second UE and the BS, a handover of the second UE, or a cell reselection of the second UE.

[0029] In the methods described herein, in some implementations of the first UE, second UE, and BS, the indication is carried in a PC5 notification message.

[0030] In the methods described herein, in some implementations of the first UE, second UE, and BS, the indication includes a PC5 unicast release message.

[0031] In the methods described herein, in some implementations of the first UE, the second UE, and the BS, the third device is the third UE, and the indication indicates one of a PC5 RLF between the second UE and the third UE, or a sidelink radio resource control (RRC) reconfiguration failure between the second UE and the third UE.

[0032] In the methods described herein, in some implementations of the first UE, second UE and BS, the indication includes a failure type indicating a sidelink RRC reconfiguration failure.

[0033] In some implementations of the methods, first UE, second UE, and BS described herein, the failure information of the indirect path includes a failure type of the indirect path, and the failure type indicates one of an RLF of the link between the second UE and BS, a handover of the second UE, or a cell reselection of the second UE.

[0034] In the methods described herein, in some implementations of the first UE, second UE, and BS, the indication from BS is carried in an RRC reconstruction message. Brief explanation of the drawing

[0035] FIG. 1 illustrates an example of a wireless communication system in which some embodiments of the present disclosure may be implemented. FIG. 2a illustrates a schematic diagram of an exemplary communication network in which some embodiments of the present disclosure may be implemented. FIG. 2b illustrates an exemplary RRC reconstruction sidelink procedure. Figure 2c illustrates exemplary flow signaling for successful indirect path addition. FIG. 2d illustrates a schematic diagram of an exemplary communication network in which some embodiments of the present disclosure may be implemented. FIG. 3 illustrates a signaling chart illustrating a communication process according to some exemplary embodiments of the present disclosure. FIG. 4 illustrates a schematic diagram of a signaling transmission according to some exemplary embodiments of the present disclosure. FIG. 5 illustrates a signaling chart illustrating a communication process for an unsolicited SIB1 according to some exemplary embodiments of the present disclosure. FIG. 6 illustrates a signaling chart illustrating a communication process for direct path release according to some exemplary embodiments of the present disclosure. FIG. 7 illustrates a signaling chart illustrating a communication process for single-path switching according to some exemplary embodiments of the present disclosure. FIG. 8a illustrates a schematic diagram of a U2U network in which some embodiments of the present disclosure may be implemented. FIG. 8b illustrates a signaling chart illustrating a communication process for an indirect path failure in U2U according to some exemplary embodiments of the present disclosure. FIG. 9 illustrates an example of a device suitable for implementing embodiments of the present disclosure. FIG. 10 illustrates an example of a processor suitable for implementing some embodiments of the present disclosure. FIG. 11 illustrates a flowchart of an exemplary method implemented in a first UE according to embodiments of the present disclosure. FIG. 12 illustrates a flowchart of an exemplary method implemented in a first UE according to embodiments of the present disclosure. FIG. 13 illustrates a flowchart of an exemplary method implemented in a first UE according to embodiments of the present disclosure. FIG. 14 illustrates a flowchart of an exemplary method implemented in a second UE according to embodiments of the present disclosure. FIG. 15 illustrates a flowchart of an exemplary method implemented in BS according to embodiments of the present disclosure. FIG. 16 illustrates a flowchart of an exemplary method implemented in a second UE according to some embodiments of the present disclosure. Throughout the drawings, identical or similar reference numbers represent identical or similar elements. Specific details for implementing the invention

[0036] The principles of the present disclosure will now be described with reference to some embodiments. It should be understood that these embodiments are described for illustrative purposes only and do not imply any limitation to the scope of the present disclosure, but are intended to help a person skilled in the art understand and implement the present disclosure. The disclosure described herein may be implemented in various ways other than those described below. In the following description and claims, unless otherwise defined, all technical and scientific terms used herein have the same meaning as generally understood by a person skilled in the art to which the present disclosure pertains.

[0037] References to “one embodiment,” “exemplary embodiment,” “embodiment,” “some embodiments,” etc., in this disclosure indicate that while the described embodiment(s) may include specific features, structures, or characteristics, not all embodiments are required to include specific features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same embodiment(s). Moreover, when a specific feature, structure, or characteristic is described in relation to one embodiment, it is considered to be within the knowledge of a person skilled in the art to have an effect on such feature, structure, or characteristic in relation to other embodiments, whether explicitly described or not.

[0038] It should be understood that while terms such as "first" and "second" may be used to describe various elements in this specification, these elements are not to be limited by these terms. These terms are used solely to distinguish one element from another. For example, without departing from the scope of the embodiments, the first element may also be referred to as the second element, and similarly, the second element may also be referred to as the first element. As used in this specification, the term "and / or" includes any and all combinations of one or more of the enumerated terms. In some examples, values, procedures, or devices are referred to as "best," "lowest," "highest," "minimum," "maximum," etc. It will be well understood that such descriptions are intended to indicate that a selection may be made among many functional alternatives used, and that such selection does not need to be superior, smaller, higher, or otherwise preferable to other selections.

[0039] The terms used herein are intended only to describe specific embodiments and are not intended to limit the embodiments. As used herein, singular forms (“a,” “an,” and “the”) are intended to include plural forms 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 the mentioned features, elements, components, etc., but do not exclude the presence or addition of one or more other features, elements, components, and / or combinations thereof. For example, the term “includes” and variations thereof should be read as open terms meaning “includes, but is not limited to.” The term “based on” should be read as “based at least in part on.” The terms "one embodiment" and "embodiment" shall be read as "at least one embodiment." The term "another embodiment" shall be read as "at least one other embodiment." The use of expressions such as "A and / or B" may mean "only A," "only B," or "both A and B." Other explicit and implicit definitions may be included below.

[0040] FIG. 1 illustrates an example of a wireless communication system (100) in which some embodiments of the present disclosure may be implemented. The wireless communication system (100) may include one or more network entities (102) (also referred to as network equipment (NE)), one or more UEs (104), a core network (106), and a packet data network (108). The wireless communication system (100) may support various radio access technologies. In some implementations, the wireless communication system (100) may be a 4G network, such as a long term evolution (LTE) network or an LTE-advanced (LTE-A) network. In some other implementations, the wireless communication system (100) may be a 5G network, such as a new radio (NR) network. In other implementations, the wireless communication system (100) may be a combination of a 4G network and a 5G network, or other suitable radio access technology including IEEE (Institute of Electrical and Electronics Engineers) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), and IEEE 802.20. The wireless communication system (100) may support radio access technologies beyond 5G. Additionally, the wireless communication system (100) may support technologies such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), or Code Division Multiple Access (CDMA).

[0041] One or more network entities (102) may be distributed across a geographical area to form a wireless communication system (100). The one or more network entities (102) described herein may be network nodes, base stations, network elements, radio access networks (RAN), base transceiver stations, access points, NodeB, eNodeB (eNB), next-generation NodeB (gNB), or other appropriate terms, may include or be referred to as such. Network entities (102) and UEs (104) may communicate via a communication link (110) which may be wireless or wired. For example, network entities (102) and UEs (104) may perform wireless communication (e.g., receive signaling, transmit signaling) through a Uu interface.

[0042] A network entity (102) may provide a geographic coverage area (112) in which the network entity (102) can support services (e.g., voice, video, packet data, messages, broadcasts, etc.) for one or more UEs (104) within the geographic coverage area (112). For example, the network entity (102) and the UE (104) may support wireless communication of signals related to services (e.g., voice, video, packet data, messaging, broadcasts, etc.) according to one or more radio access technologies. In some implementations, the network entity (102) may be mobile and may be, for example, a satellite associated with a non-terrestrial network. In some implementations, different geographic coverage areas (112) associated with the same or different radio access technologies may overlap, but different geographic coverage areas (112) may be associated with different network entities (102). The information and signals described in this specification may be represented using any of the various different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description may be represented as voltage, current, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0043] One or more UEs (104) may be distributed across the entire geographical area of ​​the wireless communication system (100). The UE (104) may include or be referred to as a mobile device, wireless device, remote device, remote unit, handheld device, or subscriber device, or some other suitable term. In some implementations, the UE (104) may be referred to as a unit, station, terminal, or client, among other examples. Additionally, or alternatively, the UE (104) may be referred to as an Internet-of-Things (IoT) device, Internet-of-Everything (IoE) device, or machine-type communication (MTC) device, among other examples. In some implementations, the UE (104) may be stationary in the wireless communication system (100). In some other implementations, the UE (104) may be mobile in the wireless communication system (100).

