On the Feasibility of Effective Opportunistic Spectrum Access
Vinod Kone
Lei Yang
Xue Yang
Ben Y. Zhao
Haitao Zheng
Proceedings of the 10th ACM SIGCOMM Internet Measurement Conference (IMC 2010)
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Paper Abstract
Dynamic spectrum access networks are designed to allow today's bandwidth hungry ``secondary devices'' to share spectrum allocated to legacy devices, or ``primary users.'' The success of this wireless communication model relies on the availability of unused spectrum, and the ability of secondary devices to utilize spectrum without disrupting transmissions of primary users. While recent measurement studies have shown that there is sufficient underutilized spectrum available, little is known about whether secondary devices can efficiently make use of available spectrum while minimizing disruptions to primary users.
In this paper, we present the first comprehensive study on the presence
of ``usable'' spectrum in opportunistic spectrum access systems, and
whether sufficient spectrum can be extracted by secondary devices to
support traditional networking applications. We use for our study
fine-grain usage traces of a wide spectrum range (20MHz-6GHz) taken at 4
locations in Germany, the Netherlands, and Santa Barbara, California.
Our study shows that on average, 54% of spectrum is never used and 26%
is only partially used. Surprisingly, in this 26% of partially used
spectrum, secondary devices can utilize very little spectrum using
conservative access policies to minimize interference with primary
users. Even assuming an optimal access scheme and extensive statistical
knowledge of primary user access patterns, a user can only extract
between 20-30% of the total available spectrum. To provide better
spectrum availability, we propose frequency bundling, where
secondary devices build reliable channels by combining multiple
unreliable frequencies into virtual frequency bundles. Analyzing our
traces, we find that there is little correlation of spectrum
availability across channels, and that bundling random channels together
can provide sustained periods of reliable transmission with only short
interruptions.