Adaptive equalization in coherent fiber optic communication
View Patent ↗An embodiment of the invention is a technique to equalize received samples. A coefficient generator generates filter coefficients using an error vector and input samples. A filter stage generates equalized samples from input samples using the filter coefficients. The received samples are provided by a receiver front end in an optical transmission channel carrying transmitted symbols. Other embodiments are also described.
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 from the input samples using the filter coefficients, the input samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols,
wherein the receiver front end comprises at least a multidimensional rotator to rotate its input signal,
wherein the coefficient generator comprises:
a coefficient adjuster to generate a coefficient adjustment vector being a product of the rotated error vector, an input sample vector representing the input 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.
2. The apparatus of claim 1 , wherein the multidimensional rotator rotates at least one of phase and polarization of its input signal.
3. The apparatus of claim 2 , wherein the multidimensional rotator is adaptively trained according to an optimality criterion.
4. The apparatus of claim 3 , wherein the optimality criterion is the minimization of the receiver mean squared error.
5. The apparatus of claim 3 , wherein the optimality criterion is the minimization of the receiver bit error rate.
6. 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 from the input samples using the filter coefficients, the input samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols,
wherein the receiver front end comprises at least a matched filter,
wherein the coefficient generator comprises:
a coefficient adjuster to generate a coefficient adjustment vector being a product of the rotated error vector, an input sample vector representing the input 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.
7. The apparatus of claim 6 , wherein the matched filter is matched to the impairments of the optical channel.
8. The apparatus of claim 6 , wherein the matched filter is matched to at least the chromatic dispersion of the optical channel.
9. The apparatus of claim 6 , wherein the matched filter is matched to at least the polarization mode dispersion of the optical channel.
10. The apparatus of claim 6 , wherein the matched filter is matched to at least the skews of the optical channel.
11. 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 from the input samples using the filter coefficients, the input samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols,
wherein the optical transmission channel operates at a data rate of at least 10 Gigabauds,
wherein the coefficient generator comprises:
a coefficient adjuster to generate a coefficient adjustment vector being a product of the rotated error vector, an input sample vector representing the input 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.
12. An apparatus comprising:
a coefficient generator to generate filter coefficients using a rotated error vector;
a filter stage coupled to the coefficient generator to generate equalized samples from input samples using the filter coefficients, the input samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols;
a rotator coupled to the filter stage to rotate the equalized samples to generate the rotated equalized samples;
a slicer coupled to the rotator to threshold a 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 a rotation matrix;
an error calculator coupled to the slicer to calculate the error vector, the error vector being a difference vector between a thresholded rotated vector and a rotated vector; and
a rotation matrix estimator coupled to the slicer to generate the rotation matrix using the equalized samples.
13. The apparatus of claim 12 , wherein the receiver front end comprises at least a multidimensional rotator to rotate its input signal.
14. The apparatus of claim 13 , wherein the multidimensional rotator rotates at least one of phase and polarization of its input signal.
15. The apparatus of claim 14 , wherein the multidimensional rotator is adaptively trained according to an optimality criterion.
16. The apparatus of claim 15 , wherein the optimality criterion is the minimization of the receiver mean squared error.
17. The apparatus of claim 15 , wherein the optimality criterion is the minimization of the receiver bit error rate.
18. The apparatus of claim 12 , wherein the receiver front end comprises at least a matched filter.
19. The apparatus of claim 18 , wherein the matched filter is matched to the impairments of the optical channel.
20. The apparatus of claim 18 , wherein the matched filter is matched to at least the chromatic dispersion of the optical channel.
21. The apparatus of claim 18 , wherein the matched filter is matched to at least the polarization mode dispersion of the optical channel.
22. The apparatus of claim 18 , wherein the matched filter is matched to at least the skews of the optical channel.
23. A method comprising:
generating filter coefficients using a rotated error vector by (i) generating a coefficient adjustment vector being a product of the rotated error vector, an input sample vector representing the input samples, and a step size parameter, and (ii) adding a previously calculated coefficient vector to the coefficient adjustment vector to generate a coefficient vector representing the filter coefficients; and
generating equalized samples from the input samples using the filter coefficients, the input samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols, wherein the optical transmission channel operates at a data rate of at least 10 Gigabauds.
24. A method comprising:
generating filter coefficients using a rotated error vector;
generating equalized samples from input samples using the filter coefficients, the input samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols;
rotating the equalized samples to generate the rotated equalized samples;
thresholding a slicer input vector to generate a slicer output vector;
generating the rotated error vector using an error vector and a rotation matrix;
calculating the error vector, the error vector being a difference vector between a thresholded rotated vector and a rotated vector; and
generating the rotation matrix using the equalized samples.