[0044] One or more UEs (104) may be devices of different forms or different capabilities. Some examples of UEs (104) are illustrated in FIG. 1. As illustrated in FIG. 1, the UE (104) may communicate with various types of devices, such as network entities (102), other UEs (104), or network equipment (e.g., a core network (106), a packet data network (108), a relay device, an integrated access and backhaul (IAB) node, or other network equipment). Additionally, or alternatively, the UE (104) may support communication with other network entities (102) or UEs (104) that can act as relays in the wireless communication system (100).

[0045] The UE (104) may also support direct wireless communication with other UEs (104) via a communication link (114). For example, the UE (104) may support direct wireless communication with other UEs (104) via a device-to-device (D2D) communication link. In some implementations, such as vehicle-to-vehicle (V2V) deployments, vehicle-to-everything (V2X) deployments, or cellular-V2X deployments, the communication link (114) may be referred to as a side link (SL). For example, the UE (104) may support direct wireless communication with other UEs (104) via a PC5 interface.

[0046] A network entity (102) may support communication with a core network (106), with other network entities (102), or with both. For example, a network entity (102) may interface with the core network (106) through one or more backhaul links (116) (e.g., through S1, N2, N3, or other network interfaces). Network entities (102) may communicate with each other through backhaul links (116) (e.g., through X2, Xn, or other network interfaces). In some implementations, network entities (102) may communicate directly with each other (e.g., between network entities (102)). In some other implementations, network entities (102) may communicate with each other or indirectly (e.g., through the core network (106)). In some implementations, one or more network entities (102) may include subcomponents such as an access network entity, which may be an example of an access node controller (ANC). The ANC may communicate with one or more UEs (104) through one or more other access network transmission entities, which may be referred to as a radio head, a smart radio head, or a transmission-reception point (TRP).

[0047] In some implementations, the network entity (102) may be configured as a disaggregated architecture that can be configured to utilize protocol stacks that are physically or logically distributed among two or more network entities (102), such as an integrated access backhaul (IAB) network, an open RAN (e.g., a network configuration sponsored by the O-RAN Alliance), or a virtualized RAN (vRAN) (e.g., a cloud RAN (C-RAN)). For example, the network entity (102) may include one or more of a central unit (CU), a distributed unit (DU), a radio unit (RU), a RAN intelligent controller (RIC) (e.g., a near-real-time RIC, a non-real-time RIC), a service management and orchestration (SMO) system, or any combination thereof.

[0048] The RU may also be referred to as a radio head, smart radio head, remote radio head (RRH), remote radio unit (RRU), or transmission receiving point (TRP). One or more components of network entities (102) in a distributed RAN architecture may be co-located, or one or more components of network entities (102) may be located in distributed locations (e.g., separate physical locations). In some implementations, one or more network entities (102) of a distributed RAN architecture may be implemented as virtual units (e.g., virtual CU (VCU), virtual DU (VDU), virtual RU (VRU)).

[0049] The functional partitioning between the CU, DU, and RU can be flexible and may support different functionalities depending on which functions (e.g., network layer functions, protocol layer functions, baseband functions, radio frequency functions, and any combination thereof) are performed in the CU, DU, or RU. For example, a functional partitioning of the protocol stack may be utilized between the CU and the DU so that the CU can support one or more layers of the protocol stack, and the DU can support one or more different layers of the protocol stack. In some implementations, the CU may host higher protocol layer (e.g., Layer 3 (L3), Layer 2 (L2)) functionalities and signaling (e.g., Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), Packet Data Convergence Protocol (PDCP)). A CU may be connected to one or more DUs or RUs, and one or more DUs or RUs may host lower protocol layers such as Layer 1 (L1) (e.g., Physical (PHY) layer) or L2 (e.g., Radio Link Control (RLC) layer, Media Access Control (MAC) layer) functionality and signaling, and each may be controlled at least partially by the CU.

[0050] Additionally or alternatively, a functional partition of the protocol stack may be utilized between the DU and the RU, so that the DU can support one or more layers of the protocol stack and the RU can support one or more different layers of the protocol stack. The DU may support one or more different cells (e.g., through one or more RUs). In some implementations, the functional partition between the CU and the DU, or between the DU and the RU, may exist within the protocol layer (e.g., some functions of the protocol layer may be performed by one of the CU, DU, or RU, while other functions of the protocol layer are performed by a different of the CU, DU, or RU).

[0051] The CU can be functionally further subdivided into CU control plane (CU-CP) and CU user plane (CU-UP) functions. The CU can be connected to one or more DUs via midhaul communication links (e.g., F1, F1-C, F1-U), and the DUs can be connected to one or more RUs via fronthaul communication links (e.g., open fronthaul (FH) interfaces). In some implementations, the midhaul communication links or fronthaul communication links may be implemented according to an interface (e.g., a channel) between layers of the protocol stack supported by each network entity (102) communicating through such communication links.

[0052] The core network (106) may support user authentication, access authorization, tracking, connectivity, and other access, routing, or mobility functions. The core network (106) may be an advanced packet core (EPC) or a 5G core (5GC), and may include a control plane entity that manages access and mobility (e.g., a mobility management entity (MME), access and mobility management functions (AMF)) and a user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW), a packet data network (PDN) gateway (P-GW), or a user plane function (UPF)). In some implementations, a control plane entity can manage non-access stratum (NAS) functions, such as mobility, authentication, and bearer management (e.g., data bearers, signal bearers, etc.), for one or more UEs (104) served by one or more network entities (102) associated with a core network (106).

[0053] The core network (106) may communicate with the packet data network (108) through one or more backhaul links (116) (e.g., via S1, N2, N3, or other network interfaces). The packet data network (108) may include an application server (118). In some implementations, one or more UEs (104) may communicate with the application server (118). The UE (104) may establish a session (e.g., a Protocol Data Unit (PDU) session) with the core network (106) through a network entity (102). The core network (106) may route traffic (e.g., control information, data, etc.) between the UE (104) and the application server (118) using the established session (e.g., an established PDU session). A PDU session may be an example of a logical connection between the UE (104) and the core network (106) (e.g., one or more network functions of the core network (106)).

[0054] In a wireless communication system (100), network entities (102) and UEs (104) may utilize the resources of the wireless communication system (100) (e.g., time resources (e.g., symbols, slots, subframes, frames, etc.) or frequency resources (e.g., subcarriers, carriers)) to perform various operations (e.g., wireless communication). In some implementations, network entities (102) and UEs (104) may support different resource structures. For example, network entities (102) and UEs (104) may support different frame structures. In some implementations, such as in 4G, network entities (102) and UEs (104) may support a single frame structure. In some other implementations, such as in 5G, and among other suitable radio access technologies, network entities (102) and UEs (104) can support various frame structures (i.e., multiple frame structures). Network entities (102) and UEs (104) can support various frame structures based on one or more numerologies.

[0055] One or more numerologies may be supported in the wireless communication system (100), and the numerologies may include subcarrier spacing and cyclic prefixes. A first numerology (e.g., μ=0) may be associated with a first subcarrier spacing (e.g., 15 kHz) and a normal cyclic prefix. In some implementations, the first numerology (e.g., μ=0) associated with the first subcarrier spacing (e.g., 15 kHz) may utilize one slot per subframe. A second numerology (e.g., μ=1) may be associated with a second subcarrier spacing (e.g., 30 kHz) and a normal cyclic prefix. A third numerology (e.g., μ=2) may be associated with a third subcarrier spacing (e.g., 60 kHz) and a normal cyclic prefix or an extended cyclic prefix. The fourth numerology (e.g., μ=3) may be associated with the fourth subcarrier interval (e.g., 120 kHz) and a normal cyclic prefix. The fifth numerology (e.g., μ=4) may be associated with the fifth subcarrier interval (e.g., 240 kHz) and a normal cyclic prefix.

[0056] The time interval of a resource (e.g., a communication resource) can be organized according to frames (also referred to as radio frames). Each frame may have a duration, e.g., 10 ms (milliseconds). In some implementations, each frame may contain multiple subframes. For example, each frame may contain 10 subframes, and each subframe may have a duration, e.g., 1 ms. In some implementations, each frame may have the same duration. In some implementations, each subframe of a frame may have the same duration.

