Open Source Software for Commercial Off-the-Shelf GPS Receivers

Andrew Greenberg and Takuji Ebinuma

Abstract:	Open source software running on inexpensive, commercially available GPS receivers promises to cut the expense and restrictions of developing extended GPS applications dramatically. Extended GPS applications, such as keeping GPS satellite signal lock in high-dynamic environments or deep coupling of inertial data, require direct access to the receiver's hardware. This access is usually only provided by very expensive and restrictive development kits, many of which still do not grant the developer direct access to the receiver chip set. Our software allows GPS developers to convert an inexpensive, commercially available GPS receiver into an open source development system that provides complete access to the receiver's hardware. The software, licensed under the GNU General Public License (GPL), is called GPL-GPS. This paper describes the motivations, principles and technical development of the GPL-GPS project. This includes choosing a GPS receiver chipset, choosing a receiver board, and porting the software necessary to make a fully functional open source GPS receiver and receiver development system. The paper concludes with results from a static positioning test, results from a GPS simulator running a simulated sounding rocket trajectory, and future work. GPL-GPS currently supports the Zarlink GP4020, a 12- channel L1 C/A GPS receiver baseband processor with an integrated 32 bit ARM7TDMI microprocessor, because of its open and extensive documentation. Commercially available receivers, coupled with an open hardware carrier board, can create a full featured development kit for less than US$300. GPL-GPS is intended to be part of an inexpensive 6 degree-of-freedom differential GPS-aided inertial navigation system designed for a small, inexpensive, and open source sounding rocket platform being developed by the Portland State Aerospace Society.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	2820 - 2829
Cite this article:	Greenberg, Andrew, Ebinuma, Takuji, "Open Source Software for Commercial Off-the-Shelf GPS Receivers," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 2820-2829.
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