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Systems-Level Support for Mobile Device Connectivity.
Nicholson, Anthony J.
Nicholson, Anthony J.
2008
Abstract: The rise of handheld computing devices has
inspired a great deal of research aimed at
addressing the unique problems posed by their
mobile, "always-on" nature. In order to help
mobile devices navigate a complex world of
overlapping, uneven public wireless coverage, one
must be mindful of the distinction between
nomadic usage and true mobility. Accordingly,
systems research must move beyond simply
optimizing for a set of local conditions (e.g.,
finding the best access point for a laptop user
in a stationary location) to considering the
"derivative of connectivity" when network
conditions are constantly in flux.
This dissertation presents a new paradigm for
networking support on mobile devices. This
project has several complementary aspects. As
devices encounter network connectivity our system
both evaluates the application-level quality of
WiFi access points and updates a device-centric
mobility model. Together, this mobility model and
AP quality database yield "connectivity
forecasts," which let applications optimize not
just for current network conditions but for
the expected big picture to come. Results of a
prototype deployment in several cities shows that
considering the application-level quality of APs
(rather than just signal strength) significantly
boosts the success rate of finding a usable
access point. Furthermore, this dissertation
shows how connectivity forecasts---even with
minimal model training time---allow several
applications commonly found on mobile devices to
reap significant benefits, such as extended
battery life.
Mobile devices are often within range of multiple
connectivity options, however, and choosing just
one therefore ignores potential connectivity.
This dissertation describes a virtual link layer
for Linux, called Juggler, that uses one network
card to simultaneously associate with many WiFi
APs, ad hoc groups or mesh networks. The results
show how Juggler can boost effective bandwidth by
striping data across multiple APs, enable
seamless 802.11 handoff by preemptively
associating with the "next" AP before the
current one become unusable, and maintain a
modest side-channel to the user's personal area
network or mesh network without impacting
foreground bandwidth to infrastructure.