Modulation and equalization in an orthonormal time-frequency shifting communications system

• US 10,637,697 B2
• Filed: 06/08/2017
• Issued: 04/28/2020
• Est. Priority Date: 05/28/2010
• Status: Active Grant

• Current Assignee: Cohere Technologies Inc
• Original Assignee: Cohere Technologies Inc
• Inventors: Hadani, Ronny, Rakib, Shlomo Selim
• Primary Examiner(s): Neff, Michael R
• Application Number:
  US15/617,962
• Publication Number:
  US 20170346665A1
• Time in Patent Office: 1,055 Days
• Field of Search: 375233
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 7/005 Control of transmission; Equalising
• CPC Class Codes: H04L 23/02 adapted for orthogonal signalling
• CPC Class Codes: H04L 25/03834 using pulse shaping
• CPC Class Codes: H04L 27/01 Equalisers baseband equalizers at the transmitter end H04L25/03343; in analogue transmission systems H04B3/04, H04B7/005
• CPC Class Codes: H04L 27/2634 Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 27/2697 in combination with other modulation techniques
• CPC Class Codes: H04L 5/0016 Time-frequency-code
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

A method of receiving data including receiving, on one or more carrier waveforms, signals representing a plurality of data elements of an original data frame wherein each of the data elements are represented by cyclically time shifted and cyclically frequency shifted versions of a known set of waveforms. The method further includes generating, based upon the signals, a received data frame and generating an equalized data frame by performing an equalization operation using elements of the received data frame, the equalization operation correcting for distortion introduced into the signals during propagation of the carrier waveforms through a channel.

Claims

1. A decision feedback equalizer, comprising

a feedforward equalizer including a first plurality of filter taps determined based upon a two-dimensional channel model wherein each of the first plurality of filter taps is represented by a two-dimensional tap matrix, the two-dimensional channel model being comprised of a weighted superposition of a combination of time and Doppler shifts and enabling channel multipath delay and Doppler shift to be profiled simultaneously;

and

a feedback equalizer in communication with the feedforward equalizer, the feedback equalizer including a second plurality of filter taps wherein each of the second plurality of filter taps is represented by a two-dimensional matrix of values.

2. The decision feedback equalizer of claim 1 wherein the decision feedback equalizer forms part of a receiver apparatus operative to receive at least a main signal and echo and frequency shifted signals, the feedforward equalizer being configured to shift the echo and frequency shifted signals to coincide with the main signal.

3. The decision feedback equalizer of claim 2 wherein the feedback equalizer is configured to remove any residual portions of the echo and frequency shifted signals not shifted onto the main signal.

4. The decision feedback equalizer of claim 3 further including a quantizer configured to round output values produced by the feedback equalizer to quantized output values.

5. A decision feedback equalizer, comprising

a feedforward equalizer including a first plurality of filter taps wherein each of the first plurality of filter taps is represented by a two-dimensional tap matrix;

and

a feedback equalizer in communication with the feedforward equalizer, the feedback equalizer including a second plurality of filter taps wherein each of the second plurality of filter taps is represented by a two-dimensional matrix of values;

wherein the decision feedback equalizer operates according to the expression;

6. An equalization method, comprising:

shifting, using a feedforward equalizer including a first plurality of filter taps, echo and frequency shifted signals to coincide with a main signal;

determining the first plurality of filter taps based upon a two-dimensional channel model, the two-dimensional channel model being comprised of a weighted superposition of a combination of time and Doppler shifts and enabling channel multipath delay and Doppler shift to be profiled simultaneously; and

removing, using a feedback equalizer in communication with the feedforward equalizer, any residual portions of the echo and frequency shifted signals not shifted onto the main signal wherein the feedback equalizer includes a second plurality of filter taps.

7. The equalization method of claim 6 wherein the first plurality of filter taps and the second plurality of filter taps are expressed in terms of a channel impulse response.

8. The equalization method of claim 7 wherein the determining the first plurality of filter taps includes computing the first plurality of filter taps without regard to feedback, the second plurality of filter taps being computed after the first plurality of filter taps have been computed.

9. The equalization method of claim 6 further including representing each of the first plurality of filter taps by a two-dimensional tap matrix and representing each of the second plurality of filter taps by a two-dimensional matrix of values.