WO2024082490A1

WO2024082490A1 - Methods and apparatuses for positioning in partial coverage scenario

Info

Publication number: WO2024082490A1
Application number: PCT/CN2023/075501
Authority: WO
Inventors: Luning Liu; Jing HAN; Jie Hu; Lihua Yang; Haiming Wang
Original assignee: Lenovo (Beijing) Limited
Priority date: 2023-02-10
Filing date: 2023-02-10
Publication date: 2024-04-25

Abstract

Embodiments of the present application are related to methods and apparatuses for positioning in a partial coverage scenario. An embodiment of the present application provides a location management function (LMF) of a wireless network including a transceiver and a processor coupled to the transceiver. The processor is configured to perform at least one of the following: transmitting, with the transceiver and to each of a set of first user equipments (UEs) in coverage of the wireless network, a discovery request for discovering a second UE which is out of coverage of the wireless network and whose position is requested; receiving, with the transceiver and from a third UE, a request for positioning the third UE, and transmitting, with the transceiver and to the third UE, a positioning result for the third UE in response to the request, wherein the third UE is in coverage of the wireless network and performing a sidelink positioning procedure with a fourth UE which is out of coverage of the wireless network for acquiring a position of the fourth UE; or receiving, with the transceiver and from a fifth UE, a positioning assistance request, and transmitting, with the transceiver and to the fifth UE, a positioning result for a target UE out of coverage of the wireless network in response to the positioning assistance request, wherein a calculation ability of the fifth UE cannot support a positioning service associated with the target UE.

Description

METHODS AND APPARATUSES FOR POSITIONING IN PARTIAL COVERAGE SCENARIO

TECHNICAL FIELD

The present disclosure generally relates to wireless communications, and especially to methods and apparatuses for positioning in a partial coverage scenario.

BACKGROUND OF THE INVENTION

In 3rd Generation Partnership Project (3GPP) Release 18, it is agreed to support sidelink positioning in in-coverage (IC) , partial coverage (PC) and out-of-coverage (OOC) scenarios. One of the cases in a PC scenario is that a target user equipment (UE) is out of coverage of a network, and at least one anchor UE is in coverage of the network. In this PC scenario, the network may be involved to trigger a positioning service or provide assistance to acquire a position of the target UE. Currently, corresponding procedures and signaling need to be designed to support network-involved positioning for an OOC target UE.

SUMMARY

Embodiments of the present application at least provide technical solutions for positioning in a PC scenario.

Some embodiments of the present disclosure provide a first UE including a transceiver and a processor coupled to the transceiver, wherein the first UE is in coverage of a wireless network and the processor is configured to: perform a discovery procedure to discover a second UE which is out of coverage of the wireless network; and perform a sidelink positioning procedure with the second UE for acquiring a position of the second UE.

In some embodiments, the processor is configured to receive, with the transceiver and from a location management function (LMF) of the wireless network, a discovery request for discovering the second UE before performing the discovery procedure.

In some embodiments, the discovery request includes at least one of: one or more Uu reference signal received power (RSRP) thresholds, a sidelink RSRP threshold, information of the second UE, a first request for positioning capability information of the first UE, a second request for positioning capability information of the second UE, a third request for a location and associated uncertainty of the first UE, a first response time for the first UE to send a discovery response to the LMF; or first information to be included in a discovery message to be sent by the first UE.

In some embodiments, the first UE satisfies the one or more Uu RSRP thresholds and the processor is further configured to: broadcast, with the transceiver, a first discovery message; and receive, with the transceiver and from the second UE, a second discovery message.

In some embodiments, in the case that the discovery request includes the second request: the first discovery message includes a request for positioning capability information of the second UE; and the processor is configured to receive, with the transceiver and from the second UE, positioning capability information of the second UE.

In some embodiments, the positioning capability information of the second UE is received via the second discovery message.

In some embodiments, the positioning capability information of the second UE is received via a broadcast message.

In some embodiments, the positioning capability information of the second UE is received periodically or received after a period of time since a last broadcast of the positioning capability information of the second UE.

In some embodiments, the processor is configured to: perform measurement for RSRP of the second discovery message; and transmit, with the transceiver and to the LMF, a discovery response before the first response time expires, wherein the RSRP of the second discovery message exceeds the sidelink RSRP threshold.

In some embodiments, the discovery response includes at least one of: a sidelink quality between the first UE and the second UE, or a Uu link quality of the first UE.

In some embodiments, in the case that the discovery request includes the first request, the discovery response includes positioning capability information of the first UE.

In some embodiments, in the case that the discovery request includes the second request, the discovery response includes positioning capability information of the second UE.

In some embodiments, in the case that the discovery request includes the third request: if the first UE knows the location of the first UE, the discovery response includes the location and associated uncertainty of the first UE, and otherwise the discovery response indicates an unknown location or includes no location information of the first UE.

In some embodiments, the processor is further configured to receive, with the transceiver and from the LMF, a relay request including at least one of: a first indication indicating a responsibility of forwarding data from the LMF to the second UE, a second indication to establish a unicast connection with the second UE, or second information to be transmitted to the second UE.

In some embodiments, the first indication further indicates a responsibility of forwarding data from the second UE to the LMF.

In some embodiments, in response to the relay request, the processor is configured to: establish a unicast connection with the second UE; and transmit, with the transceiver and to the LMF, a relay confirmation after the unicast connection is established.

In some embodiments, the processor is configured to forward, with the transceiver and via the unicast connection, the second information to the second UE, and the relay confirmation is transmitted after the second information is forwarded.

In some embodiments, the processor is configured to receive, with the transceiver and from the LMF, an indication to perform the sidelink positioning procedure with the second UE.

In some embodiments, the first information includes: a positioning request with a quality of service (QoS) requirement, and a second response time for the second UE to send a response to the discovery message.

In some embodiments, the first UE satisfies the one or more Uu RSRP thresholds and the processor is further configured to: broadcast, with the transceiver, a first discovery message including the first information; and receive, with the transceiver and from the second UE, a second discovery message before the second response time expires, wherein the second discovery message includes a confirmation indicating that the second UE accepts the positioning request and starts the sidelink positioning procedure.

In some embodiments, the processor is further configured to transmit, with the transceiver and to the LMF, a confirmation indicating that the positioning request is accepted by the second UE.

In some embodiments, the processor is configured to: receive, with the transceiver and from the LMF, a relay reselection configuration for the first UE, which includes at least one of a first relay sidelink RSRP threshold or a relay Uu RSRP threshold.

In some embodiments, the processor is configured to: transmit, with the transceiver and to the LMF, a first relay reselection indication when at least one of the following occurs: an RSRP of sidelink signal on the unicast connection between the first UE and the second UE is below the first relay sidelink RSRP threshold; the first UE detects a sidelink radio link failure (RLF) ; the first UE receives an indication from an upper layer of the first UE; or the first UE is going to lose a connection with the wireless network.

In some embodiments, the processor is configured to: receive, with the transceiver and from the LMF, a release request to release the unicast connection with the second UE; and in response to the release request, release the unicast connection with the second UE and transmit, with the transceiver and to the LMF, a release confirmation.

In some embodiments, the processor is configured to: transmit, with the transceiver and to the second UE, a relay reselection configuration for the second UE, which includes a second relay sidelink RSRP threshold.

In some embodiments, the processor is configured to receive, with the transceiver, the second relay sidelink RSRP threshold from the LMF.

In some embodiments, the processor is configured to transmit, with the transceiver and to the second UE, a second relay reselection indication when at least one of the following occurs: an RSRP of Uu signal received from a base station (BS) is below the relay Uu RSRP threshold; the first UE detects a Uu RLF; or the first UE receives an indication from an upper layer of the first UE.

In some embodiments, the processor is configured to transmit, with the transceiver and to the LMF, a request for positioning the first UE.

In some embodiments, the processor is configured to receive, with the transceiver and from the LMF, a positioning result for the first UE in response to the request for positioning the first UE.

In some embodiments, the request for positioning the first UE includes at least one of a QoS requirement of a positioning service or a positioning response time, and wherein in the case that the request for positioning the first UE includes the positioning response time, the positioning result is received before the positioning response time expires.

In some embodiments, the request for positioning the first UE is transmitted when the first UE receives a relocation request from the second UE, and the processor is configured to transmit, with the transceiver and to the second UE, a relocation response including the positioning result for the first UE.

In some embodiments, the relocation request includes at least one of a QoS requirement of a positioning service or a relocation response time, and wherein in the case that the relocation request includes the relocation response time, the relocation response is transmitted before the relocation response time expires.

In some embodiments, the request for positioning the first UE is transmitted when a sidelink position estimation computed by the first UE does not satisfy an accuracy requirement of a positioning service associated with the second UE.

In some embodiments, the processor is configured to transmit, with the transceiver and to the LMF, a relocation cancel request for canceling positioning of the first UE if the accuracy requirement is satisfied by ongoing sidelink positioning before a positioning result for the first UE is received from the LMF in response to the request for positioning the first UE.

In some embodiments, in the case that the first UE does not receive a positioning result for the first UE from the LMF before a positioning response time expires, the processor is configured to: inform an upper layer of the first UE that the accuracy requirement of the positioning service is not satisfied at present and a positioning accuracy can be potentially improved after a positioning result for the first UE is received from the LMF.

In some embodiments, the processor is configured to: transmit, with the transceiver, a positioning assistance request to the LMF when a calculation ability of at least one of the first UE or the second UE cannot support a positioning service associated with the second UE, wherein the positioning assistance request includes at least one of: an indication of sidelink-only positioning, an indication indicating a responsibility of the LMF, or information of the second UE.

