Embracing Interference in Wireless Systems

The wireless medium is a shared resource. If nearby devices transmit at thesame time their signals interfere resulting in a collision. In traditionalnetworks collisions cause the loss of the transmitted information. For thisreason wireless networks have been designed with the assumption thatinterference is intrinsically harmful and must be avoided.This book a revised version of the author's award-winning Ph.D.dissertation takes an alternate approach: Instead of viewing interferenceas an inherently counterproductive phenomenon that should to be avoided wedesign practical systems that transform interference into a harmless andeven a beneficial phenomenon. To achieve this goal we consider how wirelesssignals interact when they interfere and use this understanding in oursystem designs. Specifically when interference occurs the signals getmixed on the wireless medium. By understanding the parameters of thismixing we can invert the mixing and decode the interfered packets; thusmaking interference harmless. Furthermore we can control this mixingprocess to create strategic interference that allow decodability at aparticular receiver of interest but prevent decodability at unintendedreceivers and adversaries. Hence we can transform interference into abeneficial phenomenon that provides security.Building on this approach we make four main contributions: We present thefirst WiFi receiver that can successfully reconstruct the transmittedinformation in the presence of packet collisions. Next we introduce a WiFireceiver design that can decode in the presence of high-powercross-technology interference from devices like baby monitors cordlessphones microwave ovens or even unknown technologies. We then show how wecan harness interference to improve security. In particular we develop thefirst system that secures an insecure medical implant without anymodification to the implant itself. Finally we present a solution thatestablishes secure connections between any two WiFi devices without havingusers enter passwords or use pre-shared secret keys.