Differential coding and carrier recovery for multicarrier systems

• US 6,931,084 B1
• Filed: 04/14/1998
• Issued: 08/16/2005
• Est. Priority Date: 04/14/1998
• Status: Expired due to Term

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Fischer, Robert, Eberlein, Ernst, Gerhaeuser, Heinz, Heuberger, Albert, Badri, Sabah, Lipp, Stefan, Buchholz, Stephan
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Vartanian, Harry
• Application Number:
  US09/673,266
• Time in Patent Office: 2,681 Days
• Field of Search: 375/346, 370/32.1, 379/410
• US Class Current: 375/346
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2679 Decision-aided

Abstract

A method of performing an echo phase offset correction in a multi-carrier demodulation system involves the step of differential phase decoding phase shifts based on a phase difference between simultaneous carriers having different frequencies. An echo phase offset is determined for each decoded phase shift by eliminating phase shift uncertainties related to the transmitted information from the decoded phase shift. The echo phase offsets are averaged in order to generate an averaged offset. Finally, each decoded phase shift is corrected based on the averaged offset.

Claims

1. A method of performing an echo phase offset correction in a multi-carrier demodulation system, comprising the steps of:

differential phase decoding phase shifts based on a phase difference between simultaneous carriers having different frequencies;

determining an echo phase offset for each decoded phase shift by eliminating phase shift uncertainties related to the transmitted information from said decoded phase shift;

averaging said echo phase offsets in order to generate an averaged offset;

correcting each decoded phase shift based on said averaged offset; and

further comprising a step of comparing an absolute value of a symbol associated with a respective decoded phase shift with a threshold, wherein only phase shifts having associated therewith symbols having an absolute value exceeding said threshold are used in said step of averaging said echo phase offsets.

2. The method according to claim 1, wherein said step of differential phase decoding comprises the step of differential phase decoding phase shifts based on a phase difference between simultaneous carriers which are adjacent in the frequency axis direction.

3. The method according to claim 1, wherein said step of differential phase decoding comprises the step of differential phase decoding phase shifts based on phase differences between at least three simultaneous carriers which are equally spaced in the frequency axis direction.

4. A method of performing an echo phase offset correction in a multi-carrier demodulation system, comprising the steps of:

differential phase decoding phase shifts based on a phase difference between simultaneous carriers having different frequencies, said phase shifts defining signal points in a complex plane;

pre-rotating said signal points into the sector of said complex plane between −

45° and

+45°

;

determining parameters a, b of a straight line approximating the location of said pre-rotated signal points in said complex plane;

determining a phase offset based on said parameters a, b; and

correcting each decoded phase shift based on said phase offset.

5. The method according to claim 4, wherein said simultaneous carriers are equally spaced in the frequency axis direction.

6. The method according to claim 4, wherein said step of determining said parameters a, b comprises a least squares method for selecting those parameters which minimize the deviations of said pre-rotated signal points from said straight line.

7. The method according to claim 6, wherein said parameters a, b are determined as follows:

$b=\frac{\underset{i=1}{\overset{K}{\sum <br><br>}}<br><br>\left(x_i-\stackrel{\_}{x}\right)·<br><br>y_i}{\underset{i=1}{\overset{K}{\sum <br><br>}}<br><br>{\left(x_i-\stackrel{\_}{x}\right)}^2},<br><br>a=\stackrel{\_}{y}-\stackrel{\_}{x}·<br><br>b$$\stackrel{\_}{x}=\frac{1}{N}<br><br>\underset{i=1}{\overset{K}{\sum <br><br>}}<br><br>x_i,<br><br>\stackrel{\_}{y}=\frac{1}{N}<br><br>\underset{i=1}{\overset{K}{\sum <br><br>}}<br><br>y_i$

wherein

x and y designate the coordinates of the signal points in the complex plane,

i is an index from 1 to N, and

K is the numer of signal points.

