The Aalborg GPS Software Defined Radio Receiver

Abstract

A receiver for the Global Positioning System (GPS) signals provides information on its position and time. The position is given in an Earth-Centered and Earth-Fixed coordinate system. This means that a static receiver keeps its coordinates over time, apart from the influence of measurement errors. The system time (GPST) counts in weeks and seconds of week starting on January 6, 1980. Each week has its own number. Time within a week is counted in seconds from the beginning at midnight between Saturday and Sunday (day I of the week). GPST is maintained within the system itself. Universal Time Coordinated (UTC) goes at a different rate which is connected to the actual speed of the rotation of the Earth. At present 14 seconds have to be added to UTC to get GPST. The GPS has 6 orbital planes with at least 4 satellites. At the moment GPS consists of 29 active satellites. They complete about 2 orbits/day.