Development of a MatLab based GPS constellation simulation
for navigation algorithm developments

Abstract: This thesis is a part of a PhD project called Algorithm for Coupled
Navigation Using an Inertial Measurement Unit and the Global Positioning
System. The aim of the PhD project is to study a continuous navigation and
attitude update solution and its applicability to several aeronautical and
space missions.

In this thesis a software-based GPS receiver simulator for the L1 C/A code
signal is developed and verified. The simulator is implemented in MATLAB
although most functions are coded in C to accelerate the speed of
operation.
A mathematical model is developed to express the Pseudo Range as a function
of various errors, such as satellite clock error, ionospheric error, and
tropospheric error. The simulation program is developed so the receiver
could be spaceborne, which means that special situations have been
implemented in models for GPS satellite visibility, ionospheric and
tropospheric time delay effects.

The verifcation of the developed simulation program was performed by
comparing simulated parameters with calculated hardware code parameters
from
a real receiver, using same input. The result was satisfied and following
differences could be seen:

Calculated GPS Time < 1.3'10^-7 s

Geometric Range < 1.0'10^-2 m

Ionospheric Range Error < 4 m

tropospheric range error < 0.6 m

satellite clock range < 0.2 m