Discontinuous reception configuration and sidelink operation with mode-1 and mode-2 scheduling

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

receiving a first sidelink grant for a transmission between the first UE and a second UE;

communicating the transmission according to the first sidelink grant;

starting a configured duration of a sidelink round trip time timer after the transmission;

starting a configured duration of a sidelink retransmission timer from an end of the sidelink round trip time timer, wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a direction of the transmission;

starting an inactivity timer after receiving the first sidelink grant, wherein a duration of the inactivity timer is a configured duration for a sidelink inactivity;

allowing start of a discontinuous reception (DRX) mode for the first UE after the configured duration of the sidelink retransmission timer if a second grant for a sidelink retransmission is not received during the sidelink retransmission timer and in response to expiration of the inactivity timer.

2. The method of claim 1 , further comprising starting a second inactivity timer in response to a second grant for a second transmission on a link between the first UE and a base station during the inactivity timer, wherein a new duration of the second inactivity timer is a configured duration for an inactivity for the link between the first UE and the base station, wherein the configured duration of the sidelink inactivity is different than the configured duration of the inactivity for the link between the first UE and the base station.

3. The method of claim 1 , wherein the configured duration of the inactivity timer is specific for a direction of the transmission.

4. The method of claim 1 , wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a link with the second UE.

5. The method of claim 1 , wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a link type, a traffic type, or for the UE.

6. The method of claim 1 , wherein the DRX mode includes an on duration in which the UE monitors for grants and an off duration in which the UE does not monitor for grants.

7. The method of claim 1 , wherein allowing start of the DRX mode includes entering the DRX mode when no timer defining an active time period is running.

8. The method of claim 1 , wherein the DRX mode is defined by a set of parameters including a short cycle duration and a short cycle timer that are specific for a sidelink.

9. The method of claim 1 , wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are for transmitting the transmission and are different than a configured duration of a second sidelink round trip time timer and a configured duration of a second sidelink retransmission timer for receiving the transmission.

10. The method of claim 1 , wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are for receiving the transmission and are different than a configured duration of a second sidelink round trip time timer and a configured duration of a second sidelink retransmission timer for transmitting the transmission.

11. The method of claim 10 , wherein starting the configured duration of the sidelink round trip time timer after the transmission comprises starting the configured duration of the sidelink round trip time timer after transmission of a positive or negative acknowledgment on a physical sidelink feedback channel.

12. An apparatus for wireless communication for a first user equipment (UE), comprising:

a memory; and

at least one processor coupled to the memory and configured to:

receive a first sidelink grant for a transmission between the first UE and a second UE;

communicate the transmission according to the first sidelink grant;

start a configured duration of a sidelink round trip time timer after the transmission;

start a configured duration of a sidelink retransmission timer from an end of the sidelink round trip time timer, wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a direction of the transmission;

start inactivity timer after reception of the first sidelink grant, wherein a duration of the inactivity timer is a configured duration for a sidelink inactivity; and

allow start of a discontinuous reception (DRX) mode for the first UE after the configured duration of the sidelink retransmission timer if a third grant for a sidelink retransmission is not received during the sidelink retransmission timer and in response to expiration of the inactivity timer.

13. The apparatus of claim 12 , wherein the at least one processor is configured to start a second inactivity timer in response to a second grant for a second transmission on a link between the first UE and a base station during the inactivity timer, wherein a new duration of the inactivity timer is a configured duration for an inactivity for the link between the first UE and the base station, wherein the configured duration of the sidelink inactivity is different than the configured duration of the inactivity for the link between the first UE and the base station.

14. The apparatus of claim 12 , wherein the configured duration of the inactivity timer specific for a direction of the transmission.

15. The apparatus of claim 12 , wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a link with the second UE.

16. The apparatus of claim 12 , wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a link type, a traffic type, or for the UE.

17. The apparatus of claim 12 , wherein the DRX mode includes an on duration in which the UE monitors for grants and an off duration in which the UE does not monitor for grants.

18. The apparatus of claim 12 , wherein to allow start of the DRX mode, the at least one processor is configured to enter the DRX mode when no timer defining an active time period is running.

19. The apparatus of claim 12 , wherein the DRX mode is defined by a set of parameters including a short cycle duration and a short cycle timer that are specific for a sidelink.

20. An apparatus for wireless communication for a first user equipment (UE), comprising:

means for receiving, from a base station, a first sidelink grant for a transmission between the first UE and a second UE;

means for communicating the transmission according to the first sidelink grant;

means for monitoring a configured duration of a sidelink round trip time timer after the transmission;

means for starting a configured duration of a sidelink retransmission timer from an end of the sidelink round trip time timer, wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a direction of the transmission;

means for starting an inactivity timer after reception of the first sidelink grant, wherein a duration of the inactivity timer is a configured duration for a sidelink inactivity; and

means for allowing start of a discontinuous reception (DRX) mode for the first UE after the configured duration of the sidelink retransmission timer if a second grant for a sidelink retransmission is not received during the sidelink retransmission timer and in response to expiration of the inactivity timer.

21. The apparatus of claim 20 , wherein the means for starting the inactivity timer is configured to start a second inactivity timer in response to a second grant for a second transmission on a link between the first UE and the base station during the inactivity timer, wherein a new duration of the second inactivity timer is a configured duration for an inactivity for the link between the first UE and the base station, wherein the configured duration of the sidelink inactivity is different than the configured duration of the inactivity for the link between the first UE and the base station.

22. The apparatus of claim 20 , wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a direction of the transmission.

23. The apparatus of claim 20 , wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a link with the second UE.

24. A non-transitory computer-readable medium storing computer-executable instructions that when executed by a processor of a user equipment (UE) cause the UE to:

receive a first sidelink grant for a transmission between the first UE and a second UE;

communicate the transmission according to the first sidelink grant;

start a configured duration of a sidelink round trip time timer after the transmission;

start a configured duration of a sidelink retransmission timer from an end of the sidelink round trip time timer;

start an inactivity timer after reception of the first sidelink grant, wherein a duration of the inactivity timer is a configured duration for a sidelink inactivity, wherein the configured duration of the sidelink round trip time timer and the configured duration of the sidelink retransmission timer are specific for a direction of the transmission; and

allow start of a discontinuous reception (DRX) mode for the first UE after the configured duration of the sidelink retransmission timer if a second grant for a sidelink retransmission is not received from the base station during the sidelink retransmission timer and in response to expiration of the inactivity timer.

25. The non-transitory computer-readable medium of claim 24 , further comprising instructions that cause the UE to start a second inactivity timer in response to a second grant for a second transmission on a link between the first UE and a base station during the inactivity timer, wherein a new duration of the second inactivity timer is a configured duration for an inactivity for the link between the first UE and the base station, wherein the configured duration of the sidelink inactivity is different than the configured duration of the inactivity for the link between the first UE and the base station.