Patent Publication Number: US-2021167897-A1

Title: Low latency harq protocol for urllc services

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of copending International Application No. PCT/EP2019/071255, filed Aug. 7, 2019, which is incorporated herein by reference in its entirety, and additionally claims priority from European Applications No. EP 18 188 369.5, filed Aug. 9, 2018, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the field of mobile communication systems, more specifically to techniques checking or verifying if information sent by a transmitter has been correctly received at a receiver so as to initiate a retransmission in case of a non-successful transmission of the information. Embodiments relate to simultaneous synchronous and asynchronous HARQ, hybrid automatic repeat request, operations in a network entity of the wireless communication system, like a base station or a user equipment, UE. 
       FIG. 1  is a schematic representation of an example of a terrestrial wireless network  100  including a core network  102  and a radio access network  104 . The radio access network  104  may include a plurality of base stations gNB 1  to gNB 5 , each serving a specific area surrounding the base station schematically represented by respective cells  106   1  to  106   5 . 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 IoT 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. 1  shows an exemplary view of only five cells, however, the wireless communication system may include more such cells.  FIG. 1  shows two users UE 1  and UE 2 , also referred to as user equipment, UE, that are in cell  106   2  and that are served by base station gNB 2 . Another user UE 3  is shown in cell  106   4  which is served by base station gNB 4 . The arrows  108   1 ,  108   2  and  108   3  schematically represent uplink/downlink connections for transmitting data from a user UE 1 , UE 2  and UE 3  to the base stations gNB 2 , gNB 4  or for transmitting data from the base stations gNB 2 , gNB 4  to the users UE 1 , UE 2 , UE 3 . Further,  FIG. 1  shows two IoT devices  110   1  and  110   2  in cell  106   4 , which may be stationary or mobile devices. The IoT device  110   1  accesses the wireless communication system via the base station gNB 4  to receive and transmit data as schematically represented by arrow  112   1 . The IoT device  110   2  accesses the wireless communication system via the user UE 3  as is schematically represented by arrow  112   2 . The respective base station gNB 1  to gNB 5  may be connected to the core network  102 , e.g. via the S1 interface, via respective backhaul links  114   1  to  114   5 , which are schematically represented in  FIG. 1  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 gNB 1  to gNB 5  may connected, e.g. via the S1 or X2 interface or XN interface in NR, with each other via respective backhaul links  116   1  to  116   5 , which are schematically represented in  FIG. 1  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 one or more slots of 14 OFDM symbols depending on the cyclic prefix (CP) length and subcarrier spacing (SCS). 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 non-orthogonal 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 5G or NR, New Radio, standard. 
     The wireless network or communication system depicted in  FIG. 1  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 1  to gNB 5 , 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 5G or NR, new radio, standard. 
     In mobile communication networks, for example in a network like that described above with reference to  FIG. 1 , like a 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, i.e., 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 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. 1 , 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. 2  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  200  which, basically, corresponds to the cell schematically represented in  FIG. 1 . The UEs directly communicating with each other include a first vehicle  202  and a second vehicle  204  both in the coverage area  200  of the base station gNB. Both vehicles  202 ,  204  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 3 configuration. 
       FIG. 3  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  206 ,  208  and  210  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 4 configuration. As mentioned above, the scenario in  FIG. 3  which is an out-of-coverage scenario does not mean that the respective mode 4 UEs are outside of the coverage  200  of a base station, rather, it means that the respective mode 4 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  200  shown in  FIG. 2 , in addition to the mode 3 UEs  202 ,  204  also mode 4 UEs  206 ,  208 ,  210  are present. 
     In a wireless communication system as described above with reference to  FIG. 1 , like a LTE system or a 5G/NR system, approaches for checking or verifying if a transmission sent by a transmitter, like a BS, is correctly arrived at a receiver, like a UE, are implemented which request, in case of a non-successful transmission, a retransmission of the information or a retransmission of one or more redundancy versions of the information. Naturally, such a process may also be implemented when transmitting from the UE to the BS. In other words, for handling error packets received at a UE or a gNB, a mechanism is applied to rectify the error. In accordance with LTE or NR, a HARQ mechanism is implemented to correct error packets in the physical layer. In case a receive packet has an error, the receiver may buffer the packet and request a retransmission from the transmitter or sender. Once the receiver received the re-transmitted packet, it may combine with the buffered data prior to channel decoding and error detection, for example, by applying a chase combination approach or an incremental redundancy approach. 
       FIG. 4  describes briefly an example for a conventional HARQ mechanism as it may also be derived from TS 38.321, section 5.3.2 and 5.4.2 which describes the HARQ operation and entity.  FIG. 4  illustrates a transmitter, e.g., a gNB, which sends a data packet  1  to a receiver, e.g., a UE. The data packet  1 ( 1 ) is initially transmitted, and the receiver attempts to decode the received data packet. If the data packet was successfully decoded the receiver delivers the data packet from the MAC/PHY layer to an upper layer. If the data packet was not successfully decoded the receiver buffers the data packet in a soft buffer as is indicate at {circle around (1)} in  FIG. 4 . Further, the receiver send the NACK message to the transmitter, and, responsive to the NACK message, the transmitter sends a retransmission  1 ( 2 ) of the data packet. The buffered initial transmission is combined with the retransmission as is indicated at {circle around (2)}. The combining may use chase combination or incremental redundancy. In case the combined data can be decoded, as is indicated at {circle around (3)}, the ACK message is send to the transmitter to indicate the successful transmission. 
     The HARQ mechanism may include a synchronous HARQ process or an asynchronous HARQ process. 
     When applying the asynchronous HARQ process, the gNB may use any of the available HARQ processes, for example a process out of the 8 SAW, Stop&amp;Wait, processes for the downlink.  FIG. 5  illustrates an 8-channel Stop-and-Wait HARQ protocol according to which during a time period, which may be the minimum time until a retransmission may be send due to a missing ACK/NACK or due to received NACK, further data packets are transmitted. In the latter case (receipt of a NACK) the time period is defined by the processing time for decoding at the receiver a data packet and the processing time at the transmitter for decoding the ACK/NACK message related to the data packet. The gNB provides instructions to the UE regarding which HARQ process will be used during each sub-frame for which resources are allocated, and the respective identity or HARQ process ID may be included within a PDCCH transmission. The asynchronous HARQ process come together with an increase in the signaling overhead as it needs to include the HARQ process ID within the DCI message, but increases flexibility as retransmissions do not have to be scheduled during every sub-frame.  FIG. 6  illustrates an adaptive asynchronous HARQ at is may be used in NR.  FIG. 6  shows the minimum time until a retransmission may be send due to a missing ACK/NACK so that a retransmission for HARQ process #0 may be made at a time after this minimum time. When scheduling the retransmission, the HARQ process number #0-#7 and the location of the retransmission in frequency and transport format are signaled. Thus, the process is adaptive with regard to the location and the transport format. 
