Supporting Demanding Wireless Applications with Frequency-agile Radios

Lei Yang
Wei Hou
Lili Cao
Ben Y. Zhao
Haitao Zheng

Proceedings of 7th USENIX Symposium on Networked Systems Design and Implementation (NSDI 2010)

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Paper Abstract

With the advent of new FCC policies on spectrum allocation for next generation wireless devices, we have a rare opportunity to redesign spectrum access protocols to support demanding, latency-sensitive applications such as high-def media streaming in home networks. Given their low tolerance for traffic delays and disruptions, these applications are ill-suited for traditional, contention-based CSMA protocols.

In this paper, we explore an alternative approach to spectrum access that relies on frequency-agile radios to perform interference-free transmission across orthogonal frequencies. We describe Jello, a MAC overlay where devices sense and occupy unused spectrum without central coordination or dedicated radio for control. We show that over time, spectrum fragmentation can significantly reduce usable spectrum in the system. Jello addresses this using two complementary techniques: online spectrum defragmentation, where active devices periodically migrate spectrum usage, and non-contiguous access, which allows a single flow to utilize multiple spectrum fragments. Our prototype on an 8-node GNU radio testbed shows that Jello significantly reduces spectrum fragmentation and provides high utilization while adapting to client flows' changing traffic demands.