TECHNICAL FIELD

The present disclosure generally pertains to entities and user equipment of a mobile telecommunica- tion system, in particular to Non-Terrestrial Networks (NTN).

TECHNICAL BACKGROUND

Several generations of mobile telecommunications systems are known, e.g. the third generation (“3G”), which is based on the International Mobile Telecommunications-2000 (IMT-2000) specifi- cations, the fourth generation (“4G”) which provides capabilities as defined in the International Mo- bile Telecommunications-Advanced Standard (EMT-Advanced Standard), and the current fifth generation (“5G”) which provides a new air interface called New Radio Access Technology Systems (NR). The 5G technology is based on 4G technology such as LTE which is standardized under the control of 3GPP (“3rd Generation Partnership Project”). There exists a successor LTE-A (LTE Ad- vanced) allowing higher data rates than the basic LTE which is also standardized under the control of 3GPP. LTE was based on previous generations of mobile communications technologies such as GSM/EDGE (“Global System for Mobile Communications”/“Enhanced Data rates for GSM Evo- lution” also called EGPRS) of the second generation (“2G”) and UMTS/HSPA (“Universal Mobile Telecommunications System”/“High Speed Packet Access”) of the third generation “3G”) network technologies.

As the 5G system is based on LTE or LTE-A, respectively, specific requirements of the 5G technol- ogies are dealt with by features and methods which are already defined in the LTE and LTE-A standard documentation.

Current technical areas of interest in 5G technology are known as the “Internet of Things”, or loT for short, and “Machine to Machine Communication” (M2M), or "Machine Type Communication" (MTC). 3GPP is developing technologies for supporting narrow band (NB)-IoT using an LTE or 4G wireless access interface and wireless infrastructure. Such loT devices are expected to be low complexity and inexpensive devices requiring infrequent communication of relatively low bandwidth data. It is also expected that there will be an extremely large number of loT devices which would need to be supported in a cell of the wireless communications network.

[2] 3GPP TR38.821, “Solutions for NR to support non-terrestrial networks (NTN) (Release 16)”, Dec 2019. The technical report "Study on New Radio (NR) to support non-terrestrial networks", 3GPP TR 38.811 V15.3.0 (2020-07) relates to Non-Terrestrial Network (NTN) components of a 5G system. Non-Terrestrial Network components in the 5G system rely on space/ airborne vehicles such as sat- ellites to provide 5G service in un-served areas (isolated/ remote areas, on board aircrafts or ships, high speed trains, etc.) that cannot be covered by terrestrial 5G network and underserved areas (e.g. sub-urban/ rural areas). Non-Terrestrial Networks (NTN) also reinforce the 5G service reliability by providing service continuity for M2M/IoT devices or ensuring service availability anywhere espe- cially for critical communications, future railway/maritime/aeronautical communications, and to en- able 5G network scalability by providing efficient multicast/broadcast resources for data delivery towards the network edges or even user terminal. A role for Non-Terrestrial Network components in the 5G system is expected in the fields of transport, public safety, media and entertainment, eHealth, energy, agriculture, finance, and automotive.

Typically, in mobile communication networks such as 3G, 4G, and 5G, the time at which a User Equipment (e.g. phone) is allowed to transmit traffic within a timeslot is adjusted according to the distance between the UE and the base station (eNodeB, gNB) to cope with transmission delays and to prevent interference with adjacent users. Timing Advance (TA) is the variable controlling this ad- justment. In general, timing advance (TA) is the time that the UE has to advance its transmissions by so that the transmission arrives at the base station at the appropriate time in the uplink subframe the start of which is aligned to the downlink subframe.. This offset at the UE is necessary to ensure that the downlink and uplink subframes are synchronised at the base station (gNB). The base station (gNB) continuously measures timing of uplink signals from each UE and adjusts the uplink trans- mission timing by sending the value of Timing Advance (TA) to the respective UE. As long as a UE sends some uplink data or signal (PUSCH/PUCCH/SRS), the gNB can estimate the uplink signal arrival time which can then be used to calculate the required Timing Advance value.

As the beam footprint sizes of Non-Terrestrial Networks NTN components are bigger than normal terrestrial cells, it is expected that TAs will be larger than the typical TAs in a terrestrial network wherein cell sizes are a lot smaller. The technical specification "Solutions for NR to support non- terrestrial networks (NTN)", 3GPP TR 38.821 V16.0.0 (2019-12), describes in section 6.3 the Uplink timing advance/RACH procedure, and, addresses in section 6.3.4 the aspect of maintenance for UL timing advance and synchronization in such NTN cells, introducing a common TA that is deter- mined with respect to a common reference point defined by the non-terrestrial network entity, and UE-specific TAs. However, improvements in the technology of maintenance for UL timing advance and synchronization when Non-Terrestrial Networks NTN components are involved are needed. SUMMARY

According to a first aspect, the disclosure provides an electronic device comprising circuitry config- ured to compensate feeder link influence on the common TA in a transparent payload non-terres- trial network configuration with a non-terrestrial network component and an infrastructure equipment tethered by the non-terrestrial network component.

According to a further aspect, the disclosure provides a method an infrastructure equipment com- prising circuitry configured to provide information to a user equipment for compensating feeder link influence on the common TA in a transparent payload non-terrestrial network configuration with a non-terrestrial network component and a base station tethered by the non-terrestrial network com- ponent.

