GNSS independent NTN with network-controlled / assisted UE position

Abstract

According to some embodiments, a method is performed by a User Equipment, UE, (402) in a cellular communications system (400). The method comprises: receiving (1210) position assistance information from a Non-Terrestrial Network, NTN, node (408) in a NTN cell (410); obtaining (1220) a pseudo-position of the UE (402) based on the position assistance information; and performing (1230) one or more actions with respect to one or more NTN cells (410), based on the pseudo-position of the UE (402).

Description

[0001] GNSS INDEPENDENT NTN WITH NETWORK-CONTROLLED / ASSISTED UE POSITION

[0002] TECHNICAL FIELD

[0003] Embodiments of the present disclosure are directed to wireless communications and, more particularly to position assistance information from a Non-Terrestrial Network, NTN, for Global Navigation Satellite System, GNSS, independent positioning.

[0004] BACKGROUND

[0005] The present disclosure relates to a cellular communications system including NonTerrestrial Network (NTN) cells and, more specifically, positioning of User Equipments (UEs) in such a system.

[0006] There is an ongoing resurgence of non-terrestrial based communications, such as communications using satellites, high altitude balloons, and other non-terrestrial vehicles. The target services vary, from backhaul and fixed wireless, to transportation, to outdoor mobile, to Internet of Things (loT). Satellite networks could complement mobile networks on the ground by providing connectivity to underserved areas and multicast / broadcast services.

[0007] 3rd Generation Partnership Project (3GPP) supports since Release 17 NR, LTE-MTC and NB-IoT based Non-Terrestrial Networks (NTN). NTN includes both satellite communication and communications using high-altitude platforms (HAPS). The present disclosure focuses on satellite communication, but the provided description could also be applied to a HAPS network. A satellite radio access network usually includes the following components:

[0008] • A satellite that refers to a space-home platform.

[0009] • An earth-based gateway that connects the satellite to a base station or a core network, depending on the choice of architecture.

[0010] • Feeder link that refers to the link between a gateway and a satellite

[0011] • Service link that refers to the link between a satellite and a UE.

[0012] Depending on the orbit altitude, a satellite may be categorized as low earth orbit (LEO), medium earth orbit (MEO), or geostationary earth orbit (GEO) satellite: • LEO: typical heights ranging from 500 - 1,500 km, with orbital periods ranging from 90 - 120 minutes.

[0013] • MEO: typical heights ranging from 5,000 - 25,000 km, with orbital periods ranging from 3 - 15 hours.

[0014] • GEO: height at about 35,786 km, with an orbital period matching the rotation of earth, i.e., of 24 hours.

[0015] A communication satellite typically generates several beams over a given area. The footprint of a beam on earth is usually in an elliptic shape. Each beam is typically providing coverage to cell in a 5G or 4G network. The footprint of a beam is also often referred to as a spotbeam. The footprint of a beam may move over the earth surface with the satellite movement or may be earth fixed thanks to some beam pointing mechanism used by the satellite to compensate for its motion. The size of a spotbeam depends on the system design, which may range from tens of kilometers to a few thousands of kilometers.

[0016] Figure 1 shows an example architecture of a non-terrestrial network according to the so-called transparent architecture where the base station is part of the gateway. Another popular architecture is the regenerative architecture where the BS is located on board the satellite. The depicted elevation angle of the service link is important as it impacts the distance between the satellite and the device, and the velocity of the satellite relative to the device.

[0017] As illustrated, a satellite may support a set of beams for providing coverage to a set of cells on earth. To provide continuous coverage, adjacent beams are often configured to overlap which creates significant inter-cell interference.

[0018] Figure 2 illustrates a satellite access node (SAN) 200. A SAN 200 may include both terrestrial and non-terrestrial components. For example, the SAN 200 shown in Figure 2 includes non-NTN infrastructure 120 that may host gNB functionality, and a terrestrial gateway 106 that is connected to anon-terrestrial component, such as a satellite 102, via a feeder link 112. The satellite 102 may include various components, such as a transceiver unit, a radio distribution network (RDN) and an antenna array (AA).

[0019] Two basic architectures can be distinguished for satellite communication networks, depending on the functionality of the satellites in the system. These two architectures are:

[0020] • Transparent Payload (also referred to as bent pipe architecture): In the transparent payload architecture, the satellite forwards the received signal between the terminal (e.g., UE) and the network equipment on the ground with only amplification and a shift from uplink frequency to downlink frequency. When applied to the 3GPP NR architecture and terminology, the transparent payload architecture means that the gNodeB (gNB) is located on the ground, and the satellite forwards signals / data between the gNB and the UE.

[0021] • Regenerative Payload: In the regenerative payload architecture, the satellite includes on-board processing to demodulate and decode the received signal and regenerate the signal before sending it back to the earth. When applied to the 3 GPP NR architecture and terminology, the regenerative payload architecture means that the gNB is located in the satellite.

[0022] Figure 3A illustrates a transparent payload architecture in which various network protocol layers are 310 are hosted in terrestrial infrastructure, while Figure 3B illustrates a regenerative payload architecture in which some network protocol layers 302 are hosted in terrestrial infrastructure, while other network protocol layers 330 are hosted in satellites 102. This architecture enables various network functions, such as backhaul routing, to be performed in the non-terrestrial nodes, which can, for example, allow for routing of data over inter-satellite links 350. In the work item for NR NTN in 3GPP Release 17, only the transparent payload architecture is considered.

[0023] Propagation delays

[0024] Propagation delay is a main physical phenomenon in a satellite communication system that makes the design different from that of a terrestrial mobile system. For a bent pipe satellite network, the following delays are relevant.

[0025] • One-way delay: from the BS to the UE via the satellite, or the other way around

[0026] • Round-trip delay: from the BS to the UE via the satellite and from the UE back to the BS via the satellite

[0027] • Differential delay: the delay difference of two selected points in the same spotbeam

[0028] The propagation delay depends on the length of the signal path, which further depends on the elevation angles of the satellite seen by the BS and UE on the ground. According to 3GPP TR 38.811 V15.4.0 “Study on New Radio (NR) to support non-terrestrial networks“ round-trip delays in the range 10-30 ms for LEO and around 500 ms for a GEO satellite system are expected. In contrast, the round-trip time is normally no more than 1 ms for typical terrestrial cellular networks. Generally, within spot beam covering one cell, the delay can be divided into a common delay component and a differential delay component. The common delay is the same for all UEs in the cell and is determined with respect to a reference point in the spot beam. In contrast, the differential delay is different for different UEs and depends on the difference between the common delay and the propagation delay between the UE and the BS.

[0029] The differential delay is mainly due to the different path lengths of the service links, since the feeder link is normally the same for terminals in the same spotbeam. Further, the differential delay is mainly determined by the size of the spotbeam. It may range from submillisecond (for spotbeam on the order of tens of kilometers) to tens of milliseconds (for spotbeam on the order of thousands of kilometers).

[0030] Doppler effects

[0031] Doppler is another major physical phenomenon that shall be properly taken into account in a satellite communication system. The following Doppler effects are particularly relevant.

[0032] • Doppler shift: the shift of the signal frequency due to the motion of the transmitter, the receiver, or both.

[0033] • Doppler variation rate: the derivative of the Doppler shift function of time, i.e., it characterizes how fast the Doppler shift evolves over time.

[0034] Doppler effects depend on the relative speed of the satellites and the UE and the carrier frequency.

[0035] For GEO satellites, they are fixed in principle relative to the surface of the Earth and thus do not induce Doppler shift. In reality, however, they move around their nominal orbital positions due to for example perturbations. A GEO satellite is typically maneuvered to be within a box in space, see 3GPP TR 38.811 “Study on New Radio (NR) to support nonterrestrial networks“, which limits its Doppler shifts to become negligible. A GSO satellite may have an inclination angle relative to the Earth equator and will therefore move mainly in north-south direction relative to a fixed point on the Earth’s surface. This will create a small but non-negligible Doppler shift.

[0036] The Doppler effects become remarkable for MEO and LEO satellites. Table 1 gives example Doppler shifts and rates of NGSO satellites. We can see that the Doppler shifts and rates due to the NGSO satellite movement should be properly considered in the communications system design. Table 1: Doppler shifts and variation rates of NGSO satellites (extracted from Table 5.3.43.2-7 in 3GPP TR 38.811)

[0037] 3GPP solutions

[0038] The solution selected by 3GPP to combat the large and variable time delays and frequency offsets is based on that the satellite access node (SAN), i.e., the NTN gNB, indicates the satellite’s orbit and the satellite’s position in the orbit to the devices on earth using system information (SI) signaling. Each NTN device is GNSS capable and determines its own position using this capability. After synchronizing to the DL frame structure in time and frequency the device acquires the NTN SI and derives the current satellite position. Based on this and its own position, the device calculates an initial estimate of the timing advance (TA) used to offset its UL frame structure relative its DL frame structure, to compensate for the propagation delay of the service link. This initial TA offset secures that the UL transmissions from all devices in a cell are received in a synchronous fashion at the SAN despite the long NTN delays. The initial TA is later on, during the connection setup and the connection, corrected based on TA adjustments received from the NW, as well as TA adjustments made autonomously by the UE based on updated satellite position and UE position estimates. Optionally, the NW may also broadcast in SI a Common TA, corresponding to the propagation delay of the feeder link or a part thereof, that the UE applies in addition.

[0039] The device also uses its own position, the satellite’s position and movement, and knowledge of the downlink frequency it synchronized to, to compute the anticipated DL and UL Doppler frequency offsets on the service link. Based on this calculation, the UE can adjust its UL carrier frequency to compensate for the Doppler offsets, so that the UL transmission is received by the SAN at the intended carrier frequency. Doppler frequency offsets of the feeder link are assumed to be compensated by the NW in a way that is not specified by 3GPP.

[0040] GNSS less solutions

[0041] It has been observed that the UE dependency on GNSS introduces an unwanted dependency in the 3GPP protocol. GNSS is e.g., vulnerable to jamming, and does not work well indoors. For these reasons, solutions to reduce or even remove this dependency are being discussed in the NTN research and standards community.

[0042] One solution is that the network determines a reference point in a cell, e.g., the cell center, and advances its DL frame structure relative to its UL frame structure according to the round-trip time observed between the satellite and the reference point. A UE located at the reference point will thus apply a timing advance equal to 0. The SAN can offset its used DL carrier frequency by an amount that compensates for the anticipated DL Doppler offset so that a UE located at the reference point does not experience any DL Doppler shift of the carrier frequency. As long as all UEs are sufficiently close to the reference point, this method can be explored to offer satellite connectivity in a backwards compatible manner to regular unmodified devices not offering explicit support for NTN. This approach is believed to be used by recent commercial initiatives to connect existing 4G LTE devices to NTN.

[0043] There currently exist certain challenge(s). A problem with existing solutions is that the difference between the estimate of the UE position (e.g. a reference point) and the actual UE position will introduce time and frequency errors at the UL receiver. Therefore, the cell size needs to be small to limit the effect of these errors.

[0044] SUMMARY

[0045] Certain aspects of the disclosure and their embodiments may provide solutions to the abovementioned or other challenges. Some embodiments described herein provide methods for reducing the DL / UL time-frequency error observed by the SAN. According to some embodiments, the NTN controls the position that UE uses as its own position for time and / or frequency pre-compensation. Some embodiments further provide enhanced methods for network control of the time and frequency compensation that the UE applies in addition to the autonomous time and frequency pre-compensation.

[0046] Certain embodiments may provide one or more of the following technical advantage(s). In particular, some embodiments may limit the time-frequency error observed by the SAN. The teachings of certain embodiments may improve the speed by which a UE can connect to a cell of a NTN, which may improve data rate and / or latency of communications by a UE.

[0047] In a first aspect a method performed by a User Equipment, UE, in a cellular communications system is provided. The method comprises receiving position assistance information from a Non-Terrestrial Network, NTN, node in a NTN cell. The method further comprises obtaining a pseudo-position of the UE based on the position assistance information. The method further includes performing one or more actions with respect to one or more NTN cells, based on the pseudo-position of the UE.

[0048] In a second aspect a User Equipment, UE, for obtaining an estimate of a position of the UE in a cellular communications system is provided. The UE comprises one or more transmitters, one or more receivers and processing circuitry associated with the one or more transmitters and the one or more receivers. The processing circuitry is configured to cause the UE to receive position assistance information from a Non-Terrestrial Network, NTN, node on a NTN cell. The processing circuitry is further configured to cause the UE to obtain a pseudoposition of the UE based on the position assistance information. The processing circuitry is additionally configured to cause the UE to perform one or more actions with respect to one or more cells, based on the pseudo-position of the UE obtained based on the position assistance information.

[0049] In a third aspect a method performed by a Non-Terrestrial Network, NTN, node is provided. The method comprising the NTN node providing position assistance information to a User Equipment, UE, on a NTN cell. The position assistance information comprising information that enables the UE to select or derive a pseudo-position of the UE.

[0050] In fourth aspect A Non-Terrestrial Network, NTN, node is provided. The NTN node comprising processing circuitry configured to cause the NTN node to provide position assistance information to a User Equipment, UE, on a NTN cell. The position assistance information comprises information that enables the UE to select or derive a position of the UE.