In some embodiments, the positioning assistance request is transmitted together with or separately from a measurement report associated with the second UE.

In some embodiments, the processor is configured to receive, with the transceiver and from the LMF, a positioning result for the second UE in response to the positioning assistance request.

Some embodiments of the present disclosure provide an LMF of a wireless network, the LMF including a transceiver and a processor coupled to the transceiver, wherein the processor is configured to perform at least one of the following: transmitting, with the transceiver and to each of a set of first UEs in coverage of the wireless network, a discovery request for discovering a second UE which is out of coverage of the wireless network and whose position is requested; receiving, with the transceiver and from a third UE, a request for positioning the third UE, and transmitting, with the transceiver and to the third UE, a positioning result for the third UE in response to the request, wherein the third UE is in coverage of the wireless network and performing a sidelink positioning procedure with a fourth UE which is out of coverage of the wireless network for acquiring a position of the fourth UE; or receiving, with the transceiver and from a fifth UE, a positioning assistance request, and transmitting, with the transceiver and to the fifth UE, a positioning result for a target UE out of coverage of the wireless network in response to the positioning assistance request, wherein a calculation ability of the fifth UE cannot support a positioning service associated with the target UE.

In some embodiments, the processor is configured to transmit the discovery request in response to receiving an indication from an access and mobility management function (AMF) of the wireless network indicating to position the second UE.

In some embodiments, the discovery request transmitted to each first UE includes at least one of: one or more Uu RSRP thresholds, a sidelink RSRP threshold, information of the second UE, a first request for positioning capability information of a respective first UE, a second request for positioning capability information of the second UE, a third request for a location and associated uncertainty of the respective first UE, a first response time for the respective first UE to send a discovery response to the LMF; or first information to be included in a discovery message to be sent by the respective first UE, wherein the first information includes: a positioning request with a QoS requirement, and a second response time for the second UE to send a response to the discovery message.

In some embodiments, the processor is configured to receive, with the transceiver and from one or more first UEs within the set of first UEs, one or more discovery responses before the first response time expires.

In some embodiments, the discovery response received from a respective first UE includes at least one of: a sidelink quality between the respective first UE and the second UE, or a Uu link quality of the respective first UE.

In some embodiments, in the case that the discovery request transmitted to each first UE includes the first request, the discovery response received from a respective first UE includes positioning capability information of the respective first UE.

In some embodiments, in the case that the discovery request transmitted to each first UE includes the second request, the discovery response received from a respective first UE includes positioning capability information of the respective first UE.

In some embodiments, in the case that the discovery request transmitted to each first UE includes the third request, the discovery response received from a respective first UE includes the location and associated uncertainty of the respective first UE or indicates an unknown location or includes no location information.

In some embodiments, the processor is configured to select at least one anchor UE for acquiring a position of the second UE from the one or more first UEs according to the one or more discovery responses received from the one or more first UEs.

In some embodiments, the at least one anchor UE is selected based on at least one of the following: positioning capability information of the one or more first UEs; a sidelink quality between each of the one or more first UEs and the second UE; a location and associated uncertainty of each of the one or more first UEs; or a positioning requirement for positioning the second UE.

In some embodiments, the processor is configured to: designate an anchor UE in the at least one anchor UE as a relay anchor UE; and transmit, with the transceiver and to the relay anchor UE, a first relay request including at least one of: a first indication indicating a responsibility of forwarding data from the LMF to the second UE, a second indication to establish a unicast connection between the relay anchor UE and the second UE, or second information to be transmitted to the second UE.

In some embodiments, the processor is configured to: receive, with the transceiver and from the relay anchor UE, a first relay confirmation; and in response to the first relay confirmation, initiate sidelink positioning between the at least one anchor UE and the second UE, and interact with the second UE via the relay anchor UE.

In some embodiments, in the case that a number of the at least one anchor UE is insufficient for acquiring the position of the second UE or location information of the at least one anchor UE is not received, the processor is further configured to initiate Uu positioning for the at least one anchor UE.

In some embodiments, each of the at least one anchor UE is designated as a relay anchor UE.

In some embodiments, the processor is configured to: receive, with the transceiver and from a first UE of the set of first UEs, a confirmation indicating that the positioning request is accepted by the second UE in response to the discovery request including the first information.

In some embodiments, the processor is configured to abort a discovery procedure of other first UE (s) of the set of first UEs.

In some embodiments, in the case that the discovery request includes the first information and no confirmation indicating that the positioning request is accepted by the second UE is received from the set of first UEs during a period of time, the processor is configured to initiate a network-controlled sidelink positioning for the second UE.

In some embodiments, the processor is configured to transmit, with the transceiver and to the relay anchor UE, a relay reselection configuration for the relay anchor UE including at least one of a first relay sidelink RSRP threshold and a relay Uu RSRP threshold.

In some embodiments, the relay anchor UE is a first relay anchor UE, and the processor is configured to perform relay anchor UE reselection to select a second relay anchor UE when at least one of the following occurs: the LMF receives a first relay reselection indication from the first relay anchor UE; a Uu measurement report associated with the first relay anchor UE received from the first relay anchor UE or a BS indicates a Uu RSRP below the relay Uu RSRP threshold; a sidelink measurement report associated with the first relay anchor UE received from the first relay anchor UE indicates a sidelink RSRP below the first relay sidelink RSRP threshold; or no measurement report is received from the first relay anchor UE for a period of time.

In some embodiments, the processor is configured to: transmit, with the transceiver and to the second relay anchor UE, a second relay request.

In some embodiments, the processor is further configured to: receive, with the transceiver and from the second relay anchor UE, a second relay confirmation; transmit, with the transceiver and to the first relay anchor UE, a release request to release a unicast connection between the first relay anchor UE and the second UE in response to receiving the second relay confirmation; and receive, with transceiver and from the first relay anchor UE, a release confirmation in response to the release request.

In some embodiments, the processor is configured to transmit, with the transceiver and to the relay anchor UE, a relay reselection configuration for the second UE, which includes a second relay sidelink RSRP threshold for the second UE to perform relay anchor UE reselection.

In some embodiments, the processor is further configured to receive, with the transceiver and from an anchor UE of the at least one anchor UE different from the relay anchor UE, an indication indicates that the anchor UE is selected as a new relay anchor UE.

In some embodiments, the request for positioning the third UE includes at least one of a QoS requirement of a positioning service or a positioning response time, and upon receiving the request for positioning the third UE, the processor is configured to: initiate Uu positioning for the third UE.

In some embodiments, in the case that the request for positioning the third UE includes the positioning response time, the processor is configured to transmit, with the transceiver, a positioning result to the third UE before the positioning response time expires.

In some embodiments, the processor is configured to: receive, with the transceiver, a relocation cancel request for canceling positioning of the third UE; and stop the Uu positioning for the third UE in response to the relocation cancel request.

In some embodiments, the fifth UE is the target UE and the positioning assistance request is received via a sidelink relay UE in coverage of the wireless network, or the fifth UE is an anchor UE in coverage of the wireless network for acquiring a position of the target UE.

In some embodiments, the positioning assistance request is received together with or separately from a measurement report associated with the target UE.

In some embodiments, the positioning assistance request includes at least one of: an indication of sidelink-only positioning, an indication indicating a responsibility of the LMF, or information of the target UE.

Some embodiments of the present disclosure provide a second UE, the second UE is out of coverage of a wireless network and including a transceiver and a processor coupled to the transceiver, wherein the processor is configured to perform at least one of the following: receiving, with the transceiver and from each of one or more first UEs in coverage of the wireless network, a first discovery message, and transmitting, with the transceiver and to each of the one or more first UEs, a second discovery message; transmitting, with the transceiver and to one or more anchor UEs for acquiring a position of the second UE, a relocation request; or transmitting, with the transceiver and to an LMF of the wireless network, a positioning assistance request via a sidelink relay UE in coverage of the wireless network, and receiving, with the transceiver and from the LMF, an assistance result via the sidelink relay UE.

In some embodiments, the first discovery message includes a request for positioning capability information of the second UE, and the second discovery message includes positioning capability information of the second UE.

In some embodiments, wherein the first discovery message includes a request for positioning capability information of the second UE, and the processor is configured to broadcast positioning capability information of the second UE.

In some embodiments, the positioning capability information of the second UE is broadcast periodically or is broadcast after a period of time since a last broadcast of the positioning capability information of the second UE.

In some embodiments, the processor is configured to: establish a unicast connection with a designated first UE of the one or more UEs which is designated by the LMF as a first relay anchor UE; and receive, with the transceiver and from the first relay anchor UE, information about anchor UE (s) selected by the LMF.

In some embodiments, the processor is configured to: start sidelink positioning after transmitting the second discovery message (s) ; and transmit, with the transceiver and to the LMF, a measurement report or sidelink positioning result via a relay UE in coverage of the wireless network.

In some embodiments, the second discovery message includes a confirmation indicating that the second UE accepts a positioning request with a QoS requirement included in the first discovery message.

In some embodiments, the processor is configured to receive, with the transceiver and from the first relay anchor UE, a relay reselection configuration for the second UE including a relay sidelink RSRP threshold.

In some embodiments, the processor is configured to: reselect a second relay anchor UE other than the first relay anchor UE when the second UE receives a relay reselection indication from the first relay anchor UE, wherein an RSRP of sidelink signal received from the second relay anchor UE satisfies the relay sidelink RSRP threshold; and release a unicast connection with the first relay anchor UE.

In some embodiments, the relocation request is transmitted to the one or more anchor UEs in response to that a sidelink position estimation computed by the second UE does not satisfy an accuracy requirement of a positioning service associated with the second UE.

