Ambuj
Varshney

We enjoy building systems. This involves embedded platform design, programming, networking, and real-world deployments of embedded systems. The required skill set ranges from chip fabrication and programming microcontrollers to developing networking and wireless protocols, distributed computing concepts, machine learning frameworks, and prototyping applications for various scenarios.

Our work is interdisciplinary, and we welcome students from diverse technical backgrounds (EE, ECE, CSE, Physics, etc.).

Research directions:

• Tunnel Diodes: These are exotic and now commercially obsolete semiconductor devices operating at voltages (tens of millivolts) much lower than the sub-threshold limit of transistors. Tunnel diodes have a number of fascinating characteristics, including negative resistance at low power consumption due to quantum mechanical effects. We are designing beyond-transistor systems using tunnel diodes to enable sustainable embedded systems operating under conditions challenging for today's transistor-based electronics. For example, this includes operations on minuscule amounts of energy harvested from the environment, below the so-called cold-start voltage of harvesters (approximately 200 mV), as dictated by limits imposed by Swanson and Meindl in 1972.

  We have designed energy-efficient sensors that track light conditions and relay LiFi transmissions over radio waves [HotMobile 2023], a low-power breathing rate sensor [RFID 2024], beyond-backscatter transmitters [MobiSys 2022], [EnsSys 2023], and enhanced the range of conventional backscatter mechanisms by replacing transistor-based switches with tunnel diodes [MobiCom 2019], [MobiCom 2020].

• Embedded Systems with Stochastic Parrots: We design embedded systems that leverage the capabilities of stochastic parrots, such as language and image models. OTTER is a system that analyzes sensor data by leveraging large language models [MobiCom 2023, Short Paper, and Student Research Competition Third Winner (UG)]. Another effort, VoCopilot, has focused on designing a low-power tracker for monitoring vocal interactions [ArXiv]. Finally, through the design of PixelGen, we are rethinking the architecture of embedded cameras [ArXiv], applied to scenarios like mixed-reality headsets (IPSN 2024 Best Demonstration Runner-up).

• Beyond Radio Frequency: We devise beyond-conventional mechanisms for wireless communications in embedded systems. The need for these mechanisms is motivated by the energy challenges of conventional radio frequency-based mechanisms and the constraints of operating on a shared radio spectrum with an ever-increasing number of wireless devices. In particular, we have explored the use of Li-Fi (or visible light communication) [VLCS 2016], [HotNets 2018], [MobiSys 2020], [TON 2023]. More recently, we started efforts to use non-standard parts of the spectrum for embedded systems communications like FM broadcast [EnsSys 2023].

In the past, I have worked on:

• Backscatter Transmitters: I worked on designing energy-efficient wireless transmitters based on the backscatter mechanism. They overturned the notion that backscatter is a short-range mechanism while also tackling the reader cost challenges of the conventional (and widely deployed) RFID-based backscatter systems [SenSys 2017]. I also worked on designing a novel class of embedded platforms sans computational elements, enabling the design of a low-powered battery-free light sensor leveraging the backscatter mechanism [VLCS 2017 (Best Paper Award)] (MOBICOM 2017 (SRC) Winner), a battery-free radio tomographic imaging system (Best Demonstration at WiSec 2018), and exploiting low-power oscillator jitter for fingerprinting of the backscatter tags [HotNets 2021].

• Electronically Steerable Directional Antennas: I started my doctoral studies by exploring electronically steerable directional antennas called SPIDA. I designed one of the world's first such testbeds for wireless embedded systems. I developed a bulk forwarding protocol achieving the highest goodput over 802.15.4 links [SenSys 2015]. Another work, jointly done with CSIRO (Australia), UNSW (Australia), and the University of Utah, demonstrated device-free localization using radio tomographic imaging [IPSN 2015].

For more details, please see my full list of publications.

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I have served or am serving on the technical program committees of the following conferences:

• IMC 2025
• INFOCOM 2025
• IMC 2024
• SENSYS 2024
• EWSN 2024
• INFOCOM 2024
• SENSYS 2023
• INFOCOM 2023
• IoTDI 2023
• INFOCOM 2022
• ICDCS 2021
• INFOCOM 2021
• ICDCS 2019
• IoTDI 2019

I was also involved in the organization of the following scientific events:

• IPSN 2019 Posters (co-chair with Prof. Nirupama Bulusu, Portland State University)
• IPSN 2019 PhD Forum (panelist with Prof. Anthony Rowe, CMU, and Prof. Olga Saukh, Graz)
• SECON 2020 (Publicity Chair)
• INFOCOM 2022 (Session Chair)
• MOBICOM 2023 (Web Chair)

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Before joining the National University of Singapore, I was a Postdoctoral Scholar at the Department of Electrical Engineering and Computer Sciences of the University of California, Berkeley. I was affiliated with Lab11 and mentored by Prof. Prabal Dutta. My training was funded by the 2019 ABB Research Award in Honor of Hubertus von Grünberg.

Before that, I was a doctoral student at the Department of Information Technology of Uppsala University, Sweden (established in 1477!). My doctoral dissertation tackled the challenges of enabling sustainable deployment of embedded systems, particularly through the design of energy-efficient radio transmitters. Prior to that, I was (briefly) a software engineer at NXP Semiconductors working on the ZigBee protocol stack.

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My research has been funded through grants from government agencies (Swedish Innovation Agency, Vetenskapsrådet (Sweden), Ministry of Education (Singapore)), university funding (ODPRT, ARTIC), and grants and unrestricted gifts from industry (NCS, Google, and ABB).