Fault-Tolerant Topology Control And Connectivity Restoration In Wireless Sensor Networks

Wireless sensor networks highly intergrates modern information technologies, such as sensors, embedded computing, modern network and wireless communication. Thus wireless sensor networks have broad application prospects in the fields of national defense, environmental monitoring, life rescue and healthcare. Because of energy constraints and adverse environmental impacts, the sensors are prone to failure which has a serious impact on network performance,and even threaten the safety of human life. Thus improving the ability of fault tolerance, ensuring network connectivity are urgent problems for wireless sensor networks.Fault-tolerant topology control and connectivity restoration are important issues in wireless sensor network management. The limited energy and the bad environment determine the high failure rate of sensors.Fault-tolerant topology control obtains the fault-tolerant topological structure with certain property by setting up an effective topology control mechanism, and guarantees the network to have certain invulnerability.Network connectivity recovery can restore connectivity between network partitions and ensure normal network operation. The existing fault-tolerant topology control and connectivity recovery methods have different advantages because of their different emphases, and there are still many problems to be solved. In the existing fault-tolerant topology control algorithms, some minimum energy paths are lost after the node transmit power is adjusted, so that the network fault tolerance and energy efficiency are poor. And there is lack of effective fault-tolerant topology maintenance mechanism which make it difficult to meet the demand of network fault tolerance in dynamic topology.In the construction of fault-tolerant topology for heterogeneous wireless sensor networks, there is no restriction on the path length of the sensors to the super node set,which results in greater transmission energy consumption and longer transmission delay. In the works of restoring the netwok connectivity, the existing node mobility models assume that the existing node moving along a straight line, without considering the case that there is some obstacle on the path of the mobile nodes. In the connectivity recovery process of mobile wireless sensor networks, the existing critical nodes decision algorithm has large energy consumption or there are too many critical nodes are not global cut-nodes, and there are may many nodes participate in cascade migration in the connectivity recovery process because that the existing algorithm only considered the node degree when choose the backup for the critical nodes. In allusion to the problems mentioned above, two aspects of fault tolerant topology control and connectivity recovery of wireless sensor networks are deeply studied in this paper. The innovation of research on the following four aspects:(1) In fault-tolerant topology control of homogeneous wireless sensor networks, for the problem that the loss of some minimum energy paths and the lack of effective fault-tolerant topology maintenance mechanism, this paper proposes a based minimum energy path fault-tolerant topology control algorithm. Firstly, the definition of minimum energy path is given, the distribution range of minimum energy is determined, and the corresponding proof is given. Then, in the minimum energy path determination stage, the proposed method limits the transmission radius of the relay nodes in the minimum and minor energy paths, which solves the problem that the minimum or minor energy paths disappear after the adjustment of the node power. After that,a fault-tolerant topology maintenance algorithm is presented. Once a node fails to destroy the fault tolerance of the topology, the minimum and minor energy paths are reconstructed to ensure the fault tolerance of the topology. Simulation results show that this algorithm can effectively remove redundant links in the network, improve network fault-tolerant ability and reduce network energy consumption.(2) In fault-tolerant topology control of heterogeneous wireless sensor networks, for the problem that the path from the sensors to super node set is too long, this paper proposes a based multi-routing tree fault-tolerant topology control algorithm. Firstly, the idea of layered is introduced to construct multi-path tree, which solves the problem that the path from sensors to the super node set is too long. At the same time,hierarchical algorithm is optimized to further reduce the distance between the upper and lower nodes. Then, each node determines its minimum transmission radius required for the fault-tolerant topology according to its distance from the upper and lower neighbors of the subtree, and adjusts its transmit power according to the transmission radius to form the fault-tolerant topology. Once some node fails to destroy the fault tolerance of the topology, the fault tolerant topology reconstruction process is initiated to ensure network fault tolerance and energy efficiency. Simulation results show that this algorithm can effectively improve the fault tolerance rate of heterogeneous wireless sensor networks and reduce the total energy consumption.(3) In network partition connectivity restoration, for the shortage of mobile nodes path planning in the presence of obstacles, a connectivity recovery method based on obstacle avoidance is proposed. In this method,the connectivity restoration problem is modeled as the relay nodes placement problem on the Steiner Mimimum Tree. Firstly, this paper constructs the obstacle-avoiding Steiner Minimum Tree of the segments.And then the placement strategy of static and mobile relay nodes is given.The proposed method considers the existence of polygonal obstacles on the mobile path and makes corresponding treatment, which increases the practicability of the algorithm. Simulation results show that this algorithm can effectively reduce maximum moving distance and the total moving distance of the mobile nodes.(4) In connectivity recovery of mobile wireless sensor networks,for the problem that the existing critical nodes decision algorithm has large energy consumption or there are too many critical nodes are not global cut-nodes, and there may be too many nodes participate in cascade migration in the connectivity recovery process because that the existing algorithm only considered the node degree when choose the backup for the critical nodes, this paper proposed a noval method combined active and passive restoration to restore the network partition connectivity.Firstly, the proposed method analyzes the satisfactory trade-off between the communication overhead to gather limited local information and practical usefulness of derived criticality conclusions and proposes an energy efficient critical node determination algorithm. And then the paper presents the criteria to select an appropriate backup for each critical node.In the connectivity recovery phase, this paper considers some special cases such as there is a ring in the cascaded movement path. Simulation results show that this algorithm can effectively reduce the number of nodes moved and the total distance moved.