WO2025252995A1

WO2025252995A1 - Method for efficient tdd operation in ntn

Info

Publication number: WO2025252995A1
Application number: PCT/EP2025/065890
Authority: WO
Inventors: Thomas Haustein; Paul Simon Holt Leather; Thomas Heyn; Rashid KHOUIL
Original assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Priority date: 2024-06-07
Filing date: 2025-06-06
Publication date: 2025-12-11
Anticipated expiration: 2026-12-07

Abstract

A user equipment, UE, comprises a wireless interface for receiving wireless signals and for transmitting wireless signals. The UE is configured for operating in a cell of a wireless communication network according to a time division duplex, TDD, scheme that comprises a plurality of TDD frames, each TDD frame comprising a plurality of slots arranged according to a frame structure, the plurality of slots comprising a first number of downlink, DL, slots, a second number of uplink, UL, slots and a third number of special, S, slots e.g., arranged between the first number of UL slots and the second number of UL slots. The UE is configured for operating with a varying effective frame structure within the TDD scheme to compensate for varying distances between the UE and a base station operating the cell.

Description

METHOD FOR EFFICIENT TDD OPERATION IN NTN

Description

Embodiments of the present application relate to the field of wireless communication, and more specifically, to enhancing wireless communication in the field of non-terrestrial networks, NTN. Aspects of the present invention relate to apparatus and methods for an efficient TDD operation in NTN.

Fig. 1 is a schematic representation of an example of a terrestrial and/or non-terrestrial wireless network 100 including, as is shown in Fig. 1(a), a core network 102 and one or more radio access networks RANi, RAN2, ... RANN. Fig. 1 (b) is a schematic representation of an example of a radio access network RAN_n that may include one or more base stations gNBi to gNBs, each serving a specific area surrounding the base station schematically represented by respective cells IO61 to IO65. The base stations are provided to serve users within a cell. The term base station, BS, refers to a gNB in 5G networks, an eNB in UMTS/LTE/LTE-A/ LTE-A Pro, or just a BS in other mobile communication standards. A user may be a stationary device or a mobile device. The wireless communication system may also be accessed by mobile or stationary loT devices which connect to a base station or to a user. The mobile devices or the loT devices may include physical devices, ground based vehicles, such as robots or cars, aerial vehicles, such as manned or unmanned aerial vehicles (UAVs), the latter also referred to as drones, buildings and other items or devices having embedded therein electronics, software, sensors, actuators, or the like as well as network connectivity that enables these devices to collect and exchange data across an existing network infrastructure.

Fig. 1 (b) shows an exemplary view of five cells, however, the RAN_n may include more or less such cells, and RAN_n may also include only one base station. Fig. 1 (b) shows two users UE1 and UE2, also referred to as user equipment, UE, that are in cell IO62 and that are served by base station gNB2. Another user UE3 is shown in cell IO64 which is served by base station gNB4. The arrows IO81, IO82 and IO83 schematically represent uplink/downlink connections for transmitting data from a user UE1, UE2 and UE3 to the base stations gNB2, gNB4 or for transmitting data from the base stations gNB2, gNB4 to the users UE1, UE2, UE3.

Further, Fig. 1 (b) shows two loT devices 110i and HO2 in cell IO64, which may be stationary or mobile devices. The loT device 110i accesses the wireless communication system via the base station gNB4 to receive and transmit data as schematically represented by arrow 112i. The loT device HO2 accesses the wireless communication system via the user UE3 as is schematically represented by arrow 1122. The respective base station gNBi to gNBs may be connected to the core network 102, e.g., via the S1 interface, via respective backhaul links 114i to 114₅, which are schematically represented in Fig. 1(b) by the arrows pointing to “core”. The core network 102 may be connected to one or more external networks. Further, some or all of the respective base station gNBi to gNB₅ may connected, e.g., via the S1 or X2 interface or the Xn interface in NR, with each other via respective backhaul links 1161 to 1165, which are schematically represented in Fig. 1 (b) by the arrows pointing to “gNBs”. Embodiments described herein are not limited to terrestrial networks, TNs, but relate also to networks being implemented, at least in parts, as non-terrestrial network, NTN, as shown in Fig. 1 with reference to a satellite Si that may operate, for example, to bridge communication between different base stations, to serve one or more UE and/or a cell on the ground, e.g., as a nonterrestrial base station, to communicate with a different satellite.

Satellites such as satellite Si and/or other types of non-terrestrial communication nodes, e.g., airplanes, balloons, high altitude platforms, HAP, may form at least a part of a non-terrestrial network that may also incorporate terrestrial nodes comprising but not limited to core network functions. Optionally, a non-terrestrial network may also make sure of terrestrial nodes, e.g., base stations and/or relays and/or user equipment.

For data transmission a physical resource grid may be used. The physical resource grid may comprise a set of resource elements to which various physical channels and physical signals are mapped. For example, the physical channels may include the physical downlink, uplink and sidelink shared channels (PDSCH, PLISCH, PSSCH) carrying user specific data, also referred to as downlink, uplink and sidelink payload data, the physical broadcast channel (PBCH) carrying for example a master information block (MIB), the physical downlink shared channel (PDSCH) carrying for example a system information block (SIB), the physical downlink, uplink and sidelink control channels (PDCCH, PLICCH, PSSCH) carrying for example the downlink control information (DCI), the uplink control information (UCI) and the sidelink control information (SCI). For the uplink, the physical channels, or more precisely the transport channels according to 3GPP, may further include the physical random access channel (PRACH or RACH) used by UEs for accessing the network once a UE is synchronized and has obtained the MIB and SIB. The physical signals may comprise reference signals or symbols (RS), synchronization signals and the like. The resource grid may comprise a frame or radio frame having a certain duration in the time domain and having a given bandwidth in the frequency domain. The frame may have a certain number of subframes of a predefined length, e.g., 1ms. Each subframe may include one or more slots of 12 or 14 OFDM symbols depending on the cyclic prefix (CP) length. All OFDM symbols may be used for DL or UL or only a subset, e.g., when utilizing shortened transmission time intervals (sTTI) or a mini- slot/non-slot-based frame structure comprising just a few OFDM symbols.

The wireless communication system may be any single-tone or multicarrier system using frequency-division multiplexing, like the orthogonal frequency-division multiplexing (OFDM) system, the orthogonal frequency-division multiple access (OFDMA) system, or any other IFFT-based signal with or without CP, e.g., DFT-s-OFDM. Other waveforms, like non- orthogonal waveforms for multiple access, e.g., filter-bank multicarrier (FBMC), generalized frequency division multiplexing (GFDM) or universal filtered multi carrier (LIFMC), may be used. The wireless communication system may operate, e.g., in accordance with the LTE-Advanced pro standard or the NR (5G), New Radio, standard.

The wireless network or communication system 100 depicted in Fig. 1 may by a heterogeneous network having distinct overlaid networks, e.g., a network of macro cells with each macro cell including a macro base station, like base station gNBi to gNBs, and a network of small cell base stations (not shown in Fig. 1), like femto or pico base stations.

In addition to the above described terrestrial wireless network also non-terrestrial wireless communication networks exist including spaceborne transceivers, like satellites, and/or airborne transceivers, like unmanned aircraft systems. The non-terrestrial wireless communication network or system may operate in a similar way as the terrestrial system described above with reference to Fig. 1 , for example in accordance with the LTE-Advanced Pro standard or the NR (5G), new radio, standard.

In mobile communication networks, for example in a network like that described above with reference to Fig. 1 , like an LTE or 5G/NR network, there may be UEs that communicate directly with each other over one or more sidelink (SL) channels, e.g., using the PC5 interface. UEs that communicate directly with each other over the sidelink may include vehicles communicating directly with other vehicles (V2V communication), vehicles communicating with other entities of the wireless communication network (V2X communication), for example roadside entities, like traffic lights, traffic signs, or pedestrians. Other UEs may not be vehicular related UEs and may comprise any of the above-mentioned devices. Such devices may also communicate directly with each other (D2D communication) using the SL channels. When considering two UEs directly communicating with each other over the sidelink, both UEs may be served by the same base station so that the base station may provide sidelink resource allocation configuration or assistance for the UEs. For example, both UEs may be within the coverage area of a base station, like one of the base stations depicted in Fig. 1. This is referred to as an “in-coverage” scenario. Another scenario is referred to as an “out-of-coverage” scenario. It is noted that “out-of-coverage” does not mean that the two UEs are not within one of the cells depicted in Fig. 1 , rather, it means that these UEs may not be connected to a base station, for example, they are not in an RRC connected state, so that the UEs do not receive from the base station any sidelink resource allocation configuration or assistance, and/or may be connected to the base station, but, for one or more reasons, the base station may not provide sidelink resource allocation configuration or assistance for the UEs, and/or may be connected to the base station that may not support NR V2X services, e.g., GSM, UMTS, LTE base stations.

When considering two UEs directly communicating with each other over the sidelink, e.g., using the PC5 interface, one of the UEs may also be connected with a BS, and may relay information from the BS to the other UE via the sidelink interface. The relaying may be performed in the same frequency band (in-band-relay) or another frequency band (out-of-band relay) may be used. In the first case, communication on the Uu and on the sidelink may be decoupled using different time slots as in time division duplex, TDD, systems.

In an in-coverage scenario in which two UEs directly communicating with each other are both connected to a base station, the base station gNB has a coverage area which, basically, corresponds to the cell schematically represented in Fig. 1. The UEs directly communicating with each other may be both in the coverage area of the base station gNB. Both UEs are possibly connected to the base station gNB and, in addition, they are connected directly with each other over the PC5 interface. The scheduling and/or interference management of the V2V traffic is assisted by the gNB via control signalling over the Uu interface, which is the radio interface between the base station and the UEs. In other words, the gNB provides SL resource allocation configuration or assistance for the UEs, and the gNB assigns the resources to be used for the V2V communication over the sidelink. This configuration is also referred to as a mode 1 configuration in NR V2X or as a mode 3 configuration in LTE V2X.

In an out-of-coverage scenario in which the UEs directly communicating with each other are either not connected to a base station, although they may be physically within a cell of a wireless communication network, or some or all of the UEs directly communicating with each other are to a base station but the base station does not provide for the SL resource allocation configuration or assistance. UEs may directly communicate with each other over a sidelink, e.g., using the PC5 interface. The scheduling and/or interference management of the V2V traffic is based on algorithms implemented between the vehicles. This configuration is also referred to as a mode 2 configuration in NR V2X or as a mode 4 configuration in LTE V2X. As mentioned above, the out-of-coverage scenario does not necessarily mean that the respective mode 2 UEs (in NR) or mode 4 UEs (in LTE) are outside of the coverage of a base station, rather, it means that the respective mode 2 UEs (in NR) or mode 4 UEs (in LTE) are not served by a base station, are not connected to the base station of the coverage area, or are connected to the base station but receive no SL resource allocation configuration or assistance from the base station. Thus, there may be situations in which, within the coverage area, in addition to the NR mode 1 or LTE mode 3 UEs also NR mode 2 or LTE mode 4 UEs are present.

Naturally, it is also possible that one of the UEs is covered by the gNB, i.e. connected with Uu to the gNB, wherein the second UE is not covered by the gNB and only connected via the PC5 interface to the first UE, or that the second vehicle is connected via the PC5 interface to the first vehicle UE but via Uu to another gNB.

With an increase of an amount of communication and with an increase of requirements, flexibility of communication is an important issue for wireless communication allowing to adapt to specific needs and to increase an overall efficiency.

There is, thus, a need to improve wireless communications.

It is noted that the information in the above section is only for enhancing the understanding of the background of the invention and therefore it may contain information that does not form prior art and is already known to a person of ordinary skill in the art.

Embodiments of the present invention are described herein making reference to the appended drawings.

Fig. 1 shows a schematic representation of an example of a wireless communication system; Fig. 2 is a schematic representation of a wireless communication system comprising a transceiver, like a base station or a relay, and a plurality of communication devices, like UEs, according to an embodiment;

Fig. 3 shows a schematic diagram of UEs being located within a coverage of satellite Si; to illustrate a distance-based issue solved by embodiments described herein;

Fig. 4a-b show schematic illustrations of a non-terrestrial network with different path lengths between satellites and terrestrial UEs;

Fig. 5 shows a UE dependent/distance dependent effective TDD slot configuration according to an embodiment; and

Fig. 6 illustrates an example of a computer system on which units or modules as well as the steps of the methods described in accordance with the inventive approach may execute.

Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals or namings even if occurring in different figures.

In the following description, a plurality of details are set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

Embodiments of the present invention may be implemented in a wireless communication system or network as depicted in Fig. 1 including a transceiver, like a base station, gNB, or relay, and a plurality of communication devices, like user equipment’s, UEs. Fig. 2 is a schematic representation of a wireless communication system comprising a transceiver 200, like a base station or a relay, and a plurality of communication devices 202i to 202n, like UEs. The UEs might communicated directly with each other via a wireless communication link or channel 203, like a radio link (e.g., using the PC5 interface (sidelink)). Further, the transceiver and the UEs 202 might communicate via a wireless communication link or channel 204, like a radio link (e.g., using the llu interface). The transceiver 200 might include one or more antennas ANT or an antenna array having a plurality of antenna elements, a signal processor 200a and a transceiver unit 200b. The UEs 202 might include one or more antennas ANT or an antenna array having a plurality of antennas, a processor 202a 1 to 202an, and a transceiver (e.g., receiver and/or transmitter) unit 202b1 to 202bn. The base station 200 and/or the one or more UEs 202 may operate in accordance with the inventive teachings described herein.

