Spatio-Temporal Awareness in Mobile Wireless Sensor Networks
Over the past decade we have witnessed the evolution of wireless sensor networks, with advancements in hardware design, communication protocols, resource efficiency, and other aspects. Recently, there has been much focus on mobile sensor networks, and we have even seen the development of small profile sensing devices that are able to control their own movement. Although it has been shown that mobility alleviates several issues relating to sensor network coverage and connectivity, many challenges remain. Among these, the need for position estimation is perhaps the most important. Not only is localization required to understand sensor data in a spatial context, but also for navigation, a key feature of mobile sensors. In this dissertation we develop techniques for the synchronization, localization and navigation of resource-constrained mobile sensors. Resource constraints prevent us from using traditional coordination methods, because these typically require bulky, expensive, and sophisticated sensors, substantial memory and processor allocation, and a generous power supply. The global positioning system is able to provide synchronization and localization information, however in many situations it cannot be relied on, and alternative methods are required. We focus on techniques that rely primarily on the sensor radio, since all wireless sensor nodes are equipped with them, thus requiring no additional hardware support. Specifically, we have developed a time synchronization protocol for heterogeneous sensor networks, localization techniques in which sensor nodes measure the phase and Doppler-shift in frequency of an RF interference signal, and waypoint navigation, in which the localization results are used to derive motion vectors for the mobile sensors.