Granted Patent B1

US 7,277,517 · App. 10/298,130 · Granted Oct 2, 2007

Abstract

Claims (37)

1. A method for determining symbol boundaries in an ADSL modem, comprising:

receiving multi-frequency modulated signals in the time domain, wherein the multi-frequency modulated signals include a pilot signal at a pilot frequency;

performing a time-to-frequency transform on the multi-frequency modulated signals to recover the pilot signal;

iteratively computing a phase error for the pilot signal over a number of transform regions; and

selecting the transform region with the lowest phase error.

2. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim 1 .

3. The method of claim 1 , wherein the multi-frequency modulated signals include a plurality of frames, and wherein iteratively computing the phase error for the pilot signal comprises:

for each of the number of transform regions, computing the phase error over the plurality of frames; and

averaging the phase errors to obtain one phase error for each of the transform regions.

4. The method of claim 1 , wherein receiving multi-frequency modulated signals comprises receiving DMT signals.

5. The method of claim 1 , wherein the time-to-frequency transform is a Fourier Transform.

6. The method of claim 1 , wherein the time-to-frequency transform is a Fast Fourier Transform.

7. A method for achieving symbol alignment, comprising:

receiving a plurality of multi-carrier frames, wherein each multi-carrier frame includes a pilot signal carried at pilot frequency;

defining a transform region;

for each of a plurality of offsets of the transform region, calculating a phase error of the pilot signal for each of the plurality of frames and averaging the phase errors to obtain an average phase error for the transform region; and

selecting one of the offsets that corresponds to a lowest average phase error.

8. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim 7 .

9. The method of claim 7 , wherein calculating the phase error of the pilot signal comprises:

performing a first set of iterations, wherein the plurality of offsets are multiples of a period of the pilot signal; and

selecting a first minimum offset, wherein the first minimum offset corresponds to the transform region having the lowest phase error.

10. The method of claim 9 , further comprising:

performing a second set of iterations, wherein the offsets are over one period of the pilot signal beginning at the first minimum offset; and

selecting a second minimum offset, wherein the second minimum offset corresponds to the transform region having the lowest phase error from the second set of iterations.

11. A method of aligning symbols in an ADSL modem, comprising:

receiving a multi-carrier signal, wherein the multi-carrier signal includes a pilot signal carried at a pilot frequency;

defining a transform region for the multi-carrier signal;

iteratively shifting the transform region over a predetermined number of periods of the pilot signal and, for each iteration, computing a phase error;

for the iterations over the predetermined number of periods of the pilot signal, selecting the transform region having a lowest phase error;

iteratively shifting the transform region having the lowest phase error over one period of the pilot signal and, for each iteration, computing a phase error; and

for the iterations over one period of the pilot signal, selecting the transform region having a lowest phase error.

12. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim 11 .

13. The method of claim 9 , wherein computing the phase error comprises performing a Fourier Transform.

14. The method of claim 9 , wherein computing the phase error comprises performing a Fast Fourier Transform.

15. The method of claim 11 , wherein the multi-carrier signal includes a plurality of frames, and wherein computing the phase error comprises:

computing the phase error over the frames; and

averaging the phase errors.

Assignments (8)