Software Considerations for the Interrupted Data Acquisition Receiver

Gerald Whitworth

Abstract:	Navstar Systems Ltd. is associated with Dunstaffnage Marine Laboratory (DML) to design a GPS navigation system for the Autonomous Underwater Vehicle (AUV) currently under development. The GPS receiver is required to generate a position solution, while the AUV is surfaced, under a range of sea states that interrupt the GPS signal due to vessel roll and periodic wave washover of the GPS antenna. The limited exposure to the GPS signal, in the extreme just 2 seconds every 6-8 seconds, proved to be a very challenging development. This paper examines the various techniques that have been designed, using software alone, to overcome the problems of frequent intermittent loss of the GPS signal. Of particular interest are: 1) Initial signal acquisition and time synchronisation to GPS. Detection and decoding the preamble and Z-count fields of the TLM and HOW words, following modified BIT,WORD AND SUBFRAME synchronisation routines and search algorithms. 2) Modification of re-acquisition and tracking mechanisms to enable near instantaneous carrier lock after signal loss. 3) Ephemeris, collection by jig-saw technique and the associated problems and solutions therewith.
Published in:	Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994) September 20 - 23, 1994 Salt Palace Convention Center Salt Lake City, UT
Pages:	173 - 178
Cite this article:	Whitworth, Gerald, "Software Considerations for the Interrupted Data Acquisition Receiver," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 173-178.
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