     When applying the synchronous HARQ process retransmissions are scheduled at fixed time intervals, thereby generating a reduced overhead signaling as it is not needed to include an information about the process to be used, for example the HARQ process identifier, into the outgoing data. The process is cyclic, so that even if no resources are allocated during a specific subframe, the first process will repeat at the initially scheduled intervals, for example, after every 8 ms. 
       FIG. 7  illustrates schematically a synchronous HARQ process in a LTE wireless communication system using adaptive or non-adaptive transmissions/operations.  FIG. 7  illustrates a sub-frame n, a sub-frame n+8 and a sub-frame n+16. At sub-frame n, the synchronous ARQ process is scheduled using the PDCCH, causing the retransmissions to be scheduled in multiples of the HARQ roundtrip time, RTT, which may be 8 sub-frames. In a non-adaptive operation, the HARQ feedback on the physical hybrid ARQ indicator channel, PHICH, is used to determine, if a retransmission is needed or not. In  FIG. 7 , it is assumed that the received information in sub-frame n included an error, i.e., the transmission to a receiver, like a UE, was not successful so that, on the PHICH the non-acknowledgement message NACK is transmitted. Dependent on the scheduled initial uplink resource, there is a unique PHICH resource corresponding to the non-successful transmission, and the retransmission will be provided with the same MCS on the same frequency resource using the corresponding retransmission slot, which, in the example of  FIG. 7  is at sub-frame n+8. In other words, in a non-adaptive HARQ operation, the retransmission is triggered at the sender or transmitter once a NACK message is received on the PHICH, and, at the next time for doing a transmission, the same resources as in the previous transmission are used, i.e., MCS and resource blocks, RBs, remain unchanged.  FIG. 8  illustrates non-adaptive synchronous HARQ at is may be used for ULLRC services. The operation is synchronous in time meaning that the HARQ processes #0-#7 are served one after the other, and a retransmission occurs exactly N slots/symbols after last transmission so that there is no need to signal the process number. This limited scheduling freedom comes together with a minimum uplink signaling overhead and a minimum delay. 
     In case of an adaptive synchronous HARQ operation, the PHICH is ignored if a DCI message is received via the PDCCH indicating an adaptive retransmission, as is indicated between sub-frame n+8 and sub-frame n+16 in  FIG. 7 . Although in the adaptive operation the MCS and frequency resource may be changed using the DCI signaling the adaptive transmission operation, still, since it is a synchronous HARQ process, the retransmission sub-frame is already predetermined by the initial transmission at sub-frame n and will be carried out at the next retransmission time, which, in the example of  FIG. 7  is sub-frame n+16. 
     In accordance with the LTE Rel.8, synchronous HARQ processes are only used in the uplink, and the synchronous HARQ process may be operated either in the adaptive or non-adaptive mode, as described above. 
     NR Rel.15 introduces an asynchronous HARQ process to be used also in the uplink direction so that the retransmission is prescheduled by the gNB. However, this results in additional latency needed for scheduling, and since there is no explicit acknowledgement message, ACK, anymore, the UE needs to store relevant information in its HARQ processes until a new transmission is started on the same HARQ process. 
     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 conventional technology that is already known to a person of ordinary skill in the art. 
     SUMMARY 
     An embodiment may have an apparatus, wherein the apparatus is configured to receive one or more data packets from a transmitter in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, and request from the transmitter a retransmission for a data packet in case of a non-successful transmission of the data packet, and the apparatus includes a plurality of Hybrid ARQ, HARQ, entities, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity to perform a first HARQ operation, and the second HARQ entity to perform a second HARQ operation, the first and second HARQ operations being different, or a Hybrid ARQ, HARQ, entity performing a first HARQ operation and a second HARQ operation, the first and second HARQ operations being different. 
     Another embodiment may have an apparatus, apparatus, wherein the apparatus is configured to transmit one or more data packets to a receiver in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, and receive from the receiver a request for a retransmission for a data packet in case of a non-successful transmission of the data packet, and the apparatus includes a plurality of Hybrid ARQ, HARQ, entities, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity to perform a first HARQ operation, and the second HARQ entity to perform a second HARQ operation, the first and second HARQ operations being different, or a Hybrid ARQ, HARQ, entity performing a first HARQ operation and a second HARQ operation, the first and second HARQ operations being different. 
     Another embodiment may have a wireless communication network, including: one or more base stations, BS, and one or more user equipments, UEs, a UE being served by one or more BSs or communication directly with one or more other UEs while being in connected mode or idle mode, wherein a base station and/or a UE includes the apparatus according to the invention. 
     Another embodiment may have a method, having the steps of: receiving one or more data packets from a transmitter in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, and requesting from the transmitter a retransmission for a data packet in case of a non-successful transmission of the data packet, wherein the retransmission includes providing a first HARQ operation and/or a second HARQ operation, the first and second HARQ operations being different, wherein a plurality of Hybrid ARQ, HARQ, entities is provided, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity performing the first HARQ operation, and the second HARQ entity performing the second HARQ operation, or a Hybrid ARQ, HARQ, entity is provided performing the first HARQ operation and the second HARQ operation, the first and second HARQ operations being different. 
     Another embodiment may have a method, having the steps of: transmitting one or more data packets to a receiver in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, receiving from the receiver a request for a retransmission for a data packet in case of a non-successful transmission of the data packet, and wherein the retransmission includes providing a first HARQ operation and/or a second HARQ operation, the first and second HARQ operations being different, wherein a plurality of Hybrid ARQ, HARQ, entities is provided, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity performing the first HARQ operation, and the second HARQ entity performing the second HARQ operation, or a Hybrid ARQ, HARQ, entity is provided performing the first HARQ operation and the second HARQ operation, the first and second HARQ operations being different. 
