Patent Description:
<FIG> is a schematic representation of an example of a terrestrial wireless network <NUM> including, as is shown in <FIG> a core network <NUM> and one or more radio access networks RAN<NUM>, RAN<NUM>,. <FIG> is a schematic representation of an example of a radio access network RANn that may include one or more base stations gNB<NUM> to gNB<NUM>, each serving a specific area surrounding the base station schematically represented by respective cells <NUM>, to <NUM>. The base stations are provided to serve users within a cell. The term base station, BS, refers to a gNB in <NUM> 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 IoT 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 enable these devices to collect and exchange data across an existing network infrastructure. <FIG> shows an exemplary view of only five cells, however, the RANn may include more or less such cells, and RANn may also include only one base station. <FIG> shows two users UE<NUM> and UE<NUM>, also referred to as user equipment, UE, that are in cell <NUM><NUM> and that are served by base station gNB<NUM>. Another user UE<NUM> is shown in cell <NUM><NUM> which is served by base station gNB<NUM>. The arrows <NUM><NUM>, <NUM><NUM> and <NUM><NUM> schematically represent uplink/downlink connections for transmitting data from a user UE<NUM>, UE<NUM> and UE<NUM> to the base stations gNB<NUM>, gNB<NUM> or for transmitting data from the base stations gNB<NUM>, gNB<NUM> to the users UE<NUM>, UE<NUM>, UE<NUM>. Further, <FIG> shows two loT devices <NUM><NUM> and <NUM><NUM> in cell <NUM><NUM>, which may be stationary or mobile devices. The loT device <NUM><NUM> accesses the wireless communication system via the base station gNB<NUM> to receive and transmit data as schematically represented by arrow <NUM><NUM>. The loT device <NUM><NUM> accesses the wireless communication system via the user UE<NUM> as is schematically represented by arrow <NUM><NUM>. The respective base station gNB<NUM> to gNB<NUM> may be connected to the core network <NUM>, e.g. via the S1 interface, via respective backhaul links <NUM><NUM> to <NUM><NUM>, which are schematically represented in <FIG> by the arrows pointing to "core". The core network <NUM> may be connected to one or more external networks. Further, some or all of the respective base station gNB<NUM> to gNB<NUM> may connected, e.g. via the S1 or X2 interface or XN interface in NR, with each other via respective backhaul links <NUM><NUM> to <NUM><NUM>, which are schematically represented in <FIG> by the arrows pointing to "gNBs".

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 and uplink shared channels (PDSCH, PUSCH) carrying user specific data, also referred to as downlink and uplink payload data, the physical broadcast channel (PBCH) carrying for example a master information block (MIB) and a system information block (SIB), the physical downlink and uplink control channels (PDCCH, PUCCH) carrying for example the downlink control information (DCI). For the uplink, the physical channels may further include the physical random access channel (PRACH or RACH) used by UEs for accessing the network once a UE synchronized and 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. Each subframe may include two slots of <NUM> or <NUM> OFDM symbols depending on the cyclic prefix (CP) length. A frame may also consist of a smaller number of OFDM symbols, 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 nonorthogonal waveforms for multiple access, e.g. filter-bank multicarrier (FBMC), generalized frequency division multiplexing (GFDM) or universal filtered multi carrier (UFMC), may be used. The wireless communication system may operate, e.g., in accordance with the LTE-Advanced pro standard or the <NUM> or NR, New Radio, standard.

The wireless network or communication system depicted in <FIG> may by an 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 gNB<NUM> to gNB<NUM>, and a network of small cell base stations (not shown in <FIG>), 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>, for example in accordance with the LTE-advanced pro standard or the <NUM> or NR, New Radio, standard.

In mobile communication networks, for example in a network like that described above with reference to <FIG>, like an LTE or <NUM>/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, i.e., both UEs may be within the coverage area of a base station, like one of the base stations depicted in <FIG>. This is referred to as a "in coverage" scenario. In accordance with other examples, both UEs that communicate over the sidelink may not be served by a base station which 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>, rather, it means that these UEs are not connected to a base station, for example, they are not in a RRC connected state. Yet another scenario is called a "partial coverage" scenario, in accordance with which one of the two UEs which communicate with each other over the sidelink, is served by a base station, while the other UE is not served by the base station.

