RFID Tag Location Sensing via Multi-Frequency Signal Comparison
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Solution Overview
Problem
Conventional RFID tag ranging techniques, such as RSSI, time of flight, and frequency modulated continuous wave radar, suffer from poor accuracy, especially for short distance applications due to difficulties in measuring small round trip time or frequency delay.
Innovation Solution
The method involves using multiple RFID tag readers transmitting signals at different frequencies, with the RFID tag receiving and comparing signal strengths to determine the closest reader, and transmitting a reply message using the frequency with the greater signal strength to convey location information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional ranging techniques (RSSI, time of flight, frequency modulated continuous wave radar) are used to determine distance, then the system can operate over relatively large areas, but the accuracy deteriorates especially for short distance applications
Solution Approach 1:
The patent changes the frequency parameter of the RFID signals to resolve the accuracy contradiction. By receiving signals at multiple different frequencies and comparing their signal strengths, the system can accurately determine the closest reader even in short distance applications. This frequency-based differentiation allows precise location determination without the measurement difficulties of conventional time-of-flight or RSSI methods at close ranges.
2Measurement precision
If multiple frequencies are used for signal transmission, then location accuracy is improved, but the device complexity increases
Solution Approach 1:
The RFID tag performs the location determination function autonomously by comparing signal strengths from multiple frequencies and selectively responding to the strongest signal. This self-service approach eliminates the need for complex external processing systems, as the tag itself determines which reader is closest and transmits its location information without requiring sophisticated external computation or coordination.
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 approach improves location accuracy by selectively controlling the frequency of the reply message, reducing the impact of multi-path reflections and allowing for precise determination of the RFID tag's location relative to the readers.
Implementation Method 1
receiving a first RF identification (RFID) signal at the RFID tag at a first frequency and receiving a second RFID signal at the RFID tag at a second frequency different from the first frequency
Implementation Method 2
The IC also modulates a radio frequency (RF) signal that is transmitted or backscattered via the antenna
Data Source
AI summary
Embodiments herein describe RFID systems that include multiple RFID tag readers that each use a different frequency to communicate with an RFID tag. For example, each of the tag readers may transmit a tag query command using different modulated frequencies. In one embodiment, the RFID tag includes multiple receivers each tuned to one of the different frequencies generated by the tag readers. For example, one receiver in the tag is tuned to receive 200 MHz signals while another receiver is tuned to receive 900 MHz signals. To provide location information, the RFID tag compares power values associated with the received signals to determine which of the RFID tag readers is closest to the tag. The RFID tag conveys this location information to the tag readers by selecting one of the frequencies of the tag readers to use when generating a reply message.