EP1378865B1 - Method for controlling access to a determined space by a personalized portable object, and personalized portable object for carrying out the method - Google Patents

Description

The invention relates to a method for controlling the access of a personalized portable object to a determined space, such as a vehicle, by wireless transmission of an encoded identification signal. To do this, electronic means are provided in the space. These electronic means comprise in particular access management means connected to reception means and / or signal transmission means. The portable object for access control comprises a processing unit connected to transmission means and / or signal receiving means. The space access control method firstly consists of transmitting a coded identification signal by the transmission means of the portable object or respectively by the transmission means provided in the determined space. This coded signal is then received by the reception means in the space or respectively by the receiving means of the portable object, when the object is in a restricted area around the receiving means and / or the means for receiving the object. emission provided in space. A verification of the received coded signal is performed in the access management means or in the processing unit to allow access to the space.

The invention also relates to a personalized portable object for access to the determined space. This portable object comprises in particular a connected signal processing unit and transmission means and / or signal receiving means so as to transmit or receive a coded identification signal for access to the determined space.

With the aid of the access control method, it is possible to authorize access to a person provided with the personalized portable object in a determined space after verifying the coded identification signal of the object and the object. space to access. The transmission of the coded signal can be started automatically as soon as the presence of the object in a restricted area around the transmission means and / or the reception means provided in the space has been detected. This transmission of the coded signal can also be started manually by activating control means of the object or the space. This transmission of the coded signal can therefore be carried out from the object to the reception means provided in the space or conversely from the transmission means provided in the space to the object. As soon as the received coded signal has been recognized in the access management means of the space or in the processing unit of the object, it is then possible to access the space.

The determined space can be a security enclosure, a safe, a secure room or building with an access door controlled by the portable object, a vehicle, or any other space in which entry is permitted only to authorized persons. Access authorization allows for example to open or close a door of the enclosure, the safe or a secure building. Preferably, the space is defined by a road vehicle, such as a passenger car, whose doors and trunk can be locked or unlocked by remote control using a personalized portable object.

The personalized portable object may be an electronic key, a watch, a mobile phone, a smart card, a badge or other portable device. Preferably, this portable object is an electronic key for controlling access to a vehicle. This portable object may include an own power source for powering its electronic components. In this case, the portable object is of active type. The power supply of said electronic components may also come from a signal with a determined carrier frequency which is transmitted by transmission means provided in space and which is received in the portable object. In this case, the portable object is of the passive type. However with a portable object of the passive type, it is necessary to transmit a high frequency signal from the transmission means provided in the space to provide a sufficient power supply to the electronic components of the object. This is why in the field of remote control of parts or functions of a vehicle, the portable object, which is an electronic key, is preferably of the active type.

The electronic key includes a microcontroller connected to storage means in which are stored an encryption algorithm and / or a vehicle access code. As soon as a pressure on a button of control of the key is operated, the microcontroller calculates an encoded identification signal to be transmitted by means of sending signals towards the vehicle. After recognition of the coded signal received by the vehicle, a control of locking or unlocking parts or functions of the vehicle is performed.

To facilitate access to the vehicle without having to manipulate the electronic key, it has already been proposed an electronic key, a response signal is automatically transmitted to the vehicle based on an interrogation signal received from the vehicle. For this, the key must be in a restricted area around the vehicle to receive this interrogation signal from the vehicle. In addition, the key transmits a response signal to the vehicle only if the interrogation signal has been recognized by the key. This response signal thus makes it possible to control the locking or unlocking of parts or functions of the vehicle.

With the use of such an electronic key automatically controlled by the interrogation signal from the vehicle, there is the risk of allowing the opening of the vehicle through intermediary relays without the knowledge of the holder of the electronic key . As a result, it gives the opportunity to malicious people to use these intermediary relays between the vehicle and the holder of the electronic key to open the vehicle and turn it on. Said relays are able to reproduce, to the key or the vehicle respectively, the interrogation signal and the response signal, each of which comprises a sequence of binary data.

The figure 1 schematically represents the intermediate relay attack principle. The two relays are placed respectively close to a portable object, such as an automatic control electronic key, and the associated vehicle.

