Reception of 2-subcarriers coherent orthogonal frequency division multiplexed signals

Patent metadata

Field	Value
Publication number	US-9590833-B2
Application number	US-201414453471-A
Country	US
Kind code	B2
Filing date	Aug 6, 2014
Priority date	Aug 7, 2013
Publication date	Mar 7, 2017
Grant date	Mar 7, 2017

Abstract

A dual-polarization, 2-subcarriers code orthogonal, orthogonal frequency division multiplexed signal carrying information bits is transmitted in an optical communication network without transmitting a corresponding pilot tone or training sequence. A receiver receives the transmitted signal and recovers information bits using a blind equalization technique and by equalizing the 2-subcarriers OFDM signal as a 9-QAM signal in time domain with a CMMA (constant multi modulus algorithm) equalization method.

First claim

What is claimed is:

1. A method for recovering information bits from a two-subcarrier orthogonal frequency division multiplexed (OFDM) signal in which each subcarrier is modulated using a 4 Quadrature Amplitude Modulation (QAM) constellation, comprising:
receiving the two-subcarrier OFDM signal;
processing the two-subcarrier OFDM signal as a 9-QAM signal to generate a modulus signal; and
applying a 2 point Fourier transform to the modulus signal to recover the information bits.

2. The method of claim 1 , wherein the processing comprises using a cascaded multi-modulus algorithm (CMMA), wherein the CMMA comprises:
performing channel equalization of the received two-subcarrier OFDM signal to obtain a set of channel estimation coefficients and a stream of symbols;
partitioning, based on a modulus of the stream of symbols, the stream of symbols into three partitions;
estimating a carrier frequency offset based on the partitioned stream of symbols;
recovering a phase of the received two-subcarrier OFDM signal using a maximum likelihood algorithm.

3. The method of claim 2 , further including:
rotating at least some constellation points.

4. The method of claim 3 , wherein the rotating operation is performed during the operation of estimating the carrier frequency offset.

5. The method of claim 3 , wherein the rotating operation is performed during the operation of recovering the phase of the signal.

6. An optical receiver apparatus for recovering information bits from a two-subcarrier orthogonal frequency division multiplexed (OFDM) signal in which each subcarrier is modulated using a 4 Quadrature Amplitude Modulation (QAM) constellation, comprising:
an optical receiver module that receives the two-subcarrier OFDM signal;
a receiver processing module that processes the two-subcarrier OFDM signal as a 9-QAM signal to generate a modulus signal;
a Fourier transform module that applies a 2 point Fourier transform to the modulus signal to recover the information bits.

7. The apparatus of claim 6 , wherein the processing comprises using a cascaded multi-modulus algorithm (CMMA), wherein the CMMA comprises:
performing channel equalization of the received two-subcarrier OFDM signal to obtain a set of channel estimation coefficients and a stream of symbols;
partitioning, based on a modulus of the stream of symbols, the stream of symbols into three partitions;
estimating a carrier frequency offset based on the partitioned stream of symbols;
recovering a phase of the received two-subcarrier OFDM signal using a maximum likelihood algorithm.

8. The apparatus of claim 7 , further including:
a constellation rotation module that rotates at least some constellation points.

9. The apparatus of claim 8 , wherein the constellation rotation module performs the rotating operation during the operation of estimating the carrier frequency offset.

10. The apparatus of claim 8 , wherein the constellation rotation module performs the rotating operation during the operation of recovering the phase of the signal.

11. An optical communication apparatus, comprising:
an optical receiver that receives a two-subcarrier orthogonal frequency division multiplexed (OFDM) signal whose subcarriers have been modulated using a 4 Quadrature Amplitude Modulation (QAM) constellation;
a memory that stores instructions;
a processor that reads the instructions from the memory, processes the two-subcarrier OFDM signal as a 9-QAM signal to generate a modulus signal, and applies a 2 point Fourier transform to the modulus signal to recover the information bits.

12. The apparatus of claim 11 , wherein the processor further
performs channel equalization of the received two-subcarrier OFDM signal to obtain a set of channel estimation coefficients and a stream of symbols;
partitions, based on a modulus of the stream of symbols, the stream of symbols into three partitions;
estimates a carrier frequency offset based on the partitioned stream of symbols;
recovers a phase of the received two-subcarrier OFDM signal using a maximum likelihood algorithm.

13. The apparatus of claim 12 , wherein the processor further:
rotates at least some constellation points.

14. The apparatus of claim 13 , wherein the processor rotates at least some constellation points and estimates the carrier frequency offset based on the partitioned stream of symbols at least partially concurrently.

15. The apparatus of claim 13 , wherein the processor rotates at least some constellation points and recovers the phase of the received two-subcarrier OFDM signal at least partially concurrently.

16. An optical communication system, comprising:
an optical transmission medium;
an optical transmission apparatus transmits, over the optical transmission medium, a two-subcarrier orthogonal frequency division multiplexed (OFDM) signal in which each subcarrier is modulated using a 4 Quadrature Amplitude Modulation (QAM) constellation without transmitting a training sequence and a pilot signal; and
an optical receiver apparatus that:
receives the two-subcarrier OFDM signal;
processes the two-subcarrier OFDM signal as a 9-QAM signal to generate a modulus signal; and
applies a 2 point Fourier transform to the modulus signal to recover the information bits.

17. The system of claim 16 , wherein the processing comprises using a cascaded multi-modulus algorithm (CMMA), wherein the CMMA comprises:
performing channel equalization of the received two-subcarrier OFDM signal to obtain a set of channel estimation coefficients and a stream of symbols;
partitioning, based on a modulus of the stream of symbols, the stream of symbols into three partitions;
estimating a carrier frequency offset based on the partitioned stream of symbols;
recovering a phase of the received two-subcarrier OFDM signal using a maximum likelihood algorithm.

18. The system of claim 17 , wherein the optical receiver apparatus further:
rotates at least some constellation points.

19. The system of claim 18 , wherein the rotating operation is performed during the operation of estimating the carrier frequency offset.

20. The system of claim 18 , wherein the rotating operation is performed during the operation of recovering the phase of the signal.

Assignees

• Zte Corp

Inventors

• Yu Jianjun
• Li Fan

Classifications

• H04L27/3818

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

• H04L27/3422

  in which the constellation is not the n - fold Cartesian product of a single underlying two-dimensional constellation · CPC title

• H04L27/34

  Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems · CPC title

• H04L27/2697

  in combination with other modulation techniques · CPC title

• H04B10/65

  Intradyne, i.e. coherent receivers with a free running local oscillator having a frequency close but not phase-locked to the carrier signal · CPC title