Control device and method for a motor vehicle access or positioning system

Abstract

The invention relates to a control device for a motor vehicle access or positioning system and to a method for operating a motor vehicle access or positioning system, having the following steps: identifying a received signal which travels along the strongest signal path, i.e. the peak path, from a transmitter to a receiver of the control device as a peak path signal; determining a time of flight, ToF, of the peak path signal; determining a time interval, δ, from the time of flight of the peak path signal; determining a reliability threshold, T, of a first path search which depends on δ; performing the first path search at δ taking account of the threshold.

Description

Technical Field

[0001] This invention relates to a motor vehicle access and location system. In particular, the invention relates to a control device for a motor vehicle access or location system, a vehicle having such a control device, an access or location system having such a control device and a radio key, a method for operating a motor vehicle access or location system, a program element, and a computer-readable medium. Background Technology

[0002] In access or location systems, wireless transmission technologies can be applied, for example, in association with so-called radio keys. Various methods can be employed to prevent misuse, allowing for sufficiently secure assessments of whether appropriate use is being conducted. Summary of the Invention

[0003] The purpose of this invention is to further develop access or location systems.

[0004] This objective is achieved by means of a control device for a motor vehicle access or location system, a vehicle, an access or location system, a method for operating a motor vehicle access or location system, a computer program product, and a computer-readable medium. Further improvements to the invention will become apparent from the following description of other embodiments and examples.

[0005] A first aspect of the invention relates to a control device, particularly for a motor vehicle access or positioning system, configured to identify a received signal traveling along the strongest signal path (the so-called peak path) from a transmitter (e.g., a radio key or mobile phone) to a receiver (e.g., the antenna system of a motor vehicle). This signal is then considered a so-called peak path signal.

[0006] Furthermore, the control device is configured to determine the time-of-flight (ToF) of the peak path signal. Additionally, if relevant, a time interval δ is determined based on the specified time-of-flight of the peak path signal. Then, a threshold T for the reliability of the first path search, depending on δ, is determined. The "reliability" of the first path search corresponds to the threshold created in the first path search. This may involve, if relevant, determining the similarity between the preamble of the received signal and the expected preamble based on the signal-to-noise ratio of the received signal.

[0007] Then, taking into account the threshold, the first path search is performed at δ.

[0008] According to one embodiment, δ can be the maximum permissible time interval δ max In this case, the presence of the first path signal is not detected by checking for a longer time difference.

[0009] According to one embodiment, when the threshold T is exceeded, the signal detected in the first path search is classified as a so-called first path signal. The first path search then ends because the first path signal has been found and identified.

[0010] According to another embodiment, the control device is configured to determine that no first path signal is detected by δ, i.e., when the threshold T is not exceeded. Then, a new threshold T is determined, depending on the reliability of the updated first path search, based on the time interval δ-Δ or δ+Δ between the increase and decrease of the flight time with respect to the peak path signal. 新 Then, taking into account the new threshold, the first path search is performed again at time intervals δ-Δ or δ+Δ that are increasing or decreasing.

[0011] If the first path search also fails, the time interval for updating the first path search can be increased or decreased again, and a new threshold can then be determined. These steps can be performed until a first path signal is detected. Then the first path search ends.

[0012] According to one embodiment, if the time interval with the peak path signal is reduced, the corresponding new threshold T is... 新 It is less than or equal to the original threshold T, and less than or equal to the corresponding previously determined threshold.

[0013] Therefore, the relationship between the time interval of the current first path search and the required "safety margin" is described by a monotonically decreasing curve.

[0014] According to another embodiment, the control device is configured to adjust the threshold T and / or the new threshold T based on function, installation location, positioning, and / or time. 新 Adjustments will be made.

[0015] On the other hand, it relates to a vehicle having the control devices described above and below.

[0016] On the other hand, it relates to an access or location system having control devices as described above and below, and a radio key.

[0017] On the other hand, a method for operating a motor vehicle access or positioning system is provided, the method comprising the following steps:

[0018] The received signal that travels from the transmitter to the receiver of the control device along the strongest signal path, i.e. the peak path, is identified as the peak path signal.

