The invention relates to an access control system for an object, in particular
Motor vehicle and a method for operating an access control system,
with the permission for the
Access or for
the use of an object is checked.
State of the art
Access authorization control systems
are increasingly used in motor vehicles and replace there
mechanical locking systems
through electronic locking systems,
which offer improved comfort. Depending on whether the driver
an access function manually an action must be triggered, or this
is automatically done by the system, one distinguishes basically active
of passive access control systems. Both systems consist of
one or more base units mounted in the vehicle,
and one or more portable radio keys authorizing
Car users carried
become. A radio key,
also as a code transmitter, identification transmitter, ID transmitter, or ID tag
the electronic code that a person uses with the code transmitter
To get access to the object, or to use this. The identification process
a radio key
a radio dialogue handled in which by a transmitting and receiving device
queried the base station from the motor vehicle from the code of a remote control key
Access authorization control systems, so-called passive start and
Entry Systems (PASE), try by continually polling a coverage area
with a remote key too
communicate. Has a base station a communication to a
Code transmitter successfully recorded, the correct code of the remote key is detected
and a corresponding access action triggered automatically. This action can be, for example
unlock the central locking of the car. The system
But can also be designed so that the central locking only
Conditions, such as falling below a minimum distance to
Car or a press
the door handle,
Passive conditional access control system can but in abusive
become. For example, has the authorized user of his
Removed motor vehicle, so can an unauthorized person by a
Attack on the radio channel Access to the remote from the authorized user
Obtain motor vehicle: In a so-called full-duplex attack, im
following also briefly VDA attack, are sent by attackers and
Receiving device respectively in the vicinity of the code transmitter and the motor vehicle
positioned. The encoder is transmitted by a data transfer
the transmitting and receiving facilities queried and the code of
Radio key over the
Radio channel to the car transferred.
An access control system that covers the abusive extended radio link
does not recognize, releases the object, although the authorized one
Vehicle driver not in the detection range of the transmitting and receiving device
of the motor vehicle is located. The attack also goes unnoticed
held by the driver.
to prevent such abuse and one possible
to ensure high security
it is necessary, in addition to the verification of the key code,
at least also to check the distance between remote key and base station and
possibly also to transfer the data cryptically to abusive
To hamper intervention in communication.
In the DE 199 57 536 A1
discloses an anti-theft system for motor vehicles, in which a transmitting and receiving unit emits a broadband modulated radar signal and waits for echo signals of a code transmitter. If a code transmitter is within the detection range of the system, it receives this interrogation signal and in turn sends back an additionally modulated and coded response signal. An evaluation unit in the base station in the vehicle analyzes all received response signals not only with regard to the authorization of the code transmitter, but also with regard to the distance between the code transmitter and the motor vehicle. In this anti-theft system, as in the case of the DE 100 12 113 A1
known access control system, the distance measured value is not obtained by an evaluation of ramp pairs.
From the documents DE 100 26 032 A1
and DE 199 63 625 A1
In each case, an adaptive cruise control system is known in which an FMCW measurement signal is evaluated, which is formed of frequency ramps with different pitch.
From the DE 199 38 898 C1
For example, an access control system is known in which a high frequency carrier signal having a low frequency, ramped function is frequency modulated.
A distance-sensitive radio remote control system for motor vehicles is also from the DE 100 63 252 A1
known. Also with this keyless entry system the use of the object becomes after a dialogue between a stationary and a unlocked a mobile transceiver. During communication, range-dependent different categories of commands are used. By a first category of commands, the operation of a window or a sliding roof of the motor vehicle is initially possible from a distance. Only when the user is with the entrained transceiver in the immediate vicinity of the motor vehicle, a second category of commands allows the operation of the central lock and the steering lock. Triggering the commands requires an active action of the driver.
From the DE 199 57 557 A1
is a passive identification system for motor vehicles is known in which the encoder has a surface acoustic wave element for storing the code information. So that the code signal can not be intercepted and reproduced without authorization, the identification transmitter has two different modulators, which reflect the code signal partly modulated. The modulators influence the signal in such a way that, on the one hand, the identification and, on the other hand, a distance measurement is possible by evaluating individual reflections with regard to the signal propagation times. This makes unauthorized tapping or manipulation of the dialogue more difficult and high security against unauthorized use achieved.
A comfortable passive access control system, where usage is gradually released depending on the position of the code transmitter, is in DE 100 64 141 A1
disclosed. The position determination is similar to the well-known from the radar frequency-modulated continuous wave (FMCW) method. If the response signal of the code transmitter turns out to be justified, different control commands are used depending on the position of the code transmitter, which switch different functional levels for the use of the car. The car can thus be customized to the driver. Only when this is in the immediate vicinity of the motor vehicle, the code transmitter is verified in the vicinity of the vehicle and released in accordance with the central locking. The near zone is detected by proximity sensors on the motor vehicle.
