Wireless Communications


mmFlexible: Flexible Directional Frequency Multiplexing for Multi-user mmWave Networks [Infocom 2023]

[Webpage] [paper]

Modern mmWave systems have limited scalability due to inflexibility in performing frequency multiplexing. All the frequency components in the signal are beamformed to one direction via pencil beams and cannot be streamed to other user directions. We present a new flexible mmWave system called mmFlexible that enables flexible directional frequency multiplexing, where different frequency components of the mmWave signal are beamformed in multiple arbitrary directions with the same pencil beam. Our system makes two key contributions: (1) We propose a novel mmWave front-end architecture called a delay-phased array that uses a variable delay and variable phase element to create the desired frequency-direction response. (2) We propose a novel algorithm called FSDA (Frequency-space to delay-antenna) to estimate delay and phase values for the real-time operation of the delay-phased array. Through evaluations with mmWave channel traces, we show that mmFlexible provides a 60-150% reduction in worst-case latency compared to baselines.

Ish Kumar Jain, Rohith Reddy Vennam, Raghav Subbaraman, and Dinesh Bharadia

mmSpoof: Spoofing Attacks on Automotive FMCW Radars using Millimeter-wave Reflect Array [IEEE SnP 2023]

[Webpage] [paper]

FMCW radars are integral to automotive driving for robust and weather-proof sensing of surrounding objects. At the same time, these radars are vulnerable to spoofing attacks that may cause sensor malfunction leading to fatal accidents. Many past works tried spoofing attacks on FMCW radars using an attacker device that generates spoofing signals, but they are not very effective as they require tight synchronization between the attacker and victim. We present a novel spoofing mechanism mmSpoof that is based on the reflection of radar signal with appropriate modulation to spoof the victim’s radar. Our spoofing with a mmWave reflect array eliminates the need for synchronization and is robust to various security features and countermeasures of the victim’s radar. We provide insights and mechanisms to flexibly spoof any distance and velocity on the victim’s radar using a unique frequency shift at the mmSpoof’s reflect array. mmSpoof designs a novel algorithm for estimating this frequency shift without assuming any prior information about the victim’s radar. We develop a compact and mobile setup for mmSpoof using commercial-off-the-shelf components and show the effectiveness of spoofing in realistic automotive driving scenarios with commercial radars.

R. Vennam, I. Jain, K. Bansal, J. Orozco, P. Shukla, A. Ranganathan, D. Bharadia

BSMA: scalable LoRa networks using full duplex gateways [MobiCom 2022]

[Webpage] [Paper] [Slides]

This work develops BSMA, a scalable LoRa MAC protocol that uses full duplex gateways to improve network capacity by 100% compared to CSMA in bursty loads. Implementing BSMA requires a full duplex LoRa gateway, which we develop in the 915 MHz ISM band. The implementation of a LoRa BSMA gateway is open source, and works with COTS LoRA devices.

Raghav Subbaraman, Yeswanth Guntupalli, Shruti Jain, Rohit Kumar, Krishna Chintalapudi, and Dinesh Bharadia

VRProj: Delivering 360-degree Video With Viewport-Adaptive Truncation [WPMC 2022]

[Webpage] [paper]

Delivering Virtual Reality (VR) content wirelessly involves projecting a 360-video into a 2D format and then encoding it to satisfy the wireless bitrate requirements. However, the popular equirectangular and cubemap projections offer little flexibility to adapt to changing bitrates and headset motion. In this work, we show that the truncated square pyramid projection offers high flexibility for network and headset motion adaptation. We adapt by tuning a truncation parameter that controls the video quality for different spatial regions in the 360-video. Depending on the video, our scheme improves average video quality by up to 1.1dB in PSNR and up to 4.6 in VMAF score compared to a non-adaptive baseline.

Tian Qiu, Ish Kumar Jain, Raini Wu, Dinesh Bharadia, Pamela Cosman

Two beams are better than one: Towards Reliable and High Throughput mmWave Links [Sigcomm 2021]

[Webpage] [paper]

Millimeter-wave communication with high throughput and high reliability is poised to be a gamechanger for V2X and VR applications. However, mmWave links are notorious for low reliability since they suffer from frequent outages due to blockage and user mobility. We build mmReliable, a reliable mmWave system that implements multi-beamforming and user tracking to handle environmental vulnerabilities. It creates constructive multi-beam patterns and optimizes their angle, phase, and amplitude to maximize the signal strength at the receiver. Multi-beam links are reliable since they are resilient to occasional blockages of few constituent beams compared to a single-beam system. We implement mmReliable on a 28 GHz testbed with 400 MHz bandwidth, and a 64 element phased array supporting 5G NR waveforms. Rigorous indoor and outdoor experiments demonstrate that mmReliable achieves close to 100% reliability providing 2.3x improvement in the throughput-reliability product than single-beam systems.

Ish Kumar Jain, Raghav Subbaraman, and Dinesh Bharadia

This work won the Qualcomm Innovation Fellowship 2022

SyncScatter: Enabling WiFi like synchronization and range for WiFi backscatter Communication [NSDI 2021]

[Webpage] [paper]

WiFi backscattering can enable direct connectivity of IoT devices with commodity WiFi hardware at low power. However, most existing work in this area has overlooked the importance of synchronization and have, as a result, accepted either limited range between the transmitter and the IoT device, reduced throughput via bit repetition, or both. In this paper, we present SyncScatter, which achieves accurate synchronization to incident signals at the IoT device level, while also achieving sensitivity commensurate with the maximum possible afforded by a backscattering link budget. SyncScatter creates a novel modeling framework, and derives the maximal optimal range and synchronization error that can be achieved without major performance compromises. Next, SyncScatter builds a novel hierarchical wake-up protocol, which together with a custom ASIC, achieves a range of 30+ meters at 2Mbps, with an average power consumption of 25.2µW.