<FIG> is a schematic representation of a situation in which two UEs directly communicating with each other are both in coverage of a base station. The base station gNB has a coverage area that is schematically represented by the circle <NUM> which, basically, corresponds to the cell schematically represented in <FIG>. The UEs directly communicating with each other include a first vehicle <NUM> and a second vehicle <NUM> both in the coverage area <NUM> of the base station gNB. Both vehicles <NUM>, <NUM> are 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 signaling over the Uu interface, which is the radio interface between the base station and the UEs. The gNB assigns the resources to be used for the V2V communication over the sidelink. This configuration is also referred to as a mode <NUM> configuration in NR V2X or as a mode <NUM> configuration in LTE V2X.

<FIG> is a schematic representation of a situation in which the UEs are not in coverage of a base station, i.e., the respective UEs directly communicating with each other are not connected to a base station, although they may be physically within a cell of a wireless communication network. Three vehicles <NUM>, <NUM> and <NUM> are shown directly communicating 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 <NUM> configuration in NR V2X or as a mode <NUM> configuration in LTE V2X. As mentioned above, the scenario in <FIG> which is an out-of-coverage scenario does not mean that the respective mode <NUM> UEs are outside of the coverage <NUM> of a base station, rather, it means that the respective mode <NUM> UEs are not served by a base station or are not connected to the base station of the coverage area. Thus, there may be situations in which, within the coverage area <NUM> shown in <FIG>, in addition to the mode <NUM> UEs <NUM>, <NUM> also mode <NUM> UEs <NUM>, <NUM>, <NUM> are present.

In the above-described scenarios reference has been made to vehicular user devices, UEs, and a V2V or V2X communication using the sidelink interface. Such vehicular user devices may be employed, e.g., in the field of the transport industry in which a plurality of vehicles being equipped with vehicular user devices may be controlled by a remote driving application. Other use cases in which a plurality of user devices may communicate among each other using the sidelink include, for example, factory automation and electrical power distribution. In the case of factory automation, a plurality of mobile or stationary machines within a factory may be equipped with user devices employing a sidelink communication, for example for controlling the operation of a machine, like a motion control of a robot. In the case of electrical power distribution, entities within the power distribution grid may be equipped with respective user devices which, within a certain area of the system may communicate via a sidelink communication with each other so as to allow for monitoring the system and for dealing with power distribution grid failures and outages.

<CIT> describes methods and apparatuses that can provide sidelink grant information to out-of-coverage (OoC) sidelink devices. When one or more sidelink devices are out of a coverage area of a base station, an in-coverage device receiving sidelink grant information from the base station can retransmit, relay, or rebroadcast sidelink grant information to the OoC sidelink devices to enable sidelink communication with the OoC device or facilitate sidelink communication between OoC devices.

<CIT> refers to the problem with D2D communications that there is no physical layer feedback (e.g., HARQ feedback) for unicast sidelink communications and provides a solution by enabling HARQ feedback for unicast sidelink communications that improves the spectral efficiency and also enables better radio resource utilization for the network.

<CIT> describes a user equipment to be used as receiving user equipment in a mobile communication system supporting D2D communication. The user equipment includes a feedback unit that receives a D2D signal from transmitting user equipment, and that transmits, to the transmitting user equipment, a feedback signal with respect to the D2D signal by using a predetermined resource; and a receiver that receives a retransmission D2D signal transmitted from the transmitting user equipment based on the feedback signal.

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 that is already known to a person of ordinary skill in the art.

It is an object of the present invention to provide for an improved feedback transmission via a sidelink.

This object is achieved by an apparatus according to claim <NUM> or <NUM>, a wireless communication system according to claim <NUM>, and a method according to claim <NUM>.

Embodiments of the present invention are now described in further detail with reference to the accompanying drawings, in which:.

The subject-matter of <FIG> and <FIG> and their descriptions, even if described or named as "embodiment(s)", "invention(s)", "aspect(s)", "example(s)" or "disclosure(s)" etc., does not fully and thus only partly correspond to the invention as defined in the claims, since one or more features present in and required by the independent claims are missing in the "embodiment(s)", "invention(s)", "aspect(s)", "example(s)" or "disclosure(s)" etc. The subject-matter of <FIG> and <FIG> and their descriptions is therefore not covered by the claims and is useful to highlight specific aspects of the claims.

