Thus the energy expenditure of the clusterheads is much higher
than the rest of the nodes. Hence to ensure load balancing, and a uniform
energy drainage pattern across over the entire network, the authors propose
rotating the role of a clusterhead periodically and randomly. The authors determine
the optimum number of clusters required in the network, and also
17 Chapter 1 Design of Large-scale Sensor Networks
Aravind Iyer et al.
propose distributed protocols for clusterhead election. Other data gathering
schemes such as PEGASIS [29] and M-LEACH (Multi-hop LEACH) [34] also
use the principle of randomized role rotation for load balancing.
Node Heterogeneity
While role rotation is useful for load balancing, it also requires that each node
in the network be capable of performing the functions of a clusterhead. This
requires sophisticated clusterhead hardware in all the nodes. If the network
consists of a large number of nodes, this could result in a high overall cost of
the network. Motivated by this, the authors in [35] consider a heterogeneous
sensor network consisting of two types of nodes; sensor nodes that have simple
hardware and low battery energy, and clusterhead nodes that have sophisticated
hardware and higher battery energy required for performing complex
computations and long range communication. Thus the expensive functionality
is embedded in only a few nodes, and the overall network cost is lowered.
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