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

University essay from Luleå tekniska universitet/Rymdvetenskap, Kiruna

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 sGeometric Range < 1.0'10-2 mIonospheric Range Error < 4 mTropospheric Range Error < 0.6 mSatellite Clock Range < 0.2 m