     Another embodiment may have a non-transitory digital storage medium having a computer program stored thereon to perform the method, having the steps of: receiving one or more data packets from a transmitter in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, and requesting from the transmitter a retransmission for a data packet in case of a non-successful transmission of the data packet, wherein the retransmission includes providing a first HARQ operation and/or a second HARQ operation, the first and second HARQ operations being different, wherein a plurality of Hybrid ARQ, HARQ, entities is provided, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity performing the first HARQ operation, and the second HARQ entity performing the second HARQ operation, or a Hybrid ARQ, HARQ, entity is provided performing the first HARQ operation and the second HARQ operation, the first and second HARQ operations being different, when said computer program is run by a computer. 
     Another embodiment may have a non-transitory digital storage medium having a computer program stored thereon to perform the method, having the steps of: transmitting one or more data packets to a receiver in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, receiving from the receiver a request for a retransmission for a data packet in case of a non-successful transmission of the data packet, and wherein the retransmission includes providing a first HARQ operation and/or a second HARQ operation, the first and second HARQ operations being different, wherein a plurality of Hybrid ARQ, HARQ, entities is provided, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity performing the first HARQ operation, and the second HARQ entity performing the second HARQ operation, or a Hybrid ARQ, HARQ, entity is provided performing the first HARQ operation and the second HARQ operation, the first and second HARQ operations being different, when said computer program is run by a computer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which: 
         FIG. 1  shows a schematic representation of an example of a wireless communication system; 
         FIG. 2  shows a schematic representation of a situation in which UEs directly communicating with each other are in coverage of a base station; 
         FIG. 3  shows a scenario in which UEs directly communicating with each other are not are not in coverage of a base station, i.e., are not connected to a base station; 
         FIG. 4  describes briefly an example for a conventional HARQ mechanism as it may also be derived from TS 38.321, section 5.3.2 and 5.4.2 which describes the HARQ operation and entity; 
         FIG. 5  illustrates an 8-channel Stop-and-Wait HARQ protocol; 
         FIG. 6  illustrates an adaptive asynchronous HARQ at is may be used in NR; 
         FIG. 7  illustrates schematically a synchronous HARQ process in a LTE wireless communication system using adaptive or non-adaptive transmissions/operations; 
         FIG. 8  illustrates non-adaptive synchronous HARQ at is may be used for ULLRC services; 
         FIG. 9  is a schematic representation of a wireless communication system for communicating information between a transmitter and one or more receivers in accordance with embodiments of the present invention; 
         FIG. 10  illustrates an embodiment of a layer structure for implementing synchronous and asynchronous HARQ operation at the base station or the user equipment using a common MAC entity in the MAY layer; 
         FIG. 11  illustrates a further embodiment of a layer structure for implementing synchronous and asynchronous HARQ operation at the base station or the user equipment using separate MAC entities in the MAY layer; 
         FIG. 12  illustrates details of a UE, like a UE as described above with reference to  FIG. 9  including the antennas ANT R , the signal processor  302   a  and the transceiver  302   b;    
         FIG. 13  illustrates the above concept of using for the feedback LL-PUCCHs in case of synchronous HARQ, and multiplexing the feedback into the regular PUCCH in case of asynchronous HARQ; and 
         FIG. 14  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. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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 present invention addresses the way the HARQ processes are currently implemented, which is disadvantageous because in certain scenarios, like mobile communication scenarios, a single UE may support different service types simultaneously. The different service types may have different latency requirements, for example, a delay non-critical service, like a eMBB service, and a delay critical service like a URLLC service, may be supported simultaneously by a single UE. In such a situation, the radio transmission technology, RAT, needs to handle each service type, for example in terms of data rate, latency and reliability. However, in current releases, like LTE Rel.8 and NR Rel.15, the HARQ design is limited. For example, NR uses a synchronous HARQ in uplink and downlink transmissions, and the retransmissions are explicitly scheduled using the PDCCH resource allocation for providing high flexibility. The gNB spends time to execute scheduling before sending the resource allocation, and the HARQ feedback channel may send immediately the ACK/NACK message. However, for delay critical traffic, like URLLC traffic, the burden on scheduling HARQ retransmissions is substantial and causes additional delays in the transmission. Additionally, also for massive Machine-Type Communication (mMTC) this demands a higher receiver complexity and reduces the battery lifetime. 
     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. 1 ,  FIG. 2  and  FIG. 3  including base stations and users, like mobile terminals or IoT devices.  FIG. 9  is a schematic representation of a wireless communication system for communicating information between a transmitter  300  and one or more receivers  302   1  to  302   1 . The transmitter  300  and the receivers  302  may communicate via a wireless communication links or channels  304   a ,  304   b ,  304   c , like a radio link. The transmitter  300  may include one or more antennas ANT T  or an antenna array having a plurality of antenna elements, a signal processor  300   a  and a transceiver  300   b , coupled with each other. The receivers  302  include one or more antennas ANT R  or an antenna array having a plurality of antennas, a signal processor  302   a   1 ,  302   a   n , and a transceiver  302   b   1 ,  302   b   n  coupled with each other. 
     In accordance with an embodiment, as for example also depicted in  FIG. 2 , the transmitter  300  may be a base station and the receivers may be UEs. The base station  300  and the UEs  302  may communicate via respective first wireless communication links  304   a  and  304   b , like a radio link using the Uu interface, while the UEs  302  may communicate with each other via a second wireless communication link  304   c , like a radio link using the PC5 interface. 
     In accordance with an embodiment, as for example also depicted in  FIG. 3 , the transmitter  300  may be a first UE and the receivers may be further UEs. The first UE  300  and the further UEs  302  may communicate via respective wireless communication links  304   a  to  304   c , like a radio link using the PC5 interface. 
     The transmitter  300  and the one or more receivers  302  may operate in accordance with the inventive teachings described herein. 
     Apparatus Receiving Data, Like a UE or BS, Requesting a Retransmission, and Supporting One or More HARQ Entities 
     The present invention provides an apparatus, wherein 
     the apparatus is configured to
         receive one or more data packets from a transmitter in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, and   request from the transmitter a retransmission for a data packet in case of a non-successful transmission of the data packet, and       

