EP1058214A1 - Method of bidirectional data transfer and system for carrying out the same - Google Patents

Abstract

The method operates as an access system of the 'hands free' type which permits access to a closed space, such as the interior of an automobile. Remote exchange of data with a recognition device installed in the closed space and an identifier designed to be carried by a user. Access is only authorized when the recognition device has authenticated the identifier. Data exchange at the same radio frequency is established, called RF exchange, e.g. at 315, 434 or 868 MHz, between the recognition device and the identifier. During the course of the data exchange, the transmission of a response signal by the identifier to the recognition device for a period (tau) of about 0.8 micro seconds, with respect to the reception by the identifier of an interrogation signal from the recognition device, so that neither the recognition device nor the identifier operate simultaneously whilst transmitting or receiving the RF exchange.

Description

The present invention relates to a transmission method bidirectional data and a system for its implementation.

In an access system, for example of the so-called "hands" type free ", allowing access to an enclosed space, in particular to a vehicle automotive, such a method is used to establish a remote exchange data between a space-based recognition device closed and an identifier intended to be worn by a user, access only authorized when the recognition device has authenticated the identifier. However, such an access system runs the risk of being hacked by a set of transceivers interposed in the wireless communication between the recognition device and the identifier, this set of transmission / reception serving, in fact, only repeater.

For example, two criminals acting canned could gain access to the confined space as follows. A first criminal, equipped with a transmission / reception system installed for example in a satchel, approaches the closed vehicle that comes to leave an authorized user, while a second criminal, equipped a transceiver system similar to that of the first perpetrator, follows the authorized user carrying the identifier. When the authorized user is far enough away, the first criminal triggers an identification operation, for example by pressing a control button located on the door. Signals from the recognition device are relayed by the transmission-reception system from the first criminal to the system of the second criminal, which repeats the signals from the recognition device to the identifier. The latter will then respond with the authorized code, which is retransmitted by the repeater system to the recognition device which controls the unlocking of the locks and gives access to the criminal.

To solve this problem, the principle of the invention consists in analyzing the delay time between the signal emitted by the recognition device and the signal returned by the identifier. More the finer this measurement, the greater the possibility of detect small parasitic delays. In addition, the fineness of the measure will be all the better as the frequency used for communication round trip will be great because the delay constants due to the different filters and processing circuits will be weaker. Since we wish to prohibit access to the vehicle, when the transmission bidirectional takes place at a distance greater than about five to ten meters, it would be necessary to be able to measure a variation of communication time of the order of 200 to 300 ns, this delay time corresponding to the signal transmission time depending on the distance separating the recognition device from the identifier.

In a known system, the interrogation signal is emitted by the low frequency recognition device, for example at 125 KHz, and the identifier sends a response signal in radio frequency, for example at 433.92 MHz. In such a system, the recognition device receives the response signal with a time delay which is the sum of the time linked to the bandwidth of the circuits and time related to the distance separating the device from recognition and identifier. Time related to distance is around 6.6 ns / m, while the bandwidth time can be the order of 120 µs with a clean hopping of 8 µs. We understand so that to calculate a delay of the order of 300 ns, this delay is embedded in the system resolution which is greater than 8 µs. In fact, to detect a delay of 300 ns, it would be necessary that the time linked to the band bandwidth is not more than 1 µs with a proper hopping of 100 to 200 ns maximum.

The object of the invention is to propose a method of bidirectional data transmission, in which it is possible to detect a small delay time, depending on the distance separating the identifier of the recognition device.

To this end, the invention relates to a method of bidirectional data transmission, in an access system, by example of the so-called "hands-free" type, allowing access to an enclosed space, in particular to a motor vehicle, the method consisting in establishing remote data exchange between a recognition device installed in the enclosed space and an identifier intended to be carried by a user, access is only authorized when the recognition has authenticated the identifier, characterized in that it consists in establishing a data exchange at the same radio frequency, called RF exchange, for example at 315, 434 or 868 MHz, between the recognition device and identifier, and to be delayed, during this exchange, the transmission of a response signal by the identifier to the device for recognizing a predetermined duration, for example 0.8 µs, compared to reception by signal identifier of interrogation issued by the recognition device, so that neither the recognition device and identifier work simultaneously in transmission and reception at said exchange RF. In such a system of single-frequency communication, by delaying the retransmission of the signal by the identifier, we avoid that the transmitter-receiver set of the identifier does not work as an oscillator.

