DE102011075434B4 - Method, device and system for determining a confidentiality of a received signal - Google Patents

Abstract

Method for determining an authenticity of a received signal, - in which a quality value of a received signal is determined, and - in which the received signal is recognized as an invalid received signal, if the quality value is above a threshold value.

Description

The invention relates to a method and a device for determining a confidentiality of a received signal. Furthermore, a system comprising at least one such device is proposed.

Radio signals are used in many ways, for example for data transmission or for position determination. However, a radio transmission does not have like physical transmission physical transmission lines, which can be protected accordingly against attacks or tampering. An attacker can send out radio signals and thus disrupt the radio transmission. Accordingly, cryptographic methods are used to protect the transmitted data, e.g. For example, the data can be encrypted or authenticated.

In a based on radio signals position determination, z. For example, in a satellite navigation system, the radio signal itself must be authentic, i. H. it must be the original signal emitted by a satellite and must not be delayed or falsified. Otherwise z. B. incorrect maturities and based on incorrect distances or incorrect positions can be determined. Therefore, it is important to be able to check or check the integrity of the radio signal.

To check the integrity of the radio signal, a so-called RF fingerprint (RF: Radio Frequency) of a transmitter is known. In this case, identification and / or authentication of the transmitter based on characteristic properties, such. B. its transient response, or by a location by means of a map of stations. Based on a characteristic of a particular location property of the radio signal, z. As a signal strength of the transmitter, the current location can be determined. The transmitter can be part of a base station, a radio system, z. B. a mobile radio system to be.

For integrity monitoring of a satellite navigation service, e.g. B. GPS (Global Positioning System) or GALILEO, carried out a monitoring of the integrity of ground stations, other satellites or aircraft using an integrated in the receiver integrity monitoring (known as "Receiver Autonomous Integrity Monitoring", short: RAIM (German: receiver autonomous integrity monitoring ), compare:
http://de.wikipedia.org/wiki/Receiver_Autonomous_Integrity_Monitoring). A GPS receiver recognizes this by means of an error detection, if radio signals emitted by at least 5 satellites are inconsistent. In addition, with at least 6 received satellite signals, it is possible to determine which of the satellite signals is erroneous (inconsistent). An identified erroneous signal can be disregarded in the position determination.

Also known is a position determination of a transmitter by an observation satellite. The observation satellite, which flies over a radio transmitter, locates it by means of a measured Doppler shift of the radio signal emitted by the transmitter.

Furthermore, it is known that characteristics of a radio transmission channel depend on the movement, position and distance of a transmitter and receiver as well as statistical, variable properties due to ionosphere and troposphere. These characteristics worsen the transmission; it is therefore attempted to compensate for such effects at the receiver to ensure trouble-free reception. In this regard, it is only checked whether the signal level complies with a required minimum threshold, ie the attenuation is not too high. Such testing is well known in the RAIM method to distinguish a direct line-of-sight signal from a satellite of known transmit power and known distance from a weaker signal.

The publication US 5 715 518 A describes a method in which a quality value of the received signal is measured. If the signal strength variation is above a threshold, that signal with its signal fingerprint will not be included in the reference signal fingerprint database. The decision as to whether the signal is recognized as invalid is based solely on an educated level of confidence that the received signal with its specific characteristic actually belongs to an inadmissible transmitter. If this confidence measure is greater than a threshold value, ie if the difference from the known reference fingerprints is sufficiently large, then the received signal is rejected.

The publication US 5,420,910 A describes a method and an apparatus for identifying a radio signal signature. Here, a radio signal signature description is generated for a received signal and compared with descriptions of known radio signal signatures in a database. The database may contain known "fraudulent" or known "valid" radio signal signatures.

The object of the invention is to avoid the disadvantages mentioned above and in particular to provide an improved solution for checking an authenticity of a received signal or a receiver.

This object is achieved according to the features of the independent claims. Further developments of the invention will become apparent from the dependent claims.

• – bei dem ein Qualitätswert eines Empfangssignals bestimmt wird und
• – bei dem das Empfangssignal als ungültiges Empfangssignal erkannt wird, wenn der Qualitätswert oberhalb eines Schwellwerts liegt.