Embodiments of the present invention is now described in more detail with reference to the accompanying drawings in which the same or similar elements have the same reference signs assigned.

The initial vehicle-to-everything (V2X) specification was included in LTE Release <NUM> of the 3GPP standard. The scheduling and assignment of resources had been modified according to the V2X requirements, while the original device-to-device (D2D) communication standard has been used as a basis of the design. Cellular V2X has been agreed to operate in two configurations from a resource allocation perspective, namely in the above-described mode <NUM> and mode <NUM> configurations. As mentioned above, in the V2X mode <NUM> configuration the scheduling and interference management of resources is performed by the base station for UEs within the coverage of the base station so as to enable sidelink, SL, communications, like vehicle-to-vehicle communications. The control signaling is provided to the UE over the Uu interface, for example using the downlink control indicator, DCI, and is dynamically assigned by the base station. In the V2X mode <NUM> configuration the scheduling and interference management for SL communications is autonomously performed using distributed or decentralized algorithms among the UEs based on a preconfigured resource configuration. As is described above, there are different scenarios or use cases in which a communication among the group members is desired, which is also referred to as a groupcast communication. Such groupcast communications require that the members of the group are able to communicate with each other over shorter distances, while maintaining a high level of reliability and low latency. Examples of the mentioned use cases are vehicle platooning, extended sensors, advanced driving and remote driving.

Current implementations of the sidelink communication among a plurality of user devices include a communication channel from the transmitting UE to the receiving UE so as to transmit control data and associated user data from the transmitting UE to the receiving UE. Such a communication may be referred to as a sidelink unicast transmission, in case the communication from the transmitting UE is directed to only one other UE. Other communications may include a sidelink broadcast transmission in accordance with which the transmitting UE transmits or sends a message or data to all user devices over the sidelink communication being in range of the transmitting UE. Yet other sidelink transmissions may include so-called sidelink group transmissions concerning a certain number of user devices which are grouped together, for example, by having assigned a common group ID, and in this situation the transmitting UE transmits data that is only designated for the UEs being members of the group. The channel among the transmitting UE and the one or more receiving UEs, however, may not be stable and may change or may be affected by certain external parameters so that data sent by the transmitting UE may not be received at the UE or may be received at the UE in a condition that does not allow the UE to successfully decode the data.

Currently, there is no mechanism provided for sidelink transmissions ensuring an efficient and reliable transmission of data within low latency constraints from a transmitting UE to a receiving UE, and the present invention aims at solving the problems of an inefficient and unreliable sidelink interface among communicating user devices by providing a feedback mechanism from the receiving UE to the transmitting UE. More specifically, in accordance with embodiments of the present invention, a sidelink control channel or feedback channel from the receiving UE to the transmitting UE is provided so as to send to the transmitting UE a feedback indicating a successful/non-successful reception of data at the receiving UE, along with reports indicating the channel state and/or quality information. Currently, the existing standards do not implement a feedback channel for the sidelink from the receiving UE to the transmitting UE.

The inventive approach is advantageous as it implements a, feedback mechanism for sidelink transmissions, like sidelink unicast transmissions, within the existing frame structure for sidelink transmission. In accordance with embodiments of the inventive approach, a transmission time interval (TTI) having a structure for transmitting data from a transmitting UE to a receiving UE in such a way that, initially, an indication is transmitted towards the receiving UE indicating as to whether a feedback is to be sent or not, and, in addition, by sending the control data and, in accordance with examples, also user data within the TTI in such a way that the transmission is completed at a certain duration before the end of the interval. The duration before the end of the TTI is selected such that the receiving UE, within this duration is in the position to process the received data, like to decode the data, and if needed, to switch from receiving to transmitting for sending the feedback to the transmitter before the actual duration of the TTI ends. Stated differently, embodiments of the present invention allow for sending the feedback directly after the transmission of the data, i.e., prior or before the next TTI is transmitted.