In a normal situation without the relays, the carrier of the portable object 2 must be in a restricted zone around the vehicle 1 to control the opening of the closed vehicle, since the interrogation signal 6, 8 transmitted by an antenna 11 signal emitting means 14 of the vehicle, can be detected only at short distance. This interrogation signal has a low frequency carrier frequency LF, for example of the order of 125 kHz. A sequence of binary data in the interrogation signal is for example generated by amplitude modulation of the carrier. An antenna 21 for receiving means of the object 2 can detect this low frequency interrogation signal only in an area around the vehicle which does not exceed, for example, not 2 m. Once the interrogation signal has been able to be controlled by the portable object, an antenna 22 of the transmitting means of the portable object transmits a response signal 9, 10. This response signal has a high frequency carrier frequency UHF, for example of the order of 433 MHz. This response signal is picked up by an antenna 12 of receiving means 15 of the vehicle. Access management means 13 connected to the transmission means and to the vehicle reception means will control in particular the opening of the doors and the trunk of the vehicle as soon as the response signal is received.

The patent document EP 1 288 841 describes a method and a passive response communication system between two transponders to avoid any intermediate relay attack as explained above with reference to the figure 1 . A first transponder is a base station housed in a vehicle and a second transponder is housed for example in a key customized to the vehicle to be controlled. The second transponder responds passively with a coded identification signal after receiving an interrogation signal provided by the first transponder. For this communication between the two transponders, a series of pulses is transmitted in at least one direction in which at least one rising or falling edge of at least one of the pulses at a rate of change different from a rate of change. one flank of at least one other pulse. The receiver of one or the other transponder is thus sensitive to the analog signal added to the transmitted pulses, which makes it possible to avoid any attack by intermediate relays.

The figure 2 represents a flowchart of the steps of the access control method of a portable object, such as an electronic key, customized to the vehicle so as to control the locking or unlocking including the doors and the trunk of said vehicle.

First at step 50, the electronic key in possession of the vehicle user is in the waiting position. Once the vehicle handle has been entered by the user in step 51, an interrogation signal LF is transmitted by the means transmission in step 52 under the control of the access management means of the vehicle. In step 53, the key, placed in the restricted area around the vehicle, receives the interrogation signal and verifies the identity of the vehicle with this received signal. If this coded interrogation signal is not recognized by the key, the latter is placed in the waiting position again in step 50. On the other hand, if this interrogation signal is recognized by the key, then a response signal is calculated by a key processing unit in step 54. This high frequency response signal is transmitted by the antenna of the key transmission means in step 55. Finally, the reception means of the key vehicle captures this response signal to allow the access management means to control the opening or closing of the vehicle at step 56.

As shown in figure 1 when the holder of the electronic key moves away from the vehicle beyond the restricted area, the key is no longer able to receive an interrogation signal from the vehicle. Thus, through intermediary relays 3 and 4, it is possible to make a remote bridge between the carrier of the portable object 2 and the vehicle 1 to open. These intermediary relays are generally used by malicious people to easily steal the vehicle without the knowledge of the user of the vehicle. The opening of the vehicle can thus be performed without having to steal said key and without forcing the locks of the vehicle.

The first intermediate relay 3, placed in the restricted zone 5 around the vehicle, is able to receive by an antenna 31 a interrogation signal 6 at low frequency. This first relay converts the low frequency signal LF to transmit an RF radio signal 7 by an antenna 32 to a second relay 4 near the carrier of the portable object 2. This second relay converts the RF signal received by the RF signal. antenna 42 into a low frequency signal LF, which is the image of the interrogation signal transmitted by the vehicle. This low frequency signal 8 is transmitted by the antenna 41 to the portable object 2. This portable object receives by the antenna 21 the interrogation signal 8 provided by the second relay 4. After receiving the interrogation signal , a high frequency response signal UHF 9 is transmitted by the antenna 22, if the identity of the vehicle has been recognized. The second relay picks up the antenna 43 this high frequency signal. The second relay converts the high frequency signal received by the portable object into a radiofrequency signal that is transmitted by the antenna 42. The first relay receives the high frequency signal and converts it into a high frequency UHF signal, which is the image response signal calculated by the portable object. This high frequency response signal 10 is transmitted by the antenna 33 to the vehicle so that the antenna 12 of the receiving means 15 receives the response signal 10. Access management means 13 connected to the transmission means and the means of receiving the vehicle will control including the opening of the doors and the trunk of the vehicle upon receipt of the response signal.

