N. B. Hemesath

Peer Reviewed

Abstract: Unprecedented accuracy, global coverage, and three dimensional position fixing are GPS features unmatched by any other navigation system in existence today. These characteristics, along with its user passive nature, make the system very attractive for a wide variety of applications, both commercial and military. However, because it is a radio-based system, its potential susceptibility to jamming is a concern in military applications. The relatively low radiated power levels of the satellites and the extreme user-to-satellite distances combine to produce a received signal level of approximately -165 dbw and a signal-to-noise ratio in the 20 megahertz receiver front end on the order of -40 db. Thus, even though the transmitted signal has been carefully designed to provide 70 db of processing gain (by virtue of the 10.23 mega-bit/second PN code bi-phase modulated on the carrier), it is clear that a jammer in close proximity to a user can overcome the desired signal and thereby deny GPS navigation capability to that user. The top level partitioning of a GPS user set, shown in Fig. 1, indicates a receiving function and a navigation function. The former acquires the signals and measures ranges along the lines-of-sight to the satellites; the latter manages the overall system and projects the measured range data into the user’s navigation coordinate frame. Thus the navigation function is primarily concerned with coordinate conversion and data manipulation and does not significantly affect either system accuracy or tracking thresholds. On the other hand, the receiving function acquires and tracks the desired signals, and its design can be optimized to enhance performance. Thus the performance enhancements discussed in this paper are all associated with the receiving function and are intended to extend receiver operation into deeper and deeper noise (jamming) environments. The techniques addressed include advanced antennas, inertial aiding, and special signal processing.
Published in: NAVIGATION: Journal of the Institute of Navigation, Volume 25, Number 2
Pages: 195 - 200
Cite this article: Hemesath, N. B., "PERFORMANCE ENHANCEMENT OF GPS USER EQUIPMENT (USER EQUIPMENT)", NAVIGATION: Journal of The Institute of Navigation, Vol. 25, No. 2, Summer 1978, pp. 195-200.
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