Pseudolite Augmentation of GPS

1.1 GPS – benefits & constraints The Global Positioning System (GPS) is an all-weather, global, satellite-based, roundthe-clock system developed by the U.S. Department of Defense, which since the early 1980s has been available to the civilian community and has truly revolutionized navigation, surveying and geodesy. GPS is based on a constellation of up to 30 satellites orbiting the Earth, broadcasting signals that permit a GPS receiver to determine its position, velocity and time from observations to at least four visible satellites. GPS is the most effective general-purpose tool ever developed for geopositioning on land, at sea, in the air, and in space. GPS, and similar follow-on Global Navigation Satellite Systems (GNSS), will be the conerstone geolocation technology for the next few decades. However, standard GPS/GNSS is not ideal for ubiquitous positioning requirements as it cannot be used indoors or where the satellite signals may be obstructed by buildings or foliage.