Keyless Access Distance Determination Using GNSS Weighted Signal Strength
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Solution Overview
Problem
Keyless access systems using high-frequency RF signals, such as those from cell phones, face challenges in accurately determining the distance between the signal generator and the vehicle due to the RF field strength's dependence on distance to the second power, leading to insufficient precision for enabling distance-dependent functions.
Innovation Solution
A keyless access system employing a short-range radio link with a portable signal generator, like a smartphone, determines the distance by weighting the received signal strength indicator (RSSI) with a distance value calculated from GNSS position data, allowing for accurate distance determination comparable to LF field strength measurements, even without a vehicle-mounted GNSS receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-frequency RF signals are used for short-range radio communication, then communication speed and data transmission capability are improved, but distance determination precision deteriorates due to RF field strength being dependent on distance to the second power
Solution Approach 1:
The patent introduces GNSS position data as an intermediary element to improve distance determination. Instead of relying solely on RF field strength measurements, the system uses weighted combinations of RF signal strength and GNSS-derived distance information to achieve more accurate distance determination while maintaining the benefits of high-frequency RF communication
Solution Approach 2:
The patent changes the parameters used for distance determination by incorporating multiple measurement approaches. It combines RF field strength measurements with GNSS position data, applying different weighting factors to each parameter to optimize distance determination accuracy for RF-based keyless access systems
2Device complexity
If RF field strength measurement is used for distance determination, then device complexity is reduced compared to LF systems, but measurement precision is insufficient for distance-dependent functions
Solution Approach 1:
The patent makes the signal generator multi-functional by requiring it to provide both RF communication capabilities and GNSS positioning functions. This universal approach allows a single device to serve multiple purposes: maintaining communication while also providing accurate location data for distance determination
Solution Approach 2:
The patent introduces processed position data from GNSS as an intermediary measurement to supplement RF field strength measurements. This intermediary data source provides additional geometric information about the relative position between vehicle and signal generator, improving overall distance determination accuracy
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
Enables precise distance determination and execution of functions like window or sunroof control, similar to LF-based systems, ensuring safe and convenient access while utilizing high-frequency RF communication.
Implementation Method 1
The signal generator transmits an enable signal to a receiver unit, mounted on the motor vehicle, by means of a short-range radio link
Implementation Method 2
the receiver unit permits access to one or more doors or flaps if it is determined that the enable signal is valid and a distance criterion which represents a distance between the signal generator and the motor vehicle is satisfied
Data Source
AI summary
A keyless access system for a motor vehicle, which includes a portable signal generator for access to one or more doors or flaps of the motor vehicle, wherein the signal generator transmits an enable signal to a receiver unit, mounted on the motor vehicle, by a short-range radio link. The receiver unit permits access to one or more doors or flaps if it is determined that the enable signal is valid and a distance criterion which represents a distance between the signal generator and the motor vehicle is satisfied. The distance criterion results from a comparison of a weighted reception field strength of the short-range radio link between the signal generator and the receiver unit with a threshold value.