Locating system and method

• US 4,812,852 A
• Filed: 02/20/1987
• Issued: 03/14/1989
• Est. Priority Date: 02/20/1987
• Status: Expired due to Fees

• Current Assignee: CPC Capital Fund 2000, LLC, Science Development Lab
• Original Assignee: Science Development Lab
• Inventors: Bent, Rodney B., Casper, Paul W.
• Primary Examiner(s): Blum, Theodore M.
• Assistant Examiner(s): CAIN, DAVID C
• Application Number:
  US07/016,788
• Time in Patent Office: 753 Days
• Field of Search: 342/457, 342/390, 342/465, 364/460, 375/116
• US Class Current: 342/457
• CPC Class Codes: G01S 5/0009 Transmission of position information to remote stations involving assistance data G01S5/0236
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence

Abstract

The present invention includes both a system and a method for locating a source of a randomly modulated radio signal. In one form of the invention, at least three receiving stations at known locations receive and process the randomly modulated radio signal. A common reference level is selected for the radio signal at each of the receiving stations. The times of arrival at each receiving station of selected transitions of the radio signal with reference to the common reference level are determined. Each receiving station provides an indication of the times of arrival of the selected transitions to a central facility for processing to provide an indication of the location of the signal source.

Claims

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;

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 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.

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 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.

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 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.

5. 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.