Embodiments are based on the recognition that there are present unpaired spectra allocated to different entities or network concepts. An example thereof is Iridium when compared to 3GPP. Under periods of Iridium in 3GPP leads to an unpaired spectrum allocated to Iridium. Embodiments are based on the finding that it is of advantage to use TDD for NTN to utilize such an unpaired spectrum. However, this leads to several problems to be addressed. Those problems comprise, for example:

• Providing a guard period for switching between UL and DL

• Consideration of different distance values of various satellites over earth surface with respect to a user equipment, UE

• Defining the Timing Advance, TA, depending on different distance values between UE and satellite

• Defining the TA of a UE when connected transmitting to 2 or more satellites at the same time o A possible solution might be that the TA per satellite may be common for all UEs covered by that Satellite at a time

• Guard periods may be configured I controlled by the network to reduce impact to the UEs

• Consideration of presence of cross-link-interference, CLI, between UEs, e.g., when a first UE is connected in downlink, DL, to a first Satellite while a second UE next it the first UE is transmitting in uplink, UL, to a second satellite

Embodiments relate to provide for solutions by one or more of the following:

Defining measurements to be taken by UEs

Providing a suitable configuration of S-slots (Special) and s-symbols to be defined in

TDD slot structure of system information block 1 , SIB1 Considering resource allocation for individual UEs and groups of UEs depending on the location of the satellite and/orTA which allows predictable more DL or UL resources to be used by UEs while the satellite flies over. o Such a solution benefits from signalling (e.g., to create reduced interference situation at the UE in a multi-spot overlay scenario) between gNBs over Xn (intersat links and bend pipe satellites with interface between ground stations, (slot or symbol muting can help)

• Embodiments relate to a frame length to be extended to reduce lost overhead of the TDD frame switching (guard period) per frame - this may benefit from more ABS to reduce intercell interference (frame length should be aligned with overall RTT due to orbital delay (e.g. 10ms, 20ms or larger)

As a background for the embodiments described herein, it is noted that in wireless communication systems like 4G-LTE or 5G-NR, a base station is communicating with a number of terminals (UEs). Due to the use of OFDM the uplink (UL) signals transmitted from several UEs at the same time require a time alignment such that the transmitted OFDM symbols will arrive timely aligned within the guard interval applied chosen to handle intersymbol interference due to the delay spread of the propagation channel. In 4G and 5G this is done with a so called timing advance which serves the purpose of having UEs far away from the base station transmit their uplink signals earlier then UEs closer to the base station. The required amount of timing advance will be controlled by the BS in a closed loop fashion after initial access from the UE. In handover scenarios, the new BS might require a different timing advance (TA) due to a different distance between the UE to BS1 and UE to BS2.

In non-terrestrial networks (NTN) the link between a UE and a BS is routed e.g. via a satellite in geostationary orbit, GEO, (app. 36.000 km) or low earth orbit, LEO, (app. 800 km) satellite at high altitude, adding a substantial time of flight for signals coming from different UEs. Due to the large coverage area of GEO satellite (e. g., size of a continent, several thousand kilometres) and LEO satellites (e.g., 100-500km coverage spot size) the path length of signals origination may vary considerably.

While TA is adjusted in closed loop, relative UE positions will change, therefore TA are outdated and inter-UE interference will remain at the gNB receiver. The same happens when UE is calculating corrections autonomously using parameters provided by SIB19, SIB31 , e.g. delay and derivatives on the feeder link (open loop with assistance data from gNB). Embodiments further address challenges related to:

• Use of TDD with larger beams

• Use of higher carrier frequencies, e.g., FR2

• Use of satellites in different altitudes SIB19 and SIB31 contain already ephemeris data)

• Operating with fast UE movement, e.g. as at least a part or within an airplane

Embodiments are related, amongst others, to a Core problem for TDD: In particular, as mentioned above, due to large distance and control loop delays, an effective TA as known from the art maybe outdated for particular or many UEs. Embodiments have also recognized that this is, at least in part, possibly but not necessarily an issue in FDD.

Embodiments further address the following problem: an accurate knowledge about which slots are available entirely or in part (e.g., which symbols) for individual UEs which may cause waste of resources or UL collisions.

Such a problem might still exist in large area cells, where the maximum access delay distance increases.

When sharpening such problem statement, the embodiments may provide for one or more of the following: a feedlink delay is provided by gNB/satellite via SIB19 a UE can calculate a service link distance and delay based on ephemeris data - but this absolute delay is possibly not known to gNB for a random access procedure, RACH, the UE is estimating the correct TA to compensate all delays (e.g., time of flight, ToF). The gNB may detect residual deviation and provide a TA compensation signal/command to compensate for the deviation, e.g., by providing information indicating the deviation to the UE to determine a compensation by the UE, implicit instruction, and/or by directly or explicitly instructing the UE with a parameter. due to large round trip time, RTT, the TA command corresponding to the RACH message may be outdated, when arriving at the UE due to movement of the satellite (e.g., a movement of UE even at 1.000 km/h is equivalent to 40 m and therefore negligible in terms of TA deviation). a satellite movement may contribute to a drift of the absolute TA compensated by the UE; an additional insight relates to one or more of: o in TDD the NTN may be configured with flexible slots (S) to compensate for the maximum differential delay of a given NTN cell (e.g., based on a user distribution) o if these radio resources are not used, this may cause inefficient resource utilization and large or varying response delays.

Fig. 3 shows a schematic diagram of UEs 312i, 312₂, 312₃, e.g., UEs in accordance with the UEs described in Fig. 1 , being located within an area 332, e.g., a coverage of satellite Si, e.g., carrying a gNB. Underlying embodiments of the present invention, within a common distance d1 , a common delay, CD is present that may be determined based on the speed of light, c, and the distance d1. Additional distances d2 and d3, starting from d1 towards UE 312₂, 312₃ respectively lead to additional, UE-specific delays, from which d2 may be the maximum, by way of example. This may lead to a maximum differential delay, MDD, based on d2/c, wherein a differential delay, DD, of UE 312₃ may be determined based on d3/c. the differential delay, DD, of UE 312i being located at d1 may be considered as being 0.

Thales explains the need for timing advance in NTN in R1-1905180. In FDD they use a common TA plus an UE individual TA similar to terrestrial networks. An initial TA in NTN is calculated by the UE, based on location and ephemeris data and will be further adjusted by gNB after RACCH.

The Timing Advance reporting procedure is used in a non-terrestrial network or an air-to- ground network to provide the gNB with an estimate of the UE's Timing Advance value (i.e., a Threshold Timing Advance, 7TA, as defined in the UE's TA formula, see TS 38.211 clause 4.3.1).

RRC controls Timing Advance reporting by configuring the following parameters: -offsetThresholdTA o example: Between 1 ms and 16 ms: every drift of e.g. 1 ms the UE is configured to send a report, the report may contain an absolute value, trend, etc. o some of the drift could be compensated by the UE, but when certain slot or symbol boundaries cannot be pre-compensated by the UE, this has to be reported in advance considering scheduling delay, RTT etc. o drift may be calculated/estimated from the expected or predicted trajectory of the basestation with or without the consideration of ephemeris data. embodiments of the present invention relate to

■ a scenario where other effects cause of TA drift apart from the movement of the satellite the TA mismatch is in some embodiments related to the movement of the satellite which may cause different amounts of TA mismatch. timingAdvanceSR. a Timing Advance Report (TAR) may be triggered if any of the following events occur: o upon an indication from upper layers to trigger a Timing Advance report; o upon configuration of offsetThresholdTA by upper layers, if the UE has not previously reported Timing Advance value to current Serving Cell; o if the variation between the current estimate of the Timing Advance value and the last reported Timing Advance value is equal to or larger than offsetThresholdTA, if configured.

■ according to state of the art, SotA, a UE only reports, in case of a mismatch

■ The MAC entity shall operate according to embodiments and recognitions described herein

Fig. 4a shows a schematic block diagram of a part of a known NTN 400 that may be modified by implementing the embodiments described herein. A satellite such as satellite Si may travel on a satellite orbit 402, e.g., flying at a height 404, e.g., 800 kilometres above ground surface 406 of earth 408. Satellite Si may maintain a connection to a first UE 312i, UE A, and to a second UE 312₂, UE B, being spaced by a distance 414, e.g., 500 kilometres. Due to those large distances, a path length L_A of a path 4161 may be considerably longer when compared to a length LB of a path 4162 to UE 312₂.

In Fig. 4b, there is shown a schematic representation of wireless communication network 400 that has changed its relative positions between satellite Si of a time instance ti shown in Fig. 4a to a different relative position in time instance t₂ leading to a change of path lengths between the respective UEs and the satellite and, thereby, to a considerable change in the relative timing.

With regard to the description provided in connection with Fig. 4a and Fig. 4b, and whilst referring to a slot-based architecture as used, e.g., in TDD, embodiments provide for an efficient communication under the consideration of the fast relative movement between a satellite or other types of non-terrestrial nodes, possibly but not necessarily comprising a base station, and a terrestrial node such as a UE. Besides the fast change of the distances, the large variations of distances between same UEs such as UE 312i and 312₂ of network 400 may lead to room for improvement at least partially used by embodiments described herein. To address the problems described herein, embodiments in accordance with the present invention disclosed herein proposes to use solutions described herein. In subsections embodiments further to present the proposed technical solutions in the form of embodiments.

Embodiments are described in connection with satellites carrying or comprising a base station. However, embodiments are not limited to a use of satellites but may also be applied to any scenario in which there are significant differences in the distances of the communication links. In addition or as an alternative to satellite platforms (including all LEO, MEO and GEO orbits), airborne platforms including both manned and unmanned vehicles, drones and/or balloons are part of the invention as well as base stations on the ground.

Although embodiments described herein relate to a gNB being part of a satellite, embodiments are not limited hereto. Other types of non-terrestrial devices such as high altitude platforms, balloons, or the like may be used. Even further, also terrestrial base stations and/or terrestrial networks may benefit from the disclosure provided herein although not suffering from that large delays as well as compared to NTN-configurations.

Embodiments of the present invention relate to implement a structure of an effective frame structure that is capable of compensating for large variations of a distance between two nodes and an associated large variation of round-trip-times, times-of-flight of signals and the like. The inventors found that a frame structure such as a TDD frame may be implemented as a varying effective frame structure that may be same but also different for different terminals, e.g., UEs, operating in a cell of a wireless communication network.

Such an effective frame structure may consider that a UE may adjust the timing advance, TA, depending on its distance from the satellite (round-trip-time, RTT) so that it arrives at the satellite in line with a possibly fixed frame structure. According to embodiments, a UE possibly refrains from using certain DL slots or symbols and/or UL slots or symbols or uses them only partially, i.e., performing a non-use of at least a part of at least one slot. This may be based on or dependent from a currently relevant round trip time (RTT) of the terminal. For example, such behaviour may be controlled or triggered by scheduling. In addition or as an alternative, a halfduplex UE can either receive or transmit at an instance of time, so it is preferred that scheduled DL and UL slots do not overlap in the UE's time base. If this is the case, a UE according to an embodiment may either skip or ignore the DL reception or the UL transmission, e.g., based on an own decision, e.g., a current data traffic, priority levels or the like and/or based on a preconfigured or configured decision. For example, the UE may be adapted to implement the non- use of the resources, e.g., slot or parts thereof for the effective frame structure to avoid the use of scheduled resources DL and UL which have a temporal overlap in the effective frame structure, i.e., to resolve the conflict caused by the overlap.

The overlap may occur within the same frame and/or between different frames. When referring, for example, to Fig. 5 showing a schematic block diagram for illustrating an aspect of the present invention according to which a basestation, e.g., located at satellite Si , operates a cell of a wireless communication network according to a TDD scheme that comprises a plurality of TDD frames, a temporal overlap and, thus a conflict, at the UE may arise between DL slots and UL slots within a same frame, e.g., as a switching from DL to UL has to be performed resulting in a time for the UL where still DL is scheduled. Alternatively or in addition, when switching from UL od a first frame to a DL of a next, e.g., second frame, a similar conflict may arise. Based on a changed structure within the frame regarding a position or order of UL slots, S-Slots and DL-slots, the conflict may also arise in different instances.

The varying effective frame structure may consider or be correlated with a variation of the timing advance caused by changes of the distance between two nodes exchanging signals. Such variation may be based on, e.g., an orbit of a satellite or other reasons and may be optionally be influenced by further parameters such as an effective field of view through which the satellite may travel, the effective field of view forming boundaries between minimum and maximum distances between a user terminal and the satellite such that a variation in the effective field of view may also cause a change in the effective frame structure variation. When referring, for example, to Fig. 4b, both UE 312i and 312₂ may benefit from a possibly undisturbed LOS therefore being possibly served by satellite Si.for a large amount of a path along the orbit 402 therefore experiencing possibly a significant variation of lengths L_A and/or L_B. However, when being located near to obstacles, e.g., buildings in a city, an effective field of view of a UE towards the sky may be limited, therefore only providing a LOS to satellite Si in a narrow range, and thus, the variation of the distance to the satellite may also be limited.

In other words, the device may select one of the overlapping resources, e.g., DL resources or UL resources from the overlapping resources and use them whilst non-using the others. The overlapping resources may be part of a same frame or of different frames. The overlap is not necessarily an explicit overlap of the resources in the time-frequency grid but may, as an alternative or in addition, relate to a conflict occurring by operating on the resources, e.g., signal processing switching between DL and UL and the like, which is to be considered at a device operating in half-duplex. Devices with partial or full duplex capability may be configured for simultaneous reception and transmission wherein the non-use of particular DL or UL resources may depend on or be based on the frequency allocation pattern. Such a non-use or a decision about the non-use, optionally including the decision for a use, may be fed back by the UE, i.e. , the UE may be adapted for providing a feedback indicating whether the device has performed resolving of a conflict caused by overlapping resources and/or which resolving, e.g., whether DL, S and/or UL slots or parts thereof where unused and/or which of them and/or that it used some or all of the scheduled resourced.

Alternatively or in addition, effectively usable parts of the frame structure may differ between two UEs, e.g., due to scheduling. A UE may operate on an effective frame structure, slot structure or symbol structure that may change dynamically or may be specific to the UE due to channel parameters (e.g. UE-satellite distance, RTT, window of coverage opportunity, etc.).

As an aspect the effective frame structure, slot structure and/or symbol structure can be identical, similar or individual and would therefore be different from other UEs.

In the following, additional embodiments and aspects of the invention will be described which can be used individually or in combination with any of the features and functionalities and details described herein.

A first embodiment relates to a user equipment, UE, comprising a wireless interface for receiving wireless signals and for transmitting wireless signals; wherein the UE is configured for operating in a cell of a wireless communication network according to a time division duplex, TDD, scheme that comprises a plurality of TDD frames, each TDD frame comprising a plurality of slots arranged according to a frame structure, the plurality of slots comprising a first number of downlink, DL, slots, a second number of uplink, UL, slots and a third number of special, S, slots e.g., arranged between the first number of UL slots and the second number of UL slots; wherein the UE is configured for operating with a varying effective frame structure within the TDD scheme to compensate for varying distances between the UE and a base station operating the cell.

