RFID Backscatter Impedance Modulation for Arbitrary Signal Waveforms
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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 modulate the impedance of an antenna, allowing for the backscattering of complex modulation signals like 8-PSK, OFDM, or nQAM, by switching between different impedance values to generate 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 in the types of signals it can transmit and cannot handle arbitrary signals such as filtered QAM, sine waves, or GMSK signals
Solution Approach 1:
The patent employs a delta-sigma modulator that dynamically switches the antenna impedance between multiple discrete values to generate arbitrary modulated signals. This dynamic impedance switching enables the system to transmit complex signals like filtered QAM, sine waves, and GMSK by continuously adjusting the reflection coefficient in response to the desired signal waveform, thereby achieving high signal type flexibility without requiring complex modulation circuitry.
Solution Approach 2:
The invention changes the antenna impedance parameter from a fixed state to a dynamically variable state. By using a delta-sigma modulator to control the impedance switching between multiple values, the system can generate arbitrary signal waveforms. This parameter change approach allows simple binary switching components to produce complex modulation schemes, resolving the contradiction between signal versatility and device complexity.
2Productivity
If multiple tags transmit simultaneously using backscattering, then communication efficiency improves, but data collisions occur due to overlapping RF spectra
Solution Approach 1:
The patent enables multiple tags to transmit simultaneously without data collisions by allowing each tag to use arbitrary modulation schemes with distinct spectral characteristics. The delta-sigma modulator generates unique signal waveforms for each tag, and the reader can differentiate between tags using signal processing techniques. This parameter change in signal waveform generation allows simultaneous transmissions to be distinguished, maintaining both high productivity and reliability.
3Use of energy by moving object
If passive tags are used to reduce power consumption, then energy efficiency improves, but the tags cannot generate their own RF carrier signal
Solution Approach 1:
The patent segments the signal generation function from the power consumption function. The delta-sigma modulator and impedance switching circuitry generate arbitrary complex modulation signals by controlling the reflection coefficient of the backscattered carrier, rather than generating the carrier itself. This segmentation allows passive tags to maintain low power consumption while achieving versatile signal generation capabilities through intelligent processing of the received carrier signal.
Solution Approach 2:
The invention uses the received RF carrier from the reader as an intermediary to generate the transmitted signal. Instead of generating their own carrier, passive tags use the incoming carrier as a reference and modulate it through impedance switching controlled by the delta-sigma modulator. This intermediary approach enables complex signal generation without requiring local oscillators or carrier generation circuitry, maintaining energy efficiency while achieving signal versatility.
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 wireless devices to backscatter arbitrary signals, including filtered versions and single sideband signals, improving communication efficiency in RFID systems.
Implementation Method 1
The antenna 123 of the reader 120 couples energy 140 to the tag 130. 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
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
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.