Motor vehicles are exposed to harsh operating conditions, one is
endeavoring to proximity sensors
to refrain and by a radar distance detection, not only
the long-range, but also the safety-critical short-range
cover. Here are also small signals, as for example
Distances and disturbance
and body shadowing
occur in the radio channel, so can be processed that the actual
Distance between the code transmitter and the interrogation station and thus a VDA attack are fended off
can. In addition, an access control system for a motor vehicle
not only safe and reliable over one
long operating period work, but also with justifiable
Effort must be producible.
Presentation of the invention
The invention is to provide an access control system which
even in the vicinity of an object, the actual distance between the encoder
and interrogation station recognizes with sufficient accuracy and with
reasonable effort can be produced.
Task is according to the invention in a
Access control system by the features of claim 1 and
in a method by the features of claim 8 solved.
The access control system according to the invention comprises
- A transmitting device in a polling station, which is assigned to the object and transmits a high-frequency interrogation signal which contains frequency-modulated ramp pairs, each consisting of a rising and a falling frequency ramp, wherein the slope of all frequency ramps is chosen to be equal,
- A code transmitter with a transponder which receives the interrogation signal in a detection range at a distance to the interrogation station, sends it back with a subcarrier and a code information item as a response signal,
- • A receiving device in the interrogation station, which receives the response signal and determines the distance between the object and code transmitter in an evaluation unit of pairs of ramps of the response signal and in the case of a match of the received code information with a stored code information in the interrogation station, the use of the object in dependence predeterminable Thresholds releases.
The invention proposes FMCW radar-based remote identification, with which both a VDA attack can be averted and also faulty response signals can be processed with sufficient accuracy for the application. This is done by not only in each case an increasing and decreasing frequency ramp is used for distance measurement, but couples of such frequency ramps are time sequentially traversed. The duration of a ramp pair is chosen so that the signals between the pairs are no longer correlated. Since the measurement signal is determined by integration over the duration of several pairs of ramps, the signal-to-noise ratio (SNR) improves. As a result, a safe and accurate distance measurement is possible even in the case of shading the signal from the encoder. The consequence of this is that proximity sensors for close range omitted. In the integrating measuring method according to the invention, the signal values are correlated, that is, the signal voltages add up. The noise values, on the other hand, are uncorrelated and therefore only add up in terms of performance. Thus, the signal-to-noise ratio is increased by about 10 logN, where N indicates the number of pairs used for the evaluation. By evaluating N pairs of frequency ramps, although the measurement duration increases by a factor of N, but this is not disturbing in the case of distance determination in the context of a passive access control system for a motor vehicle.
according to the invention, integrating
Measuring method allows
it that the distance between encoder and base unit even then
sufficiently determinable, if a comparatively large radio link is bridged
must, or the radio link is disturbed by shading and that
Receive interrogation signal with only low field strength in the base station
can be. An access function is only released if
the code transmitter actually
within an adjustable position range. A
Radio link becomes reliable
recognized and the unlocking of the vehicle from a distance denied.
an interrogation signal consisting of consecutive, monotonically increasing ones
and monotonically decreasing frequency ramps with substantially linear
Slope is composed, the difference frequency can be easy
be determined after a mixture and filtering and is direct
proportional to the distance between the code transmitter and the base station. At this
the technical complexity in the realization is particularly low.
It is also favorable to limit the measuring time if about 30 frequency ramps are evaluated
become. In a development according to the invention
The invention is therefore intended that the duration of a ramp pair
1 μs and
less than 100 milliseconds is selected.
Duration of greater than
1 μs is
the effort in the technical implementation, for example
is determined by settling times of filters. The selected limit value represents
sure that's for
simple evaluation method assumed temporal stationarity of the mobile radio channel
is still given in typical application scenarios.
It is particularly advantageous if the evaluation unit is set up in this way
is that in determining the distance time in succession
lying pairs of frequency ramps are used.
the use of pairs of frequency ramps coming from an up-ramp (up-chirp)
and a down ramp
can a frequency deviation of the subcarrier modulation signal (response signal)
recognized in the key
and eliminated. The timely staggering of the ramp pairs
again an approximate
The method according to the invention comprises the following steps:
- Transmitting at least one high-frequency interrogation signal by a transmitting and receiving device of an interrogation station assigned to an object, wherein the at least one interrogation signal contains frequency-modulated ramp pairs, each consisting of a rising and a falling frequency ramp, wherein the slope of all frequency ramps is chosen to be equal;
- Coded and modulated return of a response signal by a transponder in a portable code transmitter, if it has previously received an interrogation signal,
- Determining the distance between the interrogation station and code transmitter from ramp pairs of the response signal after a demodulation and decoding of the response signal in an evaluation unit.