According to a second embodiment when referring back to the first embodiment, the UE is adapted to operate with a dynamically varying effective frame structure based on a dynamically varying distance.

According to a third embodiment when referring back to the first or second embodiment, the UE is adapted to operate with the varying effective frame structure as varying based on a channel parameter such as a round-trip-time, RTT or a window of coverage opportunity for the UE.

According to a fourth embodiment when referring back to any of the first to third embodiments, the effective frame structure is UE specific.

According to a fifth embodiment when referring back to any of the first to fourth embodiments, the base station operating the cell is a non-terrestrial base station.

According to a sixth embodiment when referring back to any of the first to fifth embodiments, the UE is configured for a non-use of at least a part of at least one of the S-slots of the plurality of slots of the TDD frame.

According to a seventh embodiment when referring back to the sixth embodiment, the UE is adapted to implement the non-use for the effective frame structure to avoid a temporal overlap of a slot scheduled for DL, e.g., a slot of the first number of slots or a slot of the third number of slots, and associated with a first frame, and a slot scheduled for UL, e.g., a slot of the second number of slots or a slot of the third number of slots, and associated with the first or a second frame.

According to an eighth embodiment when referring back to the sixth or seventh embodiment, the UE is adapted to skip or ignore one of a) at least a part of a first slot scheduled for DL and associated with a first frame and b) at least a part of a second slot scheduled for UL and associated with the first frame or a second frame in case of a temporal overlap between the first slot and the second slot; or vice versa.

According to a ninth embodiment when referring back to any of the sixth to eighth embodiments, the device is adapted for providing a feedback indicating whether the device has performed resolving of a conflict caused by overlapping resources and/or which resolving

According to a tenth embodiment when referring back to any of the first to ninth embodiments, the varying effective frame structure relates to a variation in at least one of a frame structure, a slot structure within the frame and/or a symbol structure within the frame.

According to an eleventh embodiment when referring back to any of the first to tenth embodiments, the UE is configured with the slot structure or symbol configuration by a network entity or using a stored, e.g., initial, pre-configuration. According to a twelfth embodiment when referring back to any of the first to eleventh embodiments, the user equipment, UE, is configured for operating in a flexible TDD scheme with DL slots, UL slots and flexible S slots according to the effective frame structure as a flexible frame structure and/or a flexible symbol configuration of at least one S slot configured by the base station.

According to a thirteenth embodiment when referring back to any of the first to twelfth embodiments, the UE is configured for, e.g., directly after initial access or a different time and once or multiple time, e.g., periodically, signalling slots or symbols unusable for UL and/or DL, e.g., unusable due to a timing advance, TA, drift, for DL or UL explicitly or implicitly by e.g. indicating an absolute round trip time, a drift, a first drift derivative or a second derivative etc.

According to a fourteenth embodiment when referring back to any of the first to thirteenth embodiments, the effective frame structure is based on a scheduled frame structure from which at least one slot of the third number of slots that is scheduled for uplink or downlink remains unused by the UE.

According to a fifteenth embodiment when referring back to any of the first to fourteenth embodiments, the UE is configured for predicting and reporting a drift affecting the UE

According to a sixteenth embodiment when referring back to any of the first to fifteenth embodiments, the UE is configured for monitoring additional DL slots or symbols and/or for preparing a transmission in additional UL slots or symbols according to an allocation of special, S slots provided by the base station.

According to a seventeenth embodiment when referring back to any of the first to sixteenth embodiments, the UE is adapted to align to a first frame structure or TDD scheme implemented by the base station as a first base station and to align to a second frame structure or TDD scheme implemented by a second base station for preparing a handover from the first base station to the second base station.

According to an eighteenth embodiment when referring back to the seventeenth embodiment, the UE is configured for aligning the second frame structure or TDD scheme based on at least one of:

-> an SIB1 , SIB19 or SIB31 message; an enhancement -> a sync offset indicated by the first base station; and an initial slot structure of the second base station.

According to a nineteenth embodiment when referring back to any of the first to eighteenth embodiments, the UE is configured for aligning to the first or second frame structure or TDD scheme based on at least one message received in a connected mode and/or in an idle mode of the UE.

According to a twentieth embodiment when referring back to any of the first to nineteenth embodiments, the UE is configured for temporally aligning the TDD frame with the base station for reception within the frame.

According to a twenty-first embodiment when referring back to any of the first to twentieth embodiments, the UE is configured for temporally aligning the TDD frame with the base station for a transmission of the UE within the frame.

According to a twenty-second embodiment when referring back to any of the first to twenty- first embodiments, the UE is configured for using the S-slots of the plurality of slots of the TDD frame for an UL transmission or a DL communication based on a distance of the UE from the base station.

According to a twenty-third embodiment when referring back to any of the first to twenty-second embodiments, the UE is configured to evaluate a signal received and containing an allocation of the S-slots according to a group identifier indicated in the signal and to determine, based on the group identifier, whether the UE is a part of the indicated group and to implement the allocation when being a member of the group.

According to a twenty-fourth embodiment when referring back to any of the first to twenty-third embodiments, a sequence of S-slot usage of the third number of S-slots in the TDD frame for DL or UL is predetermined and/or specific per flight path, wherein the UE determines the S- slot usage from a signalling of the base station or from information indicating the flight path.

According to a twenty-fifth embodiment when referring back to the twenty-fourth embodiment, the UE is configured for providing a measurement report to indicate, to the base station, a location of the UE with regard to the flight path. According to a twenty-sixth embodiment when referring back to any of the first to twenty-fifth embodiments, the UE is adapted to report a periodicity of timing advance and/or a granularity of reporting with an interval of at least or at most 1 ms.

A twenty-seventh embodiment relates to a base station comprising a wireless interface for receiving wireless signals and for transmitting wireless signals; wherein the base station is configured for operating a cell of a wireless communication network according to a time division duplex, TDD, scheme that comprises a plurality of TDD frames, each TDD frame comprising a plurality of slots arranged according to a frame structure, the plurality of slots comprising a first number of downlink, DL, slots, a second number of uplink, UL, slots and a third number of special, S, slots e.g., arranged between the first number of UL slots and the second number of DL slots; wherein the base station is configured for allocating to different terminals in the cell and within the TDD scheme a varying effective frame structure, e.g., a different number or position of the DL or UL slots in the frame structure and/or a different symbol configuration of at least one S slot, e.g., an OFDM symbol configuration and/or a different length of at least one slot in the time domain, to compensate for varying distances between a terminal and the base station.

According to a twenty-eighth embodiment when referring back to the twenty-seventh embodiment, the base station is adapted to simultaneously schedule same or different effective frame structures from a same TDD scheme to different terminals.

According to a twenty-ninth embodiment when referring back to the twenty-eighth embodiment, the different effective frame structures within the TDD scheme relate to at least one of a number of S slots between a last downlink slot and a first uplink slot, a number of S slots within the TDD frame, a position of the UL slots within the TDD frame and a symbol configuration within at least one S slot being scheduled differently to different terminals or used differently by different terminals.

According to a thirtieth embodiment when referring back to the twenty-ninth embodiment, the symbol configuration relates to at least one of a location of symbols in a time frequency grid, a number of symbols in the slot and a use of the symbol as uplink symbol, downlink symbol or guard symbol.

According to a thirty-first embodiment when referring back to any of the twenty-seventh to thirtieth embodiments, the base station is configured for allocating at least one of the S slots for a different use for different terminals within the cell. According to a thirty-second embodiment when referring back to any of the twenty-seventh to thirty-first embodiments, the base station is at least a part of a flying device such as a satellite, a drone or a balloon.

According to a thirty-third embodiment when referring back to the thirty-second embodiment, the base station is configured for selecting a frame structure of the TDD scheme, e.g., from a plurality of different frame structures or different TDD schemes, based on an altitude, e.g., of an orbit or flight path, of the flying device.

According to a thirty-fourth embodiment when referring back to any of the twenty-seventh to thirty-third embodiments, the base station is configured for grouping terminals in the cell and for groupwise allocating the at least one of the S slots differently for different groups of terminals.

According to a thirty-fifth embodiment when referring back to the thirty-fourth embodiment, the base station is configured for grouping the terminals based on a delay or time-of-flight of signals between the base station and the terminals.

According to a thirty-sixth embodiment when referring back to any of the twenty-seventh to thirty-fifth embodiments, the base station is configured for selecting the frame structure or TDD scheme from a plurality of frame structures or TDD schemes, the frame structures or different TDD schemes differing in at least one of a time duration of one, more or all slots of the TDD frame, a number of slots of the frame, a number of UL slots in the frame, a number of DL slots in the frame and a number of S slots in the frame.

According to a thirty-seventh embodiment when referring back to the thirty-sixth embodiment, the base station is configured for selecting the frame structure or TDD scheme based on one or more contours of or within the cell.

According to a thirty-eighth embodiment when referring back to the thirty-sixth or thirty-seventh embodiment, the base station is configured for selecting the frame structure or TDD scheme based on the position/location of a UE or a group of UEs and the location of the gNB, e.g., along a flight path of a flying device comprising the base station while providing coverage /service to the cell. According to a thirty-ninth embodiment when referring back to any of the twenty-seventh to thirty-eighth embodiments, at the base station, the S slots are arranged between the DL slots and the UL slots; wherein the base station is configured for allocating the S slots for DL or UL operation for the different terminals.

According to a fortieth embodiment when referring back to any of the twenty-seventh to thirtyninth embodiments, at the base station, the S slots are arranged between the DL slots and the UL slots; wherein the base station is configured for allocating, to one or more terminals with a larger distance from the base station a larger number of S slots to compensate a larger TA requirement for UL transmissions.

According to a forty-first embodiment when referring back to the fortieth embodiment, the base station is adapted to increase a frame length for the terminals with the larger distance, e.g., increasing the first number of DL slots and/or the second number of UL slots.

According to a forty-second embodiment when referring back to the forty-first embodiment, the base station is adapted to increase the frame length for all terminals in the cell based or in accordance with a largest round trip time or largest distance of a terminal in the cell served by the base station

According to a forty-third embodiment when referring back to any of the thirty-ninth to forty- second embodiments, the base station is configured for allocating remaining S slots for additional DL traffic and/or additional UL traffic.

According to a forty-fourth embodiment when referring back to the forty-third embodiment, the base station is configured for allocating the remaining S slots differently for different terminals.

According to a forty-fifth embodiment when referring back to any of the twenty-seventh to fortyfourth embodiments, the base station is adapted for operating the cell with a frame duration of at least 15 ms.

According to a forty-sixth embodiment when referring back to any of the twenty-seventh to forty-fifth embodiments, the base station is configured for a synchronized arrival of signals received from the different terminals, e.g., by use of a timing advance, TA.

According to a forty-seventh embodiment when referring back to any of the twenty-seventh to forty-sixth embodiments, the base station is configured for allocating the slots according to a configuration according to which, at the base station and/or the terminal, within a single frame only one transition between DL and UL is implemented.

According to a forty-eighth embodiment when referring back to any of the twenty-seventh to forty-seventh embodiments, the base station is configured for allocating the slots according to a configuration according to which, at the base station and/or the terminal within a single frame more than one transition between DL and UL is implemented.

According to a forty-ninth embodiment when referring back to any of the twenty-seventh to forty-eighth embodiments, the base station is configured for mapping resources of a wireless communication along at least two adjacent slots.

According to a fiftieth embodiment when referring back to any of the twenty-seventh to fortyninth embodiments, the base station is configured for mapping resources of a wireless communication along at least two adjacent slots, wherein the resources of a first slot are used partially at an end of the first slot and are continued with resources at the consecutive second slot wherein at least the beginning of the at least second slot is used.

According to a fifty-first embodiment when referring back to any of the twenty-seventh to fiftieth embodiments, the base station is configured for allocating additional flexible slots and/or symbols for at least one of DL, UL and a guard period and to signal such allocation, the allocation being valid for individual terminals or terminal groups.

According to a fifty-second embodiment when referring back to the fifty-first embodiment, the base station is configured for allocating only S slots for additional DL transmissions that are received partially or entirely by the targeted terminal based on a round-trip time, RTT, associated with the terminal.

According to a fifty-third embodiment when referring back to the fifty-first or fifty-second embodiment, the base station is configured for allocating only S slots for additional UL receptions that are transmitted partially or entirely by the targeted terminal based on a roundtrip time, RTT, associated with the terminal.

According to a fifty-fourth embodiment when referring back to any of the twenty-seventh to fifty-third embodiments, the base station is configured for receiving information about an absolute and/or relative slot and/or symbol level shift of the terminals and for allocating the at least one S slot to compensate for differences in the shifts. According to a fifty-fifth embodiment when referring back to any of the twenty-seventh to fiftyfourth embodiments, the base station is configured for allocating, to at least one terminal at least one of a DL slots and UL slots prior to or after regular UL slots according to the frame structure or TDD scheme.

According to a fifty-sixth embodiment when referring back to any of the twenty-seventh to fiftyfifth embodiments, the base station is configured for predicting a drift affecting the UE

According to a fifty-seventh embodiment when referring back to any of the twenty-seventh to fifty-sixth embodiments, the base station is configured for coordinating the frame structure or the TDD scheme with another base station, e.g., a base station subsequently serving the cell or the terminal.

According to a fifty-eighth embodiment when referring back to any of the twenty-seventh to fifty-seventh embodiments, the base station is configured for receiving, from at least one terminal assistance information and to allocate the slots based on the assistance information indicating at least one of: o a global navigation satellite system, GNSS, and o a timing advance, TA, used by the terminal, e.g., between last DL symbol or slot received and the first UL symbol or UL slot to be sent or a derivate of the TA.

According to a fifty-ninth embodiment when referring back to any of the twenty-seventh to fiftyeighth embodiments, the base station is configured for allocating the slots based on a concatenation of at least two different frame structures.

According to a sixtieth embodiment when referring back to the fifty-ninth embodiment, the concatenation of at least two different frame structures forms a frame set, the frame set being one of a plurality of different frame sets being formed by different concatenations of frame structures; wherein each frame set is associated with a frame set identifier, wherein the base station is configured for indicating a selected frame set form the plurality use of a specific frame set by signalling the associated frame set identifier.

According to a sixty-first embodiment when referring back to any of the twenty-seventh to sixtieth embodiments, the base station is configured for operating the cell in FR1 , FR2 and/or FR3 According to a sixty-second embodiment when referring back to any of the twenty-seventh to sixty-first embodiments, the base station is configured for selecting the frame structure for the TDD scheme to support time delays caused by distances between the terminal and the base station being exemplarily at least 600 km and/or at most 2,000 km or a different flight height or orbit.

