Signal presence detector and method
First Claim
1. A signal presence detector for an input signal having a known spectral distribution but accompanied by strong noise energy which may provide a negative signal-to-noise ratio, comprising:
- a common input for receiving the input signal;
a first bandpass filter coupled to the common input and responsive to the input signal, the first bandpass filter encompassing one selected region within the spectral distribution;
a second bandpass filter coupled to the common input and responsive to the input signal, the second bandpass filter encompassing a second selected region within the spectral distribution;
a detector;
switching means for applying the outputs of said first and second bandpass filters to said detector in time shared fashion; and
means coupled to said detector and responsive to received energy levels from said bandpass filters which differ by at least a predetermined minimum amount for indicating the presence of the input signal;
the first and second bandpass filters having center frequencies lying at different regions within the spectral distribution, the signal having a spread spectrum characteristic and the center frequency of said first bandpass filter being at the center frequency of the spread spectrum.
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Abstract
Circuitry and methods are presented for detecting the presence of a spectrally distributed signal having a known distribution, e.g. spread spectrum, in a strong noise environment. The signal is split into two channels, each filtering a predetermined frequency band within the given spectrum. The channels are tuned and balanced so that they pass differential amounts of signal energy that may be present but provide equalized noise outputs. The channels are alternately coupled to the input of an energy detector which provides a DC component responsive to the difference in the signal levels of interest, while effectively cancelling noise energy components in each channel. In the spread spectrum example the frequency bands are typically selected to the maximum and a null location in a ##EQU1## distribution.
33 Citations
15 Claims
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1. A signal presence detector for an input signal having a known spectral distribution but accompanied by strong noise energy which may provide a negative signal-to-noise ratio, comprising:
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a common input for receiving the input signal; a first bandpass filter coupled to the common input and responsive to the input signal, the first bandpass filter encompassing one selected region within the spectral distribution; a second bandpass filter coupled to the common input and responsive to the input signal, the second bandpass filter encompassing a second selected region within the spectral distribution; a detector; switching means for applying the outputs of said first and second bandpass filters to said detector in time shared fashion; and means coupled to said detector and responsive to received energy levels from said bandpass filters which differ by at least a predetermined minimum amount for indicating the presence of the input signal; the first and second bandpass filters having center frequencies lying at different regions within the spectral distribution, the signal having a spread spectrum characteristic and the center frequency of said first bandpass filter being at the center frequency of the spread spectrum. - View Dependent Claims (2)
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3. A signal presence detector for an input signal having a known spectral distribution but accompanied by strong noise energy which may provide a negative signal-to-noise ratio, comprising:
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a common input for receiving the input signal; a first bandpass filter coupled to the common input and responsive to the input signal, the first bandpass filter encompassing one selected region within the spectral distribution; a second bandpass filter coupled to the common input and responsive to the input signal, the second bandpass filter encompassing a second selected region within the spectral distribution; a detector; switching means for applying the outputs of said first and second bandpass filters to said detector in time shared fashion; means coupled to said detector and responsive to received energy levels from said bandpass filters which differ by at least a predetermined minimum amount for indicating the presence of the input signal; and means coupled to at least one of said first and second bandpass filters for balancing the outputs of the filters when the inputs thereto are noise energy alone. - View Dependent Claims (4, 5, 6)
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7. A signal presence detector for a signal having a known spectral distribution and accompanied by substantial noise comprising:
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means responsive to the signal for dividing the signal into two channels; a first bandpass filter responsive to a first channel and having a center frequency lying within the spectral distribution; a second bandpass filter responsive to the second channel and having a center frequency different from said first bandpass filter and within the spectral distribution; a power detector; switching means for mutually exclusively applying first one and then the other of the outputs of said first and said second bandpass filters to said power detector; and means coupled to said power detector and responsive to the existence of different energy levels in the two channels which differ by at least a predetermined minimum amount for indicating the presence of the signal; the signal having a spread spectrum characteristic and the center frequency of said first bandpass filter being equal to the center frequency of the spread spectrum. - View Dependent Claims (8)
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9. A signal presence detector for a signal having a known spectral distribution and accompanied by substantial noise comprising:
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means responsive to the signal for dividing the signal into two channels; a first bandpass filter responsive to a first channel and having a center frequency lying within the spectral distribution; a second bandpass filter responsive to the second channel and having a center frequency different from said first bandpass filter and within the spectral distribution; a detector; switching means to mutually exclusively apply the outputs of said first and said second bandpass filters to said detector; and means coupled to said detector and responsive to the existence of different energy levels in the two channels for indicating the presence of the signal; said switching means comprising; switching control means; summing means providing an output to said detector under control of said switching control means; a first mixer responsive to said first bandpass filter and said switching control means for providing an input to said summing means; and a second mixer responsive to said second bandpass filter and said switching control means for providing an input to said summing means. - View Dependent Claims (10, 11, 12)
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13. The method of detecting the presence of a spread spectrum signal having a spread spectrum characteristic having a center frequency comprising the steps of:
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balancing noise energy derived in two different frequency bands within the spread spectrum characteristic of the signal, the frequency bands being chosen to have a determinable relative difference in energy of the signal within the two different frequency bands and so that a first one of the two different frequency bands has a center frequency at the center frequency of the spread spectrum characteristic and a second one of the two different frequency bands has a center frequency at a different region within the spread spectrum characteristic from the center frequency of the first one of the two different frequency bands; filtering the signal in the two different frequency bands; successively sampling total energy, including noise energy, present in the two different frequency bands upon filtering the signal; and ascertaining the presence of the spread spectrum signal by the existence of an energy difference in excess of a predetermined amount in the two different frequency bands. - View Dependent Claims (14, 15)
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Specification