[0057] Additionally or alternatively, time intervals of a resource (e.g., a communication resource) may be organized according to slots. For example, a subframe may contain a number of slots (e.g., quantity). The number of slots in each subframe may also depend on one or more numerologies supported by the wireless communication system (100). For example, first, second, third, fourth, and fifth numerologies (i.e., μ=0, μ=1, μ=2, μ=3, μ=4) associated with each subcarrier interval of 15 kHz, 30 kHz, 60 kHz, 120 kHz, and 240 kHz may each utilize a single slot per subframe, two slots per subframe, four slots per subframe, eight slots per subframe, and sixteen slots per subframe, respectively. Each slot may contain a number (e.g., quantity) of symbols (e.g., OFDM symbols). In some implementations, the number of slots (e.g., quantity) for a subframe may depend on the numerology. For a normal cyclic prefix, a slot may contain 14 symbols. For an extended cyclic prefix (e.g., applicable to a 60 kHz subcarrier interval), a slot may contain 12 symbols. The relationship between the number of symbols per slot, the number of slots per subframe, and the number of slots per frame for the normal cyclic prefix and the extended cyclic prefix may depend on the numerology. It should be understood that a reference to a first numerology (e.g., μ=0) associated with a first subcarrier interval (e.g., 15 kHz) may be used interchangeably between subframes and slots.

[0058] In a wireless communication system (100), the electromagnetic (EM) spectrum may be divided into various classes, frequency bands, frequency channels, etc. based on frequency or wavelength. For example, the wireless communication system (100) may support one or more operating frequency bands such as frequency range designations FR1 (410 MHz - 7.125 GHz), FR2 (24.25 GHz - 52.6 GHz), FR3 (7.125 GHz - 24.25 GHz), FR4 (52.6 GHz - 114.25 GHz), FR4a or FR4-1 (52.6 GHz - 71 GHz), and FR5 (114.25 GHz - 300 GHz). In some implementations, network entities (102) and UEs (104) may perform wireless communication through one or more of the operating frequency bands. In some implementations, FR1 may be used by network entities (102) and UEs (104) among other equipment or devices for cellular communication traffic (e.g., control information, data). In some implementations, FR2 may be used by network entities (102) and UEs (104) among other equipment or devices for short range, high data rate capabilities.

[0059] FR1 may be associated with one or more numerologies (e.g., at least three numerologies). For example, FR1 may be associated with a first numerology including a 15 kHz subcarrier interval (e.g., μ=0); a second numerology including a 30 kHz subcarrier interval (e.g., μ=1); and a third numerology including a 60 kHz subcarrier interval (e.g., μ=2). FR2 may be associated with one or more numerologies (e.g., at least two numerologies). For example, FR2 may be associated with a third numerology including a 60 kHz subcarrier interval (e.g., μ=2); and a fourth numerology including a 120 kHz subcarrier interval (e.g., μ=3).

[0060] In the context of the present disclosure, the term “proximity communication 5 (PC5) link” may be used interchangeably with PC5 interface, side link (SL), PC5 unicast link, SL unicast link, device-to-device (D2D) link, user-to-user link, UE-to-UE (U2U) link, etc. The term “relay UE” may be used interchangeably with U2N relay UE, U2U relay UE, Layer 2 (L2) relay UE, L2 U2N relay UE, L2 U2U relay UE, etc. The term “relay UE ID” may be used interchangeably with link ID, path ID, L2 relay UE ID, etc.

[0061] A wireless communication system may include one or more devices, such as one or more base stations and / or one or more UEs. In some implementations, two different UEs may communicate with each other via a PC5 link (PC5 interface), two different base stations may communicate with each other via an Xn link (Xn interface), and UEs and base stations may communicate with each other via a Uu link (Uu interface).

[0062] FIG. 2a illustrates a schematic diagram of an exemplary communication network (210) in which some embodiments of the present disclosure may be implemented. As illustrated in FIG. 2a, a UE (211) may communicate with a base station through a relay UE. The base station may be a gNB (212) or an NG-eNB (213), and the relay UE may be a relay UE (214) or a relay UE (215). For example, the NG-eNB (213) may be an eLTE (evolved long term evolution) base station that supports an NG interface. In some embodiments, sidelink transmission and reception over a PC5 link are supported when the UE (211) is within next-generation radio access network (NG-RAN) coverage, regardless of which RRC state the UE is in, and also when the UE (211) is outside NG-RAN coverage.

[0063] FIG. 2b illustrates an exemplary RRC reconfiguration sidelink procedure (220). As illustrated in FIG. 2b, the UE (221) can send an RRCReconfigurationSidelink message to the UE (222), and the UE (222) can send an RRCReconfigurationCompleteSidelink message back to the UE (221).

[0064] The purpose of the procedure (220) is to modify the PC5-RRC connection to, for example, establish / modify / release sidelink data radio bearers (DRBs), configure NR sidelink measurement and reporting, and configure sidelink channel status indicator (CSI) reference signal resources.

[0065] A UE (such as UE(221)) may initiate a sidelink RRC reconfiguration procedure in the following cases and perform operations on the corresponding PC5-RRC connection:

[0066] - Release of sidelink DRBs associated with a peer UE (e.g., UE (222)),

[0067] - Establishment of sidelink DRBs associated with peer UEs,

[0068] - Modification of parameters included in the Sidelink Radio Bearer Configuration (SLRB-Config) of Sidelink DRBs associated with the peer UE,

[0069] - Configuration of peer UEs for performing NR sidelink measurements and reporting,

[0070] - Configuration of sidelink CSI reference signal resources.

[0071] FIG. 2c illustrates exemplary flow signaling (230) for successful addition of a second indirect path. Specifically, the remote UE (231) may perform a measurement report to the serving gNB (233) in Step 1. In Step 2, it may be determined by the serving gNB (233) that a second indirect path through the relay UE is added. Additionally, in Step 3, an RRC reconfiguration for path addition may be transmitted from the serving gNB (233) to the remote UE (231). Thus, in Step 4, a PC5 connection between the remote UE (231) and the relay UE (232) may be established based on a PC5 connection establishment message, and an RRC reconfiguration message for the remote UE (231) may be transmitted from the serving gNB (233) to the relay UE (232). In this way, in Step 6, a marked path is added after an RRC reconfiguration completion message, and in Step 7, data transmission or reception may be performed.

[0072] In a multipath scenario, a remote UE may be composed of multiple paths, for example, including direct paths and indirect paths. 3GPP discusses the possibility of failure types for indirect paths, and for example, the IE for indirect path failure reporting may include failure types including, for example, timer expiration, sl-failure, n3c-failure, relayUE-Uu-RLF, relayUE-CellReselection, relayUE-Uu-RRC-Failure, and indirectPathAddChangeFailure.

[0073] Embodiments of the present disclosure provide a solution for communication. In the solution, a relay UE may transmit a signal to a remote UE to indicate a failure of the connection between the relay UE and the BS, and thus the remote UE may further transmit failure information to the BS or ignore the signal. In this way, the behavior of the UEs can be defined in the case of failure of the indirect path, and thus communication to the remote UE can be guaranteed. The principles and implementations of the present disclosure will be described in detail below with reference to the drawings.

[0074] FIG. 2d illustrates a schematic diagram of an exemplary communication network (240) in which some embodiments of the present disclosure may be implemented. As shown in FIG. 2d, the communication network (240) may include a first UE (241), a second UE (242), and a BS (243).

[0075] BS (243) and the first UE (241) may communicate with each other via a direct path. For example, the direct path may be associated with a Uu link between them. For example, BS (243) may be a serving network device of the first UE (241), such as a serving gNB. An indirect path may exist between the first UE (241) and BS (243) through the second UE (242). For example, BS (243) may communicate with the second UE (242) via a Uu link, and the second UE (242) may communicate with the first UE (241) via a PC5 link. In this case, the first UE (241) may be a remote UE, and the second UE (242) may be a relay UE. It should be understood that multipath scenarios may be based on a DC framework or a non-DC framework, and that the present disclosure does not limit such embodiments.

[0076] In some cases, as illustrated in FIG. 2d, there may be a third UE (244), and for example, the first UE (241) and BS (243) can communicate with each other through the third UE (244).

