Backscatter Localization via Frequency Hopping Sensing
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Solution Overview
Problem
Conventional RFID systems struggle with high-precision localization due to the narrow bandwidth of communication bands, which limits the accuracy of time-of-flight measurements and distance resolution.
Innovation Solution
The use of frequency hopping to create a wide bandwidth for sensing signals, allowing for super-resolved localization by transmitting communication signals at a high power within a narrow ISM band and sensing signals at a low power across a wider band, enabling precise time-of-flight measurements and impedance modulation in backscatter nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a narrow bandwidth communication band is used for RFID tags, then wireless power transfer and communication are enabled, but time-of-flight measurement accuracy and distance resolution deteriorate
Solution Approach 1:
The system segments the RF signal into two distinct functions: a narrowband communication signal for power transfer and a wideband sensing signal for localization. The transceiver alternates between transmitting the communication signal to the RFID tag and the sensing signal for time-of-flight measurements, allowing both functions to operate independently with their respective bandwidth requirements
Solution Approach 2:
The RFID tag's antenna is made multi-functional by enabling it to both receive wireless power from the narrowband communication signal and reflect the wideband sensing signal for localization. The tag modulates the reflected sensing signal using backscatter modulation, allowing a single device to serve both power reception and localization purposes
2Measurement precision
If a wide bandwidth is used for sensing signals, then time resolution and distance resolution improve, but signal power and communication compatibility worsen
Solution Approach 1:
The system maintains continuous localization capability by rapidly alternating between communication signal transmission and sensing signal transmission. The sensing signal is transmitted in continuous wideband pulses that overlap with communication signal intervals, ensuring uninterrupted time-of-flight measurements while maintaining power transfer continuity
Solution Approach 2:
The transceiver employs periodic transmission of sensing signals at specific intervals within the communication protocol. The sensing signals are transmitted in periodic bursts that do not interfere with the periodic communication signal cycles, allowing structured alternation between power transfer and localization functions
3Productivity
If communication signals and sensing signals are transmitted simultaneously, then system efficiency improves, but signal interference and regulation compliance worsen
Solution Approach 1:
The system dynamically adjusts the transmission timing of sensing signals based on the communication protocol state. The sensing signals are transmitted during idle periods or gaps in communication signal transmission, and the transceiver adaptively schedules sensing operations to avoid overlapping with high-power communication transmissions, thereby preventing interference while maintaining efficiency
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 achieves sub-centimeter precision in localizing backscatter nodes, such as RFID tags, even in environments with limited bandwidth, by decoupling localization sensing from wireless power delivery and leveraging impedance modulation for enhanced signal reflection.
Implementation Method 1
the backscatter node modulates the power of backscattered RF signals by rapidly changing impedance in an antenna of the backscatter node
Implementation Method 2
radio signals that reflect from, and are modulated by, the backscatter node
Implementation Method 3
the spatial coordinates of a backscatter node are detected with super-resolution (e.g., less than 1 centimeter) based on time-of-flight (or phase) of radio signals
Implementation Method 4
based on time-of-flight (or phase) of radio signals
Implementation Method 5
The transceiver frequency hops the sensing signal across a wide band of frequencies
Implementation Method 6
the RFID tag harvests RF energy from the communication signal
Data Source
AI summary
A transceiver may wirelessly transmit a communication signal at a first frequency and a sensing signal at a second frequency. The communication signal may include a command that causes a backscatter node to modulate impedance of an antenna, and thereby modulate reflectivity of the backscatter node. The communication signal may also deliver wireless power to the backscatter node. While the impedance is being modulated in response to the command, the transceiver may transmit the sensing signal and measure wireless reflections. The power of the sensing signal may be much lower than that of the communication signal. The transceiver may frequency hop the sensing signal in a wide band of frequencies and take measurements at each frequency in the hopping. Based on the measurements, a computer may determine time-of-flight or phase of a reflected signal from the backscatter node and may estimate location of the backscatter node with sub-centimeter precision.