Patent Publication Number: US-2023163888-A1

Title: Distance-based hybrid automatic repeat request (harq) location unavailable configuration for group sidelink communication

Description:
CLAIM OF PRIORITY 
     The present application claims the benefit of priority to Provisional Application No. 63/028,348 entitled “Groupcast Sidelink HARQ Feedback With No Location Information”, docket number TPRO 00349 US, filed May 21, 2020, assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety. 
     CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to patent application entitled “HYBRID AUTOMATIC REPEAT REQUEST (HARQ) FEEDBACK MANAGEMENT BASED ON LOCATION INFORMATION AVAILABILITY FOR GROUP SIDELINK COMMUNICATION”, docket number TUTL 00349A PC, and patent application entitled “HYBRID AUTOMATIC REPEAT REQUEST (HARQ) FEEDBACK MANAGEMENT BASED ON LOCATION INFORMATION AVAILABILITY AND SIDELINK SIGNAL QUALITY FOR GROUP SIDELINK COMMUNICATION”, docket number TUTL 00349C PC, both filed concurrently with this application and incorporated by reference in their entirety herein. 
    
    
     FIELD 
     This invention generally relates to wireless communications and more particularly to distance-based hybrid automatic repeat request (HARQ) location unavailable configuration for group sidelink communication 
     BACKGROUND 
     Many wireless communication systems that employ several base stations that provide wireless service to user equipment (UE) devices enable sidelink communication between two or more UE devices where the UE devices can communicate directly with other UE devices. Such sidelink communications sometimes include one UE device (group leader UE device) that transmits the same data to multiple UE devices in a group. Different transmission techniques often referred to as cast types can be used to transmit the same data to multiple UE devices. Cast types include at least unicast, groupcast and broadcast. A unicast transmission can only be received by the single UE device that is the intended recipient of the data. Accordingly, multiple transmissions are required to send the same data to multiple UE devices using unicast. A broadcast transmission can typically be received by all UE devices within range of the transmission. A groupcast transmission can only be received by the UE devices that are members of a group. Accordingly, for example, the group leader UE device can transmit the same data in a single transmission using groupcast to two or more UE devices in the group or can send the same data in multiple unicast transmissions to the UE devices. 
     SUMMARY 
     A transmitting user equipment (UE) device sends a location unavailable configuration to a receiving UE device indicating whether hybrid automatic repeat request (HARQ) messages should be sent by the receiving UE device for distance-based HARQ when location information is unavailable to the receiving UE device. The receiving UE device is one of a group of UE devices receiving a groupcast data transmission from the transmitting UE device where the groupcast data transmission comprises a distance-based HARQ feedback configuration. After detecting that HARQ feedback should be provided, the receiving UE determines that location information is unavailable. The HARQ feedback is provided in accordance with the location unavailable configuration. A HARQ message is transmitted where the location unavailable configuration requires transmission of HARQ when location information is unavailable. The receiving UE refrains from transmitting a HARQ message where the location unavailable configuration requires no transmission of HARQ when location information is unavailable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of an example of a communication system including a first user equipment (UE) device, a second UE device, a third UE device, a fourth UE device, and two base stations. 
         FIG.  2    is a block diagram of an example of a communication device suitable for use as each of the base stations. 
         FIG.  3    is a block diagram of an example of a UE device suitable for use as each of the UE devices. 
         FIG.  4    is a message flow diagram for an example where a transmitting UE device provides a location unavailable configuration to a receiving UE device. 
         FIG.  5    is a flow chart of an example of a method of managing groupcast feedback based on location information availability. 
         FIG.  6    is a flow chart of an example of a method of managing groupcast feedback based on location information availability. 