According to a sixty-third embodiment when referring back to any of the twenty-seventh to sixty-second embodiments, the base station is adapted for allocating a use of the S-slots of the plurality of slots of the TDD frame for an UL transmission or a DL communication individually for different terminals or groups of terminals according to a distance of the terminal from the base station, e.g., based on a terminal-by-terminal; or group-by-group-basis.

According to a sixty-fourth embodiment when referring back to any of the twenty-seventh to sixty-third embodiments, the base station is configured for allocating different frame structures for different terminals based on a distances of the terminals from the base station.

According to a sixty-fifth embodiment when referring back to any of the twenty-seventh to sixtyfourth embodiments, the base station is configured for allocating at least one of the S-slots of the plurality of slots of the TDD frame as being unused for uplink and unused for downlink at the terminal for at least one terminal.

According to a sixty-sixth embodiment when referring back to any of the twenty-seventh to sixty-fifth embodiments, the base station is configured for maintaining a number of the third number of S-slots in the TDD frame constant over time; or for adapting the number of the third number of S-slots in the TDD frame over time.

According to a sixty-seventh embodiment when referring back to the sixty-sixth embodiment, the base station is configured for adapting the number of the third number of S-slots over time based on a changed elevation angle with regard to the base station experienced by the terminals served by the base station.

According to a sixty-eighth embodiment when referring back to any of the twenty-seventh to sixty-seventh embodiments, the base station is configured for scheduling additional DL traffic and/or additional UL traffic to a terminal in the cell based on information indicating a number of S-slots available/accessible for the terminal at a particular point/period of time. According to a sixty-ninth embodiment when referring back to any of the twenty-seventh to sixty-eighth embodiments, the base station is at least a part of a flying device and configured for scheduling data traffic such as user plane traffic for a terminal in cell and for signalling an allocation of S-slot, e.g., the number thereof, to the terminal.

According to a seventieth embodiment when referring back to any of the twenty-seventh to sixty-ninth embodiments, the base station is configured for adapting the scheduling along a flight path of the flying device with respect to the terminal.

According to a seventy-first embodiment when referring back to the sixty-ninth or seventieth embodiment, the base station is configured to schedule the S-slots for the terminal as a member of a group of terminals and commonly for the group of terminals, e.g., formed based on a proximity or distance between the terminals; wherein the base station is configured for signalling the allocation to the group of terminals, e.g., using a group identifier; or for signalling the allocation individually to the terminal.

According to a seventy-second embodiment when referring back to any of the twenty-seventh to seventy-first embodiments, a sequence of an S-slots usage for DL or UL is predetermined and/or is specific per flight path, the base station being a part of a flying device.

According to a seventy-third embodiment when referring back to any of the twenty-seventh to seventy-second embodiments, the base station is configured for selecting the frame structure for the TDD scheme to support a worst-case time delay associated with a longest distance between any of the terminals in the cell and the base station.

According to a seventy-fourth embodiment when referring back to any of the twenty-seventh to seventy-third embodiments, the base station is configured for simultaneous transmission and reception and for allocating a same S-slot or at least one symbol for an UL transmission of a first terminal or a first group of terminals in the cell and for a DL reception of a second terminal or a second group of terminals in the cell.

According to a seventy-fifth embodiment when referring back to the seventy-fourth embodiment, the base station is configured for configuring S-slots or symbols used for simultaneous reception and transmission at the base station to be operated in a Sub Band Full Duplex, SBFD, mode. According to a seventy-sixth embodiment when referring back to the seventy-fourth or seventyfifth embodiment, the base station is configured for implementing a partitioning of S-slots for simultaneous UL usage and DL usage within one S-slot according to an overlap or not-overlap fashion over a frequency domain, e.g., with respect to sub-bands, with respect to the time domain, e.g., using OFDM symbols, or a combination thereof.

According to a seventy-seventh embodiment when referring back to any of the twenty-seventh to seventy-sixth embodiments, the base station is configured for selecting at least one resource block of an S-slot for mapping user plane data for a terminal served by the base station based on information indicating that the selected resource block is accessible for the terminal, e.g., based on the base station being at least a part of a flying device.

According to a seventy-eighth embodiment when referring back to any of the twenty-seventh to seventy-seventh embodiments, the base station is configured for mapping a code word or user data to be transmitted onto a subset of OFDM symbols of one S slot, the subset selected based on information that the selected subset is accessible for the terminal, e.g., based on the base station being at least a part of a flying device.

According to a seventy-ninth embodiment when referring back to any of the twenty-seventh to seventy-eighth embodiments, the base station is configured for mapping a code word or user data to be transmitted onto a combination of a first subset of OFDM symbols of a first S slot and a second subset of OFDM symbols of a second, possibly consecutive, second S slot based on information that the selected subset is accessible for the terminal, e.g., based on the base station being at least a part of a flying device.

According to an eightieth embodiment when referring back to any of the twenty-seventh to seventy-ninth embodiments, the base station is configured for adapting a coding level to encode a code word or user data to be transmitted according to a number of usable OFDM symbols within a slot such as an S slot to use usable OFDM symbols within the slot, e.g., based on the base station being at least a part of a flying device.

According to an eighty-first embodiment when referring back to any of the twenty-seventh to eightieth embodiments, the base station is configured for signalling a list of frame structure configurations, e.g., as a dedicated signal or a broadcast signal to one or more terminals during a configuration phase and for instructing at least one terminal within at least one of a cell a beam provided by the base station or a group to activate a certain frame structure based on the distance of the at least one terminal from the base station, e.g., implicitly or explicitly. According to an eighty-second embodiment when referring back to any of the twenty-seventh to eighty-first embodiments, the base station is configured for managing the frame structure based on a topology of the network, e.g., based on a NR cell or flying device beam size, a mapping between the NR cell, NR beam (SSB), and the flying device beam.

According to an eighty-third embodiment when referring back to any of the twenty-seventh to eighty-second embodiments, the base station is a part of a flying device and configured for allocating a same TDD frame structure for all terminal within the cell based on a scenario where a small or a large NR cell is provided by the base station and a one-to-one mapping between the NR cell, a flying device beam, and a NR beam, e.g., SSB is operated by the base station; wherein the base station is configured to broadcast a list of frame structure configurations using system information messages such as SIB1 , SIB19 for NR-NTN, and SIB31 , e.g., for loT-NTN, e.g., of terminals being in an idle mode, RRCJDLE.

According to an eighty-fourth embodiment when referring back to the eighty-third embodiment, the base station is configured for updating the list of frame structure using the periodic signalling, e.g., SIB1 , SIB19, or SIB31.

According to an eighty-fifth embodiment when referring back to the eighty-third or eighty-fourth embodiment, the base station is configured for updating the list of frame structures for terminals being in an active mode, RRC_ACTIVE, e.g., using SIB messages and/or using dedicated RRC-messages.

According to an eighty-sixth embodiment when referring back to any of the eighty-third to eighty-fifth embodiments, the base station is configured for updating the list of frame structure and to indicate the terminals explicitly and/or implicitly to update their frame structure within the cell, e.g., using either DCI in the PDCCH or MAC-CE in the PDSCH, e.g., based on a changed distance between the terminal and the base station.

According to an eighty-seventh embodiment when referring back to the eighty-sixth embodiment, an explicit indication relates to an explicit indication by the base station to which frame structure the terminal may use; and/or wherein an implicit indication relates to an implicit indication of which frame structure the terminals may use by instructing the terminals within a certain time/location/group to change their frame structure after a certain time, e.g., due to a mobility of the base station. According to an eighty-eighth embodiment when referring back to any of the eighty-third to eighty-seventh embodiments, the implicit indication comprises a time-based trigger or a location-based trigger.

According to an eighty-ninth embodiment when referring back to any of the twenty-seventh to eighty-eighth embodiments, the base station is a part of a flying device and configured, in a scenario where a large NR cell, with one-to-one mapping between the NR cell and the flying device beam and multiple NR beams, e.g., SSBs, within the NR cell, for grouping group terminals in the cell based on their serving NR beam, SSB within the flying device beam/NR cell.

According to a ninetieth embodiment when referring back to the eighty-ninth embodiment, the base station is configured for mitigating interference caused by the terminals by using spatial multiplexing.

According to a ninety-first embodiment when referring back to any of the twenty-seventh to ninetieth embodiments, the base station is a part of a flying device and configured, in a scenario where a large NR cell with one-to-many mapping between the NR cell and the flying device beams is implemented, for operating according to a one-to-one mapping between the flying device beam and the NR beam (SSB); and the base station is adapted for grouping the terminals based on their serving flying device beam, and to configure all terminals served by the same satellite beam to use a same frame structure.

According to a ninety-second embodiment when referring back to the ninety-first embodiment, the base station is configured for broadcasting a list of frame structures using system information messages for all terminals in RRCJDLE and RRC_ACTIVE on a satellite-beam basis; and/or to use periodic transmission of SIB messages to periodically update the list of frame structures; and/or to update the list using RRC_messages in a dedicated manner for terminals in RRC_ACTIVE.

According to a ninety-third embodiment when referring back to any of the eighty-third to ninety- second embodiments, the base station is configured for updating the frame structure a feederlink switch-over.

According to a ninety-fourth embodiment when referring back to any of the eighty-third to ninety-third embodiments, the base station is configured for updating the frame structure in case of a feeder-link switch in connection with an unchanged, within a threshold, service link delay.

According to a ninety-fifth embodiment when referring back to any of the eighty-third to ninetyfourth embodiments, the base station is adapted for a relaying of signals via an inter satellite link, ISL, wherein the base station is configured for updating the frame structure based on an ISL changeover between a serving satellite and at least one relaying satellite based on a triggered change in distances of the terminals back to the base station.

According to a ninety-sixth embodiment when referring back to any of the twenty-seventh to ninety-fifth embodiments, the base station is configured for grouping the terminals in the cells based on a serving NR beam, e.g., SSB or serving satellite beam; and/or to allocate all terminals served by the same NR beam or satellite beam with a same frame structure.

According to a ninety-seventh embodiment when referring back to any of the twenty-seventh to ninety-sixth embodiments, the base station is a part of a flying device and configured, in a scenario where a large NR cell is operated by the base station the base station is configured for using information related to a timing advance reported by the terminals to estimate a distance of the terminals and/or a round trip time, RTT, from the base station to classify the terminals into contours or groups based on their distances.

According to a ninety-eighth embodiment when referring back to any of the twenty-seventh to ninety-seventh embodiments, the base station is configured for informing a different base station about the allocated TDD structure or frame structure, e.g., using an ISL/Xn interface, an NG for NR-NTN/X2, and S1 for loT-NTN; and/or to receive such information from a base station operating the cell prior to the base station and to operate accordingly.

According to a ninety-ninth embodiment when referring back to any of the twenty-seventh to ninety-eighth embodiments, the base station is configured for flexibly allocating OFDM symbols within at least one S slots for DL, UL or guard symbol.

A hundredth embodiment relates to a method for operating a UE, the method comprising operating the UE in a cell of a wireless communication network according to a time division duplex, TDD, scheme that comprises a plurality of TDD frames, each TDD frame comprising a plurality of slots arranged according to a frame structure, the plurality of slots comprising a first number of downlink, DL, slots, a second number of uplink, UL, slots and a third number of special, S, slots e.g., arranged between the first number of UL slots and the second number of UL slots; operating the UE with a varying effective frame structure within the TDD scheme to compensate for varying distances between the UE and a base station operating the cell.

A hundred-first embodiment relates to a method for operating a base station, the method comprising: operating a cell of a wireless communication network according to a time division duplex, TDD, scheme that comprises a plurality of TDD frames, each TDD frame comprising a plurality of slots arranged according to a frame structure, the plurality of slots comprising a first number of downlink, DL, slots, a second number of uplink, UL, slots and a third number of special, S, slots e.g., arranged between the first number of UL slots and the second number of DL slots; allocating to different terminals in the cell and within the TDD scheme a varying effective frame structure, e.g., a different number or position of the DL or UL slots in the frame structure and/or a different symbol configuration of at least one S slot, e.g., an OFDM symbol configuration and/or a different length of at least one slot in the time domain, to compensate for different distances between the different terminals and the base station.

A hundred-second embodiment relates to a computer readable digital storage medium having stored thereon a computer program having a program code for performing, when running on a computer, a method according to the hundredth or hundred-first embodiment.

Embodiments of the present invention are related to and based on a recognition that a measurement configuration for UEs may be updated, e.g., automatically, regularly, or based on an event, to avoid that UE measures when already sending uplink, UL, transmissions. For example, one or more nodes of the wireless communication network may evaluate or check how often a measurement report or a specific task, e.g., channel state information, CSI, channel quality indicator, CQI, precoding matrix indicator, PMI, or others has to be sent. Whilst considering a schedule of the network, e.g., a location of UL slots, all or more nodes may define, how the measurement has to be done, e.g., whilst not disturbing or overlapping time with the UL slots, e.g., how the measurements may be done in a punctured way around the UL slots. Embodiments also allow that if some UES are scheduled for uplink and others are not, then the measurement might average over a different number of DL slots. That is, different UEs may measure over a different number of DL slots based on their UL schedule. Alternatively or in addition, different UEs may, e.g., based on their UL schedule, provide their measurement reports with a different granularity or regularity.

Alternatively or in addition, a slot OFDM symbol and, additionally, a timing advance can be used to align/compensate a time of flight in the reverse link. It may be of advantage to perform the measurement, e.g., at the UE, preferably or only over complete slots. While not excluding such a solution, preferred embodiments relate to measuring not only on part of slots, but onto complete slots.

Further, embodiments relate to a user grouping and/or pairing, e.g., implemented as an algorithm. For example, if many users are clustered in one end of the cell with a specific delay and other users are not active, then the statistical user group being gain might be lower, but in case of a few users, more resources are available per users in return.

Alternatively or in addition, one or more of the S-slots may be filled flexibly with DL or UL resources which may allow to introduce a benefit of a slot similar to flexible, F, slots in integrated axis and backhaul, IAB networks.

Concepts described herein may be used by different UEs and the concepts are suitable especially for UEs that are not using the complete RF bandwidth.

