| dc.description.abstract | Recent advances in low-power technologies have resulted in the proliferation of
inexpensive handheld mobile computing devices. Soon, just like the Internet empow-
ered a whole new world of applications for personal computers, the development and
deployment of robust ubiquitous wireless networks will enable many new and exciting
futuristic applications. Certain to be an important part of this future is a class of
networks known as "mobile ad hoc networks." Mobile ad hoc networks (or simply
"ad hoc networks") are local-area networks formed "on the spot" between collocated
wireless devices. These devices self-organize by sharing information with their neigh-
bors to establish communication pathways whenever and wherever they are. For ad
hoc networks to succeed, however, new protocols must be developed that are capable
of adapting to their dynamic nature.
In this dissertation, we present a number of adaptive protocols that are designed
for this purpose. We investigate new link layer mechanisms that dynamically monitor
and adapt to changes in link quality, including a protocol that uses common control
messages to form a tight feedback control loop for adaptation of the link data rate
to best match the channel conditions perceived by the receiver. We also investigate
routing protocols that adapt route selection according to network characteristics. In
particular, we present two on-demand routing protocols that are designed to take
advantage of the presence of multirate links. We then investigate the performance of
TCP, showing how communication outages caused by link failures and routing delays
can be very detrimental to its performance. In response, we present a solution to this
problem that uses explicit feedback messages from the link layer about link failures to
adapt TCP's behavior. Finally, we show how link failures in heterogeneous networks
containing links with widely varying bandwidth and delay can cause repeated "modal"
changes in capacity that TCP is slow to detect. We then present a modifed version
of TCP that is capable of more rapidly detecting and adapting to these changes. | en |