[0077] It should be understood that the number of devices in FIG. 2d is given for illustrative purposes without suggesting any limitations to the present disclosure.

[0078] Further reference is made to FIG. 3, which illustrates a signaling chart illustrating a communication process (300) according to some exemplary embodiments of the present disclosure. The process (300) may include a first UE (241), a second UE (242), and a BS (243) as illustrated in FIG. 2d. It should be understood that the process (300) may also be applied to other scenarios different from those illustrated in FIG. 2d, and that the present disclosure does not limit such embodiments.

[0079] The first UE (241) may be in an RRC connection state (i.e., remain in an RRC connection state), and the first UE (241) is configured with multiple paths including at least one direct path and at least one indirect path. The first UE (241) may access a BS (243) (such as a serving gNB) via the direct path and the indirect path (through the second UE (242)). In some exemplary embodiments, the first UE (241) may transmit measurement results to the BS (243). In some examples, the first UE (241) may report measurement results associated with one or more candidate cells or candidate relay UEs based on the configuration from the BS (243).

[0080] In process (300), the second UE (242) transmits a signal to the first UE (241) in 310, where the signal may indicate a failure of connection between the second UE (242) and BS (243).

[0081] In some implementations, the second UE (242) may determine whether a failure of the connection between the second UE (242) and the BS (243) occurs. In some examples, if any of the following cases occur, the second UE (242) may decide to send a notification to the first UE (241): RLF of the link between the second UE (242) and the BS (243), handover of the second UE (242), cell reselection of the second UE (242), failure to establish or resume the RRC connection. In some examples, if the second UE (242) receives a handover command from the BS (243), it may decide to send a notification.

[0082] In some implementations, the indication may be carried in a PC5 notification message. For example, the second UE (242) may send a PC5 notification message to the first UE (241) in 310, wherein the PC5 notification message contains information indicating a failure of connection between the second UE (242) and BS (243).

[0083] In some other implementations, the indication is a PC5 unicast release message (PC5-S release message or release message). For example, the second UE (242) may send a release message to the first UE (241) at 310, where the release message may indicate a failure of connection between the second UE (242) and BS (243).

[0084] In some implementations, the indication in 310 may include a failure type (or cause value) indicating the reason for the failure of the connection between the second UE (242) and the BS (243). For example, the failure type may indicate a handover of the second UE (242), for example, that the second UE (242) handed over to a different BS different from the BS (243). For example, the failure type may indicate that the RLF of the Uu link, for example, the re-establishment or resumption of the RRC connection failed. In this case, the first UE (241) can know the reason for the failure.

[0085] In process (300), when receiving a signal from the second UE (242), the first UE (241) may perform the operation (320) or operation (340) shown in FIG. 3.

[0086] In some exemplary embodiments, the first UE (241) may ignore the indication in 325. In some examples, the second UE (242) may receive a handover command from its serving BS, and then the second UE (242) may transmit an indication. In some examples, the first UE (241) receives an indication, the indication indicates a handover of the second UE (242), and then the first UE (241) may ignore the indication. For example, a reconfiguration with synchronization of the second UE (242) may be indicated by the indication, for example, by a failure type in the indication. In this case, the indication from the second UE (242) is ignored by the first UE (241) due to the handover of the second UE (242).

[0087] In some exemplary embodiments, the first UE (241) transmits failure information to BS (243) at 342. In some examples, the first UE (241) may initiate the indirect path failure procedure upon receiving an indication (i.e., a PC5 unicast release message or a notification message) from the second UE (242). For example, the failure information may be carried in an IndirectPathFailureInformation message or implemented as an IndirectPathFailureInformation message.

[0088] In some examples, the failure information (or IndirectPathFailureInformation message) may include the failure type for the indirect path associated with the second UE (242).

[0089] In some examples, failure information (or IndirectPathFailureInformation message) may include measurement results for one or more candidate relay UEs.

[0090] BS (243) sends a route switching message (or route release message) to the first UE (241) at 344. In some implementations, BS (243) may release an indirect route upon receiving failure information. BS (243) may send a route release message to the first UE (241) at 344, and the first UE (241) may also release an indirect route according to the route release message at 346.

[0091] In some implementations, in 344, BS (243) sends a route switching message to the first UE (241), and the route switching message may indicate a candidate relay UE. In some examples, BS (243) may configure a new relay UE (i.e., indicated candidate relay UE) for the first UE (241), and, for example, the route switching message may include the ID of the candidate relay UE. Referring to FIG. 2d, the candidate relay UE may be the third UE (244).

[0092] In some examples, the route switching message may be replaced with a reconfiguration message associated with a candidate relay UE, for example, the reconfiguration message includes configuration information of the candidate relay UE. Additionally, the first UE (241) may perform a route switching procedure in 346 according to the route switching message. For example, an indirect route through the second UE (242) may be switched to another indirect route through the third UE (244).

[0093] In some examples, the first UE (241) may send an RRC reconfiguration completion message to the BS (243) to indicate that the route switching procedure was successful. For example, the BS (243) may perform an indirect route switching upon receiving the completion message from the first UE (241). Thus, the first UE (241) can still communicate with the BS (243) via the direct route and the indirect route.

[0094] FIG. 4 illustrates a schematic diagram of a signaling transmission (400) according to some exemplary embodiments of the present disclosure. As shown in FIG. 4, indication from the second UE to the first UE may be transmitted at the PC5 signaling (PC5-S) layer, whereas failure information from the first UE to the BS may be transmitted at the RRC layer.

[0095] The PC5-S layer of the second UE (relay UE) can transmit a notification (e.g., a release message) to the first UE (remote UE), the PC5-S layer of the first UE can transmit a notification to the RRC layer of the first UE, and additionally, the RRC layer of the first UE can trigger the transmission of failure information (e.g., an IndirectPathFailureInformation message). In some examples, the notification from the upper layer can be considered as a trigger condition for an indirect path failure procedure to the RRC layer of the first UE.

[0096] FIG. 5 illustrates a signaling chart illustrating a communication process (500) for an unsolicited SIB1 according to some exemplary embodiments of the present disclosure. The process (500) may include a first UE (241), a second UE (242), and a BS (243) as illustrated in FIG. 2d. It should be understood that the process (500) may also be applied to other scenarios different from those illustrated in FIG. 2d, and that the present disclosure does not limit such embodiments.

[0097] The first UE (241) may be in an RRC connection state (i.e., remain in an RRC connection state), and the first UE (241) is configured with multiple paths including at least one direct path and at least one indirect path. The first UE (241) may access a BS (243) (such as a serving gNB) via the direct path and the indirect path (through the second UE (242)). In some exemplary embodiments, the first UE (241) may transmit measurement results to the BS (243). In some examples, the first UE (241) may report measurement results associated with one or more candidate cells or candidate relay UEs based on the configuration from the BS (243).

[0098] In process (500), operation (510) and / or operation (515) may be performed. In 510, BS (243) transmits a mark to the second UE (242). In some implementations, BS (243) may transmit a reconfiguration message to the second UE (242), wherein the reconfiguration message may include a mark. In some examples, the mark may indicate that the serving BS of the first UE (241) is different from the serving BS of the second UE (242). In some examples, the mark may indicate that unsolicited SIB1 forwarding to the first UE (241) is not performed.

[0099] In 515, the first UE (241) transmits a signal to the second UE (242). In some examples, the signal may indicate that the serving BS of the first UE (241) is different from the serving BS of the second UE (242). In some examples, the signal may indicate that no unsolicited SIB1 forwarding to the first UE (241) is performed, that is, no unsolicited SIB1 forwarding is expected.

[0100] In process (500), the second UE (242) stops unsolicited SIB1 forwarding in 520 according to indication from BS (243) and / or the first UE (241). In some implementations, the second UE (242) may not perform (or stop / avoid) unsolicited SIB1 forwarding to the first UE (241).

[0101] In some cases, when some unsolicited SIB1 is forwarded from the second UE (242) to the first UE (241) in 530, the first UE (241) in 540 may ignore the unsolicited SIB1 forwarded from the second UE (242). For example, if the serving cells (or serving BSs) of the first UE (241) and the second UE (242) are different, the system information (e.g., SIB1) forwarded from the second UE (242) may be ignored.