8. The method according to claim 7, wherein said phase offset φ

_k is determined as follows;

${\mathrm{\phi <br><br>}}_k=\{\begin{array}{cc}-a<br><br><br><br>\tan <br><br>\left(\frac{a+b<br><br>\sqrt{{<br><br>v_k<br><br>}^2<br><br>\left(1+b^2\right)-a^2}}{-\mathrm{ab}+\sqrt{{<br><br>v_k<br><br>}^2<br><br>\left(1+b^2\right)-a^2}}\right)& \mathrm{for}<br><br><br><br>{<br><br>v_k<br><br>}^2\ge <br><br>\frac{a^2}{1+b^2}<br><br>\\ a<br><br><br><br>\tan <br><br>\left(\frac{1}{b}\right)& \mathrm{for}<br><br><br><br>{<br><br>v_k<br><br>}^2<<br><br>\frac{a^2}{1+b^2}\end{array}$

wherein v_k is a given decision variable.

9. An echo phase offset correction device for a multi-cattier demodulation system, comprising:

a differential phase decoder for decoding phase shifts based on a phase difference between simultaneous carriers having different frequencies;

means for determining an echo phase offset for each decoded phase shift comprising means for eliminating phase shift uncertainties related to the transmitted information from said decoded phase shift;

means for averaging said echo phase offsets in order to generate an averaged offset;

means for correcting each decoded phase shift based on said averaged offset; and

means for comparing an absolute value of a symbol associated with a respective decoded phase shift with a threshold, wherein said means for averaging said phase offsets only uses phase shifts having associated therewith symbols having an absolute value exceeding said threshold.

10. The device according to claim 9, wherein said differential phase decoder is adapted for decoding said phase shifts based on a phase difference between simultaneous carriers which are adjacent in the frequency axis direction.

11. The device according to claim 9, wherein said differential phase decoder is adapted for decoding said phase shifts based on phase differences between at least three simultaneous carriers which are equally spaced in the frequency axis direction.

12. An echo phase offset correction device for a multi-carrier demodulation system, comprising:

a differential phase decoder for decoding phase shifts based on a phase difference between simultaneous carriers having different frequencies, said phase shifts defining signal points in a complex plane;

means for pre-rotating said signal points into the sector of said complex plane between −

45° and

+45°

;

means for determining parameters a, b of a straight line approximating the location of said pre-rotated signal points in said complex plane;

means for determining a phase offset based on said parameters a, b; and

means for correcting each decoded phase shift based on said phase offset.

13. The device according to claim 12, wherein said differential phase decoder comprises means for decoding phase shifts of at least three simultaneous carriers which are equally spaced in the frequency axis direction.

14. The device according to claim 12, wherein said means for determining said parameters a, b comprises means for performing a least squares method for selecting those parameters which minimize the deviations of said pre-rotated signal points from said straight line.

15. The device according to claim 14, wherein said means for determining said parameters a, b calculates said parameters a, b as follows:

$b=\frac{\underset{i=1}{\overset{K}{\sum <br><br>}}<br><br>\left(x_i-\stackrel{\_}{x}\right)·<br><br>y_i}{\underset{i=1}{\overset{K}{\sum <br><br>}}<br><br>{\left(x_i-\stackrel{\_}{x}\right)}^2},<br><br>a=\stackrel{\_}{y}-\stackrel{\_}{x}·<br><br>b$$\stackrel{\_}{x}=\frac{1}{N}<br><br>\underset{i=1}{\overset{K}{\sum <br><br>}}<br><br>x_i,<br><br>\stackrel{\_}{y}=\frac{1}{N}<br><br>\underset{i=1}{\overset{K}{\sum <br><br>}}<br><br>y_i$

wherein

x and y designate the coordinates of the signal points in the complex plane,

i is an index from 1 to N, and

K is the number of signal points.

16. The device according to claim 15, wherein said means for determining said phase offset φ

_k calculates said phase offset φ

_k as follows;

${\mathrm{\phi <br><br>}}_k=\{\begin{array}{cc}-a<br><br><br><br>\tan <br><br>\left(\frac{a+b<br><br>\sqrt{{<br><br>v_k<br><br>}^2<br><br>\left(1+b^2\right)-a^2}}{-\mathrm{ab}+\sqrt{{<br><br>v_k<br><br>}^2<br><br>\left(1+b^2\right)-a^2}}\right)& \mathrm{for}<br><br><br><br>{<br><br>v_k<br><br>}^2\ge <br><br>\frac{a^2}{1+b^2}<br><br>\\ a<br><br><br><br>\tan <br><br>\left(\frac{1}{b}\right)& \mathrm{for}<br><br><br><br>{<br><br>v_k<br><br>}^2<<br><br>\frac{a^2}{1+b^2}\end{array}$

wherein v_k is a given decision variable.