[0019] Determine the time-of-flight (ToF) of the peak path signal;

[0020] Determine the (maximum permissible) time interval δ between the flight time of the peak path signal and the peak path signal. (max) ;

[0021] The determination depends on δ (max) The threshold T for the reliability of the first path search; and

[0022] Taking this threshold into account, in δ (max) The first path search is performed at that location.

[0023] On the other hand, it relates to a program element that, when executed on a control device of a motor vehicle access or positioning system, instructs the control device to perform the steps described above and below.

[0024] On the other hand, it relates to a computer-readable medium on which program elements as described above are stored.

[0025] Several embodiments of the present invention will now be described with reference to the accompanying drawings. The illustrations in these drawings are schematic and not drawn to scale. Attached Figure Description

[0026] Figure 1 The distribution of ranging error under LOS and NLOS conditions is shown.

[0027] Figure 2 The path loss models for UWB (free space and ground-based missiles) are shown at 6.5 GHz and 8.0 GHz.

[0028] Figure 3 shows a numerical example of the dynamic requirements for the first path.

[0029] Figure 4 The characteristic curve of the first path search is shown. As the time difference (δ) between the first path and the peak path becomes larger, the safety margin required for the first path search is higher.

[0030] Figure 5 An example implementation of the first path search using a safety margin that depends on δ is shown.

[0031] Figure 6 A vehicle access or location system is shown. Detailed Implementation

[0032] UWB (Ultra-Wideband) secure ranging is used in conjunction with vehicle access systems. To determine the distance (“range”), a “two-way ranging” method is employed; this is typically a “two-sided two-way ranging” method, which has lower accuracy requirements for the quartz frequency.

[0033] Bilateral two-way ranging describes a communication sequence where the communication partners generate timestamps for transmitted and received data packets. The time of flight (ToF) can then be calculated based on the collected timestamps. Assuming that ToF represents the direct path between the communication partners (rather than reflection), the speed of light can be used to convert between ToF and the distance between the communication partners.

[0034] For high accuracy, it is crucial that the receiver determines the arrival time (i.e., the signal arrival time) or reception timestamp of each data packet as precisely as possible. This task is not straightforward, especially in multipath propagation and reflection environments, where the direct path of interest may be obscured by reflections with higher signal levels.

[0035] It can be specified that the receiver performs signal acquisition based on the strongest signal path (called the "peak path"), and determines the channel profile by association with known symbols or sequences and accumulation over multiple symbols. In this context, "channel impulse response" (CIR) is referred to. In the reverse search, starting from the peak path, a signal path with a lower level preceding the peak path is checked in post-processing. The goal is to identify the earliest time point of signal arrival (i.e., the first path) and use that time point as the reception timestamp.

[0036] First path search represents a thresholding problem because the algorithm must distinguish between noise and valid paths. Furthermore, the highest possible dynamic range between the peak path and the first path (e.g., 30 dB) is desirable, so that the first path can still be detected even in the presence of body shadowing.

[0037] The introduction of UWB technology into vehicle access systems is partly for security reasons, as Time-of-Flight (ToF) measurement can prevent "relay attacks" (wireless link extension) that can occur in current passive access systems. Importantly, ToF measurement is configured in a manipulator-resistant manner, making attacks on ToF measurement, which could be combined with wireless link extension, unable to compromise the system. In addition to the encryption measures associated with the data transmission of the timestamps being measured, it is crucial that the timestamp determination itself cannot be advantageously influenced by attackers.

[0038] In "secure ranging," a sequence known only to the communication partner is used for this purpose. The term "secure training sequence" (STS) is also used in this context. Based on this sequence, the receiver performs correlation and accumulation of the CIR. Assuming an attacker cannot obtain further information about the STS used, he must manipulate the Time-of-Flight (ToF) based on attacks that exploit guessed STSs. For example, an attacker can extend the effective signal and attempt to mimic an earlier first path by inserting a guessed STS ("STS injection"). Manipulation of the ToF measurement in this way is called "range gain." The probability that an attacker guesses the STS that produces the effective path in the CIR represents the security level of the implementation.

