Multicast feedback based on reference signal transmissions

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

receiving an indication of one or more uplink reference signal resources for transmission by the UE of sounding reference signals, wherein the one or more uplink reference signal resources are for one or more UEs associated with multicast communications, and wherein each uplink reference signal resource of the one or more uplink reference signal resources is mapped to a respective set of channel state information;

measuring one or more multicast channels monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications;

selecting, from the one or more uplink reference signal resources, an uplink reference signal resource to indicate the set of channel state information based at least in part on the set of channel state information being mapped to the uplink reference signal resource; and

transmitting a sounding reference signal over the uplink reference signal resource.

2. The method of claim 1 , further comprising:

determining that the set of channel state information comprises a channel state information (CSI)-reference signal index, a precoding matrix index, and a channel quality index; and

identifying the uplink reference signal resource as being associated with the CSI-reference signal index, the precoding matrix index, and the channel quality index.

3. The method of claim 1 , further comprising:

identifying a set of the one or more uplink reference signal resources that is associated with one or more channel state information (CSI)-reference signal indices, wherein the uplink reference signal resource is selected from the set of the one or more uplink reference signal resources.

4. The method of claim 1 , further comprising:

identifying a set of the one or more uplink reference signal resources that is associated with one or more precoding matrix indices, wherein the uplink reference signal resource is selected from the set of the one or more uplink reference signal resources.

5. The method of claim 1 , further comprising:

identifying a set of the one or more uplink reference signal resources that is associated with one or more channel quality indices, wherein the uplink reference signal resource is selected from the set of the one or more uplink reference signal resources.

6. The method of claim 1 , further comprising:

determining that the set of channel state information comprises a channel state information (CSI)-reference signal index; and

identifying a set of the one or more uplink reference signal resources that is associated with the CSI-reference signal index, wherein the uplink reference signal resource is selected from the set of the one or more uplink reference signal resources.

7. The method of claim 6 , further comprising:

determining that the set of channel state information comprises a precoding matrix index; and

identifying, from the set of the one or more uplink reference signal resources, a subset uplink reference signal resources that is associated with a first set of precoding matrix indices comprising the precoding matrix index, wherein the uplink reference signal resource is selected from the subset uplink reference signal resources.

8. The method of claim 7 , further comprising:

determining that the set of channel state information comprises a channel quality index; and

identifying, from the subset uplink reference signal resources, a first uplink reference signal resource that is associated with a first set of channel quality indices comprising the channel quality index, wherein the first uplink reference signal resource is selected as the uplink reference signal resource.

9. The method of claim 8 , further comprising:

identifying, from the subset uplink reference signal resources, a second uplink reference signal resource that is associated with a second set of channel quality indices comprising the channel quality index, wherein the first uplink reference signal resource or the second uplink reference signal resource is selected as the uplink reference signal resource.

10. The method of claim 1 , further comprising:

receiving a first multicast transmission using a first set of transmission parameters, wherein transmitting the sounding reference signal indicates that the first multicast transmission has been unsuccessfully decoded; and

receiving, based at least in part on transmitting the sounding reference signal, a second multicast transmission that is transmitted based at least in part on the mapping between the set of channel state information and the uplink reference signal resource.

11. The method of claim 10 , wherein the receiving comprises:

receiving the second multicast transmission over a transmission beam indicated by the mapping between the set of channel state information and the uplink reference signal resource.

12. The method of claim 10 , wherein the receiving comprises:

receiving the second multicast transmission using a modulation and coding scheme indicated by the mapping between the set of channel state information and the uplink reference signal resource.

13. The method of claim 10 , wherein the second multicast transmission comprises a retransmission of data included in the first multicast transmission.

14. The method of claim 1 , further comprising:

determining the mapping between each of the one or more uplink reference signal resources and sets of channel state information, wherein the uplink reference signal resource is selected based at least in part on the mappings.

15. The method of claim 14 , further comprising:

receiving an indication of the mappings in a radio resource control message or a physical downlink control channel message.

16. The method of claim 1 , further comprising:

measuring one or more channel state information (CSI)-reference signals transmitted over the one or more multicast channels; and

determining the set of channel state information based at least in part on the one or more CSI-reference signals.

17. The method of claim 16 , further comprising:

receiving, from a network device, an indication of the one or more CSI-reference signals to measure.