To achieve the object, a method for determining an authenticity of a received signal is proposed,

• - In which a quality value of a received signal is determined and
• - In which the received signal is recognized as an invalid received signal when the quality value is above a threshold value.

Accordingly, the received signal can be recognized as a correct received signal if the quality value is below a threshold value.

For example, signals traveling a greater distance to the receiver experience more interference than signals transmitted closer to the receiver. By comparison with the threshold value, it can thus be determined whether the received signal is "too good", ie. H. whether the received signal z. From a source other than the expected correct source.

In particular, the received signal may be a wirelessly transmitted signal (eg a radio signal, an acoustic signal, a magnetically or electrostatically transmitted signal), a line-transmitted signal (eg an electrical signal, an optical signal) an optical fiber) or a signal transmitted mechanically by vibrations of a body. A radio signal may in particular be a satellite signal of a geostationary or a non-geostationary satellite or a signal of a stationary or mobile terrestrial radio transmitter.

Thus, the quality value preferably indicates a measure or a quality of the received signal. If the received signal is "too good", it is detected as invalid.

In this case, it is advantageous that a received signal recognized as "too good" can be used as an indication of an invalid received signal and can thus be deduced from a jamming transmitter.

For example, the received signal with regard to its quality, z. B. the signal-to-noise ratio are judged: If the quality value above the threshold value can be deduced an invalid received signal.

Also, any information about the received signal itself (eg., Receiving level, etc.) or from the received signal, eg. In the form of data transmitted with the received signal, to determine the quality value for the comparison with the threshold value and / or to determine additional information by means of which the decision can be made as to whether the received signal is a valid one or an invalid receive signal.

Under received signal z. B. understood as signals that are transmitted by a transmitter and received by a receiver. Furthermore, signals from multiple transmitters can also be received, processed and / or analyzed by the receiver.

It should be noted that the received signal can be recognized as invalid if it reaches or exceeds the (predetermined or predefinable) threshold. Depending on the definition, the case "equal to the threshold" may optionally be assigned to one of the two cases (i.e., the reaching of the threshold or the failure to reach the threshold) or treated as a separate case.

A further development is that a transmitter emitting the received signal is recognized as an illegal transmitter if at least one received signal recognized as invalid originates from it.

Thus, a jammer can be unmasked with high security, which provides a "too good" signal in terms of the quality value.

Due to the detected as invalid reception signal can be drawn back to a faulty, unauthenticated or fraudulently operated transmitter. For example, such a transmitter can thus be marked, so that received signals from this transmitter henceforth - z. B. up to a renewed successful authentication of this station - no longer classified as correct and z. B. discarded.

It is also an option that transmission channels of multiple stations are considered individually.

It is also possible in particular to specify permissible transmitters whose emitted signals may be taken into account exclusively or with different priority.

Another development is that the detected as invalid received signal is discarded or overwritten.

The received signal recognized as invalid can be discarded, for example, not processed, not processed and / or overwritten. So It is possible to make a preselection with respect to the receiver signal only for a receiver and z. B. make no further processing of the received signal. For example, can only be checked whether the received signal is a correct received signal and possibly classified as trustworthy and optionally forwarded to another station, which then z. B. performs the processing of the received signal.

Another option is for the receiver to make a statistical analysis based on the received signals or on a frequency of received signals recognized as correct or invalid. For example, the received signals can then at least partially, for. B. recognized as invalid received signals are discarded.

A received signal recognized as correct can be further processed. For example, it is possible to store such a received signal or to decode signals or data contained therein.

In particular, it is a development that the quality value is determined on the basis of a fingerprint.

The fingerprint is at least one property of the received signal. The fingerprint may in particular have a plurality of values characterizing the received signal or z. B. are assigned to the received signal for a certain period of time / were.

Thus, it is a development that the fingerprint comprises at least one channel property of a transmission channel of the received signal.

• – eine Dopplerverschiebung;
• – eine Phasendrehung;
• – eine Polarisation;
• – eine Dämpfung;
• – ein Rauschen.

Accordingly, it is a further development that the fingerprint comprises at least one of the following parameters or is based on one of the following effects:

• - a Doppler shift;
• A phase rotation;
• - a polarization;
• - a damping;
• - a noise.

• – mindestens einen Momentanwert,
• – mindestens eine abgeleitete Größe,
• – mindestens eine statistische Größe und/oder
• – mindestens einen zeitlichen Verlauf.

