Group feedback techniques in wireless systems

1. A method for wireless communications at a network device, comprising:

transmitting, to a first user equipment (UE) of a plurality of UEs in communication with the network device, a radio resource control (RRC) configuration message indicating a first location within a bitmap for feedback for the first UE, the feedback associated with grant-free uplink transmissions for the first UE;

monitoring a set of time-frequency resources for one or more grant-free uplink transmissions from the plurality of UEs in communication with the network device;

generating a group feedback message for the plurality of UEs, wherein the group feedback message comprises an indication of whether a respective grant-free uplink transmission was received from each UE of the plurality of UEs based at least in part on the monitoring, wherein generating the group feedback message comprises generating the bitmap that indicates feedback for each UE of the plurality of UEs, wherein the bitmap is a first type of feedback bitmap of multiple types of feedback bitmaps, and wherein the first location within the bitmap includes feedback for the first UE for the respective grant-free uplink transmission in accordance with the RRC configuration message; and

transmitting, to the plurality of UEs, the group feedback message comprising the feedback bitmap indicating the feedback for each UE of the plurality of UEs.

2. The method of claim 1 , wherein transmitting the group feedback message comprises:

transmitting a downlink shared channel that comprises the group feedback message.

3. The method of claim 2 , further comprising:

transmitting a control message to the plurality of UEs, the control message indicating a set of transmission resources for the downlink shared channel;

transmitting downlink control information (DCI) that schedules transmission of the group feedback message via the downlink shared channel; and

scrambling the DCI using a mask common to the plurality of UEs or associated with a cell identifier (ID).

4. The method of claim 1 ,

wherein each location of the bitmap corresponds to a respective UE of the plurality of UEs or multiple UEs of the plurality of UEs, wherein the first location of the bitmap is configured for the first UE based at least in part on a UE identifier (ID) for the first UE.

5. The method of claim 4 , wherein the UE ID comprises a cell radio network temporary identifier (C-RNTI) or a configured scheduling radio network temporary identifier (CS-RNTI).

6. The method of claim 4 , further comprising:

receiving a grant-free uplink shared channel transmission from a second UE of the plurality of UEs based at least in part on the monitoring; and

determining a second location within the bitmap for feedback for the second UE based at least in part on a characteristic of the grant-free uplink shared channel transmission.

7. The method of claim 6 , further comprising:

determining the second location within the bitmap based at least in part on a frequency allocation for the grant-free uplink shared channel transmission, a time allocation for the grant-free uplink shared channel transmission, a bandwidth part (BWP) associated with the grant-free uplink shared channel transmission, a transmission signature of the grant-free uplink shared channel transmission, a second UE ID of the second UE, or any combination thereof.

8. The method of claim 4 , further comprising:

determining that grant-free uplink shared channel transmission was not received over the set of time-frequency resources from a second UE of the plurality of UEs based at least in part on the monitoring;

transmitting a negative acknowledgment (NACK) indication to the second UE in the bitmap; and

receiving a retransmission from the second UE over a second set of time-frequency resources different from the set of time-frequency resources in response to the NACK indication, wherein the second set of time-frequency resources is based at least in part on a location of the NACK indication within the bitmap.

9. The method of claim 1 , wherein a second bitmap comprises a negative ACK (NACK) bitmap that indicates NACK feedback information for each of the plurality of UEs.

10. The method of claim 1 , further comprising:

monitoring for the one or more grant-free uplink transmissions from the first UE of the plurality of UEs; and

transmitting the group feedback message to the first UE, wherein the group feedback message comprises the bitmap that indicates feedback for each of the one or more grant-free uplink transmissions.

11. The method of claim 1 , wherein generating the group feedback message comprises:

generating a hash-based set membership operation that indicates feedback information for each UE of the plurality of UEs, wherein the hash-based set membership operation comprises a vector of a set of hashes for the plurality of UEs.

12. The method of claim 1 , wherein transmitting the group feedback message comprises:

transmitting the group feedback message according to a hopping scheme, wherein the hopping scheme is a time hopping scheme or a frequency hopping scheme.

13. A method for wireless communications at a user equipment (UE), comprising:

receiving, from a network device, a radio resource control (RRC) configuration message indicating a first location within a bitmap for feedback for the UE, the feedback associated with grant-free uplink transmissions for the UE;

transmitting one or more grant-free uplink transmissions to the network device via a set of time-frequency resources for grant-free transmissions; and

monitoring for a group feedback message from the network device in response to the one or more grant-free uplink transmissions, wherein the group feedback message comprises an indication of whether a respective grant-free uplink transmission was received from each of a plurality of UEs including the UE, wherein the indication comprises the bitmap that indicates feedback for each UE of the plurality of UEs, wherein the bitmap is a first type of feedback bitmap of multiple types of feedback bitmaps, and wherein the first location within the bitmap includes feedback for the UE for the respective grant-free uplink transmission in accordance with the RRC configuration message.

14. The method of claim 13 , wherein monitoring for the group feedback message comprises:

receiving a downlink shared channel that comprises the group feedback message.