Indeed, if such a delay was not foreseen, the signal emitted by the recognition device would be picked up by the identifier, amplified, then retransmitted directly to the recognition device, this re-emitted signal being picked up again by the receiving antenna the identifier, by electromagnetic radiation, generating a oscillation generally at the center frequency of the bandpass filter in head of the amplifier amplification circuit. This problem of oscillation of the identifier comes from the fact that it works as a repeater, and not simply as a reflector of the wave emitted by the vehicle.

Advantageously, the method consists in transmitting, at the level of the recognition device, a pulsating oscillating signal, the carrier frequency of each pulse corresponds to said RF exchange, the duration of each pulse being very short, for example of the order of 0.5 µs, compared to the recurrence period, by example of the order of 50 µs, pulses, to be received, at the level of the identifier, said pulsating oscillating signal and to delay its retransmission to the device for recognizing said predetermined duration, which is greater than the duration of a pulse and significantly less than said recurrence period, re-emitting said pulsed delayed oscillating signal towards the recognition device, and to receive, at the level of recognition device, said delayed pulsed oscillating signal retransmitted by identifier.

In this case, the method may include, at the level of the identifier, the following steps which consist in: amplifying the signal received, delaying said amplified received signal by said duration predetermined, to detect the end of each pulse of the received signal amplified, deactivate receiver amplification and activate amplification of the transmitter of the identifier after the detection of the end of each pulse, to amplify the delayed signal to re-emit it to the recognition device, to deactivate the amplification of the transmitter and activate the amplification of the receiver of the identifier, end of a given time delay, for example of the order of 5 µs, at count from the detection of the end of each pulse.

Preferably, the method consists, at the level of the device of recognition, to transmit said pulsating oscillating signal to the RF exchange: to generate an oscillating signal at a radio frequency of Fo reference significantly different from the exchange RF, to be generated a continuous pulsed signal known as the first control signal having the same recurrence period and the same duration of signal pulses oscillating pulsed above, to supply a frequency divider by N by said first control signal, to be entered into said divider said oscillating signal for outputting a pulsating oscillating signal having a frequency Fo / N, to mix said oscillating signal pulsed with Fo / N with said signal oscillating at Fo, filtering the outgoing mixed signal to center it on the frequency Fo + Fo / N, said central frequency corresponding to the exchange RF, and to send to the identifier said filtered mixed signal.

In the recognition device, the frequency of reference of the oscillating signal is not the exchange RF, because otherwise, the presence of a permanent oscillator near the reception of the recognition device would have the effect of saturating the receiving circuit which is intended to receive a response signal to this same frequency. The saturation of the reception circuit at reference oscillation frequency can be achieved by radiation and electrical conduction through the earths of the device, even if the oscillator is shielded against electromagnetic interference. Since the remote data exchange takes place at the same RF exchange, it is necessary that this signal be transmitted with a high accuracy, for example with a maximum variation of +/- 150 KHz. To obtain such precision, resonators can be used so-called surface wave, whose start-up time is very long, by example about 10 µs. Thus, it is not possible to use a fast cutter coupled with an oscillator whose frequency would be the RF exchange, as the oscillator would have to be restarted each time pulse, which is incompatible with generating a pulse with a duration of the order of 500 ns. In addition, the receiving circuit would be saturated at the oscillation frequency of the oscillator, during a duration of approximately 2 µs, which would prevent the receiving circuit from recognition device to receive the signal returned by the identifier, with an overall delay of approximately 1 µs.

Advantageously, the method consists in switching the recognition device on its transmission circuit or its reception, in response to the first command signal, the recognition switching on the transmission circuit during each pulse of the first control signal and on the reception circuit between the pulses of said first control signal.

According to another characteristic of the invention, the method consists, at the level of the recognition device, in receiving the signal oscillating pulsed delayed and reissued by the identifier, to mix it with said signal oscillating at Fo, to filter the signal thus mixed leaving for center it on the frequency Fo / N, to detect the signal envelope as well filtered, to measure the time interval between the rising edge of each pulse of the first control signal and the rising edge of each pulse of the envelope signal detected, to compare this time measurement with an initially memorized delay value, by example of the order of 1 µs, which is learned by the system, so prevent the exchange of identification data if the statistical difference on several pulses between the measured time and the stored time, is greater than a predetermined threshold value, for example 200 ns, in order to secure the transmission beyond a predetermined distance, for example 5 to 10 meters, in particular to avoid hacking by interposition of an unauthorized repeater between the recognition and identifier.

