There are two main ways of performing outdoor location when tracking sensor devices in a large area such as a city. The most extended is using a GPS module to get the information sent by the satellites on the 1575MHz band and extract all the information possible (latitude, longitude, speed, direction). However, this methodology is not effective when requiring mobile scenarios where the nodes can change from a clear environment to an indoor one, such as going inside buildings, garages and tunnels. For this cases we use the information provided by the Mobile Phone Cells (Cell ID, RSSI, TA) which is captured by the GPRS module. Read the complete article.