FIELD OF THE INVENTION
[0001] This invention relates to the field of compact, radio frequency (RF) transponders
of the type known to be useful in systems for security and information storage, access
control, entry validation and identification, and in other comparable systems.
[0002] Remote keyless entry systems require an interrogator circuit built into a road vehicle
or building, for example, and a remote transponder which incorporates transmitting
and receiving circuits in a compact case that may be carried by a person in a key,
a key fob, a badge, a tag or in any similar miniaturized housing. More particularly
this invention relates to a transponder in a road vehicle or automotive remote keyless
entry and immobalization system which is functional over an increased range in active
and passive modes of operation. This invention further relates to a transponder which
utilizes a secure challenge-response encryption technique to provide greater security
for the user.
[0003] Compact passive low frequency transponders, using a frequency of 134.2 kilohertz
(134.2 kHz), for example, for passive entry and immobilizer functions and radio frequency
remote control transmitters, using a frequency of 433 megahertz (433 MHz), for example,
for use in remote keyless entry and security systems for automobiles are generally
known. These systems allow access to the automobile without the use of battery power,
if the transponder is used in close proximity to the interrogator, and allow the operator
to transmit commands such as locking and unlocking doors, hood and trunk, controlling
vehicle lighting and ignition, and arming and disarming the anti-theft security system
to the vehicle over greater distances. The transponders used may employ an interrogator-responder
arrangement with an EEPROM data storage device and a small capacitor that serves as
an energy accumulator, charged by the energy provided by the radio frequency interrogation,
to provide power for the transponder. The transponder is, thus, sufficiently small
to supplement or replace a conventional vehicle door and ignition key. Such a transponder
is disclosed by Schuermann at at. In U.S. Patent 5,053,774.
[0004] In this context, reference is made to EP-A-0 690 190, which discloses a remote keyless
entry system with a key module and an in-vehicle lock module. The key module comprises
a remote control transmitter using a high frequency and a transponder for receiving
and transmitting low frequency signals. Upon actuation of a push button, the remote
control transmitter transmits an encoded high frequency signal to the lock module.
If the lock module receives the high frequency signal properly, it starts transmitting
control signals having a frequency of 125 kH. If the key module is within a distance
of about 70 cm from the lock module, it receives the control signals and responds
by sending a driving signal to the lock module for locking or unlocking the vehicle
doors.
[0005] Reference is further made to EP-A-0 767 286, which discloses a remote keyless entry
and immobilization system for automotive use. The system comprises a key, which uses
high frequency transmission for remote operation such as opening and closing the door
locks and low frequency transmission when the key is inserted in the ignition lock
of the vehicle for two way communication between the automobile and the key. The content
of the document is comprised in the state of the art according to Article 54 (3).
[0006] However, the transponder systems in current use generally have a limited operating
range. Current remote control transponder systems require battery power for proper
operation and are not functional, in a passive mode, that is, when operated without
a battery.
SUMMARY OF THE INVENTION
[0007] The present invention provides a road vehicle remote keyless entry system which is
functional over an increased range in the active and passive modes of operation while
increasing security by the use of a secure challenge-response encryption technique.
[0008] The present invention provides a secure road vehicle keyless entry system comprising
an in-vehicle communication processor and a remote transponder. The communication
processor and transponder communicate in parallel paths, a first path being a radio
frequency transmission from the transponder to the communication processor and a second
path being a low frequency, encrypted two way transmission between the transponder
and the communication processor.
[0009] The first and second paths are both used to communicate between the in-vehicle communication
processor and the transponder in response to a manual stimulus to the remote transponder.
[0010] The present invention further provides a method of vehicle keyless entry comprising
the steps of claim 12. The radio frequency transmission and the low frequency, encrypted
transmission can be compared by the communication processor for authentication of
the transmitted data or command before the communication processor authorizes the
desired operation and, if one communication channel is affected by interference, the
second communication channel may be used as a backup.
[0011] Preferably the communication processor has a radio frequency receiver, a low frequency
transmitter/receiver and a controller capable of sending and receiving signals via
the low frequency transmitter/receiver and receiving signals via the radio frequency
receiver. The transponder has a radio frequency transmitter that transmits a signal
to the communication processor upon receipt of a manual stimulus and a low frequency
transmitter/receiver capable of reading the signals received from the communication
processor and preparing an encrypted response for transmission to the communication
processor. When the transponder provides an encrypted response containing the correct
vehicle code to the communication processor, the communication processor authorizes
the desired operation such as, for example, locking or unlocking the car, arming or
disarming the anti-theft alarm system or the performance of vehicle related initialization
functions such as seat, seat belt and vehicle mirror adjustments and lighting the
vehicle interior lights.
[0012] It is further contemplated that the radio frequency receiver in the communication
processor and the radio frequency transmitter in the transponder may be transmitter/receivers,
each capable of performing both the receiving and transmitting functions. When radio
frequency transmitter/receivers are used, both the radio frequency communication and
the low frequency communication between the communication processor and the transponder
will be two way transmissions used to transmit data between the two devices.
BRIEF DESCRIPTION OF DRAWINGS
[0013] The present invention will now be further described by way of example, with reference
to the accompanying drawings in which:
FIG. 1 is a block schematic illustrating the functional elements and data paths of
one embodiment of the road vehicle keyless entry system of the present invention.
FIG. 2 is a block schematic illustrating the functional elements and data paths of
the remote transponder of this embodiment of the invention.
FIG. 3 is a block schematic illustrating the low frequency transmitter/receiver of
the remote transponder of this embodiment of the invention.
FIG. 4 is a block schematic illustrating modifications to the remote transponder of
the road vehicle keyless entry system of FIG. 1.
FIG. 5 is a block schematic illustrating modifications to the remote transponder of
the road vehicle keyless entry system of FIG. 4.
FIG. 6 is a block schematic illustrating the functional elements and data paths of
one embodiment of the write distance expander of the remove transponder of FIG. 5.
FIG. 7 is a block schematic illustrating the functional elements and data paths of
a second embodiment of the write distance expander of the remote transponder of FIG.
5 and
FIG. 8 is a block schematic illustrating a write distance expander.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENT
[0014] In the road vehicle keyless entry system of the present invention the immobilization
function, which locks the vehicle and initiates operation of the alarm system, is
separate from the remote keyless entry function, which, for example, resets the alarm
system and authorizes unlocking the vehicle and performance of vehicle related initialization
functions such as seat, seat belt and vehicle mirror adjustments and lighting the
vehicle interior lights.