Thus, the present invention aims at providing an improved approach for providing a reliable communication among UEs over a sidelink. This is addressed by the present invention as described hereinbelow in more detail, and embodiments of the present invention may be implemented in a wireless communication system as depicted in <FIG>, <FIG> including base stations and users, like mobile terminals or loT devices. <FIG> is a schematic representation of a wireless communication system including a transmitter <NUM>, like a base station, and one or more receivers <NUM><NUM> to <NUM>n, like user devices, UEs. The transmitter <NUM> and the receivers <NUM> may communicate via a wireless communication links or channels 304a, 304b, 304c, like a radio link. The transmitter <NUM> may include one or more antennas ANTT or an antenna array having a plurality of antenna elements, a signal processor 300a and a transceiver 300b, coupled with each other. The receivers <NUM> include one or more antennas ANTR or an antenna array having a plurality of antennas, a signal processor 302a<NUM>, 302an, and a transceiver 302b<NUM>, 302bn coupled with each other. The base station <NUM> and the UEs <NUM> may communicate via respective first wireless communication links 304a and 304b, like a radio link using the Uu interface, while the UEs <NUM> may communicate with each other via a second wireless communication link 304c, like a radio link using the PC5 interface.

The system, the base station <NUM> and the one or more UEs <NUM> may operate in accordance with the inventive teachings described herein.

<FIG> illustrates an approach for sending data from a transmitting UE A to a receiving UE B and to provide a feedback from the receiving UE B to the transmitting UE A, wherein the data sent by the transmitting UE A, also referred to as user A, may comprise user data as well as control data for the receiving UE B, also referred to as user B. <FIG> illustrates a design for a self-contained sidelink frame <NUM>. The frame <NUM> has a duration from a start time tS to an end time tE. The frame <NUM> may be a transmission time interval as defined by the wireless communication system in which the users A and B communicate with each other over the sidelink communication interface, or it may be any interval for which the apparatus, like the transmitting receiver or user A has reserved resources for a transmission to the user B. The frame <NUM> may be, for example, a sub-frame, a transmission time interval, a certain slot within the sub-frame or a mini-slot. In any case, it is assumed that the transmission time associated with user A starts at time tS and ends at time tE. Rather than using the entire frame <NUM> for the transmission of data from the user A to the user B, to provide the feedback for the user A without the need for using a subsequent frame for a transmission from user B to user A, the transmission of data from the user A to the user B is only over a part of the frame duration T, for example until a time tT so that the actual transmission time T is from time tS to time tT and the duration from the time tT to the end of the frame tE may be used for a transmission from the user B to the user A and may be referred to as a remaining duration or remaining frame time R. In <FIG>, it is assumed that the user A transmits data to the user B during the transmission time T which includes control data C and user data D. During the first part of the frame, during the time T, the user A transmits the control data or control signaling C followed by a secondary signal D containing the payload data and/or additional signaling, like requesting channel state information and/or reference symbols CSI-RS. This may also be referred to as piggybacking the additional signaling on the data. The transmission of data from the user A to the user B is followed by a time gap R<NUM> during the remaining duration R of the frame <NUM> to allow the user B to process the received data and/or for performing a switching between reception and transmission mode at the user B. After the time R<NUM>, during the time R<NUM>, the user B sends the feedback F which may be a HARQ feedback including acknowledgement/non-acknowledgement messages, ACK, NACK, and/or additional feedback, such as a CSI, for example the CQI, RSSI (Received Signal Strength Indicator), RSRP (Received Signal Received Power), RSRQ (Reference Signal Received Quality) and in the case of MIMO RI (Rank Indicator) or PMI (Preferred Matrix Index).

The control signaling may be a physical sidelink control channel, PSCCH, which is modified so as to include the additional information whether the UE B has to provide feedback about the information or not. After processing the received control information, like a received physical sidelink control channel PSCCH and, if also transmitted, a received physical sidelink shared channel, PSSCH, and decoding the control, user B knows whether a feedback is to be sent. If feedback is desired the user B signals a successful/non-successful reception at the user B and/or channel state information. Otherwise, in case no feedback is to be signaled, no further action is taken by the user B. For example, in case USER a indicates that there is no feedback to be signaled, then user B may consider the duration T to last till tE.

In the example of <FIG>, the control signaling C transmitted initially by user A at the beginning of the frame <NUM> includes an indication for the receiving UE B that the user B is to provide a feedback indicating a successful/non-successful reception of the control signaling and the data D. Instead of the feedback for the data transmitted by the user A or in addition to the feedback for this data, information about the channel between the user A and the user B over the sidelink may be provided as feedback F from the user B to the user A so as to allow, for example, user A to carry out a link adaption and power control. For example, the feedback message may include a binary value indicating whether to increase or decrease a modulation encoding scheme, MCS, level for the next data transmission over the sidelink, and/or whether to adjust the power level by increasing or decreasing the transmit power for the next transmission over the sidelink by a certain amount, e.g. by steps of +<NUM> dB or -<NUM> dB.

