Locating system and method

Claim 1

A method for detecting the location of a source of a randomly modulated radio signal, said method comprising the steps of: providing at least three receiving stations at known locations for receiving and demodulating said modulated radio signal; selecting a common reference level for said radio signal at each of said receiving stations and determining the time of arrival at each receiving station of selected transitions of said demodulated radio signal through said common reference level; transmitting an indication of the time of arrival of said selected transitions to a central processing means; identifying common signal segments received at pairs of the receiving stations based upon equal time differences between sequential time of arrival indications in the signal segments; determining the time of arrival difference between pairs of receiving stations from the time of arrival difference of corresponding transitions in common signal segments; computing the location of the signal source from the time of arrival differences;

Claim 2

A method for detecting the location of a source of a randomly modulated radio signal, said method comprising the steps of: providing at least three receiving stations at known locations for receiving and demodulating said modulated radio signal; selecting a common reference level for said radio signal at each of said receiving stations and determining the time of arrival at each receiving station of selected transitions of said demodulated radio signal through said common reference level; transmitting an indication of the time of arrival of said selected transitions to a central processing means; identifying common signal segments received at pairs of the receiving stations based upon equal time differences between sequential time of arrival indications in the signal segments; determining the time of arrival difference between pairs of receiving stations from the time of arrival difference of corresponding transitions in common signal segments; computing the location of the signal source from the time of arrival differences;

Claim 3

A method for detecting the location of a source of a randomly modulated radio signal, said method comprising the steps of: providing at least three receiving stations at known locations for receiving and demodulating said modulated radio signal; selecting a common reference level for said radio signal at each of said receiving stations and determining the time of arrival at each receiving station of selected transition of said demodulated radio signal through said common reference level; transmitting an indication of the time of arrival of said selected transitions to a central processing means; identifying common signal segments received at pairs of the receiving stations based upon equal time differences between sequential time of arrival indications in the signal segments; determining the time of arrival difference between pairs of receiving stations from the time of arrival difference of corresponding transitions in common signal segments; computing the location of the signal source from the time of arrival differences; synchronizing a time counter at each receiving station to a common time reference signal; inserting the time reference signal into the sequential time of arrival indications; and aligning the signal segments from each station by correspondence between the time reference signals.

Claim 4

A method for detecting the location of a source of a randomly modulated radio signal, said method comprising the steps of: providing at least three receiving stations at known locations for receiving and demodulating said modulated radio signal; selecting a common reference level for said radio signal at each of said receiving stations and determining the time of arrival at each receiving station of selected transition of said demodulated radio signal through said common reference level; transmitting an indication of the time of arrival of said selected transitions to a central processing means; identifying common signal segments received at pairs of the receiving stations based upon equal time differences between sequential time of arrival indications in the signal segments; determining the time of arrival difference between pairs of receiving stations from the time of arrival difference of corresponding transitions in common signal segments; computing the location of the signal source from the time of arrival differences; synchronizing a time counter at each receiving station to a common time reference signal; inserting the time reference signal into the sequential time of arrival indications; and aligning the signal segments from each station by correspondence between the time reference signals.

Claim 5

A method for detecting the location of a source of a randomly modulated radio signal, said method comprising the steps of: providing at least three receiving stations at known locations for receiving and demodulating said modulated radio signal; selecting a common reference level for said radio signal at each of said receiving stations and determining the time of arrival at each receiving station of selected transitions of said demodulated radio signal through said common reference level; transmitting an indication of the time of arrival of said selected transitions to a central processing means; identifying common signal segments received at pairs of the receiving stations based upon equal time differences between sequential time of arrival indications in the signal segments; determining the time of arrival difference between pairs of receiving stations from the time of arrival difference of corresponding transitions in common signal segments; computing the location of the signal source from the time of arrival differences; storing a predetermined number of selected transitions in a memory at each receiving station; and transmitting the predetermined number of selected transitions to a central processing means for computing the location of the source of radio signals.

Claim 6

A method for detecting the location of a source of a randomly modulated radio signal, said method comprising the steps of: providing at least three receiving stations at known locations for receiving and demodulating said modulated radio signal; selecting a common reference level for said radio signal at each of said receiving stations and determining the time of arrival at each receiving station of selected transitions of said demodulated radio signal through said common reference level; transmitting an indication of the time of arrival of said selected transitions to a central processing means; identifying common signal segments received at pairs of the receiving stations based upon equal time differences between sequential time of arrival indications in the signal segments; determining the time of arrival difference between pairs of receiving stations from the time of arrival difference of corresponding transitions in common signal segments; computing the location of the signal source from the time of arrival differences; storing a predetermined number of selected transitions in a memory at each receiving station; and transmitting the predetermined number of selected transitions to a central processing means for computing the location of the source of radio signals.

Claim 7

A method for detecting the location of a source of a randomly modulated radio signal, said method comprising the steps of: providing at least three receiving stations at known locations for receiving and demodulating said modulated radio signal; selecting a common reference level for said radio signal at each of said receiving stations and determining the time of arrival at each receiving station of selected transitions of said demodulated radio signal through said common reference level; transmitting an indication of the time of arrival of said selected transitions to a central processing means; identifying common signal segments received at pairs of the receiving stations based upon equal time differences between sequential time of arrival indications in the signal segments; determining the time of arrival difference between pairs of receiving stations from the time of arrival difference of corresponding transitions in common signal segments; computing the location of the signal source from the time of arrival differences; and wherein the steps of determining and computing comprise the steps of: computing the time differences for a plurality of selected transitions; determining an average for the time differences; and computing the location of the radio signal from the averaged time differences.

Claim 8

A method for detecting the location of a source of a randomly modulated radio signal, said method comprising the steps of: providing at least three receiving stations at known locations for receiving and demodulating said modulated radio signal; selecting a common reference level for said radio signal at each of said receiving stations and determining the time of arrival at each receiving station of selected transitions of said demodulated radio signal through said common reference level; transmitting an indication of the time of arrival of said selected transitions to a central processing means; identifying common signal segments received at pairs of the receiving stations based upon equal time differences between sequential time of arrival indications in the signal segments; determining the time of arrival difference between pairs of receiving stations from the time of arrival difference of corresponding transitions in common signal segments; computing the location of the signal source from the time of arrival differences; and wherein the steps of determining and computing comprise the steps of: computing the time differences for a plurality of selected transitions; determining an average for the time differences; and computing the location of the radio signal from the averaged time differences.

Claim 9

A method for determining the transmission location of a voice-modulated radio signal comprising the steps of: receiving said radio signal at three spaced receivers; demodulating said signal at each of said receivers to extract the voice component thereof; analyzing said voice component as received and demodulated at each receiver to determine the time of occurrence of selected transitions of said voice component with respect to a common reference; identifying common transitions as received at all of said receivers; and thereafter determining the location of said transmission by computing the time difference between said common transitions as received at different receivers.

Claim 10

A method for determining the transmission location of a voice-modulated radio signal comprising the steps of: receiving said radio signal at three spaced receivers; demodulating said signal at each of said receivers to extract the voice component thereof; analyzing said voice component as received and demodulated at each receiver to determine the time of occurrence of selected transitions of said voice component with respect to a common reference; identifying common transitions as received at all of said receivers; and thereafter determining the location of said transmission by computing the time difference between said common transitions as received at different receivers.