Importance

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Abstract

An interrogator-transponder system in which multiple vehicle mounted transponders which may be closely spaced in distance and moving at similar velocities, respond with a coherent identification code signal that is displaced in frequency from the interrogation signal by an amount that is identical for each transponder. The response signal spacings in time (Pulse repetition intervals) are different for each transponder but are always multiples of the pulse repetition interval of the interrogation signal. A coherent reference for the received transponder codes is obtained by combining the coherent interrogation signal with a coherent reference that is substantially identical in frequency to the displacement frequency of the transponder response signal. Means are provided in the interrogation device to determine the velocity of each transponder and its range with respect to the interrogator and to identify vehicles with inoperative transponders. The resulting data stream of identification codes and associated velocities and ranges may be used for traffic speed enforcement, wanted vehicle search, interactive traffic signal control, automated toll collection, traffic surveys, and identification of friendly forces.

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First Claim