In some embodiments, the relocation request includes at least one of the accuracy requirement of the positioning service or a relocation response time.

In some embodiments, the relocation request is transmitted via broadcast signaling or groupcast signaling, or is transmitted to at least one anchor UE of the one or more anchor UEs via unicast signaling.

In some embodiments, the relocation request is transmitted to each anchor UE of the one or more anchor UEs, and wherein the relocation request transmitted to a respective anchor UE of the one or more UEs includes a coverage request for network coverage information of the respective anchor UE of the one or more anchor UEs.

In some embodiments, in the case that the accuracy requirement of the positioning service is satisfied by ongoing sidelink positioning before one or more relocation results are received, the processor is configured to transmit a relocation cancel request to the LMF via a sidelink relay UE.

In some embodiments, in the case that no relocation result is received from at least one of the one or more anchor UEs after the relocation request is transmitted and before the relocation response time expires, the processor is configured to inform an upper layer of the second UE that the accuracy requirement of the positioning service is not satisfied at present and a positioning accuracy can be potentially improved after a relocation result is received from the at least one of the one or more anchor UEs; and in the case that at least one relocation result is received from at least one anchor UE of the one or more anchor UEs after the relocation request is transmitted and before the relocation response time expires, the processor is configured to transmit a current sidelink position estimation based on at least one relocation result received from the at least one anchor UE of the one or more anchor UEs to an upper layer of the second UE.

In some embodiments, the processor is configured to transmit the positioning assistance request in the case that a calculation ability of the second UE cannot support a positioning service associated with the second UE, wherein the positioning assistance request includes at least one of: an indication indicating a responsibility of the LMF, an indication of sidelink-only positioning, or information of the second UE.

Some embodiments of the present disclosure provide a method performed by a first UE in coverage of a wireless network. The method includes: performing a discovery procedure to discover a second UE which is out of coverage of the wireless network; and performing a sidelink positioning procedure with the second UE for acquiring a position of the second UE.

Some embodiments of the present disclosure provide a method performed by an LMF of a wireless network. The method includes at least one of: transmitting, to each of a set of first UEs in coverage of the wireless network, a discovery request for discovering a second UE which is out of coverage of the wireless network and whose position is requested; receiving, from a third UE, a request for positioning the third UE, and transmitting, to the third UE, a positioning result for the third UE in response to the request, wherein the third UE is in coverage of the wireless network and performing a sidelink positioning procedure with a fourth UE which is out of coverage of the wireless network for acquiring a position of the fourth UE; or receiving, from a fifth UE, a positioning assistance request, and transmitting, to the fifth UE, a positioning result for a target UE out of coverage of the wireless network in response to the positioning assistance request, wherein a calculation ability of the fifth UE cannot support a positioning service associated with the target UE.

Some embodiments of the present disclosure provide a method performed by a second UE out of coverage of a wireless network. The method includes at least one of: receiving, from each of one or more first UEs in coverage of the wireless network, a first discovery message, and transmitting, to each of the one or more first UEs, a second discovery message; transmitting, to one or more anchor UEs for acquiring a position of the second UE, a relocation request; or transmitting, to an LMF of the wireless network, a positioning assistance request via a sidelink relay UE in coverage of the wireless network, and receiving, from the LMF, an assistance result via the sidelink relay UE.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which advantages and features of the application can be obtained, a description of the application is rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. These drawings depict only example embodiments of the application and are not therefore to be considered limiting of its scope.

Figure 1 is a schematic diagram illustrating an exemplary wireless communication system according to some embodiments of the present disclosure.

Figure 2 illustrates a flowchart of an exemplary method for discovering and positioning an OOC target UE according to some embodiments of the present disclosure.

Figure 3 illustrates a flowchart of another exemplary method for discovering and positioning an OOC target UE according to some embodiments of the present disclosure.

Figure 4 illustrates a flowchart of an exemplary method for reselecting a relay anchor UE according to some embodiments of the present disclosure.

Figure 5 illustrates a flowchart of another exemplary method for reselecting a relay anchor UE according to some embodiments of the present disclosure.

Figure 6 illustrates a flowchart of an exemplary method for relocating an IC anchor UE for sidelink positioning according to some embodiments of the present disclosure.

Figure 7 illustrates a simplified block diagram of an exemplary apparatus for positioning according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

The detailed description of the appended drawings is intended as a description of the currently preferred embodiments of the present disclosure, and is not intended to represent the only form in which the present disclosure may be practiced. It should be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the present disclosure.

While operations are depicted in the drawings in a particular order, persons skilled in the art will readily recognize that such operations need not be performed in the particular order as shown or in a sequential order, or that all illustrated operations need be performed, to achieve desirable results; sometimes one or more operations can be skipped. Further, the drawings can schematically depict one or more example processes in the form of a flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In certain circumstances, multitasking and parallel processing can be advantageous.

Reference will now be made in detail to some embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. To facilitate understanding, embodiments are provided under specific network architecture and new service scenarios, such as 3GPP long term evolution (LTE) , LTE advanced, 5G new radio (NR) , 5G-Advanced, 6G, and so on. It is contemplated that along with the developments of network architectures and new service scenarios, all embodiments in the present disclosure are also applicable to similar technical problems; and moreover, the terminologies recited in the present disclosure may change, which should not affect the principle of the present disclosure.

Figure 1 is a schematic diagram illustrating an exemplary wireless communication system 100 according to some embodiments of the present disclosure.

As shown in Figure 1, the wireless communication system 100 includes at least one LMF 101, at least one UE (e.g., UE 102a and UE 102b) , and at least one BS 103. Although one BS, two UEs, and one LMF are depicted in Figure 1 for illustrative purpose, it is contemplated that any number of BSs, UEs, and LMFs may be included in the wireless communication system 100.

The wireless communication system 100 is compatible with any type of network that is capable of sending and receiving wireless communication signals. For example, the wireless communication system 100 is compatible with a wireless communication network, a cellular telephone network, a time division multiple access (TDMA) based network, a code division multiple access (CDMA) based network, an orthogonal frequency division multiple access (OFDMA) based network, an LTE network, a 3GPP-based network, a 3GPP 5G network, a satellite communications network, a high-altitude platform network, and/or other communications networks.

The LMF 101 (also referred to as LMF entity) may refer to a network element or network entity for supporting location services, which may be deployed in a core network (CN) or in a radio access network (RAN) of the wireless communication system 100. The LMF 101 may communicate with the BS 103 via NR positioning protocol A (NRPPa) signaling, and may communicate with a UE (e.g., the UE 102a) via LTE positioning protocol (LPP) signaling.

According to some embodiments of the present application, a UE (e.g., the UE 102a, or the UE 102b) may be a vehicle UE (VUE) or a power-saving UE (also referred to as a power sensitive UE) . The power-saving UE may be a vulnerable road user (VRU) , a public safety UE (PS-UE) , or a commercial sidelink UE (CS-UE) that is sensitive to power consumption. In an embodiment of the present application, a VRU may be a pedestrian UE (P-UE) , cyclist UE, wheelchair UE or another UE which require power saving compared with a VUE.

According to some other embodiments of the present application, a UE (e.g., the UE 102a, or the UE 102b) may be a computing device, such as a desktop computer, laptop computer, personal digital assistant (PDA) , tablet computer, smart television (e.g., a television connected to the Internet) , a set-top box, game console, security system (e.g., a security camera) , a vehicle on-board computer, a network device (e.g., a router, switcher, or modem) , or the like.

According to some other embodiments of the present application, a UE (e.g., the UE 102a, or the UE 102b) may be a portable wireless communication device, smart phone, cellular telephone, flip phone, device having a subscriber identity module, personal computer, selective call receiver, or another device that is capable of sending and receiving communication signals on a wireless network.

According to some other embodiments of the present application, a UE (e.g., the UE 102a, or the UE 102b) may be a wearable device, such as a smart watch, fitness band, optical head-mounted display, or the like.

Moreover, a UE (e.g., the UE 102a, or the UE 102b) may be referred to as a subscriber unit, mobile, mobile station, user, terminal, mobile terminal, wireless terminal, fixed terminal, subscriber station, user terminal, device, or described using other terminology used in the art.

The BS 103 may also be referred to as an access point, an access terminal, a base, a macro cell, a radio access network (RAN) node, a next generation (NG) RAN node, a node-B, an enhanced node B (eNB) , a gNB, a home node-B, a relay node, or a device, or described using other terminology used in the art. The BS 103 is generally part of a RAN that may include a controller communicably coupled to the BS 103.

In the example shown in Figure 1, the UE 102a is in coverage of a network (e.g., within a coverage area of the BS 103) and may communicate with the BS 103 via LTE or NR Uu interface, and the UE 102b is out of coverage of the network (e.g., not within a coverage area of any BS) . The UE 102a may be referred to as an IC UE, and the UE 102b may be referred to as an OOC UE. The UE 102a may communicate with the UE 102b via sidelink (for example, via PC5 interface as defined in 3GPP standard documents) .

When a location service request associated with a UE is initiated or occurs, the position of the UE (referred to as target UE or location service (LCS) target UE) needs to be known. If the target UE is within a coverage area of a BS or network, Uu positioning may be performed for the target UE, in which the target UE may transmit positioning reference signal (s) (PRS (s) ) to or receive PRS (s) from the BS and/or neighboring BS (s) and measurement (s) may be performed on the PRS (s) by the BS(s) or the target UE to obtain positioning information.

