Harmonic UHF RFID Ranging for Sub-50 Micrometer Precision
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Solution Overview
Problem
Current range finding technologies face challenges in achieving high spatial and temporal resolution, particularly in indoor environments with obstructions, and struggle with precision and reliability due to limitations in optical and radio-frequency methods, including ambiguity from multipath interference and self-jamming issues.
Innovation Solution
A radio-frequency method using a harmonic ultrahigh frequency (UHF) transponder system that modulates a reference signal to a downlink signal, receives a backscattered uplink signal at a harmonic frequency, and calculates distance based on phase information, employing a coherent transceiver and code-division multiple access (CDMA) protocol to enhance accuracy and isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase-based RF ranging is used to achieve high spatial resolution, then ranging resolution is improved, but self-jamming and antenna reflection cause reliability degradation
Solution Approach 1:
The patent applies frequency inversion by having the tag backscatter at a harmonic frequency (e.g., second harmonic) different from the downlink carrier frequency. This frequency separation inverts the traditional RFID approach where tag and reader operate at the same frequency, thereby eliminating self-jamming and antenna reflection issues while maintaining phase-based ranging resolution below 50 micrometers
Solution Approach 2:
The patent introduces a harmonic frequency converter as an intermediary element in the tag. This converter transforms the downlink signal at carrier frequency fc to an uplink backscatter signal at harmonic frequency 2fc, acting as a frequency mediator that separates the transmit and receive paths and eliminates direct interference while preserving phase information for accurate ranging
2Measurement precision
If optical methods are used to achieve high in-plane resolution, then measurement precision is improved, but line-of-sight obstruction and ambient light vulnerability cause reliability degradation
Solution Approach 1:
The patent replaces optical methods with radio-frequency electromagnetic wave-based ranging. RF waves can penetrate dielectric materials like fabrics, plastics, and building materials that block light, eliminating line-of-sight requirements while achieving sub-50-micrometer ranging resolution through phase measurement, thereby improving reliability in obstructed environments
3Measurement precision
If FMCW method is used to achieve high spatial resolution, then measurement precision is improved, but broad frequency bandwidth and FFT time window requirements increase device complexity
Solution Approach 1:
The patent extracts only the essential phase information from the backscattered signal at harmonic frequency, eliminating the need for broad frequency bandwidth sweeping and complex FFT processing required by FMCW. This extraction approach achieves high spatial resolution through simple phase comparison while significantly reducing device complexity and computational requirements
4Ease of operation
If landmark-tag method is used to achieve localization, then ease of operation is improved, but multipath interference causes measurement precision degradation
Solution Approach 1:
The patent uses code-division multiple access (CDMA) spreading codes as intermediaries to tag signals. Each tag is assigned a unique code that spreads its signal across the frequency spectrum, allowing the reader to distinguish direct-line-of-sight signals from multipath reflected signals through code correlation, thereby maintaining position accuracy in environments with multipath interference while keeping the system easy to operate
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 method achieves ranging resolution below 50 micrometers with high spatial and temporal resolution, capable of penetrating dielectrics like water and common building materials, and extends the operational range of conventional RFID systems while reducing noise interference.
Implementation Method 1
modulating a reference signal having an intermediate frequency, fIF, to a downlink signal having a carrier frequency, fc, using a clock signal
Implementation Method 2
receiving an uplink signal backscattered from the tag, the uplink signal having a frequency that is a harmonic of the carrier frequency
Implementation Method 3
demodulating the uplink signal using the clock signal; and calculating a distance between the tag and the transceiver based on a phase of the demodulated uplink signal
Implementation Method 4
capable of penetrating dielectrics like water and common building materials
Data Source
AI summary
A radio-frequency method for range finding includes modulating a reference signal having an intermediate frequency to a downlink signal having a carrier frequency using a clock signal. The downlink signal is transmitted to a tag using a transceiver. An uplink signal backscattered front the tag is received and demodulated using the clock signal. The uplink signal has a frequency that is a harmonic of the carrier frequency. A distance between the tag and the transceiver is calculated based on a phase of the demodulated uplink signal. A system for range finding includes a transceiver and a processor. The transceiver modulates a reference signal to downlink signal and transmits the downlink signal. The transceiver receives and demodulates an uplink signal. The processor is configured to receive the demodulated uplink signal and calculate a distance between the tag and the transceiver using a phase of the demodulated uplink signal.