Patent ID: 8063825

Claim:
A method of determining the location of a plurality of mobile users in an area using existing digital signals of opportunity transmitted from a plurality of transmitters proximate said area, said method comprising the steps of: providing each of said plurality of mobile users with a displacement sensor that detect displacements incurred within said area as said plurality of mobile users move through said area, therein producing displacement measurements; establishing a communications link between each of said plurality of mobile users, wherein each of said plurality of mobile users receives said digital signals of opportunity from each of said transmitters at different times, and wherein said different times are communicated among said plurality of mobile users using said communications link to determine time difference of arrival measurements; utilizing said time different of arrival measurements to form a compensated differential range measurement between at least two of said mobile users and at least one of said transmitters; forming a corrected relative range measurement between at least two of said mobile users using said communications link; transforming said compensated differential range measurement, said corrected relative range measurement collected, and said displacement measurements into a location for at least one of said mobile users; and determining a position location for each of said mobile users utilizing said differential range measurements, said corrected relative range measurements, and said displacement measurements.