Effect of interference in the calculation of the amplitude scintillation index S4

Irregular electron content in the ionosphere affects the propagation of Global Navigation Satellite Systems (GNSS) signals with a phenomenon known as scintillation. Ionospheric scintillations are rapid fluctuations in the amplitude and phase of the signal that can lead a receiver to lose lock. In recent years the number of Ionospheric Scintillation Monitoring Receivers (ISMR) have increased dramatically. This paper presents an initial analysis of the effect that interference may have in the calculation of the widely used amplitude scintillation index S4. Interference is one of the growing threats to the performance of GNSS. Our analysis shows that interference may have particular effects on GNSS receivers that can lead them to output an erroneous measurement of the S4 index.