Cooperative Wireless Mobile Sensors For Target Tracking

Target localization refers to obtaining target estimates at specific time via sensing and calculation. And target tracking aims to acquire estimates of the current state and the whole track. Wireless Sensor Network (WSN), due to its large scale and coverage, is capable to lo-calize mobile targets in the monitored field. Moreover, the computation and communication abilities of sensor nodes make it possible to track mobile targets and predict their locations. Previous research on target tracking focused on static sensor nodes. Mobility on sensor nodes, introduced in this dissertation, is employed to improve the process of target tracking. Key technologies in target tracking using cooperative mobile sensor nodes are studied and validated by practical experiments in this dissertation, in terms of target tracking using static sensors, relative self-positioning within mobile nodes, static node assisted navigation and cooperative control for tracking quality.First of all, target localization using static sensor nodes is a fundamental technique. The scenario of indoor positioning is chosen as our primary application. Rather than obtaining merely target readings in sensors, readings between sensors are also collected and utilized to evaluate the proximity between target and sensors. Experiments validate that the proposed methods is robust against unreliable hardware parameters. Later, mobility is introduced and a testbed is built to evaluate the performance of target localization and capturing.Consider mobile sensor systems without central location service, a method for mo-bile sensors to estimate their relative positions is presented. Sensors estimate radio signal strengths by periodically exchanging messages and the strength values are filtered, shared and synthesized to compute a local notion of the relative positions for the sensor team. Experimental results show that smooth relative positions under mobility is obtained and managing mobility patterns of mobile units is possible.To facilitate sensor relocation in the monitored area, static sensors are utilized to assist mobile sensor navigation, via received signal strengths. Two methods, namely oblivious and iterative, are presented for different kinds of hardware platform. The oblivious method re-quires only basic capabilities of sensing and locomotion, and the iterative one requires more advanced capabilities of computation and locomotion. Experiments validate the effective-ness of both methods, and the iterative method is proven better than the oblivious one via simulations.Finally, the problem of target tracking is revisited after studies on the interactions be-tween mobile and static sensors. Besides sensing quality, communication insurance and area coverage regarding to sensor locations are considered. As a result, qualities of sensing, com-munication and coverage are unified as a integrated objective, which is optimized via sensor movement with local computation. A tracking system for non-cooperative target is built to validate the proposed idea, and we conclude that the tradeoff of sensing quality, communi-cation quality and coverage quality should be considered in target tracking applications.The proposed algorithms are all validated with practical platforms to verify the feasi-bility and effectiveness.