Frequency tracking with sparse pilots
A method and apparatus for estimating a frequency offset of received signals. The receiving device receives a plurality of pilot signals form a transmitting device, and determines an un-aliased frequency offset estimate based on the received pilot signals. The receiving device further determines a low-noise frequency offset estimate based on the received pilot signals, wherein the low-noise frequency offset estimate is blow a threshold noise level. The receiving device then generates a hybrid frequency offset estimate based at least in part on the un-aliased and low-noise frequency offset estimates, wherein the hybrid frequency offset estimate is un-aliased and has a lower estimation noise than the un-aliased frequency offset estimate.
1. A method of estimating a frequency offset of received signals, the method comprising:
receiving a plurality of pilot signals from a transmitter;
determining an un-aliased frequency offset estimate by dividing a first pilot signal of the plurality of pilot signals into two or more split-pilot signals and taking a vector cross product of the two or more split-pilot signals;
determining a low-noise frequency offset estimate based on a vector cross product between the first pilot signal and a delayed first pilot signal, wherein an estimation noise of the low-noise frequency offset estimate is below a threshold noise level; and
generating a hybrid frequency offset estimate based at least in part on the un-aliased frequency offset estimate and the low-noise frequency offset estimate, wherein the hybrid frequency offset estimate is un-aliased and has a lower estimation noise than the un-aliased frequency offset estimate.
2. The method of claim 1 , wherein the pilot signals are received under Doppler effect.
3. The method of claim 1 , wherein the low-noise frequency offset estimate is less susceptible to noise than the un-aliased frequency offset estimate.
4. The method of claim 1 , wherein generating the hybrid frequency offset estimate comprises:
combining the un-aliased frequency offset estimate and the low-noise frequency offset estimate.
5. The method of claim 4 , wherein the low-noise frequency offset estimate is aliased.
6. The method of claim 5 , wherein the combining comprises:
de-aliasing the low-noise frequency offset estimate using the un-aliased frequency offset estimate.
7. The method of claim 6 , wherein the de-aliasing comprises:
comparing the un-aliased frequency offset estimate with the low-noise frequency offset estimate to determine an aliasing interval of the low-noise frequency offset estimate; and
re-calculating the low-noise frequency offset estimate based at least in part on the determined aliasing interval.
8. A wireless communications device, comprising:
a receiver to receive a plurality of pilot signals from a transmitter;
one or more processors; and
a memory storing instructions that, when executed by the one or more processors, cause the wireless communications device to:
determine an un-aliased frequency offset estimate by dividing a first pilot signal of the plurality of pilot signals into two or more split-pilot signals and taking a vector cross product of the two or more split-pilot signals;
determine a low-noise frequency offset estimate based on a vector cross product between the first pilot signal and a delayed first pilot signal, wherein an estimation noise of the low-noise frequency offset estimate is below a threshold noise level; and
generate a hybrid frequency offset estimate based at least in part on the un-aliased frequency offset estimate and the low-noise frequency offset estimate, wherein the hybrid frequency offset estimate is un-aliased and has a lower estimation noise than the un-aliased frequency offset estimate.
9. The wireless communications device of claim 8 , wherein the pilot signals are received under Doppler effect.
10. The wireless communications device of claim 9 , wherein the low-noise frequency offset estimate is less susceptible to noise than the un-aliased frequency offset estimate.
11. The wireless communications device of claim 8 , wherein execution of the instructions to generate the hybrid frequency offset estimate causes the wireless communications device to:
combine the un-aliased frequency offset estimate and the low-noise frequency offset estimate.
12. The wireless communications device of claim 11 , wherein the low-noise frequency offset estimate is aliased.
13. The wireless communications device of claim 12 , wherein execution of the instructions to combine the un-aliased frequency offset estimate and the low-noise frequency offset estimate causes the wireless communications device to:
de-alias the low-noise frequency offset estimate using the un-aliased frequency offset estimate.
14. The wireless communications device of claim 13 , wherein execution of the instructions to de-alias the low-noise frequency offset estimate further causes the wireless communications device to:
compare the un-aliased frequency offset estimate with the low-noise frequency offset estimate to determine an aliasing interval of the low-noise frequency offset estimate; and
re-calculate the low-noise frequency offset estimate based at least in part on the determined aliasing interval.
15. A wireless communications device, comprising:
means for receiving a plurality of pilot signals from a transmitter;
means for determining an un-aliased frequency offset estimate by dividing a first pilot signal of the plurality of pilot signals into two or more split-pilot signals and taking a vector cross product of the two or more split-pilot signals;
means for determining a low-noise frequency offset estimate based on a vector cross product between the first pilot signal and a delayed first pilot signal, wherein an estimation noise of the low-noise frequency offset estimate is below a threshold noise level; and
means for generating a hybrid frequency offset estimate based at least in part on the un-aliased frequency offset estimate and the low-noise frequency offset estimate, wherein the hybrid frequency offset estimate is un-aliased and has a lower estimation noise than the un-aliased frequency offset estimate.
16. The wireless communications device of claim 15 , wherein the pilot signals are received under Doppler effect.
17. The wireless communications device of claim 15 , wherein the low-noise frequency offset estimate is less susceptible to noise than the un-aliased frequency offset estimate.
18. The wireless communications device of claim 15 , wherein the means for generating the hybrid frequency offset estimate is to:
combine the un-aliased frequency offset estimate and the low-noise frequency offset estimate.
19. The wireless communications device of claim 18 , wherein the low-noise frequency offset estimate is aliased.
20. The wireless communications device of claim 19 , further comprising:
means for de-aliasing the low-noise frequency offset estimate using the un-aliased frequency offset estimate.
21. The wireless communications device of claim 20 , wherein the means for de-aliasing the low-noise frequency offset estimate is to:
compare the un-aliased frequency offset estimate with the low-noise frequency offset estimate to determine an aliasing interval of the low-noise frequency offset estimate; and
re-calculate the low-noise frequency offset estimate based at least in part on the determined aliasing interval.
22. A non-transitory computer-readable medium storing instructions that, when executed by one or more processors provided within a wireless communications device, causes the wireless communications device to:
receive a plurality of pilot signals from a transmitter;
determine an un-aliased frequency offset estimate dividing a first pilot signal of the plurality of pilot signals into two or more split-pilot signals and taking a vector cross product of the two or more split-pilot signals;
determine a low-noise frequency offset estimate based on a vector cross product between the first pilot signal and a delayed first pilot signal, wherein an estimation noise of the low-noise frequency offset estimate is below a threshold noise level; and
generate a hybrid frequency offset estimate based at least in part on the un-aliased frequency offset estimate and the low-noise frequency offset estimate, wherein the hybrid frequency offset estimate is un-aliased and has a lower estimation noise than the un-aliased frequency offset estimate.
23. The non-transitory computer-readable medium of claim 22 , wherein
execution of the instructions to generate the hybrid frequency offset estimate causes the wireless communications device to:
combine the un-aliased frequency offset estimate and the low-noise frequency offset estimate.
24. The non-transitory computer-readable medium of claim 22 , wherein
execution of the instructions to combine the un-aliased frequency offset estimate and the low-noise frequency offset estimate causes the wireless communications device to:
de-alias the low-noise frequency offset estimate using the un-aliased frequency offset estimate.