Cyclic shift selection for physical sidelink control channel transmission

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

monitoring one or more sidelink control information (SCI) transmissions from one or more second UEs;

determining, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE; and

selecting a cyclic shift to use for the scheduled SCI transmission by the first UE based at least on the determination,

wherein determining whether the one or more collisions occur comprises:

determining, based on the one or more SCI transmissions by the one or more second UEs, time and frequency resources for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs; and

determining that the one or more collisions occur when determining the same time and frequency resources for the scheduled SCI transmission by the first UE.

2. The method of claim 1 , wherein:

determining whether the one or more collisions occur comprises determining that a collision does not occur; and

selecting the cyclic shift to use for the scheduled SCI transmission by the first UE comprises:

randomly selecting the cyclic shift, from a set of a plurality of cyclic shifts, for an initial transmission by the first UE; and

selecting the cyclic shift that was randomly selected for the initial transmission for a retransmission by the first UE.

3. The method of claim 1 , wherein:

the determining whether the one or more collisions occur comprises determining that the one or more collisions occur; and

the method further comprises determining one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs based on one or more cyclic shifts used for the one or more SCI transmissions by the one or more second UEs.

4. The method of claim 3 , wherein selecting the cyclic shift to use for the scheduled SCI transmission by the first UE comprises randomly selecting a cyclic shift, from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs that collide with the scheduled SCI transmission by the first UE, when the scheduled SCI transmission is an initial transmission.

5. The method of claim 3 , wherein selecting the cyclic shift to use for the scheduled SCI transmission by the first UE comprises selecting a same cyclic shift used for an initial transmission by the first UE when the scheduled SCI transmission is a retransmission and a cyclic shift used for the initial transmission is different than the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmission by the one or more second UEs.

6. The method of claim 3 , wherein, when the scheduled SCI transmission is a retransmission and a cyclic shift used for an initial transmission is the same as at least one of the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs, selecting the cyclic shift to use for the scheduled SCI transmission by the first UE comprises:

selecting a same cyclic shift used for an initial transmission by the first UE, or randomly selecting the cyclic shift, from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs that collide with the scheduled SCI transmission by the first UE.

7. The method of claim 1 , wherein selecting the cyclic shift comprises determining a technique for selecting the cyclic shift based on whether a detected level of congestion is at or above a congestion threshold level.

8. The method of claim 1 , wherein a transmission is associated with a first redundancy version (RV 0 ), and a retransmission corresponding to a first SCI transmission of the one or more SCI transmissions is associated with a second RV (RV 2 ).

9. The method of claim 1 , wherein:

the first UE and the one or more second UEs are configured for cellular vehicle-to-anything (C-V2X) communications; and

the first UE monitors for the one or more SCI transmissions from the one or more second UEs in a physical sidelink control channel (PSCCH) in a subframe.

10. The method of claim 9 , wherein the first UE and the one or more second UEs are configured for a transmission mode 4 for the C-V2X communications, and wherein the first UE and the one or more second UEs autonomously select transmission resources.

11. An apparatus for wireless communication, comprising:

at least one processor; and

a memory coupled to the at least one processor, the memory comprising code executable by the at least one processor to cause the apparatus to:

monitor one or more sidelink control information (SCI) transmissions from one or more user equipments (UEs);

determine, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more UEs and a scheduled SCI transmission by the apparatus; and

select a cyclic shift to use for the scheduled SCI transmission by the apparatus based at least on the determination,

wherein the code to cause the apparatus to determine whether the one or more collisions occur comprises code to cause the apparatus to:

determine, based on the one or more SCI transmissions by the one or more UEs, time and frequency resources for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs; and

determine that the one or more collisions occur when determining the same time and frequency resources for the scheduled SCI transmission by the apparatus.

12. The apparatus of claim 11 , wherein:

the code to cause the apparatus to determine whether the one or more collisions occur comprises code to cause the apparatus to determine that a collision does not occur; and

the code to cause the apparatus to select the cyclic shift to use for the scheduled SCI transmission by the apparatus comprises code to cause the apparatus to:

randomly select the cyclic shift, from a set of a plurality of cyclic shifts, for an initial transmission by the apparatus; and

select the cyclic shift that was randomly selected for the initial transmission for a retransmission by the apparatus.

13. The apparatus of claim 11 , wherein:

the code to cause the apparatus to determine whether the one or more collisions occur comprises code to cause the apparatus to determine that the one or more collisions occur; and

the memory further comprises code to cause the apparatus to determine one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs based on one or more cyclic shifts used for the one or more SCI transmissions by the one or more UEs.

14. The apparatus of claim 13 , wherein the code to cause the apparatus to select the cyclic shift to use for the scheduled SCI transmission by the apparatus comprises code to cause the apparatus to randomly select a cyclic shift, from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs that collide with the scheduled SCI transmission by the apparatus, when the scheduled SCI transmission is an initial transmission.