The figure 3 represents a flowchart of the steps of the access control method of a portable object, such as an electronic key, the vehicle through intermediary relays for locking or unlocking including the doors and trunk of said vehicle. It should be noted that the steps of this figure 3 , which correspond to that of the figure 2 , bear identical reference signs.

After the person carrying the first intermediate relay has grasped the vehicle handle in step 51, the interrogation signal is transmitted by the vehicle in step 52. This interrogation signal is therefore picked up by the first relay in step 60 to convert it to a radio frequency signal. This conversion to a radio frequency signal is necessary for long distance transmission. The second relay picks up the radio frequency signal from the first relay in step 61 to convert it into a signal which is the image of the interrogation signal. This interrogation signal is transmitted to the electronic key.

In step 53, the key near the second relay receives the interrogation signal and verifies the identity of the vehicle by this received signal. If this coded interrogation signal is not recognized by the key, the latter is placed in the waiting position again in step 50. On the other hand, if this interrogation signal is recognized by the key, then a response signal is calculated by a key processing unit in step 54. This high frequency response signal is transmitted by the key transmitting means antenna in step 55. In step 62, the second relay captures this response signal to convert it back to a radio frequency signal. This radiofrequency signal is transmitted from the second relay to the first relay. In step 63, the first relay, having received the radiofrequency signal, converts it into a high frequency signal which is the image of the response signal transmitted by the key. This high frequency signal is transmitted to the vehicle so that in step 56, the access management means control the opening or closing of the vehicle.

It is therefore clear the need to provide an access control method that prohibits the use of such intermediate relays for controlling the locking or unlocking of parts or functions of the vehicle.

A solution to avoid the use of such intermediary relays is mentioned in the document WO 01/25060 . This document describes a detection system that prevents an intermediate relay attack for unlocking a vehicle without the knowledge of the user of said vehicle. To do this, a frequency comparison of the signals transmitted and received by the car is made in the car so as to estimate the remote response time of the key. The frequency of the signal received by the key is used to define the operations processed in the key and the frequency of the response signal of the key. The frequency of the response signal is, for example, more than 1000 times greater than the frequency of the signal received.

Once the car has transmitted the interrogation signal at a determined frequency, the frequency is varied in the car until the response signal from the key is received. The frequency of the response signal is divided to correspond to the frequency of the initially transmitted signal. Thus, a comparison between the frequency of the response signal and the frequency changed over time in the car is operated. The greater the distance between the key and the car, the more the signal frequency in the car will have changed. It can therefore be detected by this frequency change measurement, if intermediate relays were used for the unexpected opening of said car.

A disadvantage of the solution proposed in this document is the complexity of creating this frequency variation in the car in order to accurately estimate the distance between the key of the car. It is necessary to give a distance value from which the electronic means believe that intermediary relays could be used for the unlocking of the car.

The invention therefore aims to provide a method of access control of a personalized portable object to a specific space preventing the use of intermediate relays and overcoming the disadvantages of the cited prior art.

This and other objects are achieved by the method cited above which is characterized in that the coded identification signal transmitted and received comprises an analog signature defined by at least one amplitude variation of the envelope of the coded signal, said analog signature being specific to either the portable object or to the electronic means provided in the space, or to the pair constituted by the personalized portable object and the electronic means provided in the space so as to authorize the access to the space in case of recognition of said signature.