[0102] In 3GPP Release 17 (R17), relay UEs are to forward SIB1 in an unsolicited manner, but in multipath scenarios, the serving cells of the remote UE and the relay UE may be different, and in this case, it is understood that the forwarded SIB1 is useless and causes additional signaling overhead. According to embodiments with reference to FIG. 5, unsolicited SIB1 forwarding can be avoided, and thus signaling overhead can be reduced. If an unsolicited SIB1 is forwarded to the remote UE, it can be ignored, and thus additional action at the remote UE can be avoided.

[0103] FIG. 6 illustrates a signaling chart illustrating a communication process (600) for direct path release according to some exemplary embodiments of the present disclosure. The process (600) may include a first UE (241), a second UE (242), and a BS (243) as illustrated in FIG. 2d. It will be understood that the process (600) may be applied to other communication scenarios, which are not described in detail.

[0104] The first UE (241) may be in an RRC connection state (i.e., remain in an RRC connection state), and the first UE (241) is configured with multiple paths including at least one direct path and at least one indirect path. The first UE (241) may access a BS (243) (such as a serving gNB) via the direct path and the indirect path (through the second UE (242)). In some exemplary embodiments, the first UE (241) may transmit measurement results to the BS (243). In some examples, the first UE (241) may report measurement results associated with one or more candidate cells or candidate relay UEs based on the configuration from the BS (243). In some examples, the PCell is configured in the direct path.

[0105] In process (600), BS (243) sends a reconfiguration message to the first UE (241) in 610. In some implementations, the reconfiguration message may be associated with a direct path release. In some implementations, the reconfiguration message may indicate a candidate relay UE, and, for example, the reconfiguration message may include the ID of the candidate relay UE.

[0106] In some exemplary embodiments, BS (243) may decide to release the direct path between BS (243) and the first UE (241), in which case the PCell will be changed from the direct path to the indirect path.

[0107] In some examples, the indication may be included in an RRC reconfigurationWithSync message with synchronization or in a sidelink indirect path add change (SL-IndirectPathAddChange) message.

[0108] In some examples, the reconfiguration message can be considered as an implicit direct path release message.

[0109] In process (600), the first UE (241) decides to release the direct path in 620. In some implementations, after receiving a indication (reconfiguration message) from BS (243), the first UE (241) may determine whether the candidate relay UE indicated in the indication is the same as the second UE (242) of the indirect path. In some implementations, if the indicated candidate relay UE is the same as the second UE (242) of the indirect path, the first UE (241) may initiate (or perform) the direct path release procedure.

[0110] In some examples, the indication may include the ID of a candidate relay UE that is the same as the ID of the second UE (242). In some implementations, the first UE (241) may release a direct path and sustain (maintain) an indirect path through the second UE (242).

[0111] Considering the case where the first UE (241) is composed of two paths including a direct path and an indirect path, the link between the remote UE (first UE (241)) and the relay UE (second UE (242)) may be a non-3GPP link, e.g., Bluetooth. When the remote UE (first UE (241)) receives a reconfiguration message for changing or adding an indirect path, a timer for adding or changing the indirect path in the case of multipath is started. That is, the remote UE (first UE (241)) starts the timer upon receiving an RRCReconfiguration message containing n3c-indirectPathAddChange. The remote UE (first UE (241)) stops the timer upon transmitting an RRCReconfigurationComplete message (successfully).

[0112] In some implementations, when the timer for adding or changing the route is still running, the first UE (241) may decide to use the resources configured for adding or changing the route, for example, in the configured sidelink approval for the second UE (242).

[0113] In some exemplary embodiments, when a reconfigurationWithSync message with synchronization is used for indication, the first UE (241) may use the resources configured in rrc-ConfiguredSidelinkGrant (while T420 is running), for example, provided by the target cell. In some exemplary embodiments, when a route switching procedure is reused, for example, when an indirectpathadchange (SL-IndirectPathAddChange) message may be used for indication, the first UE (241) may use the configured acknowledgment for the sidelink while a timer for route switching (e.g., T420) is running, for example, provided by the target cell.

[0114] In some implementations, the first UE (241) can perform a PCell change from a direct path to an indirect path. For example, the PCell is changed from a first cell associated with a direct path to a second cell associated with an indirect path.

[0115] In this way, a direct path between the first UE (241) and the BS (243) is released, and the first UE (241) can further communicate with the BS (243) through an indirect path via the second UE (242) in 630. That is, the first UE (241) can transmit / receive data to / from the BS (243) through the second UE (242).

[0116] According to some embodiments with reference to FIGS. 3 to 6, some problems related to multipath are discussed, and thus, UE behavior is defined, signaling overhead can be reduced, and unnecessary operations can be avoided.

[0117] FIG. 7 illustrates a signaling chart illustrating a communication process (700) for single-path switching according to some exemplary embodiments of the present disclosure. The process (700) may include a first UE (241), a second UE (242), and a BS (243) as illustrated in FIG. 2d. It will be understood that the process (700) may be applied to other communication scenarios, which will not be described in detail.

[0118] The first UE (241) may be in an RRC connection state (i.e., remain in an RRC connection state), and the first UE (241) is configured with a single path that may be a direct path or an indirect path. For example, the first UE (241) may access a BS (243) (such as a serving gNB) via a direct path or an indirect path (through the second UE (242)).

[0119] In process (700), the first UE (241) transmits the measurement result from 710 to the BS (243). In some implementations, the measurement result is transmitted via a single path, i.e., a direct path or an indirect path. In some implementations, the measurement result may be associated with one or more candidate cells or candidate relay UEs based on the configuration from the BS (243).

[0120] In process (700), BS (243) sends a reconstruction message to the first UE (241) in 720. The reconstruction message may indicate a candidate relay UE, and, for example, the reconstruction message may include the ID of the candidate relay UE.

[0121] In some implementations, BS (243) may decide to perform a route switching toward a candidate relay UE based on the measurement results from the first UE (241). In some implementations, the reconfiguration message may be considered for the purpose of route switching.

[0122] In some implementations, the reconfiguration message may include a configured acknowledgment for a sidelink associated with a candidate relay UE.

[0123] In process (700), the first UE (241) performs a route switching procedure at 730. In some implementations, when the first UE (241) receives a reconfiguration message indicating a candidate relay UE, the first UE (241) may initiate a route switching procedure according to the reconfiguration message. In some examples, the first UE (241) may start a timer (such as T420) for the route switching procedure.

[0124] In some exemplary embodiments, when a reconfigurationWithSync message with synchronization is received, the first UE (241) may use the resources configured in rrc-ConfiguredSidelinkGrant (while T420 is running), for example, provided by the target cell. In some exemplary embodiments, in the case of a route switch, for example, while the timer for the route switch (e.g., T420) is running, the first UE (241) may use the configured acknowledgment for the sidelink, for example, provided by the target cell.

[0125] In some implementations, the first UE (241) may send an RRC reconfiguration completion message to the BS (243) to indicate that the route switching procedure was successful. For example, the BS (243) may perform an indirect route switching upon receiving the completion message from the first UE (241). Thus, the first UE (241) may communicate with the BS (243) via a new indirect route (through a candidate relay UE). That is, the first UE (241) may send / receive data to / from the BS (243) through the candidate relay UE.

[0126] According to some embodiments with reference to FIG. 7, a path switching procedure for a single path scenario is discussed, and thus, UE behavior is defined, and communication between the first UE and the BS is maintained.

[0127] FIG. 8a illustrates a schematic diagram of a U2U network (800) in which some embodiments of the present disclosure may be implemented. As illustrated in FIG. 8a, the U2U network (800) may include a first remote UE (810), a second remote UE (820), and a relay UE (825).

[0128] The first remote UE (810) and the second remote UE (820) can communicate with each other via a direct path. For example, the direct path may be associated with a PC5 link between them. The first remote UE (810) and the second remote UE (820) can communicate with each other via an indirect path. For example, the first remote UE (810) can communicate with the relay UE (825) via a PC5 link, and the relay UE (825) can communicate with the second remote UE (820) via a PC5 link.

[0129] It is understood that the number of devices in FIG. 8a is given for illustrative purposes without suggesting any limitations to the present disclosure.

[0130] FIG. 8b illustrates a signaling chart illustrating a communication process (850) for an indirect path failure in U2U according to some exemplary embodiments of the present disclosure. The process (850) may include a first remote UE (810), a second remote UE (820), and a relay UE (825) as illustrated in FIG. 8a. It will be understood that the process (850) may be applied to other communication scenarios, which will not be described in detail.