     
    
    
     DETAILED DESCRIPTION 
     As discussed above, different cast types can be used for communication between UE devices. Although UE device groups may be formed and used in different situations and environments, one scenario where grouping UE devices is particularly useful includes vehicle platoons where vehicles dynamically form a platoon while traveling together. All the vehicles in the platoon obtain information from the leading vehicle to manage the platoon. In some implementations, the information facilitates travel of the vehicles in the same direction in a coordinated manner and allows the vehicles to drive closer than in normal situations where there is no communication between the vehicles. Vehicles of the same platoon are involved in sharing the necessary information required to support the platoon operations where the information may include, for example, the distance between vehicles, relative speeds, and updates from roadside units (RSUs). Similar requirements also apply to the Extended Sensor use case where UE devices exchange data gathered through local sensors or live video data among vehicles, RSUs, pedestrian devices, and V2X application servers. Groupcast techniques allow efficient transmission of the information from one UE device, such as the platoon leader, to the other UE device members of the group. 
     In accordance with revisions of 3GPP communication specifications, sidelink communications between a transmitting UE device and receiving UE device(s) are managed with feedback messaging. In order to achieve reliable communications, for example, both unicast and groupcast communications support hybrid automatic repeat request (HARQ) feedback over sidelink in order for the transmitting UE device to determine if retransmissions are needed and if the modulation code scheme (MCS) needs to be relaxed to provide a more robust retransmission to reach the receiving peer UE device. With unicast transmissions, HARQ feedback for both acknowledgement (ACK) and negative acknowledgement (NACK) are supported and addressed to a single peer UE device. With groupcast transmissions, however, the transmitting UE device configures HARQ feedback which may include ACK/NACK feedback or only NACK feedback. The transmitting UE device of the groupcast transmission my receive HARQ feedback from multiple peer UE devices on the Physical Sidelink Feedback Channel (PSFCH). In order to save HARQ feedback resources on the PSFCH, the feedback for groupcast may be configured by the transmitting UE device for two general configurations. For a first configuration, the receiving UE device transmits HARQ-NACK on PSFCH if it fails to decode the corresponding transport block (TB) after decoding the associated PSCCH. With the first configuration, the receiving UE device transmits no signal on PSFCH otherwise. With a second configuration, the receiving UE device transmits HARQ-ACK on PSFCH if it successfully decodes the corresponding TB and it transmits HARQ-NACK on PSFCH if it does not successfully decode the corresponding TB after decoding the associated PSCCH targeting the receiving UE device. 
     More specifically, when the transmitting UE device transmits data to group member receiving UE devices, the packet consists of both the traffic data and the header including Sidelink Control Info (SCI). The SCI is encoded with a more robust modulation coding scheme (MCS) than the data so that the receiving UE devices will more easily receive this portion of the signal. The traffic portion of the packet is encoded with a relatively less robust MCS to ensure higher data throughput. Therefore, if the receiving UE device only successfully receives the control signal portion (SCI) without successfully receiving the data portion, the receiving UE device sends a “NACK” to the transmitting UE device. For the option where both ACK and NACK are required for feedback, the receiving UE device is required to send ACK when the data portion is received successfully. When the receiving UE device cannot decode the SCI the receiving UE device does not send either ACK nor NACK. Such a situation corresponds to the HARQ DTX case where the transmitting UE device determines that the receiving UE device did not receive the packet if no feedback is received within a HARQ feedback timer. 
     In addition, the transmitting UE device may enable distance-based HARQ feedback. With distance-based HARQ feedback, the receiving UE device sends HARQ feedback only if the receiving UE device is within a configured communication range away from the transmitting UE device. Typically, distance-based HARQ requires NACK only feedback. For conventional systems, the transmitting UE device indicates its current Zone ID and a communication range requirement in the Sidelink Control Info (SCI). The receiving UE device calculates the distance from the current location of the receiving UE device to the center of that particular Zone ID indicated in the SCI received from the transmitting UE device. If the distance is less than the communication range requirement, the receiving UE device sends the NACK for HARQ feedback. Therefore, when distance-based HARQ is configured, the receiving UE devices that are far away from the transmitting UE device do not send HARQ feedback. Such a configuration not only reduces the use of PSFCH resources, but it prevents the transmitting UE device from making unnecessary retransmissions where a NACK is received since the retransmission will likely not be successfully received by those far away receiving UE devices. 
     In some situations, location information is not available to a UE device. Typically, such a situation is temporary rather than an issue with the capability of the UE device. In most situations where the transmitting UE device does not have its own location information, the transmitting UE device will not configure distance-based HARQ feedback of the receiving UE devices of the group. 
