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Differential GPS System
by
Shrijay Dalal and John S. Novak
Advisor: Dr. J. W. Sennott
A considerable problem with widespread applications of Global Positioning
Satellite (GPS) technology today is the inherent lack of accuracy in civilian
stand-alone receivers. Errors in location of up to tens of meters are unacceptable
for all but the most rudimentary of applications. However, these errors,
caused by tropospheric and ionospheric interference, and government encryption
of ephemeris data, can be modeled as global errors over fairly wide geographic
areas.
A solution, requiring extra hardware for implementation, is differential
global positioning, which describes a system using two GPS receivers --
one stationary unit, and one mobile unit. The stationary unit, which is
placed at a precisely known location, is used to determine a global error
factor, which is used in turn to correct the errors of the mobile unit.
Our system integrates two Magnavox receivers into a differential, Kalman
filtered GPS system. In particular, existing C code was modified to take
advantage of two high- performance Magnavox 4200 GPS receivers. This software
coordinates real-time data collection from two receivers, and executes
both Kalman filtering and differential error correcting.
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