Frequency selective TDOA/FDOA cross-correlation

• US 5,874,916 A
• Filed: 01/25/1996
• Issued: 02/23/1999
• Est. Priority Date: 01/25/1996
• Status: Expired due to Term

• Current Assignee: Loral Federal Systems Company (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Desiardins, Gerard A.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US08/591,413
• Time in Patent Office: 1,125 Days
• Field of Search: 342/378, 455/137
• US Class Current: 342/378
• CPC Class Codes: G01S 1/045 Receivers

Abstract

A digital signal processing system for obtaining accurate time delay of arrival (TDOA) and frequency delay of arrival (FDOA) measuremets of a signal of interest in a dense interfering signal environment is provided. A time series of cross-spectra (called a waterfall in the art) are computed from transforms applied to overlapping data sets comprising two received digital data streams, which include the signal from an emitter of interest and one or more partially overlapping interfering signals. For each cross-spectra frequency, a transform is calculated in the time direction to create a frequency difference of arrival dimension. Regions within the transformed cross-spectrum that are associated with individual emitters are then identified based on the fact that a given emitter'"'"'s transformed cross-spectrum phase changes linearly with frequency near the peak FDOA for the emitter. The frequency region(s) associated with the emitter of interest are selected based on the approximate frequency and bandwidth information provided. Applying an inverse transform for the frequencies, identified as associated with the emitter of interest, creates a time difference of arrival dimension corresponding to each frequency difference of arrival value.

Claims

1. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest in order to derive frequency difference of arrival data and time difference of arrival data for the signal at the two spaced apart receivers, comprising in combination:

means to convert the signal received by one spaced apart receiver to a first digital data stream that digitally represents the signal as a series of values as a function of time;

means to convert the signal received by the other spaced apart receiver to a second digital data stream that digitally represents the signal as a series of values as a function of time;

means to convert said first digital data stream to a first spectrum of values that represents the signal as a series of values as a function of frequency;

means to convert said second digital data stream to a second spectrum that represents the signal as a series of values as a function of frequency;

means to cross-multiply said first spectrum and said second spectrum to generate a plurality of cross-spectra as a function of time;

means to transform each frequency in said plurality of cross-spectra to a series of frequency difference of arrival values which represent each said frequency in said plurality of cross-spectra;

means to select in said series of values which represent each said frequency those values that represent said emitter of interest; and

means to sum said frequency values that represent said emitter of interest to create a time difference of arrival value for said values that represent said emitter of interest.

3. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest as in claim 1 wherein at least one of said two spaced apart receivers has two channels which provide direction of arrival information and wherein said means to select in said series of values which represent each said frequency includes means for using the direction of arrival to select those values that represent the emitter of interest.

4. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest as in claim 1 wherein said means to convert said first digital data stream to a first spectrum of values that represents the signal as a series of values as a function of frequency includes means to Fourier transform said first digital data stream, and said means to convert said second digital data stream to a second spectrum that represents the signal as a series of values as a function of frequency includes means to Fourier transform said second digital data stream.

5. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest as in claim 1 wherein said means to convert the signal received by one spaced apart receiver to a first digital data stream that digitally represents the signal as a series of values as a function of time includes means to Fourier transform said first digital data stream, and said means to convert the signal received by the other spaced apart receiver to a second digital data stream that digitally represents the signal as a series of values as a function of time includes means to Fourier transform said second digital data stream.

6. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest as in claim 1, wherein said means to transform each frequency in said plurality of cross-spectra to a series of frequency difference of arrival values which represent each said frequency in said plurality of cross-spectra as a function of time includes means to Fourier transform said each frequency.

7. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest as in claim 1, wherein said means to sum said frequency values that represent said emitter of interest to create a time difference of arrival value includes means to Fourier transform said each frequency difference of arrival value.

2. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest in order to derive frequency difference of arrival data and time difference of arrival data for the signal at the two spaced apart receivers, comprising in combination:

means to convert the signal received by one spaced apart receiver to a first digital data stream that digitally represents the signal as a series of values as a function of time;

means to convert the signal received by the other spaced apart receiver to a second digital data stream that digitally represents the signal as a series of values as a function of time;

means to convert said first digital data stream to a first spectrum of values that represents the signal as a series of values as a function of frequency;

means to convert said second digital data stream to a second spectrum that represents the signal as a series of values as a function of frequency;

means to cross-multiply said first spectrum and said second spectrum to generate a plurality of cross-spectra as a function of time;

means to transform each frequency in said plurality of cross-spectra to a series of frequency difference of arrival values which represent each said frequency in said plurality of cross-spectra as a function of time;

means to select using the phase behavior with frequency near the peak frequency difference of arrival value said series of values which represent each said frequency whose phase changes lineally with frequency that represent said emitter of interest; and

means to sum said frequency values that represent said emitter of interest to create a time difference of arrival value for said values that represent said emitter of interest.

8. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest as in claim 2 wherein said means to convert said first digital data stream to a first spectrum of values that represents the signal as a series of values as a function of frequency includes means to Fourier transform said first digital data stream, and said means to convert said second digital data stream to a second spectrum that represents the signal as a series of values as a function of frequency includes means to Fourier transform said second digital data stream.

9. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest as in claim 2, wherein said means to transform each frequency in said plurality of cross-spectra to a series of frequency difference of arrival values which represent said each frequency in said plurality of cross-spectra as a function of time includes means to Fourier transform said each frequency.

10. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest as in claim 2, wherein said means to sum said frequency values that represent said emitter of interest to create a time difference of arrival value includes means to Fourier transform said frequency values for said each frequency difference of arrival value.

11. A digital signal processing system for processing a signal received at two spaced apart receivers from an emitter of interest as in claim 2 wherein said means to convert the signal received by one spaced apart receiver to a first digital data stream that digitally represents the signal as a series of values as a function of time includes means to Fourier transform said first digital data stream, and said means to convert the signal received by the other spaced apart receiver to a second digital data stream that digitally represents the signal as a series of values as a function of time includes means to Fourier transform said second digital data stream.

12. A digital signal processing method for processing a signal received at two spaced apart receivers from an emitter of interest in order to derive frequency difference of arrival data and time difference of arrival data for the signal at the two spaced apart receivers, comprising in combination:

converting the signal received by one spaced apart receiver to a first digital data stream that digitally represents the signal as a series of values as a function of time;

converting the signal received by the other spaced apart receiver to a second digital data stream that digitally represents the signal as a series of values as a function of time;

converting said first digital data stream to a first spectrum of values that represents the signal as a series of values as a function of frequency;

converting said second digital data stream to a second spectrum that represents the signal as a series of values as a function of frequency;

cross-multiplying said first spectrum and said second spectrum to generate a plurality of cross-spectra as a function of time;

transforming each frequency in said plurality of cross-spectra to a series of frequency difference of arrival values which represent said each frequency in said plurality of cross-spectra;

selecting in said series of values which represent each said frequency those values that represent said emitter of interest; and

summing said values that represent said emitter of interest to create a time difference of arrival value for said values that represent said emitter of interest.

13. A digital signal processing method for processing a signal received at two spaced apart receivers from an emitter of interest in order to derive frequency difference of arrival data and time difference of arrival data for the signal at the two spaced apart receivers, comprising in combination:

converting the signal received by one spaced apart receiver to a first digital data stream that digitally represents the signal as a series of values as a function of time;

converting the signal received by the other spaced apart receiver to a second digital data stream that digitally represents the signal as a series of values as a function of time;

converting said first digital data stream to a first spectrum of values that represents the signal as a series of values as a function of frequency;

converting said second digital data stream to a second spectrum that represents the signal as a series of values as a function of frequency;

cross-multiplying said first spectrum and said second spectrum to generate a plurality of cross-spectra as a function of time;

transforming each frequency in said plurality of cross-spectra to a series of frequency difference of arrival values which represent said each frequency in said plurality of cross-spectra;

selecting using the phase behavior with frequency near the peak frequency difference of arrival value in said series of values which represent each said frequency those values that represent said emitter of interest; and

summing said values that represent said emitter of interest to create a time difference of arrival value for said values that represent said emitter of interest.

14. A digital signal processing method for processing a signal received at two spaced apart receivers from an emitter of interest in order to derive frequency difference of arrival data and time difference of arrival data for the signal at the two spaced apart receivers, including the steps of:

converting the signal received by one spaced apart receiver to a first digital data stream that digitally represents the signal as a series of values as a function of time;

converting the signal received by the other spaced apart receiver to a second digital data stream that digitally represents the signal as a series of values as a function of time;

converting said first digital data stream to a first spectrum of values that represents the signal as a series of values as a function of frequency;

converting said second digital data stream to a second spectrum that represents the signal as a series of values as a function of frequency, then;

cross-correlating said first spectrum and said second spectrum to generate a plurality of cross-spectra, then;

transforming each frequency in said plurality of cross-spectra to a series of frequency difference of arrival values which represent said each frequency in said plurality of cross-spectra as a function of time, then;

selecting in said series of values which represent each said frequency those values that represent said emitter of interest; and

then,

summing said values that represent said emitter of interest to create a time difference of arrival value for said values that represent said emitter of interest.

15. A digital signal processing method for processing a signal received at two spaced apart receivers from an emitter of interest in order to derive frequency difference of arrival data and time difference of arrival data for the signal at the two spaced apart receivers, including the steps of:

converting the signal received by one spaced apart receiver to a first digital data stream that digitally represents the signal as a series of values as a function of time;

converting the signal received by the other spaced apart receiver to a second digital data stream that digitally represents the signal as a series of values as a function of time;

converting said first digital data stream to a first spectrum of values that represents the signal as a series of values as a function of frequency;

converting said second digital data stream to a second spectrum that represents the signal as a series of values as a function of frequency, then;

cross-correlating said first spectrum and said second spectrum to generate a plurality of cross-spectra, then;

transforming each frequency in said plurality of cross-spectra to a series of frequency difference of arrival values which represent said each frequency in said plurality of cross-spectra as a function of time, then;

selecting in said series of values which represent each said frequency whose phase values near a peak value change linearly with frequency and thus represent said emitter of interest; and

then

summing said values that represent said emitter of interest to create a time difference of arrival value for said values that represent said emitter of interest.