Patent ID: 6803851
Filing Date: 2004-10-12
Classification: B60R,G07C

Abstract:
A method for checking keyless access authorization of an operator, the method comprising:(I) transmitting a code signal from a base station to a mobile identification (ID) transmitter carried by the operator; (II) receiving the code signal from the base station with the ID transmitter; (III) performing an action with the ID transmitter in response to the ID transmitter receiving the code signal, wherein the action is indicative of a reply signal that is detectable by the base station; (IV) detecting the reply signal with the base station; (V) determining the difference of a signal characteristic between a reference code signal monitored at the base station and the reply signal received by the base station, wherein the signal characteristic correlates with signal propagation time and changes as a function of the distance between the base station and the ID transmitter; and (VI) determining distance between the base station and the ID transmitter on the basis of a relative determination based on the difference of the signal characteristic between the reference code signal monitored at the base station and the reply signal received by the base station.