Book Description

Depending on the type of sensor network, routing protocols can be grouped into two main categories: hierarchical-based routing for MWSNs and multi-hop routing for WASNs. In hierarchical-based routing, there are two main approaches to prolong the lifetime of MWSNs: cluster-based routing and chain-based routing. To study the cluster-based routing, some very simple network topologies are analyzed first. From the analysis, it is shown that the energy optimization process can be formulated as integer linear programming problems. Several methods are then presented to obtain the optimal results from the formulations. As these problems are proven to be NP-hard, heuristic algorithms are proposed to obtain approximate solutions. From the simulation results, solutions are derived that are very close to the optimal solutions. In chain-based routing, sensor nodes form a chain to gather data, and a node is elected to deliver the data to a base station. It is shown by analysis that the equal selection of sensor nodes as the elected cluster-head (CH) will not give the optimal lifetime. The energy efficiency can be significantly improved by optimizing the selection of each sensor node as a CH. Therefore, a new model is proposed to compute the frequency of each sensor node being selected as the CH. Simulation results show that the proposed scheme significantly improves the system lifetime. As the problem of building an optimal chain is NP-complete, a bounded model is proposed to predict the upper bounds of the lifetime. Using the model, it is shown that our proposed chain-based scheme performance is very close to the bounds. At the end of the study for the hierarchical-based routing, the performances of the best cluster-based routing method and the best chain-based routing method are compared. Simulation results show that they perform similarly. In multi-hop routing, we show that locating a path that maximizes the minimum remaining energy of sensor nodes is actually an NP-complete problem. Therefore, in the routing, there is no polynomial time for the problem, and hence heuristic algorithms are proposed. In order to overcome the problem of the existence of the reception energy of neighbouring nodes, we then propose two methods to prolong the lifetime: inserting the remaining energy of nodes into routing formulas and using a broadcast scheme to eliminate the reception energy. In summary, in this research, a number of energy-efficient routing protocls in MWSNs and WASNs are proposed. These proposed methods significantly improve the lifetime of these networks.