Bidirectional RF Distance Measurement for Keyless Entry Security
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Solution Overview
Problem
Existing distance measurement systems for secure keyless entry systems in vehicles are vulnerable to relay attacks, leading to potential theft, due to inaccuracies in calculating the distance between the key-fob and the vehicle using RF signals, especially when there are errors in reference clock frequencies.
Innovation Solution
A distance measurement device with a calculation unit that uses a GMSK signal and independent reference signal sources in both the key-fob and vehicle to accurately calculate the flight time of a distance measurement signal, averaging multiple phase information samples to reduce errors caused by clock frequency discrepancies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If flight time of RF signal is measured to calculate distance between key-fob and automobile, then distance measurement capability is achieved, but measurement precision deteriorates due to clock frequency errors
Solution Approach 1:
The patent implements feedback by having both the key-fob and automobile transmit distance measurement signals and measure flight times bidirectionally. Each device sends a signal, the other device measures the flight time, and both devices exchange their respective flight time measurements. This feedback mechanism allows for cross-validation and averaging of measurements, thereby improving distance measurement accuracy while maintaining security against relay attacks.
2Device complexity
If simple flight time measurement is used, then device complexity is reduced, but measurement precision deteriorates due to clock frequency discrepancies
Solution Approach 1:
The patent uses feedback by implementing bidirectional signal transmission and measurement. Both the key-fob and automobile transmit distance measurement signals and measure the flight time of received signals. The flight time measurements from both devices are then averaged to calculate the final distance. This feedback-based mutual measurement approach improves precision without significantly increasing device complexity, as each device performs the same measurement function.
3Ease of operation
If distance measurement is implemented using existing RF communication, then ease of operation is maintained, but measurement precision deteriorates due to vulnerability to relay attacks
Solution Approach 1:
The patent maintains ease of operation by using existing RF communication protocols for distance measurement while improving precision through bidirectional feedback. Both the key-fob and automobile transmit distance measurement signals and measure flight times, then average the results. This feedback mechanism provides more accurate distance measurement without requiring changes to the user interface or operational procedure, thus maintaining keyless entry convenience while enhancing security.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Significantly improves the accuracy of distance measurement, reducing errors and enhancing security against relay attacks by correcting for clock frequency errors, thereby preventing unauthorized access.
Implementation Method 1
a first transmitter-receiver configured to transmit a modulated first distance measurement signal, receive a modulated second distance measurement signal
Implementation Method 2
a time difference between a transmission time point and a reception time point, in other words, a flight time of the distance measurement signal is measured or estimated
Data Source
AI summary
A distance measurement device of an embodiment includes a first device including a first reference signal source and a first transmitter-receiver, a second device including a second reference signal source and a second transmitter-receiver, and a calculation unit configured to calculate a distance between the first device and the second device. One of a first distance measurement signal and a second distance measurement signal is transmitted once or more, and another is transmitted twice or more. The calculation unit calculates the distance based on a total of three or more pieces of first phase information and second phase information acquired through transmission of the distance measurement signals three times or more in total, a first sampling period based on a first reference signal, and a second sampling period based on a second reference signal.