25. 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 an error vector and input samples, and
a filter stage coupled to the coefficient generator to generate equalized samples from the input samples using the filter coefficients, the input samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols, wherein the optical transmission channel operates at a symbol rate of at least 10 Gigabauds.
26. The system of claim 25 , wherein the receiver front end comprises at least a multidimensional rotator to rotate its input signal.
27. The system of claim 26 , wherein the multidimensional rotator rotates at least one of phase and polarization of its input signal.
28. The system of claim 27 , wherein the multidimensional rotator is adaptively trained according to an optimality criterion.
29. The system of claim 28 , wherein the optimality criterion is the minimization of the receiver mean squared error.
30. The system of claim 28 , wherein the optimality criterion is the minimization of the receiver bit error rate.
31. The system of claim 25 , wherein the receiver front end comprises at least a matched filter.
32. The system of claim 31 , wherein the matched filter is matched to the impairments of the optical channel.
33. The system of claim 31 , wherein the matched filter is matched to at least the chromatic dispersion of the optical channel.
34. The system of claim 31 , wherein the matched filter is matched to at least the polarization mode dispersion of the optical channel.
35. The system of claim 31 , wherein the matched filter is matched to at least the skews of the optical channel.
36. A system comprising:
a receiver front end circuit to generate received samples transmitted in an optical transmission channel carrying transmitted symbols, wherein the optical transmission channel operates at a data rate of at least 10 Gigabauds; 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, wherein the coefficient generator comprises: (i) a coefficient adjuster to generate a coefficient adjustment vector being a product of the rotated error vector, an input sample vector representing the input samples, and a step size parameter, and (ii) 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, and
a filter stage coupled to the coefficient generator to generate equalized samples from the input samples using the filter coefficients, the input samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols.
37. The system of claim 36 , wherein the receiver front end comprises at least a multidimensional rotator to rotate its input signal.
38. The system of claim 37 , wherein the multidimensional rotator rotates at least one of phase and polarization of its input signal.
39. The system of claim 38 , wherein the multidimensional rotator is adaptively trained according to an optimality criterion.
40. The system of claim 39 , wherein the optimality criterion is the minimization of the receiver mean squared error.
41. The system of claim 39 , wherein the optimality criterion is the minimization of the receiver bit error rate.
42. The system of claim 36 , wherein the receiver front end comprises at least a matched filter.
43. The system of claim 42 , wherein the matched filter is matched to the impairments of the optical channel.
44. The system of claim 42 , wherein the matched filter is matched to at least the chromatic dispersion of the optical channel.
45. The system of claim 42 , wherein the matched filter is matched to at least the polarization mode dispersion of the optical channel.
46. The system of claim 42 , wherein the matched filter is matched to at least the skews of the optical channel.
47. 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,
a filter stage coupled to the coefficient generator to generate equalized samples from input samples using the filter coefficients, the input samples being provided by a receiver front end in an optical transmission channel carrying transmitted symbols,
a rotator coupled to the filter stage to rotate the equalized samples to generate the rotated equalized samples,
a slicer coupled to the rotator to threshold a 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 a rotation matrix,
an error calculator coupled to the slicer to calculate the error vector, the error vector being a difference vector between a thresholded rotated vector and a rotated vector, and
a rotation matrix estimator coupled to the slicer to generate the rotation matrix using the equalized samples.
48. The system of claim 47 , wherein the receiver front end comprises at least a multidimensional rotator to rotate its input signal.
49. The system of claim 48 , wherein the multidimensional rotator rotates at least one of phase and polarization of its input signal.
50. The system of claim 49 , wherein the multidimensional rotator is adaptively trained according to an optimality criterion.
51. The system of claim 50 , wherein the optimality criterion is the minimization of the receiver mean squared error.
52. The system of claim 50 , wherein the optimality criterion is the minimization of the receiver bit error rate.
53. The system of claim 47 , wherein the receiver front end comprises at least a matched filter.
54. The system of claim 53 , wherein the matched filter is matched to the impairments of the optical channel.
55. The system of claim 53 , wherein the matched filter is matched to at least the chromatic dispersion of the optical channel.
56. The system of claim 53 , wherein the matched filter is matched to at least the polarization mode dispersion of the optical channel.
57. The system of claim 53 , wherein the matched filter is matched to at least the skews of the optical channel.