[0051] In further aspects a computer program, or a carrier containing the computer program, or non-transitory computer-readable medium are provided which comprise instructions executable by processing circuitry which, when executed on at least one processor, cause the processor to carry out the method according to any of the aspects described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] For a more complete understanding of the disclosed embodiments and their features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:

[0053] FIGURE 1 illustrates an example architecture of a satellite network with bent pipe transponders;

[0054] FIGURE 2 illustrates an exemplary satellite access node (SAN);

[0055] FIGURE 3A illustrates an exemplary transparent payload architecture in which various network protocol layers are hosted in terrestrial infrastructure;

[0056] FIGURE 3B illustrates an exemplary regenerative payload architecture in which some network protocol layers are hosted in terrestrial infrastructure, while other network protocol layers are hosted in satellites;

[0057] FIGURE 4 illustrates one example of a system 400 in which embodiments of the present disclosure may be implemented;

[0058] FIGURE 5 is a flow chart that illustrates the operation of the UE 402 and the NTN node 408 in accordance with embodiments of the present disclosure;

[0059] FIGURE 6 illustrates an example where the network has selected the UE position to a reference point (RP) where the source and target cell coverage overlap;

[0060] FIGURE 7 is an illustration of the sphere and the cone calculated from respectively the propagation delay and the Doppler shift;

[0061] FIGURE 8 is a schematic illustration of narrow beam footprints;

[0062] FIGURE 9 is a schematic block diagram of a network node according to some embodiments of the present disclosure;

[0063] FIGURE 10 is a schematic block diagram of a UE according to some embodiments of the present disclosure;

[0064] FIGURE 11 is an exemplary communication system according to some embodiments of the present disclosure;

[0065] FIGURE 12 is an exemplary flow diagram depicting an embodiment according to the present disclosure;

[0066] FIGURE 13 is an exemplary flow diagram depicting an embodiment according to the present disclosure. DETAILED DESCRIPTION

[0067] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0068] Network controlled UE position for time and frequency pre-compensation

[0069] In some embodiments, the network controls / assists the UE in its estimation of its position to be used for time and frequency pre-compensation. In particular, the network may provide the UE with a position, which the UE uses as its own position when it calculates the timing and frequency pre-compensation.

[0070] Terminology:

[0071] • Pseudo-position: A position a UE uses as its own position (or as a proxy for its own position) when calculating timing and Doppler shift pre-compensation.

[0072] • Residual timing error (RTE): The transmit timing error (or the reception timing error seen at the network) that remains after the UE has performed timing pre-compensation based on its pseudo-position.

[0073] • Residual frequency error (RFE): The transmit frequency error (or the reception frequency error seen at the network) that remains after the UE has performed Doppler shift pre-compensation based on its pseudo-position.

[0074] • Residual timing advance (RTA) : A partial TA (provided by the network to the UE through one or more RTA adjustment instructions), which compensates for the residual timing error (i.e. it covers the difference between the satellite- UE Round-Trip Time (RTT) and the satellite-pseudo-position RTT).

[0075] • Residual frequency adjustment (RFA): A partial frequency adjustment, which compensates for the residual frequency error.

[0076] Embodiments of the proposed solution are described below mainly in terms of New Radio (NR) NTN, but the solutions are equally applicable to loT NTN. Adapting the embodiments disclosed herein to loT NTN implies minor adjustments such as straightforward changes of terminology, e.g. that a base station should be considered to be an evolved NodeB (eNB) rather than a gNB, and that the inter-base station communication protocol is X2AP instead of XnAP. The term “satellite” may also be referred to herein as a satellite node, satellite access node (SAN), an NTN node, node in space, HAPS node, etc. A base station (BS) or radio network node (RNN) associated with a satellite might include both a regenerative satellite, where the BS or RNN is the satellite payload, i.e. the BS or RNN is integrated with the satellite, or a transparent satellite, where the satellite payload is a relay and BS or RNN is on the ground (i.e., the satellite relays the communication between the BS or RNN on the ground and the UE).

[0077] The term “node” is used herein to refer to either a network node or a User Equipment (UE). Examples of network nodes are NodeB, base station (BS), Multi-Standard Radio (MSR) radio node such as MSR BS, eNB, gNB, Master eNB (MeNB), Secondary eNB (SeNB), Satellite Access Node (SAN), Location Measurement Unit (LMU), Integrated Access Backhaul (IAB) node, network controller, Radio Network Controller (RNC), Base Station Controller (BSC), relay, donor node controlling relay, Base Transceiver Station (BTS), Central Unit (e.g. in a gNB), Distributed Unit (e.g. in a gNB), Baseband Unit, Centralized Baseband, Cloud Radio Access Network (C-RAN), Access Point (AP), transmission points, transmission nodes, Transmission Reception Point (TRP), Remote Radio Unit (RRU), Remote Radio Head (RRH), nodes in Distributed Antenna System (DAS), core network node (e.g. Access and Mobility management Function (AMF) in the case of 5thGeneration Core (5GC), Mobility Management Entity (MME) in the case of EPC, etc.), Operations and Maintenance (O&M), Operations Support System (OSS), Self-Organizing Network (SON) node, positioning node (e.g. Evolved Serving Mobile Location Center (E- SMLC)), etc.

[0078] The non-limiting term “UE” refers to any type of wireless device communicating with a network node and / or with another UE in a cellular or mobile communication system. Examples of UE are target device, Device to Device (D2D) UE, Vehicular to Vehicular (V2V), machine type UE, Machine Type Communication (MTC) UE or UE capable of Machine to Machine (M2M) communication, Personal Digital Assistant (PDA), tablet, mobile terminals, smart phone, Laptop Embedded Equipment (LEE), Laptop Mounted Equipment (LME), Universal Serial Bus (USB) dongles, etc.

[0079] The term “radio access technology”, or RAT, may refer to any RAT, e.g. Universal Terrestrial Radio Access (UTRA), Evolved UTRA (E-UTRA), Narrow Band Internet of Things (NB-IoT), WiFi, Bluetooth, next generation RAT, New Radio (NR), 4G, 5G, 6G, NR NTN, loT NTN, LTE NTN, etc. Any of the equipment denoted by the term node, network node, or radio network node may be capable of supporting a single or multiple RATs.

[0080] The term “signal” or “radio signal” as used herein can be any physical signal or physical channel. Examples of downlink (DL) physical signals are Reference Signals (RSs) such as Cell-specific RS (CRS), NR-IoT RS (NRS), Narrowband Primary Synchronization Signal (NPSS), Narrowband Secondary Synchronization Signal (NSSS), Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), Channel State Information RS (CSI-RS), Demodulation Reference Signal (DMRS) signals in Synchronization Signal (SS)ZPhysical Broadcast Channel (PBCH) Block (SSB), Discovery Reference Signal (DRS), Positioning Reference Signal (PRS), etc. RS may be periodic, e.g. RS occasion carrying one or more RSs may occur with certain periodicity, e.g. 20 milliseconds (ms), 40 ms, etc. The RS may also be aperiodic. Each SSB carries NR-PSS, NR- SSS and NR-PBCH in 4 successive symbols. One or multiple SSBs are transmitted in one SSB burst which is repeated with certain periodicity, e.g. 5 ms, 10 ms, 20 ms, 40 ms, 80 ms, or 160 ms. The UE is configured with information about SSBs on cells of a certain carrier frequency by one or more SSB Measurement Timing Configuration (SMTC) configurations. The SMTC configuration comprises parameters such as SMTC periodicity, SMTC occasion length in time or duration, SMTC time offset with regards to a reference time (e.g. serving cell’s System Frame Number (SFN)), etc. Therefore, an SMTC occasion may also occur with certain periodicity, e.g. 5 ms, 10 ms, 20 ms, 40 ms, 80 ms, or 160 ms. Examples of uplink (UL) physical signals are RSs such as Sounding Reference Signal (SRS), DMRS, etc. The term “physical channel” refers to any channel carrying higher layer information, e.g. data, control, etc. Examples of physical channels are PBCH, Narrowband PBCH (NPBCH), Physical Downlink Control Channel (PDCCH), Physical Downlink Shared Channel (PDSCH), Physical Uplink Control Channel (PUCCH), Physical Uplink Shared Channel (PUSCH), short PDSCH (sPDSCH), short PUCCH (sPUCCH), short PUSCH (sPUSCH), MTC PDCCH (MPDCCH), Narrowband PDCCH (NPDCCH), Narrowband PDSCH (NPDSCH), Enhanced PDCCH (E-PDCCH), Narrowband PUSCH (NPUSCH), etc.

[0081] The term “carrier frequency” used herein is also referred to as Component Carrier (CC), frequency layer, layer, carrier, frequency, serving carrier, frequency channel, radio channel, radio frequency channel, Positioning Frequency Layer (PFL), Measurement Object (MO), etc. The carrier frequency belongs to a certain frequency band, which may contain one or multiple carrier frequencies based on its passband (e.g., size of the band in frequency domain) and / or bandwidth of the carriers and / or the channel raster etc. The carrier frequency related information is transmitted to the UE by a network node using a frequency channel number identifier via a message, e.g. Radio Resource Control (RRC) message. Examples of the channel number or identifier, which may be pre-defined, are Absolute Radio Frequency Channel Number (ARFCN), NR-ARFCN, etc.

[0082] The term “time resource” as used herein may correspond to any type of physical resource or radio resource expressed in terms of length of time. Examples of time resources are: symbol, time slot, subframe, radio frame, Transmission Time Interval (TTI), interleaving time, slot, sub-slot, mini-slot, System Frame Number (SFN) cycle, Hyper-SFN (H-SFN) cycle, etc.

[0083] The term Non-Terrestrial Network (NTN) as used herein may, depending on the context, refer to either or both of NR NTN and loT NTN, and sometimes the term is used to refer to only NR NTN. Thus, even though the embodiments outlined below are described mainly in terms of NR based NTNs, they are equally applicable in an NTN based on LTE technology and in particular loT NTN and similar future NTNs (e.g., an NTN in a 6th Generation (6G) system).

[0084] Any expression used herein stating that a cell performs an action (e.g., that the serving NTN cell sends a message to the UE) should be interpreted as a simplified way of writing that the base station (BS) serving the cell performs an action (e.g., that the BS serving the serving NTN cell sends a message to the UE).

[0085] The terms “serving node”, “source node”, “serving / source node”, “source / serving node”, “target node”, “candidate target node”, “serving BS”, “source BS”, “serving / source BS”, “source / serving BS”, “target BS” and “candidate target BS” may sometimes be used herein. The “node” or “BS” in these terms should be understood as typically being a Radio Access Network (RAN) node (e.g., an RNN) in an NTN based on NR technology, LTE technology, or any other RAT in which handover, conditional handover, or another mobility or conditional mobility concept is defined. In an NR based NTN, such a RAN node may be assumed to be a gNB. In an LTE based NTN (including an loT NTN), such a RAN node may be assumed to be an eNB. Alternatives to, or refinements of, these interpretations are however also conceivable. For instance, a gNB may be an en-gNB, and if a split gNB architecture is applied (dividing the gNB into multiple separate entities or notes), the term “node” may refer to a part of the gNB, such as a gNB-CU (often referred to as just CU), a gNB-DU (often referred to as just DU), a gNB-CU-Control Plane (CP) or a gNB-CU-User Plane (UP). Similarly, an eNB may be an ng-eNB, and if a split eNB architecture is applied (dividing the eNB into multiple separate entities or notes), the term “node” may refer to a part of the eNB, such as an eNB-CU, an eNB-DU, an eNB-CU-CP or an eNB-CU-UP.

[0086] Furthermore, the “node” in the terms may also refer to an lAB-donor, lAB-donor-CU, IAB- donor-DU, lAB-donor-CU-CP, or an lAB-donor-CU-UP.

[0087] The various embodiments described herein are often described in conjunction with handover (reconfiguration with sync) or conditional handover (CHO). However, these embodiments are also applicable in conjunction with other mobility procedures and conditional mobility procedures in RRC CONNECTED state. For instance, Primary Secondary Cell (PSCell) change, PSCell addition, Secondary Cell (SCell) addition, conditional PSCell change, and conditional PSCell addition.

[0088] When writing message names of a communication protocol, two equivalent principles are used herein. The writing principle “<protocol name> <message name> message”, for example “XnAP HANDOVER REQUEST message”, and the writing principle “<message name> <protocol name> message”, for example “HANDOVER REQUEST XnAP message” are equivalent, both referring to a message (i.e., “<message name>”) of a communication protocol (i.e., “<protocol name>”), e.g. the HANDOVER REQUEST message of the communication protocol XnAP. The same writing format equivalence applies to other communication protocols, such as Next Generation Application Protocol (NGAP).

[0089] The terms “Handover Command”, “HandoverCommand”, and “HO Command” are used interchangeably herein. Those terms all refer to a UE configuration the target node (of a regular handover) or candidate target node (of a conditional handover), during the (conditional) handover preparation phase, compiles for the UE to be subject to the handover or conditional handover. This UE configuration is compiled in the form of an RRCReconfiguration message which is conveyed to the UE via the source node. The RRCReconfiguration is associated with a certain target cell or candidate target cell and the UE applies the RRCReconfiguration when / if it accesses the concerned (candidate) target cell controlled by the (candidate) target node.

[0090] When Conditional Handover (CHO) is configured for a UE, a cell which the UE potentially can connect to (i.e., if the CHO execution condition is fulfilled for the cell) is denoted as “candidate target cell”. Similarly, a RAN node controlling a candidate target cell is denoted as “candidate target node”. However, once the UE has detected a fulfilled CHO execution condition for a candidate target cell, this terminology becomes a bit blurred. At this point, during the actual execution of the CHO and when the UE has connected to the new cell, the concerned cell may be referred to as either a “candidate target cell” or a “target cell”. Similarly, a RAN node controlling such a cell, may in this situation be referred to as either a “candidate target node” or a “target node”. Despite this discussion of the proper terminology for CHO, in this solution description, the word “candidate” is often skipped for simplicity (partly because the typical scenario is that there is only one candidate target cell). That is, the terms “target node”, “target gNB” and “target cell” may be used even when it would be more proper to use the terms “candidate target node”, “candidate target gNB” and “candidate target cell”.

