OPTICAL COMMUNICATION THAT ACHIEVES BAUD RATE GREATER THAN SAMPLE RATE

• US 20160248540A1
• Filed: 02/12/2016
• Published: 08/25/2016
• Est. Priority Date: 02/23/2015
• Status: Active Grant

• Current Assignee: ZTE Corporation
• Original Assignee: ZTE Corporation
• Inventors: Xin, Xiao, Yu, Jianjun, Li, Fan, Zhang, Junwen, Chien, Hung-Chang
• Granted Patent: US 9,912,431 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04B 10/5167 Duo-binary; Alternative mark inversion; Phase shaped binary transmission
• CPC Class Codes: H04B 10/548 Phase or frequency modulation
• CPC Class Codes: H04J 11/00 Orthogonal multiplex systems, e.g. using WALSH codesH04J13/00 takes precedence
• CPC Class Codes: H04L 27/2636 with FFT or DFT modulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] transmitter or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]
• CPC Class Codes: H04L 27/26526 with inverse FFT [IFFT] or inverse DFT [IDFT] demodulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] receiver or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]

Abstract

Duo-binary encoding is used for encoding I and Q data prior to performing orthogonal frequency division multiplexing based transmission using discrete Fourier transform spreading (DFT-S). Advantageously, duo-binary encoding improves robustness of the encoded signal to inter symbol interference, making the degradation caused by the subsequent DFT-S stage less susceptible to reduction in bit error rate performance.

Claims

1. A method of optical communication, implemented at a transmitter in an optical communication network, comprising:

receiving data bits for transmission over the optical communication network;

encoding the received data bits such that the encoded data bits are duo-binary comprising a zero level and two logical levels;

performing an M-point Fourier transform on the output of the duo-binary encoding, thereby producing M output signals;

generating, from the M output signals, N output signals, wherein N is less than M;

producing time domain samples from the N output signals by performing an inverse Fourier transform; and

further processing the time domain samples for transmission over the optical communication network.

2. The method of claim 1, wherein the encoding includes:

adding, to the received data bits, a delayed version of the received data bits.

3. The method of claim 1, wherein the further processing comprises:

adding a training sequence comprising a quadrature phase shift keying (QPSK) modulated pre-defined sequence to the time domain samples.

4. The method of claim 1, wherein the further processing comprises:

adding a cyclic prefix to the time domain samples.

5. The method of claim 1, wherein the generating N output signals includes:

eliminating M−

N signals representing highest frequency signals from the M output signals.

6. The method of claim 1, wherein the further processing includes performing polarization division multiplexing with another modulated optical signal.

7. A transmission apparatus for optical communication, comprising:

a module that receives data bits for transmission over the optical communication network;

a module that performs a duo-binary encoding of the received data bits in which resulting output duo-binary signal includes three logical signal levels;

a module that performs an M-point Fourier transform on the output of the duo-binary encoding, thereby producing M output signals;

a module that generates, from the M output signals, N output signals, wherein N is less than M;

a module that produces time domain samples from the N output signals by performing an inverse Fourier transform; and

a module that further processes the time domain samples for transmission over the optical communication network.

8. The apparatus of claim 7, wherein the module that performs duo-binary encoding further performs:

adding, to the received data bits, a delayed version of the received data bits.

9. The apparatus of claim 7, wherein the module that further processes the time domain samples further performs:

adding a training sequence comprising a quadrature phase shift keying (QPSK) modulated pre-defined sequence to the time domain samples.

10. The apparatus of claim 7, wherein the module that further processes the time domain samples further performs:

adding a cyclic prefix to the time domain samples.

11. The apparatus of claim 7, wherein the module that generates N output signals further performs:

eliminating M−

N signals representing highest frequency signals from the M output signals.

12. The apparatus of claim 7, wherein the module that further processes the time domain samples further performs polarization division multiplexing with another modulated optical signal.

