Multidimensional decision-directed trained adaptive equalization

1. An apparatus comprising:

an equalizer to equalize a multidimensional signal having different phase errors for each polarization, the multidimensional signal transmitted over a communication channel and having a dimensionality of four or higher, the equalizer being adaptively decision directed trained based on an optimality criterion to compensate the different phase errors;

wherein the equalizer produces soft outputs being used in soft channel decoding and iteratively produces outputs using a priori information provided by a channel decoder.

2. The apparatus of claim 1 wherein the equalizer is one of a linear equalizer, a decision-feedback equalizer, a Maximum Likelihood Sequence Estimator (MLSE) equalizer, and a combination of linear, decision-feedback, and MLSE equalizers.

3. The apparatus of claim 1 wherein the equalizer comprises a phase and polarization rotator to jointly rotate phase and polarization.

4. The apparatus of claim 3 further comprising:

a phase estimator to estimate a phase angle vector; and

a polarization angle estimator to estimate a polarization angle.

5. The apparatus of claim 4 wherein the phase angle vector and the polarization angle are used to compensate different phase errors for each polarization, the different phase errors being caused at least by phase noise of at least a laser used at a transmitter and at a local oscillator at the communication channel.

6. The apparatus of claim 2 wherein the MLSE equalizer compensates linear and nonlinear distortion in the communication channel.

7. The apparatus of claim 2 wherein the MLSE equalizer compensates for non-gaussian noise.

8. A method comprising:

equalizing a multidimensional signal having different phase errors for each polarization, the multidimensional signal transmitted over a communication channel and having a dimensionality of four or higher, equalizing comprising adaptively training in a decision directed manner based on an optimality criterion to compensate the different phase errors;

wherein equalizing comprises:

jointly rotating phase and polarization;

producing soft outputs used in soft channel decoding; and

iteratively producing outputs using a priori information provided by a channel decoder.

9. The method of claim 8 further comprising:

estimating a phase angle error and a polarization error.

10. The method of claim 9 wherein estimating the phase angle error and the polarization error comprises:

compensating the different phase error for each polarization that are caused at least by phase noise of at least one of a laser used at a transmitter and at a local oscillator at the communication channel.

11. The method of claim 8 wherein equalizing comprises:

equalizing using at least one of linear equalization, decision-feedback equalization, and Maximum Likelihood Sequence Estimator (MLSE) equalization.

12. The method of claim 11 wherein equalizing comprises:

compensating at least one of a linear distortion and a nonlinear distortion in the communication channel.

13. A receiver comprising:

a front end to mix a signal received from a communication channel with an output of a local oscillator to produce a multidimensional signal having different phase errors for each polarization and having a dimensionality of four or higher; and

an equalizer coupled to the front end to equalize the multidimensional signal, the equalizer being adaptively decision directed trained based on an optimality criterion to compensate the different phase errors;

wherein the equalizer comprises a phase and polarization rotator to jointly rotate phase and polarization.

14. The receiver of claim 13 wherein the equalizer is one of a linear equalizer, a decision-feedback equalizer, a Maximum Likelihood Sequence Estimator (MLSE) equalizer, and a combination of linear, decision-feedback, and MLSE equalizers.

15. The receiver of claim 13 wherein the equalizer further comprising:

a phase estimator to estimate a phase angle vector; and

a polarization angle estimator to estimate a polarization angle.

16. The receiver of claim 15 wherein the phase angle vector and the polarization angle are used to compensate different phase errors for each polarization, the different phase errors being caused at least by phase noise of at least a laser used at a transmitter and at a local oscillator at the communication channel.