Backscatter Communication Node for Carrier-Interference-Free RF Modulation
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Solution Overview
Problem
Existing passive and semi-passive transmitters using backscattering generate backscattered waves with low power compared to the carrier signal, causing interference and requiring sophisticated receivers, and frequency shifting methods waste half the power and generate interference to other devices.
Innovation Solution
A wireless communication node with a switch and set of impedances generates modulated RF signals by backscattering, applying a frequency offset and modulating values to create a single spectral image, using a look-up table for efficient switching to maximize backscattered energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If frequency shifting is applied to separate backscattered signal from carrier interference, then receiver filtering is simplified and interference to other devices is reduced, but half of the backscattered power is wasted and some interference is still generated
Solution Approach 1:
The patent changes the frequency parameter of the backscattered signal by introducing a frequency offset Δf in the modulation process. This frequency shifting moves the spectral image away from the carrier frequency, enabling receiver filtering while maintaining signal power efficiency through optimized modulation schemes.
2Reliability
If backscattered waveforms are made tolerant to unmodulated carrier interference through line codes and sophisticated receivers, then signal reception is improved, but the RF generator causes interference to other wireless devices and complex receiver design is required
Solution Approach 1:
The patent extracts the modulated signal from the carrier frequency by introducing a frequency offset, creating a spectral image at a different frequency. This separation removes the harmful carrier interference from the backscattered signal, eliminating interference to other devices while simplifying receiver design through frequency-based filtering.
3Use of energy by moving object
If passive and semi-passive transmitters use backscattering to achieve low power consumption, then power efficiency is improved, but the backscattered wave power is quite small compared to the carrier signal power
Solution Approach 1:
The patent optimizes the impedance values and switching patterns to maximize the backscattered signal power while maintaining low power consumption. By carefully selecting impedance values and using frequency offset modulation, the system improves backscattered power without requiring additional power amplifiers or oscillators.
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
The method increases useful reflected power by 3 dB and efficiently transmits modulated signals with minimal computation, utilizing all carrier energy for communication without creating spectral images, thus reducing interference.
Implementation Method 1
The semi- or passive devices generate transmitting signals by using an antenna mismatched to the incoming RF carrier signal, thus reflecting or backscattering the incoming radio waves
Implementation Method 2
The received illuminating RF signal at the antenna is modulated by the generated modulating values and reflected by the antenna to generate and transmit the modulated RF signal
Data Source
AI summary
A wireless communication node (500) and method therein for generating and transmitting a modulated radio frequency (RF) signal by means of backscattering are disclosed. The wireless communication node (500) comprises an antenna (510) configured to receive a illuminating RF signal, a switch (520) that has M states, a set of impedances (530) comprising Mimpedances (Z1, Z2 . . . ZM). The antenna (510) is coupled to the set of impedances (530) by the switch (520). The wireless communication node (500) further comprises a modulating value generator (540) configured to generate modulating values based on data to be transmitted and a frequency offset and a switch controller (550) configured to switch the state of the switch (520) based on the generated modulating values such that the antenna (510) is connected to a selected impedance among the M impedances. The received illuminating RF signal at the antenna (510) is modulated by the generated modulating values and reflected by the antenna (510) to generate and transmit the modulated RF signal. The switching rate is an integer multiple of the data rate, the integer is greater than 1 and the center frequency of the modulated RF signal has the frequency offset with respect to the center frequency of the received illuminating RF signal.