[0091] A condition included in a CHO configuration governing the execution of the conditionally configured procedure may be referred to as either a “CHO execution condition” or a “HO execution condition”. Similarly, phases of the procedure may be referred to as the Handover Preparation phase, the Handover Execution and / or the Handover Completion phase, or may be referred to as the Conditional Handover Preparation phase, the Conditional Handover Execution phase and / or the Conditional Handover Completion phase.

[0092] Figure 4 illustrates one example of a system 400 in which embodiments of the present disclosure may be implemented. As illustrated, the system 400 includes a UE 402 served by a NTN cell 410, which is served or managed or operated by aNTN node 408 (e.g., a SAN). The NTN cell 410 operates on a first NTN carrier frequency. The UE 402 is located in the NTN cell 410, e g., in RRC CONNECTED, RRC INACTIVE, or RRC IDLE state, and the UE 402 is configured to perform measurements on at least one carrier frequency operated by or belonging to the NTN cell 410. An example of the NTN node 408 is a satellite node, which, as described above, may also be referred to herein as a SAN. As an example, the NTN node 408 manages or serves or operates or controls one or more NTN cells 410. The NTN node 408 may host a BS, e.g., a gNB or an eNB, or it may serve as a relay between UEs and a BS (via a GW) on the ground.

[0093] In case that GNSS measurement by the UE 402 would take too long or GNSS is temporarily unavailable, it brings difficulties for the UE 402 to measure the NTN cell 410 before cell change and / or to determine a TA for random access preamble transmission on the NTN cell 410. In this case, a solution is proposed herein to enable the NTN node 408 operating the NTN cell 410 to provide position assistance information to the UE 402 that the UE 402 can use to determine a pseudo-position 420 of the UE 402, e.g., as a substitute for GNSS positioning.

[0094] Figure 5 is a flow chart that illustrates the operation of the UE 402 and the NTN node 408 in accordance with embodiments of the present disclosure. As illustrated, the NTN node 408 provides position assistance information to the UE 402 (step 502). The position assistance information is information that allows the UE 402 to choose or determine a pseudo-position of the UE 402, e.g., while the UE 402 is in a low activity RRC state (e.g., RRC IDLE or RRC INACTIVE state) or RRC CONNECTED state. In one example, the NTN node 408 provides the position assistance information to multiple UEs (including the UE 402) on the NTN cell 410 via broadcasted system information. Optionally, this broadcasted position assistance information targets UEs in RRC INACTIVE and RRC IDLE states. In one embodiment, the position assistance information is included in a System Information Block (SIB) or possibly in multiple SIBs, e.g., divided into parts where different parts are included in different SIBs. Optionally, using broadcast information to convey the position assistance information would (primarily) be intended for UEs in low activity RRC state (i.e., UEs in RRC INACTIVE state and RRC IDLE state), but as another option, UEs in RRC_CONNETED state can also receive the position system information via the broadcast information. In one example, the SIB can be configured to be on-demand to avoid the signaling load of numerous (potentially redundant) transmissions of the position assistance information. This may for instance be a new SIB, e.g., introduced for this purpose. In another example, the NTN node 408 provides the position assistance information to the UE 402 on the NTN cell 410 via a dedicated message while the UE 402 is in RRC_CONNEDCTED state, e.g. an RRC message, a Medium Access Control (MAC)-Control Element (CE), or a Downlink Control Information (DCI) message.

[0095] From the UE’s perspective, if the UE 402 is aware of its need to know its own position (to some level of accuracy) for procedures related to one or more neighbor NTN cell(s) 410, e.g. neighbor cell measurements and / or TA calculation, e.g. due to a potential cell change to an NTN cell 410 (e.g. cell reselection if the UE 402 is in a low activity RRC state or handover if the UE 402 is in RRC_CONNECTED state), and the UE 402 currently does not have valid UE position information and currently cannot perform a GNSS measurement, or cannot perform a GNSS measurement within a required time, the UE 402 obtains the position assistance information (step 504). This may include receiving position assistance information from the NTN node 408 on the NTN cell 410 via broadcast information (e.g., via a broadcast SIB). In some cases, the broadcast information containing the position assistance information (e.g., SIB(s) including the position assistance information) are transmitted by the NTN node 408 on-demand, and this may require that the UE 402 first sends, to the NTN node 408, a request for broadcast of a SI message(s) (e.g., a SIB(s)) containing the position assistance information (step 500).

[0096] Alternatively, if the UE 402 is in RRC_CONNECTED state, the obtaining (or attempt to obtain) the position assistance information may include receiving a dedicated (i.e., not broadcast but addressed to the UE) message (e.g., an RRC message, a MAC CE or a DCI message) including the position assistance information. The NTN node 408 may be triggered to send the dedicated message by a preceding request from the UE 402 to receive the position assistance information or an indication from the UE 402 that it lacks valid UE position information (step 500). The indication also may indicate that the UE 402 will not be able to autonomously obtain valid UE position information (e.g., through a GNSS measurement) fast enough e.g., for successful execution of a procedure that triggered the need for the UE position information, or that the UE 402 lacks support for GNSS position measurements. As yet another alternative for the case where the UE 402 is in RRC_CONNECTED state, the obtaining (or attempt to obtain) the position assistance information may involve triggering, or requesting the network to initiate, a network-based (or network-involved) UE positioning measurement, e.g., using a procedure in the LCS framework.

[0097] At step 506, the UE 402 then obtains a pseudo-position of the UE 402 (i.e., estimates the position of the UE 402 or uses a default or specified position) based on the obtained position assistance information for the NTN cell 410. In one example, a pseudo position of the UE 402 can be acquired based on the position assistance information obtained for the NTN cell 410. In another example, an approximate position of the UE 402 can be acquired based on the position assistance information provided by a previously serving NTN cell of the UE 402. In another example, the position of the UE 402 can be estimated based on combining position assistance information provided by one or more previously serving NTN cells and the current serving NTN cell 410 of the UE 402. In the above examples, combining the position assistance information associated with different cells may involve calculating an average position, a weighted average position (e.g. giving different weights to different ones of the position estimates obtained from the position assistance information associated with different cells), or any other calculation to obtain a pseudo-position based on the position estimates obtained from the position assistance information associated with the different cells.

[0098] The UE 402 uses the position of the UE 402 obtained based on the position assistance information in step 506 to perform one or more actions relative to one or more NTN cells (step 508). For example, the UE 402 may use the position obtained in step 506 to perform measurements on one or more neighboring NTN cells 410 and / or to perform uplink synchronization (e.g., TA and / or Doppler shift) to a particular NTN cell 410 (e.g., in order to transmit a random access preamble on the NTN cell 410).

[0099] Further Embodiments

[0100] Initial access

[0101] In one embodiment, the network indicates what position the UE shall use as its own position estimate when performing initial access. This position can be a broadcast reference point in the cell. It can also be a position estimate used by the UE in a previous transmission in RRC CONNECTED state. In some embodiments, the network broadcasts an indicator whether the UE should use its position from a previous transmission or the broadcast reference position. Alternatively, a timer value X is broadcast or preconfigured that indicates that the UE shall use its position from a previous transmission if at most time X has passed since that transmission occurred, and otherwise use the broadcast reference point. In another alternative, a timer value X is broadcast or preconfigured that indicates that the UE shall use its most recent position if at most time X has passed since that position was acquired, and otherwise use the broadcast reference point. As another alternative, the UE itself determines (based on UE implementation) whether to use a previously obtained position estimate or the broadcast reference point, e.g. based on the time that has elapsed since the UE obtained the position estimate. The UE uses the position when transmitting a PRACH preamble.

[0102] In some embodiments, the network indicates whether the UE assumes a zero velocity or uses the UE’s own velocity (if known to the UE) for pre-compensating the frequency for UL transmissions. Optionally, the network can indicate a condition under which the UE uses its own velocity for UL frequency pre-compensation, e.g., when the magnitude of the UE’s velocity exceeds a pre-determined threshold.

[0103] In one embodiment, the UE uses additional time and / or frequency pre-compensation based on closed-loop time and / or frequency adjustment commands from a previous transmission in RRC CONNECTED state when transmitting the PRACH preamble. In some embodiments, the network broadcasts an indicator whether the UE should use its closed-loop time and / or frequency pre-compensation parameters from a previous transmission or reset them to 0. Alternatively, a timer value X is broadcast or preconfigured that indicates that the UE shall use its closed-loop time and / or frequency pre-compensation parameters from a previous transmission if at most time X has passed since that transmission occurred, and otherwise reset them to 0. As one option, when the UE resets its closed-loop time and / or frequency pre-compensation parameters, it continues to use a previously obtained UE specific estimate of its own position. As another option, when the UE resets its closed-loop time and / or frequency pre-compensation parameters, it starts to use, or continues to use, or returns to using, a position provided by the network as its own position, e.g. a reference point broadcast by the network. As yet another option, after resetting its closed-loop time and / or frequency pre-compensation parameters, the UE uses a previously obtained estimate of its own position or a position provided by the network (e.g. a broadcast reference point), in accordance with previously received configuration information from the network.

[0104] In one embodiment, the network sends a UE position update command in the Random Access Response (RAR) message. The UE position update command may be a relative position adjustment command that instructs the UE to move its position estimate a given distance in a given direction. The UE position update may also be an absolute position command that instructs the UE to move its position estimate to a given position. The network can base the UE position update on measurements of the time and / or frequency offset of the PRACH preamble transmitted by the UE. The UE uses the updated position for subsequent transmissions of e.g. Msg3.

[0105] The network may also send a closed-loop time and / or frequency adjustment command in the Random Access Response (RAR) message, optionally together with the UE position estimate adjustment instruction. The UE uses the closed-loop time and / or frequency adjustment in addition to the pre-compensation based on its position estimate, for subsequent transmissions of e.g. Msg3.

[0106] In one embodiment, the network indicates a priority value associated with one or more of the following positions that can be used by the UE for determining a UE-based component of delay and / or frequency shift in the random access: a reference position broadcasted by the network, a GNSS-based UE position, a radio-network-based UE position. In some embodiments, the UE selects a position with highest priority among the positions accessible at the UE for the random access. For example, if the network indicates a higher priority for GNSS-based UE position and a lower priority for the reference position broadcasted by the network then a UE-A with access to both types of positions shall use the GNSS-based UE position for random access while a UE-B with access to only the reference position broadcasted by the network will use that position for random access. In another example, the network indicates a higher priority for the broadcasted reference position to avoid impacts of GNSS-spoofmg.

[0107] In another embodiment, in addition to or independent of the priority value in the previous embodiment, the UE is configured to or allowed to use a GNSS-based UE position or some other UE autonomously determined position if the distance between such a position and a network-broadcasted position is more than a pre-determined threshold.

[0108] Connected mode

[0109] In one embodiment, the network sends UE position updates, e.g. in MAC CE, during connected mode (e.g. in RRC CONNECTED state). The UE position updates may be relative position adjustment commands that instruct the UE to move its position estimate a given distance in a given direction. The UE position update may also be absolute position command that instructs the UE to move its position estimate to a given position. The network can base the UE position update commands on measurements of the time and / or frequency offset of one or more previous transmissions from the UE. The UE uses the updated position for subsequent transmissions.

[0110] As an alternative to, or as a complement to, the network’s estimation of the UE’s UE- specific position, the UE may itself estimate its position, and optionally continuously or repeatedly refine this position estimate based on observations of its used time precompensation (e.g. timing advance) and / or frequency pre-compensation during one or more transmissions, timing adjustment commands (e.g. Timing Advance Command MAC CEs) and / or frequency adjustment commands, and the serving satellite’s ephemeris data. In one variant, the UE may perform the following steps:

[0111] 1. Based on a received timing advance command and / or frequency adjustment command, UE calculates the position update that will result in a time / frequency precompensation update that most closely resembles the timing advance command and / or frequency adjustment command. 2. UE calculates the residual time / frequency pre-compensation needed to fully obey the timing advance command and / or frequency adjustment command.

[0112] 3. UE adjusts its position estimate based on step 1 and its time / frequency precompensation based on step 2.

[0113] The network may also send a closed-loop time and / or frequency adjustment command e.g. in a MAC CE. The UE uses the closed-loop time and / or frequency adjustments in addition to the pre-compensation based on its position estimate, for subsequent transmissions.

[0114] The network may also send UE velocity update commands. The network can base the UE velocity update commands on measurements of the time and / or frequency offset of one or more previous transmissions from the UE. The UE can use the velocity to determine the frequency pre-compensation for UL transmissions. The UE can also use the velocity to propagate the UE position versus time to calculate future time / frequency pre-compensation for UL transmissions.

[0115] Handover

[0116] In one embodiment the network indicates what position the UE should use as its own when it is configured to perform a mobility procedure while connected to the network (e.g. in RRC CONNECTED state), e.g. handover, including uplink synchronization, to a candidate or target cell (e.g., Layer 3 handover, Layer 1 / 2 handover (e.g. L1 / L2 triggered mobility, as in 5G (release 18+ of the 3GPP standard), SCell addition or SCell change (in a dual connectivity configuration)), conditional handover etc.). The position indication can e.g., be sent as part of an RRC (re)configuration message during the handover procedure (e.g. the type of message often referred to as a Handover Command, i.e. RRC (re)configuration information to be applied in the target cell when the mobility procedure is executed).