<FIG> shows one example for transmitting data from a user A to a user B using a modified frame <NUM> providing the time R at the end of the frame to allow the user B to transmit back to the user A the feedback within the duration of the frame <NUM> which may include, as mentioned above, the time for processing the receive data from the user A and/or a time for switching between receiving and transmitting at the user B as well as the time for performing the actual transmission of the feedback F. However, there is no limitation to such a structure, rather, the frame transmitted from the user A to the user B may only include control information C and no user data or payload data D.

<FIG> shows such a frame which is basically the same as the frame of <FIG> except that the payload data D is missing. Also, dependent on the amount of control signaling transmitted from the user A to the user B the transmission time T for the actual transmission of the user A may be shorter so that more time R is available for the user B. For example, the frame <NUM> depicted in <FIG> may be employed for transmitting a large feedback, like aggregated feedback for the user B to the user A following the transmission of a plurality of user data packets in a plurality of previous frames since the transmission of the first data packet (D D D F, D=data packet, F=feedback), as shall be discussed in further detail below. In addition, it can be used to send other large feedback reports, like CSI, a CQI, and/or a precoding matrix indicator (PMI) or rank indication (RI) information in case of MIMO transmissions. Also buffer status or UE capabilities can be transmitted.

<FIG> illustrates different examples for frames for transmitting data from user A to user B. <FIG> illustrates a conventional frame as it is currently used that may include control signaling and user data for the user B that is transmitted within the frame without providing any remaining time for the user B to send the feedback. In such conventional approaches, as mentioned above, following the transmission of the frame in <FIG>, in case feedback is desired, a corresponding frame is be transmitted from the user B to the user A including the feedback information. This approach, while being possible, is disadvantageous due to the increased latency for providing the feedback to the user A which may be especially disadvantageous in cases where the payload to be transmitted from user A to user B is time critical or delay critical, for example data associated with ULRCC services. <FIG> illustrates the structure of the frame as described above with reference to <FIG> allowing for sufficient time R at the end of the frame for providing feedback from the user B to the user A, as mentioned above, feedback about the reception of the data at the user B or information about the channel state. <FIG> illustrates another frame structure including, during the transmission time T, in addition to the control signaling and the payload data also reference symbols RS, on the basis of which the user B may calculate the channel condition and provide information about the channel condition as feedback. <FIG> illustrates another example for providing the reference signals. When compared to <FIG>, the frame in <FIG> may send the reference symbols or reference signals, like CSI-RS, not only within the sub-carriers defining the frame <NUM> in the frequency domain but also at higher frequencies or higher bandwidths. This is advantageous over the approach of <FIG> because it allows to measure the channel in a wider bandwidth. With this information better resources can be selected for subsequent transmissions.

The just-mentioned bundled or aggregated feedback information needs to be configured, for example using the control signaling via the physical sidelink control channel. A first frame having a structure as in <FIG> may transmit signaling in its control section that a bundled or aggregated feedback is desired for a certain number n of subsequently sent data packets. Alternatively, the initial frame transmitted may be a frame as indicated in <FIG> including in addition to the control signaling indicative of the aggregated feedback to be provided already the first data packet. The subsequent frames may either be conventional sidelink frames as in <FIG> or inventive sidelink frames as described above in <FIG> and in <FIG> including data packets, and the final frame may be a frame as in <FIG> not including any payload data but only the control section from the user A to the user B and the feedback for the preceding packets from the user B to the user A. The aggregated feedback may be an aggregated HARQ feedback or group-HARQ feedback, i.e., acknowledgement/non-acknowledgement messages may be fed back from the user B to the user A. The user A configures the user B to transmit the HARQ feedback after receiving the n-th data packet. The user B may send this information as a bitmap so that the feedback may include:.

