Positioning a UE using a plurality of aerial communication systems

Abstract

A method for positioning a UE. The method is performed by a first aerial communication system (ACS). The method includes obtaining information indicating a time window duration, TWD, for the first ACS, wherein the TWD for the first ACS was determined based on timing information for the first ACS and timing information for a second ACS (1402). The method also includes performing a positioning measurement procedure within a first window period based on the indicated TWD.

Description

POSITIONING A UE USING A PLURALITY OF AERIAL COMMUNICATION SYSTEMSTECHNICAL FIELD

[0001] Disclosed are embodiments related to positioning a UE using two or more aerial communication systems (ACSs) (e.g., two or more satellites).BACKGROUND

[0002] Non-Terrestrial Network (NTN)

[0003] There is an ongoing resurgence of satellite communications. Several plans forNTNs (a.k.a., satellite networks) have been announced in the past few years. NTNs complement mobile networks on the ground by providing connectivity to underserved areas and multicast / broadcast services.

[0004] To benefit from the strong mobile ecosystem and economies of scale, adapting the terrestrial wireless access technologies, including Long Term Evolution (LTE) and New Radio (NR), for NTNs is drawing significant interest, which has been reflected in the Third Generation Partnership Project (3 GPP) standardization work.

[0005] An NTN usually includes an aerial communication system (ACS), which comprises an aerial vehicle (AV) (i.e., one or more AVs) with communication capabilities, such as a satellite placed in orbit, an unmanned aerial vehicle (UAV), or other aerial vehicle; one or more gateways (GWs) (e.g., earth-based GWs) that communicatively connect the ACS to a core network or to a base station (depending on the choice of architecture); a feeder link (i.e., a link between a GW and the AV; and an access link (a.k.a., service link) (i.e., a link between an AV and a user equipment (UE)).

[0006] A geostationary earth orbit (GEO) satellite is fed by one or several GWs which are deployed across the satellite’s targeted coverage (e.g. regional or even continental coverage). A Non-GEO satellite is served successively by several GWs as the satellite moves relative to the earth. The system ensures service and feeder link continuity between the successive serving GWs with sufficient time duration to proceed with mobility anchoring and handover.

[0007] An ACS may implement either a transparent payload or a regenerative payload(with on board processing). The ACS typically generate several beams over a given service area bounded by its field of view. The footprints of the beams are typically of elliptic shape. The field of view of an ACS depends on the on board antenna diagram and min elevation angle.

[0008] When an ACS implements a transparent payload the ACS’s AV may perform radio frequency (RF) filtering, conversion, and / or amplification. Hence, the waveform signal is un-changed, and the AV is referred to as a “transparent” AV.

[0009] When an ACS implements a regenerative payload the ACS’ AV may perform not only RF filtering, frequency conversion, and amplification, but also demodulation, decoding, switching, routing, coding, and / or modulation. This is effectively equivalent to having a base station (e.g., a 3GPP 5G base station (a.k.a., gNB)) on board the AV.

[0010] In the scenario where an NTN comprises a constellation of AVs (e.g., satellites), the NTN may employ inter-satellite links (ISL) (e.g., links between neighboring AVs). This will require regenerative payloads on board the AVs. ISL may operate in RF frequency or optical bands.

[0011] The table below identifies different types of AVs and their typical characteristics.TABLE 1

[0012] FIGs. 1-4 illustrate different example NTN architectures. FIG. 1 illustrates a networking-RAN architecture with transparent satellite. FIG. 2 illustrates a regenerative satellite without ISL, and gNB processed payload. FIG. 3 illustrates a regenerative satellite with ISL, and gNB processed payload. FIG. 4 illustrates a Next Generation (NG) Radio Access Network (RAN) with a regenerative satellite based on a NB-DU.

[0013] In addition to the above scenarios, also multi-connectivity scenarios are being discussed, where either transparent or regenerative NTN-based NG-RAN is combined with terrestrial-based NG-RAN (NR or EUTRA) or another NTN. Hence, a UE may be connected and served simultaneously by at least: one NTN-based NG-RAN and one terrestrial-based access (NR or EUTRA) or one NTN-based NG-RAN and another NTN-based NG-RAN.

[0014] An NTN can have beam -based coverage, e.g., as shown in FIG. 5. FIG. 5 illustrates a typical NTN scenario based on regenerative payload, with beam-based coverage. In the work item for NR NTN in 3GPP release 17, only the transparent payload architecture is considered.

[0015] FIG. 6 shows an example architecture of a satellite network with bent pipe transponders (i.e., the transparent payload architecture). The base station (BS) may be integrated in the GW or connected to the GW via a terrestrial connection (wire, optic fiber, wireless link).

[0016] ACSs are characterized by a path loss that is significantly higher than what is expected in terrestrial networks. To overcome the pathloss it is often required that the access and feeder links are operated in line-of-sight conditions, and that the UE is equipped with an antenna offering high beam directivity.

[0017] An ACS typically generates several beams over a given area. The footprint of a beam is usually in an elliptic shape, which has been traditionally considered as a cell (but a cell consisting of multiple beams is not precluded). The footprint of a beam is also often referred to as a spotbeam. The spotbeam may move over the Earth surface with the AV movement (and the Earth’s rotation) or may be Earth fixed with some beam pointing mechanism used by the AV tocompensate for its motion. The size of a spotbeam depends on the system design and may range from tens of kilometers to a few thousands of kilometers.

[0018] The NTN beam may in comparison to the beams observed in a terrestrial network provide a very wide footprint and may cover an area outside of the area defined by the served cell. Beam covering adjacent cells will overlap and cause significant levels of inter-cell interference, resulting from the slow decrease of the signal strength in the outwards radial direction. This is due in part to the high elevation angle and long distance to the network-side transceiver, which, compared with terrestrial cells, results in a comparatively small relative difference between the distance from the cell center to the AV and the distance from a point at the cell edge to the AV. To overcome the large levels of interference, a typical approach in NTN is to configure different cells with different carrier frequencies and polarization modes.

[0019] Three types of beams or cells are supported in NTN: (1) Earth-fixed beams / cells: provisioned by beam(s) continuously covering the same geographical areas all the time (e.g., in the case of GEO satellites); (2) Quasi -Earth-fixed beams / cells: provisioned by beam(s) covering one geographic area for a limited period and a different geographic area during another period (e.g., in the case of NGSO satellites generating steerable beams); and (3) Earth-moving beams / cells: provisioned by beam(s) whose coverage area slides over the Earth’s surface (e.g., in the case of NGSO satellites generating fixed or non-steerable beams). Throughout this disclosure the terms beam and cell are used interchangeably, unless explicitly noted otherwise.

[0020] Of the three above cell types, quasi-Earth-fixed cells and moving cells seem to be the ones most promising for actual deployment. In the case of moving cells, each cell (the footprint of its beam(s)) moves across the surface of the Earth as its serving satellite moves along its orbit. In the case of quasi-Earth-fixed cells, the cell area (as the name implies) remains fixed to the same geographical area, regardless of satellite movements. To enable this, a serving satellite has to have means for dynamically directing its beam(s), so that the same area of the Earth is covered despite the satellite’s movement. However, since the satellites orbit around the Earth, the same satellite will only be able to cover the same area on the Earth for a limited time, unless the satellite is in a geostationary orbit (and note that LEO satellites have the most traction in the satellite communication industry).

[0021] This means that different satellites will have the task of covering a certain geographical cell area at different time periods. When this task is switched from one satellite to another, this in principle means that one cell is replaced by another, although covering the same area. A similar cell replacement occurs when satellite a covering a certain geographical area switches its feeder link (because it has moved away from its old GW / gNB and become closer to another GW / gNB). As a consequence, all UEs connected in the old cell (i.e., UEs in RRC CONNECTED state) have to be handed over (or otherwise moved, e.g. using RRC connection reestablishment) from the old to the new cell, and all UEs camping on the old cell (i.e., UEs in RRC IDLE or RRC INACTIVE state) have to perform cell reselection to the new cell.

