Accuracy of low-cost GPS receivers with and without differential corrections

U radu je dan pregled današnjih sustava satelitske navigacije. Izneseno je trenutno stanje GPS sustava i planovi njegova razvoja. Izdvojene su posebnosti vezane uz GPS, a koje se odnose na teritorij Republike Hrvatske. Detaljno je opisana interna građa i princip rada niskobudžetnog softverskog GPS prijamnika počevši od njegove antene, sklopovlja za prilagodbu i uzorkovanje RF signala, sve do postupaka akvizicije i praćenja digitaliziranog signala te uporabe navigacijskih podataka i izračuna krajnjeg položaja. Rad softverskog GPS prijamnika simuliran je u MATLAB-u te su promotrena interna stanja pojedinih dijelova prijamnika uz realan ulazni signal. Razmotreni su danas korišteni principi poboljšanja sustava u smislu točnosti i proširenja usluge. Razvijena je sklopovska i programska podrška potrebna za terensko vrednovanje Lassen LP i Lassen iQ GPS modula proizvođača Trimble i GM862-GPS modula proizvođača Telit. Ispitan je utjecaj postavki prijamnika na njegovu točnost. Uspoređene su točnosti pojedinih prijamnika u različitim uvjetima rada: stacionarno mjerenje uz dobar prijem signala, stacionarno mjerenje u urbanoj sredini, gradska vožnja i vožnja otvorenom cestom. Ispitan je utjecaj komercijalnih diferencijskih korekcija i diferencijskog mjerenja pomoću para nekorigiranih prijamnika za svaki od spomenutih uvjeta rada. Razmotren je utjecaj izmjene konstelacije. Uočena je sporo promjenjiva komponenta pogreške položaja i ispitana mogućnost njenog usrednjavanja.This thesis presents an overview of the Global Navigation Satellite Systems (GNSS). Current GPS state and modernization plans were given. Specificity of the GPS on Croatian territory was described. Internal architecture and operating principles of a low-cost software-based GPS receiver was elaborated in detail, with the emphasis on a GPS antenna, an RF front-end, signal acquisition and tracking, navigation data and position solution. A software-based GPS receiver was simulated in MATLAB. Receiver subsystems were evaluated using real-world signals. An overview of the current operating principles of GPS augmentation was given. A hardware and software platforms were developed for the evaluation of Trimble Lassen LP and Lassen iQ GPS modules and Telit GM862-GPS modules. Influence of receiver parameters on position accuracy was evaluated. Position accuracy of used receivers was compared in various environments: statitionary and moving measurement with the clear view to the sky and in the urban environment with the obscured sky view. Influence of commercial differential corrections and differential measurement using a pair of uncorrected receivers was evaluated. Influence of the constellation-switch on a measured position was demonstrated. Slow-changing mean position drift was illustrated and an averaging time considered