     An issue arises when the transmitting UE device has location information and configures distance-based HARQ feedback for groupcast transmissions, but location information is unavailable to one or more of the receiving UE devices. In this case, the receiving UE device cannot determine if it is within communication range and whether HARQ feedback should be sent. 
     One possible mechanism to address this problem is to require any receiving UE device that does not have location information to refrain from sending HARQ feedback if distance-based HARQ feedback is configured. Such a technique has the benefit that PSFCH resources can be saved for other UE devices and useless retransmissions may be avoided. In some situations, however, the receiving UE device may be well within the communication range but HARQ feedback cannot be sent. An example of such a situation occurs when the receiving UE device passes through a coverage hole. As a result, the service performance may be unnecessarily severely degraded by restricting HARQ feedback even though the receiving UE device is within communication range of the transmitting UE device. 
     Another possible way to address the problem is to require that receiving UE devices to always send HARQ even when they do not have location information and distance-based HARQ feedback is configured. Such a technique is of course beneficial from the preserving the QoS, especially for high priority service. The technique, however, may result in increased use of PSFCH resources and unnecessary retransmissions, especially where the receiving UE devices are outside the communication range and the data portion of the retransmissions is not likely to be received successfully. Such situations could render the HARQ feedback system unusable. 
     Therefore, distance-based HARQ feedback management is needed for efficient transmission of HARQ feedback when location information is unavailable to a receiving UE device. For the distance-based HARQ feedback management techniques discussed herein, the transmitting UE device configures the receiving UE device to either transmit HARQ messages or refrain from transmitting HARQ messages when location information is unavailable to the receiving UE device. For the examples herein, the transmitting device sends a location unavailable configuration to the receiving UE devices to configure the receiving UE devices. In one example, the transmitting UE device determines whether HARQ should be sent when location information is unavailable. In another examples, the base station and/or network makes the determination. In some situations, the determination is be made collaboratively by the transmitting UE device and the base station and/or the network. 
       FIG.  1    is a block diagram of an example of a communication system  100  including a first user equipment (UE) device  101 , a second UE device  102 , a third UE device  103 , a fourth UE device  104 , and two base stations  106 ,  108 . Although the techniques discussed herein may be applied to various types of systems and communication specifications, the devices of the example operate in accordance with at least one revision of a 3GPP New Radio (NR) V2X communication specification. The techniques discussed herein, therefore, may be adopted by one or more future revisions of communication specifications although the techniques may be applied to other communication specifications where sidelink or D2D is employed. More specifically the techniques may be applied to current and future releases of 3GPP NR specifications. For example, the techniques may also be applied to 3GPP NR (Rel-17). For the example, the UE devices  101 - 104  may be any type of device that can receive signals from, and transmit signals to, base stations and other UE devices. The UE devices operate in the communication system that includes a plurality of base stations that each provide wireless service within a service area. For the example of  FIG.  1   , the first UE device  101  is served by a first base station  106  and the other UE device  102 - 104  are served by either the first base station  106  or a second base station  108  and may transition between base stations in accordance with known handover techniques. Each of the UE devices  101 - 104 , therefore, may be served by a different base station even though two or more UE devices are communicating with each other using a sidelink connection. 
     For the example, the first UE device  101  is a transmitting UE device and the other UE devices  102 - 104  are receiving UE devices and are members of a group. The group data for the group may be transmitted in groupcast transmissions from the transmitting UE device  101 . In some situations, the group data may be transmitted over a unicast communication link to a member of the group. For the example, a groupcast transmission  110  including groupcast data is transmitted from the first UE device (transmitting UE device)  101  to the second UE device  102  and the third UE device  103 . The group data is also sent over a unicast communication link to the fourth UE device  104 . The first UE device  101 , therefore, may also be referred to as the transmitting UE device and source UE device, herein. Although the example includes three UE devices  102 ,  103 ,  104  in the group, the group may include any number of devices. 