[0022] In terms of such cell switches there are two alternative principles: hard switch and soft switch. With hard switch, there is an instantaneous switch from the old to the new cell (i.e., the new cell appears at the same time as the old cell disappears). This makes completely seamless (i.e., interruption free) handover in practice impossible and creates a situation which may lead to overload of the access resources in the new cell, due to potential access attempt peaks when many UEs try to access the new cell right after the cell switch. With soft switch there is a time period during which the new and the old cell coexist (i.e. overlap), covering the same geographical area. This coexistence / overlap period allows some time for connected UEs to be handed over and for camping UEs to reselect to the new cell, which facilitates distribution of the access load in the new cell and thereby also provides better conditions for handovers with shorter interruption time. Soft switch is likely to be the most prevalent cell switch principle in quasi -Earth-fixed cell deployments.

[0023] The time when a pseudo-Earth-fixed cell will stop serving the current area (i.e., the time the pseudo-Earth-fixed cell will cease to exist) is indicated by the t-Service-rl7 information element (IE), which is broadcast in system information block 19 (SIB 19) in NR NTN (and in SIB31 in loT NTN).

[0024] Positioning in NR - Architecture

[0025] Positioning (i.e., determining the location of a UE) has been a topic in LTE standardization since 3GPP Release 9. The primary objective of positioning in LTE was to fulfillregulatory requirements for emergency call localization where the target was to achieve <50m horizontal accuracy.

[0026] Starting from the release 15 (Rel-15) specification, positioning is also supported in NR. Positioning in NR is supported by the architecture shown in FIG. 7, which is a duplicate of figure 5.1-1 of 3GPP TS 38.305 V17.5.0 (“TS 38.305”). The interactions between the gNodeB and the UE is supported via the Radio Resource Control (RRC) protocol, while the location node interfaces with the UE via the LTE positioning protocol (LPP). LPP is a common protocol to both NR and LTE. There are also interactions between the location node and the gNodeB via the NRPPa protocol.

[0027] Positioning in NR - Positioning procedure

[0028] As described in clause 5.2 of TS 38.305 V 17.5.0, the overall sequence of events applicable to the UE, NG-RAN and Location Management Function (LMF) for any location service is shown in FIG. 8, which is a duplicate of figure 5.2-1 of TS 38.305.

[0029] Note that when the AMF receives a Location Service Request in case of the UE is in CM-IDLE state, the AMF performs a network triggered service request in order to establish a signalling connection with the UE and assign a specific serving gNB or ng-eNB. The UE is assumed to be in connected mode before the beginning of the flow shown in FIG. 8, that is, any signalling that might be required to bring the UE to connected mode prior to step la is not shown. The signalling connection may, however, be later released (e.g. by the NG-RAN node as a result of signalling and data inactivity) while positioning is still ongoing.

[0030] The sequence of events shown in FIG. 8 are descried below.

[0031] An entity in the 5GC (e.g. GMLC) requests some location service (e.g. positioning) for a target UE to the serving AMF (step la), or the serving AMF for a target UE determines the need for some location service (e.g. to locate the UE for an emergency call) (step lb), or the UE requests some location service (e.g. positioning or delivery of assistance data) to the serving AMF at the NAS level (step 1c).

[0032] 2. The AMF transfers the location service request to an LMF.

[0033] 3a. The LMF instigates location procedures with the serving and possibly neighbouring ng-eNB or gNB in the NG-RAN - e.g. to obtain positioning measurements or assistance data.

[0034] 3b. In addition to step 3a or instead of step 3a, the LMF instigates location procedures with the UE - e.g. to obtain a location estimate or positioning measurements or to transfer location assistance data to the UE.

[0035] 4. The LMF provides a location service response to the AMF and includes any needed results - e.g. success or failure indication and, if requested and obtained, a location estimate for the UE.

[0036] 5a. If step la was performed, the AMF returns a location service response to the5GC entity in step la and includes any needed results - e.g. a location estimate for the UE.

[0037] 5b. If step lb occurred, the AMF uses the location service response received in step 4 to assist the service that triggered this in step lb (e.g. may provide a location estimate associated with an emergency call to a GMLC).

[0038] 5c. If step 1c was performed, the AMF returns a location service response to theUE and includes any needed results - e.g. a location estimate for the UE.

[0039] Location procedures applicable to NG-RAN occur in steps 3a and 3b in FIG. 8 and are defined in greater detail in this specification. Other steps in FIG. 8 are applicable only to the 5GC.

[0040] Steps 3a and 3b can involve the use of different position methods to obtain location related measurements for a target UE and from these compute a location estimate and possibly additional information like velocity.

[0041] Radio Access Technology (RAT) Dependent positioning methods

[0042] Positioning methods supported by LTE include: Enhanced Cell ID; Assisted GNSS, Observed Time Difference of Arrival (OTDOA), and Uplink TDOA (UTDOA), each of which is described below.

[0043] Enhanced Cell ID: Cell ID information is used to associate the UE to the serving area of a serving cell, and then additional information to determine a finer granularity of UE position.

[0044] Assisted GNSS: GNSS information retrieved by the device, supported by assistance information provided to the device from E-SMLC.

[0045] Observed Time Difference of Arrival (TDOA): UE performs positioning measurement (reference signal time difference (RSTD) measurements in this case) on downlink (DL) positioning reference signal (DL-PRS) transmitted by base stations (BSs) and reports them to the E-SMLC for position estimation.

[0046] Uplink (UL) TDOA (UTDOA): Similar to observed TDOA (OTDOA) but in uplink direction. Positioning measurements are done by the network node on UE transmitted reference signal signal for positioning measurement in UL. The measurements are reported to E- SMLC where the ultimate position estimation is performed.

[0047] Positioning methods supported by NR

[0048] In comparison to LTE, NR positioning benefits from larger bandwidth and finer beamforming and can localize a user equipment (UE) with higher accuracy and supports the following positioning methods: DL-TDOA, Multi round-trip-time (RTT), UL-TDOA, DL angle of departure (DL-AoD), UL angle of arrival (UL-AoA), and NR Enhanced Cell ID (NR E-CID).

[0049] The DL TDOA positioning method makes use of the downlink reference signal time difference (DL RSTD) measurement done by UE on positioning reference signal (PRS) transmitted by multiple transmission and reception points (TRPs). This method is similar to OTDOA in LTE.

[0050] The Multi-RTT positioning method makes use of multiple round trip time (RTT) measurements for UE position estimation. For each RTT measurement UE Rx-Tx and gNB Rx- Tx time difference measurements are used.

[0051] The UL TDOA positioning method makes use of the UL TDOA (and optionally UL SRS-RSRP) at multiple TRPs of uplink signals transmitted from UE. The RPs measure the UL TDOA (and optionally UL SRS-RSRP) of the received signals using assistance data receivedfrom the positioning server, and the resulting measurements are used along with other configuration information to estimate the location of the UE.

[0052] The DL AoD positioning method makes use of the measured DL PRS RSRP of downlink signals received from multiple TRPs, at the UE. The UE measures the DL PRS RSRP of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to locate the UE.

[0053] The UL AoA positioning method makes use of the measured azimuth and zenith of arrival at multiple TRPs of uplink signals transmitted from the UE. The TRPs measure A-AoA and Z-AoA of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to estimate the location of the UE.

[0054] NR-ECID positioning refers to techniques which use additional UE measurements and / or NR radio resource and other measurements to improve the UE location estimate.

[0055] The NR positioning modes can be categorized into: UE-Assisted, UE-Based, or Stand alone. In the UE-Assisted category, the UE performs measurements with or without assistance from the network and sends these measurements to the E-SMLC where the position calculation may take place. In the UE-Based category, the UE performs measurements and calculates its own position with assistance from the network. In the Standalone category, the UE performs measurements and calculates its own position without network assistance.

[0056] Multi-RTT positioning

[0057] Multi-RTT positioning is introduced to determine the RTT from measurements in downlink and uplink for positioning purpose. Since 3 GPP R16, NR provides DL-PRS and UL sounding reference signals (SRS) signals. The DL-PRS signal is a permuted and staggered comb- QPSK signal carrying a PN sequence, while the UL-SRS signal is a regular comb signal carrying a Zadoff-Chu sequence. Both types of signals can be correlated against at the respective end point with a corresponding replica signal. The time instance where the correlation peak occurs allows to determine the delay between transmitter and receiver.

