A Preliminary Study of the Effects of Ionospheric Scintillation and Multipath in 
the Accuracy of a Receiver GPS Signal. 
 
A. O. Moraes (Comando-Geral de Tecnologia Aeroespacial CTA, S.J.C-Brazil), 
R. Walter and W.J. Perrella (Instituto Tecnologico de Aeronáutica-ITA, 
S.J.C-Brazil). 
 
 
Ionospheric Scintillation and the effects of multipath are important in the 
determination of the accuracy of the pseudorange and also carrier phase 
measurements resulting in a complete loss of lock of the receiver GPS signal. 
The objective is to analyze the performance of a simulated GPS receiver under 
ionospheric scintillation conditions and/or the multipath, i.e., quantify our 
receiver model that includes these effects on tracking performance in the 
simulated receiver which is composed with a delay locked loop (DLL) and a phase 
locked loop (PLL), which estimate the pseudorange and the phase of the carrier 
of the GPS. 
 
In order to analyze these two effects we use the following models: 
1. The simulated scintillation signals are generated using the Global 
Ionospheric Scintillation Model (GISM, from MITRE) software which provides the 
statistical characteristics of the transmitted signals, in particular the 
scintillation index S4, the fade durations and the cumulative probability of the 
signal. 
2. The simulated multipath signals are generated using specular and diffusion 
reflections with coherent and non coherent DLL structure. 
 
The results of these effects will be analyzed, also, in function of the DLL and 
PLL parameters. 
	 
References: 
R. D. J. van Nee. Multipathh and Multi-Transmitter Interference in 
Spread-Spectrum Communication and Navigation Systems, Delft University Press, 
The Netherlands, 1995 
Y. Béniguel. Global Ionospheric Propagation Model (GIM): A propagation model 
for Scintillations of Transmitted Signals, Radio Science, May-June2002