15. The method of claim 13 , wherein monitoring for the group feedback message comprises:

receiving the group feedback message, wherein the bitmap indicates feedback information for each UE of the plurality of UEs, wherein each location of the bitmap corresponds to a respective UE of the plurality of UEs or multiple UEs of the plurality of UEs;

and

determining a location of the bitmap configured for the UE based at least in part on a UE ID for the UE.

16. The method of claim 15 , wherein the UE ID comprises a cell radio network temporary identifier (C-RNTI) or a configured scheduling radio network temporary identifier (CS-RNTI).

17. The method of claim 15 , further comprising:

transmitting the one or more grant-free uplink transmissions via an uplink shared channel; and

determining the location within the bitmap based at least in part on a frequency allocation for the uplink shared channel, a time allocation for the uplink shared channel, a bandwidth part (BWP) associated with the uplink shared channel, a transmission signature of the uplink shared channel, the UE ID, or any combination thereof.

18. The method of claim 15 , further comprising:

receiving a negative acknowledgment (NACK) indication from the network device in the bitmap; and

transmitting a first retransmission of the one or more grant-free uplink transmissions to the network device over the set of time-frequency resources in response to the NACK indication.

19. The method of claim 18 , further comprising:

transmitting a second retransmission of the one or more grant-free uplink transmissions to the network device over a second set of time-frequency resources different from the set of time-frequency resources in response to the NACK indication, wherein the second set of time-frequency resources is based at least in part on the location of the NACK indication within the bitmap.

20. The method of claim 13 , wherein a second bitmap comprises a negative ACK (NACK) bitmap that indicates NACK feedback information for the plurality of UEs.

21. The method of claim 13 , wherein monitoring for the group feedback message comprises:

receiving a downlink shared channel that comprises the group feedback message;

receiving a control message from the network device, the control message indicating a set of resources for the downlink shared channel; and

receiving downlink control information (DCI) that schedules transmission of the group feedback message via the downlink shared channel, wherein the DCI is scrambled using a mask common to the plurality of UEs or associated with a cell identifier (ID).

22. The method of claim 21 , wherein the DCI schedules transmission of a data transmission via the downlink shared channel.

23. The method of claim 14 , further comprising:

receiving downlink control information (DCI) that schedules transmission of the group feedback message via the downlink shared channel, wherein the DCI is scrambled using a mask common to the plurality of UEs or associated with a cell identifier (ID).

24. The method of claim 13 , wherein monitoring for the group feedback message comprises:

receiving the group feedback message from the network device, wherein the group feedback message comprises the bitmap that indicates feedback for each of the one or more grant-free uplink transmissions.

25. The method of claim 13 , wherein monitoring for the group feedback message comprises:

receiving the group feedback message comprising a hash-based set membership operation that indicates feedback information for each UE of the plurality of UEs, wherein the hash-based set membership operation comprises a vector of a set of hashes for the plurality of UEs, wherein the feedback information for the UE of the plurality of UEs is based at least in part on a hash of the vector that corresponds to the UE.

26. The method of claim 13 , wherein monitoring for the group feedback message comprises:

receiving the group feedback message according to a hopping scheme, wherein the hopping scheme is a time hopping scheme or a frequency hopping scheme.

27. An apparatus for wireless communications at a network device, comprising:

one or more processors;

one or more memories coupled with the one or more processors; and

instructions stored in the one or more memories and executable by the one or more processors to cause the apparatus to:

transmit, to a first user equipment (UE) of a plurality of UEs in communication with the network device, a radio resource control (RRC) configuration message indicating a first location within a bitmap for feedback for the first UE, the feedback associated with grant-free uplink transmissions for the first UE;

monitor a set of time-frequency resources for one or more grant-free uplink transmissions from the plurality of UEs in communication with the network device;

generate a group feedback message for the plurality of UEs, wherein the group feedback message comprises an indication of whether a respective grant-free uplink transmission was received from each UE of the plurality of UEs based at least in part on the monitoring, wherein generating the group feedback message comprises generating the bitmap that indicates feedback for each UE of the plurality of UEs, wherein the bitmap is a first type of feedback bitmap of multiple types of feedback bitmaps, and wherein the first location within the bitmap includes feedback for the first UE for the respective grant-free uplink transmission in accordance with the RRC configuration message; and

transmit, to the plurality of UEs, the group feedback message comprising the feedback bitmap indicating the feedback for each UE of the plurality of UEs.

28. An apparatus for wireless communications at a user equipment (UE), comprising:

one or more processors;

one or more memories coupled with the one or more processors; and

instructions stored in the one or more memories and executable by the one or more processors to cause the apparatus to:

receive, from a network device, a radio resource control (RRC) configuration message indicating a first location within a bitmap for feedback for the UE, the feedback associated with grant-free uplink transmissions for the UE;

transmit one or more grant-free uplink transmissions to the network device via a set of time-frequency resources for grant-free transmissions; and

monitor for a group feedback message from the network device in response to the one or more grant-free uplink transmissions, wherein the group feedback message comprises an indication of whether a respective grant-free uplink transmission was received from each of a plurality of UEs including the UE, wherein the indication comprises the bitmap that indicates feedback for each UE of the plurality of UEs, wherein the bitmap is a first type of feedback bitmap of multiple types of feedback bitmaps, and wherein the first location within the bitmap includes feedback for the UE for the respective grant-free uplink transmission in accordance with the RRC configuration message.