GPS-Based Modem Synchronization for Man-Portable Satellite Terminals

Richard F. Vaz, Mark I. Flanzbaum

Abstract:	The need for man-portable devices for communicating over long distances is currently met by lightweight UHF and HF manpack transceivers. Although these terminals provide the required communications, they are suscep- tible to detection at great distances (> 30,000 km) by ground, airborne, and satellite interceptors due to their narrow signal bandwidth (SkHz, 25kHz) and lack of an- tenna directivity (> 80” beamwidth). The larger avail- able bandwidth (l-5 MH z or more) and greater antenna directivity (5” or less) possible at SHF frequencies can provide substantial improvement in detection range over currently employed terminals. This paper describes the architecture of an SHF portable terminal designed to provide low probability of intercept (LPI) satellite communication, with special emphasis on the issues of detectability and synchroniza- tion. Specifically, the reduction in terminal vulnerability afforded by the use of Global Positioning System (GPS) technology for acquisition of the spread-spectrum wave- form is described, along with the associated system de- sign considerations. Preliminary analysis of the feasibility and perfor- mance expectations of an SHF portable terminal indi- cates that a detection range of less than 50 km can be achieved by using a low sidelobe antenna design and a direct sequence (DS) spread-spectrum modulator. In- corporation of a GPS receiver into the design of the portable terminal could provide accurate time and posi- tion information to effect a reduction of several orders of magnitude in synchronization time. This improvement would greatly enhance the potential for LPI performance of very small aperture terminal (VSAT) networks. Fur- thermore, GPS receivers that fit within the size, weight, and power budgets of a portable terminal are being de- veloped. This paper explores the benefits of this poten- tial application of GPS technology.
Published in:	Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990) September 19 - 21, 1990 The Broadmoor Hotel Colorado Spring, CO
Pages:	143 - 148
Cite this article:	Vaz, Richard F., Flanzbaum, Mark I., "GPS-Based Modem Synchronization for Man-Portable Satellite Terminals," Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990), Colorado Spring, CO, September 1990, pp. 143-148.
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