This thesis explores the effects of solar scintillation on frequency modulation schemes used in deep-space communications. As spacecraft travel farther from Earth, maintaining reliable communication links becomes increasingly challenging due to disturbances caused by the turbulent solar wind. These fluctuations, known as solar scintillation, introduce random amplitude and phase variations that can severely distort radio signals transmitted through the interplanetary medium. The work focuses on the analysis and comparison of two digital modulation schemes-Multiple Frequency Shift Keying (MFSK) and Special Multiple Frequency Shift Keying (SMFSK)-to assess their suitability for communication systems affected by solar scintillation. A theoretical and computational framework was developed to model signal transmission, non-coherent reception, and the influence of a stochastic scintillation channel characterized by a variable scintillation index. In addition to the analytical and simulation-based study, the thesis first examines the asymptotic behaviour of the Symbol Error Rate (SER) in high signal-to-noise ratio scenarios, and subsequently develops models aimed at recreating the expected SER trends for theoretical performance evaluation.