     the apparatus comprises
         a plurality of Hybrid ARQ, HARQ, entities, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity to perform a first HARQ operation, and the second HARQ entity to perform a second HARQ operation, the first and second HARQ operations being different, or   a Hybrid ARQ, HARQ, entity performing a first HARQ operation and a second HARQ operation, the first and second HARQ operations being different.       

     Apparatus Transmitting Data, Like a BS or UE, Receiving a Request for Retransmission, and Supporting One or More HARQ Entities 
     The present invention provides an apparatus, wherein 
     wherein the apparatus is configured to
         transmit one or more data packets to a receiver in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, and   receive from the receiver a request for a retransmission for a data packet in case of a non-successful transmission of the data packet, and       

     the apparatus comprises
         a plurality of Hybrid ARQ, HARQ, entities, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity to perform a first HARQ operation, and the second HARQ entity to perform a second HARQ operation, the first and second HARQ operations being different, or   a Hybrid ARQ, HARQ, entity performing a first HARQ operation and a second HARQ operation, the first and second HARQ operations being different.       

     With respect to both apparatuses the following may apply. 
     Re application of 1st and/or 2nd HARQ operations. 
     In accordance with embodiments, responsive to a signaling or based on an association between a logical channel the data packet belongs to and the HARQ entity, the apparatus applies for the one or more data packets
         the first HARQ operation, or   the second HARQ operation, or   the first and second HARQ operations simultaneously.       

     Re what the operations may be. 
     In accordance with embodiments, the first and second HARQ operations comprise one or more of
         a Stop-and-Wait ARQ protocol,   a window based ARQ protocol,   a synchronous protocol, the synchronous protocol scheduling the one or more retransmissions and/or the one or more HARQ ACK/NACKs at pre-defined time instances after the initial transmission,   an asynchronous protocol, the asynchronous protocol scheduling the one or more retransmissions and/or the one or more HARQ ACK/NACKs dynamically in time.       

     Packets of both types may be processed. 
     In accordance with embodiments, the apparatus is configured to process both data packets of a first logical channel and data packets of a second logical channel. 
     Re what the types may be. 
     In accordance with embodiments, the data packet of the first logical channel includes
         a data packet provided by a delay critical service of the wireless communication system, like an URLLC service having, e.g., a low rate and/or a low latency, or   a data packet having associated therewith a first Quality of Service, QoS, or   a data packet having associated therewith a first guaranteed bit rate, GBR, and       

     wherein the data packet of the second logical channel includes
         a data packet provided by a delay non-critical service of the wireless communication system, like an eMBB service having, e.g., a high rate and/or a medium latency requirement or a mMTC service having, e.g., a low rate and/or a low latency requirement, or   a data packet having associated therewith a second QoS, the first QoS being higher than the second QoS, or   a data packet having associated therewith a second GBR, the first GBR being higher than the second GBR.       

     Re the configuration of HARQ entities. 
     In accordance with embodiments, the first HARQ entity is preconfigured with the first HARQ operation, and the second HARQ entity is preconfigured with the second HARQ operation, or 
     each of the first and second HARQ entities are preconfigured with a HARQ operation having different settings, the settings of the HARQ operation being configurable, responsive to the signaling or based on the association, to implement the first HARQ operation or the second HARQ operation. 
     Re establishment and configuration of settings of HARQ entities. 
     In accordance with embodiments, the apparatus is configured to receive a configuration message or a reconfiguration message, e.g. using the RRC protocol, the configuration/reconfiguration message causing the apparatus to establish the first and second HARQ entity and/or to configure/reconfigure the settings of the first and second HARQ entities to perform the first and second HARQ operations. 
     Re the possibility of the configuration being received from gNB. 
     In accordance with embodiments, the apparatus is to
         receive the configuration message or the reconfiguration message from a base station, gNB,   decode the configuration message or the reconfiguration message and   configure the MAC Layer and/or Physical Layer so as to establish and/or to configure/reconfigure the first and second HARQ entities to provide HARQ retransmissions.       

     HARQ entities may be defined by standard. 
     In accordance with embodiments, the establishment and/or configuration of first and second HARQ entities is a predefined procedure and/or configuration specified in the standard. 
     Re possible differences in 1st and/or 2nd HARQ entities 
     In accordance with embodiments, the first and second HARQ entities comprise and/or supports one or more of
         different numbers of HARQ processes,   HARQ processes supporting a different number of data packets, e.g. Transport Blocks, depending on the spatial multiplexing scheme being used   different redundancy versions,   different sequences of redundancy versions, RVs,   different channels for ACK/NACK reporting,   different ACK/NACK timings,   a different maximum number of HARQ retransmissions,   different aggregation factors for bundling transmissions of a data packet, like a Transport Block, in multiple transmission parts of the same bundle,   different target Block Error Rates, BLERs for all transmissions and/or specific retransmissions.       

     Re parallel HARQ processes. 
     In accordance with embodiments, each HARQ entity maintains one or more parallel HARQ processes, each HARQ process being associated with a HARQ process identifier, wherein the HARQ process identifier may either be selected autonomously out of a pool of HARQ processes (e.g., by timing of the initial transmission and/or retransmissions) or predefined by a sequence number or dynamically selected by an apparatus (e.g. a gNB base station) and signaled to an apparatus (e.g. a User Equipment). 
     HARQ entities may be semi-statically/dynamically associated with logical channels. 
     In accordance with embodiments, the first and second HARQ entities are semi-statically configured and/or associated to different logical channels, e.g., by RRC configuration/reconfiguration, and/or are dynamically scheduled, e.g., by the MAC scheduler. 
     DCI signaling may be used for distinguishing HARQ entities/protocols. 
     In accordance with embodiments, 
     a first and second HARQ entity are semi-statically configured and/or associated to different logical channel and 
     the apparatus is configured to determine for a received resource assignment on the PDCCH control channel which of the first and second HARQ entities to select and/or to apply either using
         one or more specific Radio Network Temporary Identifiers, RNTIs, or   one or more DCI formats, or   a HARQ Entity Selector being part of HARQ information send with a DCI format, or   a PDCCH resource assignment on configurable Control Resource Sets, CORESETs, on different physical resources, or   different Physical Channels, e.g., a low latency PDSCH or low latency PUSCH.       

     In accordance with embodiments, the first and second HARQ entities are located at the MAC layer and being associates and/or linked and/or mapped to one or more Physical Layer procedures or Physical Layer channels such as one or more of
         different downlink resource allocation methods e.g. scheduled on the PDCCH, different PDCCH monitoring periodicity.   different DCI formats for downlink, uplink and sidelink scheduling via the PDCCH on the PHY,   different RNTIs indicated in the DC&#39;s for scheduling via the PDCCH on the PHY,   different downlink control channels to request uplink retransmission e.g. a retransmission requested via a PDCCH resource allocation, a retransmission requested via a NACK transmission on a Physical HARQ ACK/NACK indicator channel, PHICH,   different physical channels for data transmission e.g. PDSCH, Low Latency PDSCH   different uplink grant methods e.g. scheduled on PDCCH, a response message to a uplink random access, pre-configured uplink grants and/or a semi-persistent scheduling,   different uplink control channels to request downlink retransmission e.g. a retransmission requested via and NACK part of the Uplink Control Information, UCI, send via a PUCCH control channel, or via a Low Latency PUCCH control channel, via PUCCHs with different formats (e.g. short and long PUCCH format), via a Compact PUCCH.       