<FIG> schematically illustrates the above-described aggregated feedback. It is assumed that four packets D<NUM> to D<NUM> of user data are transmitted from user A to user B and at only once the four packets are received, the user B is to return a feedback to user A about the four packets D<NUM> to D<NUM>. Initially, in a first frame ①, a first data packet D<NUM> is transmitted in accordance with one of the inventive frame structures which includes control signaling telling the user B that four packets are transmitted from the user A to the user B and once these four packets are completed, a feedback is to be returned. The second, third and fourth data packets D<NUM> to D<NUM> may be transmitted using one of the inventive frame structures or a conventional frame structure as in <FIG>, and following the transmission of the frames ①, ②, ③ and O, in the fifth frame ⑤, a frame structure as in <FIG> may be used including control signaling from the user A to the user B and having a remaining duration R sufficient to allow the user B to transmit the feedback F<NUM>-<NUM> to the user A for each of the data packets D<NUM> to D<NUM>.

As mentioned above, in addition to the feedback regarding the successful/non-successful reception of data packets at the user B, further fields may be included in the feedback allowing for the above-mentioned link adaption and power control.

In the examples described so far, the feedback provided by the user B concerned the data included in the current transmission of frame received from user A. However, the feedback provided by user B using the above-described frame structure may concern a feedback about the successful/non-successful reception of data in an earlier frame, for example in a frame preceding the current frame immediately or with some additional frames therebetween. In other words, after receiving data in an initial frame or transmission n, the above-described frame structure may be employed to provide the feedback from the user B in the next transmission n+<NUM>, or even later in the transmission n+<NUM> or in the transmission n+<NUM>. This approach may be used for a HARQ feedback in case a time for processing the data transmitted by user A at the user B exceeds the remaining time R so that the actual feedback for the initial data packet is transmitted in one of the following transmissions n+<NUM>, n+<NUM> or n+<NUM>.

<FIG> illustrates an HARQ process using the frame structure with a transmission of the feedback for a data packet transmitted in transmission n being sent in the next transmission n+<NUM>. A user A sends data to a user B, and user B sends the acknowledgement/non-acknowledgment feedback back to the user A which does not refer to a currently received data packet but to a data packet received prior to the current transmission. More specifically, as it is depicted in <FIG>, initially in the frame Fn, the user A transmits the data D<NUM> to the user B. It is assumed that no feedback is send at this time back to the user A. The signaling that no feedback is to be send may be handled in different ways:.

In the following frame Fn+<NUM>, user A sends control data C<NUM> and payload data D<NUM> to the user B and the control data C<NUM> indicates to the user B that a feedback is to be transmitted to the user A for the preceding data packet D<NUM>. Accordingly, user B sends back the feedback F<NUM> within the remaining duration R of the frame Fn+<NUM> which has a frame structure <NUM>n+<NUM> as described, for example, with reference to <FIG>.

The feedback F<NUM> may be an acknowledgement message ACK, "A" causing the user A in the frame Fn+<NUM> to transmit the next data packet D<NUM> together with a request for a feedback about data packet D<NUM> using a frame structure <NUM>n+<NUM>.

In case the feedback F<NUM> indicates a non-acknowledgment "N", this may be due to the fact that the data D<NUM> was not successfully decoded at the user B or that the first transmission or first frame Fn was completely missed at the user B. In the first case, the user A receiving the non-acknowledgment feedback indicating a non-successful decoding of the data packet D<NUM> retransmits in frame Fn+<NUM> the data packet D<NUM> or performs any suitable retransmission, using the inventive frame structure <NUM>'n+<NUM> so that the user B may provide the feedback F<NUM> for the data packet D<NUM> received in frame Fn+<NUM>. In case the non-acknowledgment feedback indicates that the frame Fn was completely missed at the user B, user A sends in frame Fn+<NUM> using the inventive frame structure <NUM>"n+<NUM> resending the data packet D<NUM> and requesting feedback from the user B regarding the data packet D<NUM> during the frame Fn+<NUM>.

The sidelink control information, SCI, transmitted in the physical sidelink control channel may be provided with additional fields, like a HARQ process number H, a new data indicator NDI that toggles with new data for the HARQ process, and a feedback indicator F.

