System and methods for adaptive equalization for optical modulation formats

Patent metadata

Field	Value
Publication number	US-9252988-B2
Application number	US-201113307429-A
Country	US
Kind code	B2
Filing date	Nov 30, 2011
Priority date	Nov 30, 2011
Publication date	Feb 2, 2016
Grant date	Feb 2, 2016

Abstract

A method for modifying the performance of an adaptive equalizer in a receiver is provided. A carrier wave including 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, by a processor, 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 and a second constellation by demultiplexing the first polarization state and the second polarization state, wherein the first constellation corresponds to the first polarization state and the second constellation corresponds to the second polarization state;
calculating, by the processor, a first expected value based on the first polarization state and the first constellation and a second expected value based on the second polarization state and the second constellation;
equalizing, by the processor, 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, by the processor, 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, by the processor, 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, by the processor, a feedback signal based on the first error, the second error and the correlation.

2. The method of claim 1 , wherein the 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 comprises:
receiving at an adaptive equalizer the first signal and the second signal; and
equalizing the first signal and the second signal by the adaptive equalizer.

3. The method of claim 2 , wherein the adaptive equalizer comprises a plurality of finite impulse response filters.

4. The method of claim 1 wherein the carrier wave is modulated according to a modulation format, where the modulation format is selected from the group of modulation formats consisting of:
polarization-switched m-ary phase shift keying and polarization-switched m-ary quadrature amplitude modulation.

5. The method of claim 1 , wherein the carrier wave is selected from the group consisting of:
an optical carrier wave and a radio-frequency carrier wave.

6. The method of 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.

7. The method of claim 6 , wherein the first expected value is calculated based on an expected square value of a modulus of the first constellation.

8. The method of 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.

9. The method of claim 8 , wherein the first output is equalized based on the following formula:

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Assignees

• Zhou Xiang
• Nelson Lynn
• At & T Ip I Lp

Inventors

• Zhou Xiang
• Nelson Lynn

Classifications

• H04L25/03038 Primary

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

• H04L2025/03687

  of step size · CPC title

• H04L2025/03401

  PSK · CPC title

• H04L2025/0342

  QAM · CPC title

• H04B10/6166 Primary

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