Techniques for blind equalization of high-order quadrature amplitude modulation signals

Patent metadata

Field	Value
Publication number	US-9692548-B2
Application number	US-201514661850-A
Country	US
Kind code	B2
Filing date	Mar 18, 2015
Priority date	Mar 19, 2014
Publication date	Jun 27, 2017
Grant date	Jun 27, 2017

Abstract

A blind equalization technique of high-order QAM signals is provided. A method implemented at a receiver-side in an optical communication network receives an optical signal and performs a two-step polarization tracking process on the received optical signal. Using another method, a polarization multiplexed optical transmission is received by a receiver and a polarization tracking process is performed by applying two different algorithms in parallel. One algorithm may be a decision directed least means square (DD-LMS) algorithm. Another algorithm may be a constant modulus algorithm (CMA).

First claim

What is claimed is:

1. A method of optical communication, implemented at a receiver-side in an optical communication network, comprising:
receiving a polarization multiplexed optical signal; and
performing a two-step polarization tracking process on the received optical signal to recover data carried by the polarization multiplexed optical signal; and
performing a phase recovery;
wherein the two-step polarization tracking process includes a first step and a second step;
wherein the first step employs two different error calculation algorithms in parallel to produce estimated coefficients of a finite impulse response process having a first mean square error (MSE);
wherein the second step inherits the estimated coefficients as an initial condition and updates the estimated coefficients for data recovery to obtain a second MSE that is lower than the first MSE; and
wherein the phase recovery is performed during the two-step polarization tracking process using a hybrid binary phase search (BPS) and a maximum likelihood (ML) algorithm.

2. The method of claim 1 , the performing of the two-step polarization tracking process including:
performing the first step of the two-step polarization tracking process until an equalization process reaches a steady state; and
performing the second step of the two-step polarization tracking process using coefficients of finite impulse response (FIR) filters that are obtained at the steady state.

3. The method of claim 1 , wherein the two different error calculation algorithms include a decision directed error calculation and a constant modulus based error calculation.

4. An optical receiver apparatus, comprising:
a receiver module that receives an optical signal;
a polarization tracking module that calculates feedback error and updates coefficients of a finite impulse response (FIR) process by performing a two-step polarization tracking process on the received optical signal, thereby providing digital signals,
wherein the two-step polarization tracking process comprises a first step that employs two different error calculation algorithms in parallel to produce estimated coefficients of the finite impulse response process having a first mean square error (MSE) and a second step that inherits the estimated coefficients as an initial condition to and updates the estimated coefficients to obtain a second MSE that is lower than the first MSE; and
a carrier recovery module performing a phase recovery by receiving the digital signals and estimating an optimal phase angle of the digital signals,
wherein the phase recovery is performed during the two-step polarization tracking process using a hybrid binary phase search (BPS) and a maximum likelihood (ML) algorithm.

5. The apparatus of claim 4 , wherein the polarization tracking module is configured to perform a first step of the two-step polarization tracking process to reach a steady state and perform a second step of the two-step polarization tracking process using coefficients of FIR filters that are obtained at the steady state.

6. The apparatus of claim 4 , wherein the two different error calculation algorithms include decision directed least mean square (DD-LMS) based error calculation and the second error calculation algorithm includes constant modulus algorithm (CMA) based error calculation.

7. An optical receiver apparatus, comprising:
a computer-readable memory that stores program instructions, and
a digital signal processor that reads the program instructions and implements a method, comprising:
receiving a polarization multiplexed optical signal;
performing a two-step polarization tracking process on the received optical signal to recover data carried by the polarization multiplexed optical signal; and
performing a phase recovery;
wherein the two-step polarization tracking process includes a first step and a second step;
wherein the first step employs two different error calculation algorithms in parallel to produce estimated coefficients of a finite impulse response process having a first mean square error (MSE);
wherein the second step inherits the estimated coefficients as an initial condition and updates the estimated coefficients for data recovery to obtain a second MSE that is lower than the first MSE; and
wherein the phase recovery is performed during the two-step polarization tracking process using a hybrid binary phase search (BPS) and a maximum likelihood (ML) algorithm.

8. The apparatus of claim 7 , wherein the performing of the two-step polarization tracking process includes:
performing the first step of the two-step polarization tracking process until an equalization process reaches a steady state; and
performing the second step of the two-step polarization tracking process using coefficients of finite impulse response (FIR) filters that are obtained at the steady state.

9. The apparatus of claim 7 , wherein the two different error calculation algorithms include a decision directed error calculation and a constant modulus based error calculation.

10. The method of claim 1 , wherein the second step employs a decision directed error calculation algorithm.

11. The method of claim 10 , wherein a scaling factor of 2 is added to the decision directed error calculation algorithm.

12. The apparatus of claim of 4 , wherein the second step employs an enhanced decision directed least mean square (DD-LMS) based error calculation algorithm.

13. The apparatus of claim of 12 , wherein a scaling factor of 2 is added to the enhanced DD-LMS based error calculation algorithm.

14. The apparatus of claim 7 , wherein the second step employs a decision directed error calculation algorithm.

15. The apparatus of claim 14 , wherein a scaling factor of 2 is added to the decision directed error calculation algorithm.

Assignees

• Zte Corp

Inventors

• Jia Zhensheng
• Chien Hung-Chang
• Yu Jianjun

Classifications

• H04B10/6165

  Estimation of the phase of the received optical signal, phase error estimation or phase error correction · CPC title

• H04B10/612 Primary

  for optical signals modulated with a format different from binary or higher-order PSK [X-PSK], e.g. QAM, DPSK, FSK, MSK, ASK · CPC title

• H04B10/6166

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

• H04L1/0036

  arrangements specific to the receiver · CPC title

• H04B10/613

  including phase diversity, e.g., having in-phase and quadrature branches, as in QPSK coherent receivers · CPC title