Research On The Path Coverage Problem In Wireless Sensor Networks

Wireless sensor networks(WSNs) consist of a large number of sensors, whose computing capability, storage capacity and communication ability are limited. Each sensor can sense, process and monitor a variety of information in the monitoring area. And the processed information is returned to the base station through single hop or multi-hop strategy and is further analysed. Wireless sensor networks are widely used in industry, agriculture,military, etc. Sensing coverage is a fundamental problem in wireless sensor networks. Coverage intensity is an important metric of the quality of service in wireless sensor networks,which reflects the quality of service of sensing provided by wireless sensor networks. In sensing coverage, path coverage is concerned with the analysis of the existing coverage performance. The goal of path coverage is to find one or more paths from the source point to the destination point for the target. In recent years, many scholars have conducted in-depth research on path coverage. However, few scholars have studied how to make the target to get the support path within time constraint or the safe path which can avoid the mobile sensors.In view of the above problems, this thesis has completed the following work:(1) Based on the perspective of the monitored target, this thesis studies how the target can avoid the mobile sensor nodes and safely cross the mobile wireless sensor networks.The most exiting algorithms based on breadth first search cannot ensure the target to avoid the mobile sensor nodes. Motivated by this reason, a crossing model is given and three algorithms are provided to find a minimal exposure path. All the three algorithms make the continuous path problem to a discrete problem by Voronoi diagram and calculate the exposure of each Voronoi edge. Combining with the tangent and the back-off mechanisms,respectively, the three algorithms find the optimal path and avoid mobile sensor nodes. The experimental results show that the proposed algorithms are able to solve the crossing path problem such that the target can avoid the mobile sensor nodes. The faster the target moves(the slower the mobile sensor nodes move), the easier the target avoids the mobile sensor nodes.(2) This thesis studies how the target can cross the wireless sensor networks with time constraint. In many applications(such as fire escape), the target must consider time constraint. Most exiting algorithms cannot ensure the target to cross the wireless sensor networks within time constraint. Motivated by this reason, four structural algorithms are given to find a support path within time constraint. All the four algorithms change the continuous path problem into a discrete problem by Delaunay Triangulation diagram and calculate the support value of each Delaunay Triangulation edge. Combining with the prediction, compression and tension mechanisms, respectively, the four algorithms can find the optimal path within time constraint. The experimental results show that the proposed algorithms are able to solve the crossing path problem within time constraint. When the target moves with uniform speed, larger larger the time constraint value is, the smaller the selected path support value is.In summary, we have studied the path coverage problem in order to improve the coverage quality in this thesis, which is of significance in both theory and applications.