Timing-frequency offset and carrier-frequency offset estimations for multi-carrier modulated signals using pilot tones

• US 8,270,502 B2
• Filed: 12/14/2007
• Issued: 09/18/2012
• Est. Priority Date: 12/14/2007
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Lai, Yhean-Sen
• Primary Examiner(s): Singh, Hirdepal
• Application Number:
  US11/956,589
• Publication Number:
  US 20090154613A1
• Time in Patent Office: 1,740 Days
• Field of Search: 375/150, 375/259, 375/260, 375/262, 375/267, 375/290, 375/295, 375/297, 375/299, 375/306, 375/316, 375/322, 375/271, 375/350, 375/222, 375/269, 375/302, 375/318, 375/330, 375342-346
• US Class Current: 375/260
• CPC Class Codes: H04L 27/2649 Demodulators
• CPC Class Codes: H04L 27/266 Fine or fractional frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2678 using cyclostationarities, e.g. cyclic prefix or postfix

Abstract

In one embodiment, a demodulator demodulates a multi-carrier modulated signal having two pilot tones. The demodulator calculates a first phase angle for the first pilot tone and a second phase angle for the second pilot tone based on the time-domain multi-carrier modulated signal. A timing-frequency offset estimate is calculated using the first and second phase angles. Further, a fine carrier-frequency offset estimate is calculated for each pilot tone based on the corresponding phase angle and the timing-frequency offset estimate. Each fine carrier-frequency offset estimate is combined with a coarse estimate and weighted. The weighted estimates are then combined. In further embodiments, the timing-frequency offset estimate is weighted and combined with a weighted timing-frequency offset estimate generated using a cyclic prefix. In yet further embodiments, the weighted carrier-frequency offset estimates are combined with a weighted carrier-frequency offset estimate generated using a cyclic prefix.

Claims

1. A method applied at a receiver for processing a multi-carrier modulated signal having at least two pilot tones and at least one data tone, wherein the at least one data tone is transmitted concurrently with the at least two pilot tones, the method comprising:

(a) generating a pilot-based carrier-frequency offset estimate based on the at least two pilot tones, wherein the pilot-based carrier-frequency offset estimate is generated in a time domain and independent of any cyclic prefix in the multi-carrier modulated signal; and

(b) adjusting the multi-carrier modulated signal based on the pilot-based carrier-frequency offset estimate.

2. The method of claim 1, wherein:

the method is applied, at the receiver, to the multi-carrier modulated signal that was generated at a transmitter and transmitted to the receiver;

the multi-carrier modulated signal has a plurality of carriers; and

the pilot-based carrier-frequency offset estimate is an estimate of differences between the frequency of a carrier of the multi-carrier modulated signal received at the receiver and the frequency of a corresponding carrier reference signal at the receiver.

3. The method of claim 1, further comprising:

(c) generating a pilot-based timing-frequency offset estimate based on the at least two pilot tones; and

(d) adjusting the multi-carrier modulated signal based on the pilot-based timing-frequency offset estimate.

4. The method of claim 3, wherein the pilot-based carrier-frequency offset estimate in step (b) is further generated based on the pilot-based timing-frequency offset estimate generated in step (c).

5. The method of claim 3, wherein:

the method is applied, at a receiver, to the multi-carrier modulated signal that was generated at a transmitter and transmitted to the receiver; and

the pilot-based timing-frequency offset estimate is an estimate of differences between the sample frequency of a multi-carrier modulated symbol received at a receiver and the sampling frequency used to decode that received multi-carrier modulated symbol.

6. The method of claim 3, wherein:

(i) the pilot-based timing-frequency offset estimate is generated by;

determining a complex conjugate of a first of the at least two pilot tones;

multiplying the complex conjugate by a second of the at least two pilot tones to generate a product; and

determining the pilot-based timing-frequency offset estimate based on the difference between the frequency of the resulting product and f_1s−

f_2s where,

f_1s is a reference frequency of the first pilot tone;

f_2s is a reference frequency of the second pilot tone; and

(ii) the method generates a first and a second pilot-based carrier-frequency offset estimate, wherein;

the first pilot-based carrier-frequency offset estimate is proportional to;

7. The method of claim 1, wherein:

the multi-carrier modulated signal further comprises a cyclic prefix;

step (a) further comprises;

(a1) generating a prefix-based carrier-frequency offset estimate based on the cyclic prefix; and

(a2) generating a combined carrier-frequency offset estimate based on the prefix-based carrier-frequency offset estimate and the pilot-based carrier-frequency offset estimate; and

step (b) comprises adjusting the multi-carrier modulated signal based on the combined carrier-frequency offset estimate.