     In accordance with embodiments, the first and second HARQ entities are located at the MAC layer providing downlink control information or uplink control information to the physical layer (e.g. to support the transmission or reception of data packet or to request a retransmission) for transmission and/or to support Physical Layer operation such as
         different control information bits in the Downlink Control Information e.g. different bits (incl. not bits) for HARQ process identifiers, for redundancy version number, for the new data indicator (NDI), for ACK/NACK timing/resource information, or   different control information bits in the Uplink Control Information, UCI, send from the MAC layer to the PHY layer e.g. ACK/NACKs for Code Block Groups or ACK/NACKs for Transport Blocks, single ACK/NACK, multiple ACK/NACKs, bundled ACK/NACKs,       

     In accordance with embodiments, when using the RNTI, the apparatus is configured to receive a configuration and/or reconfiguration message, e.g. via RRC signaling, the configuration message causing the apparatus to be configured with a new RNTI which is associated with the first or second HARQ entity, so that the apparatus, upon a blind decoding process testing all RNTIs, determines which of the first or second HARQ entities to select and/or apply. 
     In accordance with embodiments, the DCI format comprises a first DCI format that explicitly signals associated HARQ control information and a second DCI format that does not explicitly signal all HARQ control information, the non-signaled HARQ control information being derived by the apparatus, wherein the first DCI may be used for the initial transmission, and the second DCI format may be used for the one or more retransmissions, and 
     the apparatus is configured to
         test all PDCCH candidates against second DCI formats and against the first DCI format, and   evaluate the embedded checksum to identify which one of the first DCI format and the second DCI format has been received so as to determine which of the first or second HARQ entities to apply.       

     Re section 3.1.4: Dedicated PUCCHs for each UE HARQ entity/protocol. 
     In accordance with embodiments, each of the first and second receiving HARQ entities located at the MAC layer send ACK/NACK control information to the Physical Layer for transmission on a dedicated control channel for an HARQ ACK/NACK feedback to the transmitting HARQ entities, like a Physical Uplink Control Channel, PUCCH or a Physical Hybrid Indicator Channel, PHICH. 
     Re the possibility of the PHICH being limited to ACK/NACK} 
     In accordance with embodiments, the control channel comprises the PHICH, the PHICH transmitting only ACK/NACK messages. 
     In accordance with embodiments, the apparatus, responsive to a NACK on the PHICH, performs the retransmission with a fixed format on same resource used of the preceding transmission/retransmission, wherein a predefined sequence of RVs may be used. 
     Re the possibility of using LL-PUCCH for ACK/NACK} 
     In accordance with embodiments, the control channel comprises a low latency PUCCH including the ACK/NACK message, the low latency PUCCH being send more frequently than a regular PUCCH and/or the low latency PUCCH carrying a smaller payload than a regular PUCCH. 
     Re LL-PUCCH for ACK/NACK+CSI. 
     In accordance with embodiments, the apparatus is configured to
         estimate the radio channel (e.g. based on Demodulation Reference Symbols, DM-RS) over which the data packet is transmitted and/or decodes the control channel (e.g. PDCCH) with the resource allocation of the data packet to provide a CSI, responsive to receiving the data packet and prior to processing the data packet, and   include the CSI into a low latency PUCCH or transmit the CSI once obtained using a first low latency PUCCH and ahead of the ACK/NACK message which is send in a second low latency PUCCH.       

     Re section 3.2. DCI miss detection and rescheduling of retransmissions. 
     In accordance with embodiments, the apparatus is configured to
         detect a missing PUCCH for a HARQ ACK/NACK, which indicates that the receiver missed an initial scheduling of the transmission by the apparatus, and   responsive to detecting the miss, reschedule the same transmission or the initial transmission or the next redundancy version, RV, explicitly with a PDCCH at the next opportunity.       

     In accordance with embodiments, in case of a PUCCH format 0-1, the apparatus is configured to perform a power thresholding to detect a missing PUCCH transmission, and in case of a PUCCH format 2-41, the apparatus is configured to perform a checksum detection, and a mismatch in the embedded checksum indicates the missing of the initial grant. 
     Re the possibility that the apparatus signals HARQ entity capabilities. 
     In accordance with embodiments, the apparatus is configured to signal the capabilities (e.g. by means of a RRC UE Capability exchange message) for the first and second HARQ entities or for the apparatus one or more of
         the number of supported HARQ entities,   the number of available HARQ processes,   the available HARQ soft buffer,   the supported DCI formats,   the supported physical channels,   if a low latency PUCCH is supported.       

     The apparatus may be a BS or a UE. 
     In accordance with embodiments, the wireless system comprises one or more base stations, BS, and one or more user equipments, UEs, a UE being served by one or more BSs or communication directly with one or more other UEs while being in connected mode or idle mode, and the apparatus comprises a base station or a UE. 
     System 
     The present invention provides a wireless communication network, comprising at least one of the inventive UEs and at least one of the inventive base stations. 
     In accordance with embodiments, the receiver and the transmitter comprises one or more of: a mobile terminal, or stationary terminal, or cellular IoT-UE, or an IoT device, or a ground based vehicle, or an aerial vehicle, or a drone, or a moving base station, or road side unit, or a building, or a macro cell base station, or a small cell base station, or a road side unit, or a UE, or a remote radio head, or an AMF, or an SMF, or a core network entity, or a network slice as in the NR or 5G core context, or any transmission/reception point (TRP) enabling an item or a device to communicate using the wireless communication network, the item or device being provided with network connectivity to communicate using the wireless communication network. 
     Accordingly, according to embodiments, a wireless communication network, comprising: one or more base stations, BS, and one or more user equipments, UEs, a UE being served by one or more BSs or communication directly with one or more other UEs while being in connected mode or idle mode, 
     wherein a base station and/or a UE comprises any of the above outlined apparatuses. 
     In accordance with embodiments 
     the UE comprise one or more of
         a mobile terminal, or   stationary terminal, or   a vehicular terminal, or   cellular IoT-UE, or   an IoT device, or   a ground based vehicle, or   an aerial vehicle, or   a drone, or   a moving base station, or   road side unit, or   a building, or   any other item or device provided with network connectivity enabling the item/device to communicate using the wireless communication network, e.g., a sensor or actuator, and       

     the BS comprise one or more of
         a macro cell base station, or   a micro cell base station, or   a small cell base station, or   a central unit of a base station, or   a distributed unit of a base station, or   a road side unit, or   a UE, or   a remote radio head, or   an AMF, or   an SMF, or   a core network entity, or   a network slice as in the NR or 5G core context, or   any transmission/reception point (TRP) enabling an item or a device to communicate using the wireless communication network, the item or device being provided with network connectivity to communicate using the wireless communication network.       