[0131] The first remote UE (810) communicates with the second remote UE (820) via a direct path or an indirect path. For example, the first remote UE (810) may communicate directly with the second remote UE (820). For example, the first remote UE (810) may communicate with the second remote UE (820) via a relay UE (825). A PC5 RRC connection is established between the first UE (810) and the relay UE (825), and a PC5 RRC connection is established between the second UE (820) and the relay UE (825).

[0132] In process (850), the relay UE (825) transmits a notification to the first remote UE (810) in 860, and the notification may indicate a failure of the connection between the relay UE (825) and the second remote UE (820). For example, the notification may be a failure notification message.

[0133] In some implementations, when the relay UE (825) detects a PC5 RLF of the link between the second remote UE (820) and the relay UE (825), the relay UE (825) may send a failure notification message to the first remote UE (810). In some other implementations, when the relay UE (825) receives a sidelink RRC configuration failure message from the second remote UE (820), the relay UE (825) may send a failure notification message to the first remote UE (810).

[0134] In some exemplary embodiments, the failure notification message may indicate the type of failure of the link between the second remote UE (820) and the relay UE (825). For example, the failure type may indicate a PC5 RLF of the link between the second remote UE (820) and the relay UE (825). For example, the failure type may indicate a sidelink RRC configuration failure between the second remote UE (820) and the relay UE (825). For example, IE "NotificationMessageSidelink" includes a sl-Indication Type and a destination identity.

[0135] In some implementations, the first remote UE (810) may release an indirect path, and the first remote UE (810) may additionally perform communication with the second remote UE (820) via a direct path in 870. That is, the first remote UE (810) may transmit / receive data to / from the second remote UE (820) via a direct path.

[0136] According to the embodiments illustrated in FIGS. 8a and 8b, the problem of how to handle sidelink RRC reconfiguration failure in U2U relay is resolved, and thus UE behavior is defined and U2U communication is guaranteed.

[0137] FIG. 9 illustrates an example of a device (900) suitable for implementing embodiments of the present disclosure. The device (900) may be an example of a RAN node as described herein. The device (900) may support wireless communication with a first UE (241), a second UE (242), a BS (243), a first remote UE (810), a relay UE (825), or any combination thereof. The device (900) may include components for bidirectional communication, such as a processor (902), a memory (904), a transceiver (906), and optionally an I / O controller (908), for transmitting and receiving communications. These components may communicate electronically through one or more interfaces (e.g., a bus) or may be coupled in other ways (e.g., kinetically, communically, functionally, electronically, electrically).

[0138] A processor (902), memory (904), transceiver (906), or various combinations thereof or various components thereof may be examples of means for carrying out various aspects of the present disclosure as described herein. For example, a processor (902), memory (904), transceiver (906), or various combinations thereof or components thereof may support a method for carrying out one or more of the operations described herein.

[0139] In some implementations, the processor (902), memory (904), transceiver (906), or various combinations or components thereof may be implemented in hardware (e.g., as a communication management circuit). The hardware may include a processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof configured as a means for performing the functions described in this disclosure or otherwise supporting such means. In some implementations, the processor (902) and the memory (904) coupled with the processor (902) may be configured to perform one or more of the functions described herein (e.g., to execute instructions stored in the memory (904) by the processor (902).

[0140] For example, the processor (902) may support wireless communication in the device (900) according to the examples disclosed herein. The processor (902) may be configured to be operable to support means for the actions discussed above.

[0141] The processor (902) may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some implementations, the processor (902) may be configured to operate a memory array using a memory controller. In some other implementations, the memory controller may be integrated into the processor (902). The processor (902) may be configured to execute computer-readable instructions stored in memory (e.g., memory (904)) to enable the device (900) to perform various functions of the present disclosure.

[0142] Memory (904) may include random access memory (RAM) and read-only memory (ROM). Memory (904) may store computer-readable, computer-executable code containing instructions that, when executed by the processor (902), enable the device (900) to perform the various functions described herein. The code may be stored in a non-transient computer-readable medium, such as system memory or other types of memory. In some implementations, the code may not be directly executable by the processor (902) but may enable the computer to perform the functions described herein (e.g., when compiled and executed). In some implementations, memory (904) may include a basic I / O system (BIOS) capable of controlling basic hardware or software operations, such as interactions with peripheral components or devices, among other things.

[0143] The I / O controller (908) can manage input and output signals for the device (900). The I / O controller (908) can also manage peripherals that are not integrated into the device (M02). In some implementations, the I / O controller (908) may represent a physical connection or port to an external peripheral. In some implementations, the I / O controller (908) may use an operating system such as iOS®, ANDROID®, MS-WINDOWS®, OS / 2®, UNIX®, LINUX®, or other known operating systems. In some implementations, the I / O controller (908) may be implemented as part of a processor such as a processor (906). In some implementations, a user may interact with the device (900) through the I / O controller (908) or through hardware components controlled by the I / O controller (908).

[0144] In some implementations, the device (900) may include a single antenna (910). However, in some other implementations, the device (900) may have more than one antenna (910) (i.e., multiple antennas), including multiple antenna panels or antenna arrays capable of simultaneously transmitting or receiving multiple wireless transmissions. The transceiver (906) may communicate bidirectionally through one or more antennas (910), wired, or wireless links, as described herein. For example, the transceiver (906) may represent a wireless transceiver and may communicate bidirectionally with another wireless transceiver. The transceiver (906) may also include a modem that modulates packets, provides the modulated packets to one or more antennas (910) for transmission, and demodulates packets received from one or more antennas (910). The transceiver (906) may include one or more transmission chains, one or more reception chains, or a combination thereof.

[0145] A transmission chain may be configured to generate and transmit signals (e.g., control information, data, packets). The transmission chain may include at least one modulator for modulating data over a carrier signal and preparing the signal for transmission over a wireless medium. The at least one modulator may be configured to support one or more techniques, such as amplitude modulation (AM), frequency modulation (FM), or digital modulation schemes such as phase shift keying (PSK) or quadrature amplitude modulation (QAM). The transmission chain may also include at least one power amplifier configured to amplify the modulated signal to an appropriate power level suitable for transmission over a wireless medium. The transmission chain may also include one or more antennas (910) for transmitting the amplified signal over the air or a wireless medium.

[0146] A receiving chain may be configured to receive signals (e.g., control information, data, packets) over a wireless medium. For example, a receiving chain may include one or more antennas (910) for receiving signals over an air or wireless medium. A receiving chain may include at least one amplifier (e.g., a low-noise amplifier (LNA)) configured to amplify the received signal. A receiving chain may include at least one demodulator configured to obtain transmitted data by demodulating the received signal and reversing the modulation technique applied during the transmission of the signal. A receiving chain may include at least one decoder for decoding the demodulated signal to receive the transmitted data.

[0147] FIG. 10 illustrates an example of a processor (1000) suitable for implementing some embodiments of the present disclosure. The processor (1000) may be an example of a processor configured to perform various operations according to the examples described herein. The processor (1000) may include a controller (1002) configured to perform various operations according to the examples described herein. The processor (1000) may optionally include at least one memory (1004), such as an L1 / L2 / L3 cache. Additionally or alternatively, the processor (1000) may optionally include one or more arithmetic logic units (ALUs) (1006). One or more of these components may be electronically communicated through one or more interfaces (e.g., buses) or otherwise coupled (e.g., kinetically, communically, functionally, electronically, electrically).

[0148] The processor (1000) may be a processor chipset and may include a protocol stack (e.g., a software stack) executed by the processor chipset to perform various operations (e.g., receiving, acquiring, searching, transmitting, outputting, forwarding, storing, determining, identifying, accessing, writing, reading) according to examples described herein. The processor chipset may include one or more cores, one or more caches (e.g., memory local to or included in the processor chipset (e.g., processor (1000)) or other memory (e.g., random access memory (RAM), read-only memory (ROM), dynamic RAM (DRAM), synchronous dynamic RAM (SDRAM), static RAM (SRAM), ferroelectric RAM (FeRAM), magnetic RAM (MRAM), resistive RAM (RRAM), flash memory, phase change memory (PCM), etc.).