As part of an additional training, the fingerprint includes per parameter

• - at least one instantaneous value,
• At least one derived variable,
• - at least one statistical variable and / or
• - at least one time course.

A next development is that a similarity measure is determined based on a comparison of the fingerprint with at least one reference value.

One embodiment is that the received signal is recognized as an invalid received signal if the similarity measure has a predetermined minimum deviation.

An alternative embodiment is that the similarity measure is assigned to a trust value, by means of which it is determined whether and, if so, with what certainty the received signal is a valid or an invalid received signal.

For example, the value of the similarity measure can be assigned to the trusted value, so that it can be determined on the basis of the confidence value whether the received signal is the expected received signal and / or whether the received signal originates from the accepted transmitter. Accordingly, the confidence value can be a binary value realized z. B. by means of a flag that indicates whether the received signal is trusted or not. Alternatively, the confidence value may be a multi-level value, e.g. For example, {high, medium, low}, {0..255}, etc. Depending on the trusted value, further processing of the signal may be performed: for example, a signal is rejected or deemed less trustworthy if it is "too good". is.

In particular, the trusted value or an associated size, metric or representation may be output or displayed. This makes it possible for a user a measure of reliability or z. B. forgery-proof of the received signal.

A next embodiment is that the reference value comprises at least one expected channel property.

• – basierend auf mindestens einem fest gespeicherten Referenzwert, der insbesondere statisch oder anhand eines Vorhersagemodells zeit- und/oder ortsabhängig bestimmt wird oder wurde;
• – basierend auf mindestens einem Wert eines Online-Dienstes;
• – basierend auf mindestens einem zuvor als gültig erkannten Empfangssignal.

It is also an embodiment that the reference value is determined

• Based on at least one fixed reference value, which is or was determined to be time-dependent and / or location-dependent in particular statically or on the basis of a predictive model;
• - based on at least one value of an online service;
• - Based on at least one previously recognized as received signal.

In this case, a position and / or a movement speed of the transmitter and / or the receiver can be taken into account in order to determine a reference value dependent thereon. Furthermore, the current time, time of day, season, etc. can be taken into account in order to determine a dependent reference value.

A development consists in the fact that the received signal is recognized as valid if the quality value lies within a predetermined range.

For example, therefore, only such received signals are recognized as valid or detected and optionally further processed accordingly, the quality value is within a predetermined range, so z. B. may differ only by a predetermined range compared to at least one quality value of at least one previous received signal.

• – ein Qualitätswert eines Empfangssignals bestimmbar ist und
• – das Empfangssignal als ungültiges Empfangssignal erkennbar ist, wenn der Qualitätswert oberhalb eines Schwellwerts liegt.

To solve the problem, a device is also proposed for determining and / or checking an authenticity of a received signal with a processing unit which is set up such that

• - A quality value of a received signal can be determined and
• - The received signal is recognizable as an invalid received signal when the quality value is above a threshold value.

In particular, the processing unit may be a processor unit and / or an at least partially hardwired or logic circuit arrangement, which is set up, for example, such that the method can be carried out as described herein. Said processing unit may be or include any type of processor or computer or computer with correspondingly necessary peripherals (memory, input / output interfaces, input / output devices, etc.).

The above explanations regarding the method apply to the device accordingly. The device may be implemented in one component or distributed in several components. In particular, a part of the device can also be connected via a network interface (eg the Internet).

In particular, the device may be a station, preferably with a transmitter and / or a receiver. The station may be a mobile station or a landline station. In particular, the station may be part of a radio network and / or a circuit-based network.

In this case, it is an embodiment that the processing device is set up to reject the received signal if the received signal was recognized as an invalid received signal. It is also possible for the processing device to process the received signal if the received signal was recognized as an invalid received signal.

The above object is also achieved by means of a system, in particular a radio system comprising at least one of the devices or stations described herein.

Embodiments of the invention are illustrated and explained below with reference to the drawings.

Show it:

1 schematically components of a scenario with a plurality of transmitting stations, sources of interference and a receiving station,

2 schematically components of a receiver of such a receiving station and

3 a flowchart for a procedure for checking a confidence value of a received signal.

