OpenSource GPS Open Source Software for Learning about GPS

Clifford Kelley, Joel Barnes, and Jingrong Cheng

Abstract:	Teaching the next generation of engineers about the inner workings of GPS receivers is difficult due to the expense of acquiring appropriate hardware and software. In the past few years a number of excellent books have been written about GPS (references 1 through 5). But, in the end students learn best by doing. Even with hardware available, trying to squeeze the development of software into a quarter or a semester is asking a lot. A low cost set of hardware, along with free open source software, allows students access to the inner workings of the receiver without 'breaking the bank' in terms of time or money. This article will present open source GPS receiver software and laboratory hardware that is a straightforward modification of a COTS receiver to interface it to a PC bus. The hardware and software are based on the GEC Plessey, then Mitel, now Zarlink, chipset. In the 1990’s GEC introduced a board and software called the GPS Builder ™ which placed the down converter and correlator chips on an ISA card installed on a PC. Since the software ran on the PC it gave the user complete control and visibility into the operation of the receiver. Unfortunately GEC and Mitel found that they had to charge in excess of $1000 dollars for the board and software licenses. This served to limit its popularity among cash strapped universities and individuals. Given the success of Linux, it was apparent that complex software development could be done on free open source software. This paper describes the hardware and software architecture, the features added to allow debugging of the code and carrier tracking loops, and plans for improving the software, install it on other receiver hardware, use embedded ‘x86 hardware, and to run under Open Source real time operating systems. A comparison will also be made of the software using two receivers, and will show the results of its performance. This is similar to experiments that students could perform using the open source software and hardware discussed herein. An Internet website has been set up at http://www.home.earthlink.net/~cwkelley to describe the project, and to provide source code and sample input and output data.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2524 - 2533
Cite this article:	Kelley, Clifford, Barnes, Joel, Cheng, Jingrong, "OpenSource GPS Open Source Software for Learning about GPS," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2524-2533.
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