At least some of the embodiments described herein are based on the assumption to use a fixed guard period in a frame structure in connection with a use of fixed DL/UL patterns with flexible slots or flexible symbols, S.

Fig. 5 shows a schematic block diagram for illustrating an aspect of the present invention according to which a basestation, e.g., located at satellite Si, comprising a wireless interface for receiving wireless signals and for transmitting wireless signals is configured for operating a cell of a wireless communication network according to a TDD scheme that comprises a plurality of TDD frames such as a frame 502. Fig. 5 is based on Fig. 3 whilst only making reference to UE1 and UE3 of Fig. 3, UE3 being now named UE2.

Each TDD frame 502 may comprise a plurality of slots 504i to 504_n that are arranged according to a frame structure. The plurality of slots comprises a first number of downlink, DL, slots e.g., slots 504i to 504_a, a second number of uplink, UL, slots, e.g., slots 504d to 504_n and a third number of special, S, slots, e.g., 504b to 504_c. By way of example but not limited hereto, the special slots 504b to 504_c may be arranged between the UL slots and the DL slots. A set 506 of preferably continuously arranged S slots may provide for a guard period with a duration that is preferably larger than two times the NDD plus two times the common delay, CD with regard to the regular pattern duration, RPD, of pattern 502. With regard to Fig. 3, the common delay CD 512 may but is not required to be longer in time when compared to the regular pattern duration RPD 514. Maximum differential delay, MDD, 516 may be comparatively small when compared to common delay, CD, 512 but may still add for a considerable amount of time delay.

Fig. 5 shows a UE dependent/distance dependent effective TDD slot configuration according to an embodiment that may be applied. This may include uplink, UL, to be transmitted earlier, e.g., for UEs far away, or later, e.g., for UEs closer to the satellite. The remaining S-slots may be used for DL transmission, which again have to scheduled according to the distance of the UEs. However, those slots may remain usable whilst not being necessarily limited to a guard period.

As shown for UEi and UE2, a position and/or an amount of S-slots may be allocated differently to UE1 and UE2. For example, between UL-slots and DL-slots, a low amount of S-slots is allocated to UE1 being closer to the satellite when compared to UE2 to which a larger amount of S-slots is allocated, compare S-slots 506bi used for UE1 being lower when compared to a number of S-slots 506b2 used for UE2, e.g., based on the delay, the RTT and/or the distance. Similarly, a higher of number of S-slots may be allocated between DL-slots and UL-slots for UE1, see S-slots 506ai, when compared to UE2 which may have lower or even no S-slots therebetween. Thereby, whilst, e.g., maintaining the number of DL-slots and the number of UL-slots, usable slots may be different for different UEs at a given point in time, that is a different effective frame structure may be operated for different UEs at that given point in time.

Whilst in Fig. 5 a timing advance, TA, of UE1 may correspond to two times the CD, UE2 may operate according to a TA that is two times the CD and two times the MDD.

Based on this, embodiments are related to a consideration of a different granularity for TA control, e.g., on a slot level, a symbol level and/or a Guard Interval, Gl, level e.g., the overall timing advance may be signalled in multiples of slots, symbols and/or microseconds in units of samples, e.g., as information provided by the base station.

Embodiments of the present invention may use one or more of the following implementations. That is, items of a proposed solution that are described in the following may be implemented commonly, individually or group-wise.

For example, flexible slots can be used for additional UL or DL traffic. This may be scheduled to specific users or groups thereof which are able to continue DL reception or UL transmission in these slots. In connection with this, it may be of advantage to extend DL reception into S- slots or to have S-slots prior to DL slots to allow an early start of the downlink. Similarly, S- slots preceding UL slots may allow for an early start of UL and S-slots following UL slots may allow for extending the uplink.

Alternatively or in addition, embodiments relate to providing the base station, gNB, e.g., informed by a UE message or by the network, about an absolute and/or relative shift, e.g., on a slot level or a symbol level, to accommodate for the right slot or symbol selection in the S- slots.

Alternatively or in addition, a TA drift may cause that certain symbols or slots cannot be used by the UE for DL or UL. Embodiments relate to consider such a recognition and to avoid a schedule for such symbols and/or slots.

Alternatively or in addition, a device such as a UE may signal those slots or symbols, e.g., explicitly and/or implicitly, by e.g., a drift, drift derivate or second derivate or the like. That is, the UE may explicitly and/or implicitly inform the network, e.g., the base station, about slots and/or symbols subject to a TA drift.

Alternatively or in addition, the gNB may use additional flexible slots and symbols for at least one of DL, UL and guard period to be signalled to the individual UEs or UE groups. The UE may then be expected to receive and monitor additional DL slots or symbols to prepare for transmission in additional UL slots or symbols.

Alternatively or in addition, the DL slots and/or UL slots, as a whole or as parts thereof, located earlier and/or later compared to the regular UL slots and/or DL slots. For example, when referring to Fig. 5, additional UL slots or DL slots can be earlier than the regular UL slots and the additional DL slots can be later than the regular UL slots.

Alternatively or in addition, the drift of the UL specific usable additional slots or symbols may be predicted by the UL and/or gNB and the result of such calculation may be used. For example, various methods of signalling, prediction or the like may be used.

A trade-off may be done between a more precise calculation of a drift, e.g., using more computational resources and/or time and/or to save time whilst allowing to have some sort of impreciseness. Alternatively or in addition, embodiments consider the FTD TA reporting to be adapted for requirements in TDD. This may allow that the reporting is more frequent than defined in the current specification such as TS 38.321 section 5.4.8, timing advance report for FDD.

Alternatively or in addition, when considering seamless handover, HO, from satellite 1 to satellite 2, e.g., in a case where satellite 1 moves out of sight of the UE and satellite 2 takes over, the UE is, according to embodiments, aligned to the effective DL and/or UL slots of both satellites, satellite 1 and satellite 2. For example, SIB 19 or enhancements or serving gNB may provide synchronization of sets, SYZ offsets, and/or information indicating an initial slot structure of the new gNB for a faster synchronization and initial access.

As an example that may be used in addition or as an alternative, different gNBs may be received by the UEs with time shift depending on the position of the satellites and the positions of the UEs. As up to date RACH-less handover is not supported as RACH-less HO is only possible if the TA is assumed 0 or TA1 = TA2, which is not likely and/or in view of a consideration that may be the two satellites are able to coordinate some of the regular DL and UL slots because of the effective sync misalignment, embodiments may provide for an advantageous modification to enable an efficient use of resources within an NTN network.

Embodiments are based on a consideration of different beam diameter configurations, which may be 50 km or larger. The coverage cells may result in larger maximum differential delay and therefore may benefit from a longer frame structure. For example, when considering an Iridium constellation having, e.g., 75 satellites in space, a larger footprint on the ground may be obtained when compared to constellations having a higher number of satellites. Embodiments relate to calculating a maximum differential delay, MDD, and propose a frame structure design consisting of K DL slots + IS-slots + mUL-slots. A frame length in NTN may, but is not required to be fixed. Optionally, between frames, any number of S-slots may be introduced to provide for usable resources. For example, 11 satellites that provide, e.g., 48 spot beams in one orbital plane, e.g., 66 in total, may lead to each beam being about 600 km in diameter providing for a total footprint her satellite of approximately 4700 km. This may result in comparatively broad beams. An example slot structure used by Iridium is 90ms of a TDD frame that is divided into 20 ms DL, 4 x 8.2 ms uplink and 4x DL slots with several variable guard times.

Embodiments allow for a combination of MDD and sub-carrier spacing SCS. That is, a frame length may require more S-slots than another frame with a smaller SCS. Embodiments propose to fix a frame structure under consideration of RTT and MDD. Alternatively or in addition, the use of the S-slots may be dynamic, depending on RTT between the UE and the satellite. For example, embodiments propose to increase a frame structure for a large RTT, e.g., 40 ms frame length and 20 ms of S-slots. Such implementation may be executed by the base station, signalled to the UE and/or may be based on a feedback received from the UEs.

According to an embodiment, while a satellite is flying over UEs, the base station can schedule an additional DL and/or UL opportunities for individual UEs or UE-groups. Possible solutions may be assistance information from the UE. For example, a global navigation satellite system. GSS, report may be provided, e.g., from the UE to the satellite. Alternatively, a GNSS-less report may be transmitted, e.g., the UE may report a TA used between the last DL slot received and the first UL symbol to be sent. This may be implemented under the consideration to avoid an outdating of TA while the satellite is moving, e.g., by predicting the value for the future. Alternatively or in addition, the UE may provide future TA evolution e.g., as a first and/or derivate, by signalling which may allow to have a UE specific equivalent of signalling from gNB in SIB19.

A frame structure as proposed according to embodiments allows to be well suited for a long RTT. For example, the frame structure may comprise one or more of the following: for example, a concatenation of multiple frame structures that may be same or different when compared to each other may be used. According to a preferred embodiment, two different frame structures are combined in a combined frame structure to overcome deficiencies of known systems that allow a concatenation of two same frames.

Alternatively or in addition, a new and especially longer frame structure is proposed. This may allow to adapt to the long RTT.

Alternatively or in addition, embodiments relate to cover all numerologies, e.g., between 15 kHz and 120 kHz. For example, embodiments may be implemented in FR1 , FR2 and/or FR3.

Alternatively or in addition, a TDD spectrum may be available for S2E and E2S, i.e. , satellite- to-earth and earth-to-satellite. According to embodiments, the frame length is designed to follow the longest path when flying over the ground. For example, when considering a 600 kilometre altitude, a distance between 600 and 2000 kilometres may apply and said distance may at least influence the frame length.

Alternatively or in addition, according to an embodiment a long frame may comprise a structure according to which a first amount of downlink slots is followed by a second amount of special slots which is followed by a third amount of uplink slots as shown, for example, in Fig. 5. In such a structure, the S-slots may be used to compensate for RTT and may be used for additional DL and/or UL for specific users.

Alternatively or in addition, a frame structure may be adapted to the orbit altitude. That is, for a different altitude, e.g., a higher altitude, a slot length and/or a number of slots of group downlink, special and/or uplink may be adapted. For example, a multi-orbit constellation may rely on different frequencies to be used to different orbits and/or satellite constellations.

Alternatively or in addition, embodiments provide for frames operated by the base station that have a length which corresponds to the largest delay in the cell. For example, referring to a 600 kilometre orbit, the RTT may be between 4ms and 30ms. According to such embodiments, the frame may have a sufficient length of S-slots covering 13ms. When applying, e.g., a 20ms total frame length, embodiments may use 30ms of those 20ms for S-slots, e.g., splitting the remaining 7ms into 5ms used for DL-slots and 2ms for UL-slots or differently. According to such an example, the frame may comprise 5ms of DL-slots, 13ms of S-slots and 2ms of UL- slots. A longer total frame length may reduce loss of efficiency due to number of S-slots but may increase latency when switching from UL to DL and vice versa. A trade-off may be established, e.g., when operating a network for different purposes.

Alternatively or in addition, all S-slots which are not used by a particular UE to compensate for RTT can be used either for additional UL or DL traffic, wherein the group of S-slots may be use for one or both of UL and DL. For example, such an allocation may be scheduled by the gNB when signalled to the UE or group of UEs, e.g., using CORESETs. Alternatively or in addition, the gNB may provide different frame structures depending on a contour of the cell, e.g., when determining RTT to have a first range, e.g., between 1 and 5 ms, a first configuration A may be used and when determining a different RTT, e.g., between 6 and 10 ms, a different configuration b may be used or realized. The UE may know which configuration is valid at a certain time and/or at a certain location. This does not prevent a signalling to the UE, e.g., from the base station. The contour may refer to a UEs experiencing the same or a similar RTT or a delay, time-of-flight of the signal between the UE and the gNB. Alternatively or in addition, the TA and/or RTT may be concluded from GNSS and/or TA. Alternatively or in addition, different slot structures may be valid for the same beams. Alternatively or in addition, different slot structures may be used for different beams used by the base station. Alternatively or in addition, different slot structures may be signalled in the same or different beams.

Alternatively or in addition, embodiments solve the issue of an inter-satellite frame structure coordination to avoid inter-frame interference during handover, HO, as described herein. This may be implemented, for example, by coordinating the frame structures between satellites, e.g., under consideration of a distance to the UEs.

Alternatively or in addition, for scheduling, a gNB may use knowledge about the RTT, e.g., down to a symbol level, to use only S-slots for DL transmission which can be received entirely by the targeted UE. This may benefit from a granularity being below OFDM symbol level. This may be done, e.g., as part of the TA adjustment procedure. An accuracy thereof is advantageously down to a cyclic prefix, CP, of an OFDM symbol. That is, the base station may evaluate whether an S-slot may completely be received by a targeted UE and may only such S-slots for DL that fit to this criterion.

Alternatively or in addition, embodiments relate to implementing a power control. For example, such a power control may relate to a power used for transmitting a signal with the base station and/or the UE. According to an embodiment, the power control may be implemented in an open-loop-manner, e.g., with assistance from gNB. For example, in an orbit between 600 and 2000 km, the distance between the UE and the satellite may change with a speed of 6 km/s allowing a power control, PC, -loop to be used.

Alternatively or in addition, a misalignment of directivity/tracking of an antenna may be a considerable or a dominant influence. For example, an antenna pattern in azimuth in FR1 may vary so that a full power could be a solution.

Alternatively or in addition, measurement reports for radio resource management, RRM, e.g., a measurement configuration of the UE such as a DL measurement configuration may be used to improve communication. The UE may be informed, explicitly and/or implicitly, to know if a particular S-slot is used for DL and/or UL.

Alternatively or in addition, the UE may predict the available or useful amount of resources for a period of time in the future and may report this to the base station. Such a report may be configurable or predetermined, e.g., with regard to a varying granularity of the report, such as symbol-level, slot-level, or a set of slots. Alternatively or in addition, the UE may report such resources at different granularity as capability reporting. For example, when the reporting is provided on an OFDM symbol level, the slot mapping and the modulation coding scheme, MCS, may be adapted with a same granularity and are preferably adapted accordingly.