[0117] The network may use knowledge of the cell coverage of the source and target cell to select the position signaled to the UE. This is illustrated in Figure 6 where the network has selected the UE position to a reference point (RP) where the source and target cell coverage overlap.

[0118] In other embodiments, or in variations of the above embodiment, if the UE has obtained a refined estimate of its position, e.g. another (probably more accurate) position estimate than the common reference point broadcast in the UE’s serving cell (i.e. a UE specific position estimate), the UE uses this obtained UE specific position estimate also when accessing the network in the new cell (e.g. the target cell) and (unless the network provides a new UE specific position estimate in conjunction with the network access procedure) also after the mobility procedure. The UE may have obtained the UE specific position estimate through its own observations and / or measurements, as previously described, or from relative and / or absolute position adjustment commands from the network. As a further variation, the network can control, e.g. through configuration signaling, whether the UE should use a previously obtained UE specific position estimate during network access in the new cell and optionally after connecting in the new cell, or use another position as its own position, where this other position would be provided by the network, e.g. in conjunction with configuring or triggering the mobility procedure, and where this other position may be based at least in part of conditions or properties associated with the new (e.g. target) cell, such as cell coverage and satellite position and / or ephemeris data. As a further variation, the network may configure a UE, through dedicated or common (e.g. broadcast) signaling, to use an obtained UE specific estimate of the UE’s position, if available, and otherwise use a position provided by the network, e.g. a reference point broadcast in the new / target cell or provided as part of the configuration (e.g. RRC configuration) to be used in the new / target cell. As another variation, the network may configure a UE through dedicated or common (e.g. broadcast) signaling, to use an obtained UE specific estimate of the UE’s position, if the UE has obtained the UE specific position estimate from relative and / or absolute position adjustment commands from the network, and otherwise use a position provided by the network, e.g. a reference point broadcast in the new / target cell or provided as part of the configuration (e.g. RRC configuration) to be used in the new / target cell. As another variation, the network may configure a UE through dedicated or common (e.g. broadcast) signaling, to use an obtained UE specific estimate of the UE’s position, if the UE has obtained the UE specific position estimate based on its own observation and / or measurements, and otherwise use a position provided by the network, e.g. a reference point broadcast in the new / target cell or provided as part of the configuration (e.g. RRC configuration) to be used in the new / target cell.

[0119] Reception timing based TA and reception frequency based Doppler change prediction and advanced TA and frequency adjustment commands

[0120] As previously described, when a UE uses a common reference point (or another position, e.g. provided by the network, with low accuracy) as its own position when it calculates its transmission timing pre-compensation (e.g. its timing advance, TA), the UE’s transmission timing, and consequently the network’s (e.g. the radio base station’s) reception timing will not be perfect (unless the UE happens to be located at the reference point (or otherwise obtained position). The timing error arising from the UE position’s deviation from the position the UE uses in the timing pre-compensation calculation may be referred to as the “residual transmission timing error”, or shorter, the ’’residual timing error” (abbreviated “RTE”). The reference point or otherwise obtained position which the UE uses as its own position is henceforth referred to as the “pseudo-position”.

[0121] From the network’s point of view, the residual timing error is similar to the timing error of a UE in a legacy terrestrial network before the UE has obtained a valid timing advance. Consequently, the network can handle the residual timing error in a similar way as in a legacy terrestrial network, i.e. by providing the UE with a timing advance which is chosen to a value that will compensate for the residual timing error, such that the UE’s transmissions (when applying the timing pre-compensation the UE has calculated and the timing advance obtained from the network) arrives at the network (e.g. at the radio base station) at the desired time (e.g. with zero reception timing error). Since this TA provided by the network only compensates for the residual timing error, while the UE’s complete TA consists of the UE’s calculated timing pre-compensation in combination with this TA provided by the network (and a possible common TA accounting for the full or partial feeder link RTT as in 5GNR NTN), the TA the network provides to compensate for the residual timing error may herein be referred to as the “residual TA”, abbreviated “RTA”. Such a residual timing advance instruction from the network may have the form of an absolute RTA indication (e.g., in a Random Access Response message) or a relative RTA adjustment indication (e.g. a Timing Advance Command MAC CE (or a Residual Timing Advance Command MAC CE)).

[0122] The residual timing error results from the difference between the satellite-to-UE distance and the satellite-to-pseudo-position distance (or the difference between the satellite- UE RTT and the satellite-pseudo-position RTT). This difference is dynamic since at least one of the endpoints of both these distances, i.e. the satellite, is moving (assuming aNGSO satellite). As movements of the UE affects the satellite-to-UE distance, also UE movements impact the difference between the distances. Because of this, the network repeatedly needs to send TA adjustment instructions (e.g. Timing Advance Command MAC CEs) or RTA adjustment instructions (e.g. Residual Timing Advance Command MAC CEs) to the UE, where the required frequency of such TA adjustment instructions or RTA adjustment instructions depends on how fast the difference between the distances changes (the faster the change the more frequent TA adjustment instructions or RTA adjustment instructions are needed). (Henceforth, the term RTA adjustment instruction will primarily be used in the text.)

[0123] The required frequency of RTA adjustment instructions thus depends on two “components”: the satellite movement and the UE movement. Of these two components, the satellite movement dominates heavily (unless the UE is moving very fast). It can easily be calculated that in a scenario where a LEO satellite is serving a quasi-Earth-fixed cell as the satellite passes over the cell from a small elevation angle (as seen e.g. from the center of the cell) to being straight above the cell (e.g. 90 degrees elevation angle as seen from the center of the cell) and further to a small elevation angle on the other side of the cell, the rate of change of the difference between the satellite-to-UE distance and the satellite-to-pseudo- position distance (where the pseudo-position e.g. is a common reference point, e.g. located at the center of the cell) is comparable to a speed of several hundred kilometers per hour, which translates into a high frequency of RTA adjustment instructions required from the network to keep the arrival (at the network, e.g. a radio base station) timing of the UE’s transmissions within acceptable bounds, e.g. within the cyclic prefix. This frequency of RTA adjustment instructions may or may not be within the bounds that network can handle, but nevertheless, since a similar frequency of RTA adjustment instructions will be needed for all UEs connected in the cell, the negative consequences, e.g. on the overall performance, will be significant. For instance, a large amount of signaling resources and processing resources will have to be used, potentially overloading either of them and / or competing with other tasks and types of communication (e.g. user plane data) for the transmission resources and processing resources. Hence, there is a need for means to mitigate these negative consequences, e.g. by reducing the required frequency of TA adjustment instructions.

[0124] Network-based method

[0125] In some embodiments, such mitigating means are provided in the form of reception timing based RTA change prediction and advanced RTA adjustment instructions. This scheme leverages that in contrast to UE movements, the satellite movement, which is the dominating reason for the high RTA adjustment instruction frequency requirement is consistent and highly predictable. However, this alone does not allow the network to predict what the UE’s RTA should be at an arbitrary future point in time (even if the UE is nonmoving, e.g. stationary), because the distance between the satellite and the UE, and consequently the difference between the satellite-to-UE distance and the satellite-to-pseudo- position distance, also depends on the UE’s actual position, which is unknown to the network. (The difference between the two distances also depends on the location of the pseudo-position, but this is known to the network can thus be accounted for.)

[0126] As the UE’s location is unknown to the network, the network, in some embodiments, resorts to an indirect method to predict the future change of the UE’s residual timing error, and thus the future change of the required RTA. This is achieved by observing the changes of the reception timing of the UE’s transmissions. For instance, by detecting the reception timing error of a first UE transmission, the network can estimate the UE‘s residual timing error and thus the RTA the network should instruct the UE to use (in addition to the timing pre-compensation the UE calculates based on the pseudo-position). After having received two transmissions from the UE (with a suitable time period int between), and having observed their respective reception timing (e.g. in relation to the cyclic prefix), the network can calculate an estimate of the rate of change of the residual timing error, i.e. the drift (i.e. the ( RTF} first time derivative of the residual timing error, i.e. — — — ). After having received three transmissions from the UE (with a suitable time period in between), and having observed their respective reception timing (e.g. in relation to the cyclic prefix), the network can calculate an estimate of the rate of change of the rate of change of the residual timing error,

[0127] (RTE i.e. the drift variation (i.e. the second time derivative of the residual timing error, i.e. - - — ).

[0128] This can be extended to an arbitrary number of time derivatives of the residual timing error, e.g. the Nth time derivative calculated based on observations of N+l transmission receptions. Thus, using these observations and calculated residual timing error and time derivatives thereof, and leveraging the consistent and well-known movement of the satellite, the network can predict the future change of the UE’s residual timing error. And using a surplus of transmission timing observations, the network may refine the prediction.

[0129] To translate this predication ability into a reduced frequency of required RTA adjustment instructions, the network translates the predicted change of the residual timing error into a predicted change of the RTA needed to compensate for the changing residual timing error. As a last step to make this an effective method to reduce the required frequency of RTA adjustment instructions, an advanced form of RTA adjustment instructions (e.g. a new type of Timing Advance Command MAC CE, e.g. a Residual Timing Advance Command MAC CE) is introduced. Such an advanced RTA adjustment instruction may e.g. contain a relative RTA adjustment indication (i.e. an indication of an amount to increase or decrease the RTA), a first time derivative of the RTA (i.e.d('RTAandasecond time derivative of the RTA (i.e. dtd

[0130] As another example, an advanced RTA adjustment instruction may e.g. contain an absolute RTA indication (i.e. an indication of an RTA), a first time derivative of the RTA and a d2(RTA) second time derivative of the RTA (i.e. — — — ). More generally, an advanced RTA adjustment instruction may contain N time derivatives of the RTA combined with either a relative RTA adjustment indication or an absolute RTA indication, where N = 1, 2, 3, ...

[0131] The network can thus send such advanced RTA adjustment instructions to the UE, and when the UE receives an advanced RTA adjustment instruction, it applies it by adjusting its RTA accordingly, i.e. the UE sets the RTA to the indicated absolute RTA or increases or decreases the RTA in accordance with the relative RTA adjustment instruction, and subsequently changes the RTA over time as indicated by the N time derivatives of the RTA, e.g. by integrating the time derivatives over time.

[0132] In the above, the RTA may be said to correspond to the NTA in the TA formula used in 5G (and 5GNRNTN).

[0133] Furthermore, assuming that the network uses frequency adjustment (FA) instructions to impact the UE’s Doppler shift compensation, a similar, or corresponding approach can be used to reduce the required frequency of frequency adjustment (FA) instructions the network has to send to the UE to keep the error of the UE’s Doppler shift compensation sufficiently small. A difference from the case of the residual timing error, which depends on the difference between the satellite-to-UE distance and the satellite-to-pseudo-position distance, is that the residual frequency error (i.e. the error remaining after the UE has pre-compensated for the Doppler shift based on the pseudo-position) does not depend on this difference between the distances, but instead depends on the difference in the angles relative to the satellite’s movement direction seen respectively from the pseudo-position and the UE’s actual location. From the UE’s actual location’s point of view, this angle is the angle between the satellite’s movement direction (e.g. represented as a vector) and the line between the UE and the satellite. Similarly, from the pseudo-position’s point of view, the angle is the angle between the satellite’s movement direction (e.g. represented as a vector) and the line between the pseudo-position and the satellite. The frequency error resulting from this angle difference is herein referred to as the “residual frequency error” (abbreviated “RFE”), and an adjustment of the frequency to compensate for this residual frequency error is referred to as a “residual frequency adjustment” (abbreviated “RFA”).

[0134] As with the RTA adjustment instructions, the fast movement of the satellite may result in such a fast change of the above-described angle difference that the required frequency of RFA instructions from the network to the UE has significant negative consequences. Hence, a there is a need for a means to reduce the required frequency of RFA instructions, e.g. a similar means as the above-described means for reducing the required frequency of RTA adjustment instructions. To this end, the network may observe the frequency error of received successive transmissions from the UE and based on this determine the residual frequency d (RFE) error as well as a desired number of time derivatives (e.g. a first time derivative (i.e. — — — ), a second time derivative (i.e.d (RFEa third time derivative (i.e.d ... ) of the residual frequency error. The network can then translate this into a suitable RFA (which can be estimated based on observing the frequency error of a single reception), an RFA time derivative (which can be estimated based on observing the frequency errors of two receptions d^ (RFA) suitably separated in time), a second time derivative (i.e. — — — ) of the RFA (which can be estimated based on observing the frequency errors of three receptions suitably separated in time), etc. (e.g. N time derivatives based on observed frequency errors of N+l receptions). The network can then construct an advanced RFA instruction consisting of e.g. a frequency d( RFA adjustment indication, a first time derivative of the RFA (i.e. the drift, — — — ) and a second d^ RFA) time derivative of the RFA (i.e. the drift variation, — — — ). More generally, an advanced

[0135] RFA instruction may contain N time derivatives of the RFA combined with an RFA, where N = h 2, 3, ...

[0136] The network can thus send such advanced RFA instructions to the UE, and when the UE receives an advanced RFA instruction, it applies it by adjusting its RFA accordingly, i.e. the UE adjusts its the RFA in accordance with the received RFA instruction, and subsequently changes the RFA over time as indicated by the N time derivatives of the RFA, e.g. by integrating the time derivatives over time.

