Frequency tracking with sparse pilots

• US 9,525,477 B1
• Filed: 09/24/2015
• Issued: 12/20/2016
• Est. Priority Date: 09/24/2015
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Wu, Qiang, Black, Peter John, Ma, Jun
• Primary Examiner(s): Bhattacharya, Sam
• Application Number:
  US14/864,831
• Time in Patent Office: 453 Days
• Field of Search: 455/63.1, 455/296, 455/430, 375/224, 375/319, 375/340
• US Class Current: 1/1
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657
• CPC Class Codes: H04L 43/16 Threshold monitoring

Abstract

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.

Claims

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.