Embodiments further provide, as an alternative in addition, to a change of an effective TTD frame configuration or a change of a frame configuration e.g., so that S-slots are used differently for different UEs or different groups of UEs. For example, embodiments may relate to the aspect of being in idle mode to define at which point the UE receives the configuration. This may mean that the UE may synchronize to the SSB and may receive information such as SI B 1 , but does not perform the RACH procedure. This may be signalled in SI B 1 or SI B 19/31 or in a different SIB. Alternatively or in addition, in connected mode, e.g., using downlink control information, DCI, or a control element, CE, and/or an RRCJnactivestate, e.g., for NR, not LTE, one or more solutions may be applied. For example, a measurement configuration, e.g., according to a minimization of drive test, MDT, may be configured by gNB, e.g., to the UE based on a consideration of updated TTD frame configuration, e.g., to avoid CLI which may be caused in case where some UEs transmits, some UEs receive in proximity. A CLI for S- slots received by some UEs in DL while other UEs have to send UL signals to compensate for the TA may cause such a CLI. If such true UEs are well-separated, then the CLI may be nonharmful to the receiving UE. Embodiments therefore provide to configure specific measurements to enable detection of CLI and provide CLI reports to the gNB as scheduling input. That is, the UE may be configured for providing CLI measurement reports. Alternatively or in addition, the base station may be configured for establishing the frame structure based on CLI information related to CLI received by one or more UEs in order to mitigate or reduce the CLI. Alternatively or in addition, different granularity of measurement configurations, e.g., regarding slots, symbols, or the like and/or a periodicity or the like may be used. That is, different UEs may report, e.g., based on a local decision and/or based on configuration or instructions perform measurements on same or different granularities.

According to further examples, the UE may report a location of the UE. As an alternative or in addition, the UE may report a potential drift, however, a variation of the UE may be small when compared to satellite movement. Alternatively or in addition, when the UE may report the timing advance, TAR, from the UE to the network as described above. This may benefit from a higher periodicity than every 1 ms. That is, according to embodiments, the UE may report the timing advance with a periodicity being less than 1 ms, less than 900 ms, preferably less than 700 ms or even less than 500 ms. Combinations of such solutions may be used. Aspects of the present invention relate to signalling of TDD slot configurations when the UE is connected to different orbits to arrive at an inter-orbit configuration signalling. The signalling may be provided by a selected orbit or by each of the orbits.

Embodiments of the present invention may be used to define parts of a technical standard, e.g., through 3GPP SA 2, RAN 1 , RAN 2, RAN 4 or RAN 5.

The described embodiments relate to a TDD operation in NTN. In some situations, it may happen that the UEs already transmit whilst there is still transmitted in DL. This may benefit from a network that knows where the terminals are located to avoid a schedule of DL traffic when the UE has started to send and is, therefore, unable to receive. Embodiments allow to avoid TDD duplex-gaps or, the other way around, those S-slots are used to allocate traffic.

Further to the solution described above the inventors identified several solution options to solve the problem set described in the beginning of the document.

The following solutions address at least one of the problems identified when operation a sat communication system in low earth orbit with satellites flying over the users to be served at high speed with varying distance between the UE and the satellite, wherein the satellite communication system is considered to operate in TDD mode and the invention describes techniques to handle the long and varying distance and RTT between the satellite and the UEs.

Solution to problem of multiple UEs in a serving cell experiencing different RTT:

• Multiple Slot/frame structures configured and/or used at the same time by the gNB

The gNB could allocate different frame structures for the UEs based on their distances from the satellite/gNB. The new frame structure configurations include a number of DL slots, a number of UL slots, and a number of special slots (S-slots). Additionally, the special slots granularity could be on OFDM symbols-basis. So, a special slot within the frame structure might have newly configured symbols within the special slot, which includes DL OFDM symbols, UL OFDM symbols, and OFDM guard symbols.

UEs with larger distances from the satellite/gNB require and are provided with a larger number of special slots to compensate the large TA requires for UL transmissions. Additionally, and in order to increase the spectral efficiency, the frame length may be extended for those UEs (increasing the number of DL slots as well as UL slots). The absolute frame length may be a function of the RTT and can be configured for:

• 1.) all UEs the same and/or

• 2.) individual for each UE or group of UEs.

A list of frame structure configurations may be defined and broadcasted to several or all UEs. The gNB may instruct the UEs within a cel l/beam/g roup to activate a certain frame structure, e.g., based on their distances from the gNB/satellite either implicitly or explicitly.

• UEs group allocation may change over time, e.g., during flight of satellite

Solution to problem of slot structure design when multiple UEs in a serving cell experience different RTT:

• slot/frame structure may follow a longest delay of a user in a cell and is fixed over time; and/or

• a slot structure may follow the longest delay in the cell and can be reduced over the time the satellite is serving the cell (e.g., LEO 600km-2.000km)

Contained as a sub-figure within Fehler! Verweisquelle konnte nicht gefunden werden., an illustration is shown of a low earth orbiting (LEO) satellite which provides coverage to two UEs (UE1 and UE2). The satellite and the UEs thus comprise elements of a non-terrestrial network (NTN), wherein the satellite — or to be more precise, the payload carried by the satellite — is a gNB. However, since the satellite is orbiting the Earth at an angular speed of rotation much greater than one Earth day, the position of the satellite in the sky when observed from a fixed point on Earth will change as a function of time. The sub-figure thus shows what could be called a snapshot of the orbiting satellite. Furthermore, the UEs position on Earth or above Earth (e.g. in the case of airborne platforms) might also vary. However, as a LEO satellite with an altitude above the Earth of 600 km (a “LEO 600” orbit) flies with a speed of approximately 7.8 km/s, the effect of UE mobility is negligible even for aircraft flying at a speed of 1000 km/h. Therefore, for the purpose of analysis, the UEs can be considered as stationary. Fehler! Verweisquelle konnte nicht gefunden werden. shows that the distance between the satellite and the UEs: a) can be different; and b) as just explained, can vary as a function of time. This means that the time needed for the propagation of an electromagnetic wave from the gNB to a UE (and vice versa) is not only dependant on the relative position of the satellite and the UEs but also on the absolute position of the satellite in its orbit (the absolute position of the UEs, as already explained, has an effect which is negligible in comparison).

Referring again to Fig. 5 there is also shows an example of a slot structure 502 which is comprised of downlink (DL) slots, uplink (UL) slots and flexible or soft slots (S). The same slot structure is shown three times in Fig. 5, from top to bottom, firstly for the gNB, secondly for UE1 and finally UE2. All slot structures are drawn with reference to the same absolute time axis, running from left to right in the x-axis. With reference to the teaching of the geometry of the NTN scenario described above, it is shown that when using time division duplex (TDD) communications, measures may be used to ensure the time alignment of slots at both ends of the communication link. For example, when the gNB transmits a slot in downlink, the UE preferably ensures that its frame is appropriately aligned to receive the transmitted slot.

Similarly, when the UE transmits a slot in uplink, it must also ensure appropriate frame alignment and use of the correct slot. The soft slots contained within the slot structure can therefore either be used for the purpose of UL or the purpose of DL communication and are used on a UE-by-UE basis and according to the distance of a UE from the gNB. The assignment of the soft slots and the associated signalling is discussed elsewhere. The soft slots can also be unused, i.e., neither used for uplink nor for downlink. As the duration of each slot in the slot structure is fixed, the number of slots assigned to soft slots (between blocks of DL and UL slots) determines the longest delay that can be accommodated within the overall slot structure. This can either be fixed during the time the gNB is serving the UEs in its cell or can be reduced over time. The latter is possible due to the changing elevation angle experienced by each UE.

Solution to problem of multiple UEs in a serving cell experiencing different RTT and allocation of S-slots to the different groups of users experiencing varying RTTs:

• number of S-slots is fixed and their use per UE group is changing

Given a fixed frame structure I slot structure of the TDD configuration, e.g. DDDDDDSSSSSUUU, the S-slots (S) are to be used to compensate for the access delay due to the large distance using the mechanism of timing advance (TA). Therefore, only a subset of the S-slots is available for a particular UE at a particular time to be used in DL or UL direction. Assuming that the gNB is aware about the S-slots available/accessible for a particular UE at a particular point/period of time the gNB can schedule additional DL or UL traffic for this UE into such S-slots, therefore effectively increasing the utilization of the available radio resources.

Given the fact that during the movement of the satellite along its flightpath over the UE, the distance between gNB and UE will change and therefore the S-slots available/accessible for that UE. Assuming, that the gNB by suitable means is aware of the available/accessible S- slots for a particular UE, the gNB can schedule user plane traffic for such UE and signal the allocated S-slot numbers to the UE. The same principle can be applied to a multitude of UEs, which can be grouped into a scheduled set of UEs served by the gNB in particular S-slots in DI or UL direction. The associated signalling can be done individually per UE or for a group of UEs using e.g. a group identifier.

• a sequence of S-slots usage (DL or UL) is known and is specific per flight path of a satellite

As an alternative to the above described solution the knowledge about the flight path of the satellite can be further included into the solution allowing to further reduce the signalling overhead to the UEs or group of UEs.

The rational is the following: If the flight path and the location of the UE are known a priori, then the RTT and resulting available/accessible S-slots can be precomputed at the gNB and/or the UEs side. A resulting sequence of available /accessible S-slots can be determined and applied for further utilization of the S-slots in DL or UL direction. The sequence of S-slots can be determined at both end independently and used or in line with the usual resource allocation procedure provided by the gNB to the UE by configuration. Or by the UE to the gNB e.g. by a measurement report.

It is noted that such sequence may be location dependent therefore different UEs in cell may experience a different sequence of available/accessible S-slots. Nevertheless, particular UEs can be grouped sharing the same sequence of S-slots.

• a sequence of frame structures can be put into a set

T o further reduce signalling overhead particular sequences of available/accessible S-slots can be put into sets, wherein such sets can be signalled/configured using a set identifier for configuration overhead reduction. different slot structure per UE group using sub-band full duplex, SBFD, at gNB

Assuming the capability of transmitting and receiving simultaneously at the gNB side, certain S-slots can be used for transmission to and reception from UEs simultaneously. This requires a certain level of advanced (full) duplex capability at the gNB side, which is feasible given sufficient LIL/DL isolation of the antennas at the gNB, e.g. by using polarization discrimination. An easy to implement variant of such advance duplexing scheme would be the use of subband full duplex, wherein a frequency part of the S-slot is used in DL direction while another frequency part of the spectrum is used in UL direction. Due to the fact that a particular satellite is serving a particular footprint on the surface of the earth and an adjacent satellite is well isolated by beamforming, it may be expected very low intersatellite interference over the crosslink interference channel, therefore reducing the interference problem to self-interference at the gNB which is solvable with known techniques for self-interference cancellation (SIC).

The inventors therefore propose to allow for the simultaneous assignment of particular s-slots to be used in DL and UL direction simultaneously wherein some UE or group of UEs are served in DL direction while other UEs or group of UEs use resources of the same S-slot for UL transmission. When organized appropriately by the scheduler the UEs can operate in simple TDD fashion without any advanced duplex capability.

To support such advanced duplexing scheme the S-slots have to be configured by the gNB using further usage describing identification e.g. S-slot operated in SBFD mode or symbols operated in SBFD mode.

The partitioning of the S-slot for simultaneous UL and DL usage within one S-slot can be done in an overlapping or not-overlapping fashion over the frequency domain (subbands), the time domain (OFDM symbols) or combinations thereof.

Solution to problem of informing/configuring multiple UEs in a serving cell experiencing different RTT:

• how to inform the UEs about the configurations (explicit indication OR implicit indication based on e.g. location, timing, ... but gNB provides thresholds for parameters — > such information should be shared across neighbouring satellites (or satellites serving the same or neighbouring earth footprints/cell footprint) The management of the frame structure may depend on the topology of the network, which may be classified as the following depending on the NR cell/satellite beam size and the mapping between the NR cell, NR beam (SSB), and the satellite beam. In the following options, it is assumed that a fixed earth cell is provided by the satellite.

At least four options may be defined taking the above assumptions into account:

1 . A small NR cell, with one-to-one mapping between the NR cell, satellite beam, and NR beam (SSB).

2. A large NR cell, with one-to-one mapping between the NR cell, satellite beam, and NR beam (SSB).

3. A large NR cell, with one-to-one mapping between the NR cell and the satellite beam, but multiple NR beams (SSBs) within the NR cell.

4. A large NR cell, with one-to-many mapping between the NR cell and the satellite beams. In this case, a one-to-one mapping could be assumed between the satellite beam and the NR beam (SSB).

The management of the frame structure depends on which option to be considered:

For option 1 , the differential delay within the cell is small and can be compensated with one frame structure reflecting the largest distance within the cell. In this option, all UEs within the cell would be allocated the same frame structure. In the idle mode (RRCJDLE), the gNB broadcasts a list of frame structure configurations using system information messages such as SIB1 , SIB19 for NR-NTN, and SIB31 for loT-NTN. The gNB keeps updating the list of frame structure using the periodic SIB1 , SIB19, or SIB31.

In the active mode (RRC_ACTIVE), the gNB could update the list of frame structures using SIB messages since they are common for all UEs within a beam/cell/group. Additionally, gNB could update the list of frame structures using dedicated RRC-messages if necessary. As the satellite moves, the elevation angle of satellite beam covering the NR cell changes, which leads to a change in the largest distance in the cell. In this case, gNB could update the list of frame structure if necessary and indicates the UEs either explicitly or implicitly to update their frame structure within the cell using either DCI in the PDCCH or MAC-CE in the PDSCH. Explicit indication might be in the form of an explicit indication by the gNB to which frame structure the UEs could use. An implicit indication might be in the form of an implicit indication of which frame structure the UEs should use by instructing the UEs within a certain time/location/group to change their frame structure after a certain time due to the mobility of the satellite. Time-based trigger is preferred due the fixed earth cell. However, location-based trigger should not be excluded.

In case of option 2, the same as option 1 could be used, which might have negative impact on UEs within the cell due to the large differential delay within the cell.

In case of option 3, the gNB might group the UEs based on their serving NR beam (SSB) within the satellite beam/NR cell. In this scenario, the same mechanism could be used as in option 1 and 2, where grouping of users is based on the selected SSB beam by the UE. The gNB would be able to transmit the list of frame structures and to instruct the UEs within that NR beam to use a certain frame structure. The list of frame structure could be broadcasted in SIB messages in RRCJDLE and RRC_ACTIVE modes on an SSB-basis and transmitted in a dedicated manner to certain UEs using RRC messages in RRC_ACTIVE mode. Additionally, DCI in PDCCH and MAC CE in PDSCH might be used to activate a certain frame structure. Updating the list of frame structures or changing the active frame structure for certain UEs within a group/SSB beam is done as in option 1 and 2. In this scenario, and due to the fact that many UEs within the same cell might use different frame structures, the gNB should be able to mitigate the interference. Spatial multiplexing could be used.