Properties of a radio transmission channel depend, for example, on the movement, position and distance of a transmitter and receiver as well as statistical, variable properties of ionosphere and troposphere.

For example, transmission channel characteristics (also referred to as channel characteristics) can be measured to obtain a fingerprint of a Radio Channel Fingerprint radio channel. Such a fingerprint of the radio channel can be compared with a reference value or with at least one expected channel property. Such a comparison determines a similarity measure indicating the match between the fingerprint and the reference value. With sufficient similarity, that is, when the similarity measure reaches or exceeds a predetermined threshold value for the similarity, the received signal can be accepted as correctly accepted. Depending on the similarity, a confidence value can be assigned to the signal.

In this case, the channel properties are not treated as an interference to be compensated, but the received signal should be disturbed in an expected way in order to be recognized as a valid signal. If the received signal thus exceeds a predetermined quality value, it is recognized as invalid.

• – eine Dopplerverschiebung, z. B. ein Verlauf einer Dopplerverschiebung beim Überfliegen eines Satelliten mit einer bekannter Position);
• – eine Phasendrehung (bedingt z. B. durch die Ionosphäre bzw. die Troposphäre);
• – eine Polarisation;
• – eine Dämpfung;
• – ein Rauschen.

For example, the channel properties may include at least one of the following parameters:

• A Doppler shift, e.g. A course of a Doppler shift while flying over a satellite with a known position);
• - A phase rotation (due, for example, by the ionosphere or the troposphere);
• - a polarization;
• - a damping;
• - a noise.

• – ein Momentanwert,
• – eine abgeleitete statistische Größen (z. B. eine direkt oder nach einer Signalverarbeitung, z. B. durch ein Filter, bestimmbare Größe) und/oder
• – ein zeitlicher Verlauf

bestimmt bzw. analysiert werden.For all these parameters can

• An instantaneous value,
• A derived statistical quantities (eg a variable which can be determined directly or after a signal processing, eg by a filter) and / or
• - a time course

be determined or analyzed.

From this, features or criteria can be extracted, wherein at least one of the criteria can represent the fingerprint. The fingerprint may contain an expected reference value, e.g. B. compared to a reference fingerprint and thus a similarity measure can be determined. Thus, it is also checked whether the expected degradations of the channel actually exist.

The value of the similarity measure can be assigned to a trusted value, that is to say a value which indicates whether the received signal is the expected received signal and / or whether the received signal originates from the accepted transmitter. Accordingly, the confidence value can be a binary value realized z. By means of a flag indicating that the received signal is trustworthy or not. Alternatively, the confidence value may be a multi-level value, e.g. Eg {high, medium, low}, {0..255}, a floating-point number in the value range of -1 to +1 or in the value range of 0 to +1, etc. Depending on the confidence value, the further processing of the signal can be carried out For example, a signal is rejected or considered less trustworthy if it is too good.

• – fest gespeichert (statisch oder anhand eines Vorhersagemodells zeit- und/oder ortsabhängig bestimmt);
• – von einem Online-Dienst (z. B. einem Web-Service) über ein Datennetzwerk abfragbar (z. B. ein Online Funkwetter-Dienst);
• – ermittelt durch bekannte Sendesignale (z. B. bei Signalen von zwei nahen Sendern könnten diese ähnliche Fingerabdrücke aufweisen).

The reference information can be provided in different ways:

• - permanently stored (static or determined based on a predictive model time and / or location-dependent);
• - interrogatable by an online service (eg, a web service) over a data network (eg, an online wireless weather service);
• - detected by known transmit signals (eg for signals from two nearby transmitters, these could have similar fingerprints).

The transmission signals mentioned may be signals from multiple satellites or multiple signals from a satellite. In particular, when signals are protected by another method (eg, a cryptographic method in which monitoring of integrity is performed by monitoring stations), these signals can be used to derive (trusted) reference fingerprints for the current channel characteristics. A second radio signal which is not suitably cryptographically protected can then be checked by means of the solution presented here, i. H. it can be determined whether the fingerprint of the second radio signal is sufficiently similar to the reference fingerprint (eg, the similarity measure does not exceed a predetermined deviation).

Radio weather is generally understood to mean propagation conditions for radio communication. The wireless weather is z. B. frequency dependent and / or location-dependent and is subject to numerous influences, eg. B. time of day, season, sunspot cycle.