An advantage of the method is that with the use of an analog signature in the coded signal, this prevents any intermediate relays held by malicious people to serve as a bridge between the object and the electronic means provided in the space to access. These possible relays are only able to reproduce signals of the digital type, that is to say in which a sequence of binary data is transmitted. By adding to these signals an analog coding specific for example to the torque constituted by the portable object and the electronic means provided in the space to be accessed, the relays can no longer exactly reproduce the coded signals. The analog signature, which also depends on characteristics of the transmission means and / or the reception means, can be at least one amplitude variation of the coded signal envelope. It may be an over-modulation of the envelope of the coded signal. This analog signature can also be defined as a function of a growth time and / or amplitude decrease of the coded signal envelope at the beginning or at the end of the coded signal as described by the document. EP 1 288 841 . If the coded signal comprises a sequence of binary data, this signature can be defined as a function of a growth time and / or amplitude decrease between two bits of different value of the data sequence. The amplitude variation during the growth and / or decay time being linear or hyperbolic or random.

Preferably, the determined space is a vehicle and the portable object is an electronic key personalized to the vehicle to be controlled. The electronic components of the key are powered by power supply means which comprise a standard battery or accumulator or photovoltaic cells or oscillating weight generator.

The analog signature is preferably inserted in the coded interrogation signal transmitted by the vehicle to the electronic key. This interrogation signal comprises a data sequence obtained by amplitude modulation of the determined carrier frequency signal. This carrier frequency may be of the order of 125 kHz. Each bit of the sequence is set to a higher time period than the carrier frequency. Upon receipt of the coded interrogation signal, when the key is in a restricted area around the vehicle transmitting means, an amplitude indicator of the signal receiving means of the key provides dynamic amplitude values of the vehicle. the envelope of the coded signal. With these amplitude values of the envelope of the received coded signal, it is possible to check the analog signature of the coded signal. This verification is performed in a microcontroller by comparing the digitized amplitude values with stored reference values.

Since the interrogation signal transmitted by the vehicle is at a low frequency, the majority of the calculation operations in the microcontroller of the key are also done at low frequency, which reduces the consumption compared with a high frequency processing. In a sleep mode, the operation is also low frequency. On the other hand, once the analog signature has been recognized, a high frequency response signal must be transmitted to the vehicle for the control of the locking or unlocking of parts or functions of the vehicle. This high carrier frequency can be of the order of 433 MHz, which allows to control the vehicle at a distance between 10 to 30 m. Since the electronics of the key generating this high frequency signal only operate sporadically, the power consumption remains low. This power consumption can be of the order of 10 mA for a period of 100 ms.

The invention also aims to provide a portable object for implementing the access control method.

This and other objects are achieved by means of the aforementioned object which is characterized in that the processing unit is arranged to control the transmitting means and / or the receiving means for transmitting and / or receiving an encoded identification signal with an analog signature, which is defined by at least one amplitude variation of the coded signal envelope, said analog signature being specific to either the portable object or to the electronic means provided in the space, or to the couple constituted by the object and the space to be accessed, such as a vehicle.

• la figure 1 déjà citée représente schématiquement des relais intermédiaires placés entre l'objet portable et le véhicule pour l'ouverture ou la fermeture non autorisée du véhicule,
• la figure 2 déjà citée représente un organigramme des étapes du procédé de contrôle d'accès d'une clé électronique personnalisée au véhicule de l'art antérieur pour verrouiller ou déverrouiller des parties on fonctions du véhicule,
• la figure 3 déjà citée représente un organigramme des étapes du procédé de contrôle d'accès d'une clé électronique personnalisée au véhicule de l'art antérieur par le biais de relais intermédiaires pour le verrouillage ou le déverrouillage des parties on fonctions du véhicule,
• la figure 4 représente schématiquement les composants électroniques de l'objet portable pour la mise en oeuvre du procédé de contrôle d'accès selon l'invention,
• la figure 5 représente un organigramme des étapes du procédé de contrôle d'accès d'un objet portable, tel qu'une clé électronique, à un espace, tel qu'un véhicule selon l'invention,
• les figures 6a à 6c représentent des graphiques montrant plusieurs types de signature analogique par variation d'amplitude dans le temps de l'enveloppe du signal codé, qui comprend une séquence de données binaires pour le procédé de contrôle d'accès selon l'invention, et
• la figure 7 représente un graphique montrant de manière plus détaillée la porteuse du signal codé se terminant par une signature analogique reflétée par décroissance d'amplitude de l'enveloppe du signal codé comme illustrée à la figure 6a de l'état de la technique.