According to a further aspect, the disclosure provides a method comprising compensating feeder link influence on the common TA in a transparent payload non-terrestrial network configuration with a non-terrestrial network component and an infrastructure equipment tethered by the non-ter- restrial network component.

Further aspects are set forth in the dependent claims, the following description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are explained by way of example with respect to the accompanying drawings, in which:

Fig. 1 shows a Non-Terrestrial Network (NTN) in which a space/ aerial vehicle relays an NR signal between a gNB and a UE in a transparent manner;

Fig. 2 schematically illustrates an embodiment of uplink (UL) time synchronization in a transparent payload NTN scenario;

Fig. 3a shows a first embodiment of a process compensating a changing common TA at the UE in a transparent payload NTN;

Fig. 3b shows a variant of the first embodiment where the UE determined the common TA;

Fig. 4a shows a second embodiment of a process compensating a changing common TA in a trans- parent payload NTN;

Fig. 4b shows a variant of the second embodiment where the UE determined the common TA;

Fig. 5 shows a third embodiment of a process compensating a changing common TA in a transpar- ent payload NTN; Fig. 6 shows a fourth embodiment of a process compensating a changing common TA in a transpar- ent payload NTN;

Fig. 7 shows an example of determining a TA adjustment based on a drift figure and direction sent from the network to the UE;

Fig. 8 shows an example of representing ephemeris data;

Fig. 9 shows a schematic block diagram of a communications path between an UE and an gNB; and

Fig. 10 shows an embodiment of a controller for a UE, a gNB, a relay node or a non-terrestrial net- work component.

DETAILED DESCRIPTION OF EMBODIMENTS

Before a detailed description of the embodiments under reference of Fig. 1, some general explana- tions are made.

The embodiments described below disclose an electronic device comprising circuitry configured to compensate feeder link influence on the common TA in a transparent payload non-terrestrial net- work configuration with a non-terrestrial network component and an infrastructure equipment teth- ered by the non-terrestrial network component.

The electronic device may be a User Equipment. A User Equipment (UE) may be any device that is related to an end-user or to a terminal to communicate in e.g. a Universal Mobile Telecommunica- tions System (UMTS) and 3GPP Long Term Evolution (LTE, or aLTE) system. The UE may sup- port the New Radio Access Technology Systems in addition to the legacy system such as LTE, and other advancements. The User Equipment (UE) may also be a machine type communication (MTC) terminal. The UE may also have a relay function in which it forwards transmissions from other teth- ered UEs towards the network.

Circuitry of the electronic device may include at least one of: a processor, a microprocessor, a dedi- cated circuit, a memory, a storage, a radio interface, a wireless interface, a network interface, or the like, e.g. typical electronic components which are included in a User Equipment, such as a mobile phone.

The User Equipment (UE) may also be an aerial UE. An aerial UE may for example be a UE that is provided in, on or at an aerial vehicle. An aerial device may for example be an Unmanned Aerial Ve- hicles (UAV) (a "Drone"), or aircrafts that operate with various degrees of autonomy, e.g. under re- mote control by a human operator or autonomously by an onboard micro controller. An aerial UE may be a mobile communications device that is configured to communicate data via the transmis- sion and reception of signals representing data using a wireless access interface. In the context of this application, the term aerial UE is also used for an electronic device that is autonomously or semi-autonomously operating in an aerial device, without the operator (or “user”) of the device be- ing required to be located at or close to the device. The term User Equipment (UE) thus also relates to equipment where the user is located remote to the equipment.

The circuitry of the electronic device may be configured to absorb changes in a feeder link propaga- tion time as part of a UE-specific differential TA.

The circuitry of the electronic device may be configured to repeatedly adjust a UE-specific differen- tial TA to take account of a changing distance between the non-terrestrial network component and the infrastructure equipment.

The circuitry of the electronic device may be configured to receive information on the ephemeris of the non-terrestrial network component and a location of the infrastructure equipment, and to re- peatedly calculate a distance between the non-terrestrial network component and the infrastructure equipment based on this information.

The circuitry of the electronic device may be configured to receive information on the ephemeris of the non-terrestrial network component and an initial distance between the infrastructure equipment and the non-terrestrial network component, and to repeatedly calculate a distance between the non- terrestrial network component and the infrastructure equipment based on this information.

The circuitry of the electronic device may be configured to receive information on the location of the infrastructure equipment or information on the distance of the infrastructure equipment from the non-terrestrial network component once the electronic device enters RRC connected mode and/ or shortly after feeder link switching occurs.

The circuitry of the electronic device may be configured to receive information on the location of the infrastructure equipment or information on the distance of the infrastructure equipment from the non-terrestrial network component in encrypted form.

The circuitry of the electronic device may be configured to repeatedly receive a current TA adjust- ment and to adjust a common TA according to this TA adjustment.

The circuitry of the electronic device may be configured to repeatedly determine a current TA ad- justment according to a TA drift figure and its direction and to adjust a common TA according to this TA adjustment.

The TA drift figure and its direction may include both the drift due to the satellite movement in its orbit and also its changing displacement from the tethered infrastructure equipment. The circuitry of the electronic device may be configured to receive the TA drift figure and its direc- tion as part of the RAR response in msg2 of 4-step RACH or msgB of 2-step RACH or by regular MAC messages.