     Methods 
     The present invention provides a method, comprising: 
     receiving one or more data packets from a transmitter in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, and 
     requesting from the transmitter a retransmission for a data packet in case of a non-successful transmission of the data packet, 
     wherein the retransmission comprises providing a first HARQ operation and/or a second HARQ operation, the first and second HARQ operations being different, 
     wherein
         a plurality of Hybrid ARQ, HARQ, entities is provided, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity performing the first HARQ operation, and the second HARQ entity performing the second HARQ operation, or   a Hybrid ARQ, HARQ, entity is provided performing the first HARQ operation and the second HARQ operation, the first and second HARQ operations being different.       

     The present invention further provides a method, comprising: 
     transmitting one or more data packets to a receiver in a wireless communication system, the data packets transmitted over a radio channel of the wireless communication system, 
     receiving from the receiver a request for a retransmission for a data packet in case of a non-successful transmission of the data packet, and 
     wherein the retransmission comprises providing a first HARQ operation and/or a second HARQ operation, the first and second HARQ operations being different, 
     wherein
         a plurality of Hybrid ARQ, HARQ, entities is provided, the plurality of HARQ, entities including at least a first HARQ entity and a second HARQ entity, the first HARQ entity performing the first HARQ operation, and the second HARQ entity performing the second HARQ operation, or   a Hybrid ARQ, HARQ, entity is provided performing the first HARQ operation and the second HARQ operation, the first and second HARQ operations being different.       

     Computer Program Product 
     The present invention provides a computer program product comprising instructions which, when the program is executed by a computer, causes the computer to carry out one or more methods in accordance with the present invention. 
     Thus, in accordance with embodiments of the present invention, synchronous HARQ is introduced, for example for low latency services, like URLLC, in NR. More specifically, in the uplink, scheduling each transmission of the PDCCH leads to an additional delay, and also in the downlink extra complexity is needed which needs to be avoided for URLLC services. Also, feedback bundling, which increases the spectral efficiency and reliability of the feedback channel, has the drawback of providing for additional latency. In case of URLLC services, the feedback is needed as fast as possible and, therefore, in accordance with the inventive approach, dedicated resources are used for the URLLC HARQ feedback. In the downlink, this corresponds to a HARQ indicator channel containing only the acknowledgement/non-acknowledgement message, ACK/NACK, and in the uplink two specific PUCCH resources which are used for the feedback or for the low-latency CSI, LL-CSI. In accordance with the inventive approach, multiple Hybrid ARQ, HARQ, entities, e.g., two or more HARQ entities preforming different HARQ operations, for example asynchronous HARQ for delay non-critical services, like eMBB services, and synchronous HARQ for delay critical services, like URLLC services. 
     In accordance with embodiments, the communication systems configures data flows across multiple layers with QoS flows, Signaling and Radio Bearers, RLC flows, Logical Channels, Transport Channels and Physical Channels. Services may correspond to QoS flows and are mapped to a Radio Bearer. HARQ may be located at the MAC and/or PHY layer and may not be aware about any actual service in the upper layer. The MAC layer may only know the logical channel the packet corresponds to so that a HARQ entity may be selected per Logical Channel. 
     In other words, embodiments of the inventive approach provide for the possibility to simultaneously, i.e., at the same time, support synchronous and asynchronous HARQ operations thereby combining the advantages of the respective operations with respect to the service from which a transmission originates. For example, synchronous HARQ has the advantage that scheduling a retransmission does not require an extra PDCCH, thereby avoiding the consumption of additional time, especially for uplink transmissions and reducing the blind decoding burden. The synchronous HARQ operation uses a dedicated HARQ indicator channel for transmitting the ACK/NACK messages, and a NACK message automatically assigns a predefined resource for the retransmission, dependent on the initial transmission, i.e., no additional time is spent for scheduling resources for the retransmission. For example, a UE may use the synchronous HARQ operation when recognizing that a transmission originates from a latency critical service, like the URLLC service, or a low-complexity service, like the mMTC service, however, at the same time, the UE may also support transmissions from delay non-critical or regular complexity services, like the eMBB service, and for such transmissions, the UE may use the PDCCH for scheduling retransmissions asynchronously. For example, when applying the synchronous HARQ operation, a Stop&amp;Wait HARQ mechanism may be used, while the asynchronous HARQ protocol may be selected and used for delay non-critical services. 
     Additionally, for downlink transmissions, a HARQ protocol may be used which employ regular channel state information feedback for delay non-critical transmissions, while another HARQ protocol using low latency CSI feedback channel may be used in case of latency critical services. These CSI feedbacks may be transmitted using the PUCCH using different formats. 
       FIG. 6  illustrates schematically the layer  2  structure for implementing simultaneous synchronous and asynchronous HARQ operation at the base station or the user equipment in accordance with an embodiment of the present invention. At the MAC layer, a MAC entity is provided which performs the scheduling/priority handling  310  and the multiplexing  312 . The MAC entity further includes a synchronous HARQ entity  314  for a synchronous HARQ operation and an asynchronous HARQ entity  316  for an asynchronous HARQ operation so that dependent on the HARQ to be used either one or both of the HARQ entities  314 ,  316  may be applied or used for a transmission of one or more data packets. In accordance with other embodiments, rather than providing a single MAC entity including the HARQ entities  314 ,  316 , multiple MAC entities may be provided, each including a HARQ entity, as is shown in  FIG. 11 . Additionally, a single HARQ entity may also support a synchronous and asynchronous HARQ operation at the same time, shifting the HARQ processes between the HARQ operation modes dynamically or by re-/configuration, e.g., RRC signaling. 
     Thus, the inventive approach provides network entities and methods supporting simultaneously or at the same time different retransmission protocols or procedures. Although reference is made to two retransmission procedures it is noted that the inventive approach is not limited to such a scenario, rather, more than two retransmission procedures may be supported simultaneously at the network entity. Further, the inventive approach is not limited to asynchronous and synchronous HARQ operations, rather, other retransmission procedures, like ARQ procedures may be implemented. 
     In accordance with embodiments, the HARQ protocols to be used may be semi-statically configured via the RRC protocol. The configuration may set the criteria according to which the UE or gNB chooses which HARQ protocol to use, for example on the basis of the service type, like eMBB, URLLC or mMTC, or on the basis of specific 5QI attributes, like delay or guaranteed bitrate, GBR. 
     In accordance with further embodiments, different HARQ entities may be used for each of the supported HARQ protocols. The HARQ entities may be configured by signaling or may be hard-coded in the standard. The different HARQ entities may use different logical channels, which are defined by a logical channel identity, and may use different physical channels, which are defined by different physical resources. The different physical resources may also use different sub-carrier spacing. 
     The different HARQ entities may use different target Block Error Rates, BLERs, for the different transmissions/retransmissions and may be associated with a different number of HARQ processes. Moreover, a different order of the redundancy versions, RVs, may be applied. 
     In accordance with further embodiments, the DCI signaling may be employed for distinguishing the HARQ entities/protocols. For example, the UE needs to determine for a received grant for a transmission which HARQ entity is to processed or which HARQ protocol is to be applied. This may be accomplished either by using the Radio Network Temporary Identifier, RNTI, or a new, specific DCI format, which may be a compact format. 
     When using RNTI, for example, the UE is configured with a new RNTI, for example via an RRC signaling, and the new RNTI is associated with the HARQ entity/protocol to be used for a transmission so that during the blind decoding process, during which all RNTIs are tested, the UE may determine which HARQ protocol is to be applied. 
     The new DCI format may be used specifically for the delay critical transmissions, and since a synchronous HARQ does not require a HARQ process ID, the new DCI format may be provided which does not include a HARQ process ID. The DCI format, in case of URLLC services, may be referred to as a URLLC DCI format. A DCI format including the HARQ process ID because it relates to an asynchronous HARQ operation, e.g., for an eMBB service, may be referred to as a eMBB DCI format. In accordance with this approach, the UE may test to PDCCH candidates against its eMBB DCI formats and against the URLLC DCI format, so that the embedded checksum indicates which DCI format and, therefore, which HARQ entity/protocol, is to be applied. A DCI for signalling a DL transmission with synchronous HARQ may be referred to as a compact DCI Format 1_2 to be detected by blind decoding. The compact DCI Format 1_2 may include fields identical with DCI Format 1_0 and not include the following fields:
         HARQ process number—4 bits   Downlink assignment index   PDSCH-to-HARQ_feedback timing indicator       

