GNSS signals may experience radio wave scintillation due to refractive and diffractive processes when propagating through plasma density irregularities in the Earth's ionosphere. Scintillation can be responsible for signal degradation both in its amplitude and phase. The behavior of typical commercial GNSS receivers has in the past been analyzed in the presence of modelled ionospheric scintillation events. Here, the use of numerical or physical models was avoided. A systematic method was established to analyse GPS L1 receiver performance under scintillation conditions with the use of a Spirent simulator. The method is based on a systematic analysis of the receiver performance in response to different fade depths and durations. First, artificial signal perturbations described by simplified instances of fade depth and duration were superimposed on to nominal GPS signals generated by a Spirent simulator; to visualize a given receiver's performance. Second, scintillationinduced signal perturbations were extracted from real experimental data and superimposed on to the nominal simulated GPS signals. The receiver response to perturbed signal conditions was characterized in terms of the probability to lose lock as a function of fade depth and duration.