[0137] UE-based method The above-described methods where the network predicts the future development of the residual timing error and / or the residual frequency error can, with some modification also be performed by the UE. The UE cannot directly observe the reception timing and / or frequency errors of its own transmissions, but it can observe them indirectly by observing RTA adjustment instructions and / or RFA instructions it receives from the network. The RTA adjustments and / or RFAs indicated in these RTA adjustment instructions and / or RFA instructions serves the same purpose as the reception timing error and / or reception frequency error observations do for the network in the network-based method described above. Thus, based on observations of received RTA adjustment instructions and / or RFA instructions, the UE can calculate a first time derivative, a second time derivative etc. of the residual timing error ( vi.e.d^RTE>>d RTEetc.) and / or a first time derivative, a second time derivative etc. of dt dt2’ the residual frequency error (i.e. ete)- The UE then uses these calculated values to determine corresponding autonomous changes of its transmission timing and / or transmission frequency compensation. As an option, the UE may inform the network, e.g. using RRC signaling or MAC signaling, that it uses this method (or another method) to autonomously adjust its transmission timing and / or its transmission frequency compensation.

[0138] Pseudo-position refinement

[0139] In some embodiments, the network may refine the pseudo-position the UE uses, based on estimates of the UE’s position (or a range or set of equivalent positions), which in turn are based on the network’s knowledge of the UE’s autonomously calculated timing and Doppler shift pre-compensation based on the pseudo-position combined with the RTA and RFA instructed / provided by the network, and optionally the observed still remaining reception timing error (if any) and the observed still remaining frequency error (if any). With this knowledge the network can calculate the propagation delay between the satellite and the UE, Dprop sat-UE, and the angle, a, between the satellite’s movement direction (e.g. represented as a vector) and the line between the UE and the satellite. The propagation delay can be translated into a sphere (with the satellite at the center) on which the UE may be located, where the satellite is at the center of the sphere and the sphere’s radius, R, is R = Dprop sat- UE x c, where c is the speed of light. Furthermore, the above-mentioned angle, a, can be translated into a cone (with the satellite’s orbit as the center line at the tip) on whose surface the UE may be located, where the angle, a, is the angle between the satellite’s movement direction and a line along the surface of the cone, and where a = arccos vs°applerj, where AfDoppler is the relative Doppler shift (i. e. , AfDoppler = fDoppler / fc, where fDoppler is the absolute Doppler frequency shift and fc is the carrier frequency), vsat is the velocity of the satellite and c is the speed of light. Note that when the Doppler shift is zero (i.e. AfDoppler = 0), the cone collapses into a disc with a plane that is perpendicular to the satellite orbit, i.e. perpendicular to the satellite’s movement direction.

[0140] Thus, the intersection of the sphere and the cone (resulting in a circle) represents a range of pseudo-positions (one of which being at least close to the UE’s actual position) which are equivalent in the sense that they all result in the same calculated transmission timing pre-compensation and Doppler shift pre-compensation (i.e. any point on the circumference of the intersection circle is a potential (equivalent) pseudo-position). And if the network’s reception timing and frequency measurements are accurate, then the UE’s actual position is also located somewhere on the intersection circle. This is illustrated by Error! Reference source not found..

[0141] The network may signal to the UE a set of parameters, e.g. a position (representing the center of the above-described intersection circle) and the radius of the intersection circle, and instruct the UE to use any position on (the circumference of) the circle (note that the circle always lies in a plane that is perpendicular to the satellite orbit) as its pseudo-position when calculating the timing pre-compensation and / or the Doppler shift pre-compensation. Alternatively, the network can select an arbitrary point on the intersection circle and signal it (e.g., in the form of three coordinates) to the UE and instruct the UE to use this point as its pseudo-position when calculating the timing pre-compensation and / or the Doppler shift precompensation. In either case, the network may use dedicated signaling for this signaling, e.g. RRC signaling or MAC signaling. As a further option, the network may indicate to a UE, e.g. using RRC signaling or MAC signaling or L1 / L2 signaling (e.g. DCI on a PDCCH), an adjustment, or a correction, to the UE's pseudo-position, which the UE should apply for subsequent transmissions or for a single subsequent transmission, e.g., in case L1 / L2 signaling is used, a transmission scheduled by the L1 / L2 signaling (e.g. the DCI). This adjustment, or correction, can be in addition to any time / frequency adjustment commands sent by the network to the UE.

[0142] It may be observed that the information the network uses as input to the above determination of the sphere, the cone and the intersection circle is also known by the UE (with the exception of the possible still remaining timing error and still remaining frequency error). Thus, the UE can itself calculate the location and size of the intersection circle and select an arbitrary point on that circle as its pseudo-position when calculating the timing precompensation and / or the Doppler shift pre-compensation. Thus, in some embodiments, this UE-based approach is used instead of the previously described network-based approach. Optionally, even when the UE is using this UE-based approach, the network may indicate to the UE, e.g. using RRC signaling or MAC signaling or L1 / L2 signaling (e.g. DCI on a PDCCH), an adjustment, or a correction, to the UE's pseudo-position, which the UE should apply for subsequent transmissions or for a single subsequent transmission, e.g., in case L1 / L2 signaling is used, a transmission scheduled by the L1 / L2 signaling (e.g. the DCI). This adjustment, or correction, can be in addition to any time / frequency adjustment commands sent by the network to the UE.

[0143] In further embodiments, the network may configure the UE to use the UE-based approach or to rely on pseudo-position refinements signaled from the network (determined with the network-based approach). In still further embodiments, the network may configure the UE to use as its own position, a pseudo-position signaled from the network using dedicated signaling (wherein the signaled pseudo-position typically deviates from the broadcast reference point), or, alternatively, to use as its own position a pseudo-position the UE has determined autonomously, e.g. determined in accordance with the above-described UE-based approach, even if the UE subsequently transits to anon-connected state, e.g. RRC IDLE state or RRC INACTIVE state, and then performs a network access procedure, e.g. a random access procedure, and returns to a connected state, e.g. RRC_CONNECTED state. In a variant of these embodiments, the configuration indicates that it only applies to a subset of the non-connected states, e.g. only to RRC_INACTIVE state, while if the UE transits to another non-connected state, e.g. RRC IDLE state, the UE should discard any obtained pseudo-position (other than the broadcast reference point). As a possible extension of the configuration, the configuration may include an indication that it is valid only for a certain time, and when that time expires the UE should discard any obtained pseudo-position (other than the broadcast reference point). As an option, the configuration may be signaled to the UE together with the pseudo-position using dedicated signaling. As another option, which may be combined with the preceding option, the configuration may be signaled to the UE in an RRC message, such as an RRCReconfiguration message or a message instructing the UE to transit to a non-connected state, e.g., an RRCRelease message. Multiple reference points in narrow beams (e.g. in a large cell)

[0144] As previously described, the residual timing error depends on the difference between the satellite-to-UE distance and the satellite-to-pseudo-position distance, and the residual frequency error depends on the difference in angle between the direction towards the satellite and the satellite’s movement direction as seen respectively from the UE and from the UE’s pseudo-position. Hence, the maximum residual timing error as well as the maximum residual frequency error depend on the cell size (and the satellite orbit altitude and the location of the pseudo-position). The larger the cell, the greater are the maximum residual timing error and maximum residual frequency error. Since the concept of the solution relies on the residual timing and frequency errors not being greater than what the network can handle with a suitable access procedure, e.g. a random access procedure, this becomes a restriction of the cell size that can be supported with the previously described basic solution. This becomes a problem as operators are restricted in their deployment options, and satellite orbits with really high altitudes, even geostationary orbits, may be prohibitive to support. The following outlines a method to overcome this restriction.

[0145] In some embodiments, when the cell size is great (e.g. so great that the maximum residual timing error and / or the maximum residual frequency error in the cell becomes too large for the network to handle with the previously described basic solution), narrow beams (i.e. with footprints smaller than the cell, i.e. with each narrow beam covering only a part of the cell) can be used to broadcast multiple reference points in the cell, wherein each narrow beam broadcasts a different reference point (which may be used as a pseudo-position for UEs), so that each narrow beam’s broadcast reference point is adapted to the footprint (i.e. coverage area) of the narrow beam, e.g. located in the center of the narrow beam’s footprint. This is illustrated in Error! Reference source not found., which is a schematic illustration of narrow beam footprints, each with its own reference point. UE1 may for example use RP6 or a weighted average of RP6 and RP5 as its pseudo-position. UE2 may for example use RP3 or a weighted average of RP3, RP4 and RP7 as its pseudo-position.

[0146] Since each narrow beam covers only a part of the cell, each UE in the cell will typically only receive the reference point broadcast by the narrow beam whose footprint the UE is located in. This is the reference point the UE will use (at least initially) as its pseudo-position. With this method, the maximum residual timing error and the maximum residual frequency error are not determined by the cell size, but of the size of the footprint of a narrow beam. The narrow beams can be chosen (e.g., configured with suitable antenna weights) to have footprints of a size that limits the maximum residual timing error and the maximum residual frequency error to amounts the network can handle with a suitable access procedure, e.g., a random access procedure.

[0147] If the UE can receive the reference point broadcasts in two (or more) neighboring narrow beams, the UE may, as one option, use the reference point which it receives with the greatest signal strength. As another option, a UE that receives the reference point broadcasts of more than one narrow beam may use as its pseudo-position a point located at a point where the distance is the same from each of the reference points the UE receives. For instance, if the UE receives the reference point broadcasts of two neighboring narrow beams, the UE uses as its pseudo-position a point that is midways between the two reference points. As yet another option, a UE that receives the reference point broadcasts of more than one narrow beam may use as its pseudo-position a point that is calculated as a weighted (spatial) average of the received reference points, where the weights are based on the signal strength (e.g. RSRP) the respective reference point broadcasts are received with. This is thus similar to calculating the center of gravity of a system of point-size bodies / objects, but with the weight-determining factors changed from the mass to the signal strength. For instance, if the UE receives two reference point broadcasts from two neighboring narrow beams (broadcasting respectively reference point RP1 and RP2), and the UE receives the RP1 transmission with twice as high signal strength as the RP2 transmission, then the UE calculates its pseudo-position to be a point on a straight line between RP1 and RP2, one third of the RP1-RP2 distance from RP1, i.e. the distance from the point to RP2 is twice as long as the distance from the point to RP1.

[0148] As yet another option, or embodiment, the network can indicate, e.g. broadcast together with the reference point in a narrow beam B, a list of neighbor narrow beam(s) (i.e. neighbor(s) of narrow beam B) whose broadcast reference point(s) can be used by the UEs in beam B.

[0149] As yet another option, or embodiment, the network can indicate, e.g. broadcast together with the reference point in a narrow beam B, a list of one or more reference point(s) (e.g. the reference points of the neighboring narrow beams) a UE located in (e.g. receiving) narrow beam B may use as its reference point. In one example, the UE may use a single reference point from the list of reference point(s). In another example, the UE may use two or more reference points to calculate the position based on one or more of the methods disclosed in this disclosure (e.g. weighted averaging).

[0150] As yet another option, or embodiment, the network can indicate, e.g. broadcast together with the reference point in a narrow beam B, a list of one or more narrow beam(s) (which e.g. may be neighbor(s) of narrow beam B) whose associated reference point(s) a UE located in (e.g. receiving) narrow beam B may use a reference point. In one example, the UE may use a single reference point from the reference point(s) corresponding to the narrow beam(s) in the list. In another example, the UE may use two or more reference points to calculate the position based on one or more of the methods disclosed in this disclosure (e.g. weighted averaging).

[0151] As a further option, a UE may inform the network of the reference point it has chosen. To inform the network, the UE may e.g. perform random access on PRACH resources associated with the narrow beam associated with the chosen reference point. As a more generic option (supporting also selection of a pseudo-position that is not one of the broadcast reference points), the UE may inform the network of the pseudo-position the UE has chosen (or calculated or determined). To inform the network, the UE may e.g. use RRC signaling, e.g. a UEAssistancelnformation message, or MAC signaling, e.g. a new MAC CE.

[0152] In some embodiments, the network can indicate to a UE, e.g. using dedicated signaling, such as RRC signaling or MAC signaling or L1 / L2 signaling (e.g. DCI on a PDCCH), the narrow beam whose reference point that UE should use for subsequent transmissions or for a single subsequent transmission, e.g., in case L1 / L2 signaling is used, a transmission scheduled by the L1 / L2 signaling (e.g. the DCI). In another embodiment, the network may indicate an adjustment, or a correction, to the UE's reference point, which the UE should apply for subsequent transmissions or for a single subsequent transmission, e.g., in case L1 / L2 signaling is used, a transmission scheduled by the L1 / L2 signaling (e.g. the DCI). This adjustment, or correction, can be in addition to any time / frequency adjustment commands sent by the network to the UE.

[0153] In some embodiments, the above-described methods of using multiple narrow beams to broadcast multiple reference points (one per narrow beam) in a cell is used in a cell where a single beam with a cell-wide footprint is used for all other signaling, transmissions and communication in the cell (i.e. the narrow beams are used only for broadcasting of the reference points). In other embodiments, the above-described methods of using multiple narrow beams to broadcast multiple reference points (one per narrow beam) in a cell is used in a “regular” multi -beam cell, i.e. a cell where multiple narrow beams are used for all transmissions / communi cation in the cell. There are several conceivable options for the narrow beams and the broadcast. As one option, the reference points are broadcast as part of the system information, where this part of the system information would differ between different narrow beams. Another option is to use SSB beams. The reference point could also be part of a PBCH transmission, e.g. transmitted in conjunction with the SSB transmissions in SSB beams or as completely separate PBCH transmissions. Yet another option is to use other narrow beams used only for the purpose of broadcasting reference points. Other options are also conceivable. In some embodiments (e.g. when the protocol does not allow different information to be broadcast in different beams of the same cell), the broadcast information described in the embodiments above (e.g. reference points) for all beams of a cell is broadcast in each beam of the cell, and the UE uses the beam index to determine which broadcast information (e.g. reference point) that is associated with which beam.

