Radionavigation system having means for concealing distance and/or bearing information conveyed thereby
First Claim
1. In a radionavigation system wherein a ground station includes transmission means responsive to interrogation pulses from passing aircraft for emitting outgoing signals enabling evaluating means aboard said aircraft to derive positional information from the timing thereof,the improvement wherein said ground station comprises error-generating means for introducing an artificial delay into the emission of said outgoing signals to falsify the positional information conveyed thereby, said transmission means receiving from said error-generating means a binary message representing the magnitude of said artificial delay in coded form for communication to on-board equipment of interrogating aircraft, the on-board equipment of privileged aircraft including error-eliminating means for extracting said magnitude from said binary message and controlling said evaluating means to correct the falsified positional information derived from said outgoing signals.
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Accused Products
Abstract
A ground station of a radionavigation system, responding to interrogation pulses from aircraft passing within range, emits message pulses whose timing enables the on-board equipment of the interrogating aircraft to determine its distance from the ground station and/or its azimuthal position relative thereto. To prevent such information from being utilized by aircraft not entitled thereto, the emission of the message pulses is subjected to an artificial delay whose randomly varying magnitude is conveyed by a multibit code word subjected in a distorter to a predetermined series of transformations based upon selected bits thereof. The on-board equipment of privileged aircraft includes a decipherer complementary to the distorter which restores the original code word and derives from it an indication of the artificial delay to be deducted from the measured time interval.
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Citations
10 Claims
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1. In a radionavigation system wherein a ground station includes transmission means responsive to interrogation pulses from passing aircraft for emitting outgoing signals enabling evaluating means aboard said aircraft to derive positional information from the timing thereof,
the improvement wherein said ground station comprises error-generating means for introducing an artificial delay into the emission of said outgoing signals to falsify the positional information conveyed thereby, said transmission means receiving from said error-generating means a binary message representing the magnitude of said artificial delay in coded form for communication to on-board equipment of interrogating aircraft, the on-board equipment of privileged aircraft including error-eliminating means for extracting said magnitude from said binary message and controlling said evaluating means to correct the falsified positional information derived from said outgoing signals.
Specification