Manideep Dunna, Miao Meng, Po-Han Wang, Chi Zhang, Patrick Mercier, and Dinesh Bharadia

WiForce: Wireless Sensing and Localization of Contact Forces on a Space Continuum [NSDI 2021]


Contact force is a natural way for humans to interact with the physical world around us. However, most of our interactions with the digital world are largely based on a simple binary sense of touch (contact or no contact). Similarly, when interacting with robots to perform complex tasks, such as surgery, richer force information that includes both magnitude and contact location is important for task performance. To address these challenges, we present the design and fabrication of WiForce which is a ‘wireless’ sensor, sentient to contact force magnitude and location. WiForce achieves this by transducing force magnitude and location, to phase changes of an incident RF signal of a backscattering tag. The phase changes are thus modulated into the backscattered RF signal, which enables measurement of force magnitude and contact location by inferring the phases of the reflected RF signal. WiForce’s sensor is designed to support wide-band frequencies all the way up to 3 GHz. We evaluate the force sensing wirelessly in different environments, including through phantom tissue, and achieve force accuracy of 0.3 N and contact location accuracy of 0.6 mm.

Agrim Gupta, Cédric Girerd, Manideep Dunna, Qiming Zhang, Raghav Subbaraman, Tania Morimoto, and Dinesh Bharadia

mMobile: Building a mmWave testbed to evaluate and address mobility effects [mmNets 2020]

[Webpage] [paper]

Beamforming methods need to be critically evaluated and improvedto achieve the promised performance of mmWave 5G-NR in highmobility applications like Vehicle-to-Everything (V2X) communi-cation. Conventional beam management methods developed forhigher frequency applications do not directly carry over to the 28GHz mmWave regime, where propagation and reflection character-istics are vastly different. Further, real system deployments and testsare required to verify these methods in a practical setting. In thiswork, we develop mMobile, a custom 5G-NR compliant mmWavetestbed to evaluate beam management algorithms. We describe thearchitecture and challenges in building such a testbed. We then cre-ate a novel, low-complexity beam tracking algorithm by exploitingthe 5G-NR waveform structure and evaluate its performance onthe testbed. The algorithm can sustain almost twice the averagethroughput compared to the baseline.

Ish Kumar Jain, Raghav Subbaraman, Tejas Harekrishna Sadarahalli, Xiangwei Shao, Hou-Wei Lin, Dinesh Bharadia

A 28μW IoT Tag That Can Communicate with Commodity WiFi Transceivers via a Single-Side-Band QPSK Backscatter Communication Technique [ISSCC 2020]

[Ubiquitous IoT Project Page] [slides]

More portable, fully wireless smart home setups. Lower power wearables. Batteryless smart devices. These could all be made possible thanks to a new ultra-low power Wi-Fi radio developed by electrical engineers at the University of California San Diego. The device, which is housed in a chip smaller than a grain of rice, enables Internet of Things (IoT) devices to communicate with existing Wi-Fi networks using 5,000 times less power than today’s Wi-Fi radios. It consumes just 28 microwatts of power. And it does so while transmitting data at a rate of 2 megabits per second (a connection fast enough to stream music and most YouTube videos) over a range of up to 21 meters.

P-H. P. Wang, C. Zhang, H. Yang, D. Bharadia, P. P. Mercier

Press cover by UCSD News, Tech Explorist, ACM News, Hacker News

ScatterMIMO: Enabling Virtual MIMO with Smart Surfaces [Mobicom 2020]

[ScatterMIMO-Webpage] [paper]

In the last decade, the bandwidth expansion and MIMO spatial multiplexing have promised to increase data throughput by orders of magnitude. However, we are yet to enjoy such improvement in real-world environments, as they lack rich scattering and preclude effective MIMO spatial multiplexing. In this paper, we present ScatterMIMO, which uses smart surface to increase the scattering in the environment, to provide MIMO spatial multiplexing gain. Specifically, smart surface pairs up with a wireless transmitter device say an active AP and re-radiates the same amount of power as any active access point (AP), thereby creating virtual passive APs. ScatterMIMO avoids the synchronization, interference, and power requirements of conventional distributed MIMO systems by leveraging virtual passive APs, allowing its smart surface to provide spatial multiplexing gain, which can be deployed at a very low cost. We show that with optimal placement, these virtual APs can provide signals to their clients with power comparable to real active APs, and can increase the coverage of an AP. Furthermore, we design algorithms to optimize ScatterMIMO’s smart surface for each client with minimal measurement overhead and to overcome random per-packet phase offsets during the measurement. Our evaluations show that with commercial off-the-shelf MIMO WiFi (11ac) AP and unmodified clients, ScatterMIMO provides a median throughput improvement of 2x over the active AP alone.

Manideep Dunna, Chi Zhang, Daniel Sievenpiper, Dinesh Bharadia

Press cover by UCSD News, Hackster News

FreeRider: Backscatter Communication Using Commodity Radios [CoNext 2017]


We introduce the design and implementation of FreeRider, the first system that enables backscatter communication with multiple commodity radios, such as 802.11g/n WiFi, ZigBee, and Bluetooth, while these radios are simultaneously used for productive data communication.

Pengyu Zhang, Colleen Josephson, Dinesh Bharadia, Sachin Katti

QualComp: a new lossy compressor for quality scores based on rate distortion theory [BMC bioinformatics 2013]

Idoia Ochoa, Himanshu Asnani, Dinesh Bharadia, Mainak Chowdhury, Tsachy Weissman, Golan Yona