Robust GPS - SMS Communication Channel for the AVL System
  Universal Preprocessing GPS SMS Communication Unit (UPCU) was developed as a part of the UWI microtracking system. A GSM cellular Short Messaging Service is the main method of delivering tracking information to the central base station.   The information includes asset ID, longitude, latitude, altitude, speed and direction as well as the time the message was sent. The design of the unit is implemented as a bi-directional SMS system. 
Joseph Skobla, Andrew Young