The embodiments further disclose a system comprising an electronic device as defined in claim 1, an infrastructure equipment located on the ground, and a non-terrestrial network component config- ured to relay uplink and downlink traffic between the user equipment and the infrastructure equip- ment.

The embodiments further disclose an infrastructure equipment comprising circuitry configured to provide information to a user equipment for compensating feeder link influence on the common TA in a transparent payload non-terrestrial network configuration with a non-terrestrial network component and a base station tethered by the non-terrestrial network component.

The infrastructure equipment may also be referred to as a base station, a network element such as an entity of a core network, an enhanced Node B or a coordinating entity for example, and may pro- vide a wireless access interface to one or more communications devices within a coverage area or cell. The infrastructure equipment may for example be any entity of a telecommunications system, e.g. an entity of a New Radio Access Technology Systems, e.g. next Generation' Node B.

Circuitry of an infrastructure equipment may include at least one of: a processor, a microprocessor, a dedicated circuit, a memory, a storage, a radio interface, a wireless interface, a network interface, or the like, e.g. typical electronic components which are included in a base station, such as an gNB.

The circuitry of the infrastructure equipment may be configured to send to the user equipment in- formation on the ephemeris of the non-terrestrial network component.

The circuitry of the infrastructure equipment may be configured to send to the user equipment in- formation on the location of the infrastructure equipment tethered by the non-terrestrial network component.

The circuitry of the infrastructure equipment may be configured to send to the user equipment in- formation on an initial distance between the infrastructure equipment and the non-terrestrial net- work component.

The circuitry of the infrastructure equipment may be configured to send to the user equipment in- formation on the location of the infrastructure equipment or information on the distance of the in- frastructure equipment from the non-terrestrial network component once the electronic device enters RRC connected mode and/or shortly after feeder link switching occurs. The circuitry of the infrastructure equipment may be configured to send to the user equipment in- formation on the location of the infrastructure equipment or information on the distance of the in- frastructure equipment from the non-terrestrial network component in encrypted form.

The circuitry of the infrastructure equipment may be configured to repeatedly send to the user equipment a current TA adjustment.

The circuitry of the infrastructure equipment may be configured to send to the user equipment a TA drift figure and its direction.

The circuitry of the infrastructure equipment may be configured to send the TA drift figure and its direction (ΔT _com /Δt) as part of the RAR response in msg2 of 4-step RACH or msgB of 2-step RACH or by regular MAC messages.

The embodiments also disclose a method comprising compensating feeder link influence on the common TA in a transparent payload non-terrestrial network configuration with a non-terrestrial network component and an infrastructure equipment tethered by the non-terrestrial network com- ponent. The method may be a computer-implemented method.

The embodiments also disclose a computer program comprising instructions, which when executed by a processor, instruct the processor to compensate feeder link influence on the common TA in a transparent payload non-terrestrial network configuration with a non-terrestrial network component and an infrastructure equipment tethered by the non-terrestrial network component. The embodi- ments also disclose a computer-readable medium storing this computer program.

The embodiments are now described in more detail with reference to the accompanying drawings.

As stated in the introductory part of this application, Non-Terrestrial Network (NTN) components in the 5G system rely on space/ airborne vehicles (such as satellites) to provide 5G service in un- served or underserved areas that cannot be (sufficiently) covered by terrestrial 5G network. The pur- pose of a space/airborne network component is to provide the 5G service enablers to user equip- ment (UE) such as handheld devices.

For such space/ airborne networks, it is considered a configuration where base station functions (next Generation Node B, short gNB) are on board the space/ airborne vehicle. This scenario is called "regenerative payload NTN". There are other scenarios, where the space/airborne vehicle only relays an NR signal between a gNB and a UE in a transparent manner. In this latter scenario, which (also called "transparent payload", or "bent pipe payload"), there are no base station functions on board the space/ airborne vehicle. In general, the term "feeder link" refers to the radio link between the space/ airborne platform and the gateways that connect the satellite or aerial access network to the core network, and the term "service link" refers to the radio link between the user equipment (UE) and the space/ airborne plat- form. In addition to the service link to the space/ airborne platform, the UE may also support a ra- dio link with a terrestrial based RAN.

Fig. 1 shows a Non-Terrestrial Network (NTN) in which a space/ aerial vehicle relays an NR signal between a gNB and a UE in a transparent manner. A non-terrestrial network device NT-RN (e.g. space/aerial vehicle such as a satellite) includes functionality to relay, via a Un interface, an NR sig- nal between a UE and a terrestrial next Generation Node B gNB. The gNB communicates with NG Core components NGC, in particular a core data network. Here, the gNB comprises the functional- ity of an NTN Gateway which acts as router interfacing the NGC. Via the non- terrestrial network device NT-RN, the gNB provides NR user plane and control plane protocol terminations towards the UE, and connects via the NG interface to the NG Core (NGC).

Here, the Un interface refers to the radio interface between the UE and the gNB via the non-terres- trial network device NT-RN. Still further, NGc refers to the control plane interface between the gNB and the NGC and NGu refers to the user plane interface between the gNB and the NGC.

Transparent mode NTN configuration

In a transparent mode NTN configuration such as described in Fig. 1, the space/ airborne network component (e.g. satellite) is transparent to the UE and the one way propagation delay from the UE to the gNB incorporates the feeder link which connects the satellite to the terrestrial gNB. As the length of this feeder link changes due to satellite orbital movement and occasional feeder link switching, this needs to be reflected in the timing adjustments between the UE and the gNB.

