RFID Tag Location via Time-of-Flight Correction
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Solution Overview
Problem
Current RFID tag location methods in warehouses are imprecise due to reliance on RFID response signal strength and time-of-flight measurements, which are affected by latency and interference, leading to delays in inventory handling and supply-chain management.
Innovation Solution
A method using multiple RFID readers to determine time-of-flight and correction factors, adjusting these factors to accurately calculate distances and spatial locations of RFID tags in two or three dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RFID response signal strength is used to estimate distance, then distance estimation is possible, but the measurement precision is poor due to signal reflection and interference
Solution Approach 1:
The patent introduces time-of-flight as an intermediary measurement method to replace direct signal strength-based distance estimation. By measuring the time it takes for a signal to travel to the tag and back, the system obtains a more reliable distance measurement that is not affected by signal reflection or interference issues that plague signal strength measurements.
Solution Approach 2:
The patent replaces the electromagnetic signal strength measurement approach with a time-based measurement approach. This substitution transforms the measurement from relying on signal amplitude (which is affected by environmental factors) to relying on time-of-flight (which is more stable and predictable), thereby improving measurement precision.
2Measurement precision
If time-of-flight is used to calculate distance, then distance calculation is possible, but measurement precision deteriorates due to turn-around delay latency
Solution Approach 1:
The patent applies preliminary action by having the RFID tag prepare and hold its turn-around delay value ready before actual distance measurement occurs. The tag continuously monitors and stores its processing delay, so when a distance measurement is needed, the pre-calculated delay value is immediately available for subtraction from the total time-of-flight, eliminating the need for complex real-time delay compensation.
Solution Approach 2:
The patent implements feedback by having the RFID tag report its turn-around delay value back to the reader. This feedback mechanism allows the reader to compensate for the known delay in subsequent distance calculations, transforming a source of error into a correctable parameter and thereby improving measurement precision.
3Measurement precision
If multiple RFID readers are deployed to improve location accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the RFID tag to perform multiple functions: it not only responds to reader queries but also autonomously measures and reports its own turn-around delay characteristics. This multi-functionality reduces the need for additional specialized devices and simplifies the overall system architecture while maintaining high measurement precision.
Solution Approach 2:
The RFID tag performs self-service by autonomously measuring and reporting its own processing delay characteristics without requiring external calibration equipment or complex reader-side compensation algorithms. This self-service capability reduces system complexity by eliminating the need for external calibration systems while improving location accuracy through precise delay compensation.
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 provides more accurate spatial location determination of RFID tags, reducing delays in inventory handling and improving supply-chain management by overcoming the limitations of signal strength and latency issues.
Implementation Method 1
Radio tags (also referred to as RFID tags) are a technology that, when queried at radio frequency with a request signal reply at radio frequency with a response signal
Implementation Method 2
Another method of determining the distance between an RFID tag and an RFID reader is by determining the time-of-flight starting when an RFID reader sends a request signal and ending when the RFID reader receives a response signal from an RFID tag
Data Source
AI summary
An embodiment of the invention is a method of accurately determining the spatial location of an RFID tag in two-dimensions or three-dimensions. The method utilizes a plurality of RFID readers to make a plurality of distance, direction, and or time-of-flight determinations. Such determinations are made by sending a request signal from one of the plurality of RFID readers and listening for a response signal from an RFID tag received at each of the plurality of RFID readers. Correction factors are then determined and the time-of-flight factors adjusted. The adjusted time-of-flight factors are then used to determine more accurately the distances between the RFID tag and each of the plurality of RFID readers. These more accurate distance measurements are then used to determine the spatial location of the RFID tag.