[0154] Handling negative timing advance

[0155] When a UE uses as its own position a (possibly refined) position provided by the network, it may happen that the UE is actually located closer to the satellite (and thus closer to the base station) than the position (reference point or pseudo-position) the UE is using as its own position. As a consequence, the UE’s transmissions will arrive at the base station earlier than the ideal time, which in turn means that (unless the UE’s pseudo-position is adjusted) the UE must be provided with a negative timing advance. This should preferably be done directly upon the UE’s access to the network, e.g. in conjunction with the access procedure, e.g. in conjunction with a random access procedure. In 5GNRNTN, the network provides the UE with a TA by indicating an absolute timing advance in the Random Access Response message (or in the MsgB in case of 2-step random access), but the range of TA values that may be signaled this way includes only non-negative values. To enable signaling of negative absolute TA values to a UE, this range of values would have to be extended to include also negative values. Alternatively, possible workaround could be to provide the UE with an absolute TA of value zero, and subsequently adjust the UE’s TA to the correct value using one or more relative TA adjustment instruction(s) (or relative residual TA adjustment instruction(s), e.g. Timing Advance Command MAC CE(s) or Residual Timing Advance Command MAC CE(s). Furthermore, in an NTN where negative absolute TAs can never exist, the network, e.g. the base station, will adjust its receive window for initial access transmissions, such as random access preamble transmissions in a system using random access as a network access procedure, accordingly, e.g. so that start of the receive window matches a transmission from a UE located at zero propagation delay from the concerned gNB interface, e.g. the gNB antenna. This is the case e.g. in 5G NR NTN. To take into account that a transmission from the UE (e.g. the UE’s initial transmission in an access procedure, e.g. a random access preamble transmission) may arrive at the base station at a time that implies that the UE needs a negative absolute timing advance, the base station must adapt its receive window for the initial access transmission, e.g. the random access preamble transmission, so that transmissions arriving at the base station at the earliest possible times (or earliest supported times) arrive within the receive window. Optionally, this adaptation of the receive window may be performed by extending or shifting the receive window compared with the receive window used in a network where such early UE transmission arrival times are not possible, e.g. compared with the random access preamble receive window a gNB uses in a 5G NR NTN or in a 5G NR terrestrial network.

[0156] Signaling options

[0157] There are various conceivable options for signaling of reference points and pseudoposition points.

[0158] A common reference point, i.e. a reference point that may be used by all or multiple of the UEs in the cell, may preferably be conveyed to the UEs using broadcast signaling, e.g. broadcast system information. Dedicated signaling, e.g. RRC signaling (e.g. an RRCReconfiguration message), MAC (e.g. using a new MAC CE) signaling or L1 / L2 signaling (e.g. DCI on a PDCCH) may be used to signal a reference point to a single UE, e.g. to instruct the UE to use the reference point as its pseudo-position.

[0159] A pseudo-position may be signaled in various ways. If the pseudo-position is a reference point, it may be signaled as described above. If pseudo-position is not a reference point, but instead e.g. a UE specific refined pseudo-position, it may be signaled to a UE using dedicated signaling, e.g. RRC signaling (e.g. an RRCReconfiguration message), MAC signaling (e.g. using a new MAC CE) or L1 / L2 signaling (e.g. DCI on a PDCCH). In the other direction, i.e. from the UE to the network, a pseudo-position or a reference point may be signaled e.g. using RRC signaling (e.g. a UEAssistancelnformation message) or MAC signaling (e.g. in a new MAC CE). Signaling of a pseudo-position or reference point from the UE to the network may be used e.g. to let the UE inform the network of a pseudo-position or a reference point the UE has selected and / or is using.

[0160] When a reference point or pseudo-position is signaled (in either direction and for whatever purpose), the format of the signaled reference point or pseudo-position may be e.g. one of:

[0161] Three coordinates, e.g. longitude, latitude and altitude, e.g. in an Earth-centered Earth- fixed (ECEF) coordinate system, e.g. using the WGS 84 ellipsoid as reference.

[0162] Two coordinates, e.g. longitude and latitude, e.g. in an Earth-centered Earth-fixed (ECEF) coordinate system, e.g. using the WGS 84 ellipsoid as reference. With this option, the altitude may be assumed (e.g. implicitly indicated) to be zero (which e.g. may imply that the signaled reference point or pseudo-position is located on the surface of the WGS 84 ellipsoid).

[0163] A format based on the definition of the ellipsoid point in 3GPP TS 23.032 V18.1.0 “ Universal Geographical Area Description (GAD) “, e.g. encoded as the Ellipsoid-Point IE in 3GPP TS 37.355 V18.1.0 “ LTE Positioning Protocol (LPP) “.

[0164] A format based on the definition of the ellipsoid point with altitude in 3GPP TS 3GPP TS 23.032 V18.1.0 “ Universal Geographical Area Description (GAD) “, e.g. encoded as the EllipsoidPointWithAltitude IE in 3GPP TS 37.355 V18.1.0 “LTE Positioning Protocol (LPP)“.

[0165] The above signaling and formatting options apply to NTN deployments using Earth- fixed cells or quasi-Earth-fixed cells. For a moving cell, a common reference point, e.g. a broadcast reference point, should follow the cell as it moves. This can be achieved in the same way as specified for a reference point (for RRM measurements and mobility purposes) in a moving cell in 5G NR NTN. That is, a reference point is signaled together with an epoch time, i.e. the time at which the signaled reference point (e.g. the signaled coordinates or the signaled coordinates and altitude) is nominally valid, and subsequently this reference point moves along with the satellite serving the cell, as described by the ephemeris data associated with the satellite (which is typically broadcast in the cell). The types of signaling and messages used for this signaling, as well as the formats used for the reference point, may be the same as described above for Earth-fixed and quasi-Earth-fixed cells. The epoch time may have the form of a UTC (e.g. a UTC timestamp) or it may be signaled and defined in terms of time related radio interface entities, such as a Hyper System Frame Number (H-SFN), a frame number (e.g. a System Frame Number, SFN), a subframe number, a slot number and / or a symbol number (or any combination of any of those).

[0166] Other signaling options for moving cells deployments are not precluded.

[0167] Note that if the UE obtains (from the network or through autonomous observations and / or measurements) a UE specific (possibly refined) pseudo-position, this UE specific pseudo-position should not move with the cell (i.e. in general, UE specific pseudo-positions do not move with the moving cell).

[0168] Leveraging the terrestrial network to obtain a pseudo-position

[0169] In one embodiment, when the UEs have access to a terrestrial network, the UE may use the terrestrial gNB for estimating their own positions (e.g. pseudo-positions) for initial access. For example, the UE may use the estimated location of its closest terrestrial gNB as its own position if enabled by the network. In another example, the UE may estimate its position relative to the one or more terrestrial gNB and use the estimated position for initial access. In another embodiment, the network may indicate the list of terrestrial cells that the UE may use for estimating its own position.

[0170] Figure 9 is a schematic block diagram of a network node 800 according to some embodiments of the present disclosure. The network node 800 may be, for example, the NTN node 408 of Figure 4 or a network node that performs part of the functionality of the NTN node 408 (e.g., a gNB-DU, a gNB-CU, a gNB-CU-CP, a gNB-CU-UP, an eNB-DU, an eNB-CU, an eNB-CU-CUP, an eNB-CU-UP, or the like). As illustrated, the network node 800 includes a control system 802 that includes one or more processors 804 (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and / or the like), memory 806, and a network interface 808. The one or more processors 804 are also referred to herein as processing circuitry. In addition, the network node 800 may include one or more radio units 810 that each includes one or more transmitters 812 and one or more receivers 814 coupled to one or more antennas 816. The radio units 810 may be referred to or be part of radio interface circuitry. In some embodiments, the radio unit(s) 810 is external to the control system 802 and connected to the control system 802 via, e.g., a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit(s) 810 and potentially the antenna(s) 816 are integrated together with the control system 802. The one or more processors 804 operate to provide one or more functions of the network node 800 as described herein (e.g., one or more functions of the NTN node 408 as described herein). In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory 806 and executed by the one or more processors 804.

[0171] Figure 9 also illustrates a virtualized embodiment of the network node 800 according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. As used herein, a “virtualized” network node is an implementation of the network node 800 in which at least a portion of the functionality of the network node 800 is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, in this example, the network node 800 may include the control system 802 and / or the one or more radio units 810, as described above. The control system 802 may be connected to the radio unit(s) 810 via, for example, an optical cable or the like. The radio access node 800 includes one or more processing nodes 900 coupled to or included as part of a network(s) 902. If present, the control system 802 or the radio unit(s) are connected to the processing node(s) 900 via the network 902. Each processing node 900 includes one or more processors 904 (e.g., CPUs, ASICs, FPGAs, and / or the like), memory 906, and a network interface 908.

[0172] In this example, functions 910 of the network node 800 described herein are implemented at the one or more processing nodes 900 or distributed across the one or more processing nodes 900 and the control system 802 and / or the radio unit(s) 810 in any desired manner. In some particular embodiments, some or all of the functions 910 of the network node 800 described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 900. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) 900 and the control system 802 is used in order to carry out at least some of the desired functions 910. Notably, in some embodiments, the control system 802 may not be included, in which case the radio unit(s) 810 communicates directly with the processing node(s) 900 via an appropriate network interface(s).

[0173] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the network node 800 or a node (e.g., a processing node 900) implementing one or more of the functions 910 of the network node 800 in a virtual environment according to any of the embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., anon-transitory computer readable medium such as memory).

[0174] Figure 10 is a schematic block diagram of a UE 1000 (e.g., the UE 402) according to some embodiments of the present disclosure. As illustrated, the UE 1000 includes one or more processors 1002 (e.g., CPUs, ASICs, FPGAs, and / or the like), memory 1004, and one or more transceivers 1006 each including one or more transmitters 1008 and one or more receivers 1010 coupled to one or more antennas 1012. The transceiver(s) 1006 includes radio-front end circuitry connected to the antenna(s) 1012 that is configured to condition signals communicated between the antenna(s) 1012 and the processor(s) 1002, as will be appreciated by on of ordinary skill in the art. The processors 1002 are also referred to herein as processing circuitry. The transceivers 1006 are also referred to herein as radio circuitry. In some embodiments, the functionality of the UE 1000 (e.g., the functionality of the UE 402 described herein) may be fully or partially implemented in software that is, e.g., stored in the memory 1004 and executed by the processor(s) 1002. Note that the UE 1000 may include additional components not illustrated in Figure 10 such as, e.g., one or more user interface components (e.g., an input / output interface including a display, buttons, a touch screen, a microphone, a speaker(s), and / or the like and / or any other components for allowing input of information into the UE 1000 and / or allowing output of information from the UE 1000), a power supply (e.g., a battery and associated power circuitry), etc.

[0175] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the UE 1000 according to any of the embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

[0176] With reference to Figure 11, in accordance with an embodiment, a communication system includes a telecommunication network 1100, such as a 3 GPP-type cellular network, which comprises an access network 1102, such as a RAN, and a core network 1104. The access network 1102 comprises a plurality of base stations 1106A, 1106B, 1106C, such as Node Bs, eNBs, gNBs, or other types of wireless Access Points (APs), each defining a corresponding coverage area 1108A, 1108B, 1108C. Each base station 1106A, 1106B, 1106C is connectable to the core network 1104 over a wired or wireless connection 1110. A first UE 1112 located in coverage area 1108C is configured to wirelessly connect to, or be paged by, the corresponding base station 1106C. A second UE 1114 in coverage area 1108A is wirelessly connectable to the corresponding base station 1106A. While a plurality of UEs 1112, 1114 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 1106.

[0177] The telecommunication network 1100 is itself connected to a host computer 1116, which may be embodied in the hardware and / or software of a standalone server, a cloud- implemented server, a distributed server, or as processing resources in a server farm. The host computer 1116 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. Connections 1118 and 1120 between the telecommunication network 1100 and the host computer 1116 may extend directly from the core network 1104 to the host computer 1116 or may go via an optional intermediate network 1122. The intermediate network 1122 may be one of, or a combination of more than one of, a public, private, or hosted network; the intermediate network 1122, if any, may be a backbone network or the Internet; in particular, the intermediate network 1122 may comprise two or more sub-networks (not shown).

[0178] The communication system of Figure 11 as a whole enables connectivity between the connected UEs 1112, 1114 and the host computer 1116. The connectivity may be described as an Over-the-Top (OTT) connection 1124. The host computer 1116 and the connected UEs 1112, 1114 are configured to communicate data and / or signaling via the OTT connection 1124, using the access network 1102, the core network 1104, any intermediate network 1122, and possible further infrastructure (not shown) as intermediaries. The OTT connection 1124 may be transparent in the sense that the participating communication devices through which the OTT connection 1124 passes are unaware of routing of uplink and downlink communications. For example, the base station 1106 may not or need not be informed about the past routing of an incoming downlink communication with data originating from the host computer 1116 to be forwarded (e.g., handed over) to a connected UE 1112. Similarly, the base station 1106 need not be aware of the future routing of an outgoing uplink communication originating from the UE 1112 towards the host computer 1116.