Fig. 2 schematically illustrates an embodiment of uplink (UL) time synchronization in a transparent payload NTN scenario. A terrestrial gNB provides NR user plane and control plane protocol termi- nations towards user equipments UE1, UE2, ..., UEx via a non-terrestrial (space/ airborne) network component (e.g. a satellite) NT-RN. The non-terrestrial network component NT-RN acts as non- terrestrial relay node NT-RN and relays the uplink and downlink signals from and to gNB for user equipments UEs UE1, UE2, ..., UEx within its service area 20 (footprint of the spot beam of the space/ airborne network component NT-RN). To this end, the space/ airborne network component NT-RN connects via the NG interface to the gNB.

The network NGC which knows the ephemeris of the non-terrestrial network component (satellite) NT-RN and the location of the gNB calculates a common timing adjustment (TA) that all UEs within the given service area 20 can use to advance their UL transmissions so that at the gNB, there can be alignment of all UL received and DL transmit frames.

A common timing adjustment (common TA) T _com is defined as the delay between the gNB and a reference point RP defined in the beam footprint 20:

T _com = 2 * (D ₀₁ +D ₀₂ )/c where D ₀₁ is the distance between the reference point RP and the space/ airborne relay node NT- RN, D ₀₂ is the distance between the space/ airborne network relay node NT-RN and the gNB, and c is the speed of light. This common TA T _com may be seen as the average delay between the gNB and all locations of UEs within the footprint 20 of the spot beam.

The reference point RP may for example be taken as the center of the beam footprint 20 on the earth surface. In particular, the common TA reference point may for example be defined as the earth-based center of the beam footprint when the satellite is at zenith. This can be calculated by the network as it knows the ephemeris of the satellite and in general the beam footprint. If the reference point is on earth, then any UEs that happens to be airborne (e.g. the UE of a passenger on a plane) will be in general closer to the space/ airborne network component than the common TA reference point. For such UEs, their UE specific differential TA will be negative. In order to ensure that dif- ferential TAs for all UEs, including airborne UEs, is always positive, the reference point RP may be defined at an aerial location above the beam center on earth. The height of such a location may for example be the predetermined maximum height at which it is known a UE can potentially rise to, e.g. the highest height aircraft can fly to (for example 15000 km above sea level).

There are several ways to determine the common TA T _com . For example, the network may calculate the common TA and broadcast it within the beam for example, in system information. Alternatively, in connected mode, the network may send the UE the common TA via a MAC signaling like e.g. MAC CE message. Still further, knowing the common TA reference point of its beam and the cur- rent position of the satellite (through knowledge of the ephemeris), the UE can itself calculate the common TA. If the UE has to calculate the common TA, then the location of the common TA ref- erence point may be broadcast to the UE (respectively all UEs in the beam footprint) for example through system information so that the UE knows the reference point for computing the common TA. The ephemeris data may be provided to the UEs according to the principles set out in section 7.3.6.2 of 3GPP TR 38.821 V16.0.0 which are summarized below with regard to Fig. 8 and the cor- responding description. Each UE is supposed to derive a UE-specific differential delay adjustment T _UEx (for the x-th UE) which is related to the propagation time between the x-th UE and the reference point for the com- mon TA: T _UEx = 2 * (D _1x - D ₀₁ )/ c where D01 is the distance between the reference point RP and the gNB, D _1x is the distance between gNB and the x-th UE, and c is the speed of light. As the beam footprint sizes of NTN components are bigger than normal terrestrial cells, it is expected that even this UE specific differential TA will be larger than the typical TAs in a terrestrial network wherein cell sizes are a lot smaller. A position- ing capable UE, knowing its position and the reference point RP for the common TA can calculate its differential delay T _UEx as the propagation time to the common TA reference point. Alternatively, the network, knowing the UEs position (e.g. reported by a positioning-capable UE), can also calcu- late the UE's propagation time to the common TA reference point RP which the network also knows for any of its current beams. Then the network can send this propagation time to the UE in connected mode. Still alternatively, the UE can RACH and then receive its differential TA from the RAR. For this RACH, the UE must advance the transmission time of its RACH transmissions by the common TA. So the UE needs to know the value for the common TA before it can derive its differential TA via RACH.

From the UE-specific differential delay T _UEx and the common timing adjustment T _com a full TA T _full is obtained for each UE: T _full = T _com + T _UEx

This full TA T _full can then be used by the UE to maintain the UL timing advance and synchroniza- tion in the NTN cell.

Changing common TA in a transparent payload NTN

In a regenerative payload NTN, the gNB (or its distributed unit gNB-DU) is on the satellite and so, the common TA is essentially the height of the satellite above the reference point. This depends mostly on the orbital height of the satellite and so for a given beam or satellite, this height is to a large extent fixed the implication of which is that the common TA does not significandy change with time. In a transparent payload NTN as shown in Fig. 1, however, the gNB is located on the ground and the common TA depends on both the satellite height and the propagation delay be- tween the satellite and the terrestrial gNB. As the satellite describes its orbit, this second component changes and so the common TA also changes. The embodiments described below in more detail ad- dress this aspect of how to treat a changing common TA in a transparent payload NTN that changes because of: (a) the changing distance due to the orbiting of the satellite between the gNB and the satellite or, (b) a feeder link switch. When a feeder link switch occurs, the network switches its connection to the UE from the current serving gateway to another target gateway. The distance between the target gateway and the satellite is likely to be different from that between the original serving gateway and the satellite.

