Wireless Backscatter Modulation via Variable Impedance
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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 featuring a variable impedance coupled with a delta-sigma modulator to modulate the impedance and reflection coefficient of an antenna, allowing for the backscattering of complex modulation signals like 8PSK, OFDM, and nQAM, and enabling inductive coupling for error correction and signal filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional ASK or PSK modulation is used in RFID backscattering systems, then the system is simple to implement and requires less power, 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 applies parameter changes by dynamically adjusting the impedance of the backscattering antenna through a variable impedance element controlled by a modulator. This allows the system to transmit arbitrary signals including filtered QAM, sine waves, and GMSK signals by changing the reflection coefficient of the antenna, thereby achieving high signal type compatibility while maintaining the simplicity of passive backscattering operation
Solution Approach 2:
The patent implements dynamics by using a time-varying impedance element that can be dynamically controlled to match arbitrary signal waveforms. The variable impedance is adjusted in real-time according to the modulating signal, enabling the transmission of complex modulated signals while keeping the tag design relatively simple compared to active transmitters
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 resolves the collision problem by enabling each tag to transmit with a unique modulated signal waveform through dynamic impedance control. By changing the modulation parameters (frequency, phase, amplitude envelope) of each tag's backscattered signal, the system allows simultaneous transmission without collisions, improving both communication efficiency and data reliability
Solution Approach 2:
The patent applies segmentation by dividing the RF spectrum into multiple channels or time slots through different modulation schemes. Each tag can be assigned a unique modulation pattern or frequency offset, effectively segmenting the overlapping spectra and eliminating data collisions while maintaining high productivity
3Device complexity
If passive tags draw all power from the reader via electromagnetic energy, then the tags have no battery and are simpler, but the tags cannot provide enough power for complex modulation and signal processing
Solution Approach 1:
The patent applies self-service by having the passive tag generate its own modulated signal for impedance control using the harvested power from the reader's electromagnetic field. The tag uses a simple oscillator and modulator circuit that operates on the collected energy, enabling complex modulation without requiring external power or complex power management infrastructure
Solution Approach 2:
The patent enables complex modulation in passive tags by changing the operating parameters of the modulation circuit to match the available power level. The system adjusts the modulation depth, frequency, and impedance switching rates to operate within the power constraints of passive energy harvesting, achieving sophisticated signal transmission with minimal power
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 arbitrary modulated signals, including complex waveforms, and improves communication efficiency by reducing data collisions and signal overlap, allowing for error correction and filtering 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
Passive tags do not have their own power supply and therefore draw all power required from the reader 120 by electromagnetic energy received via the tag's antenna 133.
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
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.