     In accordance with yet further embodiments, dedicated PUCCHs may be used for each HARQ entity/protocol. For example, each HARQ/protocol may receive its dedicated PUCCH for transmitting the feedback or the LL-CSI in the uplink. This allows supporting the low latency for the URLLC HARQ protocol. Since the eMBB HARQ protocol may use bundling techniques, more processing and longer transmission times are needed, translating into a correspondingly longer PUCCH. This, however, is a bottleneck for URLLC HARQ procedures. Therefore, in accordance with the present invention, URLLC HARQ procedures uses a short PUCCH with a single ACK/NACK feedback and/or LL-CSI. 
     In accordance with yet further embodiments, RRC signaling may be used for configuring the number of HARQ processes and the UE capability. In NR and LTE, only a single HARQ protocol is used for the uplink and the downlink, respectively. Hence, configuring the number of HARQ processes for the PDSCH, the PUSCH and PSSCH is sufficient. In accordance with the present invention, the gNB may tell the UE how many HARQ processes are to be used for the synchronous HARQ protocol and the asynchronous HARQ protocol, see  FIG. 6  above indicating at  314  and  316  the respective HARQ processes. The number of available HARQ processes for each protocol may be part of the UE capability which may be signaled to the gNB by the UE. Below an example for a signaling for the PDSCH is shown in which for the asynchronous HARQ operation, see nrofHARQ-ProcessesForPDSCH, the number of HARQ processes for PDSCH is indicated, as well as the number of HARQ processes for PDSCH-URLLC, see nrofHARQ-ProcessesForPDSCH-URLLC. 
     
       
         
           
               
             
               
                   
               
             
            
               
                 PDSCH-ServingCellConfig ::= SEQUENCE { 
               
               
                 codeBlockGroupTransmission SetupRelease {PDSCH- 
               
            
           
           
               
               
            
               
                   
                 CodeBlockGroupTransmission} OPTIONAL xOverhead  ENUMERATED 
               
               
                   
                 { xOh6, xOh12, xOh18 } OPTIONAL 
               
            
           
           
               
            
               
                 nrofHARQ-ProcessesForPDSCH ENUMERATED {n2, n4, n6, n10, n12, n16} 
               
            
           
           
               
               
            
               
                   
                 OPTIONAL 
               
            
           
           
               
            
               
                 nrofHARQ-ProcessesForPDSCH-URLLC ENUMERATED {n2, n4, n6, n10, 
               
            
           
           
               
               
            
               
                   
                 n12, n16} OPTIONAL 
               
            
           
           
               
            
               
                 pucch-Cell ServCellIndex OPTIONAL , -- Cond SCellAddOnly ... } 
               
               
                   
               
            
           
         
       
     