In case of option 4, the grouping of users is based on their serving satellite beam, so all UEs served by the same satellite beam are going to use the same frame structure. The gNB broadcasts the list of frame structures using system information messages for all UEs in RRCJDLE and RRC_ACTIVE on a satellite-beam basis. Periodic transmission of SIB messages is used to periodically update the list of frame structures if necessary (as for other options). Additionally, the gNB is able to update the list using RRC_messages in a dedicated manner for UEs in RRC_ACTIVE. Activating/deactivating a certain frame structure is done as previously mentioned.

Grouping the UEs based on their serving NR beam (SSB) or serving satellite beam facilitates the classifications of UEs, as the gNB does not necessarily need an exact information of the position/distance of the UE from the gNB/satellite. All UEs served by the same NR beam or satellite beam may also be allocated the same frame structure.

Another possible approach in case of a large cell (which may substitute options 3 and 4) is to rely on the reported TA by the UE to estimate their distance and RTT from the satellite/gNB. The gNB may classify the UEs into contours (groups) based on their distances. In all options, and in case of a transparent payload, a feeder-link switch-over might occur, which triggers an update of the frame structure. The gNB should update the frame structure in case of a feeder-link switch if necessary, even if the service link delay didn’t change significantly to trigger a frame structure update.

In case of satellite relaying, where a transparent payload could provide coverage through another/other satellites over the ISL, an ISL changeover between the serving satellite and the relying satellite/satellites triggers a change in the distances of the UEs back to the gNB. In such a case, the gNB should trigger a frame structure update.

The defined frame structures should be exchanged between neighbouring satellites/gNBs over the ISL/Xn and NG for NR-NTN/X2 and S1 for loT-NTN. This may be used for satellites/gNBs, which are going to cover the same geographical area on the ground/ the same beam/the same cell. This may be used in case of a satellite/gNB switch/handover, where the UE needs to establish an RRC connection with the target gNB before receiving RRC reconfiguration message updating the list of frame structures or instructing the UE to use a specific frame structure. Alternatively or in addition, the source gNB/satellite may be able to forward this information from the target satellite/gNB to the UE before completing a handover/switchover.

• Similar principle for flexible symbols to be allocated for UL or DL within one S-slot — see below

The gNB may be configured to flexibly allocate OFDM symbols within the special slots for DL/UL in order to increase the resource allocation efficiency, and this requires a good alignment between the gNB and UE on the actual value of TA applied by the UE. Increasing the periodicity of TA reporting and the granularity of reporting below 1 ms may be required.

Solution to problem of multiple UEs in a serving cell experiencing different RTT and accessing the resources of S-slots in DL or UL which the TA restricts the usage to “incomplete” slots due to RTT:

When boundary of a slot is violated then codeword could be distributed across several slots.

In current 3GPP systems user data and control channel data is mapped within the frame structure usually bounded or constraint to a slot or a subset of it, e.g. several OFDM symbols. Given the example of user date, such information is usually segmented into a sequence of bits which will be encoded, rate matched and modulated before being mapped onto a set of allocated RBs which are then signalled e.g. via a coreset to the UE. Such RBs are distributed, for ease of operation usually within one slot or under certain configurations across consecutive slots.

In a given scenario of LEO satellites as serving gNB, the RTT will cause, depending on distance between the satellite and the UE, that the UE will start UL transmissions using a suitable TA to have all UL signals arrive in time at the gNB within the given slot structure. As a direct consequence certain S-slots which contain user plane data can’t be used for reception of transmission of particular UEs due to the TA which requires exemption of certain OFDM symbols of such S-slots. Considering the usual constraint of terminating code words or user data within a slot, all affected slots have to be vacated for DL or UL traffic to such UEs, causing a significant waste of DL or UL resources to be used.

The inventors identified a solution to use parts or slots in an efficient manner, by mapping the user plane traffic in a novel manner. Here, are given some of the implantation options proposed:

• The user plane data may be mapped only accessible RBs of an S-slot (accessible means the UE is able to transmit or receive particular OFDM symbols in TDD mode

• The code word may be mapped on to a subset of OFDM symbols of one s-Slot

• The code word may be mapped on to a subset of OFDM symbols of one s-Slot and a subset of OFDM symbols of a consecutive s-lot, thus “violating” the usual boundary of an S-slot for mapping of the code word

• As an implementation option the loss of a complete set of resources within an S-slot could be compensated by an adaptation of the coding level matched to the loss of usable OFDM symbols within a slot.

Various elements and features of the present invention may be implemented in hardware using analogue and/or digital circuits, in software, through the execution of instructions by one or more general purpose or special-purpose processors, or as a combination of hardware and software. For example, embodiments of the present invention may be implemented in the environment of a computer system or another processing system. Fig. 6 illustrates an example of a computer system 600. The units or modules as well as the steps of the methods performed by these units may execute on one or more computer systems 600. The computer system 600 includes one or more processors 602, like a special purpose or a general-purpose digital signal processor. The processor 602 is connected to a communication infrastructure 604, like a bus or a network. The computer system 600 includes a main memory 606, e.g., a random-access memory (RAM), and a secondary memory 608, e.g., a hard disk drive and/or a removable storage drive. The secondary memory 608 may allow computer programs or other instructions to be loaded into the computer system 600. The computer system 600 may further include a communications interface 610 to allow software and data to be transferred between computer system 600 and external devices. The communication may be in the form of electronic, electromagnetic, optical, or other signals capable of being handled by a communications interface. The communication may use a wire or a cable, fibre optics, a phone line, a cellular phone link, an RF link and other communications channels 612.

The terms “computer program medium” and “computer readable medium” are used to generally refer to tangible storage media such as removable storage units or a hard disk installed in a hard disk drive. These computer program products are means for providing software to the computer system 600. The computer programs, also referred to as computer control logic, are stored in main memory 606 and/or secondary memory 608. Computer programs may also be received via the communications interface 610. The computer program, when executed, enables the computer system 600 to implement the present invention. In particular, the computer program, when executed, enables processor 602 to implement the processes of the present invention, such as any of the methods described herein. Accordingly, such a computer program may represent a controller of the computer system 600. Where the disclosure is implemented using software, the software may be stored in a computer program product and loaded into computer system 600 using a removable storage drive, an interface, like communications interface 610.

The implementation in hardware or in software may be performed using a digital storage medium, for example cloud storage, a floppy disk, a DVD, a Blue-Ray, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable.

Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

Generally, embodiments of the present invention may be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine-readable carrier. Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine-readable carrier. In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be configured to be transferred via a data communication connection, for example via the Internet. A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein. A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus.

The above described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein are apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the impending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein.

Claims

1. A user equipment, UE, comprising a wireless interface for receiving wireless signals and for transmitting wireless signals; wherein the UE is configured for operating in a cell of a wireless communication network according to a time division duplex, TDD, scheme that comprises a plurality of TDD frames, each TDD frame comprising a plurality of slots arranged according to a frame structure, the plurality of slots comprising a first number of downlink, DL, slots, a second number of uplink, UL, slots and a third number of special, S, slots e.g., arranged between the first number of UL slots and the second number of UL slots; wherein the UE is configured for operating with a varying effective frame structure within the TDD scheme to compensate for varying distances between the UE and a base station operating the cell.

2. The UE of claim 1 , adapted to operate with a dynamically varying effective frame structure based on a dynamically varying distance.

3. The UE of claim 1 or 2, adapted to operate with the varying effective frame structure as varying based on a channel parameter such as a round-trip-time, RTT or a window of coverage opportunity for the UE.

4. The UE of one of previous claims, wherein the effective frame structure is UE specific.

5. The UE of one of previous claims, wherein the base station operating the cell is a nonterrestrial base station.

6. The UE of one of previous claims, configured for a non-use of at least a part of at least one of the S-slots of the plurality of slots of the TDD frame.

7. The UE of claim 6, adapted to implement the non-use for the effective frame structure to avoid a temporal overlap of a slot scheduled for DL, e.g., a slot of the first number of slots or a slot of the third number of slots, and associated with a first frame, and a slot scheduled for UL, e.g., a slot of the second number of slots or a slot of the third number of slots, and associated with the first or a second frame.

8. The UE of claim 6 or 7, adapted to skip or ignore one of a) at least a part of a first slot scheduled for DL and associated with a first frame and b) at least a part of a second slot scheduled for UL and associated with the first frame or a second frame in case of a temporal overlap between the first slot and the second slot; or vice versa.

9. The device of one of claims 6 to 8, adapted for providing a feedback indicating whether the device has performed resolving of a conflict caused by overlapping resources and/or which resolving.

10. The UE of one of previous claims, wherein the varying effective frame structure relates to a variation in at least one of a frame structure, a slot structure within the frame and/or a symbol structure within the frame.

11. The UE of one of previous claims, wherein the UE is configured with the slot structure or symbol configuration by a network entity or using a stored, e.g., initial, pre-configuration.

12. The user equipment, UE, according to one of previous claims, configured for operating in a flexible TDD scheme with DL slots, UL slots and flexible S slots according to the effective frame structure as a flexible frame structure and/or a flexible symbol configuration of at least one S slot configured by the base station.

13. The UE of one of previous claims, configured for, e.g., directly after initial access or a different time and once or multiple time, e.g., periodically, signalling slots or symbols unusable for UL and/or DL, e.g., unusable due to a timing advance, TA, drift, for DL or UL explicitly or implicitly by e.g. indicating an absolute round trip time, a drift, a first drift derivative or a second derivative etc.

14. The UE of one of previous claims, wherein the effective frame structure is based on a scheduled frame structure from which at least one slot of the third number of slots that is scheduled for uplink or downlink remains unused by the UE.

15. The UE of one of previous claims, configured for predicting and reporting a drift affecting the UE

16. The UE of one of previous claims, configured for monitoring additional DL slots or symbols and/or for preparing a transmission in additional UL slots or symbols according to an allocation of special, S slots provided by the base station.

17. The UE of one of previous claims, adapted to align to a first frame structure or TDD scheme implemented by the base station as a first base station and to align to a second frame structure or TDD scheme implemented by a second base station for preparing a handover from the first base station to the second base station.

18. The UE of claim 17, configured for aligning the second frame structure or TDD scheme based on at least one of:

-> an SIB1 , SIB19 or SIB31 message; enhancement a sync offset indicated by the first base station; and an initial slot structure of the second base station.

19. The UE of one of previous claims, configured for aligning to the first or second frame structure or TDD scheme based on at least one message received in a connected mode and/or in an idle mode of the UE.

20. The UE of one of previous claims, configured for temporally aligning the TDD frame with the base station for reception within the frame.

21. The UE of one of previous claims, configured for temporally aligning the TDD frame with the base station for a transmission of the UE within the frame.

22. The UE of one of previous claims, configured for using the S-slots of the plurality of slots of the TDD frame for an UL transmission or a DL communication based on a distance of the UE from the base station.

23. The UE of one of previous claims, wherein the UE is configured to evaluate a signal received and containing an allocation of the S-slots according to a group identifier indicated in the signal and to determine, based on the group identifier, whether the UE is a part of the indicated group and to implement the allocation when being a member of the group.

24. The UE of one of previous claims, wherein a sequence of S-slot usage of the third number of S-slots in the TDD frame for DL or UL is predetermined and/or specific per flight path, wherein the UE determines the S-slot usage from a signalling of the base station or from information indicating the flight path.

25. The UE of claim 24, wherein the UE is configured for providing a measurement report to indicate, to the base station, a location of the UE with regard to the flight path.

26. The UE of one of previous claims, adapted to report a periodicity of timing advance and/or a granularity of reporting with an interval of at least or at most 1 ms.

27. A base station comprising a wireless interface for receiving wireless signals and for transmitting wireless signals; wherein the base station is configured for operating a cell of a wireless communication network according to a time division duplex, TDD, scheme that comprises a plurality of TDD frames, each TDD frame comprising a plurality of slots arranged according to a frame structure, the plurality of slots comprising a first number of downlink, DL, slots, a second number of uplink, UL, slots and a third number of special, S, slots e.g., arranged between the first number of UL slots and the second number of DL slots; wherein the base station is configured for allocating to different terminals in the cell and within the TDD scheme a varying effective frame structure, e.g., a different number or position of the DL or UL slots in the frame structure and/or a different symbol configuration of at least one S slot, e.g., an OFDM symbol configuration and/or a different length of at least one slot in the time domain, to compensate for varying distances between a terminal and the base station.

28. The base station 27, adapted to simultaneously schedule same or different effective frame structures from a same TDD scheme to different terminals.

29. The base station of claim 28, wherein the different effective frame structures within the TDD scheme relate to at least one of a number of S slots between a last downlink slot and a first uplink slot, a number of S slots within the TDD frame, a position of the UL slots within the TDD frame and a symbol configuration within at least one S slot being scheduled differently to different terminals or used differently by different terminals.

30. The base station of claim 29, wherein the symbol configuration relates to at least one of a location of symbols in a time frequency grid, a number of symbols in the slot and a use of the symbol as uplink symbol, downlink symbol or guard symbol.

31. The base station of one of claims 27 to 30, wherein the base station is configured for allocating at least one of the S slots for a different use for different terminals within the cell.

32. The base station of one of claims 27 to 31 , being at least a part of a flying device such as a satellite, a drone or a balloon.

33. The base station of claim32, configured for selecting a frame structure of the TDD scheme, e.g., from a plurality of different frame structures or different TDD schemes, based on an altitude, e.g., of an orbit or flight path, of the flying device.

34. The base station of one of claims 27 to 33, configured for grouping terminals in the cell and for groupwise allocating the at least one of the S slots differently for different groups of terminals.

35. The base station of claim 34, configured for grouping the terminals based on a delay or time-of-f light of signals between the base station and the terminals.

36. The base station of one of claims 27 to 35, wherein the base station is configured for selecting the frame structure or TDD scheme from a plurality of frame structures or TDD schemes, the frame structures or different TDD schemes differing in at least one of a time duration of one, more or all slots of the TDD frame, a number of slots of the frame, a number of UL slots in the frame, a number of DL slots in the frame and a number of S slots in the frame.

37. The base station of claim 36, configured for selecting the frame structure or TDD scheme based on one or more contours of or within the cell.

