Using statistics to locate signals in noise
First Claim
1. A method to detect likelihood of presence of a small data signal in a signal including noise, said method comprising steps ofacquiring said signal from a transducer, a recording or other source,determining statistics of said signal,detecting changes in said statistics of said signal in a moving time window of selected duration,said determining and detecting steps being performed using a computer, anddetermining said likelihood based on results of said step of detecting changeswhereby a portion of said signal can be selected for storage or further processing based on s result of said determining step.
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Abstract
Computation of variance or variance of the autocorrelation over a moving window of various sizes of a signal containing noise and possibly a small digital signal provides a sensitive, frequency independent indication of the likelihood of the presence of a small pulse, chirp or even spread spectrum digital signal possibly obscured by noise or larger signals in the signal to much lower signal-to-noise ratios than previously possible. Large signals in the signal which may also obscure any small signal are removed to a different signal path from the noise and small signals by subtraction after compression and reconstruction of the large signal. The compression noise thus added to the signal may also increase sensitivity of the variance of the autocorrelation to small signals obscured by the large signals. Controlling storage in response to the computed variance or variance of the autocorrelation allows substantial avoidance or limitation of storage of signals which contain only noise.
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Citations
19 Claims
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1. A method to detect likelihood of presence of a small data signal in a signal including noise, said method comprising steps of
acquiring said signal from a transducer, a recording or other source, determining statistics of said signal, detecting changes in said statistics of said signal in a moving time window of selected duration, said determining and detecting steps being performed using a computer, and determining said likelihood based on results of said step of detecting changes whereby a portion of said signal can be selected for storage or further processing based on s result of said determining step.
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14. Apparatus for detecting likelihood of presence of a small data signal in a signal including noise, comprising
a filter for removing a portion of noise from an original signal to provide a filtered signal, a subtractor for performing a phased subtraction of said filtered signal and said original signal to produce a noise signal, and means for calculating a variance of an autocorrelation of said noise signal over respective moving time windows of said noise signal.
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17. A recording or monitoring instrument including
a filter for removing a portion of noise from an original signal to provide a filtered signal, a subtractor for performing a phased subtraction or addition of said filtered signal from or to said original signal or vice-versa to produce a noise signal, and means for calculating a variance of an autocorrelation of said noise signal over respective time windows of said noise signal.
Specification