8. The method of claim 7, wherein step (a2) comprises:

(a2i) comparing magnitude of the prefix-based carrier-frequency offset estimate to a specified threshold; and

(a2ii) generating the combined carrier-frequency offset estimate independent of the prefix-based carrier-frequency offset estimate, if the magnitude of the prefix-based carrier-frequency offset estimate is greater than the specified threshold.

9. The method of claim 7, further comprising:

(c) generating a pilot-based timing-frequency offset estimate based on the at least two pilot tones;

(d) generating a prefix-based timing-frequency offset estimate based on the cyclic prefix;

(e) combining the pilot-based timing-frequency offset estimate and the prefix-based timing-frequency offset estimate to generate a combined timing-frequency offset estimate; and

(f) adjusting the multi-carrier modulated signal based on the combined timing-frequency offset estimate, wherein step (f) is implemented upstream of step (b).

10. The method of claim 1, wherein:

step (a) further comprises;

(a1) receiving a coarse carrier-frequency offset estimate derived by decoding the multi-carrier modulated signal; and

(a2) generating a combined carrier-frequency offset estimate based on the coarse carrier-frequency offset estimate and the pilot-based carrier-frequency offset estimate; and

step (b) comprises adjusting the multi-carrier modulated signal based on the combined carrier-frequency offset estimate.

11. A receiver for processing a multi-carrier modulated signal having at least two pilot tones and at least one data tone, wherein the at least one data tone is transmitted concurrently with the at least two pilot tones, the receiver comprising:

a carrier-frequency offset estimator adapted to generate a pilot-based carrier-frequency offset estimate based on the at least two pilot tones, wherein the pilot-based carrier-frequency offset estimate is generated in a time domain and independent of any cyclic prefix in the multi-carrier modulated signal; and

a carrier-frequency offset compensator adapted to adjust the multi-carrier modulated signal based on the pilot-based carrier-frequency offset estimate.

12. The receiver of claim 11, further comprising:

a timing-frequency offset estimator adapted to generate a pilot-based timing-frequency offset estimate based on the at least two pilot tones; and

a timing-frequency offset compensator adapted to adjust the multi-carrier modulated signal based on the pilot-based timing-frequency offset estimate.

13. The receiver of claim 11, wherein:

the multi-carrier modulated signal further comprises a cyclic prefix;

the carrier-frequency offset estimator is further adapted to;

(i) generate a prefix-based carrier-frequency offset estimate based on the cyclic prefix; and

(ii) generate a combined carrier-frequency offset estimate based on the prefix-based carrier-frequency offset estimate and the pilot-based carrier-frequency offset estimate; and

the carrier-frequency offset compensator is further adapted to adjust the multi-carrier modulated signal based on the combined carrier-frequency offset estimate.

14. The receiver of claim 13, further comprising:

a timing-frequency offset estimator adapted to;

(i) generate a pilot-based timing-frequency offset estimate based on the at least two pilot tones;

(ii) generate a prefix-based timing-frequency offset estimate based on the cyclic prefix; and

(iii) combine the pilot-based timing-frequency offset estimate and the prefix-based timing-frequency offset estimate to generate a combined timing-frequency offset estimate; and

a timing-frequency offset compensator adapted to adjust the multi-carrier modulated signal based on the combined timing-frequency offset estimate, wherein the timing-frequency offset compensator is implemented upstream of the carrier-frequency offset compensator.

15. A method for processing a multi-carrier modulated signal having at least two pilot tones, a cyclic prefix, and at least one data tone, wherein the at least one data tone is transmitted concurrently with the at least two pilot tones, the method comprising:

(a) generating a pilot-based timing-frequency offset estimate based on the at least two pilot tones;

(b) generating a prefix-based timing-frequency offset estimate based on the cyclic prefix;

(c) combining the pilot-based timing-frequency offset estimate and the prefix-based timing-frequency offset estimate to generate a combined timing-frequency offset estimate; and

(d) adjusting the multi-carrier modulated signal based on the combined timing-frequency offset estimate, wherein;

step (a) further comprises generating a pilot-based carrier-frequency offset estimate based on the at least two pilot tones; and

step (d) further comprises adjusting the multi-carrier modulated signal based on the pilot-based carrier-frequency offset estimate.

16. The method of claim 15, wherein step (c) comprises:

(c1) comparing magnitude of the prefix-based timing-frequency offset estimate to a specified threshold; and

(c2) generating the combined timing-frequency offset estimate independent of the prefix-based timing-frequency offset estimate, if the magnitude of the prefix-based timing-frequency offset estimate is greater than the specified threshold.

