RFID Tag Ranging via Multi-Frequency Backscattering Analysis
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Solution Overview
Problem
Current RFID ranging techniques face challenges in precisely locating RFID tags, especially at low UHF frequencies, due to limitations in spatial resolution and the need for prior characterization of tag properties, which leads to errors in distance measurement.
Innovation Solution
A method that measures the modulated backscattering response of RFID tags at multiple frequencies to determine their dispersive properties, allowing for accurate distance determination without prior knowledge of tag properties, using standard readers with software modifications and compensating for power sensitivity effects by measuring at or near the threshold power level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If amplitude measurement of backscattered signal using RSSI is used for ranging, then distance calculation is simple, but measurement precision deteriorates due to unknown tag properties and impedance mismatch
Solution Approach 1:
The patent changes the measurement parameter from amplitude-only (RSSI) to include phase information and frequency response characteristics. By measuring the complex backscattered signal at multiple frequencies and analyzing its phase and amplitude characteristics, the system can determine tag distance accurately without requiring prior knowledge of tag properties, thus resolving the contradiction between simple calculation and accurate measurement.
2Measurement precision
If stepped-frequency CW radar method is used for ranging, then distance measurement can be performed, but the method requires previously characterized tags with known frequency response
Solution Approach 1:
The patent enables the tag to characterize itself by measuring its backscattered frequency response and using this information to determine its own distance from the reader. The tag's unique properties are automatically captured during the measurement process, eliminating the need for external characterization or prior knowledge of tag parameters, thus making the system adaptable to any tag without pre-characterization.
3Measurement precision
If antenna array with phase-shifters is used for spatial localization, then spatial resolution can be improved, but device complexity increases due to large antenna array requirements at low UHF frequencies
Solution Approach 1:
The patent replaces the mechanical antenna array system with a single-antenna frequency-domain measurement system. Instead of using multiple antennas with phase-shifters to achieve spatial resolution, the invention uses a single antenna to measure the frequency response and phase characteristics of the backscattered signal, extracting distance and position information through signal processing rather than spatial sampling.
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 spatial localization of RFID tags with unknown properties, improving accuracy and applicability to uncharacterized tags, and is suitable for applications like insect tracking, with potential for two or three-dimensional positioning.
Implementation Method 1
measuring the modulated backscattering response of the tag at a plurality of frequencies
Implementation Method 2
the tags response is measured at several different frequencies and its distance is solved taking the inverse Fourier-transform of the measured frequency response
Data Source
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AI summary
The invention relates to a method for ranging a radio frequency tag, comprising measuring the modulated backscattering response of the tag at a plurality of frequencies using reader and determining the dispersive properties of the tag from the amplitude of the measured backscattering response. Further, the method comprises determining a position parameter of the tag from the measured modulated backscattering response and the determined dispersive properties of the tag.