[0015] Turning to the drawings, FIG. 1 illustrates the functional elements and data paths
of one embodiment of the road vehicle keyless entry system of the present invention.
In this disclosure, the term road vehicle means all of the various types of vehicles
that are operated upon the highway system including, but not limited to, automobiles,
trucks, vans, motorcycles, buses and motorhomes. It is intended that the arrangement
shown in FIG. 1, and in the following figures, shall be interpreted as an illustrative
system configuration and that other possible configurations, more adapted to the specific
user needs, exist within the scope of the disclosure herein. Further, the use of like
reference numbers to identify components within the various figures indicates the
presence of similar elements within each of the different figures.
[0016] The road vehicle keyless entry system, generally designated as 10, includes a communication
processor 11 that is located within the vehicle and a remote, miniaturized transponder
15. Communication processor 11 may also be named an interrogator or called by other
names indicating its function as a unit which requests and receives information from
the remote transponder 15. Communication processor 11 has a radio frequency receiver
12, a low frequency transmitter/receiver 13 and a controller 14 which is capable of
sending and receiving signals via the low frequency transmitter/receiver 13 and receiving
signals via the radio frequency receiver 12. Controller 14 combined with low frequency
transmitter/receiver 13 is preferably, a TIRIS reader, the term TIRIS being an acronym
known to those skilled in the art as denoting certain types of devices or equipment
utilizing the transponder arrangement and TIRIS reader disclosed in Schuermann et
al., U.S. Patent 5,053,774. The transponder 15 has a radio frequency transmitter 16
that transmits a signal to communication processor 11 upon receipt of a stimulus manually
produced by an operator's actuation of one of a plurality of push buttons 18. While
push buttons 18 are shown for convenience, any manually operatable, pulse creating
switch such as, for example, a toggle switch or a rotary switch may be used. Transponder
15 also has a low frequency transmitter/receiver 17 capable of reading signals received
from communication processor 11, preparing an encrypted response and transmitting
the encrypted response to communication processor 11.
[0017] In the present embodiment of the invention, communication processor 11 located within
the vehicle and remote transponder 15 communicate with one another to permit a flow
of information to initiate operations at the vehicle. Communication between the two
devices is initiated by the vehicle operator who pushes a button 18 on transponder
15 which responds by transmitting a radio frequency (RF) signal to communication processor
11 and a signal to low frequency transmitter/receiver 17 to prepare it for interrogation
by communication processor 11. The signal transmission, using a rolling code for security,
is a one way communication or data transfer from transponder 15 to communication processor
11 using a radio frequency signal of 433 megahertz (433MHz), for example, or another
suitable frequency. In response to the initial signal from transponder 15, communication
processor 11 transmits a low frequency interrogation to transponder 15 requesting
identification and verification of the original radio frequency signal. Thus, the
low frequency communication between the devices, using a low frequency signal such
as, for example, 134.2 kilohertz (134.2 kHz), is a two way data exchange using the
challenge-response principle for authentication or verification of identity. Security
of the low frequency signal is maintained by using an encryption key which is known
only to communication processor 11 in the vehicle and remote transponder 15. When
transponder 15 provides an encrypted response containing the correct vehicle code
to communication processor 11 in response to the interrogation, communication processor
11 authorizes the desired operation within the vehicle. This use of encryption logic
and interrogation and response via the low frequency data transmission, in addition
to the rolling code used for security with the radio frequency signal, greatly increases
the security of the road vehicle keyless entry system.
[0018] In the description above, a radio frequency transmitter and a receiver are used.
It is further contemplated that radio frequency receiver 12 in communication processor
11 and radio frequency transmitter 16 in transponder 15 may be transmitter/receivers,
each capable of performing both the receiving and transmitting functions. When radio
frequency transmitter/receivers are used, both the radio frequency communication and
the low frequency communication between communication processor 11 and transponder
15 will be two way transmissions used to transmit data between the two devices. This
use of two way radio frequency communication is illustrated by the solid and dotted
signal lines between radio frequency receiver 12 and radio frequency transmitter 16.
[0019] FIG. 2 is a block schematic of the functional elements and data paths of remote transponder
15 of this embodiment of the invention showing radio frequency transmitter 16 and
low frequency transmitter/receiver 17. For remote security functions such as, for
example, turning on the interior vehicle lights or arming or disarming the security
system a functional range of greater than 10 meters is desired. For this purpose,
transponder 15 includes radio frequency transmitter 16 which operates at a frequency
of 433 megahertz (433MHz) using a rolling code for security. The present transponder
15 further includes low frequency transmitter/receiver 17 which provides a two way
exchange of data with the communication processor 11 in the vehicle using an encrypted
signal having a frequency of 134.2 kilohertz (134.2 kHz). Use of low frequency transmitter/receiver
17 allows access to, or enables, additional features such as, for example, programming,
the exchange and verification of identification and the use of encryption logic and
the transmission of various desired commands to the vehicle, all of which can significantly
increase the security of the road vehicle remote keyless entry system.
[0020] A vehicle operator provides a manual stimulus at the remote transponder 15 to initiate
a command - the operator pushes one of the plurality of switches or push buttons 18
to indicate the action desired at the vehicle. Transponder 15 includes radio frequency
transmitter 16 which includes control logic module 29, radio frequency modulator/driver
28 and random number generator 30. In response to the operator's action, radio frequency
transmitter 16 transmits a signal, the desired command, to radio frequency receiver
12 in communication processor 11 at the vehicle and simultaneously transfers the command
to low frequency transmitter/receiver 17 via the serial interface. For receipt of
this command signal, power to passive, low frequency transmitter/receiver 17 is provided
by battery at terminal ACT on the control logic module 21 and data are received using
clock and data input ports, terminals SC and SI. In addition to the control logic
module 21, low frequency transmitter/receiver 17 includes encryption logic module
22, memory 23, radio frequency circuitry 24, shift register 25, tuned antenna, a parallel
resonant circuit, 26 and charge or power capacitor 27. Low frequency transmitter/receiver
17 transmits the remote command to low frequency transmitter/receiver 13 which was
switched to the receive mode by controller 14 when radio frequency receiver 12 detected
the carrier and command signal from radio frequency transmitter 16. Thus, even if
external influences create interference with the radio frequency transmission of the
desired command, the command may be received by communication processor 11 through
the use of low frequency transmission signals although the transmission range for
the low frequency signal is reduced. Authentication of the command may be confirmed
by control processor 11 transmitting a challenge to the transponder 15 using low frequency
transmitter/receiver 13. When the challenge is received by low frequency transmitter/receiver
17, the encryption logic module 22 encrypts the challenge using the encryption key
stored within memory 23 (not readable) and transfers the encrypted challenge and a
serial number, which is also stored within memory 23, to the radio frequency transmitter
16. The encrypted challenge and serial number, together with the repeated command,
are transmitted in parallel to communication processor 11 by both radio frequency
transmitter 16 and low frequency transmitter/receiver 17 as a complete response to
the challenge to authenticate the first command transmission. Controller 14 executes
the command, or authorizes other devices to execute the command, if the correct vehicle
code or signature is received in response to the challenge. With bidirectional communication
using the low frequency transmitter/receivers 13 and 17, the challenge-response feature
provides greatly increased security over the rolling code system. It is now also possible
to transmit additional data or programming information between the remote transponder
15 and the communication processor 11 using the low frequency transmitter/receiver
17.
