Delta-Sigma Backscatter Modulation for Arbitrary RFID Signals
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Solution Overview
Problem
Current RFID backscattering systems are limited in the types of signals they can transmit, unable to handle arbitrary signals such as filtered QAM, sine waves, or Gaussian minimum shift keying (GMSK) signals, and face challenges with data collisions due to overlapping RF spectra.
Innovation Solution
A transmission apparatus for wireless devices using a delta-sigma modulator to vary the impedance of an antenna, allowing for the generation of complex modulation signals like 8-PSK, OFDM, or nQAM by adjusting the reflection coefficient, enabling the backscattering of arbitrary modulated signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If ASK or PSK modulation is used in RFID backscattering systems, then the system can transmit data, but the system is limited to specific modulation types and cannot transmit arbitrary signals such as filtered QAM, sine waves, or GMSK signals
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the impedance of the backscattering element across a continuous range rather than switching between discrete states. The impedance modulation depth and frequency are varied to generate different modulation schemes (ASK, PSK, QAM, OFDM, GMSK), enabling arbitrary signal transmission while maintaining a simple backscattering architecture.
Solution Approach 2:
The patent implements dynamics by using a time-varying impedance control mechanism that continuously adjusts the backscattering coefficient. This dynamic impedance modulation allows the system to adapt to different modulation requirements in real-time, transforming a static backscattering system into a versatile signal generator capable of producing complex waveforms.
2Productivity
If multiple tags transmit simultaneously using backscattering, then communication throughput increases, but data collisions occur due to overlapping RF spectra
Solution Approach 1:
The patent resolves spectrum overlap by introducing frequency diversity through OFDM modulation. By transmitting data across multiple orthogonal subcarriers in the frequency domain, the system allows multiple tags to transmit simultaneously without collision. Each tag can use different subcarrier sets or frequency offsets, effectively utilizing another dimension (frequency) to separate simultaneous transmissions.
3Measurement precision
If the reflection coefficient is precisely controlled to enable complex modulation, then signal accuracy improves, but the impedance control mechanism becomes more complex
Solution Approach 1:
The patent introduces an intermediary impedance control circuit that mediates between the simple binary state of the backscattering switch and the continuous impedance requirements for precise reflection coefficient control. This intermediary mechanism includes impedance transformation networks and modulation circuits that convert discrete control signals into continuous impedance variations, achieving precise reflection control without requiring complex direct impedance synthesis.
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
Enables the transmission of complex modulation signals and reduces data collisions by allowing for precise control of the reflection coefficient, improving communication efficiency in RFID systems.
Implementation Method 1
By modulating the reflection coefficient of the tag's antenna 133, data 150 may be transmitted between the tag 130 and the reader 120
Implementation Method 2
The antenna 123 of the reader 120 couples energy 140 to the tag 130
Implementation Method 3
a variable impedance coupled to the antenna, the variable impedance having an impedance value; a delta-sigma modulator coupled to the variable impedance for modulating the impedance value, and thereby a backscattering coefficient for the antenna
Implementation Method 4
A rectify circuit 131 in the tag 130 collects and stores the energy 140 for powering the other circuits
Data Source
AI summary
A transmission apparatus for a wireless device, comprising: an antenna for receiving an original signal and for backscattering a modulated signal containing information from the wireless device; a variable impedance coupled to the antenna, the variable impedance having an impedance value; a delta-sigma modulator coupled to the variable impedance for modulating the impedance value, and thereby a backscattering coefficient for the antenna, in accordance with the information to generate the modulated signal; and, a decoder coupled to the delta-sigma modulator for generating the impedance value from the information.