Nonlinearities Influence to RF Satellite Downlink Model with QAM and Raised Square Cosine Filter

Reliability of communications is of vital importance in military applications. Constellations are connecting coded words at different ends of the communication channel that indicate the correctness of the transmitted message. In this paper, we compare the influence of the selected nonlinearity in the transmit amplifier on the constellation diagrams in radio frequency (RF) geostationary satellite downlink and bit-error-rate (BER). Two cases were analyzed: negligible and severe noise in the communication channel. Considering the cubic, hyperbolic tangent, Saleh, Ghorbani, and Raap models, it is shown that the Raap and Saleh models can be used for the lowest BERs when the noise is negligible. In case of severe noise, it is best to use the Raap model from the set of nonlinearities considered. The ANOVA-test showed that there is a dependence between the Raap and Saleh models in the presence of negligible noise, but not in the presence of severe noise.