Fig. 3a shows a first embodiment of a process compensating a changing common TA at the UE in a transparent payload NTN. At 31, a UE receives from the network a common TA, information on the ephemeris of a satellite, and the location of the serving gNB tethered by the satellite. At 32, the UE determines the UE-specific differential TA. This may happen according to any one of the meth- ods described above (depending on the chosen method of determining the UE-specific differential TA, the network may provide additional information such as the position of the reference point RP, UE-specific propagation time, etc not displayed in Fig. 3a). Knowing the ephemeris of the satellite and hence its orbital speed, at 33, the UE calculates the position of the satellite based on the infor- mation on the ephemeris of the satellite. This calculation of the position of the satellite based on the information on the ephemeris of the satellite may be performed according to the principles set out in Annex A of 3GPP TR 38.821 VI 6.0.0 which is herewith incorporated by reference. At 34, the UE calculates the distance between the satellite and its tethered gNB based on the location of the satel- lite and the location of the gNB. Based on this distance between the satellite and its tethered gNB, the UE, at 35, adjusts its UE-specific differential TA (for example in each UL transmission) to take account of any changes in the distance between the satellite and its tethered gNB. At 36, the UE de- termines the full TA based on the (constant) common TA obtained from the network, and based on the adjusted UE-specific differential TA. The UE then uses this full TA for maintenance of UL tim- ing advance and synchronization in NTN cell. As indicated by the arrow in Fig. 3a, steps 33, 34, 35, and 36 are performed repeatedly while the UE is within the spot beam of the satellite and thus in the service area of the gNB tethered by the satellite.

In this embodiment, the common TA stays constant whilst the changes in the feeder link propaga- tion time are absorbed as part of the UE-specific differential TA. The location of the serving gNB can be provided to the UEs once they enter RRC connected mode and/ or shortly after feeder link switching occurs. The location of the serving gNB can for example be provided to the UEs in a MAC signaling e.g. MAC control element (MAC CE). In RRC connected mode, the gNB location information can be encrypted and this information is transferred either in encrypted user plane packet or protected RRC signaling. The ephemeris data may be provided to the UEs according to the principles set out in section 7.3.6.2 of 3GPP TR 38.821 V16.0.0 which are summarized below with regard to Fig. 8 and the corresponding description. In the embodiment of Fig. 3a, the UE receives, at 31, a common TA from the network. Fig. 3b shows a variant of this first embodiment. In this variant, the UE does not receive the common TA from the network. Instead, the UE, at 31a receives from the network information on the ephemeris of the satellite and the location of the gNB. At 31b, the UE determines a common TA based on the information on the ephemeris of the satellite and the location of the gNB, and then follows the same steps 33 to 36 as in the embodiment of Fig. 3a.

Fig. 4a shows a second embodiment of a process of compensating a changing common TA in a transparent payload NTN. At 41, a UE receives from the network a common TA, information on the ephemeris of a satellite, and the initial distance between the satellite and the serving gNB teth- ered by the satellite. At 42, the UE determines the UE-specific differential TA. Knowing the ephem- eris of the satellite and hence its orbital speed, at 43, the UE calculates the distance between the satellite and the gNB based on the initial distance between the satellite, and based on the infor- mation on the ephemeris of the satellite. Based on this distance between the satellite and its tethered gNB, the UE, at 44, adjust its UE-specific differential TA (for example in each UL transmission) to take account of any changes in the distance between the satellite and its tethered gNB. At 45, the UE determines its full TA based on the (constant) common TA obtained by from the network, and based on the adjusted UE-specific differential TA. The UE then uses this full TA for maintenance of UL timing advance and synchronization in NTN cell. As indicated by the arrow in Fig. 4a, steps 43, 44, and 45 are performed repeatedly while the UE is within the spot beam of the satellite and thus in the service area of the gNB tethered by the satellite.

Like in the embodiment of Fig. 3a, also in this embodiment of Fig. 4a, the common TA stays con- stant whilst the changes in the feeder link propagation time are absorbed as part of the UE-specific differential TA. The distance of the serving gNB can be provided to the UEs once they enter RRC connected mode and shortly after feeder link switching occurs. The location of the serving gNB can for example be provided to the UEs in a MAC control element (MAC CE). In RRC connected mode, the gNB distance information can be encrypted.

In the embodiment of Fig. 4a, the UE receives, at 41, a common TA from the network. Fig. 4b shows a variant of this second embodiment. In this variant, the UE does not receive the common TA from the network. Instead, the UE, at 41a receives from the network information on the ephemeris of the satellite and the distance of the gNB. At 41b, the UE determines a common TA based on the information on the ephemeris of the satellite and the location of the gNB, and then follows the same steps 43 to 45 as in the embodiment of Fig. 4a.