Sidelink positioning refers to transmitting PRS (s) over sidelink, which can operate independent of network or radio access technology (RAT) coverage. According to various embodiments of the present application, regardless of in coverage or out of coverage, a target UE may select one or more other UEs to be anchor UE (s) , which may participate in sidelink positioning and help the target UE to acquire its position, e.g., by sending/receiving sidelink PRS and doing relevant measurements. According to some other embodiments of the present application, the anchor UE (s) may be determined by the network (e.g., by an LMF or a BS) instead of being selected by the target UE. In such embodiments, the target UE and the anchor UE (s) may be in coverage of the network. The anchor UE (s) should have a positioning capability.

One or more anchor UEs may be selected to help the target UE to acquire its position. When performing sidelink positioning, the target UE and the one or more anchor UEs may be in one of the following scenarios: the target UE and all of the one or more anchor UEs are in coverage of the network (i.e., IC scenario) ; at least one of the target UE or the one or more anchor UEs is in coverage of the network and at least one of the target UE or the one or more anchor UEs is out of coverage of the network (i.e., PC scenario) ; or the target UE and all of the one or more anchor UEs are out of coverage of the network (i.e., OOC scenario) .

One of the cases for sidelink positioning in a PC scenario is that a target UE is out of coverage of a network (i.e., OOC target UE) while at least one anchor UE is in coverage of the network (i.e., IC anchor UE) . In this PC scenario, the network may be involved to trigger a positioning service or provide assistance to acquire a position of the OOC target UE. The present disclosure provides various procedures and signaling to support positioning for an OOC target UE in such a PC scenario.

According to some embodiments of the present disclosure, when a network or an OOC target UE triggers positioning for the OOC target UE, an IC UE (e.g., the UE 102a) , which may be a candidate anchor UE, may perform a discovery procedure to discover the OOC target UE. The discovery procedure may be initiated by the IC UE or the OOC target UE. In the case that the IC UE is selected (e.g., by an LMF of the network or the OOC target UE) as an anchor UE, it may perform a sidelink positioning procedure with the OOC target UE for acquiring a position of the OOC target UE.

According to some embodiments of the present disclosure, the network may trigger positioning for the OOC target UE. For example, an AMF of the network may transmit an indication indicating to position the OOC target UE to an LMF, wherein the indication may provide information of a set of IC candidate anchor UEs and information of the OOC target UE (e.g., an identity (ID) of the OOC target UE) . In some embodiments, the AMF may select the set of IC candidate anchor UEs based on the registered UE capability, a target area identified by at least one of a cell ID, a BS ID, or a tracking area identity (TAI) , or a last known cell ID of the OOC target UE.

In response to receiving the indication from the AMF, the LMF may transmit a discovery request for discovering the OOC target UE to each of the set of IC candidate anchor UEs. Then, the set of IC candidate anchor UEs may perform a discovery procedure to discover the OOC target UE in response to the discovery request.

Figure 2 illustrates a flowchart of an exemplary method 200 for discovering and positioning an OOC target UE according to some embodiments of the present disclosure, wherein the OOC target UE discovery and positioning are controlled by a network. The method 200 illustrated in Figure 2 may be performed by at least three entities, e.g., an IC candidate anchor UE (e.g., the UE 102a) , an OOC target UE (e.g., the UE 102b) , and an LMF of the network (e.g., the LMF 101) . Although the method is illustrated in a system level, persons skilled in the art can understand that the method implemented in the three entities can be separately implemented and incorporated in other apparatus with the like functions. Furthermore, although only one IC candidate anchor UE is illustrated in Figure 2, it is contemplated that there may be other IC candidate anchor UE (s) involved in the method 200 but not shown in Figure 2, and the other IC candidate anchor UE (s) may perform operations similar to those performed by the IC candidate anchor UE illustrated in Figure 2. Moreover, it is also contemplated that the method 200 may include additional steps not shown.

As shown in Figure 2, in step 201, the LMF may transmit a discovery request for discovering the OOC target UE to the IC candidate anchor UE, e.g., in response to receiving an indication indicating to position the OOC target UE from an AMF. The IC candidate anchor UE may be included in a set of IC candidate anchor UEs indicated by the AMF. The LMF may transmit a discovery request for discovering the OOC target UE to each of the set of IC candidate anchor UEs.

The discovery request transmitted to the IC candidate anchor UE may include configurations for discovering the OOC target UE. For example, the discovery request may include at least one of: one or more Uu RSRP thresholds, a sidelink RSRP threshold (e.g., a PC5 RSRP threshold) , or information of the OOC target UE (e.g., an ID of the OOC target UE) .

The one or more Uu RSRP thresholds may be used by the IC candidate anchor UE to determine whether to transmit a discovery message to the OOC target UE. In an embodiment, the one or more Uu RSRP thresholds may include a maximum Uu RSRP threshold, a minimum Uu RSRP threshold, or both. The maximum and minimum Uu RSRP thresholds may be used to filter IC candidate anchor UEs. For example, if an RSRP of Uu signal received by an IC candidate anchor UE exceeds the maximum Uu RSRP threshold, it means that the IC candidate anchor UE is very closed to a BS and may be not possible to have a good connection with the OOC target UE. If an RSRP of Uu signal received by an IC candidate anchor UE is below the minimum Uu RSRP threshold, it means that the IC candidate anchor UE does not have a good connection with the network. An IC candidate anchor UEs that does not have a good connection with the OOC target UE or the network may not be selected as an anchor UE and thus it does not need to transmit a discovery message to the OOC target UE. Since the number of IC candidate anchor UEs may be very large, it is beneficial to filter out IC candidate anchor UEs that do not have a good connection with the OOC target UE or the network.

The sidelink RSRP threshold may be used by the IC candidate anchor UE to determine whether it needs to respond to the discovery request after discovering the OOC target UE. How to use the sidelink RSRP threshold will be described later.

In some embodiments, the discovery request may include a request for positioning capability information of at least one of the IC candidate anchor UE or the OOC target UE. The positioning capability information may include at least one of a supported positioning method, positioning calculation ability, supported bandwidth, etc.

In some embodiments, the discovery request may include a request for a location and associated uncertainty of the IC candidate anchor UE. The location and associated uncertainty of each IC candidate anchor UE may be used by the LMF for anchor UE selection and positioning method determination.

In some embodiments, the discovery request may include a response time for the IC candidate anchor UE to send a discovery response to the LMF. For example, the LMF may ignore a discovery response received after the response time expires.

It is assumed that the IC candidate anchor UE illustrated in Figure 2 satisfies the one or more Uu RSRP thresholds included in the discovery request. For example, in the case that the discovery request includes a maximum Uu RSRP threshold, the RSRP of Uu signal received by the IC candidate anchor UE is below the maximum Uu RSRP threshold; in the case that the discovery request includes a minimum Uu RSRP threshold, the RSRP of Uu signal received by the IC candidate anchor UE exceeds the minimum Uu RSRP threshold. Then, in step 202, the IC candidate anchor UE may begin to discover the OOC target UE by broadcasting a discovery message.

In some embodiments, in the case that the discovery request from the LMF includes a request for positioning capability information of the OOC target UE, the discovery message broadcast by the IC candidate anchor UE may include a request for positioning capability information of the OOC target UE.

In the example illustrated in Figure 2, it is assumed that the OOC target UE receives the discovery message from the IC candidate anchor UE. Then, in step 203, it may transmit a discovery message to the IC candidate anchor UE. In some embodiments, in the case that the discovery message from the IC candidate anchor UE includes a request for positioning capability information of the OOC target UE, the OOC target UE may transmit its positioning capability information to the IC candidate anchor UE. In some embodiments, the OOC target UE may include its positioning capability information in the discovery message transmitted to the IC candidate anchor UE. In some embodiments, the OOC target UE may transmit its positioning capability information in a broadcast message. For example, since there may be multiple IC candidate anchor UEs request the positioning capability information of the OOC target UE, the OOC target UE may transmit its positioning capability information periodically, e.g., upon receiving the first request among the requests from the multiple IC candidate anchor UEs. Alternatively, the OOC target UE may broadcast its positioning capability information after a period of time since a last broadcast of its positioning capability information. The period of time may be defined as a prohibit time.

Upon receiving the discovery message from the OOC target UE, the IC candidate anchor UE may perform measurements for RSRP (such as sidelink discovery (SD) RSRP measurements) of the discovery message. In the example illustrated in Figure 2, it is assumed that the RSRP of the discovery message exceeds the sidelink RSRP threshold included in the discovery request from the LMF. Then, in step 204, the IC candidate anchor UE may transmit a discovery response to the LMF. In some embodiments, the IC candidate anchor UE may transmit the discovery response to the LMF before the response time included in the discovery request from the LMF expires. In the case that the RSRP of the discovery message received by an IC candidate anchor UE does not exceed the sidelink RSRP threshold included in the discovery request from the LMF, which means that the IC candidate anchor UE does not have a good connection with the OOC target UE and is not suitable to be selected as an anchor UE, the IC candidate anchor UE may not transmit a discovery response to the LMF.

In some embodiments, the discovery response transmitted in step 204 may include at least one of: a sidelink quality (e.g., SD PSPR) between the IC candidate anchor UE and the OOC target UE, or a Uu link quality (e.g., Uu RSRP) of the IC candidate anchor UE.

In some embodiments, in the case that the discovery request from the LMF includes a request for positioning capability information of the IC candidate anchor UE, the discovery response may include positioning capability information of the IC candidate anchor UE.

In some embodiments, in the case that the discovery request from the LMF includes a request for positioning capability information of the OOC target UE, the discovery response may include positioning capability information of the OOC target UE.