[0021] As discussed above, it is further contemplated that the radio frequency receiver
12 in communication processor 11 and radio frequency transmitter 16 in transponder
15 may be transmitter/receivers, each capable of performing both the receiving and
transmitting functions. When radio frequency transmitter/receivers are used, both
the radio frequency communication and the low frequency communication between communication
processor 11 and transponder 15 will be two way transmissions used to transmit data
between the two devices.
[0022] For remote keyless entry, a function or transmission range of at least approximately
one meter (1 m) is necessary. However, this range is difficult to reach with passive
transponders, even when the transponder has an antenna the size or a credit card.
Therefore, an active function may be provided by the inclusion of a battery as shown
in FIG. 3, a block schematic of a low frequency transmitter/receiver 50, another embodiment
of the low frequency transmitter/receiver 17 for remote transponder 15.
[0023] Low frequency transmitter/receiver 50 includes logic control module 51, receiver
control module 52, transmitter control module 53, the end of burst detector 54, the
adaptive pluck logic module 55, signal level converter 56, clock regenerator 57, divider
58, threshold detector 59, resonant circuit 60, charge capacitor 61 and diodes 62,
63 and 64 connected as shown in FIG. 3. Resonate circuit 60 has a capacitor connected
in parallel with an inductor with the value of each component selected to provide
a resonant circuit that is resonant at a radio frequency of 134.2 kilo hertz (134.2
kHz). The size of charge capacitor 61 is selected so that the fully charged capacitor
will have sufficient charge to provide the power necessary to enable the low frequency
transmitter/receiver 50 to function properly. A capacitor sufficiently large would
be, for example, a capacitor of approximately 0.12 microfarads (0.12µf). Diodes 62,
63 and 64 are symbols for the necessary one way function, that is, the signal is conducted
in only one direction. Diodes 62, 63 and 64 are preferably Schottky diodes with low
feed through voltage, if possible in the selected semiconductor process, although
they may be normal semiconductor diodes such as 1N4148 diodes or field effect transistor
(FET) circuits using switched gates.
[0024] The vehicle operator initiates a command by providing a manual stimulus at the door
handle of the vehicle or with remote transponder 15 - the operator operates the door
handle or pushes one of the plurality of switches or push buttons 18 to indicate the
action desired at the vehicle. After receipt of a radio frequency signal from transponder
15, the communication processor 11 or interrogator transmits a low frequency signal
(134.2 kHz) to low frequency transmitter/receiver 50 which, when received by resonant
circuit 60, provides electrical energy to charge capacitor 61 in addition to asking
transponder 15 for confirmation of the command or action request. The low frequency
voltage is rectified by diode 62 and charges capacitor 61. The voltage level reached
on charge capacitor 61 depends upon the distance between the communication processor
11 and the transponder 15 antennas which are typically resonance circuits having a
high quality factor such as, for example, resonant circuit 60. If sufficient energy
is accumulated so that the voltage on charge capacitor 61 exceeds a certain limit
such as one volt, for example, the threshold detector 59 switches the battery supply
voltage from battery 65, provided at terminal VBAT, to connect the battery voltage
through connections VCC to the logic circuitry of low frequency transmitter/receiver
50. The threshold detector 59 prevents discharge of battery 65 when transponder 15
is in the presence of electromagnetic interference such as, for example, if the transponder
is placed upon a television set. If the voltage limit on charge capacitor 61 is low,
the influence of the interference will increase, but the sensitivity (the signal detection
range) will also increase. As explaned hereinafter, the threshold detector 59 may
be an active or a passive device. Increasing the sensitivity requires more stand-by
current from battery 65, with a resulting decrease in battery life. The threshold
detector may also be located at the radio frequency signal input where higher signal
amplitudes are normally available. If battery 65 is not available, voltage is still
provided to the logic circuitry by charge capacitor 61 through diodes 63 and 64. The
resonant circuit 60 is separated from the integrated circuit power supply during the
reception of data, the write phase, from the communication processor 11. The signal
received by transponder 15 and the level of oscillation of the resonant circuit 60
is usually low when the distance between the communication processor 11 and the transponder
15 is great. The use of battery 65 to provide voltage to the circuit enables the low
frequency transmitter/receiver 50 circuit to receive and react to transmitted signals
having lower amplitudes than would be possible in the passive mode of operation, that
is, without battery power. voltage is monitored by the end of burst detector 54. When
the amplitude of the voltage signal drops and the resonant circuit 60 resonates with
its own frequency instead of being enhanced by the signal from communication processor
11, the end of burst detector 54 activates clock regenerator 57 and the pluck logic
module 55 which preferably provides peak pluck and slope control. The pluck logic
module 55 enhances oscillation whenever a voltage amplitude drop caused by the resonant
circuit loss factor is detected. Pluck logic, the pluck logic module 55 and the peak
detector used in pluck logic are described in U.S. Patent 5,283,529, U.S. Patent 5,227,740
and U.S. Patent 5,126,745
[0025] The provision of battery power enables the circuit to operate properly with the reception
of a lower signal amplitude than would be possible in the passive mode. Voltage amplitude
drops during and after the write phase are detected by the end of burst detector 54
over greater distances because internal current sources and digital circuits of low
frequency transmitter/receiver 50 are already fully functional as battery 65 provides
the necessary power rather than relying upon the signal received by charge capacitor
61 to provide power, as would be required in the passive mode of operation. The low
frequency transmitter/receiver 50 is able to regenerate even small signal amplitudes
which helps pluck circuit 55 enhance the oscillation during the free running times,
during the reception of write signals and during the transmission of response data.
