Coordinated Pulse Radar for Accurate RFID Distance Measurement
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Solution Overview
Problem
Existing RFID systems face challenges in accurately measuring distance to tags in cluttered and multipath environments due to limitations in bandwidth, precision, and noise interference, which affects accuracy and precision in distance measurement.
Innovation Solution
A coordinated pulse radar system is integrated with an RFID reader to create a differential signal by subtracting radar signals from the RFID tag during different modulation states, allowing for accurate measurement of round-trip time of flight and reducing the impact of multipath effects and clutter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If time-of-flight measurement methods are used for distance measurement, then distance measurement capability is provided, but accuracy is degraded in highly reflecting environments due to multipath effects and clutter
Solution Approach 1:
The patent extracts and removes multipath components from the received signal through signal processing techniques. By identifying and eliminating these interfering components, the system isolates the direct path signal from the tag, thereby resolving the contradiction between providing distance measurement capability and maintaining accuracy in multipath environments.
Solution Approach 2:
The system performs preliminary characterization of the propagation environment by measuring channel impulse responses and identifying multipath components before the actual distance measurement. This preliminary action allows the system to pre-process and compensate for multipath effects, ensuring accurate distance measurement even in highly reflecting environments.
2Measurement precision
If modulation waveforms with frequencies on the order of a megahertz or less are used, then radio regulation compliance is achieved, but nanosecond precision needed for time-of-flight methods is lacking
Solution Approach 1:
The patent transitions from relying solely on time-domain resolution to utilizing phase-domain measurements. By measuring the phase of the received signal at the modulation frequency, the system achieves distance measurement capability without requiring nanosecond-level time resolution, thus resolving the contradiction between measurement precision and modulation frequency constraints.
3Measurement precision
If phase of backscattered signals is used to calculate distance, then distance measurement is enabled, but accuracy is degraded in highly reflecting environment due to multipath effects
Solution Approach 1:
The system uses feedback from channel sounding measurements to continuously update its understanding of the propagation environment. By measuring the channel impulse response and using this information to compensate for multipath effects in subsequent distance measurements, the system maintains accuracy even in highly reflecting environments.
Solution Approach 2:
The system performs preliminary channel characterization through sounding sequences before actual distance measurement. This preliminary action allows the system to identify multipath components and their characteristics, which are then used to compensate for multipath effects during phase-based distance measurement.
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 enables accurate distance measurement to RFID tags with a resolution of 1 meter or better, even in complex RF environments, while reducing bandwidth requirements and improving signal-to-noise ratio, thus overcoming the limitations of prior art.
Implementation Method 1
The one-way distance, d, to a target is computed from the equation 2d=ct where c is the velocity of light and where t is the time between transmitted signals and received signals reflected from a target
Implementation Method 2
Modulated Backscatter RFID Systems... A continuous wave (CW) radio signal is transmitted toward a tag by a reader. The tag modulates the reflected signal sent back to the reader
Data Source
AI summary
A system for measuring range to an RFID tag including situations containing high clutter and multi-path signals is disclosed. The system includes an RFID reader; an RFID tag; and a coordinated signal compression radar system. The reader causes the tag to respond to received signals in a first backscatter state at a first time and a second backscatter state at a second time. The signal compression radar system transmits signals coordinated by the backscatter state of the tag and creates a differential signal comprised of the differences between radar signals obtained during the first and second states of the tag to obtain an uncorrupted measure of a round trip time of flight of said radar signals between the radar system and the RFID tag. The radar may use signals typical of pulse compression radar systems such as chirp modulation or Orthogonal Frequency Domain Modulation (OFDM), either pulsed or semi-continuous.