In some embodiments, in the case that the discovery request from the LMF includes a request for a location and associated uncertainty of the IC candidate anchor UE, if the IC candidate anchor UE knows its location, the discovery response may include the location and associated uncertainty; otherwise, the discovery response may indicate an unknown location or includes no location information of the IC candidate anchor UE. According to the embodiments of the present disclosure, the uncertainty associated with the location of the IC candidate anchor UE may be speculated by the IC candidate anchor UE or obtained together with the location of the IC candidate anchor UE.

In step 205, the LMF may select at least one anchor UE for acquiring the position of the OOC target UE according to discovery response (s) received from one or more IC candidate anchor UEs including the IC candidate anchor UE illustrated in Figure 2. As described above, the LMF may take into account discovery response (s) received before a response time expires and ignore discovery response (s) received after the response time expires, wherein the response time may be included in the discovery request transmitted to the IC candidate anchor UE (s) .

In some embodiments, the LMF may select the at least one anchor UE from the one or more IC candidate anchor UEs based on at least one of the followings:

● positioning capability information of the one or more IC candidate anchor UEs;

● a sidelink quality between each of the one or more IC candidate anchor UEs and the OOC target UE;

● a location and associated uncertainty of each of the one or more IC candidate anchor UEs; or

● a positioning requirement for positioning the OOC target UE: for example, the number of the at least one anchor UE may be determined by the LMF based on the positioning requirement, e.g., how many anchor UEs are needed when an absolute position of the OOC target UE is required.

After the LMF selects the at least one anchor UE, in some embodiments, the LMF may designate each anchor UE of the at least one anchor UE as a relay anchor UE for forwarding data from the LMF to the OOC target UE, and optionally forwarding data from the OOC target UE to the LMF. Each relay anchor needs to establish a unicast connection with the OOC target UE. In some embodiments, to avoid signaling overhead caused by unicast connection establishment between all the anchor UE (s) and the OOC target UE, the LMF may designate one of the at least one anchor UE as a relay anchor UE for forwarding data from the LMF to the OOC target UE, and optionally forwarding data from the OOC target UE to the LMF. The relay anchor UE is considered suitable by the LMF in terms of radio criteria if the sidelink and Uu link qualities of the relay anchor UE exceed configured thresholds. Which anchor UE is designated as a relay anchor UE is up to the LMF's implementation.

It is assumed that the IC candidate anchor UE illustrated in Figure 2 is selected as an anchor UE and also designated as a relay anchor UE. In step 206, the LMF may transmit a relay request to the relay anchor UE, wherein the relay request may include at least one of:

● an indication indicating a responsibility of forwarding data from the LMF to the OOC target UE, and optionally forwarding data from the OOC target UE to the LMF,

● an indication to establish a unicast connection between the relay anchor UE and the OOC target UE, or

● information (e.g., information of all the selected anchor UE (s) ) to be transmitted to the OOC target UE.

In step 207, upon receiving the relay request from the LMF, the relay anchor UE may establish a unicast connection with the OOC target UE. The relay anchor UE may forward the information (e.g., information of all the selected anchor UE (s) ) contained in the relay request to the OOC target UE after the unicast connection is established.

In step 208, after the unicast connection is established, the relay anchor UE may transmit a relay confirmation to the LMF. In some embodiments, the relay confirmation is transmitted to the LMF after the information contained in the relay request is forwarded to the OOC target UE.

In step 209, in response to receiving at least one relay confirmation from at least one relay anchor UE, the LMF may initiate sidelink positioning between the selected anchor UE (s) and the OOC target UE and interact with the OOC target UE via the at least one relay anchor UE. For example, the LMF may indicate to the selected anchor UE (s) to perform a sidelink positioning procedure with the OOC target UE. In some embodiments, in the case that a number of the anchor UE (s) is insufficient for acquiring the position of the OOC target UE or location information of the anchor UE (s) is not received, the LMF may further initiate Uu positioning for the anchor UE (s) .

Figure 3 illustrates a flowchart of an exemplary method 300 for discovering and positioning an OOC target UE according to some embodiments of the present disclosure, wherein the OOC target UE discovery is triggered by a network but the OOC target UE performs sidelink positioning without the control of the network. The method 300 illustrated in Figure 3 may be performed by at least three entities, e.g., an IC candidate anchor UE (e.g., the UE 102a) , an OOC target UE (e.g., the UE 102b) , and an LMF of the network (e.g., the LMF 101) . Although the method 300 is illustrated in a system level, persons skilled in the art can understand that the method implemented in the three entities can be separately implemented and incorporated in other apparatus with the like functions. Furthermore, although only one IC candidate anchor UE is illustrated in Figure 3, it is contemplated that there may be other IC candidate anchor UE (s) involved in the method 300 but not shown in Figure 3, and the other IC candidate anchor UE (s) may perform operations similar to those performed by the IC candidate anchor UE illustrated in Figure 3. Moreover, it is also contemplated that the method 300 may include additional steps not shown.

As shown in Figure 3, in step 301, the LMF may transmit a discovery request for discovering the OOC target UE to the IC candidate anchor UE, e.g., in response to receiving an indication indicating to position the OOC target UE from an AMF. The IC candidate anchor UE may be included in a set of IC candidate anchor UEs indicated by the AMF. The LMF may transmit a discovery request for discovering the OOC target UE to each of the set of IC candidate anchor UEs.

The discovery request transmitted to the IC candidate anchor UE may include configurations for discovering the OOC target UE. For example, the discovery request may include at least one of: one or more Uu RSRP thresholds, or information of the OOC target UE (e.g., an ID of the OOC target UE) .

The one or more Uu RSRP thresholds may be used by the IC candidate anchor UE to determine whether to transmit a discovery message to the OOC target UE. In an embodiment, the one or more Uu RSRP thresholds may include a maximum Uu RSRP threshold, a minimum Uu RSRP threshold, or both. The maximum and minimum Uu RSRP thresholds may be used to filter IC candidate anchor UEs, as described above with respect to Figure 2.

In some embodiments, the discovery request may include information to be included in a discovery message to be sent by the IC candidate anchor UE. For example, the information may include a positioning request with a QoS requirement, and a response time for the OOC target UE to send a response to the discovery message.

It is assumed that the IC candidate anchor UE illustrated in Figure 3 satisfies the one or more Uu RSRP thresholds included in the discovery request. For example, in the case that the discovery request includes a maximum Uu RSRP threshold, the RSRP of Uu signal received by the IC candidate anchor UE is below the maximum Uu RSRP threshold; in the case that the discovery request includes a minimum Uu RSRP threshold, the RSRP of Uu signal received by the IC candidate anchor UE exceeds the minimum Uu RSRP threshold. Then, in step 302, the IC candidate anchor UE may begin to discover the OOC target UE by broadcasting a discovery message. In some embodiments, the discovery message may include the aforementioned information included in the discovery request, e.g., a positioning request with a QoS requirement, and a response time for the OOC target UE to send a response to the discovery message.

In the example illustrated in Figure 3, it is assumed that the OOC target UE receives the discovery message from the IC candidate anchor UE. Then, in step 303, the OOC target UE may transmit a discovery message to the IC candidate anchor UE. In the case that the discovery message from the IC candidate anchor UE includes a response time, the OOC target UE may transmit the discovery message before the response time expires. The discovery message transmitted by the OOC target UE may include a confirmation indicating that the OOC target UE accepts the positioning request included in the discovery message from the IC candidate anchor UE and starts a sidelink positioning procedure.

In step 304, in response of receiving the discovery message from the OOC target UE, the IC candidate anchor UE may transmit a confirmation to the LMF indicating that the OOC target UE accepts the positioning request included in the discovery request from the LMF. Once the LMF receives such a confirmation from an IC candidate anchor UE, the LMF may abort the discovery procedure of other IC candidate anchor UE (s) .

In step 305, after transmitting the discovery message to the IC candidate anchor UE, the OOC target UE may start sidelink positioning by using the IC candidate anchor UE as an anchor UE. In some embodiments, the anchor UE may transmit a measurement report or sidelink positioning result to the LMF. In some embodiments, the OOC target UE may transmit a measurement report or sidelink positioning result to the LMF via an IC UE, which may be an anchor UE or non-anchor UE.

In some embodiments, in the case that the LMF does not receive any confirmation indicating that the OOC target UE accepts the positioning request included in the discovery request from any IC candidate anchor UE during a period of time, the LMF may initiate a network-controlled sidelink positioning for the OOC target UE, e.g., by the method 200 illustrated in Figure 2.

As described above with respect to Figure 2, for communicating with an OOC target UE, an LMF may designate a relay anchor UE for transmitting data from the LMF to the OOC target UE and optionally from the OOC target UE to the LMF. However, a current relay anchor UE may become unsuitable for the OOC target UE due to certain reasons. In such cases, a relay anchor UE reselection needs to be triggered and performed to select a new relay anchor UE. In different situations, the relay anchor UE reselection may be triggered by the current relay anchor UE or the LMF, and the entity performing the relay anchor UE reselection may be the OOC target UE or the LMF.

Figure 4 illustrates a flowchart of an exemplary method 400 for reselecting a relay anchor UE by an LMF according to some embodiments of the present disclosure. The method 400 illustrated in Figure 4 may be performed by at least four entities, e.g., an OOC target UE (e.g., the UE 102b) , a first relay anchor UE (i.e., the current relay anchor UE) , a second relay anchor UE (i.e., the new relay anchor UE) , and an LMF (e.g., the LMF 101) . Although the method 400 is illustrated in a system level, persons skilled in the art can understand that the method implemented in the four entities can be separately implemented and incorporated in other apparatus with the like functions.

