Common reference signal design based on semi-uniform pilot spacing and orthogonal cover code

1. A method for wireless communication, comprising:

applying, by a processor of a wireless communications device, a first cover code to a first pilot sequence to produce a first set of pilot symbols and a second cover code to a second pilot sequence to produce a second set of pilot symbols, wherein the first cover code and the second cover code are orthogonal to each other in time and frequency domains;

delivering the first set of pilot symbols using a first number of resource elements to a first transmit port;

delivering the second set of pilot symbols using a second number of resource elements to a second transmit port;

transmitting, from the first transmit port, the first set of pilot symbols; and

transmitting, from the second transmit port, the second set of pilot symbols, the first and second transmitted sets of pilot symbols comprising a modified common reference signal as a substitute for a common reference signal and a channel state information reference signal.

2. The method of claim 1 , wherein the applying comprises:

spreading the first pilot sequence with a first Walsh code comprising the first cover code; and

spreading the second pilot sequence with a second Walsh code comprising the second cover code.

3. The method of claim 1 , further comprising:

scrambling the first and second sets of pilot symbols with a scrambling code in the frequency domain.

4. The method of claim 1 , wherein:

the first pilot sequence is different from the second pilot sequence, and

the first and second number of resource elements are the same.

5. The method of claim 1 , wherein:

the first pilot sequence is the same as the second pilot sequence, and

the first and second number of resource elements are the same.

6. The method of claim 1 , wherein the first set of pilot symbols comprises a pair of pilot symbols in the time domain, the transmitting further comprising:

transmitting the pair of pilot symbols within a first time interval of each other in the time domain;

transmitting a third set of pilot symbols via the first transmit port within a second time interval of the pair of pilot symbols; and

transmitting a fourth set of pilot symbols via the second transmit port within the second time interval,

the first time interval being less than the second time interval and the third and fourth sets of pilot symbols comprising a second modified common reference signal.

7. The method of claim 1 , wherein the first and second numbers of resource elements are placed at different subcarriers in the frequency domain, the transmitting further comprising:

placing a first subset of the first set of pilot symbols with a first plurality of subcarriers having a first frequency spacing from each other and located within a selected frequency band in the frequency domain; and

placing a second subset of the first set of pilot symbols with a second plurality of subcarriers having a second frequency spacing from each other and surrounding and including the selected frequency band, the second frequency spacing being greater than the first frequency spacing.

8. A wireless communications device, comprising:

a processor configured to:

apply a first cover code to a first pilot sequence to produce a first set of pilot symbols and a second cover code to a second pilot sequence to produce a second set of pilot symbols, wherein the first cover code and the second cover code are orthogonal to each other in time and frequency domains;

deliver the first set of pilot symbols using a first number of resource elements for transmission; and

deliver the second set of pilot symbols using a second number of resource elements for transmission; and

a transceiver comprising a first transmit port and a second transmit port, the first transmit port configured to transmit the first set of pilot symbols and the second transmit port configured to transmit the second set of pilot symbols, the first and second transmitted sets of pilot symbols comprising a modified common reference signal as a substitute for a common reference signal and a channel state information reference signal.

9. The wireless communications device of claim 8 , wherein the processor is further configured to:

spread the first pilot sequence with a first Walsh code comprising the first cover code; and

spread the second pilot sequence with a second Walsh code comprising the second cover code.

10. The wireless communications device of claim 8 , wherein the transceiver is further configured to scramble the first and second sets of pilot symbols with respective scrambling codes in the frequency domain.

11. The wireless communications device of claim 8 , wherein the first pilot sequence is different from the second pilot sequence and the first and second number of resource elements are the same.

12. The wireless communications device of claim 8 , wherein the first pilot sequence is the same as the second pilot sequence and the first and second number of resource elements are the same.

13. The wireless communications device of claim 8 , wherein the first set of pilot symbols comprises a pair of pilot symbols in the time domain, the transceiver further configured to:

transmit the pair of pilot symbols within a first time interval of each other in the time domain by the first transmit port;

transmit a third set of pilot symbols within a second time interval of the pair of pilot symbols; and

transmit a fourth set of pilot symbols within the second time interval by the second transmit port,

the first time interval being less than the second time interval and the third and fourth sets of pilot symbols comprising a second modified common reference signal.

14. The wireless communications device of claim 8 , wherein the first and second numbers of resource elements are placed at different subcarriers in the frequency domain, the first transmit port of the transceiver further configured to:

place a first subset of the first set of pilot symbols with a first plurality of subcarriers having a first frequency spacing from each other and located within a selected frequency band in the frequency domain; and

place a second subset of the first set of pilot symbols with a second plurality of subcarriers having a second frequency spacing from each other and surrounding and including the selected frequency band, the second frequency spacing being greater than the first frequency spacing.