In this case, the method may consist, at the level of recognition device, for receiving the signal retransmitted by the identifier, to generate a continuous pulsed observation signal, the pulse duration, for example 400 ns, corresponds to a window listening, with the same recurrence period as the first signal command, said window being centered on the delay value initially memorized, and detecting the possible rising edge of a envelope signal pulse detected during each window listening. It is thus understood that the predetermined threshold value corresponds to half of a listening window, for example approximately 200 ns.

According to yet another characteristic, the method consists, at the recognition device, for signal reception re-issued by the identifier, to generate a second continuous pulsed signal command, each pulse of which begins at the end of each first control signal pulse and ends after a duration less than the recurrence period of the first signal control, said second control signal serving to supply the recognition device receiving mixer.

The method may consist, at the identifier level, of inhibit the re-emission of certain pulses in a sequence predetermined, previously transmitted by the recognition, and, at the level of the recognition device, to measure the time interval for the pulses received during the listening windows corresponding to uninhibited pulses, and to count the number of pulses possibly received during the listening windows corresponding to the inhibited pulses, in order to detect the possible presence of an unauthorized repeater nearby of the recognition device, at a distance below the limit maximum allowed. In this case, the method can consist, at the level of the identifier, to cut the delayed signal before its retransmission, according to the binary value of the bits of a coded identification signal previously transmitted by the recognition device.

The invention also relates to a transmission system bidirectional data for the implementation of the method such as previously defined, characterized in that it comprises a device recognition installed in the confined space, including a circuit radio frequency transmission, a radio frequency reception circuit, which are both connected to the same first antenna, via a two-way switch, an identifier intended to be worn by a user, comprising a radiofrequency transmitter and a receiver radio frequencies, both of which are connected to the same second antenna, via a second two-way switch, and a delay means interposed between the output of the receiver and the input of the transmitter of the identifier, to delay the retransmission of the signal by the identifier to the same exchange RF as the transmission of the signal by the recognition device, of a predetermined duration to avoid any overlap between the signals received and transmitted by the identifier or the recognition system.

According to a particular embodiment, the receiver the identifier includes a reception amplifier connected to its input, to a first terminal known as receiving the second switch and, at its , output, on the one hand, to the aforementioned retarder means, and on the other hand, to a level detector, while the identifier transmitter has a emission amplifier connected, at its input, to the output of the means self-timer and, at its output, at a second terminal known as transmitting the second switch, the third common terminal of the second switch being connected to a band pass filter centered on the RF which is in turn connected in series to said second antenna, the identifier comprising a central control unit which is capable of receive the level detector output signal to control powering or disabling amplifiers and switching from the second switch.

We can provide a cutter interposed between the transmission amplifier and the transmission terminal of the identifier, said cutter being controlled by the central control unit for inhibit the re-emission of certain pulses in a sequence predetermined.

In a particular embodiment, the circuit of the recognition device comprises an oscillator with reference frequency Fo which is intended to deliver an output signal oscillating at said reference frequency, said output signal being supplied in parallel to a frequency divider by N and to a mixer, said divider being intended to be supplied by a first signal continuous pulsed control delivered by a central management unit, the divider output terminal being connected to another input of the mixer, the mixer being connected at its output to an amplifier power gain transmission, the output of which is connected to a first so-called transmission terminal of the first switch of the recognition. In this case, the receiving circuit of the recognition may include a low gain preamplifier, connected to its entry at a second terminal known as the reception of the first switch, the output of the preamplifier being connected to a second mixer which receives, on its second input, the signal oscillating at Fo delivered in parallel by the oscillator of the transmission circuit, said second mixer being connected in series to a centered bandpass filter on the frequency Fo / N, then to a gain amplifier, and to a envelope detector which is connected to said central processing unit management.

According to another characteristic, the first switch has a third common terminal connected in series to a filter bandpass centered on the exchange RF and at said first antenna, the switch being controlled by said first control signal.

According to yet another characteristic, the central processing unit management is able to generate a second pulsed control signal continuous whose pulses are alternated with those of the first signal control, to control the power supply to the preamplifier, amplifier and mixer of the receiving device circuit recognition.