It is also contemplated that the method 400 may include additional steps not shown. For example, before the steps (at least before step 402) illustrated in Figure 4, the LMF may transmit a relay reselection configuration to the first relay anchor UE for the first relay anchor UE to determine whether a relay anchor UE reselection is needed to be triggered. The relay reselection configuration may include at least one of a relay sidelink RSRP threshold or a relay Uu RSRP threshold. As another example, before the steps (at least before step 402) illustrated in Figure 4, the OOC target UE may transmit a measurement report to the LMF via the first relay anchor UE according to associated configurations and/or in response to a request for measurement information. Alternatively or additionally, before the steps (at least before step 402) illustrated in Figure 4, the first relay anchor UE may transmit a measurement report to the LMF according to associated configurations and/or in response to a request for measurement information.

In some embodiments, the first relay anchor UE may transmit, in step 401, a relay reselection indication to the LMF when at least one of the following occurs:

● an RSRP of sidelink signal on a unicast connection between the first relay anchor UE and the OOC target UE is below the relay sidelink RSRP threshold included in the relay reselection configuration;

● the first relay anchor UE detects a sidelink RLF;

● the first relay anchor UE receives an indication from an upper layer of the first relay anchor UE: for example, the indication may indicate not to be a relay anchor UE for the OOC target UE any longer, due to certain reasons, e.g., power consumption, workload, etc.; or

● the first relay anchor UE is going to lose a connection with the network (e.g., entering a tunnel) .

In step 402, the LMF may perform a relay anchor UE reselection to select a new relay anchor UE (e.g., the second relay anchor UE) . The LMF may perform the relay anchor UE reselection when at least one of the following occurs:

● the LMF receives the relay reselection indication from the first relay anchor UE in step 401;

● a Uu measurement report associated with the first relay anchor UE received from the first relay anchor UE or a BS indicates a Uu RSRP below the relay Uu RSRP threshold included in the relay reselection configuration;

● a sidelink measurement report associated with the first relay anchor UE received from the first relay anchor UE indicates a sidelink RSRP below the relay sidelink RSRP threshold included in the relay reselection configuration; or

● no measurement report is received from the first relay anchor UE for a period of time.

The new relay anchor UE is considered suitable by the LMF in terms of radio criteria if the sidelink and Uu link qualities of the new relay anchor UE exceed configured thresholds. Which anchor UE is selected as the new relay anchor UE is up to the LMF's implementation.

In step 403, the LMF may transmit a relay request to the second relay anchor UE, which is selected as the new relay anchor UE. The definitions regarding the relay request as described with respect to Figure 2 may also apply here.

In step 404, upon receiving the relay request from the LMF, the second relay anchor UE may establish a unicast connection with the OOC target UE. The second relay anchor UE may forward the information contained in the relay request to the OOC target UE after the unicast connection is established.

In step 405, after the unicast connection between the OOC target UE and the second relay anchor UE is established, the second relay anchor UE may transmit a relay confirmation to the LMF. In some embodiments, the relay confirmation is transmitted to the LMF after the information contained in the relay request is forwarded to the OOC target UE.

In step 406, in response to receiving the relay confirmation from the second relay anchor UE, the LMF may transmit a release request to the first relay anchor UE, requesting the first relay anchor UE to release a unicast connection between the first relay anchor UE and the OOC target UE.

In response to receiving the release request from the LMF, the first relay anchor UE may release the unicast connection between the first relay anchor UE and the OOC target UE, and then transmit, in step 407, a release confirmation to the LMF.

As a result, the LMF may transmit data to the OOC target UE via the second relay anchor UE instead of the first relay anchor UE, and optionally receive data from the OOC target UE via the second relay anchor UE.

Figure 5 illustrates a flowchart of an exemplary method 500 for reselecting a relay anchor UE by an OOC target UE according to some embodiments of the present disclosure. The method 500 illustrated in Figure 5 may be performed by at least four entities, e.g., an OOC target UE (e.g., the UE 102b) , a first relay anchor UE (i.e., a current relay anchor UE) , a second relay anchor UE (i.e., a new relay anchor UE) , and an LMF (e.g., the LMF 101) . Although the method 500 is illustrated in a system level, persons skilled in the art can understand that the method implemented in the four entities can be separately implemented and incorporated in other apparatus with the like functions.

It is also contemplated that the method 500 may include additional steps not shown. For example, before the steps illustrated in Figure 5, the LMF may transmit a first relay reselection configuration to the first relay anchor UE for the first relay anchor UE to determine whether a relay anchor UE reselection is needed to be triggered. The first relay reselection configuration may include at least one of a first relay sidelink RSRP threshold or a relay Uu RSRP threshold. Optionally, the LMF may transmit a second relay reselection configuration for the OOC target UE to the first relay anchor UE. The second relay reselection configuration for the OOC target UE may be used by the OOC target UE for a relay anchor UE reselection, and may include a second relay sidelink RSRP threshold for the OOC target UE to reselect a relay anchor UE. As another example, before the steps illustrated in Figure 5, the first relay anchor UE may transmit a relay reselection configuration to the OOC target UE via, e.g., a dedicated signaling, for the OOC target UE to determine whether a relay anchor UE reselection is needed to be trigger. The relay reselection configuration may include at least a relay sidelink RSRP threshold. In some embodiments, the relay sidelink RSRP threshold is the second relay sidelink RSRP threshold received from the LMF by the first relay anchor UE. In some other embodiments, the relay sidelink RSRP threshold is determined by the first relay anchor UE.

In step 501, the first relay anchor UE may transmit a relay reselection indication to the OOC target UE when at least one of the following occurs:

● an RSRP of Uu signal received from a BS is below the relay Uu RSRP threshold;

● the first relay anchor UE detects a Uu RLF; or the first relay anchor UE receives an indication from an upper layer of the first relay anchor UE: for example, the indication may indicate not to be a relay anchor UE for the OOC target UE any longer, due to certain reasons, e.g., power consumption, workload, etc.

In step 502, in response of receiving the relay reselection indication, the OOC target UE may perform a relay anchor UE reselection to select a new relay anchor UE (e.g., the second relay anchor UE) . The new relay anchor UE may be selected from existing anchor UEs other than the first relay anchor UE. The new relay anchor UE is considered suitable by the OOC target UE in terms of radio criteria if the sidelink quality of the OOC target UE exceeds a configured threshold. For example, an RSRP of sidelink signal received from the new relay anchor UE satisfies (or exceeds) the relay sidelink RSRP threshold included in the relay reselection configuration received from the first relay anchor UE.

In some embodiments, the OOC target UE may receive a condition (such as a sidelink link quality (e.g. RSRP) threshold) for triggering a relay anchor UE reselection from the LMF via the first relay anchor UE. In such embodiments, in the case that the condition is satisfied, the OOC target UE may perform a relay anchor UE reselection.

In step 503, the OOC target UE may establish a unicast connection with the second relay anchor UE, which is selected as the new relay anchor UE.

In step 504a, the second relay anchor UE may transmit an indication to the LMF indicating that the second relay anchor UE is selected to replace the first relay anchor UE. In step 504b, the OOC target UE may release the unicast connection between the first relay anchor UE and the OOC target UE.

According to some embodiments of the present disclosure, an OOC target UE may perform sidelink positioning with at least one IC anchor UE without a network involved. However, if a QoS requirement is not satisfied and no other suitable IC anchor UE can be found, the at least one IC anchor UE may be required to be relocated via Uu positioning by an LMF, so as to eliminate the positioning error caused by the inaccurate position of the at least one IC anchor UE.

Figure 6 illustrates a flowchart of an exemplary method 600 for relocating an IC anchor UE for sidelink positioning according to some embodiments of the present disclosure. The method 600 illustrated in Figure 6 may be performed by at least four entities, e.g., an OOC target UE (e.g., the UE 102b) , an IC anchor UE (e.g., the UE 102a) , a BS (e.g., the BS 103) , and an LMF (e.g., the LMF 101) . Although the method 600 is illustrated in a system level, persons skilled in the art can understand that the method implemented in the four entities can be separately implemented and incorporated in other apparatus with the like functions. Although only one IC anchor UE is illustrated in Figure 6, it is contemplated that there may other anchor UE (s) involved in the method 600, and the other anchor UE (s) may perform operations similar to those performed by the IC anchor UE illustrated in Figure 3.

In step 601a, the OOC target UE may perform position estimate for the OOC target UE (e.g., through sidelink positioning between the OOC target UE and anchor UE (s) ) and evaluate whether the position estimate for the OOC target UE satisfies a QoS requirement of a positioning service associated with the OOC target UE. Alternatively or additionally, in step 601b, the IC anchor UE may perform position estimate for the OOC target UE (e.g., through sidelink positioning between the OOC target UE and the IC anchor UE) and evaluate whether the position estimate for the OOC target UE satisfies the QoS requirement of the positioning service.

In some embodiments, in the case that the OOC target UE determines that a sidelink position estimation of the OOC target UE computed by the OOC target UE does not satisfy an accuracy requirement (which may be included in the QoS requirement) of the positioning service associated with the OOC target UE (e.g., the sidelink position estimation is lower than a accuracy threshold specified in the QoS requirement of the positioning service) , the OOC target UE may transmit, in step 602, a relocation request to one or more anchor UEs (including the IC anchor UE) via, e.g., sidelink positioning protocol (SLPP) message. In some embodiments, the relocation request may include at least one of the QoS requirement of the positioning service or a relocation response time.

In some embodiments, only unicast between the OOC target UE and an anchor UE is supported. In the case that the OOC target UE knows network coverage information (i.e., whether in coverage or out of coverage) of its anchor UEs, the OOC target UE may transmit the relocation request to only IC anchor UE (s) via unicast signaling. In the case that the OOC target UE does not know the network coverage information of its anchor UEs, the OOC target UE may transmit the relocation request to each anchor UE, and include a coverage request for network coverage information of the anchor UE in the relocation request.