[0058] The Multi-RTT positioning method is illustrated in FIG. 9 and FIG. 10. Firstly, for each pair of gNB and UE, RTT is calculated from (gNB Rx - gNB Tx) - (UE Rx -UE Tx). After RTTs of all pairs of gNB and UE are determined, LMF shall be able to estimate the distance between UE and each gNB and in turn the UE position provided gNB position is known.

[0059] For multi -RTT based UE location verification in NTN involving LMF, the detailed procedure can be firstly, the network should configure the positioning resources. Compared to legacy multi -RTT positioning, network can also configure the period of RTT measurement. After triggering of measurement, UE and network node periodically measure the DL-PRS and transmit UL-SRS resource(s) according to the configured positioning resources. Then, network node and / or UE may report the Rx-Tx time difference every time after measurement or in one shot after all the measurements. After the measurements, LMF determine the RTTs and calculate UE position.

[0060] Timing sequence for measuring RTT is shown in FIG. 11. In each RTT measurement, after LMF operations, in downlink, gNB shall transmit PRS at tdO, satellite receives and transmit PRS to UE at tdl and UE receives and starts to measure PRS at td2. In same manner, UE transmits a sounding reference signal (SRS) at tuO, satellite node receives and transmits SRS to gNB at tul and gNB receives and starts to measure SRS at tu2.

[0061] Given that, the RTT determined at or after tu2 as RTT from gNB view = (tu2- td0)-(tu0-td2) and the practical RTT from satellite view = (tul-tdl) -(tu0-td2), which is for UE positioning. It is worth noting that the timing sequence depicted in FIG. 11 is one of definitions of RTT, there may be other definitions to get RTT but the basic rationale of RTT is the same and the invention also can be applied.

[0062] The above time sequence shall be repeated, represented by at least Tl, T2 and T3, e.g. starting or ending or triggering or initiating at least Tl, T2 and T3 shown in FIG. 12, wherein Tl indicates when to start or end or trigger or initiate the first RTT measurement occasion , T2 indicates when to or end or trigger or initiate the second RTT measurement occasion and so on within one full multi -RTT measurement , in one example Tl equal to tdO, tdl, td2, tuO, tul or tu2 depending on different views. The time sequence with respect to Tl, T2 and T3 is often used even when more appropriate terms would be positioning measurement sequence, set of positioning measurement, positioning measurement set, repeating positioning measurement and so on.

[0063] To estimate the UE location using the RTT measurements it is important to at least know the location of TRP / satellite node transmitting PRS resource(s) based on which UE perform UE Rx-Tx time difference measurement, i.e., tu2 and tdO in the RTT equation above. For this, in the NR multi-RTT positioning where TRPs are deployed at fixed locations, providing DL-PRS ID that is unique to a TRP in the assistance data is enough as it is supported today by NR positioning specification for multi-RTT positioning method. However, in the context of NTN where single satellite node is to be used for UE position estimation, due to the mobile nature of the satellite node, LMF needs to provide time instances when the UE shall perform Rx-Tx time difference measurement. LMF can also provide similar assistance data to the satellite node to help it perform meaningful Rx-Tx time difference measurement for UE position estimation. Therefore, due to the mobile nature of satellite node transmitting PRS resource(s), conversion of RTT to distance / range for position estimation from satellite point of view shall be done as:Rangesat-ue =[Pue(tul)-Psat(tdl)] / 2c -[Pue(tu0)-Psat(td2)] / 2c.

[0064] For this equation to work, the assistance data to UE shall include, for example tdl as time instance, when it shall perform positioning measurement on DL PRS resource(s) transmitted by the satellite node. The assistance data to UE shall also include, for example tuO as time instance, to configure UE to start transmission of SRS resource(s) for positioning measurement(s). It shall also be noted that the variable Pue in the equation above denotes the location of target UE which is estimated by exploiting multiple RTT measurements.

[0065] The existing NR positioning specification supports multi-RTT based positioning for cellular network where TRPs are at fixed locations that are static and do not change over time. In NTN network, there may be one or multiple satellites involved in a positioning procedure for an NTN UE. In case only single satellite is involved in the positioning procedure, the UE is expected to perform RTT measurement with the same satellite in different locations (as shown in Figure 13). Using multiple such measurements UE position on earth shall be estimated by the network. In contrast to legacy solution where LMF provides assistance data for positioning measurement to the UE based on static TRP location, for NTN assistance data shall consider mobile TRP where multiple RTT measurements are done on the PRS transmitted by the same satellite from different locations at different time instants. In order to locate a target UE, multiple measurement instants are taken together to mimic different TRPs. At eachmeasurement instant, both the UE and the satellite (gNB) need to provide RX-TX difference reports.

[0066] In addition, when the UE needs to be positioned, if there are multiple satellite available, it is also feasible to involve those multiple satellites to perform positioning for the UE.

[0067] Scheduling and Timing

[0068] As described in clause 16.14.2.1 of TS 38.300 v 17.5.0 (“TS 38.300”), to accommodate the propagation delay in NTNs, several timing relationships are enhanced by a Common Timing Advance (Common TA) and two scheduling offsets Xoffsetand kmacillustrated in FIG. 13 (illustration of timing relationship).

[0069] Common TA is a configured offset that corresponds to the RTT between the Reference Point (RP) and the NTN payload.

[0070] Koffset is a configured scheduling offset that need to be larger or equal to the sum of the service link RTT and the Common TA.

[0071] Kmac is a configured offset that need to be larger or equal to the RTT between the RP and the gNB.

[0072] DL and UL are frame aligned at the uplink time synchronization reference point (RP) with an offset given by NTA, offset (see clause 4.3 of TS 38.211 vl7.5.0 (“TS 38.211”)).

[0073] The offset kmacis used to delay the application of a downlink configuration indicated by a MAC CE command on PDSCH, and estimation of UE-gNB RTT. It may be provided by the network when downlink and uplink frame timing are not aligned at gNB. The kmac isalso used in the random access procedure, to determine the start time of RAR window / MsgB window after a Msgl / MsgA transmission.SUMMARY

[0074] The existing NR positioning specification supports positioning for terrestrial cellular network where TRPs are at fixed locations that are static and do not change over time. In an NTN network, positioning procedure involving multiple ACSs (e.g., multiple satellites) (including serving cell / satellite and one or more than one neighbor cell / satellite) can provide more accurate, more robust, shorter consumed time positioning results compared to positioningprocedure based on a single ACS (e.g., serving cell / satellite), but it may encounter more complex conditions among different satellites (e.g., between serving satellite and one or more than one neighbor cell / satellite). Therefore, positioning involving multiple satellites is down-prioritized in 3GPP Rel-18.

[0075] Certain challenges presently exist. For instance, one of the complex issues is how to handle timing among ACSs, wherein timing difference may be several micro-seconds. For a UE involved in a positioning procedure with multiple ACSs, the UE would have different propagation delay to each ACS (e.g., different propagation delay to each ACS’ AV). In a situation where each AV is moving at the same or a different speed, each AVs’ location is not static during a positioning procedure, it is not feasible to directly reuse the existing Uu positioning procedure (e.g., multi -RTT) to position a UE in NTN networks. In other words, for each UL transmission occasion, after the UE has transmitted a UL positioning reference signal (e.g., SRS), some of the selected ACSs may fail to receive the UL signal due to large timing difference compared to other ACSs and therefore fail to obtain measurements of the UL reference signal (RS). This may occur since the UE may perform UL RS transmission referring to the timing of the serving ACS. Therefore, it is necessary to develop solutions to handle timing differences between ACSs in case of positioning with multi-ACSs.

[0076] Accordingly, in one aspect there is provided a method for positioning a UE. The method is performed by a first aerial communication system (ACS). The method includes obtaining information indicating a time window duration, TWD, for the first ACS, wherein the TWD for the first ACS was determined based on timing information for the first ACS and timing information for a second ACS (1402). The method also includes performing a positioning measurement procedure within a first window period based on the indicated TWD.