In a particular embodiment, the means self-timer has a delay line, consisting for example of surface wave components. Surface wave components use the acoustic propagation of electromagnetic waves on a quartz bar, the propagation speed being around 300 m / s. To delay the re-emission of the signal, one could also memorize the signal received, then restore it. For this purpose, the signal can be memorized using a calibrated RC circuit, then reshaped and regenerated using an assembly analogous to the transmission circuit of the recognition device, in order to avoid saturation of the receiver the identifier.

To better understand the object of the invention, we will describe it now, as a purely illustrative example and not limiting, an embodiment shown in the accompanying drawing.

• la figure 1 est un schéma synoptique fonctionnel du dispositif de reconnaissance du système de l'invention ;
• la figure 2 est un schéma synoptique fonctionnel de l'identifiant du système de l'invention ; et
• la figure 3 est un graphique représentant plusieurs signaux utilisés lors du traitement des données pour la mise en oeuvre du procédé de l'invention.

On this drawing :

• FIG. 1 is a functional block diagram of the recognition device of the system of the invention;
• FIG. 2 is a functional block diagram of the identifier of the system of the invention; and
• FIG. 3 is a graph representing several signals used during the processing of the data for the implementation of the method of the invention.

In FIG. 1, the on-board recognition device on a vehicle has a central management unit 1 for control a transmission circuit E and a reception circuit R, which , are both connected to the same transmitting / receiving antenna 2.

The transmission circuit E comprises an oscillator 3 with a fixed frequency Fo, for example around 386 MHz. The output of the oscillator 3 is connected, in parallel, to an input terminal of a frequency mixer 4, and to the input terminal of a frequency divider 5. The power supply of the divider 5 is controlled by a first control signal V1 which is generated by a pulse generator integrated in the central management unit 1. This pulse generator delivers a DC voltage, in the form of slots, the duration of each pulse I1 being l 'order of 500 ns and the time interval between two pulses being of the order of 50 µs. When the signal V1 is between two pulses I1, the power supply of the divider 5 is cut, while when the signal V1 delivers a pulse I1, the divider 5 is supplied by the vehicle battery. When the power supply of the divider 5 is cut, it delivers a zero output signal. On the other hand, when the divider 5 is supplied, it delivers at output a pulsating oscillating signal, whose carrier frequency is equal to Fo / N, that is to say approximately 48 MHz, when the divisor number N is equal to 8, and whose value is zero between each pulse. The output of the divider 5 is connected to the other input terminal of the above-mentioned frequency mixer 4. The mixer 4 is very broadband and summes the spectrum received from the divider 5, with the oscillating signal coming from the oscillator 3, in order to output a pulsed oscillating signal having as carrier frequency the sum Fo + Fo / N which corresponds to the exchange RF, ie approximately 434 MHz. In fact, when the output of the divider 5 is at zero, the output of the mixer 4 will be practically zero, since it is greatly attenuated. The output of the mixer 4 is connected to the input of a power gain transmission amplifier 6, the output of which is connected to a first so-called transmission terminal 7 a , of a two-way switch 7. The transmission circuit E consists of the above elements 3 to 6.

The switch 7 is connected by a second terminal 7 b called reception to the reception circuit R. A third common terminal 7 c of the switch 7 is connected to a bandpass filter 8, broadband, centered on the exchange RF , i.e. at Fo + Fo / N. This filter 8 is connected in series to the above-mentioned antenna 2.

The position of the switch 7 is controlled by the first control signal V1 generated by the central management unit 1, via a link 9. The switch 7 can take two positions: one establishes a link between the first terminal 7 a and the common terminal 7 c , as shown in solid lines in FIG. 1, for switching the recognition device to the transmission circuit E; the other position shown in dotted lines establishes a connection between the common terminal 7 c and the second terminal 7 b , to switch the recognition device to the reception circuit R. The switch 7 switches to its transmitting position when the signal V1 generates the pulses I1, and switches to its receiving position, when the signal V1 is between the pulses I1.

The reception circuit R comprises a low noise preamplifier 10, the input of which is connected to the second terminal 7b of the aforementioned switch 7. The output of the preamplifier 10 is connected to an input of a second frequency mixer 11 which receives on its other input the signal oscillating at the frequency Fo coming from the oscillator 3 of the transmission circuit E. The output signal from the mixer 11 is supplied to a bandpass filter 12, centered on the frequency Fo / N. The filter 12 is connected in series successively to a power gain amplifier 13 and to an envelope detector 14. The output signal from the envelope detector 14 is a DC voltage V2, in the form of slots, whose pulses I2 are offset in time with respect to the pulses I1, by a delay T as a function of the distance between the recognition device and the identifier and of the time specific to their electronic circuits (see FIG. 3). This signal V2 is supplied to the central management unit 1 which includes a microprocessor for measuring the time interval T between a transmitted pulse I1 and a received pulse I2.

