Adaptive equalization in coherent fiber optic communication

• US 20060013590A1
• Filed: 07/14/2004
• Published: 01/19/2006
• Est. Priority Date: 07/14/2004
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Fundación Tarpuy
• Inventors: Crivelli, Diego Ernesto, Hueda, Mario Rafael, Carrer, Hugo Santiago
• Granted Patent: US 8,041,233 B2
• Time in Patent Office: Days
• US Class Current: 398/149
• CPC Class Codes: H04B 10/60 Receivers
• CPC Class Codes: H04B 10/6161 Compensation of chromatic dispersion
• CPC Class Codes: H04B 10/6162 Compensation of polarization related effects, e.g., PMD, PDL
• CPC Class Codes: H04B 10/63 Homodyne , i.e. coherent receivers where the local oscillator is locked in frequency and phase to the carrier signal
• CPC Class Codes: H04B 10/64 Heterodyne , i.e. coherent receivers where, after the opto-electronic conversion, an electrical signal at an intermediate frequency [IF] is obtained
• CPC Class Codes: H04B 10/6971 using equalisation

Abstract

An embodiment of the invention is a technique to equalize received samples. A coefficient generator generates filter coefficients using a rotated error vector. A filter stage generates equalized samples or slicer input vector from received samples or rotated received samples using the filter coefficients. The received samples are provided by a receiver front end in an optical transmission channel carrying transmitted symbols.

Claims

1. An apparatus comprising:

a coefficient generator to generate filter coefficients using a rotated error vector; and

a filter stage coupled to the coefficient generator to generate equalized samples or slicer input vector from received samples or rotated received samples using the filter coefficients, the received samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols.

2. The apparatus of claim 1 further comprising:

a rotator coupled to the filter stage to rotate the equalized samples using a rotation matrix to generate a slicer input vector;

a slicer coupled to the rotator to threshold the slicer input vector to generate a slicer output vector;

an inverse rotator coupled to the coefficient generator to generate the rotated error vector using an error vector and the rotation matrix;

an error calculator coupled to the slicer to calculate the error vector, the error vector being a difference vector between the thresholded rotated vector and the rotated vector; and

a rotation matrix estimator coupled to the slicer and the rotator to generate the rotation matrix using the slicer output vector and the slicer input vector.

3. The apparatus of claim 2 further comprising:

a delay conjugator coupled to the slicer to generate the delayed conjugated vector from the slicer output vector; and

a multiplier coupled to the delayed conjugator and the slicer to multiply the delayed conjugated vector with the slicer output vector to generate receiver symbols corresponding to the transmitted symbols.

4. The apparatus of claim 2 wherein the rotation matrix estimator comprises:

an angle calculator to calculate an angle between the slicer output vector and the slicer input vector;

a transpose conjugator to generate a transpose conjugate for the slicer output vector;

a phase estimator coupled to the transpose conjugator to estimate a phase vector using the transpose conjugate and the slicer input vector; and

a rotation matrix calculator coupled to the phase estimator to calculate the rotation matrix using the estimated phase vector.

5. The apparatus of claim 4 wherein the rotation matrix estimator further comprises:

a polarization angle estimator coupled to the transpose conjugator to estimate a polarization angle using the transpose conjugate and the slicer input vector.

6. The apparatus of claim 4 wherein the rotation matrix calculator calculates the rotation matrix using the estimated phase vector and the estimated polarization angle.

7. The apparatus of claim 1 wherein the coefficient generator comprises:

a coefficient adjuster to generate a coefficient adjustment vector being a product of the rotated error vector, a received sample vector representing the received samples, and a step size parameter; and

an adder coupled to the coefficient adjuster to add a previously calculated coefficient vector to the coefficient adjustment vector to generate a coefficient vector representing the filter coefficients.

8. The apparatus of claim 7 wherein the coefficient vector includes at least four filter coefficient vectors spanned on at least first and second dimensions.

9. The apparatus of claim 1 further comprising:

a rotator coupled to the filter stage to rotate the received samples using a rotation matrix to generate the rotated received samples;

a slicer coupled to the filter stage to threshold the slicer input vector to generate a slicer output vector;

an inverse rotator coupled to the coefficient generator to generate the rotated error vector using an error vector and the rotation matrix;

an error calculator coupled to the slicer to calculate the error vector, the error vector being a difference vector between the thresholded rotated vector and the rotated vector; and

a rotation matrix estimator coupled to the slicer to generate the rotation matrix using the slicer output vector and the slicer input vector.

