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Collaborative Area Monitoring Using Wireless Sensor Networks with Stationary and Mobile Nodes
EURASIP Journal on Advances in Signal Processing
Hindawi Publishing Corporation
Collaborative Area Monitoring Using Wireless Sensor Networks with Stationary and Mobile Nodes
Theofanis P. Lambrou 0
Christos G. Panayiotou 0
0 KIOS Research Center for Intelligent Systems and Networks, Department of Electrical and Computer Engineering, University of Cyprus , Nicosia 1678 , Cyprus
Monitoring a large area with stationary sensor networks requires a very large number of nodes which with current technology implies a prohibitive cost. The motivation of this work is to develop an architecture where a set of mobile sensors will collaborate with the stationary sensors in order to reliably detect and locate an event. The main idea of this collaborative architecture is that the mobile sensors should sample the areas that are least covered (monitored) by the stationary sensors. Furthermore, when stationary sensors have a “suspicion” that an event may have occurred, they report it to a mobile sensor that can move closer to the suspected area and can confirm whether the event has occurred or not. An important component of the proposed architecture is that the mobile nodes autonomously decide their path based on local information (their own beliefs and measurements as well as information collected from the stationary sensors in a neighborhood around them). We believe that this approach is appropriate in the context of wireless sensor networks since it is not feasible to have an accurate global view of the state of the environment.
1. Introduction
Recent progress in two seemingly disparate research areas
namely, distributed robotics and low power embedded
systems has led to the creation of mobile sensor networks
[
1
]. Autonomous node mobility not only brings with it
its own challenges, but also alleviates some of the
traditional problems associated with static sensor networks. It is
envisaged that in the near future, very large scale networks
consisting of both mobile and static nodes will be deployed
for applications ranging from environmental monitoring to
military applications [
2
].
In this paper we consider the problem of monitoring a
large area using wireless sensor networks (WSNs) in order to
detect and locate an event. In this context, we assume that the
event emits a signal that is propagated in the environment.
The sensors capture attenuated and noisy measurements of
the signal and the objective is to reliably detect the presence
of the event and estimate its position. By reliably we mean
that we would like to minimize the probability of miss event
(an event that remains undetected) subject to a constraint on
the probability of false alarms (the sensors report an event
due to noise). Note that in many applications false alarms
are as bad (if not worse than) as missed events. In addition
to the incurred cost for sending response personnel to the
area of the event, frequent false alarms may lead the users to
ignore all alarms, and as a result even detected events will go
unnoticed.
To achieve reliable detection in a large area, it is necessary
to deploy a huge number of sensors which with the current
technology implies a prohibitive cost [
3
]. For example,
consider a lake to be monitored for events (an event can be
a boat that spills a substance in the lake that changes the
water turbidity). If the lake has an area of 20 km × 20 km,
and we assume that each sensor has a reliable sensing range
(detection range) rd=10 m, then the number of sensor nodes
needed to monitor the entire lake is of the order of 106 which
with today’s technology implies a prohibitive cost.
Given that it is infeasible to reliably cover the entire
area with stationary nodes, in this paper we investigate
an alternative way of monitoring the area using several
stationary and some mobile sensor nodes that collaborate
in order to improve the area coverage and/or to detect an
event as fast as possible. The main idea is that the mobile
nodes will collaborate with the stationary nodes (and with
each other) in order to sample areas that are least covered by
the stationary nodes. In the context of WSNs, sensor nodes
are fairly inexpensive and unreliable devices, thus it is not
feasible to have an accurate state of each sensor node in the
field (some nodes may have failed or been carried away).
As a result one cannot have all necessary information to
centrally solve a path planning problem and predetermine
the path that each mobile sensor node should follow in
order to sample the areas least covered. In the proposed
approach, mobile nodes navigate through the sensor field
autonomously using only local information (i.e., the mobile
node’s beliefs and measurements as well as information
collected from the nodes, stationary or mobile, that are in
a neighborhood around the mobile).
This paper investigates the use of signal processing
techniques in the path planning of mobile agents for
improving the area monitoring in the context of WSNs. The
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