Fig. 5 shows a third embodiment of a process compensating a changing common TA in a transpar- ent payload NTN. At 51, a UE receives from the network a common TA. At 52, the UE determines the UE-specific differential TA. At 53, a UE in connected mode regularly receives common TA ad- justment messages. Such a message will carry the common TA adjustment calculated by the network that arises either from just normal orbital movement of the satellite or from feeder link switching. Since this signaling is UE-specific and there are likely many UEs within the large footprint of a par- ticular spot beam, it consumes a lot of resources. At 54, the UE adjusts the common TA based on the common TA adjustment received from the network. At 55, the UE determines its full TA based on the adjusted common TA and based on the UE-specific differential TA. The UE then uses this full TA for maintenance of UL timing advance and synchronization in NTN cell. As indicated by the arrow in Fig. 5, steps 53, 54 and 55 are performed repeatedly while the UE is within the spot beam of the satellite and thus in the service area of the gNB tethered by the satellite.

An adjusted common TA T _{com, adjusted} may for example be determined according to

T _{com, adjusted} = T _com T _adjust based on a constant common TA T _com initially received from the network and based on a respective current TA adjustment T _adjust repeatedly received from the network. Fig. 6 shows a fourth embodiment of a process compensating a changing common TA in a transpar- ent payload NTN. At 61, a UE receives from the network a common TA, a TA drift figure and its direction. The drift figure and the direction of the drift are derived by the network from the satellite ephemeris information. The TA drift includes both the drift due to the satellite movement in its or- bit and also its changing displacement from its serving gNB as calculated by the network. The net- work may for example send the TA drift figure and its direction to the UE as part of the RAR response in msg2 of 4-step RACH or msgB of 2-step RACH or by regular MAC messages. At 62, the UE determines the UE-specific differential TA. At 63, the UE determines a current TA adjust- ment from the drift figure and direction obtained from the network. At 64, the UE adjusts the com- mon TA according to the current TA adjustment obtained from the drift figure and direction. At 65, the UE determines its full TA based on the adjusted common TA and based on the UE-specific dif- ferential TA. The UE then uses this full TA for maintenance of UL timing advance and synchroni- zation in NTN cell. As indicated by the arrow in Fig. 6, steps 63, 64, and 65 are performed repeatedly while the UE is within the spot beam of the satellite and thus in the service area of the gNB tethered by the satellite. This embodiment works for all types of satellite orbits including elliptical orbits and allows the UEs to have three components in its TA adjustment: common TA, TA drift and UE-specific differential TA. The signaling is UE-specific with regard to the drift figure and direction, but the drift figure and direction may be provided to the UEs less frequent than in the embodiment of Fig. 5. The signaling thus consumes less resources than the signaling in the embodiment of Fig. 5. In the embodiment of Fig. 6, the UE receives from the network a TA drift figure and its direction In an alternative embodiment, the UE will receive from the network only a TA drift figure and the UE determines the direction of the drift from the ephemeris.

Fig. 7 shows an example of determining a TA adjustment based on a drift figure and direction sent from the network to the UE (or drift direction determined by the UE from the ephemeris) as de- scribed at process step 62 in the fourth embodiment above. In the example, a drift figure and direc- tion ΔT _com /Δt = +2μs/10ms = +0.0002, for example, is sent from the network to a UE. The drift figure 0.0002 indicates the amount of TA drift, whereas the plus sign indicates the direction of the TA drift (here: TA drift is increasing in time). The graph shows the time in milliseconds (ms) on the ordinate and the common TA in microseconds (ps) on the abscissa. The solid line shows the common TA T _{com, adjusted} as computed by the UE from the drift figure and direction obtained from the network. This adjusted common TA T _{com, adjusted} may for example be determined according to

T _{com, adjusted} - T _com + ( (ΔT _com /Δt) * t based on the time t, drift figure and direction ΔT _com /Δt and a predefined fixed common TA T _com received from the network.

The embodiments described above all address the issue of feeder link influence on the common TA and thus allow for a maintenance of UL timing advance and synchronization in NTN cells.

Ephemeris Data for NTN

Ephemeris Data for NTN is treated in section 7.3.6 of 3GPP TR 38.821 V16.0.0 in more detail which is herewith incorporated by reference. Ephemeris data may contain the information about the orbital trajectories of artificial satellites as described for example in Annex A of 3GPP TR 38.821

VI 6.0.0. There are different possible representations of ephemeris data.

Fig. 8 shows one possibility to represent ephemeris data. According to this example orbital parame- ters are used, e.g. semi-major axis a, eccentricity e, inclination i ₀ , right ascension Ω ₀ of the ascending node, argument ω of periapsis, mean anomaly Mo at a reference point in time, and the epoch t ₀₆ . The first five parameters can determine an orbital plane, and the other two parameters are used to deter- mine exact satellite location at a time. A description table for the orbital parameters and the corre- sponding illustrations are as below:

The embodiments are, however, not restricted to this representation of ephemeris data. Another possible option is to provide the location of the satellite in coordinates (x, y, z), e.g. ECEF coordi- nates. Additionally, a velocity vector (vx, vy, vz) and again a reference point in time may also be pro- vided.

The ephemeris data may be provided to the UEs according to the principles set out in section 7.3.6.2 of 3GPP TR 38.821 V16.0.0. A possibility of provisioning the ephemeris data or parts of the ephemeris data from the network to the UE may be via a memory card such as a uSIM. However, there is no need for a UE to store orbital parameters for all the satellites. If the orbital parameters per satellite are pre-provisioned, UE only needs to store the ephemeris data for the satellites that may serve UE. Another possible solution is to broadcast the orbital parameters of the serving satel- lite and several neighbouring satellites which will be sufficient for initial access and mobility handling at UE side.