[0077] In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of an ACS causes the ACS to perform any of the ACS methods disclosed herein. In one embodiment, there is provided a carrier containing the computer program wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium. In another aspect there is provided a ACS that is configured to perform the ACS methods disclosed herein. The ACS may include memory and processing circuitry coupled to the memory.

[0078] In another aspect there is provided a method performed by a UE. The method includes receiving reference signal configuration information indicating a reference signal resource. The method also includes obtaining first timing information for first ACS. The method also includes obtaining second timing information for a second ACS. The method also includes providing the first and second timing information to a location server, the first ACS, and / or the second ACS. The method also includes after providing the timing information, transmitting a reference signal using the indicated reference signal resource.

[0079] In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of an UE causes the UE to perform any of the UE methods disclosed herein. In one embodiment, there is provided a carrier containing the computer program wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium. In another aspect there is provided a UE that is configured to perform the UE methods disclosed herein. The UE may include memory and processing circuitry coupled to the memory.

[0080] In another aspect there is provided a method performed by a location server. The method includes receiving a location services request pertaining to a UE, wherein the UE is being served by a serving ACS. The method also includes determining whether a first nonserving ACS should be configured to perform a location measurement with respect to at least a first a reference signal to be transmitted by the UE. The determination is based on first timing information indicating a propagation delay between the UE and the serving ACS and second timing information indicating a propagation delay between the UE and the first non-serving ACS.

[0081] In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of a location server causes the location server to perform any of the location server methods disclosed herein. In one embodiment, there is provided a carrier containing the computer program wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium. In another aspect there is provided a location server that is configured to perform the location server methods disclosed herein. The location server may include memory and processing circuitry coupled to the memory.

[0082] An advantage of the embodiments disclosed herein is that they provide a solution for handle timing differences between ACSs in the case where a UE is being positioning using a plurality of ACSs. For example, each ACS involved in the positioning procedure can obtain the required positioning measurements efficiently despite of large timing differences among satellites, thereby positioning accuracy involving multiple satellites in a positioning procedure is improved.BRIEF DESCRIPTION OF THE DRAWINGS

[0083] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0084] FIG. 1 illustrates a networking-RAN architecture with transparent satellite.

[0085] FIG. 2 illustrates a regenerative satellite without ISL, and gNB processed payload.

[0086] FIG. 3 illustrates a regenerative satellite with ISL, and gNB processed payload.

[0087] FIG. 4 illustrates a Next Generation (NG) Radio Access Network (RAN) with a regenerative satellite based on aNB-DU.

[0088] FIG. 5 illustrates a typical NTN scenario based on regenerative payload.

[0089] FIG. 6 shows an example architecture of a satellite network with bent pipe transponders.

[0090] FIG. 7 illustrates the UE positioning overall architecture applicable to NG-RAN.

[0091] FIG. 8 illustrates location service support by NG-RAN.

[0092] FIG. 9 illustrates a Multi-RTT positioning method.

[0093] FIG. 10 illustrates a Multi-RTT positioning method.

[0094] FIG. 11 shows a timing sequence for measuring RTT.

[0095] FIG. 12 shows a time sequence being repeated.

[0096] FIG. 13 provides an illustration of a timing relationship.

[0097] FIG. 14 illustrates a system according to an embodiment.

[0098] FIG. 15 is a signaling diagram illustrating a process according to an embodiment.

[0099] FIG. 16 is a flowchart illustrating a process according to an embodiment.

[0100] FIG. 17 is a flowchart illustrating a process according to an embodiment.

[0101] FIG. 18 is a flowchart illustrating a process according to an embodiment.

[0102] FIG. 19 is a block diagram of a UE according to an embodiment.

[0103] FIG. 20 is a block diagram of a UE according to an embodiment.

[0104] FIG. 21 is a block diagram of a base station according to an embodiment.DETAILED DESCRIPTION

[0105] FIG. 14 illustrates a system 1400 according to an embodiment. System 1400 includes a plurality of ACSs, represented by ACS 1401 and ACS 1402, and a UE 1421 that is to be positioned. As shown in FIG. 14, each ACS includes an AV that includes at least one TRP. That is, ACS 1401 includes AV 1441 which includes a TRP 1411 (e.g., an antenna system, a base station, or other TRP) and ACS 1402 includes AV 1442 which includes a TRP 1412. ACS 1401 also includes a GW 1434, which includes TRP 1436, and ACS 1402 also includes a GW 1424 which includes TRP 1436. System 1400 also includes a core network 1428 comprising a location server (LS) 1430 (e.g., an LMF). Depending on the architecture of ACS 1401, TRP 1411 may implement the functions of a base station (regenerative architecture) or TRP 1411 may merely function as a repeater or relay (transparent architecture). Likewise, TRP 1412 may implement the functions of a base station (regenerative architecture) or TRP 1412 may merely function as a repeater or relay (transparent architecture). As used herein, the term “base station” is used broadly such that, at least in some embodiments, it means one or more control units (CUs) of a base station (e.g., one or more CUs of gNB) and / or one or more distributed units (DUs) of a base station (e.g., one or more DUs of a gNB).

[0106] This disclosure describes embodiments for handling timing differences between ACSs (e.g., between TRP 1411 of a AV 1441and a TRP 1412 of AV 1442) in a positioning procedure for positioning UE 1421. In one embodiments, for each ACS involved in the positioning procedure, time window information indicating a window period is provided to the ACS (e.g., provided to the TRP on the ground or to the TRP on board the ACS’ AV), and each ACS attempts to obtain positioning measurements within the window period defined by the time window information that the ACS received. Alternatively, the UE may transmit separate ULpositioning reference signals (PRSs) (e.g., SRS) towards each different ACS. An advantage of the embodiments is that each ACS can obtain the required positioning measurements efficiently despite a large timing difference amount the ACSs; positioning accuracy involving a plurality of ACSs is thereby improved.

[0107] Alternative 1 - Same UL reference signal (a.k.a.. measurement signal) is applied

[0108] This embodiment describes a way to handle timing differences in case the sameUL positioning RS is applied.

[0109] In a positioning procedure (a.k.a., positioning session) for positioning UE 1421, multiple ACSs (e.g., ACS 1401 and ACS 1402) may be used to determine the UE’s position. The UE performs UL transmissions towards ACSs using the same resources (e.g., same SRS and same time resources). The ACSs perform measurements of the UL transmissions from the UE. As used herein a “time resource” can be any type of physical resource or radio resource expressed in terms of length of time. Examples of time resources are: a symbol, a time slot, a subframe, a radio frame, transmission time interval (TTI), an interleaving time, a slot, a sub-slot, a mini-slot, etc.

[0110] The below option are possible for ACSs to obtain UL positioning measurements.

[0111] A time window is configured to each ACS. Each ACS performs UL measurements within the window period. The time window needs to be set with a sufficient duration to accommodate the timing differences between ACSs.

[0112] In one embodiment, within each window, the UE is required to perform at least one transmission using the SRS resource. The resource index is known by each satellite. The time window configured to each ACS is sufficiently wide to cover the transmission occasion of the SRS resource. The information of potential beams / spatial relations for the SRS transmission is also informed to each ACS.

[0113] The UE may transmit an UL positioning reference signal (e.g., SRS) after UL timing advance (TA) towards the serving satellite if it is included as one ACS in the positioning session. In this case, the time window duration can be configured for the serving ACS with a small value. The estimated receiving timing of the uplink transmission by the serving ACS iscovered by the time window. Meanwhile, a large time window can be configured for other nonserving ACSs.

[0114] In an example, the time window duration (TWD) for a non-serving ACS (e.g., referred to as ACS2) can be set referring to the serving ACS (e.g., referred to as ACS1) according to the below equation:

[0115] TWD = ABS (Koffset ACSI - Koffset Acs?) (Equation 1), where ABS stands for absolute value.

[0116] In an example, the equation can be further updated as

[0117] TWD = ABS (service link RTT of ACSI - serving link RTT of ACS2) (Equation2).

