Two-Frequency Doppler Radar Direction Detection
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Solution Overview
Problem
Existing Doppler effect speedometers with two transmission frequencies have insufficient precision for reliably determining the direction of vehicle movement, which is crucial for accurate triggering of camera devices in traffic control systems.
Innovation Solution
A method that deduces the direction of vehicle movement by analyzing the apparent phase shift between difference signals obtained from the Doppler shift frequency components, allowing for high-reliability direction determination and minimal adaptation to existing speedometer systems, with additional steps involving Fourier transforms to isolate vehicle-generated signals from parasitic components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the direction of travel is determined by measuring successive vehicle positions using propagation delay of radio frequency waves, then the method can be implemented with existing Doppler radar detectors, but the measurement accuracy is insufficient for reliable direction determination
Solution Approach 1:
The invention changes the measurement parameter from propagation delay (time-based) to phase shift (angular-based). By measuring the phase difference of the Doppler shift frequency component between two successive position measurements, the system achieves higher precision in determining direction of travel. This parameter transformation allows existing Doppler radar infrastructure to provide more accurate directional information without requiring complete system replacement.
2Manufacturing precision
If camera triggering time is adjusted according to vehicle direction of travel, then the captured image can be centered on the vehicle including its license plate, but the system requires reliable determination of direction which existing methods cannot provide
Solution Approach 1:
The invention implements a feedback mechanism where the phase shift measurement continuously provides directional information back to the camera triggering system. The measured phase difference between successive radar returns is processed to determine direction, which then feeds back to adjust camera triggering timing. This closed-loop feedback ensures that the camera is triggered at the precise moment the vehicle is centered in its field of view, capturing the license plate accurately.
3Measurement precision
If a new method for determining direction is developed, then measurement reliability can be improved, but the complexity of the speedometer system increases
Solution Approach 1:
The invention makes the existing Doppler radar system multi-functional by extracting directional information from the same signal processing chain used for speed measurement. The phase shift analysis of the Doppler frequency component serves dual purposes: it provides both speed information (through frequency measurement) and directional information (through phase difference measurement). This universal approach allows one system to perform multiple functions without adding separate dedicated directional sensing hardware.
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 approach provides a highly reliable method for determining vehicle direction, ensuring that license plates are captured in images by adjusting camera triggering times, and can be integrated with minimal modifications to existing speedometer systems, enhancing the accuracy of traffic control imaging.
Implementation Method 1
The vehicle speed can be measured using a Doppler radar speed gun of the two-frequency type, by performing the following steps for each of the two emission frequencies using time-division multiplexing: /1/ emission of a wave at this emission frequency towards the vehicle; /2/ reception of a wave which is produced by reflection of the emitted wave on the vehicle
Implementation Method 2
reception of a wave which is produced by reflection of the emitted wave on the vehicle
Data Source
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AI summary
The direction of travel (E, R) of a vehicle (100E, 100R) on a road (1000) is determined using a two-frequency Doppler radar (1). The direction of travel is deduced from a phase shift that occurs between two difference signals obtained for the two emission frequencies. The determined direction of travel can be used to select at least one triggering moment for a camera (2E, 2R) coupled to the radar within a traffic control unit (10). When two camera devices are dedicated to two opposite directions of travel on the road and are triggered simultaneously, the determined direction of travel for the vehicle can also be used to select the image captured by the camera device corresponding to the determined direction of travel.