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 comprising a pair of pilot symbols in a time domain, 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 pair of pilot symbols using a first number of resource elements to a first transmit port and 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 pair of pilot symbols within a first time interval of each other in the time domain;

transmitting, from the second transmit port, the second set of pilot symbols, the first and second transmitted sets of pilot symbols comprising a common reference signal; and

transmitting, from the first transmit port, a third set of pilot symbols within a second time interval of the pair of pilot symbols, the first time interval being less than the second time interval.

2. The method of claim 1 , further comprising:

transmitting, from the second transmit port, a fourth set of pilot symbols within the second time interval, the third and fourth sets of pilot symbols comprising a second common reference signal.

3. 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.

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 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.

7. 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 comprising a pair of pilot symbols in a time domain, 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 and 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 being configured to:

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

transmit a third set of pilot symbols within a second time interval of the pair of pilot symbols, the first time interval being less than the second time interval; and

the second transmit port being configured to transmit the second set of pilot symbols, the first and second transmitted sets of pilot symbols comprising a common reference signal.

8. The wireless communications device of claim 7 , wherein the second transmit port is further configured to:

transmit a fourth set of pilot symbols within the second time interval, the third and fourth sets of pilot symbols comprising a second common reference signal.

9. The wireless communications device of claim 7 , 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 7 , 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 7 , 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 7 , 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 7 , 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.

14. A method for wireless communication, comprising:

receiving, at a wireless communications device, a first set of pilot symbols comprising a pair of pilot symbols within a first time interval from each other in a time domain, 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 common reference signal;

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; and

receiving, at the wireless communication device, a third set of pilot symbols within a second time interval of the first set of pilot symbols in the time domain, the second time interval being greater than the first time interval.

15. The method of claim 14 , further comprising:

receiving a fourth set of pilot symbols at the wireless communications device within the second time interval, the third and fourth sets of pilot symbols comprising a second common reference signal; and

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.

16. The method of 15 , further comprising:

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

17. The method of claim 14 , 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; and

estimating a time-frequency domain joint channel estimation.

18. The method of claim 14 , further comprising:

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

19. The method of claim 14 , 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.

20. The method of claim 19 , 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.