A starting point for learning about GPS with Open
Source Software
IMPORTANT NOTICE :
NavtechGPS
is now offering Seminars on GPS Receiver Principles using OpenSource GPS
Version 2.20 package has been released on Sourceforge (OSGPS)
As
of Version 2.0 OSGPS has Linux operability as
a driver in standard Linux
Version 1.00 of SoftOSGPS has been released on
Sourceforge (OSGPS)
I would like to thank the following people who have contributed to OpenSource GPS. If I have left someone out I
apologize and ask you to please correct my oversight.
Joel Barnes
Jingrong Cheng
Georg Beyerle
Alberto Perez
Phil Bender
Doug Baker
Elmer Thomas
Andrew Greenberg
KELLEY,C.,CHENG,J., & BARNES,J.,2002 Open source software for
learning about GPS. 15th Int. Tech. Meeting of the Satellite
Division of the U.S. Inst. of Navigation, Portland, Oregon,
24-27 September.
Over the past 13 years I have been working off and on with a GPS receiver I built based on the
GEC Plessy GP1010 and GP1020 chipset connected to an IBM PC which does all of
the signal processing through I/O ports. Recently I have converted the
software for use with the Zarlink GP2021 and GP2010/2015 chipset. I am extremely grateful
to GEC and Mitel who have allowed me to buy a small quantity of chips and have
provided the documentation to go with them.
This seems an appropriate time to offer the software as an open source in a manner similar to Linux. I hope
this will provide a good starting point for others to build on.
My hope is that we can develop a community of students and professionals
interested in GPS who can as a group provide support to each other to fix bugs, improve
and develop this software into something useful to amateurs, students, and
researchers.
The programs and associated files contained in the distribution were
developed by Clifford Kelley (unless otherwise noted). The programs are
not in the public domain, but they are freely distributable without licensing
fees. These programs are provided without guarantee or warrantee expressed or
implied.
The receiver requires at a minimum a 100 MHz 486 IBM PC with 640k RAM.
This project is a 12 channel L1 only receiver. The software goes from acquisition all
the way to processing
the navigation message and producing position and velocity fixes at a programmable
rate of up to 10
Hz. It is capable of doing a cold start, warm start or hot start depending
on the data available. The source code is written in C and was compiled on a Borland 4.5 C/C++
compiler.
Since there is a great deal of information available elsewhere on the web and
in textbooks I will not dwell on the theory but rather concentrate on the
algorithms and software.
Limitations/Areas for Enhancement
Obviously no program is perfect, especially one written on ones own time
without access to sophisticated test equipment. While it appears to work
pretty well I know of a number of areas where there seem to be problems and
other areas where it could be greatly improved.
The acquisition/pull-in steps integrate over 1 ms, a longer integration
time or variable integration time may be desirable.
The tracking loops currently integrate over 20 ms, a longer integration
time or variable integration time may be desirable
The code and carrier tracking loops are 2nd order and could be much better
Comments/questions/suggestions may be
e-mailed to cwkelley@earthlink.net.
A mailing list for OpenSource GPS has
been set up at PSAS (Portland State Aerospace Society). Thanks Andrew!!. Click
to subscribe to opensource_gps
Version
2.00 under CVS is working
on sourceforge.org, Version 1.18 has been released as a package at
sourceforge under the project name OSGPS.
Version 1.00 of SoftOSGPS is also on
sourceforge. SoftOSGPS uses an IF file created from a software radio such
as the GPS1A from GPS Creations and emulates the GP2021 correlator processing
ans uses the existing OSGPS algorithms for search, track, and position, velocity
and time fixing. Work is underway to make this software hardware agnostic
as well as running in real time. Currently it supports files created by
the SiGe USB dongle and the GPS Creations GPS1A USB dongle. We would like
to add support for the USRP and others as they become available.
We are using CVS on
sourceforge for development. If you would like to be added to the
developer list please e-mail me.
Other
Open Source GPS projects.
Takuji Ebinuma, OpenSource GPS MG5001
Port, This project is dedicated to porting OpenSource
GPS for Sigtec's MG5001
OEM GPS receiver