     For the example of  FIG.  1   , the fourth UE device  104  receives the group data in a unicast transmission  111  over unicast communication link and therefore provides HARQ feedback in accordance with the unicast connection. The second UE device  102  and the third UE device  103  are sent the group data over a groupcast data transmission specifying a distance-based HARQ feedback. For the example, the third UE device  103  is in a situation where distance based HARQ is invoked. More specifically, location information is available to the third UE device  103 , the third UE device determines it is within the specified communication range, and the third UE device is unable to successfully receive the data portion of the groupcast data transmission  110 . As a result, the third UE device  103  transmits a distance-based HARQ NACK message  114  in accordance with the distance-based HARQ configuration established by the transmitting UE device  101 . The HARQ messages  112 ,  114  are transmitted over the PSFCH in accordance with known techniques. 
     The second UE device  102 , however, does not successfully receive the data portion of the groupcast data transmission but does not have location information for the example. With conventional systems, there is no established technique for dealing with such a situation. For the examples herein, however, the transmitting UE device  101  provides a location-unavailable configuration  116  to the receiving UE devices indicating how a receiving UE device should handle distance-based HARQ feedback when location information is not unavailable to the receiving UE device. After receiving the SCI in the groupcast data transmission  110  and determining that the data portion could not be successfully received, the second UE device  102  determines whether a HARQ message should be transmitted based on the location-unavailable configuration  116 . If the location-unavailable configuration  116  indicates HARQ feedback should be provided when location information is unavailable, the second UE device  102  transmits a HARQ message  118 . Otherwise, no HARQ message is transmitted. The arrow representing the HARQ message is  FIG.  1    is shown a dashed line to indicate that the HARQ message  118  is transmitted in accordance with the location-unavailable configuration  116  and, therefore, is not transmitted in some circumstances. For the examples herein, if the receiving UE device does not receive the location-unavailable configuration or if the location-unavailable configuration is not sent, the second UE device  102  transmits a HARQ message  118 . In other situations, the default can be set such that no HARQ message is sent where the location-unavailable configuration is not sent. 
       FIG.  2    is a block diagram of an example of a base station  200  suitable for use as each of the base stations  106 ,  108 . The base station  200  includes a controller  204 , transmitter  206 , and receiver  208 , as well as other electronics, hardware, and code. The base station  200  is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to the base stations  102 ,  104  may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices. The base station  200  may be a fixed device or apparatus that is installed at a particular location at the time of system deployment. Examples of such equipment include fixed base stations or fixed transceiver stations. Although the base station may be referred to by different terms, the base station is typically referred to as a gNodeB or gNB when operating in accordance with one or more communication specifications of the 3GPP V2X operation. In some situations, the base station  200  may be mobile equipment that is temporarily installed at a particular location. Some examples of such equipment include mobile transceiver stations that may include power generating equipment such as electric generators, solar panels, and/or batteries. Larger and heavier versions of such equipment may be transported by trailer. In still other situations, the base station  200  may be a portable device that is not fixed to any particular location. 
     The controller  204  includes any combination of hardware, software, and/or firmware for executing the functions described herein as well as facilitating the overall functionality of the base station  200 . An example of a suitable controller  204  includes code running on a microprocessor or processor arrangement connected to memory. The transmitter  206  includes electronics configured to transmit wireless signals. In some situations, the transmitter  206  may include multiple transmitters. The receiver  208  includes electronics configured to receive wireless signals. In some situations, the receiver  208  may include multiple receivers. The receiver  208  and transmitter  206  receive and transmit signals, respectively, through an antenna  210 . The antenna  210  may include separate transmit and receive antennas. In some circumstances, the antenna  210  may include multiple transmit and receive antennas. 
     The transmitter  206  and receiver  208  in the example of  FIG.  2    perform radio frequency (RF) processing including modulation and demodulation. The receiver  208 , therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter  206  may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the base station functions. The required components may depend on the particular functionality required by the base station. 
     The transmitter  206  includes a modulator (not shown), and the receiver  208  includes a demodulator (not shown). The modulator modulates the signals to be transmitted as part of the downlink signals and can apply any one of a plurality of modulation orders. The demodulator demodulates any uplink signals received at the base station  200  in accordance with one of a plurality of modulation orders. 
