US 4,888,593 A · Time difference of arrival geolocation method, etc.

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.

Claims17

Dependent claims

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.

3 more elements

Dependencies are inferred from the claim text.

Time difference of arrival geolocation method, etc.

Life of this patent

Time difference of arrival geolocation method, etc.

Life of this patent

Abstract

Claims17