[0149] A controller (1002) may be configured to manage and coordinate various operations of a processor (1000) (e.g., signaling, receiving, acquiring, searching, transmitting, outputting, forwarding, storing, determining, identifying, accessing, writing, reading) so that the processor (1000) supports various operations according to examples described herein. For example, the controller (1002) may operate as a control unit of the processor (1000) and generate control signals that manage the operations of various components of the processor (1000). These control signals include enabling or disabling function units, selecting data paths, initiating memory access, and coordinating the timing of operations.

[0150] The controller (1002) may be configured to fetch instructions from memory (1004) (e.g., acquire, retrieve, receive) and to determine subsequent instruction(s) to be executed in order to enable the processor (1000) to support various operations according to examples described herein. The controller (1002) may be configured to track memory addresses of instructions associated with memory (1004). The controller (1002) may be configured to decode instructions to determine operations to be performed and accompanying operands. For example, the controller (1002) may be configured to interpret instructions and determine control signals to be output to other components of the processor (1000) so that the processor (1000) can support various operations according to examples described herein. Additionally or alternatively, the controller (1002) may be configured to manage the flow of data within the processor (1000). The controller (1002) may be configured to control the transfer of data between the registers, arithmetic logic units (ALUs), and other functional units of the processor (1000).

[0151] Memory (1004) may include one or more caches (e.g., memory local to or included in the processor (1000), or other memory such as RAM, ROM, DRAM, SDRAM, SRAM, MRAM, flash memory, etc.). In some implementations, memory (1004) may reside within or on a processor chipset (e.g., local to the processor (1000)). In some other implementations, memory (1004) may reside outside the processor chipset (e.g., remotely from the processor (1000)).

[0152] Memory (1004) may store computer-readable, computer-executable code containing instructions that, when executed by the processor (1000), cause the processor (1000) to perform the various functions described herein. The code may be stored in a non-transient computer-readable medium, such as system memory or other types of memory. A controller (1002) and / or a processor (1000) may be configured to execute computer-readable instructions stored in memory (1004) to cause the processor (1000) to perform the various functions. For example, the processor (1000) and / or the controller (1002) may be coupled to or with memory (1004), and the processor (1000), the controller (1002), and memory (1004) may be configured to perform the various functions described herein. In some examples, the processor (1000) may include a plurality of processors, and memory (1004) may include a plurality of memories. One or more of the plurality of processors may be combined with one or more of the plurality of memories, and they may be configured to perform various functions as described herein, individually or collectively.

[0153] One or more ALUs (1006) may be configured to support various operations according to the examples described herein. In some implementations, one or more ALUs (1006) may reside within or on a processor chipset (e.g., processor (1000)). In some other implementations, one or more ALUs (1006) may reside outside the processor chipset (e.g., processor (1000)). One or more ALUs (1006) may perform one or more operations on data, such as addition, subtraction, multiplication, and division. For example, one or more ALUs (1006) may receive input operands and an operation code that determines the operation to be executed. One or more ALUs (1006) are composed of various logic and arithmetic circuits, including adders, subtractors, shifters, and logic gates, to process and manipulate data according to the operation. Additionally or alternatively, one or more ALUs (1006) support logical operations such as AND, OR, XOR (exclusive-OR), NOR (not-OR), and NAND (not-AND), so that one or more ALUs (1006) can handle conditional operations, comparisons, and bitwise operations.

[0154] The processor (1000) may support wireless communication according to examples as disclosed in this specification. The processor (1000) may be configured or operable to support means for operations described in some embodiments of this disclosure.

[0155] FIG. 11 illustrates a flowchart of a method (1100) performed by a first UE according to embodiments of the present disclosure. Operations of the method (1100) may be implemented by a device or its components as described herein. For example, operations of the method (1100) may be performed by the first UE (241) in FIG. 2d or the first remote UE (810) in FIG. 8a. In some implementations, the device may execute a set of instructions to control functional elements of the device to perform the described functions. Additionally or alternatively, the device may perform embodiments of the described functions using special-purpose hardware.

[0156] In 1110, the method may include receiving from the second UE an indication that the connection between the second UE and the third device has failed, and the first UE is configured with a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE. The operations of 1110 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1110 may be performed by the first UE (241) as described with reference to FIG. 2d or by the first remote UE (810) as described with reference to FIG. 8a.

[0157] In 1120, the method may include transmitting failure information of an indirect path to a third device based on a indication, or ignoring an indication from the second UE. The operations of 1120 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1120 may be performed by a first UE (241) as described with reference to FIG. 2d or a first remote UE (810) as described with reference to FIG. 8a.

[0158] FIG. 12 illustrates a flowchart of a method (1200) performed by a first UE according to embodiments of the present disclosure. Operations of the method (1200) may be implemented by the device or components thereof described herein. For example, operations of the method (1200) may be performed by the first UE (241) in FIG. 2d. In some implementations, the device may execute a set of instructions to control functional elements of the device to perform the described functions. Additionally or alternatively, the device may perform embodiments of the described functions using special-purpose hardware.

[0159] In 1210, the method may include transmitting to the second UE a indication that the serving cell of the first UE is different from an additional serving cell of the second UE, or that an unrequested SIB1 forwarding is not expected. The operations of 1210 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1210 may be performed by the first UE (241) as described with reference to FIG. 2d.

[0160] In 1220, the method may include ignoring unsolicited SIB1 forwarding from the second UE, wherein the first UE is composed of a direct path between the first UE and the BS and an indirect path between the first UE and the BS through the second UE. The operations of 1220 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1220 may be performed by the first UE (241) as described with reference to FIG. 2d.

[0161] FIG. 13 illustrates a flowchart of a method (1300) performed by a first UE according to embodiments of the present disclosure. Operations of the method (1300) may be implemented by the device or components thereof described herein. For example, operations of the method (1300) may be performed by the first UE (241) in FIG. 2d. In some implementations, the device may execute a set of instructions to control functional elements of the device to perform the described functions. Additionally or alternatively, the device may perform embodiments of the described functions using special-purpose hardware.

[0162] In 1310, the method may include receiving a reconstruction message from BS that includes an identifier of a candidate relay UE, wherein the first UE is composed of a direct path between the first UE and BS and an indirect path between the first UE and BS through a second UE. The operations of 1310 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1310 may be performed by the first UE (241) as described with reference to FIG. 2d.

[0163] In 1320, the method may include initiating a procedure to release a direct path upon determining that the candidate relay UE is identical to the second UE. The operations of 1320 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1320 may be performed by the first UE (241) as described with reference to FIG. 2d.

[0164] FIG. 14 illustrates a flowchart of a method (1400) performed by a second UE according to embodiments of the present disclosure. Operations of the method (1400) may be implemented by the device or components thereof described herein. For example, operations of the method (1400) may be performed by the second UE (242) in FIG. 2d. In some implementations, the device may execute a set of instructions to control functional elements of the device to perform the described functions. Additionally or alternatively, the device may perform embodiments of the described functions using special-purpose hardware.

[0165] In 1410, the method may include transmitting to the first UE a signal indicating that the connection between the second UE and the third device has failed in response to the failure of the connection between the second UE and the third device, wherein the first UE is composed of a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE. The operations of 1410 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1410 may be performed by the second UE (242) as described with reference to FIG. 2d.

[0166] FIG. 15 illustrates a flowchart of a method (1500) performed by a BS according to embodiments of the present disclosure. Operations of the method (1500) may be implemented by a device or its components as described herein. For example, operations of the method (1500) may be performed by the BS (243) in FIG. 2d. In some implementations, the device may execute a set of instructions to control functional elements of the device to perform the described functions. Additionally or alternatively, the device may perform embodiments of the described functions using special-purpose hardware.

[0167] In 1510, the method may include receiving failure information of an indirect path from a first UE, which is composed of a direct path between the first UE and BS and an indirect path between the first UE and BS through a second UE. The operations of 1510 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1510 may be performed by a BS (243) as described with reference to FIG. 2d.

[0168] In 1520, the method may include transmitting a route switching message to the first UE that includes an identifier of a candidate relay UE. The operations of 1520 may be performed according to examples as described herein. In some implementations, aspects of the operations of 1520 may be performed by BS (243) as described with reference to FIG. 2d.

[0169] In 1530, the method may include performing a transition from an indirect path to an additional indirect path upon a determination that a complete message is received from the first UE, wherein the additional indirect path is for a connection between the first UE and the BS through a candidate relay UE. The operations of 1530 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1530 may be performed by the BS (243) as described with reference to FIG. 2d.