17. The method of claim 15, wherein the pilot-based timing-frequency offset estimate is generated by:

determining a complex conjugate of a first of the at least two pilot tones;

multiplying the complex conjugate by a second of the at least two pilot tones to generate a product; and

determining the pilot-based timing-frequency offset estimate based on the difference between the frequency of the resulting product and f_1s−

f_2s where,

f_1s is a reference frequency of the first pilot tone; and

f_2s is a reference frequency of the second pilot tone.

18. The invention of claim 15, wherein the pilot-based timing-frequency offset estimate is generated independent of the cyclic prefix.

19. A receiver for processing a multi-carrier modulated signal having at least two pilot tones, a cyclic prefix, and at least one data tone, wherein the at least one data tone is transmitted concurrently with the at least two pilot tones, the receiver comprising:

a timing-frequency offset estimator adapted to;

(a) generate a pilot-based timing-frequency offset estimate based on the at least two pilot tones;

(b) generate a prefix-based timing-frequency offset estimate based on the cyclic prefix; and

(c) combine the pilot-based timing-frequency offset estimate and the prefix-based timing-frequency offset estimate to generate a combined timing-frequency offset estimate; and

a timing-frequency offset compensator adapted to adjust the multi-carrier modulated signal based on the combined timing-frequency offset estimate, wherein the receiver further comprises;

a carrier-frequency offset estimator adapted to generate a pilot-based carrier-frequency offset estimate based on the at least two pilot tones; and

a carrier-frequency offset compensator adapted to adjust the multi-carrier modulated signal based on the pilot-based carrier-frequency offset estimate.

20. The invention of claim 19, wherein the timing-frequency offset estimator is adapted to generate the pilot-based timing-frequency offset estimate independent of the cyclic prefix.

21. A method for processing a multi-carrier modulated signal having at least two pilot tones, the method comprising:

(a) generating a pilot-based carrier-frequency offset estimate based on the at least two pilot tones;

(b) adjusting the multi-carrier modulated signal based on the pilot-based carrier-frequency offset estimate;

(c) generating a pilot-based timing-frequency offset estimate based on the at least two pilot tones; and

(d) adjusting the multi-carrier modulated signal based on the pilot-based timing-frequency offset estimate, wherein;

(i) the pilot-based timing-frequency offset estimate is generated by;

determining a complex conjugate of a first of the at least two pilot tones;

multiplying the complex conjugate by a second of the at least two pilot tones to generate a product; and

determining the pilot-based timing-frequency offset estimate based on the difference between the frequency of the resulting product and f_1s−

f_2s where,

f_1s is a reference frequency of the first pilot tone;

f_2s is a reference frequency of the second pilot tone; and

(ii) the method generates a first and a second pilot-based carrier-frequency offset estimate, wherein;

the first pilot-based carrier-frequency offset estimate is proportional to;

22. A method for processing a multi-carrier modulated signal having at least two pilot tones and at least one data tone, wherein the at least one data tone is transmitted concurrently with the at least two pilot tones, the method comprising:

(a) generating a pilot-based carrier-frequency offset estimate based on the at least two pilot tones; and

(b) adjusting the multi-carrier modulated signal based on the pilot-based carrier-frequency offset estimate, wherein;

the multi-carrier modulated signal further comprises a cyclic prefix;

step (a) further comprises;

(a1) generating a prefix-based carrier-frequency offset estimate based on the cyclic prefix; and

(a2) generating a combined carrier-frequency offset estimate based on the prefix-based carrier-frequency offset estimate and the pilot-based carrier-frequency offset estimate; and

step (b) comprises adjusting the multi-carrier modulated signal based on the combined carrier-frequency offset estimate.

23. The method of claim 22, wherein step (a2) comprises:

(a2i) comparing magnitude of the prefix-based carrier-frequency offset estimate to a specified threshold; and

(a2ii) generating the combined carrier-frequency offset estimate independent of the prefix-based carrier-frequency offset estimate, if the magnitude of the prefix-based carrier-frequency offset estimate is greater than the specified threshold.

24. The method of claim 22, further comprising:

(c) generating a pilot-based timing-frequency offset estimate based on the at least two pilot tones;

(d) generating a prefix-based timing-frequency offset estimate based on the cyclic prefix;

(e) combining the pilot-based timing-frequency offset estimate and the prefix-based timing-frequency offset estimate to generate a combined timing-frequency offset estimate; and

(f) adjusting the multi-carrier modulated signal based on the combined timing-frequency offset estimate, wherein step (f) is implemented upstream of step (b).