[0039] Now, in the first path search, a conflicting objective arises regarding the specified threshold: to minimize the probability of an attack's success, the threshold for effective paths must be set as high as possible. A high threshold means that the identification of the first path only accepts paths that can be reliably based on actual signals (rather than noise or guessed signals), i.e., requiring the path to be as distinctive as possible in the CIR. This conflicts with the objective of achieving the highest possible dynamic range or sensitivity of the first path, which requires specifying the lowest possible threshold (paths that are not very distinctive or close to the noise floor will also be accepted). These conflicting objectives exist regardless of the specific implementation of the first path decision threshold.

[0040] As a solution to these conflicting objectives, two (or more) timestamps can be identified, one optimized for (dynamic) performance and the other for security. Therefore, two Time-of-Flight (ToF) results are ultimately obtained based on the ranging process: one highly reliable (security) but potentially inaccurate, and one highly accurate (performance) but potentially manipulated; decisions regarding the use of these two results can be made at the functional level.

[0041] Therefore, security values ​​can be used for "relay attack defense" (high security requirements, low accuracy and update rate requirements), while performance values ​​can be used for positioning (high accuracy and update rate requirements). However, problems may arise if, for example, only one or a few communication cycles can be performed, and no ranging can reach the security threshold (i.e., no secure result).

[0042] In addition to these conflicting objectives, the implementation of the first path search itself also considers other parameters, such as the actual signal amplitude or signal-to-noise ratio. Advantageously, the conflict between security and performance objectives that arises in the first path determination is resolved as simply as possible in terms of the ToF results, and these results are integrated into the first path search.

[0043] The detection of so-called peak paths can be performed at a very high level of security without compromising sensitivity or performance. Therefore, in appropriate implementations, it is assumed that an attacker cannot simulate a peak path by guessing the STS. The peak path is assumed to be trustworthy.

[0044] In addition, the following relationships can be established:

[0045] 1. Security Risks

[0046] Achieving the highest possible range gain is attractive to attackers because it allows for greater coverage over a wider wireless link. As the achievable range gain increases, the severity of the damage must be assessed as greater. To limit the risk, the probability of achieving high range gain can be reduced. Range gain is proportional to the time interval between the first path detected in the CIR and the peak path.

[0047] Conversely, if the distance gain is small, i.e., the time interval between the first path and the peak path in the CIR is small, the damage is small. In this case, a slightly higher probability of attacker success is acceptable.

[0048] Value:

[0049] A useful range gain for an attacker is a few meters (e.g., at least 3 meters). Otherwise, even attack scenarios at the extreme limits, such as so-called front-door attacks (where only a small wireless link extension is required), are theoretically impossible. It's also important to remember that the range gain requirement is significantly higher for practical implementations because any device used by the attacker will introduce delays into the signal path.

[0050] 2. Improved accuracy

[0051] Compared to the first smaller time difference between the first path and the peak path, a related improvement in accuracy can be achieved by more accurately identifying the first path, since the sought accuracy is at least an order of magnitude lower than the distance gain of the related attack.

[0052] In practice, it has also been found that in most multipath scenarios, the time difference between the first path and the peak path is small, and large time differences corresponding to a range of several meters are very rare.

[0053] Value:

[0054] For vehicle access systems, an accuracy of approximately + / - 10 cm is sought. This is necessary to ensure accurate identification of the area upon approach and to enable reliable identification of the interior / exterior.

[0055] In many multipath scenarios, the error caused by failing to identify the true direct path can be several meters, typically less than 1.5 meters. See [link to relevant documentation]. Figure 1 .

[0056] 3. Performance requirements for the dynamic range of the first path

[0057] Based on practical considerations, it can be inferred that if the time difference between the peak path and the first path increases, the required dynamic range of the first path decreases: for a given scenario, the reception level of the first path always remains constant (e.g., given distance and human body attenuation), while the reception level of the peak path (= reflected signal) decreases as the difference increases (= longer reflected path), thus reducing the ratio of the levels of the first path to the peak path.

[0058] One example of this is Figure 2 And the back pocket scene shown in Figure 3.

