A Dual Technology Femto Cell Architecture for Robust Communication using Whitespaces

We propose WhiteCell — a dual technology femto cell architecture for wide-area wireless users that addresses some of the critical challenges being faced by the cellular industry today in better meeting surging demands. WhiteCell extends the traditional notion of a femto cell in which small, low-power, shortrange access points are placed in homes to improve coverage, connectivity and spatial re-use in the cellular operator's own frequency and technology. In WhiteCell, each indoor access point is equipped with the ability to communicate over two separate blocks of spectrum — the cellular operator's own spectrum using the same technology as before, and the recently released swath of TV whitespace spectrum that allows opportunistic use under specific FCC guidelines in the US. The two spectrum blocks and their corresponding technologies complement each other very well. While whitespace spectrum allows us to add significant capacity to the otherwise constrained cellular spectrum, the cellular frequencies allows the system to support some minimal expectation of performance guarantee that whitespace alone cannot, due to license exclusivity. While this extension is conceptually simple, it provides dramatic performance gains for both the cellular operator and the end users who are putting increasing demands on the limited cellular spectrum. This paper describes the overall WhiteCell architecture, a system implementation, and various challenges addressed in efficiently utilizing whitespace spectrum including a collaborative approach in spectrum sensing, as well as in efficiently transitioning traffic across this dual technology structure. In addition, the paper demonstrates the significant performance advantages of the architecture through detailed evaluation of our WhiteCell prototype.