[Paper Review] FM Backscatter: Enabling Connected Cities and Smart Fabrics

Anran Wang, Vikram Iyer+3 more|arXiv (Cornell University)|Feb 22, 2017

Energy Harvesting in Wireless Networks17 references63 citations

TL;DR

This paper introduces a system that uses ambient FM radio signals as a backscatter source to enable outdoor communication with cars, smartphones, and smart fabrics. It achieves up to 3.2 kbps data rates over 5–60 feet with ultra-low power consumption (~11 µW).

ABSTRACT

This paper enables connectivity on everyday objects by transforming them into FM radio stations. To do this, we show for the first time that ambient FM radio signals can be used as a signal source for backscatter communication. Our design creates backscatter transmissions that can be decoded on any FM receiver including those in cars and smartphones. This enables us to achieve a previously infeasible capability: backscattering information to cars and smartphones in outdoor environments. Our key innovation is a modulation technique that transforms backscatter, which is a multiplication operation on RF signals, into an addition operation on the audio signals output by FM receivers. This enables us to embed both digital data as well as arbitrary audio into ambient analog FM radio signals. We build prototype hardware of our design and successfully embed audio transmissions over ambient FM signals. Further, we achieve data rates of up to 3.2 kbps and ranges of 5-60 feet, while consuming as little as 11.07μW of power. To demonstrate the potential of our design, we also fabricate our prototype on a cotton t-shirt by machine sewing patterns of a conductive thread to create a smart fabric that can transmit data to a smartphone. We also embed FM antennas into posters and billboards and show that they can communicate with FM receivers in cars and smartphones.

Motivation & Objective

• Explore whether ambient FM signals can serve as a ubiquitous backscatter source for outdoor connectivity.
• Design a modulation scheme that turns backscatter into additive audio signals decodable by FM receivers.
• Demonstrate overlay, stereo, and cooperative backscatter to enable audio and data transmission in outdoor environments.
• Prototype hardware and proof-of-concept applications on smart fabrics and posters to validate feasibility.

Proposed method

• Leverage ambient FM transmissions as the RF source for backscatter.
• Transform backscatter from a multiplicative RF operation into an additive operation in the FM receiver audio domain.
• Implement overlay backscatter to transmit arbitrary audio on ambient FM and data on FM channels.
• Utilize stereo backscatter by exploiting unoccupied stereo bands and pilot tones to carry information.
• Employ cooperative backscatter with two phones to emulate a MIMO-like interference cancellation scheme.

Experimental results

Research questions

• RQ1 Can ambient FM signals support reliable backscatter decoding by standard FM receivers found in cars and smartphones?
• RQ2 What modulation strategies enable overlaying audio and digital data on ambient FM without requiring new radios?
• RQ3 How can stereo and cooperative backscatter enhance data rates and resilience in outdoor environments?
• RQ4 What are the practical data rates, ranges, and power consumption achievable with FM backscatter in real-world settings?

Key findings

• Achieved data rates up to 3.2 kbps and communication ranges of 5–60 feet.
• Demonstrated decoding of backscattered signals on smartphones and car FM receivers.
• Validated overlay, stereo, and cooperative backscatter techniques for diverse scenarios.
• Prototype hardware consumes as little as 11.07 µW of power.
• Fabricated smart fabrics and posters show practical proof-of-concept for outdoor FM backscatter.
• Measured FM signal strengths in urban environments indicate sufficient ambient power for backscatter.