RFID Phase Shift Distance Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing RFID communication systems face challenges in accurately measuring the distance to tags due to variations in reflection strength and response time, especially when radio waves are reflected by floors and walls, leading to incorrect information processing and inefficiencies in communication processing.
Innovation Solution
A communication processing apparatus that changes the phase of the continuous carrier wave upon receiving the reflected wave from the tag, allowing for accurate distance measurement by calculating the time taken for the radio wave to travel from the antenna to the tag and back, while preventing false recognition of noise reflected waves as valid responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the strength of reflection of the tag is used to estimate distance, then distance estimation can be performed, but measurement precision deteriorates because reflection strength varies with tag attachment state and directional pattern
Solution Approach 1:
The patent changes the measurement parameter from reflection strength (amplitude) to phase difference. By measuring the phase difference between transmitted and reflected carrier waves at different frequencies, the system obtains distance information that is independent of tag attachment state and directional pattern, thereby improving measurement precision and reliability
Solution Approach 2:
The patent utilizes phase transitions of the carrier wave by transmitting two kinds of carrier waves with different frequencies and detecting the phase variation of the reflected wave for each frequency. The distance is calculated using the difference between phase variations, which provides a reliable measurement method that overcomes the inconsistency of reflection strength
2Measurement precision
If time length from command transmission to response reception is used to measure distance, then distance measurement can be performed, but measurement precision deteriorates because response time at the tag is not constant
Solution Approach 1:
The patent replaces the time-based measurement method (which depends on tag response time) with a phase-based measurement method. By measuring phase difference of the carrier wave, the system directly obtains distance information without being affected by the tag's processing response time, thereby improving measurement precision
3Reliability
If radio waves are transmitted continuously to maintain communication, then communication reliability is improved, but harmful factors increase because radio waves may be reflected by floors and walls and reach tags beyond the necessary distance
Solution Approach 1:
The patent replaces time-based distance measurement with phase-based measurement, enabling accurate distance determination even in environments with radio wave reflections. This allows the system to identify and exclude responses from tags beyond the necessary distance, maintaining communication reliability while reducing the harmful effects of reflections
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 precise distance measurement to the tag, reducing the impact of reflections from floors and walls, and allows for efficient communication processing without affecting the efficiency of the communication system, even with moving tags.
Implementation Method 1
the phase of the continuous carrier wave is changed in response to start of reception of the reflected wave from the RFID tag
Implementation Method 2
a time is measured from when the phase is changed to when the same change of the phase is detected in the reflected wave received from the tag
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The distance to a tag is measured precisely without compromising the efficiency of the communication processing. A communication processing apparatus 1 alternately executes transmitting a carrier wave carrying a command and receiving a response from a tag 2 while transmitting an unmodulated carrier wave (CW). A transmission control unit 111 switches the phase of the unmodulated carrier wave transmitted from a transmission/ reception circuit 100 in response to start of reception of the reflected wave from the tag 2. The transmission/reception circuit 110 includes a circuit for separating and detecting an I signal and a Q signal included in the reflected wave from the tag 2. A phase detection unit 112 uses the I signal and the Q signal to detect change of the phase of the reflected wave. A distance calculation unit 113 measures a time from switching the phase of the unmodulated carrier wave to detecting the corresponding change in the phase of the reflected wave, and uses the time to calculate the distance from the antenna 10 to the tag 2.