The aims, advantages and characteristics of the access control method and of the portable object for its implementation will appear better in the following description of at least one embodiment illustrated by the drawings in which:

• the figure 1 already mentioned schematically represents intermediary relays placed between the portable object and the vehicle for unauthorized opening or closing of the vehicle,
• the figure 2 already cited represents a flowchart of the steps of the access control method of a personalized electronic key to the vehicle of the prior art for locking or unlocking parts or functions of the vehicle,
• the figure 3 already cited represents a flowchart of the steps of the access control method of a personalized electronic key to the vehicle of the prior art by means of intermediate relays for locking or unlocking the parts or functions of the vehicle,
• the figure 4 schematically represents the electronic components of the portable object for implementing the access control method according to the invention,
• the figure 5 represents a flowchart of the steps of the access control method of a portable object, such as an electronic key, to a space, such as a vehicle according to the invention,
• the Figures 6a to 6c show graphs showing several types of analog signatures by amplitude variation over time of the coded signal envelope, which comprises a bit data sequence for the access control method according to the invention, and
• the figure 7 represents a graph showing in more detail the carrier of the coded signal ending with an analog signature reflected by amplitude decrease of the coded signal envelope as illustrated in FIG. figure 6a of the state of the art.

A preferred embodiment of the method for controlling access to a given space, such as a vehicle with a portable object preferably consisting of an active type electronic key, will be described below. Of course, all the electronic components of the vehicle and the portable object, which are known to those skilled in this technical field will not be described in detail.

As indicated above with reference to the figure 1 the portable object 2 must be in a restricted zone around the electronic means of the vehicle 1 for the implementation of the access control method according to the invention. These electronic means comprise transmitting means 11, 14 and / or receiving means 12, 15 of signals.

The portable object 2 is preferably an active electronic key in which power supply means can supply all the electronic components contained in the key. These supply means may comprise a battery, an accumulator, photovoltaic cells, an oscillating mass generator or another well-known electrical energy source.

The electronic components of the key are shown schematically with reference to the figure 4 . As explained above, it is necessary that the key has its own power source, since it must be able to respond with a high frequency coded signal which may be of the order of 433 MHz. A power supply by an interrogation signal received at low frequency of the order of 125 kHz for example, in the case of a passive key, is not sufficient to allow the generation of the high frequency coded signal transmitted by the key. .

The electronic key 2 essentially comprises a signal processing unit 26 connected to signal receiving means 21, 27, and to signal sending means 22, 28. The power consumption of the key is of the order of 5 μA in standby mode 99% of the time, and in the order of 10 mA during a period of 100 ms during the transmission of the high frequency coded signal.

The receiving means is composed of a receiving antenna 21 for receiving a low frequency coded signal from the vehicle, and a receiver 27. The coded interrogation signal, received by the receiving means, comprises a sequence of binary data. The LF receiver 27, receiving the coded signal, provides the binary data sequence to a microcontroller 24 of the processing unit 26. This LF receiver 27 also comprises an amplitude indicator (RSSI, Received Signal Strength Indicator). providing values analog dynamic dynamics of the envelope of the coded signal received at an analog-digital converter 23 of the processing unit 26. This analog-digital converter 23 scans the amplitude values provided by the indicator clocked by a clock signal of the order of 125 khZ. The digitized amplitude values, partly defining the analog signature, are compared with amplitude reference values. These reference values are stored in the storage means 25 of the processing unit 26, which are connected to the microcontroller.

Since the amplitude of the coded signal is dependent on the distance between the vehicle and the key, it is rather the derivatives of the envelope of the coded signal or the amplitude differences, which are digitized and compared in the microcontroller 24 with values reference stored. After sampling at a frequency determined in the converter 23, it is possible to evaluate these derivatives or these differences in order to identify the torque constituted by the key and the vehicle.

The LF 27 receiver, which includes the amplitude indicator, may be the electronic component referenced EM4083 produced by the company EM Microelectronic-Marin SA located in Marin, Switzerland. The microcontroller 24, used in particular for comparing the amplitude values and for calculating a response signal, may be the electronic component referenced EM6640 also produced by the company EM Microelectronic-Marin SA located in Marin, Switzerland.