<FIG> illustrates the respective values for the new fields in the SCI at the user B, in case of the example of <FIG>. <FIG> illustrates the initial state of the HARQ processes at user B, and <FIG> illustrates how the fields H, NDI, F change during the transmissions or frames in <FIG>. In <FIG> it is indicated that H+<NUM>=F, so as to indicate what the value range may be. H=HARQ Process number and F=Feedback Request number. For example H has a range of <NUM>-<NUM>, F having a value of <NUM>,<NUM>, <NUM> or <NUM> means feedback should be sent for the corresponding H process, and F=<NUM> means that no feedback is requested. In another example, when a three bit value is used, H may range from <NUM> to <NUM>, and F ranges from <NUM> to <NUM>, with F=<NUM> corresponding to no feedback.

<FIG> illustrates the initial HARQ process state. Before beginning the unicast transmission.

As is depicted in <FIG>, during the initial transmission in frame Fn H=<NUM> and NDI=<NUM> meaning data is sent for the first HARQ process and the toggled NDI indicates the HARQ buffer should be flushed as new data is sent, however F=<NUM> meaning that no feedback is to be send. In the frame Fn+<NUM> the user A transmits data D<NUM> (see <FIG>) so that the SCI at the user B indicates H=<NUM> and NDl=<NUM> meaning that data for the second HARQ process is sent. The NDI is toggled as it is a new data packet. Further, the feedback indicator F=<NUM> indicating that user B sends a feedback for the transmission of the data D<NUM> in the first frame Fn.

In case the feedback in frame Fn+<NUM> indicates that the initial transmission was successful ("✔"), in frame Fn+<NUM>, the user A may transmit a frame including the data packet D<NUM> together with a request for a feedback for the data packet D<NUM>. In this case, as is shown in <FIG> at ①, the SCI at the user B indicates H=<NUM> and NDI=<NUM> meaning new data is sent for the <NUM>rd HARQ process. Further, the feedback indicator F=<NUM> indicating that user B sends a feedback for the transmission of the data D<NUM> in the second frame Fn+<NUM>.

In case the feedback in frame Fn+<NUM> indicated that the data was not successfully decoded ("x"), in frame Fn+<NUM> the user A retransmits the data D<NUM> together with a request for a feedback regarding the transmission of the data packet D<NUM> which, when being successful, causes the user A to send the next data packet D<NUM>. In this case, as is shown in <FIG> at ②, the SCI at the user B indicates H=<NUM> and NDI=<NUM> meaning additional redundancy is sent for the first HARQ process. Further, the feedback indicator F=<NUM> indicating that user B sends a feedback for the transmission of the data D<NUM> in the second frame Fn+<NUM>.

In case the first frame Fn was not received or missed at the user B ("x1") so that in frame Fn+<NUM> user A sends again the data packet D<NUM>. In this case, as is shown in <FIG> at ③, the SCI at the user B indicates H=<NUM> and NDl=<NUM> meaning additional redundancy is sent for the first packet. Further, the feedback indicator F=<NUM> indicating that user B sends a feedback for the retransmission of the data D<NUM>.

In accordance with the examples described above, the control data and the user data have been sent at different times, i.e., using a TDM control, however, there is no limitation to a TDM control, rather, control data and user data may be sent at the same time on different resources in frequency, i.e., a FDM control may be applied, and the above described approach may be used by sending the feedback indicator in a previous control message. <FIG> shows an approach employing FDM control. Control data is transmitted in a first frequency band fc and user data is transmitted in a second frequency band fd. In a first frame Fn, a control message, SCI, may be transmitted including the above-described feedback indicator F. The feedback indicator tells the user B whether feedback for the data D1 transmitted in frame Fn is to be returned to the user A or not in the next frame Fn+<NUM>. In <FIG>, it is assumed that the feedback indicator tells the user B that a feedback regarding the data D<NUM> is to be returned to the user A so that, in frame Fn+<NUM>, the data frequency band or data channel fd is configured such that a second data packet D<NUM> is transmitted during the transmission time T which is less than the frame duration so that during the remaining duration R, the feedback may be transmitted from the user B back to the user A.

In accordance with the present invention, the feedback indication may be piggybacked in the data region, as is illustrated in <FIG> is similar to <FIG>, except that the feedback indicator is contained in the data packet D<NUM>, which is sent from user A to user B. User B decodes data packet D<NUM> in frame Fn and reads the feedback indicator, which tells the user B that a feedback regarding the data D<NUM> is to be returned to the user A so that, in frame Fn+<NUM>, the data frequency band or data channel fd is configured such that a second data packet D<NUM> is transmitted during the transmission time T which is less than the frame duration so that during the remaining duration R, the feedback may be transmitted from the user B back to the user A.