[0118] In an example, the equation can be further updated as

[0119] TWD = ABS (Koffset ACSI - Koffset ACS?) + delta (Equation 3), or

[0120] TWD = ABS (service link RTT of ACSI - serving link RTT of ACS2) + delta(Equation 4).

[0121] The variable delta is added to the equation so that additional time budget can be included in the time window to accommodate the possible timing difference due to change of the UE’s timing alignment, SRS resource length etc.

[0122] The unit of time window duration and delta might be microsecond, second, slot, subframe, DRX cycle, reference signal periodicity etc.

[0123] As yet another example, the equation may be updated as:

[0124] TWD = ABS (ACSl’s RTT of service link and feeder link - ACS2’s RTT of service link and feeder link) (Equation 5). In this equation, the values of Koffset, Kmac of each ACS would be considered as inputs to derive the proper time window for the ACS. That is, as another example TWD=ABS (Koffset ACS2 + Kmac ACS2 - Koffset ACSI - Kmac ACSI), and in another example TWD=AB S (Koffset ACS2 - common TA for ACS2 - Koffset ACSI + common TA for ACSI).

[0125] The UE may repeat SRS transmissions using the same SRS frequency resource in multiple time occasions. These time occasions may be located in time in a consecutive manner ora non-consecutive manner (e.g., gap between two consecutive occasions). In this case, it is sufficient for each ACS to receive at least one time within each time window.

[0126] In one embodiment, among ACSs involved in the positioning procedure, one ACS may exchange with another ACS information that includes or identifies: Ephemeris data, Koffset, Kmac, Common TA, sub-frame number (SFN), and / or the ACS’ time window (including the start time of the window, and the window duration).

[0127] In one embodiment, the UE provides to each ACS information indicating: the index / indices (or SFN) of SRS resources that the UE will / is transmitting towards the satellite, the time occasions during a time window on which the UE will / is transmitting SRS towards the satellite, and / or a time window (including the start time of the window, and the window duration). In some embodiments, however, the time window related configuration is configured by the base station or the location server (e.g., an LMF).

[0128] Based on the above information, each ACS may calculate an RX - TX time difference. Considering possible time occasions on which the UE may have transmitted SRS towards the ACS, the satellite may determine the transmission time of the corresponding SRS by the UE. Such information may be further reported to the location server by the ACS.

[0129] In one embodiment, the serving cell provides a list of indexes of ACSs or cells associated with ACSs to be involved in positioning measurement to the UE and / or location server. In the list, all ACSs have same or proximal propagation delay between ACSs and UE, In other words, ACSs in the list have same UL timing configuration, e.g. TA, and UE can assume that ACSs in the list is able to receive SRS with common UL timing configuration without extra assistance information being provided to the ACSs.

[0130] In one embodiment, no explicit indication is received by serving cell, the UE determines the satellites which have same or proximal (e.g. compared to serving satellite) propagation delay between satellite and UE in terms of ephemeris data and UE’s position. Accordingly, UE sends the satellite indexes or cell indexes associated with satellites to the serving cell or / and location server, then serving cell or location server requests positioning procedure to those indicated satellites. The indicated satellites further report timing information of satellites to location server.

[0131] In one embodiment, for each ACS involved in the positioning procedure, a first time window can be started by the ACS upon reception of the positioning request transmitted by the LMF. A second time window (with the same or a different window duration as the first time window) may be started after expiration of the first time window, if the ACS cannot obtain the required positioning measurements within the first time window. For each positioning procedure, the ACS may start up to N time windows in order to perform the positioning measurements for the required positioning accuracy, where N can be a configured or preconfigured value.

[0132] Alternative 2 - Different UL positioning reference signals are applied

[0133] This embodiment describes a way to handle timing differences in case the different UL positioning reference signals are applied.

[0134] In a positioning procedure, multiple ACSs are selected. The UE performs UL transmissions towards ACSs using different positioning reference signals (e.g., SRS). ACSs perform measurements towards the UL transmissions.

[0135] In one embodiment, the UE maintains a separate TA value for each satellite. In total, the UE would need to maintain multiple TA values corresponding to different satellites in the positioning procedure. Additionally, for positioning procedure, the UE reports to the location server the satellite indexes / cell indexes associated with satellites and associated TA values or offset of TA values compared to serving satellite.

[0136] In one example, the UE can establish multiple radio links towards multiple satellites wherein each link is towards a different satellite simultaneously or be shared with respect to a time pattern. Such scenario is therefore referred to as a carrier aggregation scenario or multi-connectivity scenario. The UE is then configured with a different SRS resource on each radio link. The UE then performs independent SRS transmissions on each radio link towards different satellites.

[0137] In another example, upon receiving positioning request from location server or transmitting positioning request to location server, the UE performs a TA acquisition procedure (e.g. through the UE’s transmission of one or more PRACH preambles)) towards multiple satellites, which are determined by the UE or LMF to be involved in positioning measurements.Depending on UE’s capability, acquisition procedures can be conducted per satellite or per group of satellites. After receiving TA values, e.g. through RRC, MAC-CE signaling, the UE then stores the TA value for the satellites and uses them during positioning procedure with those neighboring satellites.

[0138] In some cases, the UE also might need to acquire DL synchronization before UL timing (i.e. TA) from multiple satellites because the satellites for positioning may not always be those satellites to be measured for L3 mobility or with valid ephemeris data. The serving cell signals the DL synchronization measurement configuration to UE, meanwhile, the serving cell shall trigger transmission of reference signal for DL synchronization from neighbor satellites, which may be aperiodic, consequently UE detects reference signal and uses the acquired DL timing reference for next UL transmission operations.

[0139] Example Use Case

[0140] FIG. 15 is a signaling diagram illustrating a process according to one embodiment.

[0141] The process begins with step sl502 in which an AMF 1432 serving UE 1421 determines that there is a need for a positioning service for UE 1421. For example, as described in TS 38.305, some entity in the network 1428 (e.g. GMLC) may request some location service (e.g. positioning) for UE 1421 to the AMF, or AMF 1432 itself determines the need for some location service (e.g. to locate the UE for an emergency call), or UE 1421 requests some location service (e.g. positioning or delivery of assistance data) to AMF 1432 at the Non-Access Stratum (NAS) level.

[0142] After AMF 1432 determines that there is a need for a positioning service for UE 1421, AMF 1432 transmits to LS 1430 a location services request message ml503, which is received and processed by LS 1430.

[0143] After receiving the location services request message, LS 1430 obtains timing information for ACS 1401 (which in this example is the ACS serving UE 1421) and for one or more ACSs neighboring ACS 1401, such as, for example, ACS 1402 (step sl504).

[0144] In one example, LS 1430 may obtain the timing information from UE 1421 by sending to UE 1421 a request message ml 506 requesting the timing information (or at least aportion thereof) and receiving from UE 1421 a message ml507 containing the requested timing information. The timing information may comprise Koffset, common TA, Kmac which are ACS specific, in addition, the timing information may also comprise the UE’s TA value towards each ACS. The UE may provide timing information for up to N ACSs where N may be hard coded in specs, or configured by the serving base station, or determined according to the UE’s capability. Among all detected / reported ACSs, one of the ACSs is a serving ACS which provides a control connection to the UE, based on which the UE has established its connection to the network (in this example, ACS 1401 is the serving ACS). For each ACS, the UE obtains the associated timing information by, for example, measuring downlink (DL) radio signal (e.g., synchronization signals, SS / PBCH, or CSI-RS etc) transmitted by the ACS and / or reading system information (e.g., a System Information Block (SIB)) broadcast by the ACS.

[0145] In another example, instead of or in addition to UE providing timing information to LS 1430, an ACS may provide timing information to the LS. The timing information may comprise Koffset, common TA, Kmac. If the ACS providing the timing information is a serving ACS for the UE, the ACS may also provide the UE’s TA to the LS. The ACS may provide timing information to the LS even though the satellite is not involved in any positioning procedure. Alternatively, the UE may send a signaling to the serving ACS requesting this serving satellite to send the timing information to the LS.