Thus, the distance over which data may be received by transponder 15 using pulse width
modulation is significantly enhanced when compared to the distance possible when a
transponder operating in the passive mode is used.
[0026] After a period for the charging of charge capacitor 61, communication processor 11
transmits a challenge such as, for example, a random number to transponder 15. This
challenge is received by low frequency transmitter/receiver 50 and is encrypted, using
the encryption key stored in its memory, to become the signature of the transponder
15. This generated signature, the encrypted random number, and the serial number of
transponder 15 are transmitted to the communication processor 11 by the low frequency
transmitter/receiver 50 and, at the same time, transferred to radio frequency transmitter
16 of transponder 15 using the internal serial input/output interface circuitry. When
the internal serial input/output interface circuitry is used without low frequency
transmitter/receiver 13 being involved so that no voltage is charged in capacitor
61, the activate signal on terminal ACT of low frequency transmitter/receiver 50 switches
the battery 65 voltage, provided at terminal VBAT, to connect through connections
VCC to the level converter 56 which maintains the correct input and output signal
voltage levels under all voltage supply levels.
[0027] When the end of burst, the end of the transmission from communication processor 11,
measured by end of burst detector 54 lasts for a certain time such as, for example,
a period of 1.9 milliseconds (1.9 ms), a "timeout" or response signal is generated
in accordance with the disclosure above for transmission to communication processor
11. Divider 58 counts the radio frequency oscillations regenerated by clock regenerator
57 during the end of burst period to determine when the response or "timeout" signal
is to be generated and switches the battery voltage, terminal VBAT, to the resonant
circuit 60 to increase the transmission frequency amplitude and, therefore, to increase
the transmission reading distance and the signal robustness against noise or other
interference. Thus, similar to the enhanced reception distance, the distance over
which data may be transmitted by transponder 15 of this invention using frequency
shift keying (FSK) is enhanced when compared to the distance possible when a transponder
operating in the passive mode is used. The radio frequency transmitter 16 transmits
the signature and serial number with a command that the communication processor 11
accept the parallel low frequency response as a backup and as a security check. This
dual signal, the parallel transmission of a radio frequency signal and a low frequency
signal, enhances the security against noise and manipulation of the command signals.
[0028] Operation may also be enhanced by using transmitter/receivers as the radio frequency
receiver 12 in communication processor 11 and radio frequency transmitter 16 in transponder
15. When radio frequency transmitter/receivers are used, both the radio frequency
communication and the low frequency communication between communication processor
11 and transponder 15 will be two way transmissions, further enhancing the security
against noise and manipulation of the command signals.
[0029] The road vehicle keyless entry system 10 may also be used to replace the ignition
key of the vehicle. When the vehicle operator has entered the vehicle and wishes to
start the engine, the operator will initiate a new command process with a manual stimulus
of a push button on or near the vehicle dash board, for example. This stimulus initiates
a new challenge/response phase via the low frequency transmitter/receivers. Operation
of the keyless entry system 10 after receipt of the low frequency signal is as described
above.
[0030] Turning now to FIG. 4, a block schematic illustrates modifications to the remote
transponder 15 of the road vehicle keyless entry system 10 of FIG. 1. Communication
processor 11 is located within the vehicle and miniaturized transponder 15 is a remote
unit which may be carried by the vehicle operator. The apparatus and operation of
communication processor 11 and transponder 15 are as described in regard to FIG. 1
above except that the serial input/output interface circuitry between radio frequency
transmitter 16 and low frequency transmitter/receiver 17 is replaced by driver/demodulator
circuit 19 and coupling coil 20 to provide for the contactless transfer of data between
the two circuits. In this embodiment, battery voltage is provided to radio frequency
transmitter 16 and voltage is transferred to low frequency transmitter/receiver 17
by signal transmission through coupling coil 20. Commands are initiated by the manual
stimulation of one of the plurality of push buttons 18 on radio frequency transmitter
16 which transmits the command to communication processor 11 and at the same time
transfers the command data to low frequency transmitter/receiver 17. As described
above, it is contemplated that radio frequency receiver 12 and radio frequency transmitter
16 may be transmitter/receivers allowing two way radio frequency communication in
addition to the two way low frequency communication. It is, thus, possible to initiate
commands by manual stimulation of push buttons, similar to push buttons 18, located
on communication processor 11. Communication processor 11 would transmit the command
to radio frequency transmitter 16, which would then be a transmitter/receiver, and
it would request data from low frequency transmitter/receiver 17 to respond to the
command from communication processor 11. Solid and dotted lines are shown in FIG.
4 to illustrate the two way flow of information by the use of radio frequency transmitter/receivers.
The commands and data are transferred to low frequency transmitter/receiver 17 via
coupling coil 20 which is driven by driver/demodulator circuit 19. The response, also
via coupling coil 20, from low frequency transmitter/receiver 17, the signature, serial
number and status, are demodulated by driver/demodulator circuit 19 for reading by
radio frequency transmitter 16. Operation of communication processor 11 and transponder
15 are otherwise as described in regard to FIG. 1 above. This embodiment of the invention
may be especially useful if it is desired to separate the command function provided
by radio frequency transmitter 16, which initiates all commands by operation of one
of the push buttons 18, from the communication function provided by low frequency
transmitter/receiver 17, which provides two way communication for the transfer and
verification of data between transponder 15 and communication processor 11. Radio
frequency transmitter 16 and low frequency transmitter/receiver 17 may, thus, be in
separate compact cases, allowing separate use of a passive transponder for operation
over short distances, separate use of an active, battery powered radio frequency transponder
for remote control functions over greater distances and combined use of the passive
and active transponder functions over the full desired operating range, thus allowing
adaption of the transponder size to the size the vehicle operator is willing to carry.
[0031] FIG. 5 is a block schematic illustrating modifications to the remote transponder
of the road vehicle keyless entry system of FIG. 4. In FIG. 5 the driver/demodulator
circuit 19 interface of FIG. 4 is replaced or complimented by a write distance expander
interface circuit 19a which cooperates with radio frequency transmitter 16 and low
frequency transmitter/receiver 17 to provide a transponder 15 that is operable at
an increased distance between transponder 15 and communication processor 11 with low
frequency transmitter/receiver 17 operating in the passive mode, that is without a
voltage directly supplied by a battery.
