Phase tracking reference signal for sub-symbol phase tracking

1. A method for wireless communication, comprising:

determining a discrete Fourier transform (DFT) configuration for a plurality of symbols;

generating, based at least in part on the DFT configuration, a plurality of DFT-precoded symbols corresponding to the plurality of symbols;

mapping the plurality of DFT-precoded symbols to a corresponding plurality of subcarriers, the plurality of subcarriers including at least a subset of subcarriers that are adjacent in frequency;

mapping non-DFT precoded symbols to additional subcarriers, wherein at least one of the non-DFT precoded symbols is mapped to a subcarrier that is interposed in frequency between two subcarriers of the plurality of subcarriers; and

transmitting the plurality of DFT-precoded symbols via a wireless signal that includes the plurality of subcarriers and the additional subcarriers.

2. The method of claim 1 , wherein generating the plurality of DFT-precoded symbols comprises:

generating a first subset of the plurality of DFT-precoded symbols using a first DFT precoding unit.

3. The method of claim 2 , wherein mapping the plurality of DFT-precoded symbols to the plurality of subcarriers comprises:

mapping the first subset of the plurality of DFT-precoded symbols to the subset of subcarriers that are adjacent in frequency.

4. The method of claim 1 , wherein mapping the plurality of DFT-precoded symbols to the plurality of subcarriers comprises:

mapping subsets of the plurality of DFT-precoded symbols to respective subsets of the plurality of subcarriers, wherein each subset of the plurality of DFT-precoded symbols is associated with a respective DFT precoding unit, and wherein each respective subset of the plurality of subcarriers comprises subcarriers that are adjacent in frequency.

5. The method of claim 1 , wherein generating the plurality of DFT-precoded symbols comprises:

accessing a lookup table that associates the plurality of symbols with the plurality of DFT-precoded symbols based at least in part on the DFT configuration; and

retrieving the plurality of DFT-precoded symbols from memory.

6. The method of claim 1 , further comprising:

receiving, from a wireless device, channel quality information or signals to assist in determining channel quality information; and

determining, based at least in part on the channel quality information, at least one of the plurality of subcarriers.

7. The method of claim 6 , wherein the channel quality information comprises a signal-to-noise ratio (SNR) for at least one of the plurality of subcarriers.

8. The method of claim 1 , further comprising:

receiving, from a wireless device, an indication of one or more preferred subcarriers; and

determining, based at least in part on the indication, at least one of the plurality of subcarriers.

9. The method of claim 1 , wherein determining the DFT configuration comprises:

determining a number of DFT precoding units and a size of each DFT precoding unit.

10. The method of claim 1 , wherein determining the DFT configuration comprises:

determining the DFT configuration based at least in part on a modulation and coding scheme (MCS), a signal-to-noise ratio (SNR) of at least one of the plurality of subcarriers, a phase noise associated with at least one of the plurality of subcarriers, a carrier frequency offset (CFO) associated with at least one of the plurality of subcarriers, or any combination thereof.

11. The method of claim 1 , further comprising:

transmitting an indication of the DFT configuration, an indication of the plurality of subcarriers, or any combination thereof.

12. The method of claim 1 , wherein the plurality of symbols comprises a plurality of phase tracking reference signal (PT-RS) symbols.

13. The method of claim 12 , wherein each of the plurality of PT-RS symbols corresponds to a distinct PT-RS sequence.

14. An apparatus for wireless communication, comprising:

a processor;

memory coupled to the processor; and

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

determine a discrete Fourier transform (DFT) configuration for a plurality of symbols;

generate, based at least in part on the DFT configuration, a plurality of DFT-precoded symbols corresponding to the plurality of symbols;

map the plurality of DFT-precoded symbols to a corresponding plurality of subcarriers, the plurality of subcarriers including at least a subset of subcarriers that are adjacent in frequency;

map non-DFT precoded symbols to additional subcarriers, wherein at least one of the non-DFT precoded symbols is mapped to a subcarrier that is interposed in frequency between two subcarriers of the plurality of subcarriers; and

transmit the plurality of DFT-precoded symbols via a wireless signal that includes the plurality of subcarriers and the additional subcarriers.

