| Applications of wireless sensor networks can be mainly divided into two types:environment monitoring and target tracking. Due to energy scarce character of sensor nodes, energy-effiency is crucial in both applications. In environment monitoring applications, wireless sensor networks are deployed inside the monitored phenomenon thus smaller than it in size. In target tracking applications, on the contrary, the objects are often smaller than the area of the networks. Therefore, more sensors could go to sleep. Thus better designed protocol can save more energy in tracking applications.In target tracking applications, sensor nodes could be deployed evenly or randomly. The target could move in patterns or randomly. We design two different protocols suitable for each scenario. Two protocols can be used interchangeably for the two scenarios can transform to the other.The proposed target tracking based on path probability uses the probability information to predict the new direction of the target and uses the information of the paths and neighbors to distribute the energy of the sensing, communication and calculation. A sleeping and waking-up mechanism suitable for the distribution is proposed. Probability analysis shows that our protocol provides better surveillance quality and saves energy.CET protocol organizes the randomly distributed sensors to face structure. For one thing, the protocol reduces the acitive monitoring node to cut the consumption of the energy. For another, the protocol chooses another node as the backup node in the current face to inhance the reliability of the tracking and lower the latency caused by the lose of the target. Information acquired by the monitoring target need not to be sent to the tracker immediately. Instead, it is gathered from the monitor node in the faces along the trajectory of the target by the tracker when approaching the target.Thus more energy is conserved. When target movement prediction faces and target loss occurs, the protocol uses a layer waking strategy. The monitor node wakes up the back up node first, and then the direct face neighbor, then the indirect face neighbor(s), and other neighbor nodes at last. Only if all these steps can not find the target, the whole network wakes up by the broadcasting message. In this way, latency before finding the target can be shortened and energy can be saved.We use mobility framework on omnet++ to simulate the protocol. We compare our protocol with the Dynamic Object Tracking protocol and the protocol based on the Threshold Flooding. We study the capture time, average energy consumption, and the average distance between the tracker and the target. Our protocol shows better performance than the other two protocols in these aspects. |
