HARQ process for sidelink transmission
Apparatuses, methods, and systems are disclosed for sidelink HARQ operation. One apparatus 400 includes a transceiver 425 that receives 605 a SL grant for data transmission using SL resources, the SL grant having a first HARQ process identifier. The apparatus 400 includes a processor 405 that selects 610 a second HARQ process identifier for the data transmission using SL resources. Via the transceiver 425 , the processor 405 transmits 615 SCI containing the second HARQ process identifier and transmits 620 the SL data using the SL resources.
1. An apparatus comprising:
a transceiver; and
a processor coupled to the transceiver, wherein the processor is configured to:
receive a sidelink (“SL”) grant for a transmission of sidelink data using SL resources, the SL grant indicating a first hybrid automatic repeat request (“HARQ”) process identified by a first HARQ process identifier;
select a second HARQ process identified by a second HARQ process identifier for the transmission of the sidelink data using the SL resources, wherein the second HARQ process is selected independently from the first HARQ process in response to the SL grant indicating an initial transmission of the sidelink data, and wherein the selection of the second HARQ process is based on the first HARQ process identifier in response to the SL grant indicating a retransmission of the sidelink data;
transmit SL control information (“SCI”) containing the second HARQ process identifier; and
transmit the sidelink data using the SL resources.
2. The apparatus of claim 1 , wherein the processor is further configured to transmit HARQ feedback for the first HARQ process corresponding to the transmission of SL data using the SL resources.
3. The apparatus of claim 2 , wherein the SL grant indicates a physical uplink control channel resource and/or HARQ feedback timing information, wherein transmitting HARQ feedback for the first HARQ process is based on the SL grant.
4. The apparatus of claim 1 , wherein the first HARQ process identifier received in the SL grant is different than the second HARQ process identifier signaled within the SCI.
5. The apparatus of claim 1 , wherein selecting the second HARQ process includes autonomously selecting a second HARQ process from a pool of configured second HARQ processes.
6. The apparatus of claim 5 , wherein the pool of configured second HARQ processes is shared between network-scheduled SL data transfer and UE-scheduled SL data transfer.
7. The apparatus of claim 5 , wherein the pool of configured second HARQ processes is shared between unicast SL transmissions, groupcast SL transmission, and broadcast SL transmissions.
8. The apparatus of claim 1 , wherein the selected second HARQ process is associated with a second HARQ process for which there is no pending HARQ retransmission.
9. The apparatus of claim 1 , wherein the processor is further configured to map the first HARQ process to the second HARQ process.
10. The apparatus of claim 1 , wherein transmitting the SL data using the SL resources comprises transmitting the SCI containing the second HARQ process identifier for the second HARQ process, wherein the transceiver receives SL HARQ feedback for the second HARQ process from at least one user equipment device (“UE”).
11. The apparatus of claim 10 ,
wherein transmitting the SL data comprises performing an initial groupcast transmission,
wherein receiving SL HARQ feedback comprises receiving a negative acknowledgement indication, and
wherein the processor retransmits the SL data using unicast SL retransmission.
12. The apparatus of claim 11 , wherein the unicast SL retransmission reuses the second HARQ process identifier.
13. The apparatus of claim 11 , wherein the unicast SL retransmission uses a different redundancy version than the initial groupcast transmission.
14. A method of a remote unit comprising:
receiving a sidelink (“SL”) grant for a transmission of sidelink data using SL resources, the SL grant indicating a first hybrid automatic repeat request (“HARQ”) process identified by a first HARQ process identifier;
selecting a second HARQ process identified by a second HARQ process identifier for the transmission of the sidelink data using the SL resources, wherein the second HARQ process is selected independently from the first HARQ process in response to the SL grant indicating an initial transmission of the sidelink data, wherein the selection of the second HARQ process based on the first HARQ process identifier in response to the SL grant indicating a retransmission of the sidelink data;
transmitting SL control information (“SCI”) containing the selected second HARQ process identifier; and
transmitting the sidelink data using the SL resources.
15. The method of claim 14 , wherein the first HARQ process identifier received in the SL grant is different than the second HARQ process identifier signaled within the SCI.
16. The method of claim 14 , wherein selecting the second HARQ process includes autonomously selecting a second HARQ process from a pool of configured second HARQ processes.
17. The method of claim 16 , wherein the pool of configured second HARQ processes is shared between network-scheduled SL data transfer and UE-scheduled SL data transfer.
18. The method of claim 16 , wherein the pool of configured second HARQ processes is shared between unicast SL transmissions, groupcast SL transmission, and broadcast SL transmissions.
19. The method of claim 14 , wherein transmitting the SL data using the SL resources comprises transmitting the SCI containing the second HARQ process identifier for the second HARQ process, the method further comprising receiving SL HARQ feedback for the second HARQ process from at least one user equipment device (“UE”).
20. The method of claim 19 , wherein the SCI further contains a new data indicator, wherein a receiving UE performs soft-combining of the transmitted SL data based on at least the second HARQ process identifier and the new data indicator.