In some embodiments, the OOC target UE may transmit the relocation request via broadcast signaling or groupcast signaling. In some embodiments, the relocation request may include a coverage request for network coverage information of each anchor UE in the relocation request in the case that the OOC target UE does not know the network coverage information of its anchor UEs.

In step 603, the IC anchor UE may transmit a request for positioning the IC anchor UE to the LMF. In some embodiments, the IC anchor UE may transmit the request for positioning the IC anchor UE to the LMF when the IC anchor UE receives a relocation request from the OOC target UE. In some embodiments, the IC anchor UE may transmit the request for positioning the IC anchor UE to the LMF when a sidelink position estimation for the OOC target UE computed by the IC anchor UE does not satisfy an accuracy requirement of the positioning service associated with the OOC target UE. In some embodiments, the request for positioning the IC anchor UE may include at least one of a QoS requirement of a positioning service or a positioning response time.

In step 604, in response of receiving the request for positioning the IC anchor UE from the IC anchor UE, the LMF may initiate Uu positioning for the IC anchor UE with the BS.

In step 605, the LMF may transmit a positioning result for the IC anchor UE to the IC anchor UE after the Uu positioning for the IC anchor UE with the BS is performed. In some embodiments, in the case that the request for positioning the IC anchor UE includes the positioning response time, the LMF may transmit the positioning result to the IC anchor UE before the positioning response time expires.

In some embodiments, in the case that the IC anchor UE receives the relocation request from the OOC target UE in the step 602, after the IC anchor UE receives the positioning result from the LMF, the IC anchor UE may transmit, in step 606, a relocation response including the positioning result for the IC anchor UE to the OOC target UE. In some embodiments, in the case that the relocation request includes the relocation response time, the IC anchor UE may transmit the relocation response to the OOC target UE before the relocation response time expires.

The OOC target UE and its anchor UE (s) may still perform sidelink positioning during the process of IC anchor UE relocation. In some embodiments where the OOC target UE initiates the process of IC anchor UE relocation (i.e., the OOC target UE sends relocation request (s) to anchor UE (s) ) , in the case that the accuracy requirement (or the QoS requirement) of the positioning service associated with the OOC target UE is satisfied by ongoing sidelink positioning before one or more relocation results from one or more IC anchor UEs are received in response to one or more relocation requests, the OOC target UE may transmit a relocation cancel request to the LMF via a sidelink relay UE, which may be an IC anchor UE or IC non-anchor UE. Upon receiving the relocation cancel request, the LMF may stop the Uu positioning for the one or more IC anchor UEs.

In some embodiments where the IC anchor UE initiates the process of IC anchor UE relocation (i.e., the IC anchor UE does not receive a relocation request from the OOC target UE) , in the case that the accuracy requirement (or the QoS requirement) is satisfied by ongoing sidelink positioning before a positioning result for the IC anchor UE is received from the LMF in response to the request for positioning the IC anchor UE, the IC anchor UE may transmit a relocation cancel request for cancelling positioning of the IC anchor UE to the LMF. Upon receiving the relocation cancel request, the LMF may stop the Uu positioning for the IC anchor UE.

In some embodiments, in the case that the OOC target UE transmits a relocation request but does not receive any relocation result before the relocation response time expires, the OOC target UE may inform an upper layer of the OOC target UE that the accuracy requirement of the positioning service is not satisfied at present and a positioning accuracy can be potentially improved after a relocation result is received from at least one IC anchor UE. The upper layer may determine to stop the relocation process or wait for the relocation result.

In some embodiments, in the case that the IC anchor UE transmits a request for positioning the IC anchor UE to the LMF but does not receive any positioning result for the IC anchor UE from the LMF before the positioning response time expires, the IC anchor UE may inform an upper layer of the IC anchor UE that the accuracy requirement of the positioning service is not satisfied at present and a positioning accuracy can be potentially improved after a positioning result for the IC anchor UE is received from the LMF. The upper layer may determine to stop the relocation process or wait for the relocation result.

In some embodiments, if the OOC target UE transmits a relocation request and receives at least one relocation result from at least one (not all) IC anchor UE before the relocation response time expires, the OOC target UE may transmit a current sidelink position estimation based on the at least one relocation result received from the at least one IC anchor UE to an upper layer of the second UE.

According to some embodiments of the present disclosure, when a calculation ability of an OOC target UE or an IC anchor UE cannot support a positioning service associated with the OOC target UE, the OOC target UE or the IC anchor UE may send a positioning assistance request to an LMF to acquire network assistance. For the OOC target UE, the positioning assistance request may be sent to the LMF via a sidelink relay UE, which may be an IC anchor UE or IC non-anchor UE.

In some embodiments, in the case that a calculation ability of an OOC target UE cannot support a positioning service associated with the OOC target UE, the OOC target UE may transmit a positioning assistance request to an LMF via a sidelink relay UE. The OOC target UE may select the sidelink relay UE based on at least one of Uu RSRP or sidelink RSRP associated with the sidelink relay UE. For example, at least one of a Uu RSRP threshold or a sidelink RSRP threshold may be configured, preconfigured, or predefined for the OOC target UE for selecting the sidelink relay UE. In some embodiments, the positioning assistance request may include at least one of: an indication indicating a responsibility of the LMF (e.g., calculating a position of the OOC target UE) , an indication of sidelink-only positioning, or information of the OOC target UE. In some embodiments, the positioning assistance request may be transmitted together with a measurement report associated with the OOC target UE in the same signaling from the OOC target UE to the LMF. In some embodiments, the positioning assistance request may be transmitted separately from the measurement report associated with the OOC target UE in a different signaling from the OOC target UE to the LMF. In response of receiving the positioning assistance request, the LMF may perform the responsibility as indicated in the positioning assistance request and transmit an assistance result for the OOC target UE to the OOC target UE via the SL relay UE.

In some embodiments, in the case that a calculation ability of an IC anchor UE cannot support a positioning service associated with an OOC target UE, the IC anchor UE may transmit a positioning assistance request to an LMF. In some embodiments, the positioning assistance request may include at least one of: an indication indicating a responsibility of the LMF (e.g., calculating a position of the OOC target UE) , an indication of sidelink-only positioning, or information of the OOC target UE. In some embodiments, the positioning assistance request may be transmitted together with a measurement report associated with the OOC target UE in the same signaling from the IC anchor UE to the LMF. In some embodiments, the positioning assistance request may be transmitted separately from the measurement report associated with the OOC target UE in a different signaling from the IC anchor UE to the LMF. In response of receiving the positioning assistance request, the LMF may perform the responsibility as indicated in the positioning assistance request and transmit an assistance result for the OOC target UE to the IC anchor UE.

Figure 7 illustrates a simplified block diagram of an exemplary apparatus 700 according to some embodiments of the present disclosure.

In some embodiments, the apparatus 700 may be or include at least part of an IC anchor UE (e.g., the UE 102a) which is capable of performing any of the operations performed by an IC anchor UE as described in the present disclosure (e.g., in any of the methods described with respect to Figures 2 -6) .

In some embodiments, the apparatus 700 may be or include at least part of an OOC target UE (e.g., the UE 102b) which is capable of performing any of the operations performed by an OOC target UE as described in the present disclosure (e.g., in any of the methods described with respect to Figures 2 -6) .

In some embodiments, the apparatus 700 may be or include at least part of an LMF (e.g., the LMF 101) which is capable of performing any of the operations performed by an LMF as described in the present disclosure (e.g., in any of the methods described with respect to Figures 2 -6) .

As shown in Figure 7, the apparatus 700 may include at least a transceiver 710 and a processor 720 coupled to the transceiver 710. In some embodiments, the transceiver 710 may include a transmitter and a receiver integrated together. In some embodiments, the transceiver 710 may include a transmitter and a receiver which are separated from each other. In some embodiments, the transceiver 710 may be a wireless transceiver.

In some embodiments, the apparatus 700 may include a non-transitory computer-readable medium 730 with computer-executable instructions 740 stored thereon. The non-transitory computer-readable medium 730 may be coupled to the processor 720 and the transceiver 710, and the computer-executable instructions 740 may be configured to be executable by the processor 720. In some embodiments, the transceiver 710, the non-transitory computer-readable medium 730, and the processor 720 may be coupled to each other via one or more local buses.

Although in Figure 7, elements such as the transceiver 710, the non-transitory computer-readable medium 730, and the processor 720 are described in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. In certain embodiments of the present disclosure, the apparatus 700 may further include other components for actual usage.

In various example embodiments, the processor 720 may include, but is not limited to, at least one hardware processor, including at least one microprocessor such as a CPU, a portion of at least one hardware processor, and any other suitable dedicated processor such as those developed based on for example Field Programmable Gate Array (FPGA) and Application Specific Integrated Circuit (ASIC) . Further, the processor 720 may also include at least one other circuitry or element not shown in Figure 7.

In various example embodiments, the non-transitory computer-readable medium 730 may include at least one storage medium in various forms, such as a volatile memory and/or a non-volatile memory. The volatile memory may include, but is not limited to, for example, an RAM, a cache, and so on. The non-volatile memory may include, but is not limited to, for example, an ROM, a hard disk, a flash memory, and so on. Further, the non-transitory computer-readable medium 730 may include, but is not limited to, an electric, a magnetic, an optical, an electromagnetic, an infrared, or a semiconductor system, apparatus, or device or any combination of the above.

