GPS Acquisition Performance in the Presence of Jamming

James Campanile, Tony Nasuti, John Nigm and Michelle Engelhart

Abstract:	Global Positioning System (GPS) receiver performance can be measured in terms of satellite signal acquisition capabibty and the ability to make and process pseudorange and deltarange measurements under a variety of physical and electrical environments. Military GPS receivers are subject to environments which stress both of these aspects. Specikally. GPS receivers on certain platforms may be required to acquire and track GPS satellite signals in the presence of noise jammers. The GPS signal acquisition process can be simulated to evaluate probability of detection at various jamming levels, and to determine an approximate Time-To-First-Fix (TIFF) versus jamming level. While GPS acquisition performance is primarily determined by receiver hardware design and receiver-manager software functions, the theory and concepts of operation can be generalized for the purpose of analysis. A GPS user equipment is basically a correlation receiver, whereby an exact replica of pseudorandom noise code CpN) is generated locally at the receiver mixed with the incoming satellite signal and integrated over a given time interval. The incoming signal is correlated with the local reference signal for a specified time period (integration time) and a test statistic is generated and compared to a detection threshold. Some major areas which affect detection and correlation of GPS signals are: tbresholds, probability of false detection, Erquency/code uncertainty and the search rate. Any one or all of the aforementioned factors can be affected by proprietary design, but such investigation is beyond the scope of this study. The purpose of this study is to utilii existing concepts in GPS Receiver-3A operation to analyze receiver acquisition performance under various jamming levels, and to determine design factors which optimize performance. Tke analysis will focus on the use of GPS on the Joint Stand-Off Weapon (JSOW). JSOW is a new air launched stand-off weapon being developed by the U.S. Navy and Air Force. Included in the analysis are assumptions made of the operational enviromnent (i.e. presence of almanac, ephemerides, the availability of precise time, etc.) and parametric variations to determine sensitivity of the acquisition process to initial operating conditions.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	265 - 274
Cite this article:	Campanile, James, Nasuti, Tony, Nigm, John, Engelhart, Michelle, "GPS Acquisition Performance in the Presence of Jamming," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 265-274.
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