Researches On Topology Control And Optimization In Wireless Sensor Networks

The wireless senor networks (WSNs) have been hot research area over recent yearsdue to their promising applications in environment monitoring, battlefield surveillance,traffic and warehouse managements. Topology control is one of the core issues in WSNs.A well-designed network topology not only provides a good underlying topologysupport for upper layer protocols, but also helps improve the robustness and adaptivityof the network. Therefore how to optimize the network topology is of great significance.Topology control and optimization issues are studied in this dissertation, with specificstudies as follows:1. Suitable transmission power plays a crucial role in ensuring networkconnectivity, network coverage and prolonging network lifetime. In this dissertation, wepropose a non-cooperative game-based power control algorithm which determines theoptimal transmit power while ensuring network connectivity. The power controloptimization is cast as strategic non-cooperative games, where each sensor node is aplayer that competes against the others in resource allocation to maximize its ownpayoff function. Residual energy of each node is taken into account when designing thepayoff function. By selecting a proper utility factor and a price factor, the algorithm canconsiderably reduce the total transmit power, and thus save the network’s energy. Inaddition, the nash equilibrium is found, with its existence and uniqueness proved.Simulation results show that the proposed power control algorithm has a goodconvergence property, and can effectively prolong the network lifetime and provide awell-designed network topology.2. Effective clustering is important to the optimization of the network topologyand to the energy saving. In this dissertation, we propose a bayesian game-basedclustering algorithm. In the algorithm, the election of the cluster head is modeled as amulti-player game, in which the cluster head is elected through static games withincomplete information. The node energy consumption and the path loss are fully takeninto our consideration when designing the payoff function. Hence the algorithm canprovide a more reasonable distribution of the cluster heads, a more stable energyconsumption and a more uniform energy distribution with the optimization of networktopology. As a consequence, the network lifetime can be prolonged considerably. 3. Node deployment strategy is one of the key issues in network topology control.Traditional node deployment strategies cannot well adapt to the dynamic networkenvironment and suffer from blind spot area. To overcome these difficulties, weintroduce a fuzzy control strategy for node deployment. Through fuzzy control of themovement distance and direction, the proposed node deployment strategy provides areasonable deployment of the nodes and improves the network coverage. Since theresidual energy, path loss and the number of neighbors are considered in the design offuzzy control rules, the algorithm can effectively improve network coverage, makenetwork topology more perfect and prolong network lifetime.4. Constructing a topological structure that has a high reliability and highsurvivability is a challenging and new problem in WSNs. Two topology evolutionalgorithms are proposed based on scale-free network topologies.1) A energy-efficienttopology evolution algorithm based on scale-free network topologies is introduced. Thealgorithm first achieves a reasonable distribution of the cluster heads, and then thetopology evolves via scale-free network random walks. Since residual energy, nodedegree and other factors are sufficiently considered during the topology evolution, thefinally obtained topology has an acceptable load and a good energy balance, thus issuitable for the practical application of WSNs;2) Topology evolution algorithm withreconstruction mechanism based on scale-free network topology is proposed. Thealgorithm first achieve a reasonable distribution of cluster heads, then the topologyevolves considering those factors arising from practical requirements, such as randomnode addition or deletion, and edge deletion or reconstruction. During the evolution ofthe topology, the random failures of nodes or links are fully considered, and thereconstruction mechanism is introduced. Therefore the network topologies haveattractive quality such as self-healing ability, reconstruction ability and adjustability.Simulation results demonstrate that network topologies generated by the above twoalgorithms both have high robustness under random, deliberate attacks and can meet therequirements under harsh environmental conditions in WSNs.5. We considered the problem of evaluating node importance in WSNs. Anevaluation method is proposed in this dissertation based on topology contributions andenergy effectiveness. Firstly, by examining the relationship between topology structureand energy consumptions, we design a comprehensive evaluation index that is able tomeasure the topology invulnerability and energy consumptions. Secondly, a nodeimportance evaluation algorithm is designed based on the evaluation index. Simulation results show that the index is rational and effective, important nodes are effectivelylocated, network topology is optimized and network survivability is enhanced withimportant nodes being protected. Furthermore, we also discuss how to protect importantnodes through adding super nodes to the network.