System and methods for adaptive equalization for optical modulation formats

Patent metadata

Field	Value
Publication number	US-9515742-B2
Application number	US-201514968005-A
Country	US
Kind code	B2
Filing date	Dec 14, 2015
Priority date	Nov 30, 2011
Publication date	Dec 6, 2016
Grant date	Dec 6, 2016

Abstract

A method for modifying the performance of an adaptive equalizer in a receiver is provided. A carrier wave comprising a first polarization state and a second polarization state, wherein there is a correlation between the first polarization state and the second polarization state, is received. The first polarization state and the second polarization state are demultiplexed to generate two respective constellations. A first expected value based on the first constellation, and a second expected value based on the second constellation, are calculated. An adaptive equalizer receives a first and second signals associated with the respective polarization states. The adaptive equalizer generates outputs based on the signals. These outputs are used to generate error values. Feedback is input into the adaptive equalizer, wherein the feedback is based on the error values.

First claim

The invention claimed is:

1. A method, comprising:
receiving a carrier wave comprising a first polarization state and a second polarization state, wherein a correlation exists between the first polarization state and the second polarization state;
generating a first constellation corresponding to the first polarization state and a second constellation corresponding to the second polarization state;
calculating a first expected value based on the first constellation and a second expected value based on the second constellation;
equalizing, by an adaptive equalizer, a first output based on a first signal associated with the first polarization state and a second output based on a second signal associated with the second polarization state;
calculating a first error based on a difference between the first expected value and the first output, the first expected value being constrained based on the first output and the second output;
calculating a second error based on a difference between the second expected value and the second output, the second expected value being constrained based on the first output and the second output;
generating a feedback signal based on the first error, the second error and the correlation; and
determining coefficients for filters of the adaptive equalizer using the feedback signal.

2. The method as recited in claim 1 , where the generating a first constellation corresponding to the first polarization state and a second constellation corresponding to the second polarization state comprises:
demultiplexing the first polarization state and the second polarization state to generate the first constellation and the second constellation using a demultiplexer.

3. The method as recited in claim 1 , wherein the first constellation comprises a plurality of data points associated with the first polarization state and wherein the data points are associated with a diagram in a complex plane, the diagram comprising a plurality of vertices, each of the respective vertices located at a respective position (1, j, − 1 , −j, 0) in the complex plane.

4. The method as recited in claim 1 , wherein the first expected value is calculated based on an expected square value of a modulus of the first constellation.

5. The method as recited in claim 1 , wherein the first error and the second error are calculated using the following equations:
ε x ( n )=| Z x ( n )| 2 −R x ( n ),

ε y ( n )=| Z y ( n )| 2 −R y ( n )

wherein Z x (n) corresponds to the first output, Z y (n) corresponds to the second output, R x (n) is the first expected value, and R y (n) is the second expected value.

6. The method as recited in claim 1 , wherein the carrier wave is modulated according to at least one of polarization-switched m-ary phase shift keying and polarization-switched m-ary quadrature amplitude modulation.

7. The method as recited in claim 1 , wherein the carrier wave comprises at least one of an optical carrier wave and a radio-frequency carrier wave.

8. The method as recited in claim 1 , wherein the generating a feedback signal comprises:
generating the feedback signal using a steepest gradient algorithm.

9. The method as recited in claim 1 , wherein the adaptive equalizer comprises a plurality of finite impulse response filters.

10. A system, comprising:
a receiver for receiving a carrier wave comprising a first polarization state and a second polarization state, wherein a correlation exists between the first polarization state and the second polarization state;
an adaptive equalizer for:
generating a first constellation corresponding to the first polarization state and a second constellation corresponding to the second polarization state;
equalizing a first output based on a first signal associated with the first polarization state and a second output based on a second signal associated with the second polarization state;

a processor; and
a memory to store computer program instructions, the computer program instructions when executed on the processor cause the processor to perform operations comprising:
calculating a first expected value based on the first constellation and a second expected value based on the second constellation;
calculating a first error based on a difference between the first expected value and the first output, the first expected value being constrained based on the first output and the second output;
calculating a second error based on a difference between the second expected value and the second output, the second expected value being constrained based on the first output and the second output; and
generating a feedback signal based on the first error, the second error and the correlation;

the adaptive equalizer further for determining coefficients for filters of the adaptive equalizer using the feedback signal.

11. The system as recited in claim 10 , wherein the adaptive equalizer is further for demultiplexing the first polarization state and the second polarization state to generate the first constellation and the second constellation.

12. The system as recited in claim 10 , wherein the first constellation comprises a plurality of data points associated with the first polarization state and wherein the data points are associated with a diagram in a complex plane, the diagram comprising a plurality of vertices, each of the respective vertices located at a respective position (1, j, −1, −j, 0) in the complex plane.

13. The system as recited in claim 10 , wherein the first expected value is calculated based on an expected square value of a modulus of the first constellation.

14. The system as recited in claim 10 , wherein the first error and the second error are calculated using the following equations:
ε x ( n )=| Z x ( n )| 2 −R x ( n ),

ε y ( n )=| Z y ( n )| 2 −R y ( n )

wherein Z x (n) corresponds to the first output, Z y (n) corresponds to the second output, R x (n) is the first expected value, and R y (n) is the second expected value.

15. The system as recited in claim 10 , wherein the carrier wave is modulated according to at least one of polarization-switched m-ary phase shift keying and polarization-switched m-ary quadrature amplitude modulation.

16. A non-transitory computer readable medium storing computer program instructions for processing a carrier wave to provide feedback to an adaptive equalizer, the carrier wave comprising a first polarization state and a second polarization state, wherein a correlation exists between the first polarization state and the second polarization state, the computer program instructions, when executed on a processor, cause the processor to perform operations comprising:
calculating a first expected value based on a first constellation corresponding to the first polarization state and a second expected value based on a second constellation corresponding to the second polarization state;
calculating a first error based on a difference between the first expected value and a first output, the first output being generated by equalizing a first signal associated with the first polarization state, the first expected value being constrained based on the first output and the second output;
calculating a second error based on a difference between the second expected value and a second output, the second output being generated by equalizing a second signal associated with the second polarization state, the second expected value being constrained based on the first output and the second output;
generating a feedback signal based on the first error, the second error and the correlati

Assignees

• At & T Ip I Lp
• At & T Ip I Lp

Inventors

• Zhou Xiang
• Nelson Lynn

Classifications

• H04L25/03038

  with a non-recursive structure (H04L25/03031 takes precedence) · CPC title

• H04L2025/0342

  QAM · CPC title

• H04B10/6166 Primary

  Polarisation demultiplexing, tracking or alignment of orthogonal polarisation components · CPC title

• H04J14/06

  Polarisation multiplex systems · CPC title

• H04B10/532 Primary

  Polarisation modulation · CPC title