Localization in time and space for sensor networks

Monitoring applications define an important class of Wireless Sensor Networks (WSNs). In these applications, the network perceives the environment and searches for event occurrences (phenomena) by sensing different physical properties, such as temperature, humidity, pressure, ambient light, and movement. In such cases, location in time and space of both phenomenon and nodes are usually required for tracking and correlation purposes. In the former case, nodes' clocks are synchronized, while in the latter, nodes' physical location (e.g., latitude, longitude) are discovered. The need for such information in WSNs and the proximity and similarity of both problems suggest they can be addressed as a single problem, which we call the Localization in Time-Space. In this paper, we discuss the relationship between these problems and also propose the Synapse (SYNchronization And Positioning for SEnsor networks), a time-space localization system for sensor networks. Simulation results show that the proposed algorithm is able to find the nodes' location while synchronizing their clocks with a precision of a few microseconds. A key advantage of Synapse is that it reduces the communication cost compared to the situation wherein localization and synchronization are separately solved.