The central management unit 1 is capable of delivering a second control signal V3 which consists of a voltage continues, in the form of slots, each pulse I3 of the signal V3 having a rising edge which coincides with the falling edge of a associated I1 pulse, the end of the I3 pulse occurring before the front amount of the next pulse I1 of the first control signal V1. The signal V3 is intended to control by line 15 the supply of the preamplifier 10, mixer 11 and amplifier 13. The duration of each I3 pulse is long enough to allow reception of the signal by the identifier, its processing by the identifier, its return from the identifier to the recognition device, and the reception of the signal by the recognition device.

To measure whether the above time interval T corresponds at a normal delay, the central management unit 1 generates a signal observation V4 which consists of a DC voltage, in the form of niche, of which each pulse I4 corresponds to a window listening time of which is around 400 ns, and whose center corresponds to the predetermined average delay time which is for example on the order of 1 µs. Thus, during each listening window I4, the unit control center observes whether a rising edge of an I2 pulse from the V2 signal is detected. If such a rising edge is detected during a listening window I4, the microprocessor validates the correct delay and the stores in an incremental variable. So for a number pulse I1, if the number of correct delays is sufficiently high, for example greater than 50%, communication between the identifier and the recognition device will be authorized. AT As an example, the possible validation of a correct delay is carried out, using a triggered rocker called "rocker D", whose input Cℓ receives the second control signal V3, the input Ck of which receives the signal V2, whose input D receives the observation signal V4, for deliver on its output Q, a binary signal 1 or 0, the value 1 corresponding to a validation of a correct delay, while the value 0 corresponds to the absence of a rising edge of signal V2 in a listening window I4. This binary value is supplied to the microprocessor of the central management unit 1.

Referring now to FIG. 2, it can be seen that the identifier comprises a single transmitting / receiving antenna 21 which is connected in series successively to a bandpass filter 22 centered on the exchange RF, and to the common terminal 23 has a two-way switch 23. The switch 23 can take two positions: a first position shown in solid lines in Figure 2, for which the common terminal 23 a is connected to a terminal 23 b called reception; a second position shown in dotted lines, for which a third so-called transmission terminal 23 c is connected to the common terminal 23 a . The position of the switch 3 is controlled by a central control unit 24, thanks to a link 25 at the output of this unit 24.

The reception terminal 23 b is connected to the input of a reception amplifier 26 with power gain, the output of this reception amplifier 26 being connected, on the one hand, to an analog delay line 27, and d on the other hand, to a level detector 28. The delay line 27 is intended to output the signal received with a predetermined delay τ, for example of the order of 800 ns. In this case, if the duration of a pulse I1 is 500 ns, this same pulse will be retransmitted about 300 ns after the end of reception of this pulse. The output of the delay line 27 is connected to the input of a transmission amplifier 29, the output of which is connected to the transmission terminal 23 c of the switch 23, by means of a cutter 30.

The output of level detector 28 is connected to the unit control unit 24, which can be of the microcontroller type. Unit 24 has three other control outputs 31 to 33, the line control 31 used to control the power supply to the amplifier 26, the command line 32 used to control the supply of the transmission amplifier 29 and the command line 33 used to control the cutter 30, as illustrated in the figure 2.

The level detector 28 is intended to detect the end of each pulse I1, so that the central control unit 24 immediately sends a command signal to deactivate the reception amplifier 26, via line 31. Thus, the amplifier reception 26 then presents an input / output attenuation, instead gain. Simultaneously, the power of the transmission amplifier 29 is activated, via line 32, in response to a signal command issued by the central control unit 24. At the same time time, the central control unit 24 switches the switch 23 to the position shown in dotted lines.

