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Abstract
In a large-scale wireless sensor network, it is often desirable to count the number of
nodes in the network, or the number of nodes that are within communications range
of a particular node. In such networks, nodes are deployed for a wide variety of
military and civilian applications. These applications require a balance among the
number of operating nodes, energy efficiency, and the lifetime of the network. The
number of operating nodes is a very crucial factor for the networks. However, the
number of operating nodes can vary with time due to various artificial as well as
natural reasons (for example, some nodes might fail and some could be damaged
because of fouling and corrosion, or batteries might fail). It is therefore a matter of
great interest for a communication network to know how many operating nodes or
transmitters are available in the region at any point in time to ensure proper network
operation (such as routing), as well as to obtain optimum performance or to prevent
failure of the mission by network maintenance (such as replacement of faulty nodes).
Similarly, a concurrent estimation of the dimensionality of the network might also be
important for localising the nodes and estimating their number in a deployed
network. To date, techniques employed to estimate the number of nodes and
dimensionality have been based on some aspect of the communications protocol(s) in
use. The protocol technique can be very hard to implement in harsh environment
(e.g. underwater) due to the unavoidable capture effect, poor efficiency due to long
propagation delay, high path loss, etc. In this thesis, we propose a novel estimation
technique based on cross-correlation of random signals, in which the ratio of the
mean of the cross-correlation function to its standard deviation determines the
number of nodes. Within the limited scope of this thesis, we have provided some
estimation techniques to estimate the number of nodes and network dimensionality.
The proposed number of node estimation techniques also addresses a number of
practical issues in a digital receiver and channel, including fractional-sample delays,
multipath reception, noise etc. An error analysis is provided with comparison to
conventional protocol techniques that demonstrates the superior performance of this
technique to protocol-based methods. The thesis includes an initial verification of the
performance of the proposed techniques and suggests other issues for future
verification.