On wireless sensor networks

Wireless sensor networks (WSNs) are a valuable technology to support a huge range of applications spanning from military to commercial, such as battlefield surveillance, habitat monitoring, forest fire detection, disaster salvage, and inventory control management. It has the capability to reveal previously unobservable phenomena in the physical world and significant flexibility of installation and manipulation. The major challenges of WSNs design come from the requirements of energy constraint, distributed control and scalability. In this thesis we studied three topics on WSNs. The first one was energy-efficient medium access control (MAC) protocol design. We proposed a MAC protocol which schedules the send and receive times for all nodes within the network. As all nodes only wake up when they send or receive, significant energy is saved by reducing idle listening, collisions and overhearing. And we evaluated the protocol performance by using the GloMoSim simulator. The second topic was about distributed transmission power control of wireless sensor nodes. We proposed a simple scheme which employs request-to-send (RTS) and clear-to-send (CTS) frames to exchange channel gain information, based on which concurrent senders determine their own transmission power without a central controller to coordinate them. Simulation results showed that our scheme can save 30% to 50% of the energy, and also reduce transmissionlatency.The third topic was on event detection. Due to the fact that wireless sensor nodes are spatially distributed throughout the area of interest, this application has to been implemented in distributed form. We proposed a scheme which does not need a pre-designated fusion node, and this greatly improves network scalability. We provided close-form expressions to estimate the probabilities of detection failure and false alarm, and validated them by extensive simulation.