25. A receiver for processing a multi-carrier modulated signal having at least two pilot tones and at least one data tone, wherein the at least one data tone is transmitted concurrently with the at least two pilot tones, the receiver comprising:

a carrier-frequency offset estimator adapted to generate a pilot-based carrier-frequency offset estimate based on the at least two pilot tones;

a carrier-frequency offset compensator adapted to adjust the multi-carrier modulated signal based on the pilot-based carrier-frequency offset estimate, wherein;

the multi-carrier modulated signal further comprises a cyclic prefix;

the carrier-frequency offset estimator is further adapted to;

(i) generate a prefix-based carrier-frequency offset estimate based on the cyclic prefix; and

(ii) generate a combined carrier-frequency offset estimate based on the prefix-based carrier-frequency offset estimate and the pilot-based carrier-frequency offset estimate; and

the carrier-frequency offset compensator is further adapted to adjust the multi-carrier modulated signal based on the combined carrier-frequency offset estimate.

26. The receiver of claim 25, further comprising:

a timing-frequency offset estimator adapted to;

(i) generate a pilot-based timing-frequency offset estimate based on the at least two pilot tones;

(ii) generate a prefix-based timing-frequency offset estimate based on the cyclic prefix; and

(iii) combine the pilot-based timing-frequency offset estimate and the prefix-based timing-frequency offset estimate to generate a combined timing-frequency offset estimate; and

a timing-frequency offset compensator adapted to adjust the multi-carrier modulated signal based on the combined timing-frequency offset estimate, wherein the timing-frequency offset compensator is implemented upstream of the carrier-frequency offset compensator.

27. A method for processing a multi-carrier modulated signal having at least two pilot tones and a cyclic prefix, the method comprising:

(a) generating a pilot-based timing-frequency offset estimate based on the at least two pilot tones;

(b) generating a prefix-based timing-frequency offset estimate based on the cyclic prefix;

(c) combining the pilot-based timing-frequency offset estimate and the prefix-based timing-frequency offset estimate to generate a combined timing-frequency offset estimate; and

(d) adjusting the multi-carrier modulated signal based on the combined timing-frequency offset estimate, wherein step (c) comprises;

(c1) comparing magnitude of the prefix-based timing-frequency offset estimate to a specified threshold; and

(c2) generating the combined timing-frequency offset estimate independent of the prefix-based timing-frequency offset estimate, if the magnitude of the prefix-based timing-frequency offset estimate is greater than the specified threshold.

28. A method for processing a multi-carrier modulated signal having at least two pilot tones and a cyclic prefix, the method comprising:

(a) generating a pilot-based timing-frequency offset estimate based on the at least two pilot tones;

(b) generating a prefix-based timing-frequency offset estimate based on the cyclic prefix;

(c) combining the pilot-based timing-frequency offset estimate and the prefix-based timing-frequency offset estimate to generate a combined timing-frequency offset estimate; and

(d) adjusting the multi-carrier modulated signal based on the combined timing-frequency offset estimate, wherein the pilot-based timing-frequency offset estimate is generated by;

determining a complex conjugate of a first of the at least two pilot tones;

multiplying the complex conjugate by a second of the at least two pilot tones to generate a product; and

determining the pilot-based timing-frequency offset estimate based on the difference between the frequency of the resulting product and f_1s−

f_2s where,

f_1s is a reference frequency of the first pilot tone; and

f_2s is a reference frequency of the second pilot tone.

29. A method for processing a multi-carrier modulated signal having at least two pilot tones, the method comprising:

(a) generating a pilot-based carrier-frequency offset estimate based on the at least two pilot tones; and

(b) adjusting the multi-carrier modulated signal based on the pilot-based carrier-frequency offset estimate, wherein;

the multi-carrier modulated signal further comprises a cyclic prefix;

step (a) further comprises;

(a1) generating a prefix-based carrier-frequency offset estimate based on the cyclic prefix; and

(a2) generating a combined carrier-frequency offset estimate based on the prefix-based carrier-frequency offset estimate and the pilot-based carrier-frequency offset estimate; and

step (b) comprises adjusting the multi-carrier modulated signal based on the combined carrier-frequency offset estimate, wherein step (a2) comprises;

(a2i) comparing magnitude of the prefix-based carrier-frequency offset estimate to a specified threshold; and

(a2ii) generating the combined carrier-frequency offset estimate independent of the prefix-based carrier-frequency offset estimate, if the magnitude of the prefix-based carrier-frequency offset estimate is greater than the specified threshold.