Patent ID: 6657536
Filing Date: 2003-12-02
Classification: G07C

Abstract:
A process for the bidirectional transmission of data, in an access system, allowing access to an enclosed space, the process consisting in setting up a remote exchange of data between a recognition device installed in the enclosed space and an identifier intended to he carried by a user, access being authorized only when the recognition device has authenticated the identifier, which process consists in setting up an RF exchange of data at the same radio frequency between the recognition device and the identifier, and in delaying, in the course of this exchange, the transmission of a response signal by the identifier to the recognition device by a predetermined duration (&tgr;) with respect to the reception by the identifier of an interrogation signal transmitted by the recognition device, so that neither the recognition device nor the identifier operate simultaneously in transmission and in reception at said RF exchange,which consists in transmitting, at the level of the recognition device, a pulsed oscillating signal, the carrier frequency of each pulse (I1) of which correspond, to said RF exchange, the duration of each pulse being very short with respect to the recurrence period of the pulses, in receiving, at the level of the identifier, said pulsed oscillating signal and in delaying its retransmission to the recognition device by said predetermined duration (&tgr;), which is greater than the duration of a pulse and less than said recurrence period, in retransmitting said delayed pulsed oscillating signal to the recognition device, and in receiving, at the level of the recognition device, said delayed pulsed oscillating signal retransmitted by the identifier, and which consists, at the level of the recognition device, in order to transmit said pulsed oscillating signal at the RF exchange: in generating an oscillating signal at a reference radio frequency Fo substantially different from the RF exchange, in generating a continuous pulsed signal (V1), which defines a first control signal, having the same recurrence period and the same duration of the pulses (I1) as the aforesaid pulsed oscillating signal, in feeding a frequency divider by N (5) with said first control signal, in inputting into said divider said oscillating signal so as to output a pulsed oscillating signal having a frequency Fo/N, in mixing said pulsed oscillating signal at Fo/N with said oscillating signal at Fo, in filtering the outgoing mixed signal so as to center it on the frequency Fo+Fo/N, said central frequency corresponding to the RF exchange, and in transmitting said filtered mixed signal to the identifier.