Design And Implementation Of A Tiered Wireless Sensor Network For Data Gathering

In recent years along with the rapid development of wireless communication technology, sensor technology and embedded technology, wireless sensor network(WSN) has become a new research area of computer science. In data gathering network, an important application of wireless sensor network, sensor nodes sample, process information of monitored objects and transfer the processed information to users. However, in order to improve scalability and reliability, tiered architecture is usually adopted to fit the complex deployment environment.This thesis reviews existing WSN protocols and analyzes the requirements of data gathering networks, then presents a tiered network model which consists of sensor network, forwarding network and long-distance wireless network. Header nodes, which is the gateway between sensor network and forwarding network, collect data from sensor nodes and transfer the data to relay nodes. While relay nodes, the gateway between forwarding network and long-distance wireless network, are responsible for collecting and forwarding data from header nodes.Based on the proposed model, the thesis proposes the design of a multi-tier protocol which integrates routing, time synchronization and MAC for data delivery in forwarding network and sensor network. Directed diffusion and repair request mechanisms are used for route discovery in sensor network and forwarding network respectively. ARQ scheme is adopted for real-time clock synchronization between header nodes and relay nodes, while DMTS scheme for time synchronization between header nodes and sensor nodes. Duty-cycle working and CSMA/CA mechanisms are two major technologies at MAC layer. Duty-cycle working mechanism is used for power saving, while CSMA/CA mechanism is used to reduce the chance of channel collision.In addition, according to the requirements of data gathering networks, we have developed a specially designed sensor node. After presenting the architecture of software, the thesis focuses on how to implement above protocols on our sensor nodes. Then, the thesis describes h6w to construct the experiment environment and analyzes the performance of experimental system from two aspects -- power-efficiency and network reliability. The thesis also introduces a real system deployment at the Mogao Grottoes in China, a well-known wildland cultural heritage, and the reliability of the above protocols is verified in real deployment environment.