The advantage of this approach is that a spurious or invalid signal originating from an invalid transmitter (also referred to as a jammer or jammer) can be detected with high probability. So the jammer transmits its interference signal over other transmission paths than the correct (original) transmitter. Associated with this, other channel characteristics and other fingerprints emerge that are likely to be invalidated even in a larger area covered by the jammer.

Thus, if the jammer is located elsewhere than the transmitter to be disturbed (original transmitter), it is very likely that different fingerprints will result in the jammer being detected as an invalid transmitter. This is especially true if the original transmitter is in an exposed location, eg. B. on a mountain or in orbit. In the case of several observation stations for observing a satellite signal, in particular the Doppler shift and its progression on the basis of the jamming transmitter can hardly be reproduced such that it satisfies the course of the original signal at different, spatially remote measuring points.

1 shows an environment with a hilly terrain 101 , where on a mountain a transmitter 108 and in the valley a receiver 102 is arranged. Furthermore, as a transmitter satellites 105 . 106 and 107 over the terrain 101 shown. Also shows 1 a jammer 104 in the valley near the receiver 102 and a jammer 103 which is designed as a satellite or other flying unit.

Without the two jammers 103 and 104 send the channels 108 . 105 to 107 Radio signals off, that of the receiver 102 be received and decoded.

The two jammers 103 and 104 in 1 each send an interference signal, z. B. an additional signal on another frequency or on another (additional) channel or a signal which is a signal of one of the transmitter 108 . 105 to 107 covered.

The recipient 102 analyzes the characteristics of the received signals in order to be able to distinguish between original signals and interfering signals or simulated signals.

2 shows a basic structure of the receiver 102 , A received signal 208 is through an antenna 201 received and by means of a high-frequency processing unit 202 (including, for example, filters and amplifiers). In a frequency conversion 203 The signal is converted by mixing (multiplying) with one from an oscillator 204 provided signal and filtered by filtering to a lower intermediate frequency. Subsequently, the signal is passed through an analogue to digital converter 205 converted into a digital signal (possibly split into two sub-signals, which are acted upon by a signal phase-shifted by 90 °, the so-called in-phase component I and the quadrature component Q). This is followed by digital signal processing in one component 206 (typically embodied as an integrated circuit (eg, a Field Programmable Gate Array (FPGA), an application-specific integrated circuit (ASIC), or a Digital Signal Processor (DSP)) in which the signal is decoded (including, for example, digital filtering, channel equalization, correlation, demodulation, error correction) .The decoded signal is sent to a processor 209 forwarded, which processes the decoded data. For example, the processor 209 perform a determination of position, time, speed in a satellite navigation system receiver or processing of control commands or payload. The results of processing the processor 209 be on a display 207 shown. In addition, controls can be provided.

The solution proposed here may, for example, (at least in part) in the component 206 be implemented. The processor 209 can from the component 206 z. For example, a signal may be provided that indicates or includes the confidence value of the received signal. The processor 209 can store reference data (transmission channel fingerprint) and the component 206 provide. In another variant, the component extracts 206 a transmission channel fingerprint information and presents it to the processor 209 ready. The examination of an extracted transmission channel fingerprint can then be done in the processor in the solution proposed here 209 be realized.

3 shows a schematic flow diagram with steps of a method for determining an authenticity of a received signal.

In one step 301 a signal is received and in one step 302 a fingerprint of the received signal is determined. For this purpose, channel-dependent or transmission-dependent properties and / or parameters of the received signal can be determined. In one step 303 For example, a similarity measure is determined by comparing the fingerprint with a (eg, predetermined) reference fingerprint. In one step 304 a comparison is made as to whether the determined similarity measure exceeds (reaches or exceeds) a predetermined threshold. If this is the case, ie if the received signal has the expected interference, then it becomes a step 306 branches, the received signal is decoded and in a subsequent step 307 the decoded received signal is processed or processed.

Will in the query step 304 If it is determined that the condition is not met, ie the similarity measure indicates that the determined fingerprint of the received signal and the reference fingerprint do not match sufficiently, then it becomes a step 305 branches and the received signal is discarded. In this case, therefore, the fingerprint of the received signal is worse than or better than the reference fingerprint more than the allowable threshold value and is therefore classified as invalid. In the present example, the received signal classified as invalid is discarded, alternatively another type of processing or no processing is possible.

