(Georgia Institute of Technology, 2006)
Jun, Hyewon; Ammar, Mostafa H.; Corner, Mark D.; Zegura, Ellen W.
Disruption tolerant networks (DTNs) are wireless mobile networks
that are characterized by frequent partitions and long delays. Such
networks can be used in highly-challenged environment in which
energy resources are limited. Efficient power management, therefore,
is essential for their success. In this paper, we present a hierarchical
power management in DTNs where nodes are equipped with
two complementary radios: a long-range, high power radio and a
short range, low-power radio. In this architecture, energy can be
conserved by using the low-power radio to discover communication
opportunities with other nodes and then wake up the high-power radio
to undertake the data transmission. We develop a generalized
power management framework and its variations around this idea
and evaluate their relative performance. In addition, for the case in
which traffic load can be predicted, we devise approximation algorithms
to control the sleep/wake-up cycling to provide maximum
energy conservation while discovering enough communication opportunities
to handle a given traffic load. We evaluate our schemes
and our choice of parameters through ns-2 simulations. Our simulation
results show that the generalized power management mechanism
could augment the usefulness of the low power radio and
achieve better energy efficiency than mechanisms relying on one
radio for discovery. In addition, our approximation algorithms reduce
energy consumption from 73% to 93% compared with the
case without power management. We also observe that while an
additional low power radio does reduce the energy consumption
needed for discovery, the improvement could be negligible in mobile
DTNs due to the low density of nodes.
(Georgia Institute of Technology, 2006)
Zhao, Wenrui; Chen, Yang; Ammar, Mostafa H.; Corner, Mark D.; Levine, Brian; Zegura, Ellen W.
Delay tolerant networks (DTNs) are a class of
emerging networks that are subject to frequent and long-duration
partitions. Due to intermittent connectivity, DTNs might
be significantly limited in supporting application needs, for
example, leading to low throughput or high delay. To address
this problem, we propose the use of throw-boxes to improve
data delivery performance. Throw-boxes are small, inexpensive
devices equipped with wireless interfaces and deployed to relay
data between mobile nodes. Being small and inexpensive, throwboxes
represent a flexible and cost-effective approach to enhance
network capacity.
In this paper, we systematically study two inter-related issues,
namely deployment and routing, in using throw-boxes for
throughput enhancement. Specifically, we develop algorithms
for throw-box deployment and data forwarding under various
routing strategies, including single path, multi-path and epidemic
routing. Using extensive ns simulations, we evaluate the utility of
throw-boxes and the impact of various routing and deployment
strategies on network performance. Our objective is to guide
the design and operations of throw-box-enhanced DTNs. We
find that throw-boxes are very effective in improving both data
delivery ratio and delay, especially for multi-path routing and
environments with regular node movement.