WARP Featured Heavily at MobiCom 2015 in Paris

WARP has a significant presence at this year's MobiCom conference in Paris. Typical acceptance rate at the conference is between 10-15%. Out of 200+ submissions, this highly selective peer review process produced only 38 papers high quality papers for the main conference. Of those papers a total of 5 papers are built on WARP.

Main Conference Papers

ToneTrack: Leveraging Frequency-Agile Radios for Time-Based Indoor Wireless Localization - J Xiong, K Sundaresan, and K Jamieson, University College London and NEC Labs


Indoor localization of mobile devices and tags has received much attention recently, with encouraging fine-grained localization re- sults available with enough line-of-sight coverage and hardware infrastructure. Some of the most promising techniques analyze the time-of-arrival of incoming signals, but the limited bandwidth available to most wireless transmissions fundamentally constrains their resolution. Frequency-agile wireless networks utilize band- widths of varying sizes and locations in a wireless band to effi- ciently share the wireless medium between users. ToneTrack is an indoor location system that achieves sub-meter accuracy with min- imal hardware and antennas, by leveraging frequency-agile wire- less networks to increase the effective bandwidth. Our novel signal combination algorithm combines time-of-arrival data from differ- ent transmissions as a mobile device hops across different chan- nels, approaching time resolutions previously not possible with a single narrowband channel. ToneTrack’s novel channel combina- tion and spectrum identification algorithms together with the tri- angle inequality scheme yield superior results even in non-line-of- sight scenarios with one to two walls separating client and APs and also in the case where the direct path from mobile client to an AP is completely blocked. We implement ToneTrack on the WARP hardware radio platform and use six of them served as APs to lo- calize Wi-Fi clients in an indoor testbed over one floor of an office building. Experimental results show that ToneTrack can achieve a median 90 cm accuracy when 20 MHz bandwidth APs overhear three packets from adjacent channels.

FreeBee: Cross-technology Communication via Free Side-channel - Song Min Kim, and Tian He, University of Minnesota


This paper presents FreeBee, which enables direct unicast as well as cross-technology/channel broadcast among three popular wireless technologies: WiFi, ZigBee, and Bluetooth. Our design aims to shed the light on the opportunities that cross-technology communication has to offer including, but not limited to, cross-technology interference mitigation and context-aware smart operation. The key concept of FreeBee is to modulate symbol messages by shifting the timing of periodic beacon frames already mandatory for wireless stan- dards without incurring extra traffic. Such a generic cross- technology design consumes zero additional bandwidth, alllowing continuous broadcast to safely reach mobile and/or duty-cycled devices. A new interval multiplexing technique is proposed to enable concurrent broadcasts from multiple senders or boost the transmission rate of a single sender. Theoretical and experimental exploration reveals that Free- Bee offers a reliable symbol delivery under a second and supports mobility of 30mph and low duty-cycle operations of under 5%.

Acoustic Eavesdropping through Wireless Vibrometry - Teng Wei, Shu Wang, Anfu Zhou, and Xinyu Zhang, University of Wisconsin-Madison, Institute of Computing Technology, Chinese Academy of Sciences


Loudspeakers are widely used in conferencing and infotainment systems. Private information leakage from loudspeaker sound is often assumed to be preventable using sound-proof isolators like walls. In this paper, we explore a new acoustic eavesdropping at- tack that can subvert such protectors using radio devices. Our ba- sic idea lies in an acoustic-radio transformation (ART) algorithm, which recovers loudspeaker sound by inspecting the subtle distur- bance it causes to the radio signals generated by an adversary or by its co-located WiFi transmitter. ART builds on a modeling frame- work that distills key factors to determine the recovered audio qual- ity. It incorporates diversity mechanisms and noise suppression al- gorithms that can boost the eavesdropping quality. We implement the ART eavesdropper on a software-radio platform and conduct experiments to verify its feasibility and threat level. When targeted at vanilla PC or smartphone loudspeakers, the attacker can success- fully recover high-quality audio even when blocked by sound-proof walls. On the other hand, we propose several pragmatic counter- measures that can effectively reduce the attacker’s audio recovery quality by orders of magnitude.

mTrack: High-Precision Passive Tracking Using Millimeter Wave Radios - Teng Wei and Xinyu Zhang, University of Wisonsin-Madison


Radio-based passive-object sensing can enable a new form of per- vasive user-computer interface. Prior work has employed various wireless signal features to sense objects under a set of predefined, coarse motion patterns. But an operational UI, like a trackpad, often needs to identify fine-grained, arbitrary motion. This paper explores the feasibility of tracking a passive writing object (e.g., pen) at sub- centimeter precision. We approach this goal through a practical design, mTrack, which uses highly-directional 60 GHz millimeter- wave radios as key enabling technology. mTrack runs a discrete beam scanning mechanism to pinpoint the object’s initial location, and tracks its trajectory using a signal-phase based model. In ad- dition, mTrack incorporates novel mechanisms to suppress inter- ference from background reflections, taking advantage of the short wavelength of 60 GHz signals. We prototype mTrack and evaluate its performance on a 60 GHz reconfigurable radio platform. Exper- imental results demonstrate that mTrack can locate/track a pen with 90-percentile error below 8 mm, enabling new applications such as wireless transcription and virtual trackpad.

Control Channel Design for Many-Antenna MU-MIMO - Clayton Shepard, Abeer Javed, and Lin Zhong, Rice University


Many-antenna MU-MIMO faces a critical, previously unad- dressed challenge: it lacks a practical control channel. At the heart of this challenge is that the potential range of MU- MIMO beamforming systems scales with up to the square of the number of base-station antennas once they have chan- nel state information (CSI), whereas the range of traditional control channel operations remains constant since they take place before or during CSI acquisition. This range gap be- tween no-CSI and CSI modes presents a critical challenge to the efficiency and feasibility of many-antenna base stations, as their operational range is limited to the no-CSI mode.

We present a novel control channel design for many-antenna MU-MIMO, Faros, that allows the number of base-station antennas to scale up to 100s in practice. Faros leverages a combination of open-loop beamforming and coding gains to bridge the range gap between the CSI and no-CSI modes. Not only does Faros provide an elegant and efficient control channel for many-antenna MU-MIMO, but on a more fun- damental level it exposes flexible, fine-grained, control over space, time, and code resources, which enables previously impossible optimizations. We implement our design on the Argos many-antenna base station and evaluate its perfor- mance in bridging the range gap, synchronization, and pag- ing. With 108 antennas, Faros can provide over 40 dB of gain, which enables it to function reliably at over 250 me- ters outdoors with less than 100 μW of transmit power per antenna, 10 mW total, at 2.4 GHz.

Workshops, Posters, and Demos

Poster: SoftNull: All-digital Massive MIMO Full-duplex Wireless - Evan Everett, Clayton Shepard, Lin Zhong, Ashu Sabharwal, Rice University

Last modified 3 years ago Last modified on Sep 6, 2015, 3:58:21 PM