Communications: electrical – Selective – Intelligence comparison for controlling
Reexamination Certificate
2000-05-31
2003-12-02
Zimmerman, Brian (Department: 2635)
Communications: electrical
Selective
Intelligence comparison for controlling
C340S005620, C340S005630, C340S005720
Reexamination Certificate
active
06657536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the bidirectional transmission of data and to a system for the implementation thereof.
2. Description of Related Art
In an access system, for example of the so-called “hands-free” type, allowing access to an enclosed space, in particular to a motor vehicle, such a process is used to set up a remote exchange of data between a recognition device installed in the enclosed space and an identifier intended to be carried by a user, access being authorized only when the recognition device has authenticated the identifier. However, such an access system runs the risk of being tampered with by a transmission/reception assembly interposed into the wireless communication between the recognition device and the identifier, this transmission/reception assembly serving, in fact, solely as a repeater.
For example, two criminals acting in concert could obtain access to the enclosed space in the following manner. A first criminal, equipped with a transmission/reception system installed for example in a bag, approaches the closed vehicle from which an authorized user has just alighted, whilst a second criminal, equipped with a transmission/reception system similar to that of the first criminal, follows the authorized user carrying the identifier. When the authorized user is sufficiently far away, the first criminal triggers an identification operation, for example by pressing on a control button situated on the door. Signals transmitted by the recognition device are relayed by the transmission/reception system of the first criminal to the system of the second criminal, which repeats the signals of the recognition device to the identifier. The latter will then respond with the authorized code, which is forwarded by the repeater system to the recognition device which orders the unlocking of the locks and grants access to the criminal.
To solve this problem, the principle of the invention consists in analyzing the delay time between the signal transmitted by the recognition device and the signal returned by the identifier. The finer the measurement of this time, the greater will be the possibility of detecting small spurious delays. Furthermore, the greater the frequency used for the outward/return communication, the better will be the fineness of the measurement since the delay constants due to the various filters and processing circuits will be smaller. Given that one wishes to bar access to the vehicle, when bidirectional transmission is performed at a distance of greater than around 5 to 10 meters, it would be necessary to be able to measure a communication time variation of the order of from 200 to 300 ns, this delay time corresponding to the duration of transmission of the signal as a function of the distance separating the recognition device from the identifier.
In a known system, the interrogation signal is transmitted by the recognition device at low frequency, for example at 125 kHz, and the identifier returns a response signal at radio frequency, for example at 433.92 MHz. In such a system, the recognition device receives the response signal with a delay time which is the sum of the time related to the passband of the electronic circuits and of the time related to the distance separating the recognition device and the identifier. The time related to the distance is of the order of 6.6 ns/m, whilst the time related to the passband may be of the order of 120 &mgr;s with inherent flutter of 8 &mgr;s. It is therefore understood that in order to calculate a delay of the order of 300 ns, this delay is swamped by the resolution of the system which is greater than 8 &mgr;s. In fact, to detect a delay of 300 ns, the time related to the passband would have to be not greater than 1 &mgr;s with inherent flutter of at most 100 to 200 ns.
SUMMARY OF THE INVENTION
The aim of the invention is to propose a process for the bidirectional transmission of data, in which it is possible to detect a small delay time, as a function of the distance separating the identifier from the recognition device.
For this purpose, the subject of the invention is a process for the bidirectional transmission of data, in an access system, for example of the so-called “hands-free” type, allowing access to an enclosed space, in particular to a motor vehicle, 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 be carried by a user, access being authorized only when the recognition device has authenticated the identifier, which process consists in setting up an exchange of data at the same radio frequency, so-called exchange RF, for example at 315, 434 or 868 MHz, 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, for example 0.8 &mgr;s, 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 exchange RF. In such a monofrequency communication system, by delaying the retransmission of the signal by the identifier, the transmitter/receiver assembly of the identifier is prevented from operating as an oscillator.
Indeed, if such a delay were not provided, the signal transmitted by the recognition device would be picked up by the identifier, amplified, then retransmitted directly to the recognition device, this retransmitted signal being picked up again by the receiving antenna of the identifier, through electromagnetic radiation, generating an oscillation generally at the central frequency of the bandpass filter at the head of the amplification circuit of the identifier. This problem of the oscillation of the identifier originates from the fact that the latter operates as a receiver, and not simply as a reflector of the wave transmitted by the vehicle.
Advantageously, the process consists in transmitting, at the level of the recognition device, a pulsed oscillating signal, the carrier frequency of each pulse of which corresponds to said exchange RF, the duration of each pulse being very short, for example of the order of 0.5 &mgr;s, with respect to the recurrence period, for example of the order of 50 &mgr;s, 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, which is greater than the duration of a pulse and markedly 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.
In this case, the process can comprise, at the level of the identifier, the following steps which consist: in amplifying the received signal, in delaying said amplified received signal by said predetermined duration, in detecting the end of each pulse of the amplified received signal, in deactivating the amplification of the receiver and in activating the amplification of the transmitter of the identifier after the detection of the end of each pulse, in amplifying the delayed signal so as to retransmit it to the recognition device, in deactivating the amplification of the transmitter and in activating the amplification of the receiver of the identifier, at the conclusion of a given timeout, for example of the order of 5 &mgr;s, counting from the detection of the end of each pulse.
Preferably, the process consists, at the level of the recognition device, in order to transmit said pulsed oscillating signal at the exchange RF: in generating an oscillating signal at a reference radio frequency Fo substantially different from the exchange RF, in generating a continuous pulsed signal, the so-called first control signal,
Liniak Berenato & White
Valeo Securite Habitacle
LandOfFree
Process for the bidirectional transmission of data and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the bidirectional transmission of data and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the bidirectional transmission of data and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3162479