RFID Tag Location via Signal Phase Correlation
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Solution Overview
Problem
Existing methods for locating RFID tags using electromagnetic signals are not sufficiently precise and accurate due to variations in signal intensity caused by obstacles and environmental factors, and often require complex and costly reader devices with directive or adjustable antennas.
Innovation Solution
A method that tracks RFID tags by analyzing the variations in the coherent information signal, specifically the demodulated components I and Q or phase of the electromagnetic signal, as the tag moves along a known trajectory, using a reader device with an antenna capable of multiple interrogations per second and actuating means to maintain relative motion, allowing for accurate positioning without the need for complex hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If signal intensity is used for locating RFID tags, then the locating process is simple, but the measurement precision is insufficient due to signal variations from obstacles and environmental factors
Solution Approach 1:
The patent changes the measurement parameter from signal intensity to signal phase. Phase information is extracted from the coherent signal received from the RFID tag, and phase unwrapping is applied to convert phase differences into distance measurements. This parameter change maintains operational simplicity while dramatically improving locating accuracy, as phase measurements are not affected by obstacles or environmental factors in the same way intensity measurements are.
2Measurement precision
If very directive antennas or adjustable aerial antennas are used for locating, then the measurement precision is improved, but the device complexity increases significantly
Solution Approach 1:
The patent extracts and utilizes the phase information that is already present in the signal received by a simple omnidirectional antenna. Instead of adding complex antenna structures, the method extracts the coherent phase component from the received signal and applies phase unwrapping algorithms. This extraction approach achieves high-precision locating while maintaining the simplicity of the antenna structure.
3Device complexity
If signal intensity-based locating is used, then the device complexity is low, but the reliability is insufficient due to environmental interference
Solution Approach 1:
The patent changes the measurement parameter from signal intensity to signal phase, which is inherently more reliable in complex environments. Phase information from the coherent signal is extracted and processed through phase unwrapping to determine distance. Phase measurements are not attenuated by obstacles or environmental factors in the same way intensity measurements are, providing reliable locating results even in complex warehouse or industrial environments.
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 method enables accurate and cost-effective localization of RFID tags, even in complex environments, by recognizing the history of variations in the signal phase, which correlates with the tag's position, thus overcoming the limitations of existing methods and maintaining simplicity and affordability.
Implementation Method 1
These passive RFID tags are therefore provided with a suitable antenna adapted to passively enable communication of the memory contents in response to the reading request signal of the reader device
Implementation Method 2
suitable reader devices are present which are adapted to send a reading request signal to the RFID tag and receive, interpret and communicate, through display or the like, the RFID tag's response signal
Data Source
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AI summary
There is provided a method for determining the location of an RFID tag moving along a known path with known speed. The phases of the tag response signals from successive interrogations are stored. For a given location of the tag at the time of the first reading, the phase relative to the first response changes in a characteristic way for a given distance. The set of obtained phase values (phase history) is correlated to nominal phase trend curves, each representing the phases for successive readings where the distance between the reader and the tag at the first reading had a respective particular value, i.e. a particular distance is associated with a predetermined phase change pattern. Since the trajectory and speed are known, the position at a given time is implicitly known, i.e. it can be extrapolated from the position determined for the first reading.