     In accordance with yet further embodiments, a DCI miss detection and rescheduling of retransmissions may be implemented. For example for downlink transmissions, the UE may miss an initial scheduling of the transmission, and in this case, naturally, also the following retransmissions are missed. The gNB may detect the missing PUCCH, namely the missing feedback or the missing LL-SCI, for example, dependent on the indicated PUSCH format. In case the gNB detects the miss of a DCI, the same transmission or the next redundancy version is rescheduled explicitly using a PDCCH at the next opportunity. The gNB, in case of a PUSH format 0-1 may perform a power thresholding so as to detect a missing PUCCH transmission, and in case of a PUCCH format 2-4, it may perform a checksum detection, wherein a mismatch in the embedded checksum indicates the missing of the initial grant. 
     In accordance with embodiments, a base station, gNB, may schedule a UL HARQ retransmission. For example an adaptive retransmission used, e.g., in NR, may be applied and the gNB may schedule an UL resource allocation for the retransmission using regular DCI formats on the PDCCH to indicate a new location and format. Thus, a full signaling of the HARQ control information is provided including, e.g., the process ID, the RV, the NDI. 
     Also an non adaptive and synchronous ARQ retransmission may be scheduled, and, in accordance with embodiments, the gNB has different options to trigger a retransmission by a UE. 
     In accordance with a first embodiment, a Physical Hybrid Indicator Channel, PHICH, may be used that is limited to ACK/NACKs, i.e., includes only the ACK/NACK messages. Once the UE received a NACK the UE retransmits with a fixed format on the same resource, optionally fixed to a predefined sequence of RVs. The signaling of a fast ACK is beneficial, e.g., to stop autonomous retransmissions and in URLLC scenarios retransmissions may be send without waiting for a NACK. 
     In accordance with a second embodiment, a PDCCH with a new Compact DCI format may be implemented so that only limited control information may be send, causing a reduced load when compared to a regular DCI format. For example, there may be no need to send the process ID because the same resources are used as for the initial transmission. 
     For example, for an initial transmission a regular DCI may be used with detailed information, and later, for the retransmissions or for an initial transmission of new data only the compact DCI format is used, e.g., when using a synchronous protocol. 
     Further, the gNB may request a new initial uplink transmission from the UE if no UL ACK/NACK on the first transmission is received, i.e., no ACK, or no NACK or nothing was received. Alternatively the gNB may request a specific redundancy version with compact DCI. 
     Further embodiments for a feedback, like UE feedback for a DL HARQ Retransmission, are now described.  FIG. 12  illustrates details of a UE, like a UE as described above with reference to  FIG. 9  including the antennas ANT R , the signal processor  302   a  and the transceiver  302   b . As is illustrated in  FIG. 12  following the receipt of a transmission, initially, using the reference signals in the transmission, a channel estimation may be made so as to generate a CQI. Also further PMI and RI may be provided. The ACK/NACK message is created only once the data has been processed to see whether decoding is successful or not. 
     Embodiments may provide for a synchronous HARQ a low latency, LL, PUCCH that is send more frequently than a regular PUCCH, e.g., using a smaller transmission time interval. The LL-PUCCH may not support HARQ ACK/NACK bundling as this involves waiting for the receipt and decoding processing of a plurality of data packets. The LL-PUCCH enables the sending of HARQ ACK/NACKs immediately, they may even overtake HARQ ACK/NACKs of an asynchronous HARQ protocol as conventionally ACK/NACK have to be send in a FIFO, first in first out, sequence. 
     Asynchronous HARQ uses the regular PUCCH, and embodiments of the invention allow to multiplex the feedback into a regular PUSCH. If latency is not critical the multiplexing into the PUSCH is beneficial, e.g., a better link adaptation is possible, since PRBs are scheduled, a larger payload is provided, and the like. 
       FIG. 13  illustrates the above concept of using for the feedback LL-PUCCHs in case of synchronous HARQ, and multiplexing the feedback into the regular PUCCH in case of asynchronous HARQ. 
     According to further embodiments, the LL-PUCCH may be employed for transmitting a low latency, LL, CSI, e.g., to support RV selection and adaptive retransmission in case for the initial transmission the channel situation, e.g. estimated by using DM-RS, was not ok, as well as a low latency, LL, HARQ, e.g., to provide faster ACK/NACK compared to slower eMBB decoding. For example, first, a LL-PUCCH is send with a fast CSI feedback based on frontloaded DM-RS of the initial transmission which is faster since it is based on a channel estimation and not on the decoding of the packet. If a fast CSI feedback is not received a new initial transmission may be send, e.g., in case the PDCCH resource allocation and therefore DM-RS are not received. The LL-CSI feedback may be interpreted or understood as an ACK for the PDCCH+DM-RS and/or the data itself. Following the LL-CSI feedback, a LL-PUCCH with the ACK/NACK may be send. The feedback may be combined with one or more additional or incremental CSI feedback, and may use the same or a different PUCCH format as the fast CSI feedback. 
     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 3 configuration, or vehicles being in the idle mode, also referred to as mode 4 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, scheduling the resources in accordance with the aspects described above is advantageous as it allows for a more efficient scheduling of resources for sidelink communication avoiding resource collisions and the like. 
     Some embodiments of the present invention have been described above with reference to a communication system in which the transmitter is a base station serving a user equipment, and in which the receiver is the user equipment served by the base station. However, the present invention is not limited to such embodiments and may also be implemented in a communication system in which the transmitter is a user equipment station, and in which the receiver is the base station serving the user equipment. In accordance with other embodiments, the receiver and the transmitter may both be UEs communicating directly with each other, e.g., via a sidelink interface. 
     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 receiver 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. 
     Although some aspects of the described concept have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or a device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. 
     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. 14  illustrates an example of a computer system  350 . The units or modules as well as the steps of the methods performed by these units may execute on one or more computer systems  350 . The computer system  350  includes one or more processors  352 , like a special purpose or a general purpose digital signal processor. The processor  352  is connected to a communication infrastructure  354 , like a bus or a network. The computer system  350  includes a main memory  356 , e.g., a random access memory (RAM), and a secondary memory  358 , e.g., a hard disk drive and/or a removable storage drive. The secondary memory  358  may allow computer programs or other instructions to be loaded into the computer system  350 . The computer system  350  may further include a communications interface  360  to allow software and data to be transferred between computer system  350  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  362 . 
     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  350 . The computer programs, also referred to as computer control logic, are stored in main memory  356  and/or secondary memory  358 . Computer programs may also be received via the communications interface  360 . The computer program, when executed, enables the computer system  350  to implement the present invention. In particular, the computer program, when executed, enables processor  352  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  350 . Where the disclosure is implemented using software, the software may be stored in a computer program product and loaded into computer system  350  using a removable storage drive, an interface, like communications interface  360 . 
     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 performed by any hardware apparatus. 
     While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations and equivalents as fall within the true spirit and scope of the present invention. 
     LIST OF ACRONYMS AND SYMBOLS 
     V2X Vehicle-to-Everything 
     3GPP Third Generation Partnership Project 
     D2D Device-to-Device 
     BS Base Station 
     eNB Evolved Node B (3G base station) 
     UE User Equipment 
     NR New Radio 
     REFERENCES 
     
         
         [1] RP-180889, Views on NR URLLC work in Rel-16, Huawei, HiSilicon 
         [2] RP-181477, SID on Physical Layer Enhancements for NR URLLC, Huawei, 
       
    
     HiSilicon, Nokia, Nokia Shanghai Bell