13. A method of recovering data from an orthogonal frequency division multiplexing (OFDM) modulated optical signal, implemented at an optical receiver, comprising:

digitizing a received signal to generate digital samples of the OFDM modulated optical signal;

transforming the digital samples using an N point Fourier transform to generate N intermediate output signals;

spreading, using a spreading technique, the N intermediate output signals into M signals, wherein M is an integer greater than N;

producing time domain representation of symbols of modulated data by performing an M-point Fourier transform on the M signals; and

performing differential decoding on the symbols of modulated data to recover data from the modulated optical signal.

14. The method of claim 13, further including:

performing polarization domain demultiplexing of the received signal.

15. The method of claim 13, further including:

making decision maximum likelihood sequence detection to recover data from the modulated optical signal.

16. The method of claim 13, wherein the performing differential decoding includes performing duo-binary decoding.

17. The method of claim 13, wherein the spreading includes generating M−

N signals having zero values.

18. The method of claim 17, wherein the M−

N zero values are added at a center of the N signals.

24. The optical receiver of claim 17, wherein the M−

N zero values are added at a center of the N signals.

19. An optical receiver for recovering data from an orthogonal frequency division multiplexing (OFDM) modulated optical signal comprising a digital signal processor that reads instructions from a computer-readable storage medium and implements a method, comprising:

controlling a digitizer to digitize a received signal to generate digital samples of the OFDM modulated optical signal;

transforming the digital samples using an N point Fourier transform to generate N intermediate output signals;

spreading, using a spreading technique, the N intermediate output signals into M signals, wherein M is an integer greater than N;

producing time domain representation of symbols of modulated data by performing an M-point Fourier transform on the M signals; and

performing differential decoding on the symbols of modulated data to recover data from the modulated optical signal.

20. The optical receiver of claim 19, further including:

performing polarization domain demultiplexing of the received signal.

21. The optical receiver of claim 19, further including:

making decision maximum likelihood sequence detection to recover data from the modulated optical signal.

22. The optical receiver of claim 19, wherein the performing differential decoding includes performing duo-binary decoding.

23. The optical receiver of claim 19, wherein the spreading includes generating M−

N signals having zero values.

25. An optical communication system comprising an optical transmitter and at least one optical receiver, wherein the optical transmitter implements a method comprising:

receiving data bits for transmission over the optical communication network,

encoding the received data bits such that the encoded data bits are duo-binary comprising a zero level and two logical levels,

performing an M-point Fourier transform on the output of the duo-binary encoding, thereby producing M output signals,

generating, from the M output signals, N output signals, wherein N is less than M,

producing time domain samples from the N output signals by performing an inverse Fourier transform, and

further processing the time domain samples for transmission over the optical communication network;

and the at least one optical receiver implements a method of recovering data, comprising;

digitizing a received signal to generate digital samples of the OFDM modulated optical signal,

transforming the digital samples using an N point Fourier transform to generate N intermediate output signals,

spreading, using a spreading technique, the N intermediate output signals into M signals, wherein M is an integer greater than N,

producing time domain representation of symbols of modulated data by performing an M-point Fourier transform on the M signals, and

performing differential decoding on the symbols of modulated data to recover data from the modulated optical signal.

26. The system of claim 25, wherein the encoding includes:

adding, to the received data bits, a delayed version of the received data bits.

27. The system of claim 25, wherein the further processing comprises:

adding a training sequence comprising a quadrature phase shift keying (QPSK) modulated pre-defined sequence to the time domain samples.

28. The system of claim 25, wherein the further processing comprises:

adding a cyclic prefix to the time domain samples.

29. The system of claim 25, wherein the generating N output signals includes:

eliminating M−

N signals representing highest frequency signals from the M output signals.

30. The system of claim 25, wherein the further processing includes performing polarization division multiplexing with another modulated optical signal.

31. The system of claim 25, wherein the method of recovering data further includes:

performing polarization domain demultiplexing of the received signal.

32. The system of claim 25, wherein the method of recovering data further includes:

making decision maximum likelihood sequence detection to recover data from the modulated optical signal.

33. The system of claim 25, wherein the performing differential decoding includes performing duo-binary decoding.

34. The system of claim 25, wherein the spreading includes generating M−

N signals having zero values.

35. The system of claim 34, wherein the M−

N zero values are added at a center of the N signals.