VLS: a DTOA system for position location

A vehicle location system (VLS) is described. It is a derivative of the military position location and reporting system and offers higher accuracies and a lower vehicle electronics cost than any comparable system. The original design concept envisioned a satellite-based implementation in the radio determination satellite service band at 1.6 GHz for the location of surface vehicles on a nationwide basis. A second version of the system has evolved which is suitable for the tracking of aircraft to accuracies of 30 m in areas of interest and achieves those accuracies through the use of auxiliary ground enhancement stations. Terrestrial adaptations utilizing the cellular telephone infrastructure are in the exploratory phase. Experimental systems suitable for local area coverage have reached the field evaluation engineering model state. Some preliminary field test results are presented. Geostationary satellites are often optimal, though very good results are obtained for local systems without them