Time difference of arrival geolocation method, etc.
First Claim
1. Apparatus for determining the time difference of arrival of signals from a transmitter to determine the geographical location of the transmitter relative to a receiver, comprising(a) first and second antennas spaced apart by a fixed distance for receiving modulated signals having a given baud rate from the transmitter, said first and second antennas generating first and second electrical signals corresponding with the received signals, said second signal being delayed in time from said first signal;
- (b) signal processing means connected with the outputs of said first and second antennas for producing an output signal proportional to the time difference between said first and second signals, said signal processing means including(1) variable time delay means connected with said first antenna for delaying said first signal by a variable time;
(2) means connected with said variable time delay means and with said second antenna for mixing said delayed first signal and said second signal to produce a combined signal output; and
(3) means connected with said mixing means for generating the cyclic crosscorrelation function of said combined signal output in accordance with the transmitted signal baud rate and the variable time delay, whereby as the time delay is varied, the output of said cyclic crosscorrelation function means determines the time difference of arrival of said received signals.
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Abstract
A direction finding method and apparatus for a radio signal source, modulated by a digital information signal and existing in a heavy interference environment, is based on cyclic crosscorrelation. The direction finding technique exploits the second order periodicity of a transmitted signal having digital modulation, whereby the technique is immune to narrow-band interference. Radio frequency signals are received by two spaced antennas, and the signal of interest can be considered as a cyclostationary process. The signal time of arrival difference between the two antennas is determined using a cyclic crosscorrelation method. This is implemented by sending the electrical signals, developed by the antennas, through a variable delay device, then to a balanced mixer. The composite signal from the mixer is sent to a band-pass filter whose center frequency is equal to the baud rate of the signal of interest. The output energy of the filter is proportional to that portion of the cyclic crosscorrelation function where the cyclic frequency corresponds to the baud rate. With the use of a peak detector, which finds the peak values of the cyclic crosscorrelation function, the time difference of arrival between the two antennas is determined. This, in turn, determines a line of position to the radio source.
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Citations
17 Claims
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1. Apparatus for determining the time difference of arrival of signals from a transmitter to determine the geographical location of the transmitter relative to a receiver, comprising
(a) first and second antennas spaced apart by a fixed distance for receiving modulated signals having a given baud rate from the transmitter, said first and second antennas generating first and second electrical signals corresponding with the received signals, said second signal being delayed in time from said first signal; (b) signal processing means connected with the outputs of said first and second antennas for producing an output signal proportional to the time difference between said first and second signals, said signal processing means including (1) variable time delay means connected with said first antenna for delaying said first signal by a variable time; (2) means connected with said variable time delay means and with said second antenna for mixing said delayed first signal and said second signal to produce a combined signal output; and (3) means connected with said mixing means for generating the cyclic crosscorrelation function of said combined signal output in accordance with the transmitted signal baud rate and the variable time delay, whereby as the time delay is varied, the output of said cyclic crosscorrelation function means determines the time difference of arrival of said received signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for determining the time difference of arrival of signals from a transmitter to determine the geographical location of the transmitter relative to a receiver, comprising the steps of
(a) receiving modulated signals having a given baud rate from the transmitter at separate locations spaced by a given distance; -
(b) generating first and second electrical signals corresponding with the received signals, said second signal being delayed in time from said first signal; (c) applying a variable time delay to said first signal; (d) mixing said variable time delayed first signal with said second signal to produce a combined signal output; and (e) generating the cyclic cross correlation function of the combined signal output in accordance with the transmitted signal baud rate and the variable time delay applied to said first signal, whereby as the time delay is varied, the output of said cyclic crosscorrelation function means determines the time difference of arrival of the received signals corresponding with the first and second electrical signals. - View Dependent Claims (15, 16)
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17. A method of determining the time difference of arrival of digitally modulated electromagnetic signals having a given baud rate in a heavy interference environment to determine the line of position of the signal transmitter, comprising the steps of
(a) receiving the transmitted signals at spaced locations to provide two received electrical signals; -
(b) generating an estimate of the cyclic crosscorrelation function of said two received signals; (c) adding a variable time delay to at least one of the received signals; (d) multiplying said two received signals to produce a composite electrical signal; and (e) generating a signal proportional to the electrical energy contained in a frequency band corresponding with the signal baud rate and the immediately surrounding frequencies thereof, said generated signal corresponding with the time difference of arrival of said two signals which is a function of the line of position of the transmitter.
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Specification