Wireless connectivity remains a bottleneck for scalable, sustainable embedded deployments: the ISM bands are congested and conventional transmitters dominate a tag’s energy budget. AudioCast sidesteps both problems by transmitting in the 88–108 MHz FM broadcast band, where path loss is at least 10x lower than at 2.4 GHz and where billions of FM receivers already exist.
A single tunnel-diode oscillator generates the carrier and is self-modulated with data encoded as baseband audio. The result is a frequency-modulated transmission that consumes under 200 µW yet travels over 130 m line-of-sight. Because the tag needs no external carrier or ambient signal, AudioCast defines a new class of beyond-backscatter transmitters that keep backscatter-like power consumption without its infrastructure dependence.
AudioCast was published in IMWUT 2025 and received a Distinguished Paper Award at UbiComp ‘26. It was demonstrated at MobiSys ‘25 and UbiComp ‘25, and was featured by NUS Computing.
Publications
AudioCast: Enabling Ubiquitous Connectivity for Embedded Systems through Audio-broadcasting Low-power Tags
C. Rajashekar Reddy*, Dhairya Shah*, Nobel Ang, and Ambuj Varshney
@article{audiocast_imwut25,author={Reddy, C. Rajashekar and Shah, Dhairya and Ang, Nobel and Varshney, Ambuj},title={AudioCast: Enabling Ubiquitous Connectivity for Embedded Systems through Audio-broadcasting Low-power Tags},year={2025},issue_date={June 2025},publisher={Association for Computing Machinery},address={New York, NY, USA},volume={9},number={2},url={https://doi.org/10.1145/3729471},doi={10.1145/3729471},journal={Proc. ACM Interact. Mob. Wearable Ubiquitous Technol.},series={ACM IMWUT '25},month=jun,articleno={27},numpages={32},keywords={Beyond-backscatter transmitters, Embedded systems, FM-broadcast spectrum}}
Enabling Low-power Ubiquitous Connectivity for Embedded Systems through Audio-Broadcasting Tags
Dhairya Shah, Rajashekar Reddy Chinthalapani, and Ambuj Varshney
The challenges in wireless connectivity continue to hinder the widespread, scalable, and sustainable deployment of embedded systems. We introduce AudioCast to address the issues of spectrum scarcity-induced contention and high power consumption of transmitters. It leverages the availability of FM radio receivers operating within the 88–108 MHz spectrum, taking advantage of the superior radio-wave propagation characteristics afforded by lower-frequency bands. Specifically, AudioCast achieves at least a 10x reduction in path loss compared to the 2.4 GHz and 5 GHz ISM bands. This capability enables reliable long-distance communication while minimizing congestion and interference. AudioCast employs a single tunnel diode oscillator to generate carrier signals, which are then self-modulated with data encoded in baseband audio signals. This results in frequency-modulated transmissions that consume under 200 ?W of power, yet travel over 130 m in line-of-sight conditions. Unlike backscatter-based systems, AudioCast does not require an external carrier or depend on ambient signals, introducing a new category of transmitters termed Beyond-Backscatter transmitters, all while maintaining similar low power consumption.
@article{audiocast_ubicomp25demo,author={Shah, Dhairya and Chinthalapani, Rajashekar Reddy and Varshney, Ambuj},title={Enabling Low-power Ubiquitous Connectivity for Embedded Systems through Audio-Broadcasting Tags},year={2026},isbn={9798400714771},publisher={Association for Computing Machinery},address={New York, NY, USA},url={https://doi.org/10.1145/3714394.3754406},doi={10.1145/3714394.3754406},booktitle={Companion of the 2025 ACM International Joint Conference on Pervasive and Ubiquitous Computing},pages={357–361},numpages={5},keywords={fm-broadcast spectrum, wireless transmitters, embedded systems, internet of things, tunnel diodes},location={Finland},series={ACM UbiComp '25}}
Demo: Enabling Ubiquitous Connectivity for Embedded Systems through Audio-broadcasting Low-power Tags
C. Rajashekar Reddy*, Dhairya Shah*, and Ambuj Varshney
@article{audiocast_mobisys25demo,author={Reddy, C. Rajashekar and Shah, Dhairya and Varshney, Ambuj},title={Demo: Enabling Ubiquitous Connectivity for Embedded Systems through Audio-broadcasting Low-power Tags},year={2025},publisher={Association for Computing Machinery},address={New York, NY, USA},url={https://doi.org/10.1145/3711875.3734380},doi={10.1145/3711875.3734380},series={ACM MobiSys '25},journal={The 23rd Annual International Conference on Mobile Systems, Applications and Services (MobiSys '25)}}
AudioCast: Enabling Ubiquitous Connectivity for Embedded Systems through Audio-broadcasting Low-power Tags