Pilot-assisted doppler frequency estimation

• US 8,311,132 B2
• Filed: 11/30/2005
• Issued: 11/13/2012
• Est. Priority Date: 11/30/2005
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Kind, Adriel P.
• Primary Examiner(s): Lam, Kenneth
• Assistant Examiner(s): Ghulamali, Qutbuddin
• Application Number:
  US11/289,943
• Publication Number:
  US 20070121739A1
• Time in Patent Office: 2,540 Days
• Field of Search: 375/259, 375/260, 375/267, 375/299, 375/316, 375/347, 375/344, 375/342
• US Class Current: 375/260
• CPC Class Codes: H04L 2027/0065 Frequency error detectors H04L2027/0067 takes precedence
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657

Abstract

A technique for estimating the Doppler frequency of an input signal comprising a pilot signal. In one embodiment, the technique comprises: (a) accumulating a plurality of samples from the input signal over a specified time duration to derive a channel tap estimate; (b) obtaining a sequence of channel tap estimates by repeating step (a) until a specified number of channel tap estimates have been accumulated; (c) performing a Fourier transform of the sequence of channel tap estimates to obtain a complex sequence of values; (d) finding the smallest index value for which a power spectral distribution function of the complex sequence of values exceeds a specified threshold; and (e) obtaining an estimate of the Doppler frequency by dividing the smallest index value found in step (d) by the product of the specified number of channel tap estimates and the specified time duration.

Claims

1. A method of estimating the Doppler frequency of an input signal comprising a pilot signal, the method comprising:

(a) accumulating a plurality of samples from the input signal over a specified time duration to derive a channel tap estimate;

(b) obtaining a sequence of channel tap estimates by repeating step (a) until a specified number of channel tap estimates have been accumulated;

(c) performing a Fourier transform of the sequence of channel tap estimates to obtain a complex sequence of values;

(d) finding an index value for which a power spectral distribution function of the complex sequence of values exceeds a specified threshold; and

(e) obtaining an estimate of the Doppler frequency by dividing the index value found in step (d) by the product of the specified number of channel tap estimates and the specified time duration.

2. The invention of claim 1, further comprising descrambling the plurality of samples.

3. The invention of claim 2, wherein the accumulating and descrambling steps are performed using equation

4. The invention of claim 1, wherein the Fourier transform is a discrete Fourier transform.

5. The invention of claim 1, wherein the specified time duration corresponds to an accumulation of 7680 samples.

6. The invention of claim 1, wherein the specified time duration is less than or equal to

7. The invention of claim 1, wherein the specified number of channel tap estimates is an integer power of 2.

8. The invention of claim 1, wherein the power spectral distribution function PSD[k] is defined recursively by

9. The invention of claim 1, wherein the specified threshold is defined as

10. The invention of claim 9, wherein A=0.93 and B=0.1.

11. The invention of claim 1, wherein the specified threshold is between approximately 93% and 98%.

12. The invention of claim 1, wherein the index value found in step (d) is the smallest index value.

13. The invention of claim 1, wherein the index value correlates with a frequency below which nearly all of the signal energy from a remote transmitter lies.

14. Apparatus for estimating the Doppler frequency of an input signal comprising a pilot signal, the apparatus comprising:

a signal estimator block adapted to (a) accumulate a plurality of samples from the input signal over a specified time duration to derive a channel tap estimate, and (b) obtain a sequence of channel tap estimates by repeating step (a) until a specified number of channel tap estimates have been accumulated;

a Fourier transform block adapted to perform a Fourier transform of the sequence of channel tap estimates to obtain a complex sequence of values;

a power spectral distribution block adapted to find an index value for which a power spectral distribution function of the complex sequence of values exceeds a specified threshold; and

a Doppler estimation block adapted to obtain an estimate of the Doppler frequency by dividing the index value found by the power spectral distribution block by the product of the specified number of channel tap estimates and the specified time duration.

15. The invention of claim 14, wherein the signal estimator block is further adapted to descramble the plurality of samples.

16. The invention of claim 15, wherein the signal estimator block is adapted to perform the accumulating and descrambling operations using equation

17. The invention of claim 14, wherein the specified time duration is less than or equal to

18. The invention of claim 14, wherein the power spectral distribution function PSD[k] is defined recursively by

19. The invention of claim 14, wherein the specified threshold is defined as

20. The invention of claim 14, wherein the index value found in step (d) is the smallest index value.

21. The invention of claim 14, wherein the index value correlates with a frequency below which nearly all of the signal energy from a remote transmitter lies.

22. A machine-readable storage medium, having encoded thereon program code, wherein, when the program code is executed by a machine, the machine implements a method for estimating the Doppler frequency of an input signal, the method comprising:

(a) accumulating a plurality of samples from the input signal over a specified time duration to derive a channel tap estimate;

(b) obtaining a sequence of channel tap estimates by repeating step (a) until a specified number of channel tap estimates have been accumulated;

(c) performing a Fourier transform of the sequence of channel tap estimates to obtain a complex sequence of values;

(d) finding an index value for which a power spectral distribution function of the complex sequence of values exceeds a specified threshold; and

(e) obtaining an estimate of the Doppler frequency by dividing the index value found in step (d) by the product of the specified number of channel tap estimates and the specified time duration.

23. The invention of claim 22, wherein the index value correlates with a frequency below which nearly all of the signal energy from a remote transmitter lies.