A Hybrid Solution for 3D Location and Time Synchronization in WSN

Localization and synchronization are fundamental services in Wireless Sensor Networks (WSNs). Many WSN applications often need to know the sensor position and the global time to report a given event detection with a specific location and time. However, such services are performed after the sensors deployment in the sensed field. In this case, setting up each sensor manually becomes an impractical activity, requiring some system that automatically locates and synchronizes the sensor nodes. For this purpose, we developed a joint solution to 3D localization and clock synchronization problems using a hybrid approach, which combines mobile and recursive localization. In our work, an unmanned aerial vehicle (UAV) equipped with a GPS is used to fly over the sensor field and broadcast its geographical position and timestamp. Using the messages received from the UAV, the sensor nodes are able to estimate their geographic positions and synchronize their clocks. When a node is located in time and space, it transmits its own position and timestamp to the neighbor nodes. The neighbors use the received information to locate themselves so that this iterative process is propagated throughout the network. Simulations results showed that the proposed solution presents low clock synchronization and positioning errors. In our solution, the cost of the network is also reduced because only one GPS receiver is used for the entire sensor field.