In some of the embodiments described above, reference has been made to respective vehicles being either in the connected mode, also referred to as mode <NUM> or mode <NUM> configuration, or vehicles being in the idle mode, also referred to as mode <NUM> or mode <NUM> configuration. However, the present invention is not limited to V2V communications or V2X communications, rather it is also applicable to any device-to-device communications, for example non-vehicular mobile users or stationary users that perform a sidelink communication, e.g., over the PC5 interface. Also in such scenarios, the inventive aspects described above may be employed.

In accordance with embodiments, the wireless communication system may include a terrestrial network, or a non-terrestrial network, or networks or segments of networks using as a receiver an airborne vehicle or a spaceborne vehicle, or a combination thereof.

in accordance with embodiments, a UE may comprise one or more of a mobile or stationary terminal, an IoT device, a ground based vehicle, an aerial vehicle, a drone, a building, or any other item or device provided with network connectivity enabling the item/device to communicate using the wireless communication system, like a sensor or actuator. In accordance with embodiments, a transmitter may comprise one or more of a macro cell base station, or a small cell base station, or a spaceborne vehicle, like a satellite or a space, or an airborne vehicle, like a unmanned aircraft system (UAS), e.g., a tethered UAS, a lighter than air UAS (LTA), a heavier than air UAS (HTA) and a high altitude UAS platforms (HAPs), or any transmission/reception point (TRP) enabling an item or a device provided with network connectivity to communicate using the wireless communication system.

Various elements and features of the present invention may be implemented in hardware using analog 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> illustrates an example of a computer system <NUM>. The units or modules as well as the steps of the methods performed by these units may execute on one or more computer systems <NUM>. The computer system <NUM> includes one or more processors <NUM>, like a special purpose or a general purpose digital signal processor. The processor <NUM> is connected to a communication infrastructure <NUM>, like a bus or a network. The computer system <NUM> includes a main memory <NUM>, e.g., a random access memory (RAM), and a secondary memory <NUM>, e.g., a hard disk drive and/or a removable storage drive. The secondary memory <NUM> may allow computer programs or other instructions to be loaded into the computer system <NUM>. The computer system <NUM> may further include a communications interface <NUM> to allow software and data to be transferred between computer system <NUM> and external devices. The communication may be in the from electronic, electromagnetic, optical, or other signals capable of being handled by a communications interface. The communication may use a wire or a cable, fiber optics, a phone line, a cellular phone link, an RF link and other communications channels <NUM>.

Some embodiments, not being according to the invention as claimed, 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.

A further embodiment, not being according to the invention as claimed, 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 not being according to the invention as claimed, is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. A further embodiment, not being according to the invention as claimed, 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, not being according to the invention as claimed, comprises a computer having installed thereon the computer program for performing one of the methods described herein.

In some embodiments, not being according to the invention as claimed, 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, not being according to the invention as claimed, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein.

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.

Claim 1:
An apparatus for a wireless communication system,
wherein the apparatus is configured to be connected to at least one user device, UE, of the wireless communication system via a sidelink for a sidelink communication with the at least one UE,
wherein, for a unicast transmission to the UE, the apparatus is configured to transmit a sidelink frame (Fn) having a certain frame duration, a first part of the sidelink frame including control signaling (C<NUM>) and a second part of the sidelink frame including a data packet (D<NUM>), the sidelink frame indicating to the UE whether a feedback is to be returned to the apparatus, the feedback indicating a successful reception of data at the UE and/or a sidelink channel condition, and
wherein, in case the feedback from the UE is desired, the apparatus is configured to
- transmit in the second part of the sidelink frame (Fn) an indication (FI) that the feedback is to be provided by the UE, and
- receive from the UE, in a subsequent sidelink frame (Fn+<NUM>), the feedback (B) for data transmitted in the sidelink frame, the subsequent sidelink frame (Fn+<NUM>) including a control signaling (C<NUM>) and a data packet (D<NUM>), the data packet (D<NUM>)being shortened by a remaining duration (R), and the feedback (B) being transmitted during the remaining duration (R) in the subsequent sidelink frame (Fn+<NUM>).