[0032] Road vehicle keyless entry system 10 has communication processor 11 and transponder
15. The functional elements and operation of communication processor 11 are described
above. Transponder 15 has a low frequency transmitter/receiver 17 that operates on
a low frequency such as, for example, 134.2 kilohertz (134.2 kHz) to provide two way
communication, a challenge and encrypted response, with communication processor 11.
Transponder 15 also has a radio frequency transmitter 16 that operates on a radio
frequency such as, for example, 433 megahertz (433 MHz). Radio frequency transmitter
16 is equipped with a battery and the range in which transponder 15 can receive the
low frequency signal is increased by write distance expander interface circuit 19a.
The radio frequency transmitter 16 and low frequency transmitter/receiver 17 must
be in a common housing for operation over extended distances, but may be separated
from one another while providing basic operations at shorter operating ranges.
[0033] The radio frequency transmitter 16 is typically used to provide security functions
such as, for example, light switching, alarm arming and disarming and similar functions.
The low frequency transmitter/receiver 17 is typically used in the passive operating
mode to provide keyless entry and immobilization functions at short range, for example
at distances less than one meter (1 m). When a request or command is made by the manual
operation of one of a plurality of push buttons 18 on transponder 15 or by a mechanical
switch such as the vehicle door handle, a challenge or interrogation, a random number,
is transmitted from communication processor 11 using a ferrite or air coil antenna
and pulse pause modulation at a frequency of, for example, 134.2 kilohertz (134.2
kHz) to the low frequency transmitter/receiver 17 of transponder 15. Low frequency
transmitter/receiver 17 encrypts the challenge using a secret encryption key held
in its memory (not readable) to produce a signature and responds by transmitting the
encrypted challenge, its signature, and the transponder serial number to the communication
processor 11 using a frequency shift keying (FSK), frequency modulation, signal at
a frequency of, for example, 134.2 kilohertz (134.2 kHz). If the distance between
communication processor 11 and transponder 15 is too far, this communication will
fail. To achieve a greater functional range, the write distance expander 19a interface
circuit is provided.
[0034] One embodiment of the write distance expander 19a is shown in FIG. 6 in a block schematic
illustrating the expander's functional elements and data paths. A block schematic
is used in FIG. 7 to illustrate the functional elements and data paths of a second
embodiment of the write distance expander 19a.
[0035] Write distance expander 19a interface circuit includes resonant circuit 80 which
consists of coil 81, which also serves as a coupling coil, and a capacitor tuned to
a frequency of 134.2 kilohertz (134.2 kHz); radio frequency voltage limiter 82 with
a battery charge circuit; diode 83 connected to charge capacitor 84; threshold detector
85; clock regenerator 86, an operational amplifier used as a comparator; envelope
rectifier 87; end of burst detector 88; and a 134.2 kilohertz (134.2 kHz) clock generator
module 89 which may, for example, be a pluck logic module or a separate oscillator
with a divider gated by activation signal TXCT.
[0036] Coil 81, which is, for example, a small ferrite or air coil, is located proximate
the antenna of low frequency transmitter/receiver 17 at a position in which the coil
81 can receive the radio frequency signals from communication processor 11 and the
resonant circuit of low frequency transmitter/receiver 17. The write distance expander
19a resonant circuit 80 has a high quality factor to achieve a radio frequency voltage
amplitude of at least about 1 to 2 volts at the desired maximum reading distance between
the transponder 15 and communication processor 11. When communication processor 11
transmits a challenge to transponder 15 and the distance between the two devices is
too great, the low frequency transmitter/receiver 17 will not function properly because
the challenge is not received or the signal is too weak. If the challenge is not properly
received by low frequency transmitter/receiver 17, encryption of the challenge is
not started and no response will be transmitted to the communication processor 11.
The write distance expander 19a circuit has a threshold detector 85 which detects
the radio frequency voltage increase during the charge phase, the period in which
the radio frequency signal from communication processor 11 is used to charge charge
capacitor 84. The threshold detector 85 activates the supply voltage for the active
devices and turns on the controller within the radio frequency transmitter 16. The
threshold detector 85 may be an N-channel FET with low gate source-voltage, a circuit
that does not consume power as long as the FET is not in the conductive state. The
threshold detector 85 can also be an active device which consumes a certain amount
of standby current from the battery. The pulses of the PET, or of the active device,
can be used to trigger a retriggerable monoflop or can be used directly to turn on
the controller within radio frequency transmitter 16 which activates the power supply
to the write distance expander 19a. The oscillation of the write distance expander
is rectified by diode 83 and filtered by charge capacitor 84 to provide a reference
voltage for the comparators, clock regenerator 86 and end of burst detector 88.
[0037] During transmission of the command and the challenge to the low frequency transmitter/receiver
17, the radio frequency signal is pulsed and the length of the pulse pauses are the
indication for a low or a high bit. The envelope rectifier 87 detects the pulse pauses
by rectifying the output of the clock regenerator 86. The envelope rectifier 87 output
signal is compared to the voltage reference level by the end of burst detector 88
and this signal is conducted to the controller of radio frequency transmitter 16.
The controller monitors the output from end of burst detector 88, detects the length
of the pulse pauses and determines whether a low bit or a high bit is received. Threshold
detector 85, envelope rectifier 87 and comparator 88 may be combined in the simplest
case using a field effect transistor (FET) with low gate/source voltage as shown in
FIG. 8, an illustration of a simple write distance expander. When an encryption command
is received, the challenge is received and stored in controller memory. The controller
of radio frequency transmitter 16 switches the voltage provided by battery 90 to the
clock regenerator 86 when the response from the low frequency transmitter/receiver
17 is expected and clock regenerator 86 amplifies and limits the radio frequency signal
oscillation and generates a digital clock signal. This clock signal is conducted directly
to the controller of radio frequency transmitter 16 or to the controller through a
digital or analog demodulator circuit 91 if the controller is not capable of demodulating
the signal. The controller checks the frequency shift keying (FSK) modulated response
from the low frequency transmitter/receiver 17 to determine whether it is valid and
complete. The encrypted response to the challenge from the communication processor
11 is transmitted by the low frequency transmitter/receiver 17 and the response, the
signature, status and other desired information, may be sent in parallel by the radio
frequency transmitter 16 to confirm and authenticate the response. When only the challenge,
but no response from the low frequency transmitter/receiver 17, is detected by the
controller of radio frequency transmitter 16, the controller transfers the challenge
stored in memory to the low frequency transmitter/receiver 17 using the 134.2 kilohertz
(134.2 kHz) clock generator 89 which may be a pluck logic circuit or a gated oscillator
with divider as shown in the demodulator circuit 91. When low frequency transmitter/receiver
17 receives the challenge, it will generate an encrypted signature from the challenge
and will transmit the encrypted signature at a frequency of 134.2 kilohertz (134.2
kHz) as the response to communication processor 11. This response will also be transferred
to radio frequency transmitter 16 and will be transmitted at a radio frequency of
433 megahertz (433 MHz) to communication processor 11 in parallel with the low frequency
transmission of the response. The radio frequency voltage limiter circuit 82 necessary
to protect the components can be used to charge battery 90. If the threshold detector
85, and the controller of radio frequency transmitter 16, detects a continuous radio
frequency signal for a long period of time, then radio frequency voltage limiter 82
will switch the voltage to a higher level for use to charge battery 90. Depending
upon the low frequency voltage initiated in the write distance expander 19a resonant
circuit 81 (antenna size) and the threshold detector level sensitivity, distances
of from about 1 meter (1 m) to about 2 meters (2 m) between transponder 15 and communication
processor 11 can be bridged for remote keyless entry communications. This greater
or expanded signal reception distance combined with the greater transmission distance
for radio frequency remote control transmitter 16, greater than 10 meters (>10 m)
allows the operator to gain access to the vehicle or authorize other vehicle actions
from a greater distance or without removing the transponder 15 from the pocket.
