Special Issue on Global Positioning System - Proceedings of the IEEE

The Global Positioning System (GPS) is a great technological success story. It was developed by the Department of Defense (DoD) primarily for the U.S. military to provide precise estimates of position, velocity, and time. Civil use was a secondary objective. On the basis of national security considerations, the civil users of GPS have been limited to a purposefully degraded subset of the signals. Nevertheless, the civil applications of GPS have grown at an astonishing rate. Applications unforeseen by the designers of the system are thriving, and many more are on the way. GPS has found applications in land transportation, civil aviation, maritime commerce, surveying and mapping, construction, mining, agriculture, earth sciences, electric power systems, telecommunications, and outdoor recreational activities. The civil community has found ways to get around the purposeful degradation of the signal and to use the military signals, encryption notwithstanding. The system is being used to provide accuracy levels which would have been unthinkable 20 years ago. The commerce in GPS-related products and services has grown rapidly in the 1990’s. The U.S. Department of Commerce estimates that the annual worldwide sales will reach $8 billion in the year 2000, and could exceed $16 billion by 2003. GPS is on its way to become a part of our daily lives as an essential element of the commercial and public infrastructure. This Special Issue of this PROCEEDINGS offers a survey of the GPS technology and some of its civil applications. We begin this essay with a short introduction to GPS: the system, signals, and performance. The objective is to provide the necessary background and to introduce the basic concepts and vocabulary needed for the papers which follow. GPS is not the first satellite navigation system. The first operational system was fielded by the U.S. Navy in 1964, and was named the Navy Navigation Satellite System [1]. This system, better known as Transit, was based on a novel concept discovered in the late 1950’s following the launch of the Soviet Sputnik: measurements of Doppler shift in the signals broadcast by a satellite in a known, well-defined orbit could be used to estimate one’s position. The system was realized with five satellites in low-altitude (1100km), nearly circular, polar orbits. Each satellite broadcast