     The base station  200  includes a communication interface  212  for transmitting and receiving messages with other base stations. The communication interface  212  may be connected to a backhaul or network enabling communication with other base stations. In some situations, the link between base stations may include at least some wireless portions. The communication interface  212 , therefore, may include wireless communication functionality and may utilize some of the components of the transmitter  206  and/or receiver  208 . 
       FIG.  3    is a block diagram of an example of a UE device  300  suitable for use as each of the UE devices  101 - 104 . In some examples, the UE device  300  is any wireless communication device such as a mobile phone, a transceiver modem, a personal digital assistant (PDA), a tablet, or a smartphone. In other examples, the UE device  300  is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. The UE device  300 , therefore is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to UE device  300  may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices. 
     The UE device  300  includes at least a controller  302 , a transmitter  304  and a receiver  306 . The controller  302  includes any combination of hardware, software, and/or firmware for executing the functions described herein as well as facilitating the overall functionality of a communication device. An example of a suitable controller  302  includes code running on a microprocessor or processor arrangement connected to memory. The transmitter  304  includes electronics configured to transmit wireless signals. In some situations, the transmitter  304  may include multiple transmitters. The receiver  306  includes electronics configured to receive wireless signals. In some situations, the receiver  306  may include multiple receivers. The receiver  304  and transmitter  306  receive and transmit signals, respectively, through antenna  308 . The antenna  308  may include separate transmit and receive antennas. In some circumstances, the antenna  308  may include multiple transmit and receive antennas. 
     The transmitter  304  and receiver  306  in the example of  FIG.  3    perform radio frequency (RF) processing including modulation and demodulation. The receiver  304 , therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter  306  may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the communication device functions. The required components may depend on the particular functionality required by the communication device. 
     The transmitter  306  includes a modulator (not shown), and the receiver  304  includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted as part of the uplink signals. The demodulator demodulates the downlink signals in accordance with one of a plurality of modulation orders. 
       FIG.  4    is a message flow diagram  400  for an example where a transmitting UE device  101  provides a location unavailable configuration  116  to a receiving UE device  102 . 
     At transmission  402 , the transmitting UE device  101  sends a location unavailable configuration message to the receiving UE device  102 . Transmission  402 , therefore, is an example of the location unavailable configuration transmission  116  discussed with reference to  FIG.  1   . The location unavailable configuration message provides the configuration information to the receiving UE device to configure the receiving UE device  102  for HARQ messages for distance-based HARQ when location information is unavailable to the receiving UE device  102 . Accordingly, the configuration indicates whether the receiving UE device transmits a HARQ message for data transmitted with a distance-based HARQ when the receiving UE device  102  does not know its location. For the example, the location unavailable configuration message is a Medium Access Control (MAC) Control Element (CE) in the Sidelink Control Channel (SCCH) transmitted in a groupcast transmission. In some cases, the location unavailable configuration message may be a PC5-S (upper layer message) delivered in the SCCH. Furthermore, the location unavailable configuration message may be transmitted as a 1-bit indicator in the SCI. Other techniques can be used to transmit the location unavailable configuration. 
     At event  404 , a groupcast transmission is transmitted from the transmitting UE device  101  to the receiving UE devices of the group. At transmission  406 , the transmitting UE device  101  sends a distance-based HARQ configuration to the receiving UE device  102  to configure the receiving UE device for distance-based HARQ. At transmission  408 , a groupcast transmission is sent by the transmitting UE device to the members of the group. The groupcast transmission includes data and the associated SCI. For the examples herein, the distance-based HARQ configuration is sent in the header of a groupcast data transmission. More specifically, the HARQ configuration is sent in the SCI of the groupcast transmission. As discussed above, the SCI is encoded with more robust modulation coding scheme (MCS) than the data so that the receiving UE devices will receive this portion of the signal with a much greater success rate. The traffic portion of the packet might be encoded with a lesser robust MCS to ensure higher data throughput. Accordingly, for the examples herein, transmission  406  and transmission  408  are part of the same transmission at event  404 . The two transmissions  406 ,  408  are shown as separate arrows in the figures to illustrate that the SCI can be successfully received while the data may not be successfully received in some situations. For the examples, the SCI portion of transmission  406  is successfully received and the data of transmission  408  is not successfully received by the receiving UE device  102 . In some situations, information related to the HARQ configuration is transmitted over multiple channels. For example, in at least one revision of the NR V2X communication specification, the SCI is sent in two stages where a first part is carried by the physical channel PSCCH and the second part is carried in PSSCH. As specified in Rel-16, one of the fields in the first stage SCI in PSCCH indicates which 2nd-stage SCI (format A or B) is used and a second stage SCI is in the PSSCH indicates either format-2A for HARQ ACK/NACK and format-2B for NACK-only. The zone ID and communication range requirement is sent in the 2B. Accordingly, the transmitting UE device could implicitly request the receiving UE device to send a distance-based HARQ by indicating the groupcast type in the SCI. 