[0170] FIG. 16 illustrates a flowchart of a method (1600) performed by a second UE according to embodiments of the present disclosure. Operations of the method (1600) may be implemented by the device or components thereof described herein. For example, operations of the method (1600) may be performed by the second UE (242) in FIG. 2d. In some implementations, the device may execute a set of instructions to control functional elements of the device to perform the described functions. Additionally or alternatively, the device may perform embodiments of the described functions using special-purpose hardware.

[0171] In 1610, the method may include receiving a indication from the first UE or BS indicating that the serving cell of the first UE is different from an additional serving cell of the second UE, or that an unrequested SIB1 forwarding is not expected. The operations of 1610 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1610 may be performed by the second UE (242) as described with reference to FIG. 2d.

[0172] In 1620, the method may include stopping unsolicited SIB1 forwarding from BS to the first UE based on indication, wherein the first UE is composed of a direct path between the first UE and BS and an indirect path between the first UE and BS through the second UE. The operations of 1620 may be performed according to the examples described herein. In some implementations, aspects of the operations of 1620 may be performed by the second UE (242) as described with reference to FIG. 2d.

[0173] It should be noted that the methods described in this specification describe possible implementations, and that operations and steps may be rearranged or modified in other ways, and that other implementations are possible. Additionally, aspects from two or more of the methods may be combined.

[0174] The various exemplary blocks and components described in connection with the disclosures in this specification may be implemented or performed as general-purpose processors, DSPs, ASICs, CPUs, FPGAs or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in this specification. A general-purpose processor may be a microprocessor, but alternatively, the processor may be any processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices (e.g., a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors associated with a DSP core, or any other combination of such configurations).

[0175] The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. When implemented in software executed by a processor, the functions may be stored on a computer-readable medium or transmitted therethrough as one or more instructions or codes on a computer-readable medium. Other examples and implementations are within the scope of this disclosure and the appended claims. For example, due to the nature of the software, the functions described herein may be implemented using software executed by a processor, hardware, firmware, hardwiring, or any combination thereof. Features implementing the functions may be physically placed in various locations, including distributed so that parts of the functions are implemented in different physical locations.

[0176] Computer-readable media include both non-transient computer storage media and communication media, comprising any medium that facilitates the transfer of computer programs from one place to another. Non-transient storage media may be any available medium that can be accessed by a general-purpose or special-purpose computer. For example, non-transient computer-readable media may include RAM, ROM, EEPROM (electrically erasable programmable ROM), flash memory, CD (compact disk) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transient medium that can be used to carry or store desired means of program code in the form of instructions or data structures and can be accessed by a general-purpose or special-purpose computer or a general-purpose or special-purpose processor.

[0177] As used herein, including in the claims, the singular expression (article "a") preceding an element is not limited and is understood to refer to "at least one" of such elements or "one or more" of such elements. The terms singular expression (article "a"), "at least one," "one or more," and "at least one of one or more" may be interchangeable. As used herein, including in the claims, the word "or" as used in a list of items (e.g., a list of items followed by phrases such as "at least one of," "one or more of," or "one or both of") indicates a comprehensive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A, B, and C). Furthermore, as used herein, the phrase "based on" should not be interpreted as a reference to a closed set of conditions. For example, an exemplary step described as “based on Condition A” may be based on both Condition A and Condition B without departing from the scope of the present disclosure. That is, as used herein, the phrase “based on” should be interpreted in the same way as the phrase “at least partially based on”. Additionally, as used herein, including in the claims, a “set” may include one or more elements.

[0178] The description in this specification is provided to enable a person skilled in the art to make or use the present disclosure. Various modifications to the present disclosure will be apparent to a person skilled in the art, and the general principles defined in this specification may be applied to other variations without departing from the scope of the present disclosure. Accordingly, the present disclosure is not limited to the examples and designs described in this specification, but should be given the broadest scope consistent with the principles and novel features disclosed in this specification.

Claims

Claim 1 A first user device (UE) comprising at least one memory; and at least one processor coupled to the at least one memory, wherein the at least one processor enables the first UE to receive a signal from a second UE indicating that a connection between the second UE and a third device has failed - the first UE is configured with a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE -; and the first UE is configured to transmit failure information of the indirect path to the third device based on the signal, or to ignore the signal from the second UE. Claim 2 In paragraph 1, the third device is a base station (BS), and the indication is, Radio link failure (RLF) of the link between the second UE and the BS, The handover of the above-mentioned second UE, or A first UE displaying one of the cell reselections of the second UE. Claim 3 In paragraph 2, the first UE is further configured such that the at least one processor causes the first UE to receive a route switching message from the BS including an identifier of a candidate relay UE; and, based on the route switching message, to perform a transition from the indirect path to an additional indirect path—the additional indirect path being for a connection between the first UE and the BS through the candidate relay UE. Claim 4 In claim 1, the third device is a BS, and the at least one processor is further configured to cause the first UE to ignore the indication based on a determination that the indication indicates a handover of the second UE, the first UE. Claim 5 In paragraph 1, the above indication is the first UE carried in the PC5 notification message. Claim 6 In paragraph 1, the above indication is a first UE including a PC5 unicast release message. Claim 7 In claim 1, the third device is a third UE, and the indication is a first UE indicating one of a PC5 RLF between the second UE and the third UE, or a sidelink radio resource control (RRC) reconfiguration failure between the second UE and the third UE. Claim 8 In paragraph 7, the first UE, wherein the above indication includes a failure type indicating the sidelink RRC reconstruction failure. Claim 9 A first user device (UE) comprising at least one memory; and at least one processor coupled to the at least one memory, wherein the at least one processor enables the first UE to receive a reconfiguration message from a base station (BS) comprising an identifier of a candidate relay UE, wherein the first UE comprises a direct path between the first UE and the BS and an indirect path between the first UE and the BS through a second UE; and the first UE is configured to initiate a procedure for releasing the direct path upon a determination that the candidate relay UE is identical to the second UE. Claim 10 In claim 9, the first UE is further configured such that the at least one processor allows the first UE to maintain the indirect path as unchanged; and to perform a PCell (primary cell) change from a first cell associated with the direct path to a second cell associated with the indirect path. Claim 11 In claim 9, the first UE is further configured such that the at least one processor causes the first UE to decide to use resources configured for a configured sidelink approval for the second UE, upon a determination that a timer for path addition or path change is running. Claim 12 A second user device (UE) comprising at least one memory; and at least one processor coupled to the at least one memory, wherein the at least one processor is configured such that the second UE transmits to the first UE an indication indicating that the connection between the second UE and the third device has failed in response to the failure of the connection between the second UE and the third device - the first UE is configured with a direct path between the first UE and the third device and an indirect path between the first UE and the third device through the second UE. Claim 13 In paragraph 12, the above-mentioned third device is a base station (BS), and the above-mentioned indication is, Radio link failure (RLF) of the link between the second UE and the BS, The handover of the above-mentioned second UE, or A second UE displaying one of the cell reselections of the second UE. Claim 14 In Clause 12, the above indication is the 2nd UE carried in the PC5 notification message. Claim 15 In paragraph 12, the above indication is a second UE including a PC5 unicast release message. Claim 16 In paragraph 12, the third device is a third UE, and the indication is a second UE indicating either a PC5 RLF between the second UE and the third UE, or a sidelink radio resource control (RRC) reconfiguration failure between the second UE and the third UE. Claim 17 In Clause 16, the above indication includes a failure type indicating the sidelink RRC reconfiguration failure, a second UE. Claim 18 A base station (BS) comprising at least one memory; and at least one processor coupled to the at least one memory, wherein the at least one processor is configured such that the BS receives failure information of the indirect path from a first user device (UE) comprising a direct path between a first UE and the BS and an indirect path between the first UE and the BS through a second UE; transmits a path switching message to the first UE including an identifier of a candidate relay UE; and, upon a determination that a complete message is received from the first UE, performs a transition from the indirect path to an additional indirect path—the additional indirect path being for a connection between the first UE and the BS through the candidate relay UE. Claim 19 In paragraph 18, the failure information of the indirect path includes the failure type of the indirect path, and the failure type is, Radio link failure (RLF) of the link between the second UE and the BS, The handover of the above-mentioned second UE, or BS, indicating one of the cell reselections of the above 2 UE.

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