Vehicle Distance Estimation Using BLE Time-of-Flight
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Solution Overview
Problem
Existing vehicle detection systems using BLE signals face significant errors in estimating distance due to multipath signal distortions and the limitations of sampling frequencies, leading to inaccuracies in activating vehicle functions, especially when the user needs to be within specific distances for unlocking or remote parking.
Innovation Solution
A method involving multiple measurement phases with random restarts of the electronic clock to refine distance estimation, calculating the average or median of determined distances, and using BLE communication to reduce errors to less than 50 centimeters with repeated iterations, thereby improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RSSI measurement is used to determine distance from BLE signals, then distance estimation is achieved, but measurement precision deteriorates due to multipath signal distortions
Solution Approach 1:
The patent extracts the timing information from BLE signal exchanges and uses it separately from signal power measurements. By measuring the time of flight based on the known transmission interval (150 microseconds) and signal propagation time, the system obtains distance information without being affected by multipath distortions that corrupt RSSI measurements.
Solution Approach 2:
The patent introduces time measurement as an intermediary parameter to indirectly determine distance. Instead of directly measuring signal power (which is distorted), the system measures the time interval between signal transmission and reception, which provides an accurate proxy for distance calculation without being affected by signal reflections.
2Measurement precision
If sampling frequency is increased to improve distance measurement accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent utilizes the existing electronic clock that is already present in the BLE communication module for its normal operation. By repurposing this existing timing mechanism to also perform distance measurement, the system achieves accurate timing-based distance estimation without adding separate high-precision timing hardware or increasing sampling frequency requirements.
3Measurement precision
If multiple measurement phases with random clock restarts are implemented, then measurement precision improves, but loss of time increases due to repeated measurements
Solution Approach 1:
The patent implements periodic measurement phases where the electronic clock is restarted at random intervals during BLE signal exchanges. This periodic restarting creates multiple independent timing measurements that can be averaged or selected to improve accuracy, while the random nature prevents systematic errors from recurring at the same sampling points.
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
The method effectively reduces estimation errors, enhancing the accuracy of distance measurement between a vehicle and an authentication device, allowing for precise activation of vehicle functions even at close distances, such as within two or six meters.
Implementation Method 1
the vehicle and the device communicate over LF/RF (Low Frequency/Radiofrequency) wireless communication links. In this solution, the vehicle periodically transmits a detection signal over an LF communication link. When the device receives this detection signal, it responds to the vehicle over an RF communication link
Implementation Method 2
In order to determine the distance between the user and the vehicle, the vehicle measures the power of the signals received from the authentication device during these exchanges and deduces the distance therefrom
Implementation Method 3
The exchanges are carried out on such an interface using frames encoded in a signal called a "BLE signal". The vehicle receives the BLE signals transmitted by the smartphone
Implementation Method 4
the RSSI measurement may be distorted when the signal sent by the smartphone splits into a signal received in a direct line and one or more signals that bounce off one or more obstacles before reaching the vehicle (called a "multipath" signal)
Implementation Method 5
The vehicle, knowing the instant of transmission of the request signal, the period between the reception of the request signal and the transmission of the response signal by the device and the instant of reception of the response signal, then deduces therefrom the average time of flight of the signals and the distance between the vehicle and the device
Data Source
AI summary
A method for estimating the distance between an authentication device and a vehicle, in particular a motor vehicle, the vehicle including a computer and a plurality of communication modules capable of communicating with the device by exchanging signals over a wireless communication link, each communication module including an electronic clock that defines the sampling frequency of the signals received from the device. The method includes a plurality of measurement phases each comprising determination, by the computer, of the distance between the vehicle and the device and stopping and restarting of the electronic clock, and estimation of the actual distance between the vehicle and the device based on the plurality of distances determined during the measurement phases.