RFID Distance Measurement Using Multi-Frequency Phase Analysis
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Solution Overview
Problem
Conventional RFID tag distance measurement systems fail to accurately measure distance in multipath environments due to interference from reflected waves through various paths, leading to unreliable communication.
Innovation Solution
An RFID tag distance measuring system that uses multiple frequencies and diversity means, such as multiple antennas or a scan antenna, to selectively obtain strong reflected signals and estimate distance based on phase changes, reducing field holes and improving precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single-frequency and single-antenna RFID distance measurement is used, then the system construction is simple, but the measurement precision deteriorates in multipath environments due to signal interference
Solution Approach 1:
The patent segments the measurement process by using multiple frequencies and multiple antennas independently. Each frequency-antenna combination provides an independent measurement channel, allowing the system to select or combine results from multiple segments to achieve high precision without requiring all components to operate simultaneously, thus managing complexity.
Solution Approach 2:
The patent changes the frequency parameter by transmitting carrier signals at multiple different frequencies to the RFID tag. This parameter change allows the system to obtain reflected signals with different phase characteristics, enabling accurate distance measurement even in multipath environments where single-frequency measurement would fail due to signal interference.
2Measurement precision
If multiple frequencies and diversity means are used to obtain strong reflected signals, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent implements dynamic antenna selection and signal processing. The system dynamically switches between different antenna combinations and frequency pairs based on which provides the strongest reflected signal or most accurate phase measurement. This dynamic approach allows the system to achieve high precision adaptively without permanently deploying all possible antenna and frequency combinations simultaneously.
Solution Approach 2:
The patent makes the antenna system multi-functional by using the same set of antennas for both transmission and reception, and for selecting different spatial diversity paths. The signal processing unit handles multiple frequencies and antenna combinations universally, reducing the need for dedicated components for each function and thereby managing overall system complexity.
3Reliability
If phase-based distance calculation is used in multipath environments, then the distance can be calculated from phase changes, but the reliability deteriorates due to signal interference from multiple paths
Solution Approach 1:
The patent changes the frequency parameter to multiple values, which alters the phase characteristics of reflected signals from different paths. By measuring phase changes at multiple frequencies, the system can distinguish between direct and reflected signals, thereby maintaining reliability in multipath environments where single-frequency phase measurement would be unreliable.
Solution Approach 2:
The patent implements feedback through the selection process where the system evaluates the strength and quality of reflected signals from multiple antenna-frequency combinations and selects the most reliable measurement. This feedback mechanism ensures that only high-quality, interference-free measurements are used for final distance calculation, thereby maintaining high reliability despite multipath interference.
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
The system securely measures distance to an RFID tag with high precision in multipath environments by reducing the number of field holes and increasing measurement accuracy through phase difference analysis.
Implementation Method 1
a reader 10 that outputs a predetermined carrier signal to an RFID tag and receives a reflected signal of the carrier signal from the RFID tag
Implementation Method 2
receives a reflected signal of the carrier signal from the RFID tag
Implementation Method 3
using the fact that the phase of a reflected wave from an RFID tag in response to a carrier signal from a reader depends on the distance between the reader and the RFID tag
Data Source
AI summary
An RFID tag distance measuring system includes a reader that outputs a predetermined carrier signal to a tag and receives a reflected signal of the carrier signal from the tag. The reader has signal output means for outputting signals at multiple frequencies, which are different from each other, as the carrier signal, a transmitting section that transmits a signal output by the signal output means to the tag, a receiving section that receives reflected signals of the signals at multiple frequencies, which are different from each other, from the tag and estimating means for estimating the distance between the tag and the reader based on the amount of change in phase between the reflected signals received by the receiving section and the carrier signals and the frequencies of the carrier signals. The transmitting section and the receiving section have two pairs of transmit and receive antennas that obtain multiple receive signals in which the strengths of the reflected signals vary differently when the receiving section receives the reflected signals.