04651156 is referenced by 239 patents and cites 9 patents.

An integrated radio location and communication system comprising a plurality of radio locator-transmitter devices which may be fixed to vehicles and/or carried by persons and which are capable of transmitting the position and identity of said devices to two or more centrally located fixed receiver sites. Each of said locator-transmitters is continuously phase-locked to the RF carrier of a nearby commercial broadcast station, which station is modified slightly to provide periodic transmission of a "range-tone" which is on the order of a few kilohertz in frequency and is phase-locked to the RF carrier. An identical phase-locked range-tone is likewise generated within each locator-transmitter. The two centrally located fixed receivers are also phase-locked to the broadcast station RF carrier and likewise generate a range-tone. Thus the broadcast station, the plurality of locator-transmitters and the two fixed receiver sites all generate identical range-tones and these are continuously kept in synchronism with each other by virtue of a phase-lock loop arrangement wherein all range-tones are derived from (and locked to) the RF carrier of the AM broadcast station signal. The fixed receiver sites can compute the position of each locator-transmitter by comparing the phase of the range-tone sent to them directly by the locator-transmitter with the phase of the range-tone received directly from the broadcast station. A novel frame synchronization method is disclosed whereby the position (i.e., "time-slot") of each locator-transmitter emission and its RF subchannel uniquely identifies the emitting source and thus the location as well as identity of each of the many locator-transmitters.

Title
Integrated radio location and communication system
Application Number
346862
Publication Number
4651156
Application Date
February 28, 1985
Publication Date
March 17, 1987
Inventor
Louis Martinez
Carson
CA, US
Agent
Blakely Sokoloff Taylor & Zafman
Assignee
McGraw Edison Co
IL, US
IPC
G01S 3/02
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