     At event  410 , the receiving UE device  102  determines data in the transmission  408  was not successfully received. After successfully receiving the SCI portion of the groupcast transmission, the receiving UE device  102  unsuccessfully attempts to receive the data portion. 
     At event  412 , the receiving UE device  102  determines that location information is unavailable. For example, the receiving UE device  102  may determine that GPS service is unavailable where GPS provides the information required for the UE device to determine UE device location. In some situations, the location determination is performed at a location server at the base station with assistance from the UE device. If the UE device determines that the base station cannot provide the location information where this technique is used, the receiving UE device determines that location information is unavailable. 
     At event  414 , the receiving UE device applies the location unavailable configuration previously received from the transmitting UE device  101  to determine if a HARQ message should be sent. If it is determined that the HARQ message should be sent, a HARQ message is sent at transmission  416 . Otherwise, no HARQ message is sent. The arrow representing the HARQ message is shown with a dashed line in  FIG.  4    to indicate that the message is not sent where the configuration does not include HARQ feedback messages for distance-based HARQ when location information is unavailable. 
       FIG.  5    is a flow chart of an example of a method  500  of managing groupcast feedback based on location information availability. For the example, the method is performed by a UE device operating in a NR V2X system such as the system  100  described above. Accordingly, the method may be performed by the second UE device (receiving UE device)  102  when part of a group of the first UE device (transmitting UE device)  101 . 
     At step  501 , a location unavailable configuration message is received from the transmitting UE device. As discussed above, the location unavailable configuration message provides the configuration information to the receiving UE device to configure the receiving UE device  102  for HARQ messages for distance-based HARQ when location information is unavailable to the receiving UE device  102 . Accordingly, the configuration indicates whether the receiving UE device transmits a HARQ message for data transmitted with a distance-based HARQ when the receiving UE device  102  does not know its location. For the example, the location unavailable configuration message is a Medium Access Control (MAC) Control Element (CE) in the Sidelink Control Channel (SCCH) transmitted in a groupcast transmission. In some cases, the location unavailable configuration message may be a PC5-S (upper layer message) delivered in the SCCH. Furthermore, the location unavailable configuration message may be transmitted as a 1-bit indicator in the SCI. Other techniques can be used to transmit the location unavailable configuration. 
     At step  502 , a groupcast data transmission with distance-based HARQ configuration is received. For the example, at least the SCI portion is successfully received. The data portion may not be successfully received at step  502 . 
     At step  504 , it is determined whether the data portion of the groupcast data transmission is successfully received. In accordance with known techniques, the receiving UE device  102  evaluates the information in the transmission to determine if the data has been successfully received. If the data is successfully received, the method returns to step  502  for reception of the next transmission. Otherwise, the method proceeds to step  506 . 
     At step  506 , it is determined whether location information is available. If the location of the receiving UE device  102  is known or can be determined, the method continues at step  508 . Otherwise, the method proceeds to step  510 . 
     At step  508 , it is determined whether the receiving UE device  102  is within the distance range for sending HARQ feedback. The distance based on the criteria specified by the transmitting UE device is calculated and evaluated to determine if HARQ feedback is required. If the receiving UE device is not within the distance range, the method returns to step  502  to receive the next transmission without sending HARQ feedback. Otherwise, the HARQ feedback is transmitted at step  512 . As discussed above, distance-based HARQ feedback includes only NACK for the example. Accordingly, the receiving UE device  102  sends a NACK indicating that the data in the groupcast transmission was not successfully received before returning to step  502 . 