[0146] After receiving the timing information (from the UE and / or one or more ACSs), LS 1430 uses the obtained timing information to select one or more non-serving ACSs which have same or similar timing (e.g., same or similar propagation delay towards the UE) as ACS 1401 (the serving ACS) (step sl508). The propagation delay between the UE and each ACS is determined (e.g., estimated) using the timing information (e.g., Koffset, common TA, Kmac).

[0147] In an example, a non-serving ACS gives similar propagation delay as the serving ACS if both ACSs have similar Koffset values (e.g., the difference between the Koffset values of both ACSs is less than a given threshold). In another example, a non-serving ACS gives similar propagation delay as the serving ACS if both ACSs have similar RTT (equal to Koffset plus Kmac) values (the difference between RTT values of both ACSs is less than a given threshold).

[0148] After selecting the ACSs, LS 1430 calculates, for each selected ACS, a time window duration (TWD) for the ACS using, for example, one of the TWD equations described above (step si 510).

[0149] LS 1430 further sends positioning configurations to each selected ACS (e.g., to the TRP on the AV of the ACS or to the TRP of the GW of the ACS) and the UE (see message ml512, ml514, and ml516 in FIG. 15). A positioning configuration may comprise at least SRS resource configuration (e.g., information identifying an SRS, a time resource that will be used by UE to transmit the SRS, and frequency resource that will be used by UE to transmit the SRS) and a measurement window configuration, which includes the calculated TWD. A configuration provided to the UE may comprise at least the SRS resource configuration.

[0150] Upon reception of a positioning configuration comprising SRS resource configuration and a time window configuration for an ACS, the UE may forward the positioning configuration to the ACS if the ACS has not received that configuration from LS 1430.

[0151] The UE starts transmission of SRS towards ACSs according to the received positioning configuration. In one embodiment, each ACS shall start a measurement window (a.k.a., reception window) sufficiently before the time when the SRS transmitted by the UE is expected to arrive at the ACS. Each ACS may determine when to start the window by the itself according to the time when the UE will start to transmit SRS. Alternatively, LS 1430 may signal a time offset to a ACS referring to SRS transmission time, based on which, the ACS can determine the start time for the measurement window. Each ACS shall keep active during the duration of the window (a.k.a., the window period) in order to not miss reception of the corresponding SRS transmissions initiated by the UE.

[0152] Each ACS obtains positioning measurements towards SRS. For example, with respect to ACS 1401, TRP 1411 obtains the positioning measurements or TRP 1436 obtains the positioning measurement, depending on choses architecture. Additionally, in the case where the ACSs are further configured to transmit DL positioning reference signals (PRSs), the UE may obtain positioning measurements based on the PRSs transmitted by the ACSs. After the UE and each ACS sends positioning measurements to LS 1430 (see messages ml 520, ml 521, and ml522). LS 1430 can compute the UE’s location.

[0153] Any signaling exchanged between a UE and the location server may be carried via one of the following: an LPP message or a Non-Access Stratum (NAS) message. Any signaling exchanged between a base station (e.g., gNB) and the location server is carried via one of the below signaling alternatives: an NRPPa message or NGAP signaling.

[0154] FIG. 16 is a flowchart illustrating a process 1600 according to an embodiment for positioning UE. Process 1600 is performed by ACS 1401 (hereafter the first ACS). Process 1600 may begin in step sl602.

[0155] Step si 602 comprises obtaining information indicating a time window duration, TWD, for the first ACS, wherein the TWD for the first ACS was determined based on timing information for the first ACS and timing information for a second ACS (e.g., ACS 1402).

[0156] Step sl604 comprises performing a positioning measurement procedure within a first window period based on the indicated TWD.

[0157] In some embodiments, the first ACS comprises AV 1441 and GW 1434, and AV 1441 comprises TRP 1411, and the method is performed by AV 1441.

[0158] In some embodiments, the first ACS comprises AV 1441 and GW 1434, and GW 1434 comprises TRP 1436, and the method is performed by the GW.

[0159] In some embodiments, the first ACS is a serving ACS serving the UE, or the second ACS is the serving ACS serving the UE.

[0160] In some embodiments, the timing information for the first ACS comprises a first offset value and / or a first timing advance value, and the timing information for the second ACS comprises a second offset value and / or a second timing advance value.

[0161] In some embodiments, the TWD for the first ACS was determined by calculating: K0ffset_Acsi - Koffset_Acs2, where Koffset_Acsi is the first offset value, and Koffset_Acs2 is the second offset value.

[0162] In some embodiments, the positioning measurement procedure comprises attempting to obtain positioning measurements within the first window period.

[0163] In some embodiments, the method further comprises the first ACS obtaining the positioning measurements within the first window period, and the method optionally furthercomprises the first ACS obtaining positioning measurements within N other window periods, where N > 1.

[0164] In some embodiments, the first ACS does not obtain the positioning measurements within the first window period, and as a result of not obtaining the positioning measurements within the first window period, the method further comprises the first ACS attempting to obtain positioning measurements within a second window period.

[0165] FIG. 17 is a flowchart illustrating a process 1700, according to an embodiment, performed by UE 1421. Process 1700 may begin in step sl702.

[0166] Step si 702 comprises receiving reference signal configuration information indicating a reference signal resource.

[0167] Step sl704 comprises obtaining first timing information for a first ACS (e.g., ACS 1401).

[0168] Step si 706 comprises obtaining second timing information for a second ACS (e.g., ACS 1402).

[0169] Step si 708 comprises providing the first and second timing information to a location server (e.g., LS 1430), the first ACS, and / or the second ACS.

[0170] Step si 710 comprises, after providing the timing information, transmitting(si 710) a reference signal using the indicated reference signal resource.

[0171] In some embodiments, the first ACS is a serving ACS serving the UE, or the second ACS is the serving ACS serving the UE.

[0172] In some embodiments, the timing information for the first ACS comprises a first offset value and / or a first timing advance value, and the timing information for the second ACS comprises a second offset value and / or a second timing advance value.

[0173] FIG. 18 is a flowchart illustrating a process 1800, according to an embodiment, that is performed by LS 1430. Process 1800 may begin in step sl802.

[0174] Step si 802 comprises receiving a location services request pertaining to a user equipment, UE (1421), wherein the UE is being served by a serving aerial communication system, ACS (1401, 1402).

[0175] Step sl804 comprises determining whether a first non-serving ACS (e.g., ACS 1401 or ACS 1402) should be configured to perform a location measurement with respect to at least a first a reference signal to be transmitted by the UE, wherein the determination is based on first timing information indicating a propagation delay between the UE and the serving ACS and second timing information indicating a propagation delay between the UE and the first nonserving ACS.

[0176] In some embodiments, the method further comprises, prior to determining whether a first non-serving ACS should be configured to perform the location measurement, obtaining the first timing information and the second timing information.

[0177] In some embodiments, obtaining the first timing information and the second timing information comprises transmitting a request message to the UE and receiving a response message responsive to the request message, and the response message comprises the first and second timing information.

[0178] In some embodiments, the method further comprises, as a result of determining that first non-serving ACS should be configured to perform the location measurement, initiating providing a positioning configuration to the first non-serving ACS.

[0179] In some embodiments, the method further comprises, prior to initiating providing a positioning configuration to the first non-serving ACS, calculating a time window duration for the first non-serving ACS using at least some of the first timing information and at least some of the second timing information.

[0180] In some embodiments, the first timing information comprises a first offset value and / or a first timing advance value, and the second timing information comprises a second offset value and / or a second timing advance value.

[0181] In some embodiments, the determination is based a difference between the propagation delay between the UE and the serving ACS and the propagation delay between the UE and the first non-serving ACS.