The delay line 27 delivers to the amplifier 29, of which the power supply was previously activated, the signal with a delay τ. Each pulse of the signal thus delayed is re-emitted by the identifier, if the cutter 30 closes the transmission circuit. The opening sequence and closing the cutter 30 is determined by a sequence known by both the identifier and the recognition device. This sequence can correspond to the identification code specific to each vehicle, this identification code being transmitted by the device of recognition to the identifier, at the start of each interrogation. In this case, if the identification code is a three-digit numeric code bytes, we can expect each bit of the code to be associated with a signal pulse, so as to close the transmission circuit when the bit is at 1, and open the transmission circuit when the bit at 0, so obscuring an impulse, as shown in dotted lines in FIG. 3, the obscured pulse being designated by the reference I2 '. The signal control bit of the cutter 30 is indicated by the arrow B on the figure 3. Since the identification code is known by the recognition device, the latter's central management unit 1 will check if a pulse is received during the observation window I4 which corresponds to a normally hidden impulse.

If certain impulses were not obscured by the identifier, the system according to the invention would be very effective because it actually allows very small delay variations to be detected, but if potential hackers know that when the RF signal by the vehicle, the recognition device waits simply the same signal returned by the identifier, but simply staggered in time, hackers could directly place a repeater near the vehicle, to send the signal directly to the vehicle, thus avoiding the remote journey by the suitcases. The fact occulting certain pulses by the identifier avoids this disadvantage because pirates are then forced to go through the identifier, which necessarily generates a delay time which will be detected by the recognition device. So if the unit control unit 1 detects certain pulses in the windows the corresponding impulses, the system will prohibit access to the vehicle.

Finally, after the possible retransmission of an impulse by the identifier, the central control unit 24 will control both the switching switch 23 to its receiving position illustrated in solid lines in FIG. 2, the deactivation of the supply of the emission amplifier 29 and the activation of the supply of the reception amplifier 26, at the end of a time delay predetermined, for example of the order of 5 µs, which is initialized by the detection of the end of each pulse, by the level detector 28. So the identifier is ready to process the next signal pulse resignation.

The operation of the system according to the invention will now be briefly explained.

When the recognition device formulates a request for identification, the central management unit 1 switches the switch 7 towards its position in solid line in FIG. 1. The recognition device then transmits, via antenna 2, a signal oscillating pulsed, whose carrier frequency corresponds to the exchange radio frequency, and whose signal envelope corresponds to signal V1. This interrogation signal is received by the identifier whose switch 23 is switched to the position shown in solid lines on Figure 2, to receive the identification signal. After identification correct code by identifier, this code is stored in the unit control unit 24, so that the cutter can be controlled 30. After a delay time τ, the identifier retransmits the signal, at the same carrier frequency, whose envelope corresponds to signal V2, with certain pulses I2 'having been obscured, in accordance with the bit sequence of identification code B.

The response signal sent by the identifier is received by the recognition device which has meanwhile switched the switch 7 to the reception circuit R. The signal thus received by the recognition device is processed in the reception circuit R, in order to deliver the signal V2 to the central management unit 1. If the signal went through an authorized identifier, located at a distance less than a predetermined vehicle limit, the correct delay time is around 1 µs. In this case, the pulse I2 of the signal V2 has an edge amount located in a listening window I4 centered on the average delay 1 µs, with a margin of error of +/- 200 ns. Of course, the recognition device knows it should not receive a pulse in the response signal, when the pulse corresponds to an equal bit to 0 of the identification code.

If there is introduction of a relay transmitter in the loop formed by the recognition device and the identifier, the time of transit in this loop will increase, and the pulse of the received signal will then be outside the aforementioned listening windows, which will give a incorrect delay information.

In addition, if a repeater is simply placed nearby of the vehicle, without going through the identifier, the recognition will receive all the pulses previously emitted, with a correct delay time, but without obscuring certain impulses. Thus, the system will be able to differentiate the presence of a simple repeater from that of the authorized identifier.

Thus, the proposed system makes it possible to secure a bidirectional radio frequency transmission by detecting the presence relay transmitter between the vehicle identification circuit and the badge integrating the identifier, using it as a partial repeater of the identification signal, and by prohibiting access to the vehicle or confined space, when such relay transmitters are detected due too long a delay or the receipt of an impulse to be obscured according to the vehicle identification code.

Although the invention has been described in connection with several particular embodiments, it is obvious that it is not there in no way limited and that it includes all technical equivalents means described as well as their combinations, if these enter in the context of the invention.

