Hybrid automatic repeat request (HARQ) process when using sidelink for retransmission

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

obtaining first data, from a network entity, intended for a second UE, wherein the obtaining includes decoding a first transmission of the first data intended for the second UE;

receiving signaling indicating the first UE is to retransmit the first data to the second UE; and

in response to the signaling:

transmitting sidelink control information (SCI) scheduling a physical sidelink shared channel (PSSCH) transmission from the first UE to the second UE, wherein the SCI includes a hybrid automatic repeat request (HARQ) process identifier (ID), and wherein the SCI indicates the HARQ process ID is associated with a retransmission of data from the network entity; and

retransmitting the first data to the second UE via the PSSCH.

2. The method of claim 1 , further comprising:

measuring channel quality of a sidelink between the first UE and the second UE; and

reporting the measured channel quality to the network entity.

3. The method of claim 1 , further comprising:

receiving signaling indicating the first UE is part of a group of one or more UEs that retransmit data to the second UE.

4. The method of claim 1 , further comprising:

obtaining second data, from the network entity, intended for the second UE, wherein the obtaining includes decoding a second transmission of the second data intended for the second UE; and

providing a first acknowledgment feedback for the second transmission.

5. The method of claim 4 , further comprising:

obtaining third data, from the network entity, intended for the first UE, wherein the obtaining includes decoding a third transmission of the third data targeting the first UE; and

providing a second acknowledgment feedback for the third transmission.

6. The method of claim 5 , wherein the first acknowledgment feedback for the second transmission and the second acknowledgment feedback for the third transmission are jointly coded.

7. The method of claim 1 , wherein the first transmission includes the HARQ process ID.

8. The method of claim 1 , further comprising:

transmitting second SCI scheduling a second PSSCH transmission from the first UE to the second UE, wherein the second SCI includes a second HARQ process ID, and wherein the second SCI indicates the second HARQ process ID is associated with a sidelink data; and

transmitting the sidelink data to the second UE.

9. The method of claim 1 , wherein the a bit in the SCI indicates the HARQ process ID is for the associated with a retransmission of data from the network entity or is associated with sidelink data.

10. The method of claim 1 , further comprising:

selecting a value for the HARQ process ID from a first subset of HARQ process IDs, wherein the first subset of HARQ process IDs reserved for retransmission by the first UE of data from the network entity intended for the first UE, and wherein a second subset of the HARQ process IDs are reserved for transmission of sidelink data from the first UE to the second UE.

11. A method for wireless communications by a network entity, comprising:

outputting first data intended to a second UE in a first transmission;

outputting second data intended to a first UE in a second transmission;

obtaining, from the first UE, first acknowledgment feedback for the first transmission and second acknowledgment feedback for the second transmission, wherein the first acknowledgment feedback and the second acknowledgment feedback are jointly coded; and

signaling the first UE to retransmit the first data to the second UE via a sidelink when the network entity fails to receive the first acknowledgment feedback indicating that the second UE successfully received the first data in the first transmission.

12. The method of claim 11 , further comprising:

receiving, from the first UE, a report of measured channel quality of the sidelink;

including the first UE in a group of one or more UEs that retransmit data to the second UE; and

signaling the first UE indicating the first UE is part of the group.

13. A first user equipment (UE), comprising:

a processing system configured to:

obtain first data, from a network entity, intended for a second UE, wherein the processing system being configured to obtain the first data includes the processing system being configured to decode a first transmission of the first data intended for the second UE;

a receiver configured to receive signaling indicating the first UE is to retransmit the first data to the second UE; and

a transmitter configured to, in response to the signaling:

transmit sidelink control information (SCI) scheduling a physical sidelink shared channel (PSSCH) transmission from the first UE to the second UE, wherein the SCI includes a hybrid automatic repeat request (HARQ) process identifier (ID), and wherein the SCI indicates the HARQ process ID is associated with a retransmission of data from the network entity; and

retransmit the first data to the second UE via the PSSCH.

14. The first UE of claim 13 , wherein the processing system is further configured to:

measure channel quality of a sidelink between the first UE and the second UE; and

report the measured channel quality to the network entity.

15. The first UE of claim 13 , wherein the receiver is further configured to:

receive signaling indicating the first UE is part of a group of one or more UEs that retransmit data to the second UE.

16. The first UE of claim 13 , wherein the processing system is further configured to:

obtain second data, from the network entity, intended for the second UE, wherein the processing system being configured to obtain the second data includes the processing system being configured to decode a second transmission of the second data intended for the second UE; and

provide a first acknowledgment feedback for the second transmission.

17. The first UE of claim 16 , wherein:

the processing system is further configured to obtain third data, from the network entity, intended for the first UE, wherein the processing system being configured to obtain the third data includes the processing system being configured to decode a third transmission of the third data targeting the first UE; and

the processing system is further configured to provide a second acknowledgment feedback for the third transmission.

18. The first UE of claim 17 , wherein the first acknowledgment feedback for the second transmission and the second acknowledgment feedback for the third transmission are jointly coded.

19. The first UE of claim 13 , wherein the first transmission includes the HARQ process ID.

20. The first UE of claim 13 , wherein the transmitter is further configured to:

transmit second SCI scheduling a second PSSCH transmission from the first UE to the second UE, wherein the second SCI includes a second HARQ process ID, and wherein the second SCI indicates the second HARQ process ID is associated with a sidelink data; and

transmit the sidelink data to the second UE.

21. The first UE of claim 13 , wherein the a bit in the SCI indicates the HARQ process ID is associated with a retransmission of data from the network entity or is associated with sidelink data.

22. The first UE of claim 13 , wherein the processing system is further configured to:

select a value for the HARQ process ID from a first subset of HARQ process IDs, wherein the first subset of HARQ process IDs reserved for retransmission by the first UE of data from the network entity intended for the first UE, and wherein a second subset of the HARQ process IDs are reserved for transmission of sidelink data from the first UE to the second UE.

23. A network entity, comprising:

a processing system configured to generate first data intended to a second UE and second data intended to a first UE; and

a transmitter configured to:

send the first data intended to the second UE in a first transmission; and

send the second data intended to the first UE in a second transmission; and

a receiver configured to receive, from the first UE, first acknowledgment feedback for the first transmission and second acknowledgment feedback for the second transmission, wherein the first acknowledgment feedback and the second acknowledgment feedback are jointly coded, and wherein

the transmitter is configured to signal the first UE to retransmit the first data to the second UE via a sidelink when the network entity fails to receive the first acknowledgment feedback indicating that the second UE successfully received the first data in the first transmission.

24. The network entity of claim 23 , wherein:

the receiver configured to receive, from the first UE, a report of measured channel quality of the sidelink;

the processing system is further configured to include the first UE in a group of one or more UEs that retransmit data to the second UE; and

the transmitter is further configured to signal the first UE indicating the first UE is part of the group.