Selective retransmission of groupcast data

1. An apparatus comprising:

a processor, and

a memory coupled to the processor, the memory comprising instructions executable by the processor to cause the apparatus to:

transmit groupcast data via sidelink communication to a set of user equipments (“UEs”) using a first cast-type;

receive negative acknowledgement feedback via sidelink communication from at least one UE of the set of UEs, the negative acknowledgement feedback comprising sidelink Channel State Information (“S-CSI”);

determine a retransmission mode based on the S-CSI, wherein the retransmission mode indicates a second cast-type that is different from the first cast-type; and

perform selectively beamformed retransmission of the groupcast data according to the determined retransmission mode.

2. The apparatus of claim 1 , wherein the second cast-type comprises unicast retransmission with beamforming or groupcast retransmission with partial beam sweeping.

3. The apparatus of claim 1 , wherein the instructions are executable by the processor to cause the apparatus to determine the retransmission mode based on a Quality of Service (“QoS”) priority of the groupcast data.

4. The apparatus of claim 1 , wherein the instructions are executable by the processor to cause the appatatus to receive a sidelink groupcast hybrid automatic repeat request (“HARQ”) retransmission profile from a base station in a mobile communication network, the sidelink communication not passing through the base station.

5. The apparatus of claim 1 , wherein the instructions are executable by the processor to cause the apparatus to transmit sidelink control information (“SCI”) to the set of UEs.

6. The apparatus of claim 5 , wherein the sidelink control information includes a data transmission index and a transmission occasion.

7. The apparatus of claim 5 , wherein the sidelink control information indicates a physical sidelink feedback channel (“PSFCH”) format for feedback, and wherein the instructions are executable by the processor to cause the apparatus to receive the negative acknowledgement using the indicated PSFCH format.

8. The apparatus of claim 1 , wherein the S-CSI comprises best beam information, and wherein, to perform selectively beamformed retransmission of the groupcast data, the instructions are executable by the processor to cause the apparatus to retransmit the groupcast data on one or more beams selected using the best beam information.

9. The apparatus of claim 1 , wherein, to receive the negative acknowledgement feedback, the instructions are executable by the processor to cause the apparatus to receive location information for the at least one UE, and wherein, to perform selectively beamformed retransmission of the groupcast data, the instructions are executable by the processor to cause the apparatus to retransmit the groupcast data on one or more beams selected using the location information.

10. The apparatus of claim 1 , wherein the instructions are executable by the processor to cause the apparatus to implicitly determine a best beam for retransmission based on beam information used by a respective UE of the set of UEs to transmit hybrid automatic repeat request (“HARQ”) feedback for the groupcast data transmission.

11. The apparatus of claim 1 , further comprising a plurality of antenna panels, wherein to transmit the groupcast data, the instructions are executable by the processor to cause the apparatus to transmit two or more data transmission blocks (“TBs”) simultaneously using different antenna panels.

12. The apparatus of claim 1 , wherein the instructions are executable by the processor to cause the apparatus to determine the retransmission mode based also on a number of UEs sending a respective negative acknowledgement feedback.

13. A method of a transmitting device, the method comprising:

transmitting groupcast data via sidelink communication to a set of user equipments (“UEs”) using a first cast-type;

receiving negative acknowledgement feedback via sidelink communication from at least one UE of the set of UEs, the negative acknowledgement feedback comprising sidelink Channel State Information (“S-CSI”);

determining a retransmission mode based on the S-CSI, wherein the retransmission mode indicates a second cast-type that is different from the first cast-type; and

performing selectively beamformed retransmission of the groupcast data according to the determined retransmission mode.

14. An apparatus comprising:

a processor; and

a memory coupled to the processor, the memory comprising instructions executable by the processor to cause the apparatus to:

receive, from a transmitter user equipment (“Tx UE”), a groupcast signal using a first cast-type;

detect an unsuccessful decoding the groupcast signal;

determine sidelink Channel State Information (“S-CSI”);

transmit negative acknowledgement feedback to the Tx UE via sidelink communication, the negative acknowledgement feedback comprising the S-CSI; and

receive, from the Tx UE, a retransmission using a retransmission mode associated with a second cast-type that is different from the first cast-type.

15. The apparatus of claim 14 , wherein the second cast-type comprises unicast retransmission with beamforming or groupcast retransmission with partial beam sweeping.

16. The apparatus of claim 14 , wherein the instructions are executable by the processor to cause the apparatus to receive a sidelink reference signal associated with the groupcast signal and derive best beam information using the sidelink reference signal.

17. The apparatus of claim 14 , wherein the S-CSI comprises best beam information.

18. The apparatus of claim 14 , wherein the instructions are executable by the processor to cause the apparatus to receive sidelink control information (“SCI”) prior to receiving the groupcast signal.

19. The apparatus of claim 18 , wherein the SCI is received together with a sidelink reference signal associated with the groupcast signal, and wherein the S-CSI is determined using the sidelink reference signal.

20. The apparatus of claim 14 , wherein sending feedback to the Tx UE comprises transmitting the feedback towards the Tx UE using beam sweeping.