[0059] Figure 2 The path loss models for UWB (free space and ground-based) at 6.5 GHz and 8.0 GHz are shown. Figure 3 shows a numerical example of the first path dynamic requirement.

[0060] For example, a user stands 2 meters in front of a car. The direct path (2 meters) is severely attenuated (35 dB) by the human body. However, reflected signals (e.g., signals reflected from a garage wall) are very strong.

[0061] According to the UWB path loss model ( Figure 2 For a distance of 2m, the attenuation of the direct path is 55dB. Therefore, the total attenuation, including the 35dB human body occlusion, is 90dB.

[0062] If we assume that the reflected path is only slightly longer than the direct path (the garage wall is very close), for example, 1m longer than the direct path (row 25 in the table of Figure 3), then the attenuation of the reflected path is 59dB, and the necessary first path dynamic range is 31dB (=90dB-59dB).

[0063] If we assume a longer reflection path (farther from the garage wall), for example, 10m longer than the direct path (see row 30 in the table of Figure 3), then the attenuation of the reflection path is already 71dB, and the necessary first path dynamic range is only 19dB (=90dB-71dB).

[0064] Based on the above considerations, the following solutions are proposed:

[0065] 1. During the first path search, a characteristic curve with a variable safety margin is implemented with a threshold.

[0066] 2. The safety margin increases with increasing δ, or increases monotonically. δ, in the following text, refers to the time interval between the flight time of the peak path signal and a point in the CIR; see also... Figure 4 .

[0067] 3. At a specific interval δ max If it is surpassed, the first path will no longer be accepted.

[0068] 4. The characteristic curve shows the minimum safety margin M1, which can also be 0.

[0069] 5. The characteristic curve shows the maximum safety margin M2, which is in δ max It can be achieved before it is reached.

[0070] 6. The precise characteristics of a characteristic curve can be defined using a functional specification or a lookup table (LUT).

[0071] Figure 4 The characteristic curve of this safety margin is shown by way of example.

[0072] from Figure 4 As can be seen from the characteristic curve, the first path search typically requires a higher safety margin as the time difference between the first path and the peak path increases. However, some segments of the curve can also extend horizontally or have positive gradients. The precise form of the curve can depend on the associated application.

[0073] Figure 5 A flowchart is shown for a method of operating a motor vehicle access or positioning system. First, a first path search is performed, i.e., identifying the received signal traveling from the transmitter to the receiver of the control unit along the strongest signal path (peak path). Once this peak path signal is identified, the search advantageously begins from the maximum possible time interval δ of the flight time from the peak path signal. max The process begins at this point. If successful, that is, when the first path signal is identified, the method can be terminated earlier.

[0074] It can be specified that, subsequently, a lookup table is used to determine the safety margin M for the current search interval δ. At the start of the method, the current search interval δ is, for example, δ0. max Then gradually decrease the value until the first path or the corresponding flight time is determined.

[0075] Then, a threshold T for the expected reliability of the (error-free) first path search is determined as a function of M. The specification of T may include further dependencies and, for example, may depend on the signal-to-noise ratio. If, for the current search interval δ, the threshold T (positive criterion) for the reliability of the first path search is exceeded, then δ is declared as the "first path". In this case, the search ends because no earlier time point can be found for the first path.

[0076] If it can be adjusted according to purpose and situation Figure 4 Additional optimizations can be achieved by adjusting the parameters of the characteristic curves shown in the diagram and thus the safety profile of the implementation method.

[0077] Adjusting the safety profile based on functionality can occur, for example, when a vehicle's access function must meet more stringent safety requirements than, for example, "Welcome Lighting".

[0078] The installation location can also affect the adjustment of the security profile. For example, an internally installed transceiver has a different characteristic profile than an externally installed transceiver because the expected reflection behavior (and therefore the requirements for the first path of detection) are different. The security profile can also be adjusted according to the location, for example, particularly in locations with a high risk of theft, where the profile may become steeper and / or shift upwards.

[0079] The safety profile can also be adjusted based on time. For example, the curve can be shifted upwards at night compared to daytime. The safety level can also be increased when the vehicle remains stationary for an extended period.