38. The base station of claim 36 or 37, configured for selecting the frame structure or TDD scheme based on the position/location of a UE or a group of UEs and the location of the gNB, e.g., along a flight path of a flying device comprising the base station while providing coverage /service to the cell.

39. The base station of one of claims 27 to 38, wherein at the base station, the S slots are arranged between the DL slots and the UL slots; wherein the base station is configured for allocating the S slots for DL or UL operation for the different terminals.

40. The base station of one of claims 27 to 39, wherein at the base station, the S slots are arranged between the DL slots and the UL slots; wherein the base station is configured for allocating, to one or more terminals with a larger distance from the base station a larger number of S slots to compensate a larger TA requirement for UL transmissions.

41. The base station according to claim 40, adapted to increase a frame length for the terminals with the larger distance, e.g., increasing the first number of DL slots and/or the second number of UL slots.

42. The base station according to claim 41 , adapted to increase the frame length for all terminals in the cell based or in accordance with a largest round trip time or largest distance of a terminal in the cell served by the base station

43. The base station of one of claims 39 to 42, configured for allocating remaining S slots for additional DL traffic and/or additional UL traffic.

44. The base station of claim 43, configured for allocating the remaining S slots differently for different terminals.

45. The base station of one of claims 27 to 44, wherein the base station is adapted for operating the cell with a frame duration of at least 15 ms.

46. The base station of one of claims 27 to 45, configured for a synchronized arrival of signals received from the different terminals, e.g., by use of a timing advance, TA.

47. The base station of one of claims 27 to 46, configured for allocating the slots according to a configuration according to which, at the base station and/or the terminal, within a single frame only one transition between DL and UL is implemented.

48. The base station of one of claims 27 to 47, configured for allocating the slots according to a configuration according to which, at the base station and/or the terminal within a single frame more than one transition between DL and UL is implemented.

49. The base station of one of claims 27 to 48, configured for mapping resources of a wireless communication along at least two adjacent slots.

50. The base station of one of claims 27 to 49, configured for mapping resources of a wireless communication along at least two adjacent slots, wherein the resources of a first slot are used partially at an end of the first slot and are continued with resources at the consecutive second slot wherein at least the beginning of the at least second slot is used.

51. The base station of one of claims 27 to 50, configured for allocating additional flexible slots and/or symbols for at least one of DL, UL and a guard period and to signal such allocation, the allocation being valid for individual terminals or terminal groups.

52. The base station of claim 51 , configured for allocating only S slots for additional DL transmissions that are received partially or entirely by the targeted terminal based on a round-trip time, RTT, associated with the terminal.

53. The base station of claim 51 or 52, configured for allocating only S slots for additional UL receptions that are transmitted partially or entirely by the targeted terminal based on a round-trip time, RTT, associated with the terminal.

54. The base station of one of claims 27 to 53, configured for receiving information about an absolute and/or relative slot and/or symbol level shift of the terminals and for allocating the at least one S slot to compensate for differences in the shifts.

55. The base station of one of claims 27 to 54, configured for allocating, to at least one terminal at least one of a DL slots and UL slots prior to or after regular UL slots according to the frame structure or TDD scheme.

56. The base station of one of claims 27 to 55, configured for predicting a drift affecting the UE

57. The base station of one of claims 27 to 56, configured for coordinating the frame structure or the TDD scheme with another base station, e.g., a base station subsequently serving the cell or the terminal.

58. The base station of one of claims 27 to 57, configured for receiving, from at least one terminal assistance information and to allocate the slots based on the assistance information indicating at least one of: o a global navigation satellite system, GNSS, and o a timing advance, TA, used by the terminal, e.g., between last DL symbol or slot received and the first UL symbol or UL slot to be sent or a derivate of the TA.

59. The base station of one of claims 27 to 58, configured for allocating the slots based on a concatenation of at least two different frame structures.

60. The base station of claim 59, wherein the concatenation of at least two different frame structures forms a frame set, the frame set being one of a plurality of different frame sets being formed by different concatenations of frame structures; wherein each frame set is associated with a frame set identifier, wherein the base station is configured for indicating a selected frame set form the plurality use of a specific frame set by signalling the associated frame set identifier.

61. The base station of one of claims 27 to 60, configured for operating the cell in FR1 , FR2 and/or FR3

62. The base station of one of claims 27 to 61 , configured for selecting the frame structure for the TDD scheme to support time delays caused by distances between the terminal and the base station being exemplarily at least 600 km and/or at most 2,000 km or a different flight height or orbit.

63. The base station of one of claims 27 to 62, adapted for allocating a use of the S-slots of the plurality of slots of the TDD frame for an UL transmission or a DL communication individually for different terminals or groups of terminals according to a distance of the terminal from the base station, e.g., based on a terminal-by-terminal; or group-by-group- basis.

64. The base station of one of claims 27 to 63, configured for allocating different frame structures for different terminals based on a distances of the terminals from the base station.

65. The base station of one of claims 27 to 64, configured for allocating at least one of the S-slots of the plurality of slots of the TDD frame as being unused for uplink and unused for downlink at the terminal for at least one terminal.

66. The base station of one of claims 27 to 65, configured for maintaining a number of the third number of S-slots in the TDD frame constant over time; or for adapting the number of the third number of S-slots in the TDD frame over time.

67. The base station of claim 66, configured for adapting the number of the third number of S-slots over time based on a changed elevation angle with regard to the base station experienced by the terminals served by the base station.

68. The base station of one of claims 27 to 67, configured for scheduling additional DL traffic and/or additional UL traffic to a terminal in the cell based on information indicating a number of S-slots available/accessible for the terminal at a particular point/period of time.

69. The base station of one of claims 27 to 68, wherein the base station is at least a part of a flying device and configured for scheduling data traffic such as user plane traffic for a terminal in cell and for signalling an allocation of S-slot, e.g., the number thereof, to the terminal.

70. The base station of one of claims 27 to 69, wherein the base station is configured for adapting the scheduling along a flight path of the flying device with respect to the terminal.

71. The base station according to claim 69 or 70, wherein the base station is configured to schedule the S-slots for the terminal as a member of a group of terminals and commonly for the group of terminals, e.g., formed based on a proximity or distance between the terminals; wherein the base station is configured for signalling the allocation to the group of terminals, e.g., using a group identifier; or for signalling the allocation individually to the terminal.

72. The base station of one of claims 27 to 71 , wherein a sequence of an S-slots usage for DL or UL is predetermined and/or is specific per flight path, the base station being a part of a flying device.

73. The base station of one of claims 27 to 72, configured for selecting the frame structure for the TDD scheme to support a worst-case time delay associated with a longest distance between any of the terminals in the cell and the base station.

74. The base station of one of claims 27 to 73, being configured for simultaneous transmission and reception and for allocating a same S-slot or at least one symbol for an UL transmission of a first terminal or a first group of terminals in the cell and for a DL reception of a second terminal or a second group of terminals in the cell.

75. The base station of claim 74, being configured for configuring S-slots or symbols used for simultaneous reception and transmission at the base station to be operated in a Sub Band Full Duplex, SBFD, mode.

76. The base station of claim 74 or 75, wherein the base station is configured for implementing a partitioning of S-slots for simultaneous UL usage and DL usage within one S-slot according to an overlap or not-overlap fashion over a frequency domain, e.g., with respect to sub-bands, with respect to the time domain, e.g., using OFDM symbols, or a combination thereof.

77. The base station of one of claims 27 to 76, configured for selecting at least one resource block of an S-slot for mapping user plane data for a terminal served by the base station based on information indicating that the selected resource block is accessible for the terminal, e.g., based on the base station being at least a part of a flying device.

78. The base station of one of claims 27 to 77, configured for mapping a code word or user data to be transmitted onto a subset of OFDM symbols of one S slot, the subset selected based on information that the selected subset is accessible for the terminal, e.g., based on the base station being at least a part of a flying device.

79. The base station of one of claims 27 to 78, configured for mapping a code word or user data to be transmitted onto a combination of a first subset of OFDM symbols of a first S slot and a second subset of OFDM symbols of a second, possibly consecutive, second S slot based on information that the selected subset is accessible for the terminal, e.g., based on the base station being at least a part of a flying device.

80. The base station of one of claims 27 to 79, configured for adapting a coding level to encode a code word or user data to be transmitted according to a number of usable OFDM symbols within a slot such as an S slot to use usable OFDM symbols within the slot, e.g., based on the base station being at least a part of a flying device.

81. The base station of one of claims 27 to 80, configured for signalling a list of frame structure configurations, e.g., as a dedicated signal or a broadcast signal to one or more terminals during a configuration phase and for instructing at least one terminal within at least one of a cell a beam provided by the base station or a group to activate a certain frame structure based on the distance of the at least one termina from the base station, e.g., implicitly or explicitly.

82. The base station of one of claims 27 to 81 , configured for managing the frame structure based on a topology of the network, e.g., based on a NR cell or flying device beam size, a mapping between the NR cell, NR beam (SSB), and the flying device beam.

83. The base station of one of claims 27 to 82, being a part of a flying device and configured for allocating a same TDD frame structure for all terminal within the cell based on a scenario where a small or a large NR cell is provided by the base station and a one-to- one mapping between the NR cell, a flying device beam, and a NR beam, e.g., SSB is operated by the base station; wherein the base station is configured to broadcast a list of frame structure configurations using system information messages such as SIB1 , SIB19 for NR-NTN, and SIB31 , e.g., for loT-NTN, e.g., of terminals being in an idle mode, RRCJDLE.

84. The base station of claim 83, configured for updating the list of frame structure using the periodic signalling, e.g., SIB1 , SIB19, or SIB31.

85. The base station of claim 83 or 84, configured for updating the list of frame structures for terminals being in an active mode, RRC_ACTIVE, e.g., using SIB messages and/or using dedicated RRC-messages.

86. The base station of one of claims 83 to 85, configured for updating the list of frame structure and to indicate the terminals explicitly and/or implicitly to update their frame structure within the cell, e.g., using either DCI in the PDCCH or MAC-CE in the PDSCH, e.g., based on a changed distance between the terminal and the base station.

87. The base station of claim 86, wherein an explicit indication relates to an explicit indication by the base station to which frame structure the terminal may use; and/or wherein an implicit indication relates to an implicit indication of which frame structure the terminals may use by instructing the terminals within a certain time/location/group to change their frame structure after a certain time, e.g., due to a mobility of the base station.

88. The base station of claim 83 or 87, wherein the implicit indication comprises a time-based trigger or a location-based trigger.

89. The base station of one of claims 27 to 88, being a part of a flying device and configured, in a scenario where a large NR cell, with one-to-one mapping between the NR cell and the flying device beam and multiple NR beams, e.g., SSBs, within the NR cell, for grouping group terminals in the cell based on their serving NR beam, SSB within the flying device beam/NR cell.

90. The base station of claim 89, configured for mitigating interference caused by the terminals by using spatial multiplexing.

91. The base station of one of previous claims, being a part of a flying device and configured, in a scenario where a large NR cell with one-to-many mapping between the NR cell and the flying device beams is implemented, for operating according to a one-to-one mapping between the flying device beam and the NR beam (SSB); and the base station is adapted for grouping the terminals based on their serving flying device beam, and to configure all terminals served by the same satellite beam to use a same frame structure.

92. The base station of claim 91 , configured for broadcasting a list of frame structures using system information messages for all terminals in RRCJDLE and RRC_ACTIVE on a satellite-beam basis; and/or to use periodic transmission of SIB messages to periodically update the list of frame structures; and/or to update the list using RRC_messages in a dedicated manner for terminals in RRC_ACTIVE.

93. The base station of one of claims 83 to 92, configured for updating the frame structure a feeder-link switch-over.

94. The base station of one of claims 83 to 93, configured for updating the frame structure in case of a feeder-link switch in connection with an unchanged, within a threshold, service link delay.

95. The base station of one of claims 83 to 94, adapted for a relaying of signals via an inter satellite link, ISL, wherein the base station is configured for updating the frame structure based on an ISL changeover between a serving satellite and at least one relaying satellite based on a triggered change in distances of the terminals back to the base station.

96. The base station of one of claims 27 to 95, configured for grouping the terminals in the cells based on a serving NR beam, e.g., SSB or serving satellite beam; and/or to allocate all terminals served by the same NR beam or satellite beam with a same frame structure.

97. The base station of one of claims 27 to 96, being a part of a flying device and configured, in a scenario where a large NR cell is operated by the base station the base station is configured for using information related to a timing advance reported by the terminals to estimate a distance of the terminals and/or a round trip time, RTT, from the base station to classify the terminals into contours or groups based on their distances.

98. The base station of one of claims 27 to 97, configured for informing a different base station about the allocated TDD structure or frame structure, e.g., using an ISL/Xn interface, an NG for NR-NTN/X2, and S1 for loT-NTN; and/or to receive such information from a base station operating the cell prior to the base station and to operate accordingly.

99. The base station of one of claims 27 to 98, configured for flexibly allocating OFDM symbols within at least one S slots for DL, UL or guard symbol.

100. A method for operating a UE, the method comprising operating the UE in a cell of a wireless communication network according to a time division duplex, TDD, scheme that comprises a plurality of TDD frames, each TDD frame comprising a plurality of slots arranged according to a frame structure, the plurality of slots comprising a first number of downlink, DL, slots, a second number of uplink, UL, slots and a third number of special, S, slots e.g., arranged between the first number of UL slots and the second number of UL slots; operating the UE with a varying effective frame structure within the TDD scheme to compensate for varying distances between the UE and a base station operating the cell.

101 . A method for operating a base station, the method comprising: operating a cell of a wireless communication network according to a time division duplex, TDD, scheme that comprises a plurality of TDD frames, each TDD frame comprising a plurality of slots arranged according to a frame structure, the plurality of slots comprising a first number of downlink, DL, slots, a second number of uplink, UL, slots and a third number of special, S, slots e.g., arranged between the first number of UL slots and the second number of DL slots; allocating to different terminals in the cell and within the TDD scheme a varying effective frame structure, e.g., a different number or position of the DL or UL slots in the frame structure and/or a different symbol configuration of at least one S slot, e.g., an OFDM symbol configuration and/or a different length of at least one slot in the time domain, to compensate for different distances between the different terminals and the base station.

102. A computer readable digital storage medium having stored thereon a computer program having a program code for performing, when running on a computer, a method according to claim 100 or 101.