Method and apparatus for communicating two stage sidelink control information

1. A User Equipment (UE) for wireless communication, comprising:

at least one memory; and

at least one processor coupled with the at least one memory and configured to cause the UE to:

determine first stage Sidelink Control Information (SCI), the first stage SCI including a modification periodicity, the modification periodicity being for the periodicity of modification of second stage SCI; and

periodically transmit the first stage SCI,

determine the second stage SCI, and

transmit the second stage SCI.

2. The UE according to claim 1 , wherein the first stage SCI includes a modification periodicity bit map field that includes a time slot index and a periodicity.

3. The UE according to claim 1 ,

wherein the modification periodicity comprises a first modification periodicity,

wherein the at least one processor is configured to cause the UE to:

start a modification period timer, and

transmit another first stage SCI including a second modification periodicity.

4. The UE according to claim 1 , wherein the first stage SCI includes parameters for the second stage SCI and Physical Sidelink Shared Channel (PSSCH), where the parameters include at least one parameter selected from Modulation and Coding Scheme (MCS), Transmit Power Control (TPC) command, Sidelink Channel State Information (S-CSI) request, Codebook Block Group (CBG) transmission information, CBG flushing information, Demodulation Reference Signal (DMRS) sequence initialization, source identifier, beam/Transmission Configuration Indicator (TCI) state, and spatial relation for S-CSI.

5. The UE according to claim 1 , wherein the at least one processor is configured to cause the UE to:

transmit a first transport block in accordance with the second stage SCI, and

transmit a second transport block in accordance with a same second stage SCI, where the second transport block is different from the first transport block.

6. The UE according to claim 1 , wherein the at least one processor is configured to cause the UE to:

receive a request to transmit second stage SCI with updated scheduling information, and

transmit the second stage SCI with the updated scheduling information.

7. The UE according to claim 1 , wherein the at least one processor is configured to cause the UE to:

transmit a transport block on a Physical Sidelink Shared Channel (PSSCH) in accordance with the second stage SCI, and

retransmit the transport block on the same PSSCH in accordance with the second stage SCI if the first stage SCI indicates absence of a presence of the second stage SCI or a modification period timer has not expired.

8. A base station for wireless communication, comprising:

at least one memory; and

at least one processor coupled with the at least one memory and configured to cause the base station to:

receive first stage Sidelink Control Information (SCI), the first stage SCI including a modification periodicity and second stage SCI parameters, the modification periodicity being for the periodicity of modification of the second stage SCI, and

receive the second stage SCI including data parameters.

9. The base station according to claim 8 , wherein the at least one processor is configured to cause the base station to:

start a modification period timer,

decode a data channel based on the SCI, and

restart the modification period timer when the base station receives a second first stage SCI including an indication of the second stage SCI.

10. The base station according to claim 8 , wherein the at least one processor is configured to cause the base station to:

determine second stage SCI is not present in a time slot, and

decode a physical sidelink shared channel based on a previously received second stage SCI.

11. The base station according to claim 8 ,

wherein the at least one processor is configured to cause the base station to:

determine second stage SCI is not present in a time slot, and

send a request, via layer 1 or layer 2 signaling, to transmit the second stage SCI.

12. The apparatus base station according to claim 8 ,

wherein the at least one processor is configured to cause the base station to:

determine second stage SCI has not been decoded in resources indicated by the first stage SCI, and

send a request to retransmit the second stage SCI.

13. The base station according to claim 8 ,

wherein the second stage SCI comprises first second stage SCI;

wherein the at least one processor is configured to cause the base station to:

receive another first stage SCI including information for a second second stage SCI,

determine the second second stage SCI has not been decoded in resources indicated by the another first stage SCI, and

abstain from decoding a physical sidelink shared channel using the first second stage SCI if the second second stage SCI has not been decoded.

14. The base station according to claim 8 , wherein the at least one processor is configured to cause the base station to abstain from decoding the second stage SCI if the first stage SCI indicates absence of a presence of the second stage SCI or a modification period timer has not expired.

15. The base station according to claim 8 , wherein the at least one processor is configured to cause the base station to assume a current physical sidelink shared channel transmission is a retransmission of a transport block corresponding to a most recently received second stage sidelink control information if the first stage SCI indicates an absence of a presence of the second stage SCI or a modification period timer has not expired.

16. The base station according to claim 8 , wherein the at least one processor is configured to cause the base station to:

transmit Sidelink Channel State Information (S-CSI) when the second stage SCI is received, and

abstain from transmitting S-CSI when the second stage SCI is not received.

17. A method comprising:

determining, at a UE, first stage Sidelink Control Information (SCI), the first stage SCI including a modification periodicity, the modification periodicity being for the periodicity of modification of second stage SCI;

periodically transmitting, by the UE, the first stage SCI;

determining the second stage SCI; and

transmitting the second stage SCI.

18. The method according to claim 17 , wherein the first stage SCI includes a modification periodicity bit map field that includes a time slot index and a periodicity.

19. The method according to claim 17 ,

wherein the modification periodicity comprises a first modification periodicity,

wherein the method comprises:

starting a modification period timer; and

transmitting another first stage SCI including a second modification periodicity.

20. A processor for wireless communication, comprising:

at least one controller coupled with at least one memory and configured to cause the processor to:

determine first stage Sidelink Control Information (SCI), the first stage SCI including a modification periodicity, the modification periodicity being for the periodicity of modification of second stage SCI;

periodically transmit the first stage SCI;

determine the second stage SCI; and

transmit the second stage SCI.