[0182] In some embodiments, the determination is based a difference between the propagation delay between the UE and the serving ACS and the propagation delay between the UE and the first non-serving ACS.1

[0183] FIG. 19 is a block diagram of location server 1430, according to some embodiments. As shown in FIG. 19, location server 1430 may comprise: processing circuitry (PC) 1902, which may include one or more processors (P) 1955 (e.g., one or more general purpose microprocessors and / or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (e.g., location server 1430 may be a distributed computing apparatus comprising two or more computers or a monolithic computing apparatus consisting of a single computer); at least one network interface 1948 (e.g., a physical interface or air interface) comprising a transmitter (Tx) 1945 and a receiver (Rx) 1947 for enabling location server 1430 to transmit data to and receive data from other nodes connected to network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1948 is connected (physically or wirelessly) (e.g., network interface 1948 may be coupled to an antenna arrangement comprising one or more antennas for enabling location server 1430 to wirelessly transmit / receive data); and a storage unit (a.k.a., “data storage system”) 1908, which may include one or more non-volatile storage devices and / or one or more volatile storage devices. In embodiments where PC 1902 includes a programmable processor, a computer readable storage medium (CRSM) 1942 may be provided. CRSM 1942 may store a computer program (CP) 1943 comprising computer readable instructions (CRI) 1944. CRSM 1942 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1944 of computer program 1943 is configured such that when executed by PC 1902, the CRI causes location server 1430 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, location server 1430 may be configured to perform steps described herein without the need for code. That is, for example, PC 1902 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and / or software.

[0184] FIG. 20 is a block diagram of UE 1421, according to some embodiments. As shown in FIG. 20, UE 1421 may comprise: processing circuitry (PC) 2002, which may include one or more processors (P) 2055 (e.g., one or more general purpose microprocessors and / or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like); communication circuitry 2048, which is coupled to an antenna arrangement 2049 comprising one or more antennas and which comprises a transmitter (Tx) 2045 and a receiver (Rx) 2047 for enabling UE 1421 to transmit data and receive data (e.g., wirelessly transmit / receive data); and a storage unit (a.k.a., “data storage system”) 2008, which may include one or more non-volatile storage devices and / or one or more volatile storage devices. In embodiments where PC 2002 includes a programmable processor, a computer readable storage medium (CRSM) 2042 may be provided. CRSM 2042 may store a computer program (CP) 2043 comprising computer readable instructions (CRI) 2044. CRSM 2042 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 2044 of computer program 2043 is configured such that when executed by PC 2002, the CRI causes UE 1421 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, UE 1421 may be configured to perform steps described herein without the need for code. That is, for example, PC 2002 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and / or software.

[0185] FIG. 21 is a block diagram of a base station 2100 (e.g., TRP 1411, 1412, 1424, or 1436), according to some embodiments for performing the TRP methods disclosed herein. As shown in FIG. 21, base station 2100 may comprise: processing circuitry (PC) 2102, which may include one or more processors (P) 2155 (e.g., a general purpose microprocessor and / or one or more other processors, such as an application specific integrated circuit (ASIC), field- programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (i.e., base station may be a distributed computing apparatus or a monolithic computing apparatus); a network interface 2168 comprising a transmitter (Tx) 2165 and a receiver (Rx) 2167 for enabling base station 2100 to transmit data to and receive data from other nodes connected to a network 110 (e.g., an Internet Protocol (IP) network) to which network interface 2168 is connected; communication circuitry 2148 (e.g., radio transceiver circuitry comprising an Rx 2147 and a Tx 2145) coupled to an antenna system 2149 for wireless communication with UEs or other nodes; and a storage unit (a.k.a., “data storage system”) 2108, which may include one or more nonvolatile storage devices and / or one or more volatile storage devices. In embodiments where PC2102 includes a programmable processor, a computer readable storage medium (CRSM) 2142 may be provided. CRSM 2142 may store a computer program (CP) 2143 comprising computer readable instructions (CRI) 2144. CRSM 2142 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 2144 of computer program 2143 is configured such that when executed by PC 2102, the CRI causes base station 2100 to perform steps described herein (e.g., steps described herein with reference to one or more flow charts). In other embodiments, base station 2100 may be configured to perform steps described herein without the need for code. That is, for example, PC 2102 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and / or software.

[0186] Summary of Various Embodiments

[0187] Al. A method for positioning a UE, the method being performed by a first ACS (e.g., by a base station of the first ACS) and comprising: obtaining information indicating a time window duration (TWD) for the first ACS, wherein the TWD for the first ACS was determined based on timing information for the first ACS and timing information for a second ACS; wherein the first ACS is configured to obtain (or attempt to obtain) positioning measurements within a window period based on the indicated TWD.

[0188] A2. The method of embodiment Al, wherein the first ACS comprises a first aerial vehicle, AV, and a first gateway, GW, the first AV comprises a base station, and the method is performed by the base station on board the first AV.

[0189] A3. The method of embodiment Al, wherein the first ACS comprises a first aerial vehicle, AV, and a first gateway GW, the first GW comprises a base station, and the method is performed by the base station of the GW.

[0190] A4. The method of embodiment Al or A2 or A3, wherein the first ACS is a serving ACS serving the UE, or the second ACS is the serving ACS serving the UE.

[0191] A5. The method of any one of embodiments A1-A4, wherein the timing information comprises: a first offset value (e.g, Koffset), a second offset value (e.g,. Kmac), a first timing advance value (e.g., common TA), and / or a second timing advance value (e.g., UE’s TA)associated with a serving ACS, and / or a first offset value (e.g, Koffset), a second offset value (e.g,. Kmac), a first timing advance value (e.g., common TA), and / or a second timing advance value (e.g., UE’s TA) associated with a non-serving ACS.

[0192] A6. The method of any one of embodiments A1-A6, wherein the method further comprises the first ACS attempting to obtain positioning measurements within a window period based on the indicated TWD.

[0193] A7. The method of embodiment A6, wherein the method further comprises the first ACS obtaining the positioning measurements within the window period.

[0194] A8. The method of embodiment A6, wherein the method further comprises the first ACS not obtaining the positioning measurements within the window period; and as a result of not obtaining the positioning measurements within the window period, attempting to obtain positioning measurements within a second window period.

[0195] A9. An ACS configured to perform the method of any one of embodiments Al-A8.

[0196] Bl. A method performed by UE 1421, the method comprising: receiving reference signal configuration information indicating a reference signal resource; obtaining first timing information for first ACS; obtaining second timing information for a second ACS; providing the first and second timing information to a location server, the first ACS 1401, and / or the second ACS; and after providing the timing information, transmitting a reference signal using the indicated reference signal resource.

[0197] B2. The method of embodiment Bl, wherein the first ACS is a serving ACS serving the UE, or the second ACS is the serving ACS serving the UE.

[0198] B3. The method of embodiment Bl or B2, wherein the timing information comprises: a first offset value (e.g, Koffset), a second offset value (e.g,. Kmac), a first timing advance value (e.g., common TA), and / or a second timing advance value (e.g., UE’s TA) associated with the serving ACS, and / or a first offset value (e.g, Koffset), a second offset value (e.g,. K mac ), a first timing advance value (e.g., common TA), and / or a second timing advance value (e.g., UE’s TA) associated with the non-serving ACS.

[0199] B4. A UE configured to perform the method of embodiment Bl or B2 or B3.

[0200] Cl. A method performed by location server, the method comprising: receiving a location services request pertaining to a UE, wherein the UE is being served by a serving ACS; and determining whether a first non-serving ACS should be configured to perform a location measurement with respect to at least a first a reference signal to be transmitted by the UE, wherein the determination is based on first timing information indicating a propagation delay between the UE and the serving ACS and second timing information indicating a propagation delay between the UE and the first non-serving ACS.

[0201] C2. The method of embodiment Cl, wherein the method further comprises, prior to determining whether a first non-serving ACS should be configured to perform the location measurement, obtaining the first timing information and the second timing information.

[0202] C3. The method of embodiment C2, wherein obtaining the first timing information and the second timing information comprises transmitting a request message to the UE and receiving a response message responsive to the request message, and the response message comprises the first and second timing information.

[0203] C4. The method of any one of embodiments C1-C3, wherein the method further comprise, as a result of determining that first non-serving ACS should be configured to perform the location measurement, initiating providing a positioning configuration to the first non-serving ACS.

[0204] C5. The method of embodiment C4, wherein the method further comprises, prior to initiating providing a positioning configuration to the first non-serving ACS, calculating a time window duration for the first non-serving ACS using at least some of the first timing information and at least some of the second timing information.