[0179] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according to one or more embodiments of the present disclosure.

[0180] In some embodiments, the telecommunication network 1100 includes anon-terrestrial network, NTN. Unless otherwise described herein, embodiments applicable for NTN may be implanted according to the following clauses. An NTN is telecommunication network where the radio access payload is conveyed via satellite to a ground station. E-UTRAN supports radio access over non-terrestrial networks for BL UEs, UEs in enhanced coverage and NB-IoT UEs. Support for non-terrestrial networks encompasses platforms that provide radio access through Geosynchronous orbits (GSO), Non-Geosynchronous Orbit (NGSO), which includes Low-Earth Orbit (LEO) and Medium Earth Orbit (MEO) or High Altitude Platform Systems (HAPS). Another example of a Non-Terrestrial Network (NTN) provides non-terrestrial NR access to the UE by means of an NTN payload and an NTN Gateway, a service link between the NTN payload and a UE, and a feeder link between the NTN Gateway and the NTN payload exists. An access network QQ104 may include an NTN access network such as the 3GPP Satellite Access Node (SAN) which comprises Non-NTN infrastructure base station functions (e.g. eNB / gNB) a terrestrial Gateway which provides the interface to the feeder link to an NTN payload RF node. In some embodiments a network node 800 comprises a SAN, wherein the location of base station functions for a network node 800 (described above for the general terrestrial access) vary between residing in the terrestrial access network node part of the SAN and the NTN Payload RF node functions depending on the supported architecture. One example of NTN architecture is called bent pipe or transparent architecture where the radio frequency processing function (transceiver) on a satellite platform is interconnected with a terrestrial base station, also known as transparent architecture, and the NTN payload is passed transparently, no unpacking. Another example of NTN architecture is called regenerative architecture, where part or all of the eNB / gNB can be in the satellite.

[0181] In some examples a SAN includes an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O-CU-CP) or an O- CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or anon-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification).

[0182] Figure 12 is a flow chart that illustrates an example method 1200 performed by User Equipment, UE, 402 in a cellular communications system 400. The method includes the step of receiving 1210 position assistance information from a Non-Terrestrial Network, NTN, node 408 in a NTN cell 410. The position assistance information is information that allows the UE 402 to choose or determine a pseudo-position of the UE 402, e.g., while the UE 402 is in a low activity RRC state (e.g., RRC IDLE or RRC IN ACTIVE state) or RRC_CONNECTED state. In one example, the NTN node 408 provides the position assistance information to multiple UEs (including the UE 402) on the NTN cell 410 via broadcasted system information. Optionally, this broadcasted position assistance information targets UEs in RRC INACTIVE and RRC IDLE states. In one embodiment, the position assistance information is included in a System Information Block (SIB) or possibly in multiple SIBs, e.g., divided into parts where different parts are included in different SIBs. Optionally, using broadcast information to convey the position assistance information would (primarily) be intended for UEs in low activity RRC state (i.e., UEs in RRC INACTIVE state and RRC IDLE state), but as another option, UEs in RRC CONNETED state can also receive the position system information via the broadcast information. In one example, the SIB can be configured to be on-demand to avoid the signaling load of numerous (potentially redundant) transmissions of the position assistance information. This may for instance be a new SIB, e.g., introduced for this purpose. In another example, the NTN node 408 provides the position assistance information to the UE 402 on the NTN cell 410 via a dedicated message while the UE 402 is in RRC_CONNEDCTED state, e.g. an RRC message, a Medium Access Control (MAC)-Control Element (CE), or a Downlink Control Information (DCI) message.

[0183] From the UE’s perspective, if the UE 402 is aware of its need to know its own position (to some level of accuracy) for procedures related to one or more neighbor NTN cell(s) 410, e.g. neighbor cell measurements and / or TA calculation, e.g. due to a potential cell change to an NTN cell 410 (e.g. cell reselection if the UE 402 is in a low activity RRC state or handover if the UE 402 is in RRC_CONNECTED state), and the UE 402 currently does not have valid UE position information and currently cannot perform a GNSS measurement, or cannot perform a GNSS measurement within a required time, the UE 402 obtains the position assistance information (step 1210). This may include receiving position assistance information from the NTN node 408 on the NTN cell 410 via broadcast information (e.g., via a broadcast SIB). In some cases, the broadcast information containing the position assistance information (e.g., SIB(s) including the position assistance information) are transmitted by the NTN node 408 on-demand, and this may require that the UE 402 first sends, to the NTN node 408, a request for broadcast of a SI message(s) (e.g., a SIB(s)) containing the position assistance information.

[0184] Alternatively, if the UE 402 is in RRC_CONNECTED state, the obtaining (or attempt to obtain) the position assistance information may include receiving a dedicated (i.e., not broadcast but addressed to the UE) message (e.g., an RRC message, a MAC CE or a DCI message) including the position assistance information. The NTN node 408 may be triggered to send the dedicated message by a preceding request from the UE 402 to receive the position assistance information or an indication from the UE 402 that it lacks valid UE position information (step 500). The indication also may indicate that the UE 402 will not be able to autonomously obtain valid UE position information (e.g., through a GNSS measurement) fast enough e.g., for successful execution of a procedure that triggered the need for the UE position information, or that the UE 402 lacks support for GNSS position measurements. As yet another alternative for the case where the UE 402 is in RRC_CONNECTED state, the obtaining (or attempt to obtain) the position assistance information may involve triggering, or requesting the network to initiate, a network-based (or network-involved) UE positioning measurement, e.g., using a procedure in the LCS framework.

[0185] The method proceeds with the UE obtaining 1220 a pseudo-position of the UE 402 based on the position assistance information (i.e., estimates the position of the UE 402 or uses a default or specified position) based on the obtained position assistance information for the NTN cell 410. In one example, a pseudo position of the UE 402 can be acquired based on the position assistance information obtained for the NTN cell 410. In another example, an approximate position of the UE 402 can be acquired based on the position assistance information provided by a previously serving NTN cell of the UE 402. In another example, the position of the UE 402 can be estimated based on combining position assistance information provided by one or more previously serving NTN cells and the current serving NTN cell 410 of the UE 402. In the above examples, combining the position assistance information associated with different cells may involve calculating an average position, a weighted average position (e.g. giving different weights to different ones of the position estimates obtained from the position assistance information associated with different cells), or any other calculation to obtain a pseudo-position based on the position estimates obtained from the position assistance information associated with the different cells.

[0186] In the example method 1200, the final step involves the UE performing 1230 one or more actions with respect to one or more NTN cells 410, based on the pseudo-position of the UE 402. The UE 402 uses the position of the UE 402 obtained based on the position assistance information in step 1220 to perform one or more actions relative to one or more NTN cells. For example, the UE 402 may use the position obtained in step 1220 to perform measurements on one or more neighboring NTN cells 410 and / or to perform uplink synchronization (e.g., TA and / or Doppler shift) to a particular NTN cell 410 (e.g., in order to transmit a random access preamble on the NTN cell 410).

[0187] Figure 13 is a flow chart that illustrates an example method 1300 performed by a NonTerrestrial Network, NTN, node 402. The method 1300 includes the step of providing 1310 position assistance information to a User Equipment, UE, 402 on a NTN cell 410, wherein the position assistance information comprises information that enables the UE 402 to select or derive a pseudo-position of the UE 402. The position assistance information is information that allows the UE 402 to choose or determine a pseudo-position of the UE 402, e.g., while the UE 402 is in a low activity RRC state (e.g., RRC IDLE or RRC INACTIVE state) or RRC_CONNECTED state. In one example, the NTN node 408 provides the position assistance information to multiple UEs (including the UE 402) on the NTN cell 410 via broadcasted system information. Optionally, this broadcasted position assistance information targets UEs in RRC INACTIVE and RRC IDLE states. In one embodiment, the position assistance information is included in a System Information Block (SIB) or possibly in multiple SIBs, e.g., divided into parts where different parts are included in different SIBs. Optionally, using broadcast information to convey the position assistance information would (primarily) be intended for UEs in low activity RRC state (i.e., UEs in RRC INACTIVE state and RRC IDLE state), but as another option, UEs in RRC CONNETED state can also receive the position system information via the broadcast information. In one example, the SIB can be configured to be on-demand to avoid the signaling load of numerous (potentially redundant) transmissions of the position assistance information. This may for instance be a new SIB, e.g., introduced for this purpose. In another example, the NTN node 408 provides the position assistance information to the UE 402 on the NTN cell 410 via a dedicated message while the UE 402 is in RRC_CONNEDCTED state, e.g. an RRC message, a Medium Access Control (MAC)-Control Element (CE), or a Downlink Control Information (DCI) message. The NTN node 408 may be triggered to send the dedicated message by a preceding request from the UE 402 to receive the position assistance information or an indication from the UE 402 that it lacks valid UE position information. The indication also may indicate that the UE 402 will not be able to autonomously obtain valid UE position information (e.g., through a GNSS measurement) fast enough e.g., for successful execution of a procedure that triggered the need for the UE position information, or that the UE 402 lacks support for GNSS position measurements. As yet another alternative for the case where the UE 402 is in RRC_CONNECTED state, the obtaining (or attempt to obtain) the position assistance information may involve triggering, or requesting the network to initiate, a network-based (or network-involved) UE positioning measurement, e.g., using a procedure in the LCS framework.

[0188] The method 1300 may optionally include the step of estimating 1320 a positioning related value. In some examples this may be a velocity of the UE, in other examples this may be a position of the UE.

[0189] The method 1300 may further include the step of generating and transmitting 1330 an update command for the positioning related value. In some examples this may be generating a velocity update command based on the estimated velocity of the UE and transmitting the velocity update command to the UE. In other examples this may be generating a closed-loop time and / or frequency adjustment command for the UE; and transmitting the time and / or frequency adjustment command to the UE. In yet other examples this may be generating a position update command based on the pseudo-position of the UE and transmitting the position update command to the UE. While processes in the figures may show a particular order of operations performed by certain embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.). Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

[0190] EMBODIMENTS

[0191] 1. A method performed by a User Equipment, UE, (402) in a cellular communications system (400), the method comprising: receiving (504) position assistance information from a Non-Terrestrial Network, NTN, node (408) in a NTN cell (410); obtaining (506) a pseudo-position of the UE (402) based on the position assistance information; and performing (508) one or more actions with respect to one or more NTN cells (410), based on the pseudo-position of the UE (402) obtained based on the position assistance information.

[0192] 2. The method of Embodiment 1, wherein the one or more actions comprise accessing one of the NTN cells (410), based on the pseudo-position of the UE (402) obtained based on the position assistance information.

[0193] 3. The method of Embodiment 1 or 2, wherein the one or more actions comprise performing uplink synchronization with respect to a NTN cell (410) from among the one or more NTN cells (410), based on the pseudo-position of the UE (402) obtained based on the position assistance information.

[0194] 4. The method of any of Embodiments 1 to 3, wherein the pseudo-position obtained based on the position assistance information is used to perform the one or more actions in place of a position of the UE obtained via a Global Navigation Satellite System, GNSS, receiver.

[0195] 5. The method of any of Embodiments 1 to 4, wherein receiving (504) the position assistance information comprises receiving broadcast information comprising the position assistance information in the NTN cell (410).

[0196] 6. The method of any of Embodiments 1 to 4, wherein receiving (504) the position assistance information comprises receiving the position assistance information via one or more dedicated messages. 7. The method of any of Embodiments 1 to 6, wherein the position assistance information comprises a refinement of a previously estimated position of the UE.

[0197] 8. The method of any of Embodiments 1 to 7, wherein the position assistance information comprises position assistance information for the NTN cell (410).

[0198] 9. The method of any of Embodiments 1 to 8, wherein the position assistance information comprises position assistance information for the NTN cell (410) and position assistance information for one or more additional NTN cells.

[0199] 10. The method of any of Embodiments 1 to 9, wherein the one or more actions comprise performing an initial access or random access to the NTN cell.

[0200] 11. The method of any of Embodiments 1 to 10, wherein the one or more actions comprise determining a time and / or frequency pre-compensation value to be applied to transmissions by the UE.

[0201] 12. The method of any of Embodiments 1 to 11, wherein obtaining the pseudo-position of the UE comprises: determining whether a timer has expired; and in response to determining that the timer has not expired, using a previously estimated position of the UE as the pseudo-position of the UE.

[0202] 13. The method of Embodiment 12, wherein the previous position of the UE is a position of the UE at the time of a previous transmission by the UE.

[0203] 14. The method of Embodiment 12, wherein the previous position of the UE is a previously determined position estimate of the UE.

[0204] 15. The method of any of Embodiments 1 to 14, further comprising receiving a timer value for the timer from the NTN node and applying the timer value.

[0205] 16. The method of any of Embodiments 1 to 15, further comprising: estimating a velocity of the UE; and determining a frequency pre-compensation based on the estimated velocity and the pseudoposition of the UE.

[0206] 17. The method of Embodiment 16, further comprising: receiving a velocity update command from the NTN node.

[0207] 18. The method of any of Embodiments 1 to 17, further comprising: receiving a closed-loop time and / or frequency adjustment command from the NTN node; and applying the time and / or frequency adjustment command when performing a transmission in the NTN node.

[0208] 19. The method of any of Embodiments 1 to 18, further comprising: receiving a position update command from the NTN node; and updating the pseudo-position of the UE based on the position update command.

[0209] 20. The method of Embodiment 19, wherein the position update command is received in a random access response, RAR.

[0210] 21. The method of Embodiment 20, wherein the RAR further comprises a time and / or frequency adjustment command.