18. The method of claim 16 , further comprising:

determining, by the UE, a quantity of CSI-reference signals to measure;

selecting the one or more CSI-reference signals based at least in part on the determining, the one or more CSI-reference signals comprising the quantity of CSI-reference signals.

19. The method of claim 1 , further comprising:

measuring a plurality of demodulation reference signals transmitted over the one or more multicast channels, the plurality of demodulation reference signals being associated with a plurality of precoding resource block groups; and

determining the set of channel state information based at least in part on the plurality of demodulation reference signals.

20. The method of claim 19 , further comprising:

determining that a demodulation reference signal of the plurality of demodulation reference signals has a highest signal-to-noise ratio based at least in part on the measuring, the demodulation reference signal being associated with a precoding resource block group; and

identifying a set of the one or more uplink reference signal resources that is associated with the precoding resource block group based at least in part on the determining, wherein the uplink reference signal resource is selected from the set of the one or more uplink reference signal resources.

21. The method of claim 1 , further comprising:

determining, for the set of channel state information, a precoding matrix indicator, channel quality indicator, or channel state information-reference signal resource indicator, or any combination thereof, based at least in part on measuring the one or more multicast channels.

22. The method of claim 1 , further comprising:

receiving a radio resource control message comprising the indication of the one or more uplink reference signal resources; and

determining, based at least in part on the radio resource control message, that the one or more uplink reference signal resources occur periodically, wherein the sounding reference signal is transmitted in one instance of the periodically occurring one or more uplink reference signal resources.

23. The method of claim 22 , further comprising:

receiving a control element in a multicast data channel, wherein transmitting the sounding reference signal is based at least in part on receiving the control element.

24. The method of claim 22 , further comprising:

receiving a downlink control information format that schedules a multicast data channel, wherein transmitting the sounding reference signal is based at least in part on receiving the downlink control information format.

25. The method of claim 1 , further comprising:

receiving a multicast data channel over the one or more multicast channels; and

transmitting the sounding reference signal based at least in part on failing to decode multicast data conveyed in the multicast data channel.

26. The method of claim 25 , further comprising:

determining that transmitting the sounding reference signal over the uplink reference signal resource conflicts with transmitting an uplink control channel or uplink data channel; and

prioritizing the sounding reference signal over the uplink control channel or uplink data channel by transmitting the sounding reference signal and dropping the transmission of the uplink control channel or uplink data channel.

27. The method of claim 25 , further comprising:

receiving a re-transmission of the multicast data based at least in part on transmitting the sounding reference signal.

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

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

receive an indication of one or more uplink reference signal resources for transmission by the UE of sounding reference signals, wherein the one or more uplink reference signal resources are for one or more UEs associated with multicast communications, and wherein each uplink reference signal resource of the one or more uplink reference signal resources is mapped to a respective set of channel state information;

measure one or more multicast channels monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications;

select, from the one or more uplink reference signal resources, an uplink reference signal resource to indicate the set of channel state information based at least in part on the set of channel state information being mapped to the uplink reference signal resource; and

transmit a sounding reference signal over the uplink reference signal resource.

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

means for receiving an indication of one or more uplink reference signal resources for transmission by the UE of sounding reference signals, wherein the one or more uplink reference signal resources are for one or more UEs associated with multicast communications, and wherein each uplink reference signal resource of the one or more uplink reference signal resources is mapped to a respective set of channel state information;

means for measuring one or more multicast channels monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications;

means for selecting, from the one or more uplink reference signal resources, an uplink reference signal resource to indicate the set of channel state information based at least in part on the set of channel state information being mapped to the uplink reference signal resource; and

means for transmitting a sounding reference signal over the uplink reference signal resource.

30. A non-transitory computer-readable medium storing code for wireless communications at a user equipment (UE), the code comprising instructions executable by a processor to:

receive an indication of one or more uplink reference signal resources for transmission by the UE of sounding reference signals, wherein the one or more uplink reference signal resources are for one or more UEs associated with multicast communications, and wherein each uplink reference signal resource of the one or more uplink reference signal resources is mapped to a respective set of channel state information;

measure one or more multicast channels monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications;

select, from the one or more uplink reference signal resources, an uplink reference signal resource to indicate the set of channel state information based at least in part on the set of channel state information being mapped to the uplink reference signal resource; and

transmit a sounding reference signal over the uplink reference signal resource.