[0205] C6. The method of any one of embodiments C1-C5, wherein the timing information comprises: a first offset value (e.g, Koffset), a second offset value (e.g,. Kmac), a first timing advance value (e.g., common TA), and / or a second timing advance value (e.g., UE’s TA) associated with the serving ACS, and / or a first offset value (e.g, Koffset), a second offset value (e.g,. K mac ), a first timing advance value (e.g., common TA), and / or a second timing advance value (e.g., UE’s TA) associated with the non-serving ACS.

[0206] C7. A location server configured to perform the method of any one of embodiments C1-C6.

[0207] DI. A computer program comprising instructions, executable by processing circuitry of an apparatus, for configuring the apparatus to perform the method of any one of the above embodiments.

[0208] D2. A carrier containing the computer program of embodiment DI, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

[0209] Conclusion

[0210] As described herein, this disclosure describes selection criteria for selecting satellites / TRPs (e.g., satellites with same or similar timing are selected) to participate in the position process for positioning a UE. Moreover, a window is configured to each satellite to accommodate timing differences between satellites. During the window period, the UE transmits one or multiple SRS signals to ensure each satellite at least receives one SRS transmission and therefore able to obtain corresponding UL measurement. Additionally, timing information may be exchanged between UE and LMF, between satellite and LMF, between satellites.

[0211] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0212] As used herein transmitting a message “to” or “toward” an intended recipient encompasses transmitting the message directly to the intended recipient or transmitting the message indirectly to the intended recipient (i.e., one or more other nodes are used to relay the message from the source node to the intended recipient). Likewise, as used herein receiving a message “from” a sender encompasses receiving the message directly from the sender or indirectly from the sender (i.e., one or more nodes are used to relay the message from the sender to the receiving node). Further, as used herein “a” means “at least one” or “one or more.”

[0213] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

Claims

CLAIMS1. A method (1600) for positioning a user equipment, UE (1421), the method being performed by a first aerial communication system, ACS (1401), and the method comprising: obtaining (si 602) information indicating a time window duration, TWD, for the first ACS, wherein the TWD for the first ACS was determined based on timing information for the first ACS and timing information for a second ACS (1402); and performing (si 604) a positioning measurement procedure within a first window period based on the indicated TWD.

2. The method of claim 1, wherein the first ACS (1401) comprises a first aerial vehicle, AV (1441), and a first gateway (1434), GW, the first AV comprises a transmission and reception point, TRP (1411), and the method is performed by the first AV.

3. The method of claim 1, wherein the first ACS (1401) comprises a first aerial vehicle, AV (1441), and a first gateway GW (1434), the first GW comprises a transmission and reception point, TRP (1436), and the method is performed by the GW.

4. The method of claim 1 or 2 or 3, wherein the first ACS is a serving ACS serving the UE, or the second ACS is the serving ACS serving the UE.

5. The method of any one of claims 1-4, wherein the timing information for the first ACS comprises a first offset value and / or a first timing advance value, and the timing information for the second ACS comprises a second offset value and / or a second timing advance value.

6. The method of claim 5, wherein the TWD for the first ACS was determined by calculating:Koffset_Acsi - Koffset_Acs2, whereKOffset_Acsi is the first offset value, andKOffset_Acs2 is the second offset value.

7. The method of any one of claims 1-6, wherein the positioning measurement procedure comprises attempting to obtain positioning measurements within the first window period.

8. The method of claim 7, wherein the method further comprises the first ACS obtaining the positioning measurements within the first window period, and the method optionally further comprises the first ACS obtaining positioning measurements within N other window periods, where N > 1.

9. The method of claim 7, wherein the first ACS does not obtain the positioning measurements within the first window period, and as a result of not obtaining the positioning measurements within the first window period, the method further comprises the first ACS attempting to obtain positioning measurements within a second window period.

10. A first aerial communication system, ACS (1401), the first ACS being configured to perform a process comprising: obtaining (si 602) information indicating a time window duration, TWD, for the first ACS, wherein the TWD for the first ACS was determined based on timing information for the first ACS and timing information for a second ACS (1402); and performing (si 604) a positioning measurement procedure within a first window period based on the indicated TWD.

11. The first ACS of claim 10, wherein the first ACS is further configured to perform the method of any one of claims 2-9.

12. A method (1700) performed by a user equipment, UE (1 21), the method comprising: receiving (si 702) reference signal configuration information indicating a reference signal resource; obtaining (si 704) first timing information for a first aerial communication system, ACS (1401); obtaining (sl706) second timing information for a second ACS (1402); providing (sl708) the first and second timing information to a location server (1430), the first ACS (1401), and / or the second ACS (1402); and after providing the timing information, transmitting (si 710) a reference signal using the indicated reference signal resource.

13. The method of claim 12, wherein the first ACS is a serving ACS serving the UE, or the second ACS is the serving ACS serving the UE.

14. The method of claim 12 or 13, wherein the timing information for the first ACS comprises a first offset value and / or a first timing advance value, and the timing information for the second ACS comprises a second offset value and / or a second timing advance value.

15. A user equipment, UE (1421), the UE being configured to perform a method comprising: receiving (si 702) reference signal configuration information indicating a reference signal resource; obtaining (si 704) first timing information for a first aerial communication system, ACS(1401); obtaining (s!706) second timing information for a second ACS (1402);providing (sl708) the first and second timing information to a location server (1430), the first ACS (1 01), and / or the second ACS (1402); and after providing the timing information, transmitting (si 710) a reference signal using the indicated reference signal resource.

16. The UE of claim 15, wherein the timing information for the first ACS comprises a first offset value and / or a first timing advance value, and the timing information for the second ACS comprises a second offset value and / or a second timing advance value.

17. A method (1800) performed by a location server (1430), the method comprising: receiving (sl802) a location services request pertaining to a user equipment, UE (1421), wherein the UE is being served by a serving aerial communication system, ACS (1401, 1402); and determining (sl804) whether a first non-serving ACS (1401, 1402) should be configured to perform a location measurement with respect to at least a first a reference signal to be transmitted by the UE, wherein the determination is based on first timing information indicating a propagation delay between the UE and the serving ACS and second timing information indicating a propagation delay between the UE and the first non-serving ACS.

18. The method of claim 17, wherein the method further comprises, prior to determining whether a first non-serving ACS should be configured to perform the location measurement, obtaining the first timing information and the second timing information.

19. The method of claim 18, wherein obtaining the first timing information and the second timing information comprises transmitting a request message to the UE and receiving a response message responsive to the request message, and the response message comprises the first and second timing information.

20. The method of any one of claims 17-19, wherein the method further comprises, as a result of determining that first non-serving ACS should be configured to perform the location measurement, initiating providing a positioning configuration to the first non-serving ACS.

21. The method of claim 20, wherein the method further comprises, prior to initiating providing a positioning configuration to the first non-serving ACS, calculating a time window duration for the first non-serving ACS using at least some of the first timing information and at least some of the second timing information.

22. The method of any one of claims 17-21, wherein the first timing information comprises a first offset value and / or a first timing advance value, and the second timing information comprises a second offset value and / or a second timing advance value.

23. The method of any one of claims 17-22, wherein the determination is based a difference between the propagation delay between the UE and the serving ACS and the propagation delay between the UE and the first non-serving ACS.

24. The method of claim 23, wherein the determination is based a difference between the propagation delay between the UE and the serving ACS and the propagation delay between the UE and the first non-serving ACS.

25. A location server (1430), the location server being configured to perform a method comprising: receiving (sl802) a location services request pertaining to a user equipment, UE (1421), wherein the UE is being served by a serving aerial communication system, ACS (1401, 1402); anddetermining (sl804) whether a first non-serving ACS (1401, 1402) should be configured to perform a location measurement with respect to at least a first a reference signal to be transmitted by the UE, wherein the determination is based on first timing information indicating a propagation delay between the UE and the serving ACS and second timing information indicating a propagation delay between the UE and the first non-serving ACS.

26. The first location server of claim 25, wherein the location server is further configured to perform the method of any one of claims 18-24.

27. A computer program comprising instructions, executable by processing circuitry of an apparatus, for configuring the apparatus to perform the method of any one of the above method claims.

28. A carrier containing the computer program of claim 27, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

Images