Once the analog signature has been verified in the microcontroller 24, a calculation of a response signal is performed in said microcontroller to control the transmission of this response signal to the transmitting means 22, 28. These transmission means are composed of a UHF transmitter 28 and an antenna 22. As the components of the transmitter are well known in this technical field, they will not be explained below. However, for the transmission of the high frequency response signal, a voltage controlled oscillator of the transmitter is in principle used, which consumes a lot of electrical energy. Thus, the UHF transmitter 28 is not continuously engaged in the electronic key so as to avoid discharging too quickly the energy source that includes the key. This transmitter is only engaged if the microcontroller 24 has recognized the analog signature of the interrogation signal received. This analog signature specifically defines the torque constituted by the personalized key and the vehicle, as it depends on specific characteristics of the transmission means and the means for receiving the key and the vehicle.

The coded interrogation signal transmitted by the vehicle comprises a carrier at a frequency of 125 kHz on which a sequence of binary data is obtained by amplitude modulation of the envelope of the carrier. Each bit of the sequence is thus defined over a longer time period than the inverse of the carrier frequency. Each bit takes the value 1, respectively 0, when the amplitude level of the envelope of the bit of the coded signal is greater, respectively less than a determined threshold amplitude level. At this low frequency, the coded interrogation signal is captured at a distance of less than 2 m which defines the restricted area around the vehicle.

Of course, the carrier frequency of the coded signal transmitted by the vehicle may be different from 125 kHz. It may be envisaged to fix this carrier frequency for example at 90 kHz.

The response signal transmitted by the key to the vehicle comprises a carrier at a frequency of the order of 433 MHz. Normally at this frequency, the coding of the response signal is not achieved by amplitude modulation, as well-known problems of multiple paths would influence the recognition of the transmitted coding.

As for the case of the low frequency coded signal, the carrier frequency of this response signal may be different from 433 MHz. The value of this carrier frequency of the response signal may be dependent on certain requirements of the country where the access control method is applied. With such a carrier frequency, it is possible to control parts or functions of the vehicle up to a distance of 30 m.

The figure 5 represents a flow diagram of the steps of the access control method of a personalized electronic key to the vehicle for locking or unlocking including doors and trunk of said vehicle according to the invention. It should be noted that the steps of this figure 5 , which correspond to that of the figure 2 , bear identical reference signs.

In step 50, the electronic key carried by the user of the vehicle is in the waiting position. Once the vehicle handle has been grasped by the user's hand in step 51, an interrogation signal LF is transmitted by the transmitting means in step 52 under the control of the control means. access of the vehicle. The electronic key, placed in the restricted area around the vehicle, receives the interrogated coded signal in step 70. In this step 70, the amplitude indicator of the RF receiver provides analog magnitude values to the converter. The converter digitizes these amplitude values to enable control of these digitized amplitude values in the microcontroller, defining the analog signature of the received signal, with stored reference values. If the analog signature is not recognized, the electronic key goes to step 50 of setting waiting. By cons, if the analog signature is recognized, the vehicle is identified in step 53. If the vehicle is not recognized, the key is placed in the standby position again in step 50. In case of recognition of the vehicle to be controlled, a response signal is calculated by a key processing unit in step 54. This high frequency response signal is transmitted by the antenna of the key transmitting means in step 55. Finally , the vehicle receiving means senses this response signal to enable the access management means to control the opening or closing of the vehicle in step 56. It may also be provided to control at this step 56, the function of starting the vehicle. In the latter case, instead of grasping the handle as explained above, it is for example the gear knob that is touched by the hand of the user.

Of course, it is not mandatory for example to enter the handle of the vehicle for the access control method is turned on. Any other means of detecting the presence of the key near the vehicle can be envisaged to order the vehicle to transmit a coded interrogation signal with an analog signature. Acoustic or optical means, for example, may be used to order the transmission of the coded interrogation signal of the vehicle.

As mentioned above, the analog signature of the coded signal is defined by at least one amplitude variation of the envelope of the coded signal. Several non-limiting examples of analog signatures are represented on the Figures 6a to 6c . The signals represented on these Figures 6a to 6c are for example those provided by the amplitude indicator.

