Channel estimation for per-tone continuous precoding in downlink MIMO transmission

1. An apparatus for wireless communications, comprising:

a processing system configured to:

receive, through a plurality of antennas, a transmission over a precoded channel, the transmission comprising a layer having a plurality of symbols, each symbol having a plurality of modulated tones precoded on a per-tone basis, the layer comprising a reference signal comprising one or more of the plurality of symbols and being associated with a power delay profile;

estimate a time support of the power delay profile from the reference signal received through one of the plurality of antennas; and

estimate the precoded channel based on the time support of the power delay profile.

2. The apparatus of claim 1 , wherein the processing system is further configured to estimate the time support of the power delay profile from a dominant path of the layer.

3. The apparatus of claim 1 , wherein the transmission further comprises an additional layer, the additional layer having a second plurality of symbols, each symbol having a second plurality of modulated tones precoded on a per-tone basis.

4. The apparatus of claim 1 , wherein the reference signal comprises an apparatus specific reference signal.

5. The apparatus of claim 1 , wherein the processing system is further configured to receive an indicator identifying said one of the plurality of antennas through which the reference signal is received, wherein the reference signal is used to estimate the time support of the power delay profile.

6. The apparatus of claim 1 , wherein the processing system is further configured to locate a dominant path of the layer by applying an IFFT to the reference signal received through said one of the plurality of antennas and the processing system is further configured to estimate the time support of the power delay profile using the dominant path.

7. The apparatus of claim 2 , wherein the processing system is further configured to estimate the time support by aligning a center of the time support of the power delay profile with the dominant path.

8. The apparatus of claim 7 , wherein the processing system is further configured to estimate the time support by using a value proportional to a delay spread for a propagation channel as a length of the time support of the precoded channel.

9. The apparatus of claim 8 , wherein the processing system is further configured to receive a cell specific reference signal and estimate the delay spread for the propagation channel from the cell specific reference signal.

10. The apparatus of claim 7 , wherein the processing system is further configured to receive a delay spread for the layer from a remote apparatus and estimate the time support using the delay spread as a length of the time support of the precoded channel.

11. The apparatus of claim 2 , wherein at least one of the plurality of modulated tones precoded on a per-tone basis are phase ramp compensated, and wherein the processing system is further configured to use the dominant path to adjust a position of an FFT window of a receiver.

12. A method of wireless communications, comprising:

receiving, through a plurality of antennas, a transmission over a precoded channel, the transmission comprising a layer having a plurality of symbols, each symbol having a plurality of modulated tones precoded on a per-tone basis, the layer comprising a reference signal comprising one or more of the plurality of symbols and being associated with a power delay profile;

estimating a time support of the power delay profile from the reference signal received through one of the plurality of antennas; and

estimating the precoded channel based on the time support of the power delay profile.

13. The method of claim 12 , further comprising estimating the time support of the power delay profile from a dominant path of the layer.

14. The method of claim 12 , wherein the transmission further comprises one or more additional layers, each of the one or more additional layers having a plurality of symbols, each symbol having a plurality of modulated tones precoded on a per-tone basis.

15. The method of claim 12 , wherein the reference signal comprises an apparatus specific reference signal.

16. The method of claim 12 , further comprising receiving an indicator identifying said one of the plurality of antennas through which the reference signal is received and estimating the time support of the power delay profile using the reference signal.

17. The method of claim 12 , further comprising locating a dominant path of the layer by applying an IFFT to the reference signal received through said one of the plurality of antennas, wherein estimating the time support of the power delay profile comprises using the dominant path.

18. The method of claim 13 , further comprising estimating the time support by aligning a center of the time support of the power delay profile with the dominant path.

19. The method of claim 18 , further comprising estimating the time support by using a value proportional to a delay spread for a propagation channel as a length of the time support of the precoded channel.

20. The method of claim 19 , further comprising:

receiving a cell specific reference signal; and

estimating the delay spread for the propagation channel from the cell specific reference signal.

21. The method of claim 18 , further comprising receiving a delay spread for the layer from a remote apparatus and estimating the time support using the delay spread as a length of the time support of the precoded channel.

22. The method of claim 13 , wherein the plurality of modulated tones precoded on a per-tone basis are phase ramp compensated, the method further comprising using the dominant path to adjust a position of an FFT window of a receiver.

23. An apparatus for wireless communications, comprising:

means for receiving, through a plurality of antennas, a transmission over a precoded channel, the transmission comprising a layer having a plurality of symbols, each symbol having a plurality of modulated tones precoded on a per-tone basis, the layer comprising a reference signal comprising one or more of the plurality of symbols and being associated with a power delay profile;

means for estimating a time support of the power delay profile from the reference signal received through one of the plurality of antennas; and

means for estimating the precoded channel based on the time support of the power delay profile.

24. The apparatus of claim 23 , further comprising means for estimating the time support of the power delay profile from a dominant path of the layer.

25. The apparatus of claim 23 , wherein the transmission further comprises one or more additional layers, each of the one or more additional layers having a plurality of symbols, each symbol having a plurality of modulated tones precoded on a per-tone basis.

26. A non-transitory computer-readable medium storing computer executable code, comprising code that when executed by a processor cause the processor to be configured to:

receive, through a plurality of antennas, a transmission over a precoded channel, the transmission comprising a layer having a plurality of symbols, each symbol having a plurality of modulated tones precoded on a per-tone basis, the layer comprising a reference signal comprising one or more of the plurality of symbols and being associated with a power delay profile;

estimate a time support of the power delay profile from the reference signal received through one of the plurality of antennas; and

estimate the precoded channel based on the time support of the power delay profile.