10. The apparatus of claim 6 wherein the filter stage comprises:

at least four finite impulse response (FIR) filters to operate on the at least four filter coefficient vectors and the received samples, to produce at least four filtered results; and

at least two adders coupled to the at least four FIR filters to add the at least four filtered results on the at least first and second dimensions, respectively, to produce the equalized samples

11. The apparatus of claim 4 wherein the phase estimator comprises:

a phase angle calculator to calculate a phase angle vector;

a phase loop filter coupled to the phase angle calculator to filter the phase angle vector; and

an adder coupled to the loop filter to add the filtered phase angle vector to a previously estimated phase vector to generate the estimated phase vector.

12. The apparatus of claim 5 wherein the polarization angle estimator comprises:

a polarization angle calculator to calculate a polarization angle;

a polarization loop filter coupled to the polarization angle calculator to filter the polarization angle; and

an adder coupled to the previously estimated polarization angle to generate the estimated polarization angle.

13. The apparatus of claim 1 wherein the optical transmission channel operates at a data rate of at least 10 Gigabauds.

14. The apparatus of claim 5 wherein at least one of the phase estimator, the polarization angle estimator, the rotation matrix estimator, the coefficient generator, and the filter stage is implemented by an analog circuit, a digital circuit, a mixed mode circuit, a sequence of instructions, or a program.

15. A method comprising:

generating filter coefficients using a rotated error vector; and

generating equalized samples or slicer input vector from received samples or rotated received samples using the filter coefficients, the received samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols.

16. The method of claim 15 further comprising:

rotating the equalized samples using a rotation matrix to generate a slicer input vector;

thresholding the slicer input vector to generate a slicer output vector;

generating the rotated error vector using an error vector and the rotation matrix;

calculating the error vector, the error vector being a difference vector between the slicer output vector and the slicer input vector; and

generating the rotation slicer matrix using the output vector and the slicer input vector.

17. The method of claim 16 further comprising:

generating the delayed conjugated vector from the slicer output vector; and

multiplying the delayed conjugated vector with the slicer output vector to generate received symbols corresponding to the transmitted symbols.

18. The method of claim 16 wherein generating the rotation matrix comprises:

calculating an angle between the slicer output vector and the slicer input vector;

generating a transpose conjugate for the slicer output vector;

estimating a phase vector using the transpose conjugate and the slicer input vector; and

calculating the rotation matrix using the estimated phase vector.

19. The method of claim 18 wherein generating the rotation matrix comprises:

estimating a polarization angle using the transpose conjugate and the slicer input vector.

20. The method of claim 18 wherein calculating the rotation matrix comprises calculating the rotation matrix using the estimated phase vector and the estimated polarization angle.

21. The method of claim 15 wherein generating the filter coefficients comprises:

generating a coefficient adjustment vector being a product of the rotated error vector, a received sample vector representing the received samples, and a step size parameter; and

adding a previously calculated coefficient vector to the coefficient adjustment vector to generate a coefficient vector representing the filter coefficients.

22. The method of claim 21 wherein the coefficient vector includes at least four filter coefficient vectors spanned on at least first and second dimensions.

23. The method of claim 15 further comprising:

rotating the received samples using a rotation matrix to generate the rotated received samples vector;

thresholding the slicer input vector to generate a slicer output vector;

generating the rotated error vector using an error vector and the rotation matrix;

calculating the error vector, the error vector being a difference vector between the slicer output vector and the slicer input vector; and

generating the rotation matrix using the slicer output vector and the slicer input vector.

24. The method of claim 20 wherein generating the equalized samples comprises:

operating on at least four filter coefficient vectors and the received samples to produce at least four filtered results; and

adding the at least four filtered results on the at least first and second dimensions, respectively, to produce the equalized samples.

25. The method of claim 18 wherein estimating the phase vector comprises:

calculating a phase angle;

filtering the phase angle; and

adding the filtered phase angle to a previously estimated phase vector to generate the estimated phase vector.

26. The method of claim 19 wherein estimating the polarization angle comprises:

calculating a polarization angle;

filtering the polarization angle; and

generating the estimated polarization angle.

27. The method of claim 15 wherein the optical transmission channel operates at a data rate of at least 10 Gigabauds.

28. The method of claim 17 wherein at least one of the phase estimator, the polarization angle estimator, the rotation matrix estimator, the coefficient generator, and the filter stage is implemented by an analog circuit, a digital circuit, a mixed mode circuit, a sequence of instructions, or a program.

