Block oriented digital communication system and method

1. A method for estimating a time shift required for symbol synchronization in a block oriented digital communication system for receiving PHY symbols, the method comprising steps of:

producing a first sequence (u(n)) by sampling a received real signal N times over a duration of one PHY symbol;

producing a second sequence (U(k)) by performing an N point discrete Fourier transform (DFT) on u(n);

producing a third sequence (Y(k)) by multiplying U(k) by a fourth sequence (S*(k)) comprising a complex conjugate of a DFT of a synch symbol;

producing a fifth sequence (Y′(k)) by multiplying Y(k) by a window of length N/(2d) from k 1 to k 1 +N/(2d)−1 where d is a decimation factor and 0≦k 1 ≦N/2−N/(2d);

producing a sixth sequence (Y″(k)) by shifting Y′(k) by k 1 samples;

producing a seventh sequence (X(k)) by forming a conjugate symmetric spectrum from Y″(k);

producing a eighth sequence (x(n)) by performing an N/d inverse DFT (IDFT) of X(k); and

estimating the time shift required for symbol synchronization by detecting a position in time of a peak value in x(n).

2. A method as claimed in claim 1 wherein d is chosen such that N/d is a power of 2.

3. A method as claimed in claim 2 wherein the IDFT is an inverse fast Fourier transform (IFFT).

4. A method as claimed in claim 1 wherein a type of the window is selected from the group consisting of rectangular, Hamming, Hanning, Blackman, Bartlett and Kaiser.

5. A method as claimed in claim 1 further comprising a step of choosing k 1 such that a set of contiguous tones from k 1 to k 1 +N/(2d)−1 of Y(k) is a set of tones having a highest average signal power.

6. A method as claimed in claim 1 further comprising a step of choosing k 1 such that a set of contiguous tones from k 1 to k 1 +N/(2d)−1 of Y(k) is a set of tones having a highest average signal-to-noise ratio.

7. A method as claimed in claim 1 further comprising a step of setting a tone of Y(k) to zero.

8. A method as claimed in claim 1 further comprising a step of smoothing x(n).

9. A method as claimed in claim 1 further comprising a step of producing a filtered absolute value of x(n).

10. A method as claimed in claim 9 further comprising a step of detecting a position in time of a peak in the filtered absolute value of x(n) relative to an alignment window.

11. A method as claimed in claim 1 further comprising a step of pre-summing weighted samples from a cyclic prefix with weighted samples of a PHY symbol.

12. A method as claimed in claim 1 wherein the step of producing the eighth sequence (x(n)) comprises a step of producing a ninth sequence (X c (k)) and performing an N/(2d) point IDFT of X c (k).

13. A method as claimed in claim 1 further comprising a step of detecting a position in time of a peak value in x(n) relative to an alignment window.

14. A method for estimating a time shift required for symbol synchronization in a block oriented digital communication system comprising PHY symbols, the method comprising steps of:

producing a first sequence (u(n)) of by sampling a received complex signal N times over a duration of one PHY symbol;

producing a second sequence (U(k)) by performing an N point discrete Fourier transform (DFT) on u(n);

producing a third sequence (Y(k)) by multiplying U(k) by a fourth sequence (S*(k)) comprising a complex conjugate of a DFT of a synch symbol;

producing a fifth sequence (Y′(k)) by multiplying Y(k) by a window of length N/(d) from k 1 to k 1 +N/(d)−1 where d is a decimation factor and 0≦k 1 ≦N−N/(d);

producing a sixth sequence (X(k)) by shifting Y′(k) by k 1 samples;

producing a seventh sequence (x(n)) by performing an N/d inverse DFT (IDFT) of X(k); and

estimating the time shift required for symbol synchronization by detecting a position in time of a peak value in x(n).

15. A method as claimed in claim 14 wherein d is chosen such that N/d is a power of 2.

16. A method as claimed in claim 15 wherein the IDFT is an inverse fast Fourier transform (IFFT).

17. A method as claimed in claim 14 wherein a type of the window is selected from the group consisting of rectangular, Hamming, Hanning, Blackman, Bartlett and Kaiser.

18. A method as claimed in claim 14 further comprising a step of choosing k 1 such that a set of contiguous tones from k 1 to k 1 +N/(d)−1 of Y(k) is a set of tones having a highest average signal power.

19. A method as claimed in claim 14 further comprising a step of choosing k 1 such that a set of contiguous tones from k 1 to k 1 +N/(d)−1 of Y(k) is a set of tones having a highest average signal-to-noise ratio.

20. A method as claimed in claim 14 further comprising a step of setting a tone of Y(k) to zero.

21. A method as claimed in claim 14 further comprising a step of smoothing x(n).

22. A method as claimed in claim 14 further comprising a step of producing a filtered absolute value of x(n).

23. A method as claimed in claim 22 further comprising a step of detecting a position in time of a peak in the filtered absolute value of x(n) relative to an alignment window.

24. A method as claimed in claim 14 further comprising a step of pre-summing weighted samples from a cyclic prefix with weighted samples of a PHY symbol.

25. A method as claimed in claim 14 further comprising a step of detecting a position in time of the peak value in x(n) relative to an alignment window.

