Carrier Phase Ranging for Vehicle Access Security
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Solution Overview
Problem
Conventional passive entry/passive start systems are susceptible to range extender type relay station attacks and struggle to accurately determine the distance and location of key fobs relative to the vehicle due to cross-polarization of antennas, leading to potential unauthorized access.
Innovation Solution
The implementation of a vehicle access system with RF antennas providing polarization diversity, using unmodulated carrier tone exchange and round trip timing measurements to prevent relay attacks and ensure accurate distance determination, combined with carrier phase-based ranging to determine the location of portable access devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional passive entry systems use traditional signal strength-based location determination, then the system is simpler to implement, but the system becomes susceptible to relay station attacks and cannot accurately determine distance
Solution Approach 1:
The patent changes the measurement parameter from signal strength (RSSI) to carrier phase difference. By measuring the phase difference of the carrier signal between transmitted and received signals, the system can calculate precise distance through time-of-flight measurements, making relay attacks detectable since the physical distance cannot be spoofed. This parameter change fundamentally improves security while maintaining system feasibility.
Solution Approach 2:
The patent replaces the conventional RF signal strength measurement approach with carrier phase-based ranging. Instead of relying on amplitude-based RSSI measurements that are vulnerable to relay attacks, the system uses phase-locked loops and carrier synchronization to measure the phase difference of continuous wave signals, enabling precise distance calculation and attack detection.
2Measurement precision
If the system uses carrier phase-based ranging with music algorithm, then accurate distance and location determination is achieved, but the computational complexity increases
Solution Approach 1:
The patent performs preliminary carrier synchronization and phase locking before the actual ranging measurement. By pre-synchronizing the local oscillator with the received carrier signal and establishing phase lock, the system prepares the measurement infrastructure in advance, reducing the computational burden during the actual distance calculation and enabling precise phase difference measurement.
Solution Approach 2:
The patent introduces a phase-locked loop (PLL) as an intermediary mechanism between the received signal and the distance calculation. The PLL serves as a mediator that automatically tracks and synchronizes the carrier phase, converting the complex signal processing task into a simpler phase difference measurement that can be processed with reduced computational complexity.
3Reliability
If the system implements round trip timing measurements, then relay attacks can be detected, but the authentication process takes longer
Solution Approach 1:
The patent uses periodic continuous wave carrier signals for round trip timing measurements. By transmitting periodic CW signals and measuring the phase difference between transmitted and received signals, the system can calculate distance through time-of-flight without requiring lengthy measurement sequences, thus detecting relay attacks quickly while minimizing authentication time.
Solution Approach 2:
The patent rushes through the authentication process by using direct phase difference measurement of carrier signals rather than performing multiple sequential signal strength measurements or complex challenge-response protocols. The carrier phase measurement provides immediate distance information, allowing the system to quickly detect relay attacks and complete authentication without significant time loss.
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
This solution effectively prevents range extender type relay station attacks and accurately determines the distance and location of portable access devices, enhancing security and reliability in vehicle access systems.
Implementation Method 1
measuring a phase of the received signal at the receiver relative to a locally generated carrier signal at the receiver
Implementation Method 2
distance determinations based on time-of-flight measurements
Implementation Method 3
synchronizing a local oscillator at the receiver to a frequency of the received signal
Implementation Method 4
measuring a time difference of arrival of the received signal at a plurality of antennas at the vehicle
Data Source
AI summary
An access system for a vehicle is provided. The access system includes antennas and an access module. The antennas are configured to each receive a signal transmitted from a portable access device to the vehicle. The signal is transmitted on a 2.4 gigahertz frequency. The access module is configured to: downconvert the received signal to generate an in-phase signal and a quadrature phase signal; perform carrier phase based ranging including implementing a music algorithm to (i) determine a distance between the portable access device and the vehicle, and (ii) determine angles of arrival of the received signal as received at the antennas; determine a location of the portable access device relative to the vehicle based on the distance and the angles of arrival; and permit access to the vehicle based on the location.