[0080] Adjustments can also be made according to the protocol. For example, different methods for preventing relay attacks can be used in parallel. For instance, if other mechanisms are used to prevent relay attacks, the security level can be adjusted (reduced) accordingly. Examples of such mechanisms include user identification via lidar / radar, facial recognition, legitimacy checks on access using motion sensor data from keys / moving parts, or repeated execution of ToF measurements.

[0081] The parameter control of the security level of the implementation method can be performed using the method described above. It can be easily integrated into existing implementation methods (first path search).

[0082] Figure 6 An access or location system 200 is shown, which has a control device 100 installed in a vehicle 103 and a radio key 102 representing a transmitter further described above.

Claims

1. A control device (100) for a motor vehicle access or positioning system (200), the control device being configured to: The received signal along the strongest signal path, i.e. the peak path, that has traveled from the transmitter to the receiver of the control device is identified as the peak path signal. Determine the Time-of-Flight (ToF) of the signal along the peak path. Determine the time interval δ between the signal flight time of the peak path signal; Determine a threshold T, which depends on δ, for the reliability of the first path search; The first path search is performed at δ, taking this threshold into account. If the threshold T is not exceeded, it is determined that no first path signal was detected. A new threshold T is determined, depending on the new time interval δ-Δ or δ+Δ between the signal flight time and the peak path signal, for the reliability of the updated first path search. 新 ; The updated first path search is performed at the new time interval δ-Δ or δ+Δ, taking into account the new threshold.

2. The control device (100) as claimed in claim 1, wherein the control device is configured to: When the threshold T has been exceeded, the signal detected in the first path search will be classified as a first path signal; End the first path search.

3. The control device (100) as described in claim 1 or 2, in, If the time interval between the signal flight time and the peak path signal is reduced, then the new threshold T 新 It is less than or equal to the threshold T.

4. The control device (100) as claimed in claim 1 or 2, wherein the control device is configured to: Based on the function, the threshold T and / or the new threshold T 新 Adjustments will be made.

5. The control device (100) as claimed in claim 1 or 2, wherein the control device is configured to: The threshold T and / or the new threshold T are adjusted based on the installation location, positioning, and / or time. 新 Adjustments will be made.

6. A vehicle (103) having a control device (100) as described in any one of claims 1 to 5.

7. An access or location system (200) having a control device (100) as described in any one of claims 1 to 5 and a radio key (102).

8. A method for operating a motor vehicle access or positioning system (200), the method comprising the steps of: The receiver signal that has traveled from the transmitter to the control device along the strongest signal path, i.e. the peak path, is identified as the peak path signal. Determine the Time-of-Flight (ToF) of the signal along the peak path. Determine the time interval δ between the signal flight time of the peak path signal; Determine a threshold T, which depends on δ, for the reliability of the first path search; The first path search is performed at δ, taking this threshold into account. If the threshold T is not exceeded, it is determined that no first path signal was detected. A new threshold T is determined, depending on the new time interval δ-Δ or δ+Δ between the signal flight time and the peak path signal, for the reliability of the updated first path search. 新 ; The updated first path search is performed at the new time interval δ-Δ or δ+Δ, taking into account the new threshold.

9. A computer program product comprising a computer program that, when executed on a control device (100) of a motor vehicle access or positioning system (200), instructs the control device to perform the following steps: The receiver signal that has traveled from the transmitter to the control device along the strongest signal path, i.e. the peak path, is identified as the peak path signal. Determine the Time-of-Flight (ToF) of the signal along the peak path. Determine the time interval δ between the signal flight time of the peak path signal; Determine a threshold T, which depends on δ, for the reliability of the first path search; The first path search is performed at δ, taking this threshold into account. If the threshold T is not exceeded, it is determined that no first path signal was detected. A new threshold T is determined, depending on the new time interval δ-Δ or δ+Δ between the signal flight time and the peak path signal, for the reliability of the updated first path search. 新 ; The updated first path search is performed at the new time interval δ-Δ or δ+Δ, taking into account the new threshold.

10. A computer-readable medium having a computer program stored thereon in the computer program product of claim 9.

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