Locating system and method

DETAILED DESCRIPTION Among the several objects of the present invention is the provision of a relatively simple system and method for locating a number of vehicles or carriers in a defined area without using a predetermined tone or time slot and in which the vehicle transmitting equipment requires little or no modification.
A principal object of the present present invention is to provide a system and method for locating each of a plurality of signal transmitters without use of special tones or timed signal generation.
It is another object of the present invention to provide a system and method for processing received signals at each of a plurality of receiving sites and transmitting time of arrival data over standard telephone lines to a central site.
It is yet another object of the present invention to provide a method and system for locating a plurality of vehicles in a real time operational environment.
It is a further object of the present invention to provide a method and system for determining the location of a signal transmitter using any waveform transmitted over a voice frequency bandpass channel.
These as well as other objects and advantageous features of the present invention will be in part apparent and in part pointed out hereinafter.
In general, 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.
In one form of the invention, a microprocessor based radio receiving system determines the time of occurrence of specific events in a voice modulated signal from a remote transmitter whose location is to be identified