Means for updating ephemeris data stored in a UE may be foreseen such as set out in section 7.3.6.3 of 3GPP TR 38.821 V16.0.0 which is herewith incorporated by reference.

Given a specific point in time, it is straightforward to calculate the satellite location according to the principles set out in Annex A of 3GPP TR 38.821 V16.0.0 which is herewith incorporated by refer- ence.

Implementation

Fig. 9 shows a schematic block diagram of a communications path between a UE 800, a non-terres- trial (space/ airborne) relay node NT-RN 820 (e.g. satellite), and a gNB 830. As shown in Fig. 9 the UE includes a transmitter 801, a receiver 802, and a controller 803 to control the transmission of signals to and the reception of signals from the gNB. The Uplink signals are represented by an arrow 860. Downlink signals are shown by an arrow 850. The space/ airborne relay node RT-RN 820 in- cludes a transmitter 821 a receiver 822 and a controller 823 which may include functionality for re- laying downlink and uplink signals between the UE 800 and the gNB 820 in accordance with a wireless access interface. The gNB 830 includes a transmitter 831 a receiver 832 and a controller 833 which may include a scheduler for scheduling the transmission and reception of signals on the downlink and the uplink in accordance with a wireless access interface.

Fig. 10 describes an embodiment of a controller 900. This controller 900 can be implemented such that it can basically function as any type of apparatus or entity, base station, relay node, transmission and reception point, or user equipment as described herein. Controller 900 can thus act as control- lers 803, 823, or controller 833 of Fig. 9. The controller 900 has components 931 to 940, which can form a circuitry, such as any one of the circuitries of the entities, base stations, and user equipment, as described herein.

Embodiments which use software, firmware, programs or the like for performing the methods as described herein can be installed on controller 900, which is then configured to be suitable for the concrete embodiment.

The controller 900 has a CPU 931 (Central Processing Unit), which can execute various types of procedures and methods as described herein, for example, in accordance with programs stored in a read-only memory (ROM) 932, stored in a storage 937 and loaded into a random access memory (RAM) 933, stored on a medium 940, which can be inserted in a respective drive 939, etc.

The CPU 931, the ROM 932 and the RAM 933 are connected with a bus 941, which in turn is con- nected to an input/ output interface 934. The number of CPUs, memories and storages is only ex- emplary, and the skilled person will appreciate that the controller 900 can be adapted and configured accordingly for meeting specific requirements which arise when it functions as a base station, and user equipment.

At the input/ output interface 934, several components are connected: an input 935, an output 936, the storage 937, a communication interface 938 and the drive 939, into which a medium 940 (com- pact disc, digital video disc, compact flash memory, or the like) can be inserted.

The input 935 can be a pointer device (mouse, graphic table, or the like), a keyboard, a microphone, a camera, a touchscreen, etc. The output 936 can have a display (liquid crystal display, cathode ray tube display, light emittance diode display, etc.), loudspeakers, etc. The storage 937 can have a hard disk, a solid state drive and the like.

The communication interface 938 can be adapted to communicate, for example, via a local area net- work (LAN), wireless local area network (WLAN), mobile telecommunications system (GSM, UMTS, LTE, etc.), Bluetooth, infrared, etc. When the controller 900 functions as a base station, the communication interface 938 can further have a respective air interface (providing e.g. E-UTRA protocols OFDMA (downlink) and SC-FDMA (uplink)) and network interfaces (implementing for example protocols such as S1-AP, GTP-U, S1-MME, X2-AP, or the like). Moreover, the controller 900 may have one or more antennas and/ or an antenna array. The present disclosure is not limited to any particularities of such protocols.

***

It should be recognized that the embodiments describe methods with an exemplary ordering of method steps. The specific ordering of method steps is however given for illustrative purposes only and should not be construed as binding. For example the ordering of the process steps 31b and 32 in Fig. 3b may be changed. Other changes of the ordering of method steps may be apparent to the skilled person.

It should also be noted that the division of the control or circuitry of Fig. 10 into units 931 to 940 is only made for illustration purposes and that the present disclosure is not limited to any specific divi- sion of functions in specific units. For instance, at least parts of the circuitry could be implemented by a respective programmed processor, field programmable gate array (FPGA), dedicated circuits, and the like.

All units and entities described in this specification and claimed in the appended claims can, if not stated otherwise, be implemented as integrated circuit logic, for example on a chip, and functionality provided by such units and entities can, if not stated otherwise, be implemented by software.

In so far as the embodiments of the disclosure described above are implemented, at least in part, us- ing software-controlled data processing apparatus, it will be appreciated that a computer program providing such software control and a transmission, storage or other medium by which such a com- puter program is provided are envisaged as aspects of the present disclosure.

Note that the present technology can also be configured as described below:

(1) An electronic device (UE) comprising circuitry configured to compensate feeder link influ- ence on the common TA (T _com ) in a transparent payload non-terrestrial network (NTN) configura- tion with a non-terrestrial network component (NT-RN) and an infrastructure equipment (gNB) tethered by the non-terrestrial network component (NT-RN).

(2) The electronic device (UE) of (1) in which the circuitry is configured to absorb changes in a feeder link propagation time as part of a UE-specific differential TA (T _UEx ).

(3) The electronic device (UE) of (1) or (2) in which the circuitry is configured to repeatedly ad- just (35, 44) a UE-specific differential TA (T _UEx ) to take account of a changing distance between the non-terrestrial network component (NT-RN) and the infrastructure equipment (gNB).

