Backscatter RFID Channel Generation Using Band-Pass Delta Sigma Modulation
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Solution Overview
Problem
RFID systems face tag collisions and data throughput issues due to overlapping backscattered signals on the same frequency channel, leading to signal differentiation problems and reduced performance, especially when reading multiple tags simultaneously, and existing solutions like separate antennas or adaptive tuners increase complexity and cost.
Innovation Solution
The use of band-pass signal modulation with a variable impedance circuit and band-pass delta sigma modulation to generate dedicated frequency channels for each tag, reducing DC offset and phase noise effects by offsetting the IQ signal by the frequency of a digital signal source, allowing complex modulation schemes like QAM and OFDM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple tags transmit data on the same frequency channel using backscatter technology, then the RFID system can maintain simplicity in hardware design, but tag collisions occur and data throughput decreases
Solution Approach 1:
The patent segments the single frequency channel into multiple orthogonal sub-channels using QAM modulation. Each tag is assigned a unique combination of in-phase (I) and quadrature (Q) components, creating orthogonal signal spaces. This allows multiple tags to transmit simultaneously on the same frequency without collision, as their signals occupy different orthogonal dimensions rather than overlapping in the frequency domain.
2Device complexity
If multiple tags transmit data on the same frequency channel, then hardware simplicity is maintained, but signal differentiation becomes difficult
Solution Approach 1:
The patent transitions from one-dimensional frequency-based signal separation to multi-dimensional signal separation by introducing both in-phase (I) and quadrature (Q) components. This creates a two-dimensional signal space where tags can be differentiated by their position in the I-Q plane rather than by frequency, enabling the reader to distinguish between multiple tags' signals through orthogonal decomposition.
3Object-affected harmful factors
If separate transmit and receive antennas are used to reduce reflected signal interference, then DC offset is reduced, but device complexity and cost increase
Solution Approach 1:
The patent converts the harmful reflected signal from the single antenna into a useful reference by using it as the local oscillator signal for the QAM modulation system. The reflected signal, which causes DC offset in conventional systems, is instead utilized as the carrier for generating orthogonal I and Q components, transforming the interference problem into a functional advantage while maintaining the single-antenna simple configuration.
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 clear differentiation of signals from multiple tags on dedicated channels, improving data throughput and reducing errors, while maintaining system simplicity and cost-effectiveness by using existing RFID infrastructure with minimal modifications.
Implementation Method 1
The use of band-pass signal modulation with a variable impedance circuit and band-pass delta sigma modulation to generate dedicated frequency channels for each tag
Implementation Method 2
Modulating the signal received by the tag and re-radiating the modulated signal backscattered to the reader device is known, using such signal modulation schemes, such as phase shift keying (PSK) and amplitude shift keying (ASK), where the tag changes its reflection coefficient by changing the impedance match between states
Implementation Method 3
Tags use backscatter technology to reflect the reader's RF signal back to the reader, modulating the signal to encode and transmit data
Data Source
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AI summary
A communication apparatus comprising an antenna for backscattering an incoming RF signal in accordance with a reflection coeflicient of the antenna. The communication apparatus comprises at least one band-pass delta sigma modulator which modulates the signal at its input and digitally controls the output of a variable impedance circuit, wherein the reflection coefficient of the antenna is varied based on the output of the variable impedance circuit. This communication device can be used in applications such as RFTD tags.