Variable Impedance Antenna for Complex Backscatter Modulation
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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, and face challenges with data collisions due to overlapping RF spectra.
Innovation Solution
A transmission apparatus for wireless devices featuring a variable impedance antenna and a decoder that modulates the impedance value to generate complex modulated signals, allowing for the backscattering of arbitrary signals like QAM, PSK, and OFDM by switching an array of impedances based on digital waveforms or I and Q data inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If backscatter coupling is used to transmit energy and data between reader and tag, then power consumption is reduced and system simplicity is improved, but the types of signals that can be transmitted are limited and arbitrary complex modulations cannot be achieved
Solution Approach 1:
The patent applies dynamics by making the antenna impedance variable rather than fixed. The antenna impedance is dynamically adjusted based on the desired modulation type and data being transmitted, enabling complex modulations like QAM while maintaining backscatter efficiency. This dynamic adaptation allows the system to achieve arbitrary signal types without sacrificing the energy efficiency of backscatter coupling.
Solution Approach 2:
The patent changes the impedance parameter of the antenna to enable different modulation schemes. By varying the antenna impedance according to the modulation requirements (e.g., different values for I and Q components in QAM), the system can transmit arbitrary complex signals while still using power-efficient backscatter coupling. This parameter adjustment is controlled by the reader based on the desired communication mode.
2Quantity of substance
If multiple tags interact with a main reader device using backscattering, then system capacity is increased, but data collisions occur due to overlapping RF spectra
Solution Approach 1:
The patent segments the RF spectrum by assigning different center frequencies to different tags. Each tag operates at a uniquely assigned frequency within the broader RF band, which eliminates spectral overlap and data collisions. This frequency segmentation allows multiple tags to communicate simultaneously with the reader without interference, maintaining both high system capacity and reliable data transmission.
3Device complexity
If ASK or PSK modulation is used in backscattering systems, then implementation simplicity is maintained, but arbitrary complex modulations such as QAM cannot be transmitted
Solution Approach 1:
The patent creates a universal backscatter antenna system that can perform multiple modulation functions through impedance control. The same antenna structure can transmit ASK, PSK, QAM, or any arbitrary complex modulation by adjusting its impedance according to the desired signal type. This multi-functionality is achieved without adding separate transmission paths or complex modulation circuits at the tag, maintaining implementation simplicity while enabling full modulation flexibility.
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, including 8PSK, OFDM, and nQAM, and corrects for encoding errors by varying the impedance value, improving communication efficiency and reducing data collisions in RFID systems.
Implementation Method 1
an antenna for receiving an original signal and for backscattering a modulated signal containing information from the wireless device
Implementation Method 2
a variable impedance coupled to the antenna, the variable impedance having an impedance value; and, a decoder coupled to the variable impedance for modulating the impedance value, and thereby a backscattering coefficient for the antenna
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; and, a decoder 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.