Claims (18)

Bidirectional data transmission method, in an access system, for example of the so-called "hands-free" type, allowing access to an enclosed space, in particular to a vehicle automotive, the process of establishing a remote exchange of data between a recognition device installed in the confined space and an identifier intended to be worn by a user, access being allowed only when the recognizer has authenticated the identifier, characterized by the fact that it consists in establishing an exchange of data at the same radio frequency, called exchange RF, for example at 315, 434 or 868 MHz, between the recognition device and the identifier, and to delay, during this exchange, the issuance of a response signal by identifier to the recognition device of a predetermined duration (τ), for example 0.8 µs, relative to the reception by the identifier of an interrogation signal emitted by the recognition device, so that neither the recognition device neither the identifier operate simultaneously in transmission and reception at said exchange RF. Method according to claim 1, characterized in that that it consists in transmitting, at the level of the recognition device, a pulsating oscillating signal, including the carrier frequency of each pulse (I1) corresponds to said exchange RF, the duration of each pulse being very short, for example of the order of 0.5 µs, compared to the recurrence period, for example of the order of 50 µs, pulses, to be received, at the identifier, said oscillating signal pulsed and to delay its re-transmission to the device for recognizing said predetermined duration (τ), which is greater than the duration of a momentum and significantly less than said recurrence period, at re-emitting said delayed pulsed oscillating signal to the recognition, and to be received, at the level of the recognition, said delayed pulsed oscillating signal re-emitted by the identifier. Method according to claim 2, characterized in that that it includes, at the identifier level, the following steps which consist of: amplifying the received signal, delaying said received signal amplified by said predetermined duration (τ), to detect the end of each pulse (I1) of the amplified received signal, to deactivate the amplification of the receiver and activate the amplification of the identifier transmitter after detecting the end of each pulse, amplifying the delayed signal to re-issue it to the recognition device, to deactivate amplification of the transmitter and activate the amplification of the receiver the identifier, at the end of a given time delay, for example of around 5 µs, from the detection of the end of each impulse. Method according to claim 2 or 3, characterized by that it consists, at the level of the recognition device, for transmit said pulsating oscillating signal to the exchange RF: to generate a signal oscillating at a reference radio frequency Fo substantially different from the exchange RF, to generate a continuous pulsed signal (V1) says first control signal having the same recurrence period and the same duration of the pulses (I1) of the aforementioned pulsed oscillating signal, at supplying a frequency divider by N (5) by said first signal command, to enter said divider said oscillating signal to output a pulsed oscillating signal having a frequency Fo / N, at mixing said pulsed oscillating signal at Fo / N with said oscillating signal at Fo, to filter the outgoing mixed signal to center it on the frequency Fo + Fo / N, said central frequency corresponding to the exchange RF, and transmitting said filtered mixed signal to the identifier. Method according to claim 4, characterized in that that it consists in switching the recognition device on its circuit transmission (E) or its reception circuit (R), in response to the first control signal (V1), the recognition device switching on the transmission circuit during each pulse (I1) of the first control signal and on the receiving circuit between the pulses said first control signal. Method according to claim 4 or 5, characterized by that it consists, at the level of the recognition device, in receiving the oscillating pulsed signal delayed and re-emitted by the identifier, to mix it with said signal oscillating at Fo, to filter the signal thus mixed leaving to center it on the Fo / N frequency, to detect the signal envelope thus filtered, to measure the time interval (T) between the rising edge of each pulse (I1) of the first control signal (V1) and the rising edge of each pulse (I2) of the detected envelope signal (V2), compare this time measurement with a delay value initially memorized, for example of the order of 1 µs, which is learned by the system to prevent the exchange of identification data if the statistical difference over several pulses between the measured time and the stored time, is greater than a predetermined threshold value, by example 200 ns, in order to secure the transmission beyond a predetermined distance, for example 5 to 10 meters, especially for avoid hacking by interposing an unauthorized repeater between the recognition device and identifier. Method according to claim 6, characterized in that that it consists, at the level of the recognition device, for the reception of the signal re-emitted by the identifier, to generate a pulsed signal continuous observation (V4), including the duration of the pulses (I4), by example 400 ns, corresponds to a listening window, with the same recurrence period as the first control signal (V1), said window being centered on the delay value initially memorized, and detecting the possible rising edge of a signal pulse envelope detected (V2) during each listening window. Method according to claim 6 or 7, characterized by that it consists, at the level of the recognition device, for the reception of the signal retransmitted by the identifier, to generate a second continuous pulsed control