design.tex
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\section{System Design}
\label{sec-design}
\begin{figure}[t!]
\centering
\includegraphics[width=0.46\textwidth]{./figures/system-crop.pdf}
\vspace*{3mm}
\caption{\textbf{System Components}}
\label{fig:system}
\end{figure}
\PS{} collects two types of measurements from clients---spectrum utilization,
and network performance and healthiness information---in two different
ways---synchronously and asynchronously. Figure~\ref{fig:system} shows
the main components of \PS{}.
Idle smartphones can be used to improve nearby device's network performance. For
example, in Figure~\ref{fig:system}, when \PS{} Access Point (AP) sends
synchronous query about active device's spectrum condition, \PS{} clients,
depending on proximity with interested device, will perform detailed spectrum measurements on
behalf of nearby devices. This information can then be feed into AP adaption
algorithms for channel assignment, rate adaption or power control---all without
disturbing the active client.
On other hand, to cope with rapidly-changing network environment caused by mobility,
smartphones already perform aggressive network exploration and thus naturally
generate a high-resolution flow of measurements. Harnessing this behavior for
network monitoring purpose only requires to deliver the measurements to those
who can make use of it. Besides, lightweight network performance tests can be
conducted using smartphones' idle cycles without consuming noticeable amount of
energy. All these measurements can be uploaded in a energy neutral way
asynchronously for long-term network monitoring purpose.