Signal processing apparatus and signal processing method

Patent metadata

Field	Value
Publication number	US-9485033-B2
Application number	US-201214350125-A
Country	US
Kind code	B2
Filing date	Oct 5, 2012
Priority date	Oct 5, 2011
Publication date	Nov 1, 2016
Grant date	Nov 1, 2016

Abstract

Signal processing means includes carrier compensation means for compensating for a phase difference and a frequency difference between signal light and local light in relation to two polarization signals, so as to generate two carrier compensated signals, symbol determination means for demodulating the two carrier compensated signals on the basis of a signal arrangement of multi-value modulation, symbol rough-determination means for demodulating the two carrier compensated signals on the basis of a signal arrangement in which the number of multi-values of the multi-value modulation is reduced, selection means for selecting either of an output of the symbol determination means and an output of the symbol rough-determination means, and coefficient setting means for updating filter coefficients of polarized wave separation means by using an output selected by the selection means.

First claim

The invention claimed is:

1. A signal processing apparatus comprising:
polarized wave separation unit for receiving four digital signals and generating two polarization signals corresponding to two polarization components of signal light from the four digital signals by using filters having filter coefficients, the four digital signals being generated by performing photoelectric conversion and analog-digital conversion on four output light beams which are generated by making the signal light having undergone polarization division multiplexing and multi-value modulation and local light interfere with each other by using a 90° optical hybrid;
carrier compensation unit for compensating for a phase difference and a frequency difference between the signal light and the local light in relation to the two polarization signals, so as to generate two carrier compensated signals;
determination unit for demodulating the two carrier compensated signals;
selection unit for selecting whether the determination unit performs the demodulation based on a signal arrangement of the multi-value modulation or based on a signal arrangement in which a number of multi-values of the multi-value modulation is reduced; and
coefficient setting unit for updating the filter coefficients of the polarized wave separation unit by using an output selected by the selection unit.

2. The signal processing apparatus according to claim 1 ,
wherein the determination unit includes
symbol determination unit for demodulating the two carrier compensated signals based on the signal arrangement of the multi-value modulation; and
symbol rough-determination unit for demodulating the two carrier compensated signals based on the signal arrangement in which the number of multi-values of the multi-value modulation is reduced, and
wherein the selection unit selects either one of an output of the symbol determination unit and an output of the symbol rough-determination unit.

3. The signal processing apparatus according to claim 1 ,
wherein the selection unit selects either one of first reference data for performing demodulation based on the signal arrangement of the multi-value modulation and second reference data for performing demodulation based on the signal arrangement in which the number of multi-values of the multi-value modulation is reduced, and causes the determination unit to use the selected reference data.

4. The signal processing apparatus according to claim 1 ,
wherein the determination unit performs demodulation based on the signal arrangement of the multi-value modulation until the filter coefficients converge.

5. The signal processing apparatus according to claim 4 ,
wherein the determination unit performs demodulation based on the signal arrangement in which the number of multi-values of the multi-value modulation is reduced after the filter coefficients converge.

6. The signal processing apparatus according to claim 4 , further comprising:
error calculation unit for calculating an error of an output of the determination unit by using the two polarization signals and the output of the determination unit,
wherein the selection unit determines whether or not the filter coefficients converge by using the error calculated by the error calculation unit.

7. The signal processing apparatus according to claim 6 ,
wherein the error calculation unit calculates an average value of the errors related to a plurality of symbols for every constant number of symbols; and
wherein the selection unit determines whether or not the filter coefficients converge by comparing the average value with a predetermined threshold value.

8. The signal processing apparatus according to claim 6 ,
wherein the error calculation unit calculates an average value of the errors related to a plurality of symbols for every constant number of symbols; and
wherein the selection unit determines whether or not the filter coefficients converge by comparing a variation in the average value with a predetermined threshold value.

9. The signal processing apparatus according to claim 1 ,
wherein at least two signal arrangements of the multi-value modulation are signal arrangements of 22n-value quadrature amplitude modulation signals and 22m-value quadrature amplitude modulation signals (where n>m), and when coordinates of four corners of the signal arrangement of the 22n-value quadrature amplitude modulation signals are respectively set to [+a,+a], [−a,+a], [−a,−a], and [+a,−a], coordinates of four corners of the signal arrangement of the 22m-value quadrature amplitude modulation signals are respectively set to [+b,+b], [−b,+b], [−b,−b], and [+b,−b](where a>b).

10. The signal processing apparatus according to claim 9 ,
wherein at least two signal arrangements of the multi-value modulation are signal arrangements of 256-value quadrature amplitude modulation signals and 16-value quadrature amplitude modulation signals, and a ratio of distances between symbols of the 256-value quadrature amplitude modulation signals and the 16-value quadrature amplitude modulation signals is 1:4.

11. The signal processing apparatus according to claim 9 ,
wherein at least two signal arrangements of the multi-value modulation are signal arrangements of 64-value quadrature amplitude modulation signals and 16-value quadrature amplitude modulation signals, and a ratio of distances between symbols of the 64-value quadrature amplitude modulation signals and the 16-value quadrature amplitude modulation signals is 2:4.

12. The signal processing apparatus according to claim 1 ,
wherein the signal arrangement in which the number of multi-values is reduced is a signal arrangement of quadrature phase shift keying.

13. The signal processing apparatus according to claim 1 ,
wherein a signal arrangement of the multi-value modulation is the signal arrangement of the 256-value quadrature amplitude modulation signals, and a ratio of distances between symbols of the 256-value quadrature amplitude modulation signals and the quadrature phase shift keying is 1:10.

14. The signal processing apparatus according to claim 1 ,
wherein a signal arrangement of the multi-value modulation is the signal arrangement of the 64-value quadrature amplitude modulation signals, and a ratio of distances between symbols of the 64-value quadrature amplitude modulation signals and the quadrature phase shift keying is 2:10.

15. The signal processing apparatus according to claim 1 ,
wherein a signal arrangement of the multi-value modulation is the signal arrangement of the 16-value quadrature amplitude modulation signals, and a ratio of distances between symbols of the 16-value quadrature amplitude modulation signals and the quadrature phase shift keying is 4:10.

16. The signal processing apparatus according to claim 1 , further comprising:
the 90° optical hybrid;
photoelectric conversion unit for converting the four output light beams of the 90° optical hybrid into electrical signals, respectively; and
analog-digital conversion unit for converting the four outputs from the photoelectric conversion unit into the digital signals, respectively.

17. A signal processing method comprising:
receiving four digital signals;
generating two polarization signals corresponding to two polarization components of signal light from the four digital signals by using filters having filter coefficients, the four digital signals being generated by performing photoelectric conversion and analog-digital conversion on four output light beams which are generated by making the signal light having undergone p

Assignees

• Yasuda Wakako
• Ogasahara Daisaku
• Fujisawa Shinsuke
• Nec Corp

Inventors

• Yasuda Wakako
• Ogasahara Daisaku
• Fujisawa Shinsuke

Classifications

• H04J14/06

  Polarisation multiplex systems · CPC title

• H04L27/3818

  using coherent demodulation, i.e. using one or more nominally phase synchronous carriers (H04L27/227 and H04L27/389 take precedence) · CPC title

• H04B10/6164

  Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator · CPC title

• H04B10/6165

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

• H04B10/612

  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