In these Figures 6a to 6c a coded interrogation signal transmitted by the vehicle comprises a data sequence obtained by amplitude modulation of the coded signal envelope. This data sequence is defined by a succession of bits. A bit represents the value 1 when the amplitude of the envelope is above the threshold amplitude level As, while this bit represents the value 0 when the amplitude of the envelope is below the level As. Preferably, the amplitude of the envelope defining the bit element 0 is close to 0. In a simplified manner in these figures, the data sequence comprises a succession of bits of different value. The sequence 10101010 is represented on these Figures 6a to 6c . Normally, this data sequence may represent a vehicle identification code.

To the figure 6a , the analog signature transmitted and received in the coded identification signal is defined as a function of a growth time and / or amplitude decrease Δt of the envelope of the coded signal of the passage between two bits of value different from the data sequence as described by the document EP 1 288 841 of the state of the art. The amplitude variation during the growth and / or decay time may be linear or hyperbolic or random to specifically represent the torque constituted by the vehicle and the personalized key. As described above, the digitized values provided by the converter of the processing unit make it possible to define derivatives of the curve of growth and / or decay of the envelope of the coded signal to be compared with reference stored values.

It should be noted that this analog signature depends in particular on the specific characteristics of the transmission means and the means for receiving the key and the vehicle. The amplitude growth or decay of the envelope defining the signature can be obtained by a resonator of the RC type.

In the case of a signal whose encoding is not generated by amplitude modulation, the analog signature may be defined at the beginning or the end of the coded signal, depending on a growth time and / or decay time. amplitude of the coded signal envelope.

To the figure 6b , the analog signature transmitted and received in the coded identification signal is defined by an over-amplitude modulation of the envelope of the coded signal. This over-modulation is applied for example to the bits representing the value 1 of the data sequence. An amplitude growth of the binary elements equal to 1 is represented in this figure. However, it is also possible to provide an amplitude decrease of the envelope of the series of said bits being 1 of the data sequence.

To the Figure 6c , the analog signature transmitted and received in the coded identification signal is defined by an over-modulation of each bit. Preferably, this over-amplitude modulation is applied only to bits 1 of the data sequence. Thus, several variations of amplitude per binary element equal to 1 are found after passing through the converter and comparing in the microcontroller of the processing unit. This over-modulation of each binary element equal to 1 may be a sinusoidal or rectangular amplitude variation of the envelope.

Since the data sequence is defined by amplitude modulation of a carrier of the coded signal, the figure 7 more precisely represents the coded signal form in the case of an analog signature shown in FIG. figure 6a .

From the description that has just been given, multiple variants of the access control method and the portable object can be designed by those skilled in the art without departing from the scope of the invention. The principle of analog signature on a coded signal transmitted by a transmitter to a receiver can also apply to a space, such as a safe or an access door to a secret place. In this case, the portable object may be a watch, a badge, a mobile phone, a smart card with or without a power supply. Similarly, the analog signature can be transmitted in a response signal transmitted by the portable object.

Claims (11)

1. Method for controlling access via a personalised portable object (2) to a determined space (1) via wireless transmission of an encoded identification signal, electronic means, which include access control means (13) connected to signal reception means (12. 14) and/or transmission means (11, 15), provided in the space, and the portable object including a processing unit (26) connected to signal transmission means (22, 28) and/or reception means (21, 27), the method including steps of:

   - transmitting an encoded identification signal via the transmission means of the portable object or respectively via the transmission means provided in the determined space,

   - receiving the encoded identification signal via the reception means provided in the space or respectively via the reception means of the portable object, when the object is in a restricted zone (5) around electronic means provided in the space, and

