Channel access for discovery reference signal (DRS) transmission in new radio-unlicensed (NR-U)

1. A method of wireless communication, comprising:

identifying, by a first wireless communication device, a plurality of allowable transmission starting locations within a discovery reference signal measurement time configuration (DMTC) window, wherein at least one of the plurality of allowable transmission starting locations is offset from boundaries of a plurality of transmission slots of the DMTC window, and wherein the plurality of allowable transmission starting locations is associated with a maximum allowable number of listen-before-talks (LBTs) within the DMTC window;

communicating at least one of a filler signal or a reference signal based on a successful LBT; and

communicating, by the first wireless communication device with a second wireless communication device based on the successful LBT, a discovery reference signal (DRS) beginning at a first transmission starting location of the plurality of allowable transmission starting locations.

2. The method of claim 1 , wherein the plurality of allowable transmission starting locations is based on at least one of a synchronization signal block (SSB) transmission boundary or a remaining system information (RMSI) control information transmission boundary.

3. The method of claim 1 , wherein the plurality of allowable transmission starting locations is based on at least one of a subcarrier spacing associated with the DRS, a number of SSBs associated with the DRS, or a transmission duration of the DRS.

4. The method of claim 1 , wherein a number of the plurality of allowable transmission starting locations is based on a duration of the DMTC window.

5. The method of claim 1 , further comprising:

communicating, by the first wireless communication device with the second wireless communication device, a configuration indicating the plurality of allowable transmission starting locations.

6. The method of claim 1 , further comprising:

determining, by the first wireless communication device, the plurality of allowable transmission starting locations based on the maximum allowable number of LBTs within the DMTC window.

7. The method of claim 1 , wherein the communicating includes:

transmitting, by the first wireless communication device, the DRS beginning at the first transmission starting location based on the successful LBT.

8. The method of claim 7 , further comprising:

performing, by the first wireless communication device, the LBT based on one or more LBT starting locations determined based on the maximum allowable number of LBTs in the DMTC window.

9. The method of claim 8 , wherein the performing the LBT is further based on a first LBT starting location of the one or more LBT starting locations associated with the first transmission starting location.

10. The method of claim 9 , further comprising:

transmitting, by the first wireless communication device to the second wireless communication device, at least one of the filler signal or the reference signal before the DRS in response to the LBT.

11. The method of claim 8 , further comprising:

determining, by the first wireless communication device, the one or more LBT starting locations based on the maximum allowable number of LBTs within the DMTC window.

12. The method of claim 1 , further comprising:

determining, by the first wireless communication device, the maximum allowable number of LBTs within the DMTC window based on at least one of a subcarrier spacing associated with the DRS, a number of SSBs associated with the DRS, or a duration of the DRS.

13. The method of claim 1 , further comprising:

determining, by the first wireless communication device, the maximum allowable number of LBTs within the DMTC window based on a periodicity of the DMTC window.

14. The method of claim 1 , further comprising:

determining, by the first wireless communication device, the maximum allowable number of LBTs within the DMTC window based on whether a CAT2 LBT or a category 4 (CAT4) LBT is performed for a DRS transmission in a previous DMTC window.

15. The method of claim 1 , further comprising:

performing, by the first wireless communication device, a CAT2 LBT based on a plurality of allowable transmission starting locations in another DMTC window;

performing, by the first wireless communication device, a category 4 (CAT4) LBT within the another DMTC window in response to a failure of the CAT2 LBT; and

transmitting, by the first wireless communication device, another DRS during the another DMTC window based on the CAT4 LBT.

16. The method of claim 15 , wherein the performing the CAT2 LBT is based on a first subset of the plurality of allowable transmission starting locations in the another DMTC window associated with a CAT2 LBT, and wherein the performing the CAT4 LBT is further based on a second subset of the plurality of allowable transmission starting locations in the another DMTC window associated with a CAT4 LBT.

17. The method of claim 1 , further comprising:

monitoring, by the first wireless communication device, for the DRS based on the plurality of allowable transmission starting locations.

