Embracing Interference in Wireless Systems

The wireless medium is a shared resource. If nearby devices transmit at the

same time, their signals interfere, resulting in a collision. In traditional

networks, collisions cause the loss of the transmitted information. For this

reason, wireless networks have been designed with the assumption that

interference 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 interference

as an inherently counterproductive phenomenon that should to be avoided, we

design practical systems that transform interference into a harmless, and

even a beneficial phenomenon. To achieve this goal, we consider how wireless

signals interact when they interfere, and use this understanding in our

system designs. Specifically, when interference occurs, the signals get

mixed on the wireless medium. By understanding the parameters of this

mixing, we can invert the mixing and decode the interfered packets; thus,

making interference harmless. Furthermore, we can control this mixing

process to create strategic interference that allow decodability at a

particular receiver of interest, but prevent decodability at unintended

receivers and adversaries. Hence, we can transform interference into a

beneficial phenomenon that provides security.

Building on this approach, we make four main contributions: We present the

first WiFi receiver that can successfully reconstruct the transmitted

information in the presence of packet collisions. Next, we introduce a WiFi

receiver design that can decode in the presence of high-power

cross-technology interference from devices like baby monitors, cordless

phones, microwave ovens, or even unknown technologies. We then show how we

can harness interference to improve security. In particular, we develop the

first system that secures an insecure medical implant without any

modification to the implant itself. Finally, we present a solution that

establishes secure connections between any two WiFi devices, without having

users enter passwords or use pre-shared secret keys.