26. A block oriented digital communication system for receiving PHY symbols, comprising:

means for producing a first sequence (u(n)) of by sampling a received real signal N times over a duration of one PHY symbol;

means for producing a second sequence (U(k)) by performing an N point discrete Fourier transform (DFT) on u(n);

means for producing a third sequence (Y(k)) by multiplying U(k) by a fourth sequence (S*(k)) comprising a complex conjugate of a DFT of a synch symbol;

means for producing a fifth sequence (Y′(k)) by multiplying Y(k) by a window of length N/(2d) from k 1 to k 1 +N/(2d)−1 where d is a decimation factor and 0≦k 1 ≦N/2−N/(2d);

means for producing a sixth sequence (Y″(k)) by shifting Y′(k) by k 1 samples;

means for producing a seventh sequence (X(k)) by forming a conjugate symmetric spectrum from Y″(k);

means for producing a eighth sequence (x(n)) by performing an N/d inverse DFT (IDFT) of X(k); and

means for estimating a time shift required for symbol synchronization by detecting a position in time of a peak value in x(n).

27. A system as claimed in claim 26 wherein the block oriented digital communication system is an orthogonal frequency division multiplexing (OFDM) system.

28. A system as claimed in claim 26 wherein the block oriented digital communication system is a discrete multi-tone (DMT) data system.

29. A system as claimed in claim 26 wherein the PHY symbols comprise cyclic prefixes.

30. A system as claimed in claim 26 wherein d is chosen such that N/d is a power of 2.

31. A system as claimed in claim 29 wherein the IDFT is an inverse fast Fourier transform (IFFT).

32. A system as claimed in claim 26 wherein a type of the window is selected from the group consisting of rectangular, Hamming, Hanning, Blackman, Bartlett and Kaiser.

33. A system as claimed in claim 26 further comprising means for choosing k 1 such that a set of contiguous tones from k 1 to k 1 +N/(2d)−1 of Y(k) is a set of tones with a highest average signal power.

34. A system as claimed in claim 26 further comprising means for choosing k 1 such that a set of contiguous tones from k 1 to k 1 +N/(2d)−1 of Y(k) is a set of tones with a highest average signal-to-noise ratio.

35. A system as claimed in claim 26 further comprising means for setting a tone of Y(k) to zero.

36. A system as claimed in claim 26 further comprising means for smoothing x(n).

37. A system as claimed in claim 26 further comprising means for producing a filtered absolute value of x(n).

38. A system as claimed in claim 37 further comprising means for detecting a position in time of a peak in the filtered absolute value of x(n) relative to an alignment window.

39. A system as claimed in claim 26 further comprising means for pre-summing weighted samples from a cyclic prefix with weighted samples of a PHY symbol.

40. A system as claimed in claim 26 further comprising means for detecting a position in time of the peak value in x(n) relative to an alignment window.

41. A system as claimed in claim 26 wherein means for producing the eighth sequence (x(n)) comprises means for producing a ninth sequence (X c (k)) and means for performing an N/(2d) point IDFT of X c (k).

42. A block oriented digital communication system for receiving PHY symbols, comprising:

means for producing a first sequence (u(n)) of by sampling a received complex signal N times over a duration of one PHY symbol;

means for producing a second sequence (U(k)) by performing an N point discrete Fourier transform (DFT) on u(n);

means for producing a third sequence (Y(k)) by multiplying U(k) by a fourth sequence (S*(k)) comprising a complex conjugate of a DFT of a synch symbol;

means for producing a fifth sequence (Y′(k)) by multiplying Y(k) by a window of length N/(d) from k 1 to k 1 +N/(d)−1 where d is a decimation factor and 0≦k 1 ≦N−N/(d);

means for producing a sixth sequence (X(k)) by shifting Y′(k) by k 1 samples;

means for producing a seventh sequence (x(n)) by performing an N/d inverse DFT (IDFT) of X(k); and

means for estimating a time shift required for symbol synchronization by detecting a position in time of a peak value in x(n).

43. A system as claimed in claim 42 wherein the block oriented digital communication system is an orthogonal frequency division multiplexing (OFDM) system.

44. A system as claimed in claim 42 wherein the block oriented digital communication system is a discrete multi-tone (DMT) data system.

45. A system as claimed in claim 42 wherein the PHY symbols comprise cyclic prefixes.

46. A system as claimed in claim 42 wherein d is chosen such that N/d is a power of 2.

47. A system as claimed in claim 45 wherein the IDFT is an inverse fast Fourier transform (IFFT).

48. A system as claimed in claim 42 wherein a type of the window is selected from the group consisting of rectangular, Hamming, Hanning, Blackman, Bartlett and Kaiser.

49. A system as claimed in claim 42 further comprising means for choosing k 1 such that a set of contiguous tones from k 1 to k 1 +N/(d)−1 of Y(k) is a set of tones having a highest average signal power.

50. A system as claimed in claim 42 further comprising means for choosing k 1 such that a set of contiguous tones from k 1 to k 1 +N/(d)−1 of Y(k) is a set of tones having a highest average signal-to-noise ratio.

51. A system as claimed in claim 42 further comprising means for setting a tone of Y(k) to zero.

52. A system as claimed in claim 42 further comprising means for smoothing x(n).

53. A system as claimed in claim 42 further comprising means for producing a filtered absolute value of x(n).

54. A system as claimed in claim 53 further comprising means for detecting a position in time of a peak in the filtered absolute value of x(n) relative to an alignment window.

55. A system as claimed in claim 42 further comprising means for pre-summing weighted samples from a cyclic prefix with weighted samples of a PHY symbol.

56. A system as claimed in claim 42 further comprising means for detecting a position in time of the peak value in x(n) relative to an alignment window.