Ambient ISM Backscatter Codeword Translation for Commodity Radios
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Solution Overview
Problem
Existing backscatter communication systems require specialized hardware for generating excitation RF signals and decoding backscattered signals, limiting their deployment to commodity devices like smartphones and tablets.
Innovation Solution
A low-power backscatter communication system that uses codeword translation to modulate data on existing wireless signals, allowing decoding by commodity radios, and employs frequency shifting to reduce interference, with a MAC protocol for coordinating multiple tags.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If specialized hardware is used to generate and decode RF signals for backscatter communication, then communication reliability is improved, but device complexity and deployment difficulty increase
Solution Approach 1:
The patent enables standard WiFi radios to perform multiple functions: serving both as excitation signal sources and as backscatter signal decoders. This eliminates the need for specialized backscatter hardware while maintaining communication reliability through the use of commercially available, well-tested WiFi devices that can be deployed ubiquitously.
Solution Approach 2:
The invention uses copies of existing WiFi communication protocols and signal structures. By leveraging the familiar OFDM modulation, packet formats, and frequency structures of standard WiFi, the system allows conventional radios to decode backscattered signals without requiring specialized hardware design, thus reducing complexity while preserving reliability.
2Stability of the object's composition
If a dedicated continuous wave signal generator is used as excitation RF signal source, then signal stability is improved, but device complexity and cost increase
Solution Approach 1:
Standard WiFi radios inherently generate stable RF signals through their OFDM modulation process. The patent leverages this existing signal generation capability, using the WiFi radio's transmitted packets as the excitation source for backscatter communication, thereby eliminating dedicated signal generators while maintaining sufficient signal stability for reliable backscatter decoding.
3Ease of operation
If backscatter communication uses commodity devices, then ease of deployment is improved, but signal decoding capability deteriorates
Solution Approach 1:
The patent modifies the WiFi packet structure by introducing controllable variations in packet length and inter-packet timing. These parameter changes create detectable patterns in the backscattered signals that commodity WiFi radios can decode using their existing signal processing capabilities, thus enabling easy deployment with off-the-shelf devices without sacrificing decoding performance.
4Adaptability or versatility
If multiple tags communicate on the same channel, then system versatility is improved, but signal collision and interference increase
Solution Approach 1:
The patent implements a structured communication protocol where multiple tags transmit backscatter signals in periodic time slots. By coordinating transmission timing and using variable packet lengths, the system allows multiple tags to share the same channel without collisions, as each tag transmits during its designated time window while others remain silent, thus enabling multi-tag support without interference.
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 effective communication using commodity devices, achieving throughput of up to 60 kbps in line-of-sight and 20 kbps in non-line-of-sight deployments, supporting up to 20 tags with fair uplink communication.
Implementation Method 1
Backscatter communication has attracted interest for applications such as implantable sensors, wearables, and smart home sensing because of its ability to offer low power connectivity to these sensors
Implementation Method 2
A low-power backscatter communication system that uses codeword translation to enable communication on existing wireless devices by modifying the amplitude, phase, or frequency of the excitation signal
Data Source
AI summary
A backscatter tag device includes, in part, a receiver configured to receive a packet conforming to a communication protocol defining a multitude of codewords, a codeword translator configured to translate at least a first subset of the multitude of codewords disposed in the packet to a second multitude of codewords defined by the protocol in response to a data the backscatter tag is invoked to transmit, and a transmitter configured to transmit the packet supplied by the codeword translator at a frequency different than the first frequency at which the packer is received. The communication protocol may optionally be the 802.11g/n, ZigBee or the Bluetooth communication protocol.