Efficient Communication in Stationary Wireless Sensor Networks
Thesis, Ayad Salhieh)
Wireless sensor networks have
become possible because of the on-going improvements in sensor
technology and VLSI. An important issue in smart sensor networks is
achieving efficient operation because of the limited available power.
Energy conservation is a critical issue in wireless sensor networks for
nodes and network life, as the nodes are powered by batteries only. In
order to maximize the lifetime of the nodes and the network, the
traffic should be routed such that the energy consumption is balanced
among the nodes in proportion to their energy reserves, instead of
routing to minimize the absolute consumed power for each message.
In this dissertation we focus
on three major points toward an efficient communication for stationary
sensor networks. First, we study the relationship between the choice of
topology and the power dissipated in the network. Second, we evaluate
the effect of power metrics on the choice of routing and the power
dissipated in the network. Finally,we determine the effect of using
local information instead of using global information on extending the
lifetime of the network.
Routing packets within a
large-scale wireless sensor network without storage overhead and
routing table updates is a challenging problem. With a large number of
sensors the overhead plays a significant role in the scalability of the
routing protocol. In order to avoid this communication overhead, sensor
network routing demands new and efficient methods for routing packets.
In order to remove or reduce this overhead, the routing protocol needs
some way of implicitly, rather than explicitly, defining paths.
We introduce first the idea
of directional routing, which requires only that each sensor know its
location within the network relative to the sending node and the
destination. This allows the use of simple directional routing based on
local information only. For dense networks, sensors near a trajectory
from the source to the destination can be found. However, sensors are
energy-constrained devices, so selecting paths within this network
could benefit from an energy-aware routing process.
Secondly, the problem of
selecting paths leads us to examine the relationship between power
usage and the number of neighbors in a wireless sensor network.
Selecting the number of neighbors controls the type of topology to be
used. The question that we are seeking to answer is what is the best
topology for a wireless network of sensors, assuming we can control the
placement of these sensors and the sensor locations are fixed relative
to each other. Because the number of neighbors differs with different
topologies, one expects different topologies to have different power
usage rates. Even our simulations of the contention-free case show that
different topologies have different levels of power efficiency. The
results show that the total power consumption is reduced for topologies
with fewer neighbors even though topologies with more neighbors require
Third, a routing protocol for
wireless sensor networks need to be power aware. In order to be power
aware we evaluate a number of power-aware routing protocols based on
local information only. The simulations show that basing the routing
decision on the remaining power of neighboring nodes is not enough by
itself. Instead, using the directional value and the sum of power
remaining at the next neighbors gives the routing protocol a broader
perspective about the condition of the network from a local point of
view and enhances the routing decision process.
Finally, in order to
gain some understanding of the quality of these local metrics, we also
compare the energy usage and path length of these local methods with
respect to some routing techniques based on global information. This
evaluation demonstrates that changing the routing metric can
dramatically affect the performance of the sensor network. These
results also shows trade-off between extending the lifetime of the
sensor network and reducing the average number of hops a message
travels to the base station.