Research On Broadcast Routing And Localization Technologies In Wireless Sensor Networks

Wireless sensor networks (WSNs), made by the convergence of micro-electro-mechanical systems technology, wireless communications and digital electronics, is a novel technology to acquire and process information. It is composed of a large number of miniature sensor nodes which collaboratively monitor target field and delivery information to observers hop by hop. Compared to traditional sensors, WSN poses unique advantages such as rapid deployment, fault tolerance and accurate data acquirision.There are many theoretical and technical challenges in WSNs for that it consists of a large number of nodes which are small-sized, low-cost, and battery-powered, with limited computation and communication abilities. The hot research topics in WSNs include topology control, routing protocols, MAC protocols, localization, object tracking, time synchronization, data aggregation and energy management.This dissertation aims at studying broadcast routing and localization problems in WSNs. Broadcast is used for one-to-all message delivery and can be simply implemented with the flooding operation. However, uncontrolled flooding will cause so-called Broadcast Storm Problem, which is especially harmful for WSNs due to its large number of nodes and resource-constrained characters. Localization is another key technique of WSNs. Many of its applications such as battlefield reconnaissance, traffic management and environment monitoring depend on nodes'position information. Without position information, the data acquired by sensor nodes are useless.The major works and contributions of this dissertation include:(1) An energy-efficient broadcast routing protocol called vertex forwarding is proposed, which minimizes the flooding traffic by using location information of 1-hop neighbor nodes. Vertex forwarding works as if there is a hexagonal grid in the network to guide the flooding. Only the vertices located at or nearest to the vertices of the grid should be nominated to forward the message. A distributed algorithm is provided to find the forwarding nodes. Simulation results show that this scheme is so efficient that it is almost able to reduce the number of forwarding nodes to the lower bound.(2) The drawbacks of the node layering based broadcast schemes are analyzed, and then an energy-efficient broadcast routing protocol based on the branch and bound algorithm is proposed. In this algorithm, the broadcast routing is determined by the shortest spanning tree with the maximum number of leaves. Analysis and simulation results show that the proposed algorithm can achieve a lower forwarding ratio compared with the node layering based protocols, while keeping the number of layers at the same level; therefore, the proposed algorithm can save more energy and bandwidth resource.(3)A beacon discovery protocol is designed that helps the unknown nodes find the beacons nearby for WSN localization. Then an energy efficient scheme is presented that for the beacons receiving the request from the unknown node to adjust the proper transmission range. The relationship between the mean energy consumption and the number of adjustments is obtained by the mathematical model and analysis. Numerical results show that great energy saving is achieved when the optimal number of adjustments are made.(4)A range-based WSN localization system is designed and implemented. To solve the problem of insufficient beacon nodes caused by the short scope of TDOA range technology, a hybrid localization algorithm is presented that combines RSSI and TDOA range technologies. Moreover, a weighted correction scheme is proposed, and simulation results show that this correction scheme with proper weight values is able to reduce the RSSI's adverse effects on localization results efficiently.