Method and apparatus for acquistion and tracking of orthogonal frequency division multiplexing symbol timing, carrier frequency offset and phase noise

• US 7,532,693 B1
• Filed: 05/08/2007
• Issued: 05/12/2009
• Est. Priority Date: 03/05/2001
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Narasimhan, Ravi
• Primary Examiner(s): Ghebretinsae; Temesghen
• Application Number:
  US11/801,032
• Time in Patent Office: 735 Days
• Field of Search: 375/355, 375/344, 375/149, 375/326, 370/208, 370/203
• US Class Current: 375/355
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 27/2659 Coarse or integer frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/266 Fine or fractional frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2695 with channel estimation, e.g. determination of delay spread, derivative or peak tracking channel estimation H04L25/0202

Abstract

A method for estimating symbol timing of a guard interval in an orthogonal frequency division multiplexing receiver of a wireless local area network comprises receiving a preamble including a plurality of short training symbols; sampling said short training symbols of said preamble at a first rate; correlating a first short training symbol with a second short training symbol that is adjacent to said first short training symbol and generating a correlation signal; normalizing said correlation signal to generate a normalized correlation signal; and calculating a mean absolute difference of said normalized correlation signal.

Claims

1. A method for estimating symbol timing of a guard interval in an orthogonal frequency division multiplexing receiver of a wireless local area network, comprising:

receiving a preamble including a plurality of short training symbols;

sampling said short training symbols of said preamble at a first rate;

correlating a first short training symbol with a second short training symbol that is adjacent to said first short training symbol and generating a correlation signal;

normalizing said correlation signal to generate a normalized correlation signal; and

calculating a mean absolute difference of said normalized correlation signal.

2. The method of claim 1 further comprising repeating said sampling, correlating and normalizing steps for all of said short training symbols.

3. The method of claim 2 further comprising multiplying a maximum value of said normalized correlation signal by a threshold value to identify left and right edges of a plateau defined by said normalized correlation signal.

4. The method of claim 3 further comprising identifying left and right time index values corresponding to said left and right edges.

5. The method of claim 4 further comprising identifying a center time index value using said left and right time index values and calculating a value K that is based on said left and right time index values divided by 2, wherein K is a number of terms in an estimate of the mean absolute difference.

6. The method of claim 1 wherein said method is a software method.

7. The method of claim 5 further comprising calculating said mean absolute difference from K/2 before said center time index value to K/2 after said center time index value.

8. The method of claim 7 further comprising identifying a guard interval time index value when an absolute difference between one normalized correlation value and a preceding normalized correlation value exceeds said mean absolute difference multiplied by a threshold value.

9. The method of claim 8 further comprising adjusting said guard interval time index by a tolerance factor.

10. A symbol timing estimator of a guard interval for an orthogonal frequency division multiplexing receiver of a wireless local area network, comprising:

receiving means for receiving a preamble including a plurality of short training symbols;

sampling means for sampling said short training symbols of said preamble at a first rate;

correlating means for correlating a first short training symbol with a second short training symbol that is adjacent to said first short training symbol and generating a correlation signal;

normalizing means for normalizing said correlation signal to generate a normalized correlation signal; and

first calculating means for calculating a mean absolute difference of said normalized correlation signal.

11. The symbol timing estimator of claim 10 further comprising first multiplying means for multiplying a maximum value of said normalized correlation signal by a threshold value to identify left and right edges of a plateau defined by said normalized correlation signal.

12. The symbol timing estimator of claim 11 further comprising first identifying means for identifying left and right time index values corresponding to said left and right edges.

13. The symbol timing estimator of claim 12 further comprising second identifying means for identifying a center time index value using said left and right time index values.

14. The symbol timing estimator of claim 13 further comprising second calculating means for calculating a value K that is based on said left and right time index values divided by 2, wherein K is a number of terms in an estimate of the mean absolute difference.

15. The symbol timing estimator of claim 14 further comprising third calculating means for calculating said mean absolute difference from K/2 before said center time index value to K/2 after said center time index value.

16. The symbol timing estimator of claim 15 further comprising third identifying means for identifying a guard interval time index value when an absolute difference between one normalized correlation value and a preceding normalized correlation value exceeds said mean absolute difference multiplied by a threshold value.

17. The symbol timing estimator of claim 16 further comprising adjusting means for adjusting said guard interval time index by a tolerance factor.

18. A symbol timing estimator of a guard interval for an orthogonal frequency division multiplexing receiver of a wireless local area network, comprising:

a receiver that receives a preamble including a plurality of short training symbols and samples said short training symbols of said preamble at a first rate;

a correlator that correlates a first short training symbol with a second short training symbol that is adjacent to said first short training symbol and generating a correlation signal;

a normalizer that normalizes said correlation signal to generate a normalized correlation signal; and

a first calculator that calculates a mean absolute difference of said normalized correlation signal.

19. The symbol timing estimator of claim 18 further comprising a first multiplier that multiplies said a maximum value of said normalized correlation signal by a threshold value to identify left and right edges of a plateau defined by said normalized correlation signal.

20. The symbol timing estimator of claim 19 further comprising a first identifier circuit that identifies left and right time index values corresponding to said left and right edges.

21. The symbol timing estimator of claim 20 further comprising a second identifier circuit that identifies a center time index value using said left and right time index values.

22. The symbol timing estimator of claim 21 further comprising a second calculator that calculates a value K that is based on said left and right time index values divided by 2, wherein K is a number of terms in an estimate of the mean absolute difference.

23. The symbol timing estimator of claim 22 further comprising a third calculator that calculates said mean absolute difference from K/2 before said center time index value to K/2 after said center time index value.

24. The symbol timing estimator of claim 23 further comprising a third identifier circuit that identifies a guard interval time index value when an absolute difference between one normalized correlation value and a preceding normalized correlation value exceeds said mean absolute difference multiplied by a threshold value.

25. The symbol timing estimator of claim 24 further comprising a guard interval adjustor that adjusts said guard interval time index by a tolerance factor.