On the one hand, this procedure can be used at close range to the actual one
Distance detected and a VDA attack are fended off as an abusive
the channel length
can be detected. Access to the car is therefore only released
if the determined distance signal is set below an adjustable
Threshold (in the near range below 2 m) are. On the other hand, this allows
Procedure also disturbed
Signals, as with large
Distances (long range 10 m to 40 m) and shading in
Channel occur, evaluate with sufficient accuracy.
Advantages of the method are the subject of dependent method claims.
Brief description of the drawing
The invention is described below with reference to the drawings
further clarified. Show it:
1 An embodiment of the access control system according to the invention in a block diagram,
2 a diagram of a first interrogation signal with associated response signal as a function of time,
3 the associated frequency spectrum to the in 2 represented signals,
4 a diagram of a second interrogation signal with associated response signal as a function of time.
Embodiment of the invention
1 shows an access control system 1 that from a query unit or base station 20 and a coder 30 consists. The base station 20 is placed on a car, the code transmitter 30 is designed as a portable radio key and is carried by the driver. The control of access to the car via a data dialogue, in a radio channel 4 between the base station 20 and the identification transmitter 30 is handled. This data exchange has the goal, on the one hand the radio key 30 On the other hand, to detect its actual position in the vicinity of the vehicle in order to prevent a VDA attack. If the system can identify the encoder for a legitimate use, and this encoder is also recognized as within a predetermined position range, the control system gives 1 Access functions to the car free. Otherwise, access to the car is denied.
The base station 20 includes a transmitter signal source 21 which generates a signal Sig 1 and via the transmitting antenna 22 as a query signal 2 the radiated. In the radio channel 4 reaches the interrogation signal 2 after the signal delay, the receiving antenna 32 of the code transmitter 30 , That at the antenna 32 received signal Sig 2 becomes a modulator 31 supplied and with a coded subcarrier signal of a carrier generator 34 modulated. The result of this modulation is the signal Sig 3, that of a transmitting antenna 33 of the code transmitter 30 is supplied. From the transmitting antenna 33 becomes the response signal 3 emitted after the signal propagation time in the radio channel 4 the antenna 23 the base station 20 reached. Together with that of the transmission source (S1) 21 through a directional coupler or power divider 25 branched signal Sig 1 is the through the antenna 23 received Sig 4 of an evaluation unit (AE) 24 fed. In the evaluation unit (AE) 24 after a frequency mixing and filtering by known methods of LMF-FMCW radar signal processing technology, the determination of a distance signal d, which is the actual distance between the base station 20 and radio key 30 equivalent.
Signal processing in the evaluation unit (AE) 24 can be done in analog and digital form, it can be realized by hardware, firmware or software. By using a circulator or a quasi-circulator, for example a directional coupler, the base station can 20 or the code transmitter 30 also have only a single antenna.
The code transmitter 30 can be designed as a passive reflector or as an active reflector. In the case of a passive reflector, the code information can be modulated, for example by changing the impedance of a load (passive backscatter). In the case of a code transmitter which operates as an active reflector, the modulated signal is additionally amplified, ie actively amplified by an amplifier in front of the transmitting antenna. In both embodiments, the data source of the code information may be different. The data source can be for example a memory in the radio key. The code information can also be the result of a cryptic data exchange between the code transmitter and the base station. It is also possible that the code information is stored in a surface acoustic wave element in the code transmitter. For the present invention, however, the manner in which the coding is performed technically is not essential; what is decisive is rather that the interrogation signal is coded in the code transmitter and is radiated back as a modulated coded response signal to the transmitting and receiving device of the base station.
Regardless of whether the transponder works as an active or passive reflector, it usually contains a backup battery. The individual function blocks in 1 can be realized by hardware or by software.
