Phase Difference Range Measurement for Moving RFID Tags
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Solution Overview
Problem
Existing range measuring apparatuses face challenges in accurately calculating the distance to a non-contacted IC medium, especially when it is in motion, due to timing deviations during frequency transmission and reception.
Innovation Solution
A method and apparatus that transmit an inquiry signal at a single frequency, modulate it using a second frequency to generate a response signal with upper and lower side band components, and calculate the range by extracting and analyzing the phase difference between these components from the received signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple frequencies are transmitted at different timings to measure range, then measurement precision can be improved through frequency comparison, but timing deviations occur when the non-contacted IC medium is in motion, degrading measurement accuracy
Solution Approach 1:
The patent transmits a continuous wave signal at a single frequency rather than transmitting multiple discrete frequency signals at different timings. This continuous transmission eliminates timing deviations that occur when the target moves between transmissions, ensuring the measured phase difference accurately reflects the instantaneous range to the moving RFID tag.
Solution Approach 2:
Instead of varying frequency over time (time dimension), the patent modulates a single continuous carrier wave with a second frequency to generate upper and lower side bands (frequency dimension). This allows range measurement through phase difference between side bands without the timing issues inherent in sequential frequency transmission.
2Reliability
If a single frequency is transmitted and modulated to generate upper and lower side bands, then timing lag is eliminated for moving targets, but the device complexity increases due to additional signal processing requirements
Solution Approach 1:
The patent replaces complex mechanical or procedural methods of transmitting multiple frequencies sequentially with an electronic modulation approach. By using frequency modulation to generate upper and lower side bands from a single carrier, the system achieves accurate range measurement for moving targets through electronic signal processing rather than complex transmission timing control.
3Measurement precision
If phase difference calculation between upper and lower side bands is performed, then range measurement accuracy is improved, but the difficulty of detecting and measuring increases due to the need for complex signal analysis
Solution Approach 1:
The patent uses the phase difference between upper and lower side bands as an intermediary measurement quantity. Instead of directly measuring range, the system measures the phase difference caused by the round-trip time delay, which is then converted to range through a known relationship. This intermediary approach simplifies the measurement process while maintaining high 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 highly accurate range measurements even when the non-contacted IC medium is moving, as it eliminates timing lag and allows for precise calculation using phase differences, improving measurement accuracy and noise separation.
Implementation Method 1
performing modulation at the RFID tag to modulate the first frequency by using a second frequency to obtain a modulated frequency, and responding to the inquiry signal at the RFID tag by returning a response signal at the modulated frequency
Implementation Method 2
acquiring at the reader unit a plurality of frequency components of the response signal by extracting I and Q components from the response signal; calculating from the extracted I and Q components a phase difference between the upper side band (USB) signal component and lower side band (LSB) signal component
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3B
AI summary
A method of measuring a range from a reader unit to a non-contacted IC medium, includes: transmitting an inquiry signal at a first frequency from the reader unit to the non-contacted IC medium; causing the non-contacted IC medium to perform modulation to modulate the first frequency by using a second frequency to obtain a modulated frequency, and causing the non-contacted IC medium to respond to a response signal at the modulated frequency; causing the reader unit to receive the response signal to acquire a plurality of frequency components; calculating a phase difference between signals of at least two of the acquired plurality of frequency components; and measuring the range by using the phase difference.