Front loaded sounding reference signal and physical random access channel signal

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

identifying a gap period following a downlink portion of a time division duplexing (TDD) frame;

selectively performing, based at least in part on a comparison of the gap period with a threshold, a clear channel assessment (CCA) on a channel of a radio frequency spectrum band;

transmitting at least one of a sounding reference signal (SRS) or a physical random access channel (PRACH) preamble in a set of initial symbols of an uplink portion of the TDD frame following the gap period, wherein the SRS or PRACH preamble is frequency-domain multiplexed during the set of initial symbols with one or more of: a demodulation reference signal (DMRS), an uplink data transmission, an uplink control transmission, or a random access transmission;

transmitting the DMRS from a first set of antenna ports during a first subset of the set of initial symbols; and

transmitting the DMRS from a second set of antenna ports during a second subset of the set of initial symbols.

2. The method of claim 1 , wherein transmitting at least one of the SRS or the PRACH preamble is on a first comb of a resource block, the method further comprising:

identifying the first comb of the resource block.

3. The method of claim 1 , wherein the PRACH preamble is frequency-domain multiplexed during the set of initial symbols with the uplink data transmission, the method further comprising:

transmitting the PRACH preamble frequency-domain multiplexed with the uplink data transmission during the first subset of the set of initial symbols.

4. The method of claim 3 , further comprising:

transmitting the PRACH preamble frequency-domain multiplexed with the DMRS from the first set of antenna ports or the second set of antenna ports during the second subset of the set of initial symbols.

5. The method of claim 4 , wherein the PRACH preamble and the DMRS are transmitted on different combs of a resource block.

6. The method of claim 1 , further comprising:

transmitting the PRACH preamble on a first interlace of a channel bandwidth and the DMRS, or the uplink data transmission, or the uplink control transmission, or the random access transmission on a second interlace of the channel bandwidth.

7. The method of claim 1 , wherein the PRACH preamble is frequency-domain multiplexed during the set of initial symbols with an uplink data transmission, the method further comprising:

transmitting an additional uplink data transmission over a physical uplink shared channel (PUSCH) during one or more symbols occurring after the set of initial symbols.

8. The method of claim 1 , wherein selectively performing the CCA on the channel of the radio frequency spectrum band based at least in part on the gap period comprises:

performing a CCA procedure when a duration of the gap period exceeds the threshold.

9. The method of claim 1 , wherein selectively performing the CCA on the channel of the radio frequency spectrum band based at least in part on the gap period comprises:

transmitting the PRACH preamble without performing a CCA procedure when a duration of the gap period is less than the threshold.

10. The method of claim 1 , wherein the set of initial symbols comprise one or more symbols immediately following the gap period.

11. An apparatus for wireless communication at a user equipment (UE), comprising:

a processor, memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

identify a gap period following a downlink portion of a time division duplexing (TDD) frame;

selectively perform, based at least in part on a comparison of the gap period with a threshold, a clear channel assessment (CCA) on a channel of a radio frequency spectrum band;

transmit at least one of a sounding reference signal (SRS) or a physical random access channel (PRACH) preamble in a set of initial symbols of an uplink portion of the TDD frame following the gap period, wherein the SRS or PRACH preamble is frequency-domain multiplexed during the set of initial symbols with one or more of: a demodulation reference signal (DMRS), an uplink data transmission, an uplink control transmission, or a random access transmission;

transmit the DMRS from a first set of antenna ports during a first subset of the set of initial symbols; and

transmit the DMRS from a second set of antenna ports during a second subset of the set of initial symbols.

12. The apparatus of claim 11 , wherein the instructions to transmit the at least one of the SRS or the PRACH preamble is on a first comb of a resource block are further executable by the processor to cause the apparatus to:

identify the first comb of the resource block.

13. The apparatus of claim 11 , wherein the PRACH preamble is frequency-domain multiplexed during the set of initial symbols with the uplink data transmission, and wherein the instructions are further executable by the processor to cause the apparatus to:

transmit the PRACH preamble frequency-domain multiplexed with the uplink data transmission during the first subset of the set of initial symbols.

14. The apparatus of claim 13 , wherein the instructions are further executable by the processor to cause the apparatus to:

transmit the PRACH preamble frequency-domain multiplexed with the DMRS from the first set of antenna ports or the second set of antenna ports during the second subset of the set of initial symbols.

15. The apparatus of claim 14 , wherein the PRACH preamble and the DMRS are transmitted on different combs of a resource block.

16. The apparatus of claim 11 , wherein the instructions are further executable by the processor to cause the apparatus to:

transmit the PRACH preamble on a first interlace of a channel bandwidth and the DMRS, or the uplink data transmission, or the uplink control transmission, or the random access transmission on a second interlace of the channel bandwidth.

