Joint Colloquium Distinguished Lecture Series

Fundamental Trade-offs for Opportunistic Radio Systems

photo of Anant Sahai Wednesday, December 6th

Anant Sahai
Assistant Professor, EECS Dept, UC Berkeley


As communication systems within fixed bands approach their Shannon limits, it is now widely recognized that the real slack is in the current approach to wireless spectrum sharing. I argue that this seeming waste is a natural consequence of the current "open-loop" approach to *robustness* and the gap between the spatiotemporal scales of spectrum control and potential spectrum use. This suggests that "closed-loop" strategies will be required to improve utilization. Taking a basic physical-layer perspective, I discuss some of the trade-offs involved in the operation of opportunistic radio systems (AKA cognitive radios) that attempt to do this. The core difficulty is that cognitive radio involves sensing a "negative", namely the absence of a primary signal. This means that issues that are safely ignored in classical communication become fundamental, especially the role of modeling uncertainty.

Consideration of this allows us to rule out otherwise plausible seeming architectures. In particular, it shows that there is essentially no such thing as a cognitive radio that can operate in isolation --- cooperation and coordination is required to guarantee robust operation in the face of model uncertainty. I close with some speculation regarding what is going to be required for systems to benefit from opportunistic spectrum use.


Before joining the faculty at Berkeley in 2002, I spent 2001 at the startup Enuvis, Inc. where I was on the theoretical/algorithmic side of a team that developed new techniques for GPS detection in very low SNR environments (such as those encountered indoors in urban areas). From 1994-2000, I was a graduate student at MIT studying Electrical Engineering and Computer Science (Course 6 in MIT-speak) and was based in the Laboratory for Information and Decision Systems under Prof. Sanjoy Mitter. My research interests there started in machine understanding but shifted toward the intersection of control and information theory. I did my undergraduate work in EECS here at the University of California at Berkeley from 1990-1994.

  Return to EECS Joint Colloquium