15. The apparatus of claim 14 , wherein the instructions to generate the plurality of DFT-precoded symbols are executable by the processor to further cause the apparatus to:

generate a first subset of the plurality of DFT-precoded symbols using a first DFT precoding unit.

16. The apparatus of claim 15 , wherein the instructions to map the plurality of DFT-precoded symbols to the plurality of subcarriers are executable by the processor to further cause the apparatus to:

map the first subset of the plurality of DFT-precoded symbols to the subset of subcarriers that are adjacent in frequency.

17. The apparatus of claim 14 , wherein the instructions to map the plurality of DFT-precoded symbols to the plurality of subcarriers are executable by the processor to further cause the apparatus to:

map subsets of the plurality of DFT-precoded symbols to respective subsets of the plurality of subcarriers, wherein each subset of the plurality of DFT-precoded symbols is associated with a respective DFT precoding unit, and wherein each respective subset of the plurality of subcarriers comprises subcarriers that are adjacent in frequency.

18. The apparatus of claim 14 , wherein the instructions to generate the plurality of DFT-precoded symbols are executable by the processor to further cause the apparatus to:

access a lookup table that associates the plurality of symbols with the plurality of DFT-precoded symbols based at least in part on the DFT configuration; and

retrieve the plurality of DFT-precoded symbols from memory.

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

receive, from a wireless device, channel quality information or signals to assist in determining channel quality information; and

determine, based at least in part on the channel quality information, at least one of the plurality of subcarriers.

20. The apparatus of claim 19 , wherein the channel quality information comprises a signal-to-noise ratio (SNR) for at least one of the plurality of sub carriers.

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

receive, from a wireless device, an indication of one or more preferred subcarriers; and

determine, based at least in part on the indication, at least one of the plurality of subcarriers.

22. The apparatus of claim 14 , wherein the instructions to determine the DFT configuration are executable by the processor to further cause the apparatus to:

determine a number of DFT precoding units and a size of each DFT precoding unit.

23. The apparatus of claim 14 , wherein the instructions to determine the DFT configuration are executable by the processor to further cause the apparatus to:

determine the DFT configuration based at least in part on a modulation and coding scheme (MCS), a signal-to-noise ratio (SNR) of at least one of the plurality of subcarriers, a phase noise associated with at least one of the plurality of subcarriers, a carrier frequency offset (CFO) associated with at least one of the plurality of subcarriers, or any combination thereof.

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

transmit an indication of the DFT configuration, an indication of the plurality of subcarriers, or any combination thereof.

25. The apparatus of claim 14 , wherein the plurality of symbols comprises a plurality of phase tracking reference signal (PT-RS) symbols.

26. The apparatus of claim 25 , wherein each of the plurality of PT-RS symbols corresponds to a distinct PT-RS sequence.

27. An apparatus for wireless communication, comprising:

means for determining a discrete Fourier transform (DFT) configuration for a plurality of symbols;

means for generating, based at least in part on the DFT configuration, a plurality of DFT-precoded symbols corresponding to the plurality of symbols;

means for mapping the plurality of DFT-precoded symbols to a corresponding plurality of subcarriers, the plurality of subcarriers including at least a subset of subcarriers that are adjacent in frequency;

means for mapping non-DFT precoded symbols to additional subcarriers, wherein at least one of the non-DFT precoded symbols is mapped to a subcarrier that is interposed in frequency between two subcarriers of the plurality of subcarriers; and

means for transmitting the plurality of DFT-precoded symbols via a wireless signal that includes the plurality of subcarriers and the additional subcarriers.

28. A non-transitory computer-readable medium storing code for wireless communication, the code comprising instructions executable by a processor to:

determine a discrete Fourier transform (DFT) configuration for a plurality of symbols;

generate, based at least in part on the DFT configuration, a plurality of DFT-precoded symbols corresponding to the plurality of symbols;

map the plurality of DFT-precoded symbols to a corresponding plurality of subcarriers, the plurality of subcarriers including at least a subset of subcarriers that are adjacent in frequency;

map non-DFT precoded symbols to additional subcarriers wherein at least one of the non-DFT precoded symbols is mapped to a subcarrier that is interposed in frequency between two subcarriers of the plurality of subcarriers; and

transmit the plurality of DFT-precoded symbols via a wireless signal that includes the plurality of subcarriers and the additional subcarriers.