29. A system comprising:

a receiver front end circuit to generate received samples transmitted in an optical transmission channel carrying transmitted symbols; and

a signal processor coupled to the receiver front end circuit to generate received symbols corresponding to the transmitted symbols, the signal processor comprising;

a coefficient generator to generate filter coefficients using a rotated error vector, and

a filter stage coupled to the coefficient generator to generate equalized samples or slicer input vector from received samples or rotated received samples using the filter coefficients, the received samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols.

30. The system of claim 29 wherein the signal processor further comprises:

a rotator coupled to the filter stage to rotate the equalized samples using a rotation matrix to generate a slicer input vector;

a slicer coupled to the rotator to threshold the slicer input vector to generate a slicer output vector;

an inverse rotator coupled to the coefficient generator to generate the rotated error vector using an error vector and the rotation matrix;

an error calculator coupled to the slicer to calculate the error vector, the error vector being a difference vector between the slicer output vector and the slicer input vector; and

a rotation matrix estimator coupled to the slicer and the rotator to generate the rotation matrix using the slicer output vector and the slicer input vector.

31. The system of claim 30 further comprising:

a delay conjugator coupled to the slicer to generate the delayed conjugated vector from the slicer output vector; and

a multiplier coupled to the delayed conjugator and the slicer to multiply the delayed conjugated vector with the slicer output vector to generate received symbols corresponding to the transmitted symbols.

32. The system of claim 30 wherein the rotation matrix estimator comprises:

an angle calculator to calculate an angle between the slicer output vector and the slicer input vector;

a transpose conjugator to generate a transpose conjugate for the slicer output vector;

a phase estimator coupled to the transpose conjugator to estimate a phase vector using the transpose conjugate and the slicer input vector; and

a rotation matrix calculator coupled to the phase estimator to calculate the rotation matrix using the estimated phase vector.

33. The system of claim 32 wherein the rotation matrix estimator further comprises:

a polarization angle estimator coupled to the transpose conjugator to estimate a polarization angle using the transpose conjugate and the slicer input vector.

34. The system of claim 32 wherein the rotation matrix calculator calculates the rotation matrix using the estimated phase vector and the estimated polarization angle.

35. The system of claim 29 wherein the coefficient generator comprises:

a coefficient adjuster to generate a coefficient adjustment vector being a product of the rotated error vector, a received sample vector representing the received samples, and a step size parameter; and

an adder coupled to the coefficient adjuster to add a previously calculated coefficient vector to the coefficient adjustment vector to generate a coefficient vector representing the filter coefficients.

36. The system of claim 35 wherein the coefficient vector includes at least four filter coefficient vectors spanned on at least first and second dimensions.

37. The system of claim 29 wherein the signal processor further comprises:

a rotator coupled to the filter stage to rotate the received samples using a rotation matrix to generate the rotated received samples;

a slicer coupled to the filter stage to threshold the slicer input vector to generate a slicer output vector;

an inverse rotator coupled to the coefficient generator to generate the rotated error vector using an error vector and the rotation matrix;

an error calculator coupled to the slicer to calculate the error vector, the error vector being a difference vector between the thresholded rotated vector and the rotated vector; and

a rotation matrix estimator coupled to the slicer to generate the rotation matrix using the slicer output vector and the slicer input vector.

38. The system of claim 34 wherein the filter stage comprises:

at least four finite impulse response (FIR) filters to operate on the at least four filter coefficient vectors and the received samples, to produce at least four filtered results; and

at least two adders coupled to the at least four FIR filters to add the at least four filtered results on at least first and second dimensions, respectively, to produce the equalized samples.

39. The system of claim 32 wherein the phase estimator comprises:

a phase angle calculator to calculate a phase angle vector;

a phase loop filter coupled to the phase angle calculator to filter the phase angle vector; and

an adder coupled to the loop filter to add the filtered phase angle vector to a previously estimated phase vector to generate the estimated phase vector.

40. The system of claim 33 wherein the polarization angle estimator comprises:

a polarization angle calculator to calculate a polarization angle;

a polarization loop filter coupled to the polarization angle calculator to filter the polarization angle; and

an adder coupled to the previously estimated polarization angle to generate the estimated polarization angle.

41. The system of claim 29 wherein the optical transmission channel operates at a data rate of at least 10 Gigabauds.

42. The system of claim 33 wherein at least one of the phase estimator, the polarization angle estimator, the rotation matrix estimator, the coefficient generator, and the filter stage is implemented by an analog circuit, a digital circuit, a mixed mode circuit, a sequence of instructions, or a program.