[0038] In addition to the described function, write distance expander 19a may also be used
as a low cost radio frequency module with receive and transmit capabilities. Such
modules could be used in transponders useful over short distances.
[0039] In view of the foregoing description, it will be seen that several advantages are
attained by the present invention.
[0040] Although the foregoing includes a description of the best mode contemplated for carrying
out the invention, various modifications could be made in the constructions herein
described and illustrated without departing from the scope of the invention. It is
intended that all material contained in the foregoing description or shown in the
accompanying drawing should be interpreted as illustrative rather than limiting.
1. A secure road vehicle keyless entry system (10) comprising an in-vehicle communication
processor (11) and a remote transponder (15), the communication processor (11) and
transponder (15) communicating in parallel paths, a first path being a radio frequency
transmission from the transponder (15) to the communication processor (11) and a second
path being a low frequency, encrypted two way transmission between the transponder
(15) and the communication processor (11) where the first and second paths are both
used to communicate between the in-vehicle communication processor (11) and the transponder
(15) in response to a manual stimulus to the remote transponder (15).
2. The secure road vehicle keyless entry system (10) of claim 1 wherein the radio frequency
transmission and the low frequency transmission are compared for authentication of
the transmitted data.
3. The secure road vehicle keyless entry system (10) of claim 1 wherein the radio frequency
transmission is a two way transmission between the transponder (15) and the communication
processor (11).
4. The secure road vehicle keyless entry system (10) of claim 1 further comprising: the
communication processor (11) having a radio frequency receiver (12), a low frequency
transmitter/receiver (13) and a controller (14) capable of reading the signals sent
and received by the low frequency transmitter/receiver (13); and
the transponder (15) having a radio frequency transmitter (16) for transmitting
a signal to the radio frequency receiver (12) of said communication processor (11)
upon receipt of a manual stimulus and a low frequency transmitter/receiver (17) capable
of reading signals received from the communication processor (11) and transmitting
an encrypted response to the communication processor (11).
5. The road vehicle keyless entry system (10) of claim 4 wherein the transponder (15)
further includes an interface circuit and a coupling coil to provide contactless transfer
of data between the radio frequency transmitter and the low frequency transmitter/receiver.
6. The road vehicle keyless entry system (10) of claim 4 or claim 5 wherein the radio
frequency transmitter (16) of the transponder (15) and the radio frequency receiver
(12) of the communication processor (11) send and receive a signal having a frequency
of 433 megahertz.
7. The road vehicle keyless entry system (10) of any of claims 4 to 6 wherein the low
frequency transmitter/receivers (17) of the transponder (15) and the communication
processor (11) send and receive a signal having a frequency of 134.2 kilohertz.
8. The road vehicle keyless entry system (10) of claim 5 wherein the manual stimulus
is the manual actuation of one of a plurality of push buttons (18).
9. The road vehicle keyless entry system (10) of any of claims 4 to 8 wherein the communication
processor radio frequency receiver (12) and the transponder radio frequency transmitter
(16) are radio frequency transmitter/receivers capable of two way transmissions between
the communication processor (11) and the transponder (15).
10. The road vehicle keyless entry system (10) of any of claims 4 to 9 wherein the transponder
(15) supplements or replaces the vehicle door and ignition keys, signals from the
transponder (15) being received by the communication processor (11) that, after reception
and verification of access codes, authorizes unlocking the vehicle and performance
of vehicle related initialization functions such as seat, seat belt and vehicle mirror
adjustments.
11. The road vehicle keyless entry system (10) of any of claims 5 to 9 wherein the transponder
radio frequency transmitter (16) and low frequency transmitter/receiver (17) are in
separate cases.
12. A method of vehicle keyless entry comprising the steps of:
providing an in-vehicle communication processor (11) and a remote, miniaturized transponder
(15), the communication processor (11) having a radio frequency receiver (12), a low
frequency transmitter/receiver (13) for transmitting low frequency signals and a controller
(14) for reading the signals sent and received by the low frequency transmitter/receiver
(13) and the transponder (15) having a radio frequency transmitter (16) that transmits
a signal to the communication processor (11) upon receipt of a manual stimulus thereat
and a low frequency transmitter/receiver (17) for reading low frequency signals received
from the communication processor (11) and transmitting an encrypted response to the
communication processor (11);
providing said manual stimulus to cause said transponder (15) to send an RF signal
to said communication processor (11) and sending a low frequency signal to said low
frequency transmitter/receiver (13) at said communication processor (11) in response
to said manual stimulus;
then sending a low frequency signal from said low frequency transmitter/receiver (13)
at said communication processor (11) to said transmitter/receiver (17) at said transponder
(15) in response to at least one of said signals from said transponder (15) to said
communication processor (11); and then sending a signal from said transponder (15)
to said communication processor (11) in response to said signal from said communication
processor (11) to said transponder (15).
13. The method of claim 12 wherein said signal from said low frequency transmitter/receiver
(13) at said communication processor (11) to said low frequency transmitter/receiver
(17) at said transponder (15) is an encoded signal.
