Research On Fault Tolerant Technologies Of Data Transmission And Delivery In Wireless Sensor Networks

Wireless sensor network (WSN) consists of a large number of inexpensive minia-ture sensor nodes which are deployed in monitoring region, forming a multi-hop,self-organized network system through wireless communication. And the aim of wire-less sensor networks is sensing, gathering and processing the information in the regioncovered by the network and transferring the data to sink node.In the applications of data centric wireless sensor networks, there are often somefaults happened, such as node failure, wireless link break, etc. It is because themassive nodes in sensor networks are energy constrained and usually deployed inharsh environments, with the unreliable wireless communication channel. Therefore,the protocols and algorithms designed by researchers are not suitable for practicalsensor networks applications. In recent years, the researchers have come to a commonrealization that fault tolerance is a critical issue in the researches on wireless sensornetworks.Generally, fault tolerance means the system works normally even if some fail-ures happen. Accordingly, fault tolerance in wireless sensor networks means thatwhen some nodes or links fail, the network has ability to recover the lost data orstart self-healing mechanism to reduce the performance degradation. Now there arethree primary fields which researchers focus on about fault tolerance issues in sensornetworks:Fault tolerance in deployment and covering. In the stage of network deployment,study on how to optimally deploy sensor nodes to cover the monitoring regionand keep the network connective, when some nodes and links fail.Fault tolerance in event detection. Many wireless sensor networks are applied inspecial event detection, such as fire alarm, intrusion etc. The study issues are:under the situation of nodes and links failing, how to judge the information sentby sensors are correct, and how to make right decision with the consideration oflocal sensor reports, and how to detect the special event successfully.Fault tolerance in data transmission. Wireless sensor network is a new typeof data gathering technic, therefore data transmission is very important. Theresearch issues are in the condition of nodes and links fault, how to storage,fuse, transfer and recover the sensing data. And the corresponding fault toleranttechnics and schemes ares mainly considered in network layer and applicationlayer. To solve the above problems, this thesis addresses on the data redundancy andpath redundancy technologies of fault tolerant data transmission in sensor networks.The content of this thesis includes five issues: (1) modeling and analysis of the senornodes fault; (2) In data source nodes, Forward Error Correct (FEC) codes, which isconstrained by the speciality of sensor networks; (3) Fault tolerant coding technologybased on network coding in data relay nodes; (4) Fault tolerant delivery of datapackets at the relaying nodes based on path redundancy and cross-layer design; (5)E?ciency and fault tolerance of intra-cluster data exchange and inter-cluster datatransmission in clustered sensor networks.The contributions of this thesis include:1. Self-adaptive FEC algorithm based on data redundancy to provide better perfor-mance on delay and loss ratio: There are some existing channel coding algo-rithms, but they are not suitable for applying in sensor networks, due to theirhigh computing, storage, delay cost and in?exibility. We adopt a lightweightXOR-based FEC algorithm in network layer which uses information about packetloss to adjust the coding level according to the dynamics of the network.2. Fault tolerant coding algorithm in data relay nodes based on network coding: Adata transmission mechanism combined with multi-path routing and randomnetwork coding is presented. In routing discovery phase, we constructed multi-path for network coding and a low complexity random network coding algorithmis adopted to recover the loss of data packets with good energy e?ciency.3. Fault tolerant routing protocol with energy e?ciency based on path redundancy:Most routing protocols for sensor networks try to extend network lifetime byminimizing the energy consumption, but have not taken the network reliabilityinto account. To be adaptive to the harsh environment, we propose an energy-aware, load-balancing and fault-tolerant routing scheme. We adopt a cross-layer design to measure the transmission delay so as to detect the failed nodes.The routing scheme works with ACK feedback mechanism to transfer controlmessages to avoid producing extra control overhead messages.4. Fault tolerant schemes in cluster-based wireless sensor networks: Based on clus-tered sensor networks, the intra-cluster nodes topology models are proposed withsome intra-cluster data exchange algorithms. More specially, the network codingalgorithm is discussed in detail. And we improve the inter-cluster data transmis-sion method of the classical clustering protocol in sensor networks, LEACH. Thegateway nodes which are in the overlap of multiple clusters, is used to constructinter-cluster routing. Considering the procedure of data transmission, we apply FEC coding and fault tolerant routing algorithm to enhance the fault tolerantability of sensor networks.