| Mobile ad hoc networks consist of mobile nodes communicating with each other without a fixed network infrastructure. The nodes create a multihop network, which changes its topology dynamically. One of the approaches for routing is to organize the network as clusters of nodes. Some nodes assume the role of clusterhead, thus playing an active role in keeping track of the topology and feasible routing paths. The role of clusterhead is a temporary role, which changes dynamically, as the topology or other factors affecting it change. There are some existing mechanisms for cluster formation, e.g. node-id based, and degree-based, each focusing on a particular characteristic of the network. A new clustering mechanism based on clusterhead-time is presented. The objective of this mechanism is to try to distribute the clusterhead load evenly among the nodes. These three clustering mechanisms are combined into one clustering mechanism. This is a step towards unification of clustering mechanisms. We call this combination the NCT (Node-id, Connectivity, and clusterhead-Time based) clustering mechanism. The NCT clustering mechanism helps in comparing the individual clustering mechanisms. This mechanism is also useful in the implementation of various clustering mechanisms in a node, and also introducing new mechanisms in future. Applying the concepts of control systems theory, it is shown that the NCT clustering mechanism is non-linear. This has provided a base for analyzing the stability of a system, from the control systems perspective. Also we introduce a method of measuring various performance metrics of clustering mechanisms, e.g. clusterhead load distribution, and clusterhead stability, of a mobile ad hoc network. The theoretical analysis of the clustering mechanisms is described from the perspective of clustering performance metrics. The theoretical analysis and the simulation experiments show that the clusterhead load distribution and the clusterhead stability of the clustering mechanisms are inversely proportional to each other. Two key parameters of this NCT mechanism are: availability factor threshold, aTH, and clustering gap, Deltag, i.e., the time between two consecutive clustering decisions. The results of the experiments conducted to observe the effect of these two key parameters on the performance of clustering mechanisms are also presented here. |