18. An apparatus comprising:

a processor configured to identify a plurality of allowable transmission starting locations within a discovery reference signal measurement time configuration (DMTC) window, wherein at least one of the plurality of allowable transmission starting locations is offset from boundaries of a plurality of transmission slots of the DMTC window, and wherein the plurality of allowable transmission starting locations is associated with a maximum allowable number of listen-before-talks (LBTs) within the DMTC window;

a transceiver configured to communicate at least one of a filler signal or a reference signal based on a successful LBT; and

a transceiver configured to communicate, with a wireless communication device based on the successful LBT, a discovery reference signal (DRS) beginning at a first transmission starting location of the plurality of allowable transmission starting locations.

19. The apparatus of claim 18 , wherein the plurality of allowable transmission starting locations is based on at least one of a synchronization signal block (SSB) transmission boundary or a remaining system information (RMSI) control information transmission boundary.

20. The apparatus of claim 18 , wherein the plurality of allowable transmission starting locations is based on at least one of a subcarrier spacing associated with the DRS, a number of SSBs associated with the DRS, or a transmission duration of the DRS.

21. The apparatus of claim 18 , wherein a number of the plurality of allowable transmission starting locations is based on a duration of the DMTC window.

22. The apparatus of claim 18 , wherein the transceiver is further configured to:

communicate, with the wireless communication device, a configuration indicating the plurality of allowable transmission starting locations.

23. The apparatus of claim 18 , wherein the processor is further configured to:

determine the maximum allowable number of LBTs within the DMTC window based on at least one of:

a subcarrier spacing associated with the DRS;

a number of SSBs associated with the DRS;

a duration of the DRS;

a periodicity of the DMTC window; or

whether a CAT2 LBT or a category 4 (CAT4) LBT is performed for a DRS transmission in a previous DMTC window; and

determine the plurality of allowable transmission starting locations based on the maximum allowable number of LBTs within the DMTC window.

24. The apparatus of claim 18 , wherein the transceiver configured to communicate the DRS is further configured to:

transmit the DRS beginning at the first transmission starting location based on the successful LBT.

25. The apparatus of claim 18 , wherein:

the processor is further configured to:

perform a CAT2 LBT based on a plurality of allowable transmission starting locations in another DMTC window; and

perform a category 4 (CAT4) LBT within the another DMTC window in response to a failure of the CAT2 LBT, and

the transceiver is further configured to:

transmit another DRS during the another DMTC window based on the CAT4 LBT.

26. The apparatus of claim 18 , wherein the processor is further configured to:

monitor for the DRS based on the plurality of allowable transmission starting locations.

27. A non-transitory computer-readable medium having program code recorded thereon, the program code comprising:

code for causing a first wireless communication device to identify a plurality of allowable transmission starting locations within a discovery reference signal measurement time configuration (DMTC) window, wherein at least one of the plurality of allowable transmission starting locations is offset from boundaries of a plurality of transmission slots of the DMTC window, and wherein the plurality of allowable transmission starting locations is associated with a maximum allowable number of listen-before-talks (LBTs) within the DMTC window;

code for causing the first wireless communication device to communicate at least one of a filler signal or a reference signal based on a successful LBT; and

code for causing the first wireless communication device to communicate, with a second wireless communication device based on the successful LBT, a discovery reference signal (DRS) beginning at a first transmission starting location of the plurality of allowable transmission starting locations.

28. The non-transitory computer-readable medium of claim 27 , wherein the plurality of allowable transmission starting locations is based on at least one of:

a synchronization signal block (SSB) transmission boundary;

a remaining system information (RMSI) control information transmission boundary;

a subcarrier spacing associated with the DRS;

a number of SSBs associated with the DRS;

a transmission duration of the DRS; or

a duration of the DMTC window.

29. The non-transitory computer-readable medium of claim 27 , further comprising:

code for causing the first wireless communication device to communicate, with the second wireless communication device, a configuration indicating the plurality of allowable transmission starting locations.

30. The non-transitory computer-readable medium of claim 27 , further comprising:

code for causing the first wireless communication device to determine the plurality of allowable transmission starting locations based on the maximum allowable number of LBTs within the DMTC window.