(4) The electronic device (UE) of any one of (1) to (3), in which the circuitry is configured to receive (31) information on the ephemeris of the non-terrestrial network component (NT-RN) and a location of the infrastructure equipment (gNB), and to repeatedly calculate (33, 34) a distance be- tween the non- terrestrial network component (NT-RN) and the infrastructure equipment (gNB) based on this information.

(5) The electronic device (UE) of any one of (1) to (4), in which the circuitry is configured to receive (41) information on the ephemeris of the non-terrestrial network component (NT-RN) and an initial distance between the infrastructure equipment (gNB) and the non-terrestrial network com- ponent (NT-RN), and to repeatedly calculate (43) a distance between the non-terrestrial network component (NT-RN) and the infrastructure equipment (gNB) based on this information.

(6) The electronic device (UE) of any one of (1) to (5), in which the circuitry is configured to receive (31) information on the location of the infrastructure equipment (gNB) or information on the distance of the infrastructure equipment (gNB) from the non-terrestrial network component (NT-RN) once the electronic device (UE) enters RRC connected mode and/or shortly after feeder link switching occurs.

(7) The electronic device (UE) of any one of (1) to (6), in which the circuitry is configured to receive (31) information on the location of the infrastructure equipment (gNB) or information on the distance of the infrastructure equipment (gNB) from the non-terrestrial network component (NT-RN) in encrypted form.

(8) The electronic device (UE) of any one of (1) to (7), in which the circuitry is configured to repeatedly receive (53) a current TA adjustment (Tadjust) and to adjust (54) a common TA (T _com ) ac- cording to this TA adjustment (T _adjust ).

(9) The electronic device (UE) of any one of (1) to (8), in which the circuitry is configured to repeatedly determine (63) a current TA adjustment ( (ΔT _com /Δt) * t) according to a TA drift figure and its direction ΔT _com /Δt and to adjust (64) a common TA (T _com ) according to this TA adjustment (T _ad - just). (10) The electronic device (UE) of (9), in which the TA drift figure and its direction (ΔT _com /Δt) includes both the drift due to the satellite movement in its orbit and also its changing displacement from the tethered infrastructure equipment (gNB).

(11) The electronic device (UE) of (9) or (10), in which the circuitry is configured to receive the TA drift figure and its direction (ΔT _com /Δt) as part of the RAR response in msg2 of 4-step RACH or msgB of 2-step RACH or by regular MAC messages.

(12) A system comprising an electronic device ( UE) as defined in any one of (1) to 12, an infra- structure equipment (gNB) located on the ground, and a non-terrestrial network component (NT- RN) configured to relay uplink and downlink traffic between the user equipment (UE) and the infra- structure equipment (gNB).

(13) An infrastructure equipment (gNB; NTC) comprising circuitry configured to provide infor- mation to a user equipment (UE) for compensating feeder link influence on the common TA (T _com ) in a transparent payload non-terrestrial network (NTN) configuration with a non-terrestrial network component (NT-RN) and a base station (gNB) tethered by the non-terrestrial network component (NT-RN).

(14) The infrastructure equipment (gNB; NTC) of (13) in which the circuitry is configured to send to the user equipment (UE) information on the ephemeris of the non-terrestrial network com- ponent (NT-RN).

(15) The infrastructure equipment (gNB; NTC) of (13) or (14) in which the circuitry is configured to send to the user equipment (UE) information on the location of the infrastructure equipment (gNB) tethered by the non-terrestrial network component (NT-RN).

(16) The infrastructure equipment (gNB; NTC) of any one of (13) to (15) in which the circuitry is configured to send to the user equipment (UE) information on an initial distance between the infra- structure equipment (gNB) and the non-terrestrial network component (NT-RN).

(17) The infrastructure equipment (gNB; NTC) of any one of (13) to (16) in which the circuitry is configured to send to the user equipment (UE) information on the location of the infrastructure equipment (gNB) or information on the distance of the infrastructure equipment (gNB) from the non-terrestrial network component (NT-RN) once the electronic device (UE) enters RRC con- nected mode and/or shortly after feeder link switching occurs.

(18) The infrastructure equipment (gNB; NTC) of any one of (13) to (17) in which the circuitry is configured to send to the user equipment (UE) information on the location of the infrastructure equipment (gNB) or information on the distance of the infrastructure equipment (gNB) from the non-terrestrial network component (NT-RN) in encrypted form.

(19) The infrastructure equipment (gNB; NTC) of any one of (13) to (18) in which the circuitry is configured to repeatedly send to the user equipment (UE) a current TA adjustment (T _adjust ).

(20) The infrastructure equipment (gNB; NTC) of any one of (13) to (19) in which the circuitry is configured to send to the user equipment (UE) a TA drift figure, or a TA drift figure and its direc- tion (ΔT _com /Δt). (21) The infrastructure equipment (gNB; NTC) of (20) in which the circuitry is configured to send the TA drift figure and its direction (ΔT _com /Δt) as part of the RAR response in msg2 of 4-step RACH or msgB of 2-step RACH or by regular MAC messages.

(22) A method comprising compensating feeder link influence on the common TA (T _com ) in a transparent payload non-terrestrial network (NTN) configuration with a non-terrestrial network component (NT-RN) and an infrastructure equipment (gNB) tethered by the non-terrestrial net- work component (NT-RN).