In 2 is a first frequency modulated interrogation signal 2 represented as a function of time. In a preferred embodiment of the invention, the interrogation signal 2 composed of monotonically increasing frequency ramps. The ramp pairs are identified by the reference symbols R1 and R2. The distance information is in the phase or frequency difference Δφ or Δf between the signal 2 and the signal 3 contain. Will this interrogation signal 2 from the antenna 22 the base station 20 sent out, so it reaches after the signal delay in the radio channel 4 the antenna 32 in the code transmitter 30 , The code transmitter 30 sends a response signal with negligible delay 3 to the base station 20 , This response signal is in the case of a passive reflector, an echo signal, which after the signal propagation time in the radio channel of the antenna 24 the base station 20 Will be received. Opposite the original query signal 1 this response signal is out of phase. It has a difference frequency to the interrogation signal. As known from the FMCW (Frequency Modulated Continuous Wave) radar technique, in a so-called linear frequency modulation (LFM), the distance between an object and a polling station can be determined from a measurement of this frequency difference. In contrast to the pulsed radar, the FMCW radar becomes a continuum ierliches frequency modulated interrogation signal sent out. The distance measurement takes place in a linear frequency modulation (LFM) indirectly via a difference frequency f diff . This difference frequency can be determined by comparison, by at a given time the received response signal 2 with the simultaneous function value of the originally transmitted interrogation signal 3 is compared. The measure of the difference frequency is a measure of how long actually the distance covered radio link in the radio channel 4 is. In a conditional access control system, this measure of the difference frequency is used to detect and fend off an attack on the radio channel: Used by the base station 20 the code of a wireless key is recognized as authentic, but the actual distance is outside a predetermined threshold, then there is no authorized driver in the vicinity of the car and access is denied.
becomes a broadband modulated radar signal with a bandwidth
60 MHz, more preferably with a center frequency in the range
of 2.5 GHz, 5.8 GHz and 25 GHz. For the purposes of the invention
broadband, that an oscillator frequency within a comparatively
Frequency band is varied when sending or receiving.
As in the presentation of 2 shown is the response signal 3 noisy. As a result, a distance measurement based on known methods of LMF-FMCW radar technology would be faulty. In contrast, the pairwise evaluation of N frequency ramps according to the invention effects an integration which makes it possible to determine in the frequency spectrum ( 3 ) the distance can be shown sharper.
In 3 In a spectral representation, the amplitude A of the echo signals over the frequency f is shown. The response signal is mixed with a subcarrier f HT and contains the code information of the radio key. By mixing with the subcarrier, the response signal of reflections 50 the environment can be distinguished. In the case of a backscatter transponder, the signal travels back and forth between the interrogation station and the code transmitter. The SNR ratio decreases with the fourth power of the distance. Because of the freefield attenuation, which increases strongly with frequency, the reflected GHz signal is weak at long distances. However, the integrating measurement method increases the SNR ratio by 10 logN. As a result, even very weak signals can be evaluated. This is qualitatively in 3 represented, in which the maxima are shown pronounced in the spectrum. The difference frequency f DIFF and thus the actual distance between the code transmitter and the base station can be determined with sufficient accuracy. This is particularly advantageous if the response signal is subject to noise due to interference in the radio channel or due to a long transmission distance (10 m to 40 m).
In 4 is shown as a diagram a second interrogation signal with associated response signal as a function of time. The signal path has gaps between the ramp pairs R1 * and R2 *.
in the ramp can be due
be used advantageously in the technical realization of the method.
For example, at this time in the case of realization of the
Method by means of digital signal processing one after the analog-digital converter befindlicher
Latch (FIFO) are read. Advantageously
the duration of the gap clearly
chosen smaller than the duration of a ramp.
The exact distance measurement is a precise zone formation in the long range possible. Approaches
a vehicle driver his vehicle, so may in an outer detection zone
Falling below a threshold limit, for example manually on
Remote control key,
the interior lighting of the motor vehicle is turned on,
what the finding of the motor vehicle in the dark or in a
Parking deck relieved. After identification, the vehicle can
individually to the needs
be configured by the driver. For example, the
Adjustment of the driver's seat, the air conditioner, the outside mirrors,
the gearbox of the transmission as well as the preferred radio stations,
as well as personal
be preset to the handlebars. The automatic unlocking
facilitates boarding, especially if by the driver
a load is being carried and his hands are not free to do that
Lock open by a mechanical key. The system can be designed that way
be that the engine without ignition key and
can be started by pressing a button. For increased safety requirements
can also be provided, the start of another condition,
For example, depending on a biometric authentication too
do. In this way, the person of the driver is clearly identified.
reversed order allows
the system of course
a secure automatic locking of the vehicle when the
Vehicle driver with his remote control key away from the vehicle.
Of course, the threshold values can also be set dynamically, so that from Depending on whether the handlebar moves towards his vehicle, or moves away from it, the position ranges are specified differently.
portable identification transmitter can be executed in key or card form.
It fits comfortably in the jacket pocket of a driver and can
Functions such as functions for manual operation of a
Radio device for
a garage door, be formed.
described radio-based access control system is by no means up
the application is limited in motor vehicles, but also on building, computer
or other electronic systems or devices applicable.