[0211] 22. The method of any of Embodiments 1 to 21, wherein the position assistance information is received while the UE is in a connected mode.

[0212] 23. The method of Embodiment 22, wherein the position assistance information is received in a medium access control, MAC, control element, CE.

[0213] 24. The method of any of Embodiments 1 to 23, wherein the one or more actions comprise performing a mobility operation towards a second NTN node.

[0214] 25. The method of any of Embodiments 1 to 24, wherein the position assistance information comprises a time derivative of a frequency adjustment parameter, and wherein the UE adjusts the frequency adjustment parameter based on the time derivative of the frequency adjustment parameter.

[0215] 26. The method of any of Embodiments 1 to 25, wherein the position assistance information comprises a time derivative of a timing adjustment parameter, and wherein the UE adjusts the timing adjustment parameter based on the time derivative of the timing adjustment parameter.

[0216] 27. A User Equipment, UE, (402) for obtaining an estimate of a position of the UE (402) in a cellular communications system (400), the UE adapted to: receive (504) position assistance information from a Non-Terrestrial Network, NTN, node (408) in a NTN cell (410); obtain (506) a pseudo-position of the UE (402) based on the position assistance information; and perform (508) one or more actions with respect to one or more cells (410), based on the pseudo-position of the UE (402) obtained based on the position assistance information.

[0217] 28. The UE of Embodiment 28 further adapted to perform the method of any of Embodiments 2 to 26.

[0218] 29. A User Equipment, UE, (402; 1000) for obtaining an estimate of a position of the UE (402) in a cellular communications system (400), the UE (402; 1000) comprising: one or more transmitters (1008); one or more receivers (1010); and processing circuitry (1002) associated with the one or more transmitters (1008) and the one or more receivers (1010), the processing circuitry (1002) configured to cause the UE (402; 1000) to: receive (504) position assistance information from a Non-Terrestrial Network, NTN, node (408) on a NTN cell (410); obtain (506) a pseudo-position of the UE (402) based on the position assistance information; and perform (508) one or more actions with respect to one or more cells (410), based on the pseudo-position of the UE (402) obtained based on the position assistance information. 30. The UE (402; 1000) of Embodiment 30, wherein the processing circuitry (1002) is further configured to cause the UE (402; 1000) to perform the method of any of Embodiments 2 to 26.

[0219] 31. A computer program comprising instructions which, when executed on at least one processor, cause the processor to carry out the method according to any of Embodiments 1 to 26.

[0220] 32. A carrier containing the computer program of Embodiment 31 , wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

[0221] 33. A non-transitory computer-readable medium comprising instructions executable by processing circuitry of a User Equipment, UE, whereby the UE is operable to: receive (504) position assistance information from a Non-Terrestrial Network, NTN, node (408) on a NTN cell (410); obtain (506) a pseudo-position of the UE (402) based on the position assistance information; and perform (508) one or more actions with respect to one or more cells (410), based on the pseudo-position of the UE (402) obtained based on the position assistance information.

[0222] 34. A method performed by a Non-Terrestrial Network, NTN, node (402), comprising: providing (502) position assistance information to a User Equipment, UE, (402) on a

[0223] NTN cell (410); wherein the position assistance information comprises information that enables the UE (402) to select or derive a pseudo-position of the UE (402).

[0224] 35. The method of Embodiment 34, wherein providing (504) the position assistance information to the UE (402) comprises transmitting broadcast information comprising the position assistance information on the NTN cell (410).

[0225] 36. The method of Embodiment 34, wherein providing (504) the position assistance information comprises transmitting the position assistance information to the UE (402) via one or more dedicated messages.

[0226] 37. The method of any of Embodiments 34 to 36, wherein the position assistance information comprises position assistance information for the NTN cell (410).

[0227] 38. The method of any of Embodiments 34 to 37, further comprising providing a timer value to the UE for the UE to use to determine whether to apply the position assistance information.

[0228] 39. The method of Embodiment 38, further comprising: estimating a velocity of the UE; generating a velocity update command based on the estimated velocity of the UE; and transmitting the velocity update command to the UE.

[0229] 40. The method of any of Embodiments 34 to 39, wherein the position assistance information comprises a refinement of a previously estimated position of the UE.

[0230] 41. The method of any of Embodiments 34 to 40, further comprising: generating a closed-loop time and / or frequency adjustment command for the UE; and transmitting the time and / or frequency adjustment command to the UE.

[0231] 42. The method of any of Embodiments 34 to 41, further comprising: estimating a position of the UE; generating a position update command based on the pseudo-position of the UE; and transmitting the position update command to the UE.

[0232] 43. The method of Embodiment 42, wherein the position update command is transmitted to the UE in a random access response, RAR.

[0233] 44. The method of Embodiment 43, wherein the RAR further comprises a time and / or frequency adjustment command for the UE. 45. The method of any of Embodiments 34 to 44, wherein the position assistance information is transmitted to the UE while the UE is in a connected mode.

[0234] 46. The method of Embodiment 45, wherein the position assistance information is transmitted to the UE in a medium access control, MAC, control element, CE.

[0235] 47. The method of any of Embodiments 34 to 46, wherein the position assistance information comprises a time derivative of a frequency adjustment parameter, and wherein the UE adjusts the frequency adjustment parameter based on the time derivative of the frequency adjustment parameter.

[0236] 48. The method of any of Embodiments 34 to 47, wherein the position assistance information comprises a time derivative of a timing adjustment parameter, and wherein the UE adjusts the timing adjustment parameter based on the time derivative of the timing adjustment parameter.

[0237] 49. A Non-Terrestrial Network, NTN, node (408) adapted to: provide (502) position assistance information to a User Equipment, UE, (402) on a NTN cell (410); wherein the position assistance information comprises information that enables the UE (402) to select or derive a pseudo-position of the UE (402).

[0238] 50. The NTN node (408) of Embodiment 51 further adapted to perform the method of any of Embodiments 35 to 49.

[0239] 51. A Non-Terrestrial Network, NTN, node (408) comprising processing circuitry configured to cause the NTN node (408) to: provide (502) position assistance information to a User Equipment, UE, (402) on a NTN cell (410); wherein the position assistance information comprises information that enables the UE (402) to select or derive a position of the UE (402).

[0240] 52. The NTN node (408) of Embodiment 53, wherein the processing circuitry is further configured to cause the NTN node (408) to perform the method of any of Embodiments 35 to 49.

[0241] 53. A computer program comprising instructions which, when executed on at least one processor, cause the processor to carry out the method according to any of Embodiments 34 to 49.

[0242] 54. A carrier containing the computer program of Embodiment 53, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

[0243] 55. A non-transitory computer-readable medium comprising instructions executable by processing circuitry of a Non-Terrestrial Network, NTN, node, whereby the NTN node is operable to: provide (504) position assistance information to a User Equipment, UE, (402) on a NTN cell (410); wherein the position assistance information comprises information that enables the UE (402) to select or derive a pseudo-position of the UE (402).

Claims

CLAIMS1. A method (1200) performed by a User Equipment, UE, (402) in a cellular communications system (400), the method comprising: receiving (1210) position assistance information from a Non-Terrestrial Network, NTN, node (408) in a NTN cell (410); obtaining (1220) a pseudo-position of the UE (402) based on the position assistance information; and performing (1230) one or more actions with respect to one or more NTN cells (410), based on the pseudo-position of the UE (402).

2. The method of claim 1, wherein the one or more actions comprise accessing one of the NTN cells (410), based on the pseudo-position of the UE (402).

3. The method of claim 1 or 2, wherein the one or more actions comprise performing uplink synchronization with respect to an NTN cell (410) from among the one or more NTN cells (410), based on the pseudo-position of the UE (402).

4. The method of any of claims 1 to 3, wherein the pseudo-position obtained based on the position assistance information is used to perform the one or more actions in place of a position of the UE obtained via a Global Navigation Satellite System, GNSS, receiver.

5. The method of any of claims 1 to 4, wherein receiving (1210) the position assistance information comprises receiving broadcast information comprising the position assistance information in the NTN cell (410).

6. The method of any of claims 1 to 4, wherein receiving (1210) the position assistance information comprises receiving the position assistance information via one or more dedicated messages.

7. The method of any of claims 1 to 6, wherein the position assistance information comprises a refinement of a previously estimated position of the UE.

8. The method of any of claims 1 to 7, wherein the position assistance information comprises position assistance information for the NTN cell (410).

9. The method of any of claims 1 to 8, wherein the position assistance information comprises position assistance information for the NTN cell (410) and position assistance information for one or more additional NTN cells.

10. The method of any of claims 1 to 9, wherein the one or more actions comprise performing an initial access or random access to the NTN cell.

11. The method of any of claims 1 to 10, wherein the one or more actions comprise determining a time and / or frequency pre-compensation value to be applied to transmissions by the UE.

12. The method of any of claims 1 to 11, wherein obtaining the pseudo-position of the UE comprises: determining whether a timer has expired; and in response to determining that the timer has not expired, using a previously estimated position of the UE as the pseudo-position of the UE.

13. The method of claim 12, wherein the previous position of the UE is a position of the UE at the time of a previous transmission by the UE.

14. The method of claim 12, wherein the previous position of the UE is a previously determined position estimate of the UE.

15. The method of any of claims 1 to 14, further comprising receiving a timer value for the timer from the NTN node and applying the timer value.

16. The method of any of claims 1 to 15, further comprising: estimating a velocity of the UE; and determining a frequency pre-compensation based on the estimated velocity and the pseudo-position of the UE.

17. The method of claim 16, further comprising: receiving a velocity update command from the NTN node.

18. The method of any of claims 1 to 17, further comprising: receiving a closed-loop time and / or frequency adjustment command from the NTN node; and applying the time and / or frequency adjustment command when performing a transmission in the NTN node.

19. The method of any of claims 1 to 18, further comprising: receiving a position update command from the NTN node; and updating the pseudo-position of the UE based on the position update command.

20. The method of claim 19, wherein the position update command is received in a random access response, RAR.

21. The method of claim 20, wherein the RAR further comprises a time and / or frequency adjustment command.

22. The method of any of claims 1 to 21, wherein the position assistance information is received while the UE is in a connected mode.

23. The method of claim 22, wherein the position assistance information is received in a medium access control, MAC, control element, CE.

24. The method of any of claims 1 to 23, wherein the one or more actions comprise performing a mobility operation towards a second NTN node.

25. The method of any of claims 1 to 24, wherein the position assistance information comprises a time derivative of a frequency adjustment parameter, and wherein the UE adjusts the frequency adjustment parameter based on the time derivative of the frequency adjustment parameter.

26. The method of any of claims 1 to 25, wherein the position assistance information comprises a time derivative of a timing adjustment parameter, and wherein the UE adjusts the timing adjustment parameter based on the time derivative of the timing adjustment parameter.

27. A User Equipment, UE, (402; 1000) for obtaining an estimate of a position of the UE (402) in a cellular communications system (400), the UE (402; 1000) comprising: one or more transmitters (1008); one or more receivers (1010); and processing circuitry (1002) associated with the one or more transmitters (1008) and the one or more receivers (1010), the processing circuitry (1002) configured to cause the UE (402; 1000) to: receive (504) position assistance information from a Non-Terrestrial Network, NTN, node (408) on a NTN cell (410); obtain (506) a pseudo-position of the UE (402) based on the position assistance information; and perform (508) one or more actions with respect to one or more cells (410), based on the pseudo-position of the UE (402) obtained based on the position assistance information.

28. The UE (402; 1000) of claim 27, wherein the processing circuitry (1002) is further configured to cause the UE (402; 1000) to perform the method of any of claims 2 to 26.

29. A method (1300) performed by a Non-Terrestrial Network, NTN, node (402), comprising: providing (1310) position assistance information to a User Equipment, UE, (402) on a NTN cell (410); wherein the position assistance information comprises information that enables the UE (402) to select or derive a pseudo-position of the UE (402).

30. The method of claim 29, wherein providing (1310) the position assistance information to the UE (402) comprises transmitting broadcast information comprising the position assistance information on the NTN cell (410).

31. The method of claim 29, wherein providing (1310) the position assistance information comprises transmitting the position assistance information to the UE (402) via one or more dedicated messages.

32. The method of claim 29, further comprising: estimating (1320) a velocity of the UE; generating a velocity update command based on the estimated velocity of the UE; and transmitting (1330) the velocity update command to the UE.

33. The method of any of claims 29 to 32, further comprising: generating a closed-loop time and / or frequency adjustment command for the UE; and transmitting (1330) the time and / or frequency adjustment command to the UE.

34. The method of any of claims 29 to 33, further comprising:Estimating (1320) a position of the UE; generating a position update command based on the pseudo-position of the UE; and transmitting (1330) the position update command to the UE.

35. The method of claim 34, wherein the position update command is transmitted to the UE in a random access response, RAR.

36. A Non-Terrestrial Network, NTN, node (408) comprising processing circuitry configured to cause the NTN node (408) to: provide (502) position assistance information to a User Equipment, UE, (402) on a NTN cell (410); wherein the position assistance information comprises information that enables the UE (402) to select or derive a position of the UE (402).

37. The NTN node (408) of claim 36, wherein the processing circuitry is further configured to cause the NTN node (408) to perform the method of any of claims 30 to 35.

38. A computer program, a carrier containing the computer program, or non-transitory computer-readable medium comprising instructions executable by processing circuitry which,when executed on at least one processor, cause the processor to carry out the method according to any of claims 1 to 26 or to 29 to 35.

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