signal (V3), each pulse of which (I3) starts at the end of each pulse (I1) of the first signal command (V1) and ends after a period shorter than the period of recurrence of the first control signal, said second control signal control used to supply the mixer (11) for receiving the recognition device. Method according to one of claims 6 to 8, characterized by the fact that it consists, at the identifier level, of inhibiting the re-transmission of certain pulses in a predetermined sequence (B), previously transmitted by the recognition device, and, at level of the recognition device, to measure the time interval for the pulses (I2) received during the listening windows corresponding to the uninhibited pulses, and to count the number of pulses possibly received during windows listening corresponding to the inhibited pulses (I2 '), in order to detect the possible presence of an unauthorized repeater near the recognition device, at a distance below the limit maximum allowed. Method according to claim 9, characterized in that that it consists, at the level of the identifier, in cutting the delayed signal before its retransmission, according to the binary value of the bits of an encoded signal identification (B) previously transmitted by the recognition. Bidirectional data transmission system for implementing the method according to one of claims 1 to 9, characterized by the fact that it includes a recognition device installed in the confined space, including an emission circuit radio frequency (E), a radio frequency receiving circuit (R) which are both connected to the same first antenna (2), via a two-way switch (7), an identifier intended to be worn by a user, comprising a radiofrequency transmitter (29) and a radio frequency receiver (26), which are both connected to the same second antenna (21), via a second switch (23) two-way, and a delay means (27) interposed between the output of the receiver and the input of the transmitter of the identifier, to delay the re-emission of the signal by the identifier at the same exchange RF as transmission of the signal by the recognition device, for a duration predetermined (τ) to avoid overlapping between signals received and issued by the identifier or the recognition device. System according to Claim 11, characterized in that the identifier receiver comprises a reception amplifier (26) connected, at its input, to a first terminal (23 b ) called the receiver of the second switch (23) and, to its output, on the one hand, to the aforementioned retarder means (27), and on the other hand, to a level detector (28), while the transmitter of the identifier comprises a transmission amplifier (29) connected , at its input, at the output of the delay means and, at its output, at a second so-called transmitting terminal (23 c ) of the second switch, the third common terminal (23 a ) of the second switch being connected to a bandpass filter (22) centered on the exchange RF which is in turn connected in series to said second antenna (21), the identifier comprising a central control unit (24) which is capable of receiving the output signal from the level detector to control power supply or deactivation of amplifiers and switching the second switch. Method according to claim 12, characterized in that a cutter (30) is interposed between the transmit amplifier (29) and the transmit terminal (23 c ) of the identifier, said cutter being controlled by the central control unit (24) for inhibiting the re-transmission of certain pulses (I2 ') according to a predetermined sequence (B). Method according to one of claims 11 to 13, characterized in that the emission circuit (E) of the recognition device comprises an oscillator (3) with reference frequency Fo which is intended to deliver an output signal oscillating at said reference frequency, said output signal being supplied in parallel to a frequency divider by N (5) and to a mixer (4), said divider being intended to be supplied by a first continuous pulsed control signal (V1) delivered by a central management unit (1), the output terminal of the divider (5) being connected to another input of the mixer (4), the mixer being connected at its output to a gain amplifier (6) power, the output of which is connected to a first so-called transmission terminal (7 a ) of the first switch (7) of the recognition device. Method according to Claim 14, characterized in that the reception circuit (R) of the recognition device can comprise a low gain preamplifier (10), connected at its input to a second terminal known as the reception ( 7b ) of the first switch (7), the output of the preamplifier being connected to a second mixer (11) which receives, on its second input, the oscillating signal at Fo delivered in parallel by the oscillator (3) of the transmission circuit (E), said second mixer being connected in series to a bandpass filter (12) centered on the Fo / N frequency, then to a gain amplifier (13), and to an envelope detector (14) which is connected to said unit central management (1). Method according to claim 15, characterized in that the first switch (7) has a third common terminal (7 c ) connected in series to a bandpass filter (8) centered on the exchange RF and to said first antenna (2), the first switch being controlled by said first control signal (V1). Method according to claim 15 or 16, characterized by the fact that the central management unit (1) is able to generate a second continuous pulsed control signal (V3) including pulses (I3) are alternated with those of the first control signal (V1), to control the power supply to the preamplifier (10), the amplifier (13) and the mixer (11) of the receiving circuit (R) of the recognition device. Method according to one of claims 11 to 17, characterized in that the delay means (27) has a line delay, consisting for example of wave components area.

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