1. Sicheres, schlüsselloses Straßenfahrzeug-Zugangssystem (10), das einen fahrzeuginternen
Kommunikationsprozessor (11) und einen Femtransponder (15) umfasst, wobei der Kommunikationsprozessor
(11) und der Transponder (15) auf parallelen Wegen kommunizieren, wovon ein erster
Weg eine Hochfrequenzübertragung vom Transponder (15) zum Kommunikationsprozessor
(11) ist und ein zweiter Weg eine verschlüsselte Niederfrequenz-Zweiwegeübertragung
zwischen dem Transponder (15) und dem Kommunikationsprozessor (11) ist, wobei sowohl
der erste Weg als auch der zweite Weg dazu verwendet werden, in Reaktion auf eine
manuelle Stimulation des Ferntransponders (15) zwischen dem fahrzeuginternen Kommunikationsprozessor
(11) und dem Transponder (15) zu kommunizieren.
2. Sicheres, schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach Anspruch 1, bei dem
die Hochfrequenzübertragung und die Niederfrequenzübertragung für die Authentifizierung
der gesendeten Daten miteinander verglichen werden.
3. Sicheres, schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach Anspruch 1, bei dem
die Hochfrequenzübertragung eine Zweiwegeübertragung zwischen dem Transponder (15)
und dem Kommunikationsprozessor (11) ist.
4. Sicheres, schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach Anspruch 1, das ferner
umfasst: den Kommunikationsprozessor (11) mit einem Hochfrequenzempfänger (12), einem
Niederfrequenz-Sender/Empfänger (13) und einer Steuereinheit (14), die die von dem
Niederfrequenz-Sender/Empfänger (13) gesendeten und empfangenen Signale lesen kann;
und
den Transponder (15) mit einem Hochfrequenzsender (16), der bei Empfang einer manuellen
Stimulation ein Signal an den Hochfrequenzempfänger (12) des Kommunikationsprozessors
(11) sendet, und einem Niederfrequenz-Sender/Empfänger (17), der die von dem Kommunikationsprozessor
(11) empfangenen Signale lesen und an den Kommunikationsprozessor (11) eine verschlüsselte
Antwort senden kann.
5. Schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach Anspruch 4, bei dem der Transponder
(15) ferner eine Schnittstellenschaltung und eine Kopplungsspule umfasst, um eine
kontaktlose Übertragung von Daten zwischen dem Hochfrequenzsender und dem Niederfrequenz-Sender/Empfänger
zu schaffen.
6. Schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach Anspruch 4 oder Anspruch 5,
bei dem der Hochfrequenzsender (16) des Transponders (15) und der Hochfrequenzempfänger
(12) des Kommunikationsprozessors (11) ein Signal senden und empfangen, das eine Frequenz
von 433 Megahertz besitzt.
7. Schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach einem der Ansprüche 4 bis 6,
bei dem die Niederfrequenz-Sender/Empfänger (17) des Transponders (15) und des Kommunikationsprozessors
(11) ein Signal senden und empfangen, das eine Frequenz von 134,2 Kilohertz besitzt.
8. Schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach Anspruch 5, bei dem die manuelle
Stimulation die manuelle Betätigung eines von mehreren Druckknöpfen (18) ist.
9. Schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach einem der Ansprüche 4 bis 8,
bei dem der Hochfrequenzempfänger (12) des Kommunikationsprozessors und der Hochfrequenzsender
(16) des Transponders Hochfrequenz-Sender/Empfänger sind, die Zweiwegeübertragungen
zwischen dem Kommunikationsprozessor (11) und dem Transponder (15) ausführen können.
10. Schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach einem der Ansprüche 4 bis 9,
bei dem der Transponder (15) die Fahrzeugtür- und Zündschlüssel ergänzt oder ersetzt,
wobei Signale vom Transponder (15) von dem Kommunikationsprozessor (11) empfangen
werden, der seinerseits nach Empfang und Verifikation von Zugangscodes die Entriegelung
des Fahrzeugs und die Ausführung von auf das Fahrzeug bezogenen Initialisierungsfunktionen
wie etwa Sitz-, Sicherheitsgurt- und Fahrzeugspiegel-Einstellungen zulässt.
11. Schlüsselloses Straßenfahrzeug-Zugangssystem (10) nach einem der Ansprüche 5 bis 9,
bei dem der Hochfrequenzsender (16) und der Niederfrequenz-Sender/Empfänger (17) des
Transponders in verschiedenen Gehäusen untergebracht sind.
12. Verfahren für den schlüssellosen Fahrzeugzugang, das die folgenden Schritte umfasst:
Vorsehen eines fahrzeugintemen Kommunikationsprozessors (11) und eines entfernten,
miniaturisierten Transponders (15), wobei der Kommunikationsprozessor (11) einen Hochfrequenzempfänger
(12), einen Niederfrequenz-Sender/Empfänger (13) zum Übertragen von Niederfrequenzsignalen
und eine Steuereinheit (14) zum Lesen der durch den Niederfrequenz-Sender/Empfänger
(13) gesendeten und empfangenen Signale besitzt und der Transponder (15) einen Hochfrequenzsender
(16), der bei Empfang einer manuellen Stimulation des Transponders (15) ein Signal
zu dem Kommunikationsprozessor (11) sendet, und einen Niederfrequenz-Sender/Empfänger
(17), der die von dem Kommunikationsprozessor (11) empfangenen Niederfrequenzsignale
liest und an den Kommunikationsprozessor (11) eine verschlüsselte Antwort sendet,
besitzt;
Schaffen einer manuellen Stimulation, um den Transponder (15) dazu zu veranlassen,
in Reaktion auf die manuelle Stimulation ein HF-Signal an den Kommunikationsprozessor
(11) zu senden und ein Niederfrequenzsignal an den Niederfrequenz-Sender/Empfänger
(13) in dem Kommunikationsprozessor (11) zu senden;
anschließend in Reaktion auf wenigstens eines der Signale vom Transponder (15)
zu dem Kommunikationsprozessor (11) Senden eines Niederfrequenzsignals von dem Niederfrequenz-Sender/Empfänger
(13) in dem Kommunikationsprozessor (11) zu dem Sender/Empfänger (17) in dem Transponder
(15); und anschließend in Reaktion auf das Signal von dem Kommunikationsprozessor
(11) zu dem Transponder (15) Senden eines Signals von dem Transponder (15) zu dem
Kommunikationsprozessor (11).
