Backscatter Transponder Range Rate Determination
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Solution Overview
Problem
In open road electronic toll collection systems, accurately correlating vehicle information from sensors with transponder communication transactions is challenging, particularly in determining the path traveled by vehicles to associate them with toll transactions and enforcement, due to the lack of precise position correlation between transponder communication zones and vehicle detection systems.
Innovation Solution
The method involves determining the range rate of a vehicle-mounted backscatter transponder using Doppler shift analysis from modulated response signals, which allows for estimating the vehicle's position and velocity, enabling accurate correlation with sensor data and toll transactions by identifying the zero-crossing point of the range rate and using curve-fitting techniques with multiple measurements to refine position estimates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Doppler shift analysis is used to determine range rate, then vehicle position and velocity estimation precision is improved, but system complexity increases due to signal processing requirements
Solution Approach 1:
The transponder's backscatter modulation signal, which is necessary for identification, is simultaneously used to measure Doppler shift for velocity estimation. The existing modulated response signal serves dual purposes: transponder identification and range rate determination, eliminating the need for separate measurement systems.
Solution Approach 2:
The patent uses the phase information of the backscatter modulated signal as an intermediary to extract Doppler shift. By analyzing phase changes in the received signal over time, the system derives velocity information without requiring additional sensors or complex hardware modifications.
2Measurement precision
If additional roadside equipment is deployed to improve vehicle position correlation, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The moving transponder serves as its own velocity sensor by exploiting the Doppler effect on the backscatter signal. The system extracts velocity information from the phase modulation already present in the transponder's response, eliminating the need for external velocity sensors or additional roadside detection equipment.
Solution Approach 2:
The backscatter communication signal performs multiple functions simultaneously: it provides transponder identification, maintains communication linkage, and enables velocity estimation through Doppler analysis. This multi-functionality eliminates the need for separate dedicated measurement systems.
3Measurement precision
If multiple signal measurements are taken to refine position estimates, then measurement precision is improved, but loss of time increases due to multiple measurements
Solution Approach 1:
The system continuously tracks the phase of the backscatter signal over multiple cycles, accumulating phase information to improve velocity estimation accuracy. By processing the continuous signal stream and using curve-fitting techniques on the phase data, the system achieves high precision without requiring discrete measurement interruptions.
Solution Approach 2:
The patent performs curve-fitting on the measured phase data to predict the zero-crossing point of the range rate, which corresponds to the vehicle's position at the center of the reader's coverage area. This preliminary analysis allows the system to estimate position and velocity before making enforcement decisions, reducing processing time.
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 enables precise estimation of vehicle position and velocity, effectively correlating transponder data with sensor information, enhancing the accuracy of toll transactions and enforcement in open road systems without requiring additional roadside equipment, suitable for both active and passive transponder systems.
Implementation Method 1
Passive transponders rely upon energy supplied by the roadside reader in the form of a continuous wave RF signal. The continuous wave signal energizes the transponder and the transponder transmits its response signal by way of backscatter modulation of the continuous wave signal.
Implementation Method 2
The frequency of the modulated reflected response signal is measured and the range rate is determined based upon a Doppler shift corresponding to the measured frequency.
Data Source
AI summary
Methods for determining a range rate of a backscatter transponder and readers implementing the methods are described. The reader transmits a continuous wave signal and receives a modulated reflected response signal from the transponder, mixes the modulated reflected response signal with the carrier frequency to produce a downconverted signal, bandpass filters the downconverted signal to pass a bandpass filtered signal containing at least the modulation frequency, applies a non-linear amplitude transfer function to produce a modulation-suppressed signal, and measures the frequency of the modulation-suppressed signal and determines the range rate from the measured frequency.