Pre-equalization using phase correction

Patent metadata

Field	Value
Publication number	US-9479252-B2
Application number	US-201414274669-A
Country	US
Kind code	B2
Filing date	May 9, 2014
Priority date	May 9, 2013
Publication date	Oct 25, 2016
Grant date	Oct 25, 2016

Abstract

An optical transmitter determines the transfer function in the reference-based pre-equalization for applying to an optically modulated signal at the transmitter. The determined pre-equalization transfer function is made robust to linewidth inaccuracy of the optical source by performing phase correction during the calculation of the pre-equalization transfer function. The phase correction includes averaging a number of consecutive received phase samples. The determined pre-equalization transfer function is applied to modulated signals prior to the transmission over an optical medium.

First claim

What is claimed is what is described and illustrated, including:

1. A method for use at a transmitter-side in an optical communication network, comprising:
determining a pre-equalization transfer function for applying to an optically modulated signal at the transmitter by:
performing digital to analog conversion of a reference signal to generate an analog reference signal;
modulating an optical source by the analog reference signal using a first modulation scheme to generate a modulated signal;
digitizing the modulated signal to generate a received estimate of the modulated signal;
phase correcting the estimate of the modulated signal to generate an estimate of the reference signal; and
computing the pre-equalization transfer function using the reference signal and the estimate of the reference signal, wherein the estimate of the reference signal is based on a phase corrected estimate of the modulated signal, wherein the phase corrected estimate includes averaging over a sliding window of length N samples and wherein the sliding window slides less than N samples, where N is a whole number representing a filter block size.

2. The method of claim 1 , further comprising:
transmitting, using a second modulation scheme, data upon applying the pre-equalization transfer function to the data.

3. The method of claim 1 , wherein the phase correcting comprises:
filtering phase values of N consecutive samples of the estimate of the modulated signal, where N is a whole number representing a filter block size.

4. The method of claim 3 , wherein the filtering comprises averaging the N consecutive samples.

5. The method of claim 4 , wherein averaging the N consecutive samples includes parallel processing over a number of blocks, each having a size N.

6. The method of claim 3 , wherein N is selected based on a product of a linewidth of the optical source and a symbol rate of the modulated signal.

7. An optical communication transmitter apparatus comprising:
a memory for storing instructions; and
a processor that reads the instructions and implements an optical communication method, comprising:
determining a pre-equalization transfer function for applying to an optically modulated signal at the transmitter by:
performing digital to analog conversion of a reference signal to generate an analog reference signal;
modulating an optical source by the analog reference signal using a first modulation scheme to generate a modulated signal;
digitizing the modulated signal to generate a received estimate of the modulated signal;
phase correcting the estimate of the modulated signal to generate an estimate of the reference signal; and
computing the pre-equalization transfer function using the reference signal and the estimate of the reference signal, wherein the estimate of the reference signal is based on a phase corrected estimate of the modulated signal, wherein the phase corrected estimate includes averaging over a sliding window of length N samples and wherein the sliding window slides less than N samples, where N is a whole number representing a filter block size.

8. The apparatus of claim 7 , wherein the method further comprises:
transmitting, using a second modulation scheme, data upon applying the pre-equalization transfer function to the data.

9. The apparatus of claim 7 , wherein the phase correcting comprises:
filtering phase values of N consecutive samples of the estimate of the modulated signal, where N is a whole number representing a filter block size.

10. The apparatus of claim 9 , wherein the filtering comprises averaging the N consecutive samples.

11. The apparatus of claim 9 , wherein N is selected based on a product of a linewidth of the optical source and a symbol rate of the modulated signal.

12. An optical transmitter apparatus, comprising:
a transfer function determination module that determines a pre-equalization transfer function for applying to an optically modulated signal at the transmitter;
a digital to analog conversion module that performs digital to analog conversion of a reference signal to generate an analog reference signal;
a reference signal modulation module that modulates an optical source by the analog reference signal using a first modulation scheme to generate a modulated signal;
an analog to digital conversion module that digitizes the modulated signal to generate a received estimate of the modulated signal;
a phase correction module that phase corrects the estimate of the modulated signal to generate an estimate of the reference signal; and
a transfer function estimation module that estimates the pre-equalization transfer function using the reference signal and the estimate of the reference, wherein the estimate of the reference signal is based on a phase corrected estimate of the modulated signal, wherein the phase corrected estimate includes averaging over a sliding window of length N samples and wherein the sliding window slides less than N samples, where N is a whole number representing a filter block size.

13. The apparatus of claim 12 , further comprising:
a transmission module that transmits, using a second modulation scheme, data upon applying the pre-equalization transfer function to the data.

14. The apparatus of claim 12 , wherein the phase correction module comprises:
a filtering module that filters phase values of N consecutive samples of the estimate of the modulated signal, where N is a whole number representing a filter block size.

15. The apparatus of claim 14 , wherein the filtering module comprises an averaging module that averages the N consecutive samples.

16. The apparatus of claim 14 , further comprising a selection module that selects N based on a product of a linewidth of the optical source and a symbol rate of the modulated signal.

Assignees

• Zte Corp

Inventors

• Yu Jianjun
• Dong ze

Classifications

• H04B10/2507 Primary

  for the reduction or elimination of distortion or dispersion · CPC title

• H04B10/073 Primary

  using an out-of-service signal (H04B10/071 takes precedence) · CPC title

• H04B10/516

  Details of coding or modulation · CPC title

• H04B10/63

  Homodyne {, i.e. coherent receivers where the local oscillator is locked in frequency and phase to the carrier signal} · CPC title