Receivers for the NAVSTAR global positioning system

The NAVSTAR global positioning system (g.p.s.) is being actively developed by the USA and is likely to become operational for both civilian and military users in the mid-1980s. Accuracy of position in three dimensions of afew metres and velocity within 0.1 m/s is predicted. The user equipment, essentially a receiver and an antenna, will employ a considerable volume of signal-processing hardware and software. This paper aims to provide for the signal-processing community some basic understanding of the system outline and its operation as a navigation aid; a typical receiver outline is broken into a number of units whose operation is described with some emphasis on the signal-processing aspects. Areas in which improved signal-processing methods could contribute to improved performance, particularly in interference conditions, are examined. The potential of the antenna in improving user equipment performance by providing angular selectivity against interference is examined briefly; results from the literature indicate improvement of up to 30dB. New signal-processing technologies, surface-accoustic-wave devices and c.c.d.s are likely to contribute to g.p.s receiver development in both frequency-generation and signal-processing areas.