   - verifying the encoded signal in the access control means (13) or respectively in the processing unit (26) for authorising access to the space,

   the method being characterized in that the transmitted and received encoded identification signal includes an analogue signature defined by at least one amplitude variation obtained by an over-modulation added to the encoded signal envelope, said analogue signature being specific either to the electronic means provided in the space (1), or to the portable object (2), or to the pair formed by the personalised portable object and the electronic means provided in the space so as to authorise access to the space if said signature is recognised.
2. Method according to claim 1, characterized in that the encoded identification signal is defined by a binary data sequence obtained by amplitude modulation of the signal with a determined carrier frequency, each binary element of the sequence being defined over a time period greater than the inverse of the carrier frequency, and in that each binary element takes the value 1, respectively 0, when the envelope amplitude level of the encoded signal binary element is greater, or respectively less than a determined threshold level.
3. Method according to claim 2, characterized in that an amplitude over-modulation of the encoded signal envelope is applied to the binary elements of the data sequence corresponding to the value 1 by the envelope amplitude rise or fall of the series of said binary elements of the sequence, or by several envelope amplitude variations of said binary elements with a value of 1, and in that the amplitude level of the envelope of the encoded signal for a binary element corresponding to the value 0 is close to 0.
4. Method according to any of the preceding claims, for controlling access by a personalised portable object (2), such as an electronic key, to a vehicle (1) so as to control the locking or unlocking of parts or functions of the vehicle (1), the method being characterized in that it includes the steps of:

   - transmitting via transmission means (11, 15) of the vehicle a first encoded signal defined as an interrogation signal (6, 8) with an analogue signature specific to the pair formed by the personalised object and the vehicle,

   - receiving the interrogation signal via reception means (21, 27) of the object, when the object is located in a restricted zone (5) around the transmission means (11, 15) of the vehicle (1),

   - comparing the received analogue signal with a reference signature stored in the processing unit (26) of the object,

   - calculating a second encoded signal defined as a response signal in the processing unit of the object if the specific analogue signal is recognised, and

   - transmitting the response signal (9, 10) so as to command the locking or unlocking of parts or functions of the vehicle.
5. Method according to claim 4, characterized in that an analogue signal specific to the pair formed by the vehicle and the personalised portable object is transmitted with the first and second encoded signals.
6. Method according to any of the preceding claims, characterized in that a received signal strength indicator (27) for the encoded signal envelope, provided in the reception means (21, 27) of the object, such as an electronic key, or the space, such as a vehicle, supplies dynamic amplitude values for the encoded signal envelope to the control means (13) or to the processing unit (26) to compare the received analogue signature with a stored reference signature.
7. Method according to claim 6, wherein the processing unit of the object and/or the control means of the space include an analogue-digital converter (23), a signal processing micro-controller (24) and storage means (25) that include, in particular, a ciphering algorithm and a reference signature, characterized in that the amplitude values provided by the indicator are digitalised by the analogue-digital converter (23), in that the converter clocked by a clock signal supplies digitalised amplitude values for the received encoded signal envelope to the micro-controller (24), and in that the micro-controller carries out a comparison between the digitalised amplitude values with the amplitude values of the stored reference signature.
8. Personalised portable object (2) for implementing the method according to any of the preceding claims, the object comprising a processing unit (26) connected to signal transmission means (22, 28) and/or reception means (21, 27), characterized in that the processing unit is arranged to control the transmission means and/or the reception means for the transmission and/or reception of an encoded identification signal with an analogue signature, which is defined by at least one amplitude variation of the encoded signal envelope, said analogue signature being specific either to the electronic means provided in the space, or to the portable object (2), or to the pair formed by the object and the electronic means provided in the space to be accessed, such as a vehicle.
9. Object according to claim 8, characterized in that it includes high frequency signal transmission means (22, 28) and low frequency signal reception means (21, 27), and in that the reception means include a received signal strength indicator (27) for the received encoded signal envelope to provide dynamic amplitude values for the encoded signal envelope to the processing unit (26) to compare the received analogue signature with a reference signature stored in storage means (25) of the processing unit.
10. Object according to claim 9, characterized in that the processing unit includes an analogue-digital converter (23) for digitising the amplitude values provided by the indicator, and a signal processing micro-controller (24) for comparing the digitalised amplitude values provided by the converter with amplitude values of the stored reference signature.
11. Object according to claim 8, characterized in that the object is an electronic key with electric power supply means for the integrated electronic components, the supply means including a battery or an accumulator or photo-voltaic cells or an oscillating weight generator.

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