Data transmission via multi-path channels using orthogonal multi-frequency signals with differential phase shift keying modulation

• US 9,769,004 B2
• Filed: 11/23/2015
• Issued: 09/19/2017
• Est. Priority Date: 10/05/2007
• Status: Active Grant

• Current Assignee: Innurvation Incorporated
• Original Assignee: Innurvation Incorporated
• Inventors: Okunev, Yuri
• Primary Examiner(s): Burd, Kevin M
• Application Number:
  US14/949,187
• Publication Number:
  US 20160218907A1
• Time in Patent Office: 666 Days
• Field of Search: 375259, 375260, 375267
• CPC Class Codes: H04B 1/1081 Reduction of multipath noise by equalising H04B7/005
• CPC Class Codes: H04L 27/206 using a pair of orthogonal carriers, e.g. quadrature carriers
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/2627 Modulators
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2676 Blind, i.e. without using known symbols
• CPC Class Codes: H04L 27/2697 in combination with other modulation techniques

Abstract

A method and an apparatus relating to an OFDM data communications system where the sub-carriers are modulated using differential quadrature phase-shift keying (DQPSK). The multi-carrier transmitted signal is directly generated by means of summation of pre-computed sample points. As part of the multi-carrier signal generation, a signal for the guard interval is established. In an acoustic application of this approach, direct radiation of the sub-carrier approach is facilitated. Symbol synchronization in the receiver is based on signal correlation with the missed sub-carrier. Separation of the sub-carriers in the receiver by means of correlation of the received signal and reference signals that are derived from a table of pre-computed values. Optimal non-coherent processing of the sub-carriers without any phase tracking procedures is achieved.

Claims

1. A data communications system, for use over a multi-path channel, comprising:

an orthogonal frequency division multiplexing (OFDM) sub-carrier signal generator that outputs a plurality of OFDM sub-carrier signals;

a differential quadrature phase shift keying (DQPSK) modulator that modulates each OFDM sub-carrier signal of the plurality of OFDM sub-carrier signals in response to input data, and forms a plurality of modulated OFDM sub-carrier signals in response to the input data;

a summer that combines the plurality of modulated OFDM sub-carrier signals to form a transmitted signal;

a receiver to output a received signal in response to the transmitted signal transmitted through the multi-path channel, the received signal having a missing sub-carrier signal at a center frequency located in the middle of a frequency spectrum of the received signal, the missing sub-carrier signal having zero amplitude;

an OFDM sub-carrier reference generator that outputs a plurality of OFDM sub-carrier reference signals, the plurality of OFDM sub-carrier reference signals including an OFDM sub-carrier reference signal located at the center frequency;

a non-coherent synchronizer that synchronizes an OFDM symbol interval to a demodulating interval by nulling a correlation between the received signal and the OFDM sub-carrier reference signal located at the center frequency; and

a demodulator, using a DQPSK multi-carrier detector, that demodulates the received signal to form an output signal.

2. The data communications system of claim 1, wherein the OFDM sub-carrier signal generator uses pre-computed sample points.

3. The data communications system of claim 1, wherein the synchronizer nulls the correlation between the received signal and the OFDM sub-carrier reference signals OFDM sub-carrier reference signal located at the center frequency by shifting a synchronization pulse based on a comparison of respective correlations of an advanced time interval and a delayed time interval.

4. The data communications system of claim 1, wherein the transmitted signal is an acoustical signal.

5. The data communications system of claim 1, wherein the demodulator does not use a phase tracking approach.

6. The data communications system of claim 1, wherein the DQPSK modulator comprises a decimal transformation device, a modulo-4 summation device, and a switch controller device.

7. The data communications system of claim 1, wherein the demodulator comprises a correlation device, a transformation device, and a decision device.

8. The data communications system of claim 1, wherein the synchronizer nulls the correlation between the received signal and the OFDM sub-carrier reference signal located at the center frequency by locating a timeframe that minimizes a length of a vector formed by correlating the received signal and the OFDM sub-carrier reference signal located at the center frequency.

9. A data receiver, for use over a multi-path channel, comprising:

a receiver to output a received signal in response to a transmitted signal transmitted through the multi-path channel, the received signal having a missing sub-carrier signal at a center frequency located in the middle of a frequency spectrum of the received signal, the missing sub-carrier signal having zero amplitude;

an orthogonal frequency division multiplexing (OFDM) sub-carrier reference generator that outputs a plurality of OFDM sub-carrier reference signals, the plurality of OFDM sub-carrier reference signals including an OFDM sub-carrier reference signal located at the center frequency;

a non-coherent synchronizer that synchronizes an OFDM symbol interval to a demodulating interval by nulling a correlation between the received signal and the OFDM sub-carrier reference signal located at the center frequency; and

a demodulator, using a differential quadrature phase shift keying (DQPSK) multi-carrier detector, that demodulates the received signal to form an output signal.

10. The data receiver of claim 9, wherein the synchronizer nulls the correlation between the received signal and the OFDM sub-carrier reference signal located at the center frequency by locating a timeframe that minimizes a length of a vector formed by correlating the received signal and the OFDM sub-carrier reference signal located at the center frequency.

11. The data receiver of claim 9, wherein the demodulator does not use a phase tracking approach.

12. The data receiver of claim 9, wherein the demodulator comprises a correlation device, a transformation device, and a decision device.

13. The data receiver of claim 9, wherein the synchronizer nulls the correlation between the received signal and the OFDM sub-carrier reference signal located at the center frequency by shifting a synchronization pulse based on a comparison of respective correlations of an advanced time interval and a delayed time interval.

14. A method for data communications, comprising:

receiving a received signal via a channel, the received signal having a missing sub-carrier signal at a center frequency located in the middle of a frequency spectrum of the received signal, the missing sub-carrier signal having zero amplitude;

generating a plurality of orthogonal frequency division multiplexing (OFDM) sub-carrier reference signals, the plurality of OFDM sub-carrier reference signals including an OFDM sub-carrier reference signal located at the center frequency;

non-coherently synchronizing an OFDM symbol interval and a demodulating interval by nulling a correlation between the received signal and the OFDM sub-carrier reference signal located at the center frequency; and

demodulating, using a DQPSK multi-carrier detector, the received signal to form an output signal,

wherein the generating, synchronizing and demodulating are performed by one or more circuits.

15. The method of claim 14, wherein the synchronizing by nulling the correlation between the received signal and the OFDM sub-carrier reference signal located at the center frequency includes locating a timeframe that minimizes a length of a vector formed by correlating the received signal and the OFDM sub-carrier reference signal located at the center frequency.

16. The method of claim 14, wherein the generating the plurality of OFDM sub-carrier reference signals uses pre-computed sample points.

17. The method of claim 14, wherein the synchronizing by nulling the correlation between the received signal and the OFDM sub-carrier reference signal located at the center frequency includes shifting a synchronization pulse based on a comparison of respective correlations of an advanced time interval and a delayed time interval.

18. The method of claim 14, wherein the transmitted signal is an acoustical signal.