Method and system for locating an unknown transmitter
First Claim
1. A method of locating an unknown radio-frequency transmitter by remote and passive observation, comprising the steps of:
- (a) receiving a signal radiated from the transmitter into space, a plurality of receivers at different locations receiving the radiated signal;
(b) retransmitting, from each of the plurality of receivers, the signal radiated from the transmitter to a plurality of antennas, each at a known location, one of each of the antennas receiving the retransmtited signal from one of the receivers, each of the received retransmitted signals being delayed by a first path length equal to a distance between the transmitter and one of the receivers and by a second path length equal to a distance between one of the receivers and one of the antennas;
(c) receiving the retransmitted signals by the antennas;
(d) converting the received retransmitted signals to a plurality of digital signals;
(e) performing pre-detection cross-correlation on the plurality of digital signals to obtain a set of data from which a time difference of arrival calculation and a frequency difference of arrival calculation can be made;
(f) performing the time difference of arrival calculation which compensates for a relative delay value in the received retransmitted signals from the receivers, the relative delay value being a function of the first path lengths, the second path lengths, and a value equal to the speed of light;
(g) performing the frequency difference of arrival calculation which compensates for a relative frequency value in the received retransmitted signals from the receivers, the relative frequency value being related to a difference between a first relative velocity of one of the receivers with respect to the velocity of Earth and a second relative velocity of another of the receivers with respect to the velocity of Earth;
(h) repeating each of the prior steps a plurality of times; and
(i) determining the location of the transmitter by generating isodelay lines of position based on a plurality of the time difference of arrival calculations, by generating isodoppler lines of position based on a plurality of the frequency difference of arrival calculations, and locating the intersections of paired, generated isodelay and isodoppler lines of position, the intersections defining a region in which the transmitter is located.
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Accused Products
Abstract
The method of locating an unknown radio-frequency transmitter includes: (a) receipt of signals radiated from the transmitter by a plurality of receivers; (b) retransmission of the received signals to a plurality of antennas; (c) performing a time difference of arrival (TDOA) calculation which compensates for a relative delay value, which is a function of the distances from the transmitter to each of the receivers, the distances from each of the receivers to the antennas, and the speed of light; (d) performing a frequency difference of arrival (FDOA) calculation which compensates for a relative frequency value, which is a function of the relative velocity of each receiver with respect to the velocity of the Earth; (e) repeating these steps a plurality of times; and (f) determining the location of the unknown transmitter based on the plurality of TDOA and FDOA calculations.
161 Citations
21 Claims
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1. A method of locating an unknown radio-frequency transmitter by remote and passive observation, comprising the steps of:
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(a) receiving a signal radiated from the transmitter into space, a plurality of receivers at different locations receiving the radiated signal; (b) retransmitting, from each of the plurality of receivers, the signal radiated from the transmitter to a plurality of antennas, each at a known location, one of each of the antennas receiving the retransmtited signal from one of the receivers, each of the received retransmitted signals being delayed by a first path length equal to a distance between the transmitter and one of the receivers and by a second path length equal to a distance between one of the receivers and one of the antennas; (c) receiving the retransmitted signals by the antennas; (d) converting the received retransmitted signals to a plurality of digital signals; (e) performing pre-detection cross-correlation on the plurality of digital signals to obtain a set of data from which a time difference of arrival calculation and a frequency difference of arrival calculation can be made; (f) performing the time difference of arrival calculation which compensates for a relative delay value in the received retransmitted signals from the receivers, the relative delay value being a function of the first path lengths, the second path lengths, and a value equal to the speed of light; (g) performing the frequency difference of arrival calculation which compensates for a relative frequency value in the received retransmitted signals from the receivers, the relative frequency value being related to a difference between a first relative velocity of one of the receivers with respect to the velocity of Earth and a second relative velocity of another of the receivers with respect to the velocity of Earth; (h) repeating each of the prior steps a plurality of times; and (i) determining the location of the transmitter by generating isodelay lines of position based on a plurality of the time difference of arrival calculations, by generating isodoppler lines of position based on a plurality of the frequency difference of arrival calculations, and locating the intersections of paired, generated isodelay and isodoppler lines of position, the intersections defining a region in which the transmitter is located. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 19)
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17. A method of locating an unknown ground-based radio-frequency transmitter by remote and passive observation from space, comprising the steps of:
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(a) receiving a signal radiated from the transmitter into space, a plurality of satellites receiving the radiated signal; (b) retransmitted from each of the plurality of satellites, the signal radiated from the transmitter to a plurality of ground-based antennas, each at a known location, one of each of the antennas receiving the retransmitted signal from one of the satellites, the received retransmitted signals being delayed by a first path length equal to a distance between the transmitter and one of the satellites and by a second path length equal to a distance between one of the satellites and one of the antennas; (c) receiving the retransmitted signals by the antennas; (d) converting the received retransmitted signals to a plurality of common intermediate frequency signals; (e) downconverting the intermediate frequency signals to a baseband value; (f) sampling the downconverted signals; (g) converting the downconverted signals to a plurality of digital signals; (h) performing pre-detection cross-correlation on the plurality of digital signals to obtain a set of data from which a time difference of arrival calculation and a frequency difference of arrival calculation can be made; (i) performing the time difference of arrival calculation which compensates for a relative delay value in the received retransmitted signals from the satellites, the relative delay value being a function of the first path lengths, the second path lengths, and a value equal to the speed of light; (j) performing the frequency difference of arrival calculation which compensates for a relative frequency value in the received retransmitted signals from the satellites, the relative frequency value being related to a difference between a first relative velocity of one of the satellites with respect to the velocity of Earth and a second relative velocity of another of the satellites with respect to the velocity of Earth; (k) repeating each of the prior steps a plurality of times; and (l) determining the location of the transmitter by generating isodelay lines of position based on a plurality of the time difference of arrival calculations, by generating isodoppler lines of position based on a plurality of the frequency difference of arrival calculations, and locating the intersection of the paired, generated isodelay and isodoppler lines of position to define a region in which the transmitter is located.
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20. A system for locating an unknown radio-frequency transmitter by remote and passive observation, the unknown transmitter radiating a signal, comprising:
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(a) a plurality of receivers at different locations for receiving the radiated signal and retransmitted the radiated signal to Earth; (b) a plurality of antennas, each at known location on Earth, for receiving the retransmitted signals, each of the received retransmitted signals being delayed by a first path length equal to a distance between the transmitter and one of the receivers and by a second path length equal to a distance between one of the receivers and one of the antennas; (c) means for performing a pre-detection cross-correlation on the received retransmitted signals to obtain both a relative delay value and a relative frequency value of the received retransmitted signals; (d) means for determining the time difference of arrival and the frequency difference of arrival from the relative delay values and the relative frequency values, respectively, obtained from the received retransmitted signals; and (e) means for generating an isodelay line of position based on the time difference of arrival determination and an isodoppler line of position based on the frequency difference of arrival, the intersection of the generated lines of position defining the location of the unknown transmitter. - View Dependent Claims (21)
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Specification