     At step  510 , the receiving UE device determines whether the location unavailable configuration requires transmission of HARQ feedback when location is not available. If HARQ feedback is required by the configuration, the method proceeds to step  512  where a HARQ message is transmitted. Otherwise, the method continues at step  514  where the receiving UE device refrains from sending HARQ feedback. For the example, the method returns to step  502  where a new groupcast message is received. In some situations, the method returns to step  501  to receive a new location unavailable configuration before receiving the next groupcast message at step  502 . 
       FIG.  6    is a flow chart of an example of a method  600  of managing groupcast feedback based on location information availability. For the example, the method is performed by a UE device operating in a NR V2X system such as the system  100  described above. Accordingly, the method may be performed by the first UE device (transmitting UE device)  101  when transmitting groupcast transmission to a group of UE devices including the second UE device (receiving UE device)  102 . 
     At step  602 , it is determined whether distance-based HARQ will be used for groupcast messages. The transmitting UE device evaluates factors such as the QoS, number of UE devices in the group, and the available PSFCH resources. If it is determined that distance-based HARQ feedback should be used, the method continues at step  604 . Otherwise, the method proceeds to step  606  where groupcast data is transmitted in a groupcast transmission with a groupcast HARQ not based on distance configuration. 
     At step  604 , the location unavailable configuration is determined. For the example, the transmitting UE device  101  evaluates factors such as the QoS, number of UE devices in the group, and the available PSFCH resources to determine whether a receiving UE device should transmit HARQ messages when location information is unavailable. In some situations, the determination on whether HARQ feedback should be used by a receiving UE device that does not have location information is at least partially performed by a base station or the network. Accordingly, the transmitting UE device  101  may provide information to the serving base station and receive instructions on whether HARQ feedback should be used when location information is unavailable. Also, the base station may provide criteria or information that assists the transmitting UE device in determining the location unavailable configuration. 
     At step  608 , the location unavailable configuration is transmitted to the receiving UE devices. As discussed above, the location unavailable configuration message provides the configuration information to the receiving UE devices to configure the receiving UE devices for HARQ messages for distance-based HARQ when location information is unavailable to the receiving UE device  102 . Accordingly, the configuration indicates whether the receiving UE device transmits a HARQ message for data transmitted with a distance-based HARQ when the receiving UE device  102  does not know its location. For the example, the location unavailable configuration message is a Medium Access Control (MAC) Control Element (CE) in the Sidelink Control Channel (SCCH) transmitted in a groupcast transmission. In some cases, the location unavailable configuration message may be a PC5-S (upper layer message) delivered in the SCCH. Furthermore, the location unavailable configuration message may be transmitted as a 1-bit indicator in the SCI. Other techniques can be used to transmit the location unavailable configuration. 
     At step  610 , a groupcast data transmission with distance-based HARQ configuration is transmitted to a group of UE device including the second UE device (receiving UE device  102 . The groupcast data transmission includes distance-based HARQ feedback configuration. 
     At step  612 , it is determined whether the groupcast transmissions to the UE devices should continue use distance-based HARQ or if the HARQ feedback should be switched to HARQ feedback that is not based on distance. The transmitting UE device evaluates factors such as the QoS, number of UE devices in the group, and the available PSFCH resources. If it is determined that distance-based HARQ feedback should continue to be used, the method continues at step  614 . Otherwise, the method proceeds to step  606  where the next groupcast transmission uses HARQ feedback that is not based on distance. 
     At step  614 , it is determined whether a new location unavailable configuration should be used for groupcast transmissions using distance-based HARQ. The transmitting UE device  101  evaluates factors such the QoS required for the receiving UE device, available resources and the number of UE devices in the group to determine if the configuration should be changed from the previous transmission. If no change in configuration is required, the method returns to step  610  where the transmitting UE device  101  transmits the next groupcast transmission. If configuration is change is required, the method returns to step  604  where the new configuration is determined. For the example of  FIG.  6   , therefore, a new location unavailable configuration is transmitted only where the configuration has changed from the previous transmission. In some situations, however, the location unavailable configuration is transmitted with each groupcast transmission. Other techniques may also be used. 
     Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.