13. Verfahren nach Anspruch 12, bei dem das Signal von dem Niederfrequenz-Sender/Empfänger
(13) in dem Kommunikationsprozessor (11) zu dem Niederfrequenz-Sender/Empfänger (17)
in dem Transponder (15) ein codiertes Signal ist.
1. Système sécurisé (10) d'entrée sans clé dans un véhicule routier, comprenant un processeur
de communication (11) situé dans le véhicule et un transpondeur distant (15), le processeur
de communication (11) et le transpondeur (15) communiquant selon des trajets parallèles,
un premier trajet étant une transmission à fréquence radio s'étendant du transpondeur
(15) au processeur de communication (11) et un second trajet étant une transmission
bidirectionnelle cryptée à basse fréquence entre le transpondeur (15) et le processeur
de communication (11), les premier et second trajets étant tous deux utilisés pour
l'établissement d'une communication entre le processeur de communication (11) situé
dans le véhicule et le transpondeur (15) en réponse à un stimulus manuel envoyé au
transpondeur distant (15).
2. Système sécurisé (10) d'entrée sans clé dans un véhicule routier selon la revendication
1, dans lequel la transmission à fréquence radio et la transmission à basse fréquence
sont comparées pour une authentification des données transmises.
3. Système sécurisé (10) d'entrée sans clé dans un véhicule routier selon la revendication
1, dans lequel la transmission à fréquence radio est une transmission bidirectionnelle
entre le transpondeur (15) et le processeur de communication (11).
4. Système sécurisé (10) d'entrée sans clé dans un véhicule routier selon la revendication
1, comprenant en outre : le processeur de communication (11) possédant un récepteur
à fréquence radio (12), un émetteur/récepteur à basse fréquence (13) et un contrôleur
(14) apte à lire les signaux émis et reçus par l'émetteur-récepteur à basse fréquence
(13); et
le transpondeur (15) possédant un émetteur à fréquence radio (16) pour émettre
un signal en direction du récepteur à fréquence radio (12) et du processeur de communication
(11) lors de la réception d'un stimulus manuel, et un émetteur-récepteur à basse fréquence
(17) pouvant lire des signaux reçus de la part du processeur de communication (11)
et émettre une réponse cryptée au processeur de communication (11).
5. Système (10) d'entrée sans clé dans un véhicule routier selon la revendication 4,
dans lequel le transpondeur (15) inclut en outre un circuit d'interface et une bobine
de couplage pour établir un transfert sans contact de données entre l'émetteur à fréquence
radio et l'émetteur-récepteur à basse fréquence.
6. Système (10) d'entrée sans clé dans un véhicule routier selon la revendication 4 ou
la revendication 5, dans lequel l'émetteur à fréquence radio (16) du transpondeur
(15) et le récepteur à fréquence radio (12) du processeur de communication (11) émettent
et reçoivent un signal possédant une fréquence de 433 mégahertz.
7. Système (10) d'entrée sans clé dans un véhicule routier selon l'une quelconque des
revendications 4 à 6, dans lequel les émetteurs/récepteurs à basse fréquence (17)
du transpondeur (15) et du processeur de communication (11) émettent et reçoivent
un signal possédant une fréquence de 134,2 kilohertz.
8. Système (10) d'entrée sans clé dans un véhicule routier selon la revendication 5,
dans lequel le stimulus manuel est l'actionnement manuel de l'un d'une pluralité de
boutons-poussoirs (18).
9. Système (10) d'entrée sans clé dans un véhicule routier selon l'une quelconque des
revendications 4 à 8, dans lequel le récepteur de fréquences radio (12) du processeur
de communication et l'émetteur à fréquence radio (16) du transpondeur sont des émetteurs/récepteurs
de fréquences radio aptes à réaliser des transmissions bidirectionnelles entre le
processeur de communication (11) et le transpondeur (15).
10. Système (10) d'entrée sans clé dans un véhicule routier selon l'une quelconque des
revendications 4 à 9, dans lequel le transpondeur (15) complète ou remplace la clé
de la portière du véhicule et la clé de contact, des signaux provenant du transpondeur
(15) étant reçus par le processeur de communication (11) qui, après réception et vérification
de codes d'accès, autorise le déverrouillage du véhicule et l'exécution de fonctions
d'initialisation associées au véhicule, comme par exemple des ajustement du siège,
de la courroie de siège et de rétroviseurs du véhicule.
11. Système (10) d'entrée sans clé dans un véhicule routier selon l'une quelconque des
revendications 5 à 9, dans lequel l'émetteur à fréquence radio (16) du transpondeur
et l'émetteur-récepteur à basse fréquence (17) sont situés dans des boîtiers séparés.
12. Procédé d'entrée sans clé dans un véhicule comprenant les étapes consistant à :
prévoir un processeur de communication (11) situé dans le véhicule et un transpondeur
miniaturisé (15) situé à distance, le processeur de communication (11) possédant un
récepteur à fréquence radio (12), un émetteur/récepteur à basse fréquence (13) pour
transmettre les signaux à basse fréquence et un contrôleur (14) pour lire les signaux
émis et reçus par l'émetteur/le récepteur à basse fréquence (13) et le transpondeur
(15) comportant un émetteur à fréquence radio (16) qui transmet un signal au processeur
de communication (11) lors de la réception d'un stimulus manuel dans ce dernier, et
un émetteur/récepteur à basse fréquence (17) pour lire des signaux à basse fréquence
reçus depuis le processeur de communication (11) et transmettant une réponse cryptée
au processeur de communication (11);
produire ledit stimulus manuel pour amener ledit transpondeur (15) à émettre un signal
RF en direction dudit processeur de communication (11) et envoyer un signal à basse
fréquence audit émetteur/récepteur à basse fréquence (13) dans ledit processeur de
communication (11) en réponse audit stimulus manuel;
puis envoyer un signal à basse fréquence depuis ledit émetteur/récepteur à basse fréquence
(13) dans ledit processeur de communication (11) audit émetteur/récepteur (17) dans
ledit transpondeur (15) en réponse à au moins l'un desdits signaux transmis dudit
transpondeur (15) audit processeur de communication (11), puis envoyer un signal dudit
transpondeur (15) audit processeur de communication (11) en réponse audit signal envoyé
par ledit processeur de communication (11 ) audit transpondeur (15).
13. Procédé selon la revendication 12, selon lequel ledit signal provenant dudit émetteur/récepteur
à basse fréquence (13) dans ledit processeur de communication (11) et aboutissant
audit émetteur/récepteur à basse fréquence (17) dans ledit transpondeur (15) est un
signal codé.