15. The apparatus of claim 13 , wherein the code to cause the apparatus to select the cyclic shift to use for the scheduled SCI transmission by the apparatus comprises code to cause the apparatus to select a same cyclic shift used for an initial transmission by the apparatus when the scheduled SCI transmission is a retransmission and a cyclic shift used for the initial transmission is different than the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmission by the one or more UEs.

16. The apparatus of claim 13 , wherein, when the scheduled SCI transmission is a retransmission and a cyclic shift used for an initial transmission is the same as at least one of the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs, the code to cause the apparatus to select the cyclic shift to use for the scheduled SCI transmission by the apparatus comprises code to cause the apparatus to:

select a same cyclic shift used for an initial transmission by the apparatus, or

randomly select the cyclic shift, from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs that collide with the scheduled SCI transmission by the apparatus.

17. The apparatus of claim 11 , wherein the code to cause the apparatus to select the cyclic shift comprises code to cause the apparatus to determine a technique for selecting the cyclic shift based on whether a detected level of congestion is at or above a congestion threshold level.

18. The apparatus of claim 11 , wherein a transmission is associated with a first redundancy version (RV 0 ), and a retransmission corresponding to a first SCI transmission of the one or more SCI transmissions is associated with a second RV (RV 2 ).

19. The apparatus of claim 11 , wherein:

the apparatus and the one or more UEs are configured for cellular vehicle-to-anything (C-V2X) communications; and

the memory further comprises code to cause the apparatus to monitor for the one or more SCI transmissions from the one or more UEs in a physical sidelink control channel (PSCCH) in a subframe.

20. The apparatus of claim 19 , wherein the apparatus and the one or more UEs are configured for a transmission mode 4 for the C-V2X communications, and wherein the apparatus and the one or more UEs autonomously select transmission resources.

21. An apparatus for wireless communication, comprising:

means for monitoring one or more sidelink control information (SCI) transmissions from one or more user equipment (UEs);

means for determining, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more UEs and a scheduled SCI transmission by the apparatus; and

means for selecting a cyclic shift to use for the scheduled SCI transmission by the apparatus based at least on the determination,

wherein the means for determining whether the one or more collisions occur comprises:

means for determining, based on the one or more SCI transmissions by the one or more UEs, time and frequency resources for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs; and

means for determining that the one or more collisions occur when determining the same time and frequency resources for the scheduled SCI transmission by the apparatus.

22. The apparatus of claim 21 , wherein:

means for determining whether the one or more collisions occur comprises means for determining that a collision does not occur; and

means for selecting the cyclic shift to use for the scheduled SCI transmission by the apparatus comprises:

means for randomly selecting the cyclic shift, from a set of a plurality of cyclic shifts, for an initial transmission by the apparatus; and

means for selecting the cyclic shift that was randomly selected for the initial transmission for a retransmission by the apparatus.

23. The apparatus of claim 21 , wherein:

the means for determining whether the one or more collisions occur comprises means for determining that the one or more collisions occur; and

the apparatus further comprises means for determining one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs based on one or more cyclic shifts used for the one or more SCI transmissions by the one or more UEs.

24. The apparatus of claim 23 , wherein the means for selecting the cyclic shift to use for the scheduled SCI transmission by the apparatus comprises means for randomly selecting a cyclic shift, from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs that collide with the scheduled SCI transmission by the apparatus, when the scheduled SCI transmission is an initial transmission.

25. The apparatus of claim 23 , wherein the means for selecting the cyclic shift to use for the scheduled SCI transmission by the apparatus comprises means for selecting a same cyclic shift used for an initial transmission by the apparatus when the scheduled SCI transmission is a retransmission and a cyclic shift used for the initial transmission is different than the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmission by the one or more UEs.

26. The apparatus of claim 23 , wherein, when the scheduled SCI transmission is a retransmission and a cyclic shift used for an initial transmission is the same as at least one of the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs, the means for selecting the cyclic shift to use for the scheduled SCI transmission by the apparatus comprises:

means for selecting a same cyclic shift used for an initial transmission by the apparatus, or

means for randomly selecting the cyclic shift, from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more UEs that collide with the scheduled SCI transmission by the apparatus.

27. A non-transitory computer readable medium storing computer executable code thereon for wireless communication by a first user equipment (UE), comprising:

code for monitoring one or more sidelink control information (SCI) transmissions from one or more second UEs;

code for determining, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE; and

code for selecting a cyclic shift to use for the scheduled SCI transmission by the first UE based at least on the determination,

wherein the code for determining whether the one or more collisions occur comprises:

code for determining, based on the one or more SCI transmissions by the one or more second UEs, time and frequency resources for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs; and

code for determining that the one or more collisions occur when determining the same time and frequency resources for the scheduled SCI transmission by the first UE.