Phase-Based Distance Measurement for Passive RFID Tags
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional radar systems are not suitable for accurately measuring the distance to a passive RFID tag due to size limitations, cost, complexity, and power requirements, and existing methods for precise location determination are either inaccurate or require modifications to the tag or reader hardware.
Innovation Solution
A system using a modulated backscatter RFID reader with phase-sensitive receivers to calculate the distance between the reader and tag by analyzing the phase relationships of modulated backscattered signals, allowing for precise distance measurement without modifying existing tags or protocols, and enabling accurate location determination of the tag.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional radar systems are used to measure distance to RFID tags, then the measurement capability is provided, but the system is not suitable due to size limitations, cost, and complexity
Solution Approach 1:
The patent extracts only the essential phase measurement capability from conventional radar systems, eliminating the need for complex radar hardware. By using the phase information already present in the backscattered RFID signal, the invention achieves distance measurement without requiring full radar systems, thus reducing device complexity while maintaining measurement precision.
Solution Approach 2:
The patent uses the phase-sensitive receiver as an intermediary to extract distance information from the backscattered signal. Instead of directly measuring distance using complex radar, the system uses the phase relationship between transmitted and received signals as an intermediary parameter to calculate distance, simplifying the overall system architecture.
2Measurement precision
If active transmitter tags are used for location measurement, then the angle of arrival can be measured, but the cost, complexity, power requirements and size of the tags are barriers
Solution Approach 1:
The patent enables passive RFID tags to perform self-measurement of distance by utilizing the phase information naturally present in the backscattered signal. The tag does not require active transmission or additional power sources; instead, it leverages the existing backscatter modulation to encode distance information, achieving location measurement without increasing power requirements.
Solution Approach 2:
The patent changes the measurement parameter from active signal transmission to phase analysis of backscattered signals. By measuring the phase relationship of the modulated backscatter signal, the system achieves location determination without requiring active tags, thus reducing power consumption while maintaining measurement precision.
3Measurement precision
If multiple readers are used to measure signal strength for triangulation, then location can be inferred, but the method is not accurate since signal strength varies due to many factors not only distance
Solution Approach 1:
The patent replaces the mechanical/triad-based signal strength comparison method with an electromagnetic phase measurement approach. By using phase-sensitive receivers to measure the phase relationship of backscattered signals, the system achieves more accurate location determination without requiring multiple readers, thus reducing hardware complexity while improving accuracy.
4Measurement precision
If conventional radar systems are used, then distance measurement is provided, but high bandwidth is required which is not allowed in many countries for passive RFID systems
Solution Approach 1:
The patent changes the measurement approach from bandwidth-dependent time-of-flight methods to phase-based measurement. By measuring the phase relationship of the backscattered signal at the operating frequency, the system achieves sub-meter accuracy without requiring high bandwidth, thus maintaining compliance with regulatory constraints for passive RFID systems while preserving measurement precision.
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 accurate distance measurement to a passive RFID tag with sub-centimeter resolution, overcoming the limitations of conventional radar systems and existing methods, and allowing for precise location determination without additional hardware or protocol modifications.
Implementation Method 1
Backscatter tags modulate and reflect (or retransmit) the radio signal that is received by the tag antenna
Implementation Method 2
measuring the phase of a signal from the tag and calculating the distance to the tag from the measured phase
Data Source
AI summary
Distance to a modulated backscatter tag is measured with a RFID reader that measures changes in phase with frequency of modulated backscattered RF signals. Measured distances are linked to a specific tag. The effects of other sources of reflected and interfering signals are mitigated. The techniques eliminate the need for high RF bandwidth used in time-of-flight methods, and may be used with linear, limiting or other types of amplifiers in the reader receiver. Unambiguous distance to a tag may be found using the derivative of phase with RF frequency of the modulated signal backscattered by a tag. The distance to a tag can be measured with an accuracy on the order of a centimeter. The techniques utilize the characteristics of cooperative backscatter tags (transponders, labels, etc.). New readers implement the techniques which may use unmodified tags.