Further, in various example embodiments, the apparatus 700 may also include at least one other circuitry, element, and interface, for example antenna element, and the like.

According to some embodiments, the apparatus 700 is a UE in coverage of a wireless network. The transceiver 710 and the processor 720 may be configured to perform operations in any methods described above which are performed by an IC UE. For example, the processor 720 may be configured to: perform a discovery procedure to discover a second UE which is out of coverage of the wireless network; and perform a sidelink positioning procedure with the second UE for acquiring a position of the second UE.

According to some embodiments, the apparatus 700 is an OOC target UE. The transceiver 710 and the processor 720 may be configured to perform operations in any methods described above which are performed by an OOC target UE. For example, the processor 720 may be configured to perform at least one of the following: receiving, with the transceiver 710 and from each of one or more first UEs in coverage of a wireless network, a first discovery message, and transmitting, with the transceiver 710 and to each of the one or more first UEs, a second discovery message; transmitting, with the transceiver 710 and to one or more anchor UEs for acquiring a position of the second UE, a relocation request; or transmitting, with the transceiver 710 and to an LMF of the wireless network, a positioning assistance request via a sidelink relay UE in coverage of the wireless network, and receiving, with the transceiver 710 and from the LMF, an assistance result via the sidelink relay UE.

According to some embodiments, the apparatus 700 is an LMF of a wireless network. The transceiver 710 and the processor 720 may be configured to perform operations in any methods described above which are performed by an LMF. For example, the processor 720 may be configured to perform at least one of the following: transmitting, with the transceiver 710 and to each of a set of first UEs in coverage of the wireless network, a discovery request for discovering a second UE which is out of coverage of the wireless network and whose position is requested; receiving, with the transceiver 710 and from a third UE, a request for positioning the third UE, and transmitting, with the transceiver 710 and to the third UE, a positioning result for the third UE in response to the request, wherein the third UE is in coverage of the wireless network and performing a sidelink positioning procedure with a fourth UE which is out of coverage of the wireless network for acquiring a position of the fourth UE; or receiving, with the transceiver 710 and from a fifth UE, a positioning assistance request, and transmitting, with the transceiver 710 and to the fifth UE, a positioning result for a target UE out of coverage of the wireless network in response to the positioning assistance request, wherein a calculation ability of the fifth UE cannot support a positioning service associated with the target UE.

In various example embodiments, the circuitry, parts, elements, and interfaces in exemplary apparatus, including processor and non-transitory computer-readable medium, may be coupled together via any suitable connections including, but not limited to, buses, crossbars, wiring and/or wireless lines, in any suitable ways, for example electrically, magnetically, optically, electromagnetically, and the like.

The methods of the present disclosure can be implemented on a programmed processor. However, controllers, flowcharts, and modules may also be implemented on a general purpose or special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit elements, an integrated circuit, a hardware electronic or logic circuit such as a discrete element circuit, a programmable logic device, or the like. In general, any device that has a finite state machine capable of implementing the flowcharts shown in the figures may be used to implement the processing functions of the present disclosure.

While the present disclosure has been described with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. For example, various components of the embodiments may be interchanged, added, or substituted in other embodiments. Also, all of the elements shown in each figure are not necessary for operation of the disclosed embodiments. For example, one skilled in the art of the disclosed embodiments would be capable of making and using the teachings of the present disclosure by simply employing the elements of the independent claims. Accordingly, the embodiments of the present disclosure as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the present disclosure.

The terms "includes, " "includes, " "including, " or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "a, " "an, " or the like does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that includes the element. Also, the term "another" is defined as at least a second or more. The terms "including, " "having, " and the like, as used herein, are defined as "comprising. " In this disclosure, relational terms such as "first, " "second, " and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

Claims

A first user equipment (UE) , wherein the first UE is in coverage of a wireless network, the first UE comprising:

a transceiver; and

a processor coupled to the transceiver and configured to:

perform a discovery procedure to discover a second UE which is out of coverage of the wireless network; and

perform a sidelink positioning procedure with the second UE for acquiring a position of the second UE.
The first UE of Claim 1, wherein the processor is configured to:

transmit, with the transceiver, a positioning assistance request to the LMF when a calculation ability of at least one of the first UE or the second UE cannot support a positioning service associated with the second UE, wherein the positioning assistance request includes at least one of:

an indication of sidelink-only positioning,

an indication indicating a responsibility of the LMF, or

information of the second UE.
A location management function (LMF) of a wireless network, comprising:

a transceiver; and

a processor coupled to the transceiver and configured to perform at least one of the following:

transmitting, with the transceiver and to each of a set of first user equipments (UEs) in coverage of the wireless network, a discovery request for discovering a second UE which is out of coverage of the wireless network and whose position is requested;

receiving, with the transceiver and from a third UE, a request for positioning the third UE, and transmitting, with the transceiver and to the third UE, a positioning result for the third UE in response to the request, wherein the third UE is in coverage of the wireless network and performing a sidelink positioning procedure with a fourth UE which is out of coverage of the wireless network for acquiring a position of the fourth UE; or

receiving, with the transceiver and from a fifth UE, a positioning assistance request, and transmitting, with the transceiver and to the fifth UE, a positioning result for a target UE out of coverage of the wireless network in response to the positioning assistance request, wherein a calculation ability of the fifth UE cannot support a positioning service associated with the target UE.
The LMF of Claim 3, wherein the processor is configured to transmit the discovery request in response to receiving an indication from an access and mobility management function (AMF) of the wireless network indicating to position the second UE.
The LMF of Claim 3, wherein the discovery request transmitted to each first UE includes at least one of:

one or more Uu reference signal received power (RSRP) thresholds,

a sidelink RSRP threshold,

information of the second UE,

a first request for positioning capability information of a respective first UE,

a second request for positioning capability information of the second UE,

a third request for a location and associated uncertainty of the respective first UE,

a first response time for the respective first UE to send a discovery response to the LMF; or

first information to be included in a discovery message to be sent by the respective first UE, wherein the first information includes:

a positioning request with a quality of service (QoS) requirement, and

a second response time for the second UE to send a response to the discovery message.
The LMF of Claim 5, wherein the processor is configured to receive, with the transceiver and from one or more first UEs within the set of first UEs, one or more discovery responses before the first response time expires.
The LMF of Claim 6, wherein the processor is configured to select at least one anchor UE for acquiring a position of the second UE from the one or more first UEs according to the one or more discovery responses received from the one or more first UEs.
The LMF of Claim 7, wherein the processor is configured to:

designate an anchor UE in the at least one anchor UE as a relay anchor UE; and

transmit, with the transceiver and to the relay anchor UE, a first relay request including at least one of:

a first indication indicating a responsibility of forwarding data from the LMF to the second UE,

a second indication to establish a unicast connection between the relay anchor UE and the second UE, or

second information to be transmitted to the second UE.
The LMF of Claim 8, wherein the processor is configured to transmit, with the transceiver and to the relay anchor UE, a relay reselection configuration for the relay anchor UE including at least one of a first relay sidelink RSRP threshold and a relay Uu RSRP threshold.
The LMF of Claim 9, wherein the relay anchor UE is a first relay anchor UE, and the processor is configured to perform relay anchor UE reselection to select a second relay anchor UE when at least one of the following occurs:

the LMF receives a first relay reselection indication from the first relay anchor UE;

a Uu measurement report associated with the first relay anchor UE received from the first relay anchor UE or a base station (BS) indicates a Uu RSRP below the relay Uu RSRP threshold;

a sidelink measurement report associated with the first relay anchor UE received from the first relay anchor UE indicates a sidelink RSRP below the first relay sidelink RSRP threshold; or

no measurement report is received from the first relay anchor UE for a period of time.
A second user equipment (UE) , wherein the second UE is out of coverage of a wireless network, the second UE comprising:

a transceiver; and

a processor coupled to the transceiver and configured to perform at least one of the following:

receiving, with the transceiver and from each of one or more first UEs in coverage of the wireless network, a first discovery message, and transmitting, with the transceiver and to each of the one or more first UEs, a second discovery message;

transmitting, with the transceiver and to one or more anchor UEs for acquiring a position of the second UE, a relocation request; or

transmitting, with the transceiver and to a location management function (LMF) of the wireless network, a positioning assistance request via a sidelink relay UE in coverage of the wireless network, and receiving, with the transceiver and from the LMF, an assistance result via the sidelink relay UE.
The second UE of Claim 11, wherein the first discovery message includes a request for positioning capability information of the second UE, and the processor is configured to broadcast positioning capability information of the second UE.
The second UE of Claim 11, wherein the relocation request is transmitted to the one or more anchor UEs in response to that a sidelink position estimation computed by the second UE does not satisfy an accuracy requirement of a positioning service associated with the second UE.
The second UE of Claim 13, wherein in the case that the accuracy requirement of the positioning service is satisfied by ongoing sidelink positioning before one or more relocation results are received, the processor is configured to transmit a relocation cancel request to the LMF via a sidelink relay UE.
The second UE of Claim 13, wherein:

in the case that no relocation result is received from at least one of the one or more anchor UEs after the relocation request is transmitted and before the relocation response time expires, the processor is configured to inform an upper layer of the second UE that the accuracy requirement of the positioning service is not satisfied at present and a positioning accuracy can be potentially improved after a relocation result is received from the at least one of the one or more anchor UEs; and

in the case that at least one relocation result is received from at least one anchor UE of the one or more anchor UEs after the relocation request is transmitted and before the relocation response time expires, the processor is configured to transmit a current sidelink position estimation based on at least one relocation result received from the at least one anchor UE of the one or more anchor UEs to an upper layer of the second UE.