17. The apparatus of claim 11 , wherein the instructions are further executable by the processor to cause the apparatus to:

transmit an additional uplink data transmission over a physical uplink shared channel (PUSCH) during one or more symbols occurring after the set of initial symbols.

18. The apparatus of claim 11 , wherein the instructions to selectively performing the CCA on the channel of the radio frequency spectrum band based at least in part on the gap period are executable by the processor to cause the apparatus to:

perform a CCA procedure when a duration of the gap period exceeds the threshold.

19. The apparatus of claim 11 , wherein the instructions to selectively performing the CCA on the channel of the radio frequency spectrum band based at least in part on the gap period are executable by the processor to cause the apparatus to:

transmit the PRACH preamble without performing a CCA procedure when a duration of the gap period is less than the threshold.

20. The apparatus of claim 11 , wherein the set of initial symbols comprise one or more symbols immediately following the gap period.

21. An apparatus for wireless communication at a user equipment (UE), comprising:

means for identifying a gap period following a downlink portion of a time division duplexing (TDD) frame;

means for selectively performing, based at least in part on a comparison of the gap period with a threshold, a clear channel assessment (CCA) on a channel of a radio frequency spectrum band;

means for transmitting at least one of a sounding reference signal (SRS) or a physical random access channel (PRACH) preamble in a set of initial symbols of an uplink portion of the TDD frame following the gap period, wherein the SRS or PRACH preamble is frequency-domain multiplexed during the set of initial symbols with one or more of: a demodulation reference signal (DMRS), an uplink data transmission, an uplink control transmission, or a random access transmission;

means for transmitting the DMRS from a first set of antenna ports during a first subset of the set of initial symbols; and

means for transmitting the DMRS from a second set of antenna ports during a second subset of the set of initial symbols.

22. The apparatus of claim 21 , wherein the means for transmitting at least one of the SRS or the PRACH preamble is on a first comb of a resource block, the apparatus further comprising:

means for identifying the first comb of the resource block.

23. The apparatus of claim 21 , wherein the PRACH preamble is frequency-domain multiplexed during the set of initial symbols with the uplink data transmission, the apparatus further comprising:

means for transmitting the PRACH preamble frequency-domain multiplexed with the uplink data transmission during the first subset of the set of initial symbols.

24. The apparatus of claim 23 , further comprising:

means for transmitting the PRACH preamble frequency-domain multiplexed with the DMRS from the first set of antenna ports or the second set of antenna ports during the second subset of the set of initial symbols.

25. The apparatus of claim 21 , further comprising:

means for transmitting the PRACH preamble on a first interlace of a channel bandwidth and the DMRS, or the uplink data transmission, or the uplink control transmission, or the random access transmission on a second interlace of the channel bandwidth.

26. A non-transitory computer-readable medium storing code for wireless communication at a user equipment (UE), the code comprising instructions executable by a processor to:

identify a gap period following a downlink portion of a time division duplexing (TDD) frame;

selectively perform, based at least in part on a comparison of the gap period with a threshold, a clear channel assessment (CCA) on a channel of a radio frequency spectrum band;

transmit at least one of a sounding reference signal (SRS) or a physical random access channel (PRACH) preamble in a set of initial symbols of an uplink portion of the TDD frame following the gap period, wherein the SRS or PRACH preamble is frequency-domain multiplexed during the set of initial symbols with one or more of: a demodulation reference signal (DMRS), an uplink data transmission, an uplink control transmission, or a random access transmission;

transmit the DMRS from a first set of antenna ports during a first subset of the set of initial symbols; and

transmit the DMRS from a second set of antenna ports during a second subset of the set of initial symbols.

27. The non-transitory computer-readable medium of claim 26 , wherein the code comprising instructions executable by the processor to transmit at least one of the SRS or the PRACH preamble is on a first comb of a resource block, the code further comprising instructions executable by the processor to:

identify the first comb of the resource block.

28. The non-transitory computer-readable medium of claim 26 , wherein the PRACH preamble is frequency-domain multiplexed during the set of initial symbols with the uplink data transmission, the code further comprising instructions executable by the processor to:

transmit the PRACH preamble frequency-domain multiplexed with the uplink data transmission during the first subset of the set of initial symbols.

29. The non-transitory computer-readable medium of claim 28 , the code further comprising instructions executable by the processor to:

transmit the PRACH preamble frequency-domain multiplexed with the DMRS from the first set of antenna ports or the second set of antenna ports during the second subset of the set of initial symbols.

30. The non-transitory computer-readable medium of claim 26 , the code further comprising instructions executable by the processor to:

transmit the PRACH preamble on a first interlace of a channel bandwidth and the DMRS, or the uplink data transmission, or the uplink control transmission, or the random access transmission on a second interlace of the channel bandwidth.