An alternative to the in 3 variant shown is that the received signal is not dependent on the in step 303 the similarity measure determined is further processed (or possibly discarded), but it can (if necessary also in addition) a confidence value be determined. This can z. B. a user can be displayed to inform him whether the received signal is a plausible valid signal.

Another variant is that the receiver receives several signals in parallel (eg in a satellite navigation system). Preferably, only those received signals are processed whose similarity measure exceeds the predetermined threshold. It is also possible that those signals with the highest similarity measure further processed, for. B. decoded to be a reference value z. B. to determine the position and time. The further signals with a lower similarity measure are then processed only if they are consistent (ie within a permissible range) with the already determined position and time.

With several received signals, those received signals for which a higher confidence value has been determined can be weighted more heavily.

This can be z. For example, such measurements may be weighted more heavily than measurements based on less trusted radio signals when adjusting the estimates on higher trusted radio signals. A satellite signal receiver may receive a plurality of satellite receive signals to determine position, time and speed, and determine a distance (a so-called "pseudo-range") from the runtime estimate of a satellite signal, respectively. By estimating the distance to several satellites whose position is known in orbit, the position, velocity and time, the so-called "PVT information" (P: Position, V: Velocity, T: Time) can be determined. It can be z. B. a Kalmann filter can be used. Input variables are the determined distance estimates for the individual satellites. It is possible to consider a respective statistical uncertainty (eg variance and / or standard deviation) of the multiple input variables ("pseudo-ranges") in the estimation of the PVT information, i. H. those inputs with low statistical uncertainty are more weighted in the PVT estimate than others with greater statistical uncertainty.

Now it is possible to increase or decrease the value of the statistical uncertainty used depending on the specific confidence measure of a received signal. If z. For example, if a confidence measure is used with the discrete levels "high", "medium", "low", the value for the static uncertainty of a signal can remain unchanged for "medium", divided by a factor of 2 for "high", and multiplied by a factor of 2 when "low". Accordingly, other factors, such. "3" or "5" or "1.5".

Claims (15)

Method for determining an authenticity of a received signal, - In which a quality value of a received signal is determined and - In which the received signal is recognized as an invalid received signal when the quality value is above a threshold value. Method according to Claim 1, in which a transmitter emitting the received signal is recognized as an inadmissible transmitter if at least one received signal, which is recognized as invalid, originates from said receiver. Method according to one of Claims 1 or 2, in which the received signal recognized as invalid is rejected or overwritten. Method according to Claim 1 or 2, in which the quality value is determined on the basis of a fingerprint. The method of claim 4, wherein the fingerprint comprises at least one channel characteristic of a transmission channel of the received signal. Method according to one of Claims 4 or 5, in which the fingerprint comprises at least one of the following parameters or is based on one of the following effects: - a Doppler shift; A phase rotation; - a polarization; - a damping; - a noise. Method according to one of claims 4 to 6, wherein the fingerprint per parameter - at least one instantaneous value, At least one derived variable, - at least one statistical variable and / or - at least one time course includes. Method according to one of claims 4 to 7, wherein a similarity measure is determined based on a comparison of the fingerprint with at least one reference value. The method of claim 8, wherein the received signal is recognized as an invalid received signal when the similarity measure has a predetermined minimum deviation. Method according to one of Claims 8 or 9, in which the similarity measure is assigned to a trust value, by means of which it is determined whether and, if so, with what certainty the received signal is a valid or an invalid received signal. Method according to one of claims 8 to 10, wherein the reference value comprises at least one expected channel property. Method according to one of claims 8 to 11, wherein the reference value is determined - based on at least one permanently stored reference value, which is determined in particular statically or on the basis of a predictive model time and / or location-dependent; - based on at least one value of an online service; - Based on at least one previously recognized as received signal. Method according to one of the preceding claims, in which the received signal is recognized as valid if the quality value is within a predetermined range. Contraption ( 102 ) for determining a confidentiality of a received signal with a processing unit which is set up in such a way that - a quality value of a received signal can be determined and - the received signal is recognizable as an invalid received signal if the quality value is above a threshold value. System with at least one device according to claim 14.

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