Partial discrete fourier transform-spread in an orthogonal frequency division multiplexing system

Patent metadata

Field	Value
Publication number	US-9438460-B2
Application number	US-201514885264-A
Country	US
Kind code	B2
Filing date	Oct 16, 2015
Priority date	Oct 17, 2014
Publication date	Sep 6, 2016
Grant date	Sep 6, 2016

Abstract

A method of transmitting data may include converting a stream of serial data bits into a set of parallel quadrature amplitude modulation (QAM) symbols. The method may additionally include applying a partial discrete Fourier transform-spread technique to transform a block of low-frequency subcarriers into a single-carrier QAM signal. The single-carrier QAM signal may bear information of a first subset of QAM symbols from the set of parallel QAM symbols. The method may additionally include transforming one or more remaining QAM symbols to form one or more subcarriers. Each of the one or more subcarriers may bear information of a corresponding QAM symbol from the one or more remaining QAM symbols. The method may additionally include generating a hybrid signal that includes the single-carrier QAM signal and the one or more subcarriers. The method may additionally include transmitting the hybrid signal.

First claim

What is claimed is:

1. A method comprising:
converting a first stream of serial data bits into a set of parallel quadrature amplitude modulation (QAM) symbols;
applying a partial discrete Fourier transform-spread (DFT-S) technique to transform a first subset of QAM symbols from the set of parallel QAM symbols into a single carrier QAM signal;
transforming one or more remaining QAM symbols from the set of parallel QAM symbols to form one or more high-frequency subcarrier signals, wherein each of the one or more high frequency subcarrier signals bears information of a corresponding QAM symbol from the one or more remaining QAM symbols;
generating a hybrid signal that includes the single-carrier QAM signal and the one or more high frequency subcarrier signals; and
transmitting the hybrid signal.

2. The method of claim 1 , wherein applying the partial DFT-S technique to transform the first subset of QAM symbols into the single-carrier QAM signal comprises:
performing a discrete Fourier transform (DFT) on the first subset of QAM symbols to generate a DFT output;
pre-equalizing the DFT output to generate a pre-equalized output; and
performing an inverse discrete Fourier transform on the pre-equalized output to generate the single-carrier QAM signal.

3. The method of claim 2 , wherein pre-equalizing the DFT output to generate the pre-equalized output comprises multiplying the DFT output with real numbers that correspond to a pre-equalization transfer function.

4. The method of claim 1 , wherein transforming the one or more remaining QAM symbols to form the one or more high-frequency subcarrier signals comprises performing an inverse discrete Fourier transform on the one or more remaining QAM symbols to generate the one or more high-frequency subcarrier signals.

5. The method of claim 1 , wherein transmitting the hybrid signal comprises:
converting the hybrid signal to a second stream of serial data bits;
adding a cyclic prefix to the second stream of serial data bits;
converting the second stream of serial data bits to an analog signal; and
generating, based on the analog signal, a transmit laser beam configured to transmit through an optical channel.

6. The method of claim 1 , wherein:
the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and
each of the one or more high-frequency subcarrier signals has a corresponding frequency higher than a frequency of any of the low-frequency subcarrier signals.

7. The method of claim 1 , wherein the single-carrier QAM signal is orthogonal to each of the one or more high-frequency subcarrier signals.

8. The method of claim 1 , wherein:
the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and
the single-carrier QAM signal occupies a frequency bandwidth associated with the low-frequency subcarrier signals.

9. The method of claim 1 , wherein converting the first stream of serial data bits into the set of parallel QAM symbols comprises:
converting the first stream of serial data bits into parallel streams of data bits; and
converting corresponding data bits in each parallel stream to a corresponding QAM symbol based on a corresponding QAM constellation.

10. The method of claim 1 , wherein:
the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and
the low-frequency subcarrier signals and the one or more high frequency subcarrier signals include discrete multitone subcarrier signals.

11. A system comprising:
a serial-to-parallel quadrature amplitude modulation (QAM) module configured to receive a first stream of serial data bits and to convert the first stream of serial data bits into a set of parallel QAM symbols; and
a partial discrete Fourier transform-spread (DFT-S) module communicatively coupled to the serial-to-parallel QAM module, the partial DFT-S module configured to apply a partial DFT-S technique to transform a first subset of QAM symbols from the set of parallel QAM symbols into a single-carrier QAM signal, wherein:
the partial DFT-S module includes a discrete Fourier transform (DFT) module and an inverse discrete Fourier transform (IDFT) module;
the IDFT module is configured to transform one or more remaining QAM symbols from the set of parallel QAM symbols to form one or more high-frequency subcarrier signals, wherein each of the one or more high-frequency subcarrier signals bears information of a corresponding QAM symbol from the one or more remaining QAM symbols; and
the IDFT module is configured to generate a hybrid signal that includes the single-carrier QAM signal and the one or more high-frequency subcarrier signals, wherein the hybrid signal is configured to transmit to a receiver.

12. The system of claim 11 , wherein:
the partial DFT-S module further includes a pre-equalizer;
the DFT module is configured to perform a discrete Fourier transform on the first subset of QAM symbols to generate a DFT output;
the pre-equalizer is configured to pre-equalize the DFT output to generate a pre-equalized output; and
the IDFT module is configured to perform an inverse discrete Fourier transform on the pre-equalized output to generate the single-carrier QAM signal.

13. The system of claim 12 , wherein the pre-equalizer is configured to pre-equalize the DFT output to generate the pre-equalized output by multiplying the DFT output with real numbers that correspond to a pre-equalization transfer function.

14. The system of claim 11 , wherein the IDFT module is configured to transform the one or more remaining QAM symbols to form the one or more high-frequency subcarrier signals by performing an inverse discrete Fourier transform on the one or more remaining QAM symbols to generate the one or more high-frequency subcarrier signals.

15. The system of claim 11 , further comprising:
a parallel-to-serial module configured to convert the hybrid signal to a second stream of serial data bits and to add a cyclic prefix to the second stream of serial data bits; and
a digital-to-analog converter configured to convert the second stream of serial data bits to an analog signal, wherein the analog signal is used to generate a transmit laser beam configured to transmit through an optical channel.

16. The system of claim 11 , wherein:
the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and
each of the one or more high-frequency subcarrier signals has a corresponding frequency higher than a frequency of any of the low-frequency subcarrier signals.

17. The system of claim 11 , wherein the single-carrier QAM signal is orthogonal to each of the one or more high-frequency subcarrier signals.

18. The system of claim 11 , wherein:
the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and
the single-carrier QAM signal occupies a frequency bandwidth associated with the low-frequency subcarrier signals.

19. The system of claim 11 , wherein the serial-to-parallel QAM module is configured to convert the first stream of serial data bits into the set of parallel QAM symbols by:
converting the first stream of serial data bits into parallel s

Assignees

• Finisar Corp

Inventors

• Ling William
• Lyubomirsky Ilya

Classifications

• H04B10/616

  Details of the electronic signal processing in coherent optical receivers · 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

• H04B10/541

  Digital intensity or amplitude modulation · CPC title

• H04L27/2636

  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 title

• H04L27/362

  Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated (H04L27/366 takes precedence) · CPC title