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

code for causing a wireless communications device to apply a first cover code to a first pilot sequence to produce a first set of pilot symbols and a second cover code to a second pilot sequence to produce a second set of pilot symbols, wherein the first cover code and the second cover code are orthogonal to each other in time and frequency domains;

code for causing the wireless communications device to deliver the first set of pilot symbols using a first number of resource elements to a first transmit port;

code for causing the wireless communications device to deliver the second set of pilot symbols using a second number of resource elements to a second transmit port;

code for causing the wireless communications device to transmit, from the first transmit port, the first set of pilot symbols; and

code for causing the wireless communications device to transmit, from the second transmit port, the second set of pilot symbols, the first and second sets of pilot symbols comprising a modified common reference signal as a substitute for a common reference signal and a channel state information reference signal.

16. The non-transitory computer-readable medium of claim 15 , further comprising:

code for causing the wireless communications device to scramble the first and second sets of pilot symbols with a scrambling code in the frequency domain.

17. The non-transitory computer-readable medium of claim 15 , wherein the first pilot sequence is different from the second pilot sequence and the first and second number of resource elements are the same.

18. The non-transitory computer-readable medium of claim 15 , wherein the first pilot sequence is the same as the second pilot sequence and the first and second number of resource elements are the same.

19. The non-transitory computer-readable medium of claim 15 , wherein the first set of pilot symbols comprises a pair of pilot symbols in the time domain, further comprising:

code for causing the wireless communications device to transmit the pair of pilot symbols within a first time interval of each other in the time domain; and

code for causing the wireless communications device to transmit a third set of pilot symbols via the first transmit port within a second time interval of the pair of pilot symbols, the first time interval being less than the second time interval.

20. The non-transitory computer-readable medium of claim 15 , wherein the first and second numbers of resource elements are placed at different subcarriers in the frequency domain, further comprising:

code for causing the wireless communications device to place a first subset of the first set of pilot symbols with a first plurality of subcarriers having a first frequency spacing from each other and located within a selected frequency band in the frequency domain; and

code for causing the wireless communications device to place a second subset of the first set of pilot symbols with a second plurality of subcarriers having a second frequency spacing from each other and surrounding and including the selected frequency band, the second frequency spacing being greater than the first frequency spacing.

21. A method for wireless communication, comprising:

receiving, at a wireless communications device, a first set of pilot symbols using a first number of resource elements and spread with a first cover code;

receiving, at the wireless communications device, a second set of pilot symbols using a second number of resource elements and spread with a second cover code, the first and second cover codes being orthogonal to each other in time and frequency domains, the first and second sets of pilot symbols comprising a modified common reference signal as a substitute for a common reference signal and a channel state information reference signal; and

de-spreading the first and second sets of pilot symbols in the frequency domain to recover at least two pilot observations in the time domain.

22. The method of claim 21 , further comprising:

de-spreading the first and second sets of pilot symbols in the time domain to recover a pilot observation in the time domain and a dense pilot spread in the frequency domain.

23. The method of claim 22 , further comprising:

estimating a time-frequency domain joint channel estimation.

24. The method of claim 21 , further comprising:

updating a frequency tracking loop with the at least two pilot observations in the time domain.

25. The method of claim 21 , wherein the first set of pilot symbols comprises a pair of pilot symbols received within a first time interval from each other in the time domain, the method further comprising:

receiving a third set of pilot symbols at the wireless communications device within a second time interval of the first set of pilot symbols in the time domain; and

receiving a fourth set of pilot symbols at the wireless communications device within the second time interval,

the second time interval being greater than the first time interval and the third and fourth sets of pilot symbols comprising a second modified common reference signal.

26. The method of claim 25 , further comprising:

computing a fine-resolution frequency error of a channel that conveyed the first and third sets of pilot symbols based on an observation of channel variation during the second time interval.

27. The method of 26 , further comprising:

de-aliasing the fine-resolution frequency error based on an observation of channel variation during the first time interval.

28. The method of claim 21 , wherein the first and second numbers of resource elements are placed at different subcarriers in the frequency domain, the receiving the first and second sets of pilot symbols further comprising:

receiving a first subset of the first set of pilot symbols placed with a first plurality of subcarriers having a first frequency spacing from each other and located within a selected frequency band; and

receiving a second subset of the first set of pilot symbols placed with a second plurality of subcarriers having a second frequency spacing from each other and surrounding and including the selected frequency band,

wherein the second frequency spacing is greater than the first frequency spacing.

29. The method of claim 28 , further comprising:

determining a wideband channel estimate based on de-spreading the received second subset of the first set of pilot symbols; and

de-aliasing the wideband channel estimate based on de-spreading the received first subset of the first set of pilot symbols.