(Georgia Institute of Technology, 2004)
Zhao, Wenrui; Ammar, Mostafa H.; Zegura, Ellen W.; Lee, Chungki; Jun, Hyewon
Power management is a critical issue in wireless ad hoc
networks where the energy supply is limited. In this paper,
we investigate a routing paradigm, Message Ferrying (MF), to
save energy while trading off data delivery delay. In MF, special
nodes called ferries move around the deployment area to deliver
messages for nodes. The reliance on the movement of ferries to
deliver data increases the delivery delay. However, nodes can save
energy by disabling their radios when ferries are far away. To
exploit this feature, we present a power management framework,
in which nodes switch their power management modes based on
the knowledge of ferry location. We evaluate the performance of
our scheme using ns-2 simulations and compare it with Dynamic
Source Routing (DSR). Our simulation results show that MF
achieves energy savings as high as 95%
compared to DSR without
power management and still delivers more than 98%
of data. In
contrast, a power-managed DSR delivers much less data than
MF to achieve similar energy savings. In the scenario of heavy
traffic load, the power-managed DSR delivers less than 20%
of
data. MF also shows robust performance for highly mobile nodes,
while the performance of DSR suffers significantly. Thus, delay
tolerant applications should use MF rather than a multihop
routing protocol to save energy efficiently when both routing
approaches are available.
(Georgia Institute of Technology, 2004)
Ammar, Mostafa H.; Zegura, Ellen W.; Zhao, Wenrui
The performance of large-scale wireless ad hoc
networks is often limited by the broadcasting nature of the
wireless medium and the inherent node energy constraints. While
the impact of the former on network capacity has been studied
extensively in the literature, the impact of energy constraints
has not received as much attention. In this paper, we study
the capacity limitations resulting from the energy supplies in
wireless nodes. We define the energy-limited capacity of a wireless
network as the maximum amount of data the network can
deliver before the nodes run out of energy. This energy-limited
capacity is an important parameter in networks where operating
lifetime is critical, such as ad hoc networks deployed in hazardous
environments and sensor networks. We study two types of
static networks, networks without any infrastructure support and
networks where base stations with unlimited energy are deployed
to support data forwarding. We consider two kinds of traffic
models motivated by ad hoc networks and sensor networks. We
derive upper and lower bounds on the energy-limited capacity
of these networks. While throughput has been shown to not
scale with node density in static networks by previous studies,
our results show that, depending on the energy consumption
characteristics of wireless communication, the energy-limited
capacity can scale well under both traffic models. In addition,
we show that the deployment of base stations can improve the
energy-limited capacity of the network, especially for networks
with sensor traffic.